Full Issue, Vol. 61 No. 1

Western North American Naturalist

Volume 61 Number 1 Article 19

1-29-2001

Follow this and additional works at: https://scholarsarchive.byu.edu/wnan

Recommended Citation (2001) "Full Issue, Vol. 61 No. 1," Western North American Naturalist: Vol. 61 : No. 1 , Article 19. Available at: https://scholarsarchive.byu.edu/wnan/vol61/iss1/19

This Full Issue is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 61(1), © 2001, pp. 1–10

NATURAL HISTORY AND INVASION OF RUSSIAN OLIVE ALONG EASTERN MONTANA RIVERS

Peter Lesica1 and Scott Miles1

ABSTRACT.—Russian olive (Elaeagnus angustifolia) is an exotic tree considered invasive in the western U.S. There is concern it will replace native riparian forests, resulting in a loss of biological diversity. We studied the dynamics of Russ- ian olive invasion on the Marias River in north central Montana and the lower Yellowstone River in southeastern Mon- tana to determine where and in what habitats it occurs, how it is interacting with plains cottonwood (Populus deltoides) and green ash (Fraxinus pennsylvanica), the dominant native riparian trees, and how these interactions will alter future riparian forests. We measured size, density, and age of Russian olive, cottonwood, and green ash as well as vegetative composition and overstory canopy cover in sample plots in alluvial bar and terrace habitats at randomly chosen sites. Russian olive occurred in multiple-age stands on terraces along both rivers but was rarely found establishing in recently flood-deposited alluvium. Diameter growth rates decreased with increasing overstory canopy cover but did not vary significantly with soil moisture as reflected by ground-layer vegetation. Russian olive grew at nearly 3 times the rate of the native late-successional green ash at sites where both occurred together. Russian olive attained reproductive maturity at ca 10 years of age on both rivers, and, on average, there was less than 1 new plant recruited per mature tree per year. Beaver felled a high proportion of cottonwood within 50 m of both river channels, but Russian olive was little damaged. Russian olive will establish with increasing frequency in riparian forests as well as wet meadows and along ditches and overflow channels in eastern Montana. Native riparian forests will be replaced by Russian olive as old cottonwoods die on upper terraces or are removed by beaver near active channels. Cottonwood establishment and dominance will not be precluded on rivers where flooding regularly reinitiates primary succession beyond the zone of beaver activity. However, Russian olive may preclude cottonwood recruitment by shading seedlings along streams where flooding does not occur or merely deposits alluvium on top of existing vegetation rather than creating new channels or broad point bars. Because of its long maturation time and low recruitment rate, Russian olive invasion in Montana will proceed slowly compared with many exotics.

Key words: Russian olive, Elaeagnus angustifolia, exotic, cottonwood, riparian habitat, Montana, beaver.

Riparian areas provide important wildlife extensively naturalized throughout the west- habitat in the semiarid landscapes of western ern United States, especially in riparian areas North America (reviewed in Finch and Rug- (Christiansen 1963, Olson and Knopf 1986a, giero 1993, Naiman et al. 1993). Numerous 1986b). In Montana an average of 40,000 Russ- species of plants and animals are restricted to ian olive nursery stock are distributed by the these habitats, and productivity of riparian state each year (Montana Department of Nat- systems is usually much higher than water- ural Resources and Conservation nursery data, limited uplands (Brinson et al. 1981). Exotic 1997). Russian olive has been planted as wind- species invade these dynamic systems and alter breaks in Montana since at least 1953 (Mon- processes and species composition (deWaal et tana Department of Natural Resources and al. 1994, Stohlgren et al. 1998), often causing a Conservation nursery data, 1997), and natural- loss of biological diversity (Drake et al. 1989). ized trees occur along most major rivers in the Russian olive (Elaeagnus angustifolia) is Great Plains portion of the state (Olson and native to southern Europe and western Asia Knopf 1986a). (Little 1961) and was introduced into North Russian olive can enhance habitat for some America during Colonial times, probably for wildlife species (Knopf and Olson 1984). On the ornamental purposes (Elias 1980). Since ca other hand, there is speculation that Russian 1900 it has been planted for windbreak and olive may hinder recruitment of native cotton- wildlife enhancement purposes and has become woods (Populus) and willows (Salix; Currier

1Conservation Biology Research, 929 Locust, Missoula, MT 59802.

1 2 WESTERN NORTH AMERICAN NATURALIST [Volume 61

1982). A decline of these dominant native ripar- plains underlain by late Cretaceous sandstone ian woody plants could cause the loss of habitat of the Fort Union formation (Alt and Hynd- for species such as cavity-nesting and insectiv- man 1986). The upper reach generally has a orous birds (Knopf and Olson 1984, Olson and braided channel and relatively level flood- Knopf 1986a). plain. In much of the lower reach the river has The purpose of our study was to document a single channel confined between high ter- the dynamics of Russian olive invasion along races or low bluffs. Surface elevations of the the regulated lower Marias and unregulated Yellowstone River are 939 m at Billings, 711 m lower Yellowstone rivers in eastern Montana. at Miles City, and 662 m at Terry. Both rivers have peak discharges dominated Climate along both rivers is similar: semi- by late spring/early summer snowmelt. In par- arid and continental. Mean annual precipita- ticular we ask: (1) What habitats does Russian tion in 1950–1980 for the Marias (at Loma) olive occupy? (2) How are growth, reproduc- and Yellowstone (at Hysham) was 32 cm with tion, and recruitment affected by habitat and 70–75% falling in April through August. Mean how do these vital rates influence its invasive- annual temperature in 1950–1980 was 6.8°C ness? (3) How does beaver herbivory affect and 8.0°C for Loma and Hysham, respectively the interaction between plains cottonwood (NOAA 1982). (Populus deltoides; hereafter referred to as cot- Upland vegetation in the study areas is tonwood) and Russian olive? We then use this shrub-steppe or mixed-grass prairie domi- information to speculate on how Russian olive nated by sagebrush (Artemisia tridentata ssp. will affect riparian vegetation in the future and wyomingensis) and/or perennial grasses includ- the implications for management. ing needle-and-thread (Stipa comata), western wheatgrass (Agropyron smithii), and blue grama STUDY AREAS (Bouteloua gracilis). Vegetation of uppermost river terraces is dominated by silver sagebrush The Marias River has its headwaters along (Artemisia cana), western wheatgrass, and green the eastern front of the Rocky Mountains needlegrass (Stipa viridula); however, extensive 60–150 km south of the Canadian border. areas of upper terrace along the Yellowstone Tiber Dam on the Marias was completed in River have been converted for agricultural 1956 ca 135 river km above its confluence crops. Terraces closer to the river channel sup- with the Missouri River just below the town of port riparian vegetation dominated by cotton- Loma. We conducted our study between Tiber wood (Populus deltoides, some P. angustifolia), Dam and Loma (Fig. 1). The lower Marias willow (Salix spp.), buffaloberry (Shepherdia cuts through sedimentary plains composed argentea), and hydrophytic grasses, sedges, and primarily of Cretaceous shales and sandstones bulrushes. Vascular plant nomenclature fol- (Alt and Hyndman 1986) glaciated during the lows Great Plains Flora Association (1986). Illinoian Ice Age (Perry 1962). The lower river Cottonwood forests may be hundreds of meters valley is between a few hundred meters and wide in meandering reaches of the rivers. >1 km wide and frequently bounded by steep breaks eroded from the soft sedimentary for- RUSSIAN OLIVE mations. Surface elevations of the Marias River just below Tiber Dam and at Loma are Russian olive is a small tree; naturalized 861 and 779 m, respectively. plants may reach 10 m tall in Montana. It The Yellowstone River has its headwaters occurs on soils with low to moderate soluble in the mountains of southwestern Montana and salt concentrations (Carman and Brotherson northwestern Wyoming. In Montana it flows 1982). Our observations indicate that Russian north and then east from Yellowstone National olive frequently branches at ground level, only Park to the confluence with the Missouri River 1–2 dm above root flare in moist, unshaded just east of the Montana–North Dakota border. sites. However, it branches well above ground It is unregulated its entire length. We con- level more often in drier, shaded habitats. ducted our study on 2 reaches of the lower Twigs have spines, and branches elongate each Yellowstone River: (1) from Pompeys Pillar to year by growth from a lateral bud near the ter- Hysham and (2) from Sheffield to Terry (Fig. 1). minus of the previous year’s growth. Russian The river flows through unglaciated, dissected olive is capable of sprouting from the base 2001] RUSSIAN OLIVE NATURAL HISTORY 3

Fig. 1. Location of study reaches on the Marias and Yellowstone rivers in Montana. when damaged. Mature trees bear nectar-proof the stands being sampled. For each sample ducing flowers (Hayes 1976) that mature into plot we estimated mean distance to the edge numerous clusters of small, edible, berry-like of the nearest river channel and recorded the fruits in late summer. Seeds germinate under a distance above the September river level with wide variety of moisture conditions at differ- a hand-held level and gauging pole. Estimates ent times of the growing season (Shafroth et for 6 plots on the Yellowstone were inadver- al. 1995). Russian olive fixes nitrogen in its tently lost during fieldwork. roots through a symbiotic relationship with In each sample plot we estimated canopy the bacteria Frankia spp. (Huss-Danell 1997). cover (Daubenmire 1959) of all common (≥1% cover) vascular plant species to the nearest 5% METHODS and estimated tall-tree canopy cover with a spherical densiometer at the center of circular Field Methods plots and at 2 equidistant points in rectangular We conducted our study on the Marias and plots. Estimates of seedling density on alluvial Yellowstone rivers in spring and summer of bars were made from ten 1- or 2-m2 circular 1997 and 1998, respectively. During spring microplot samples spaced evenly throughout canoe trips we mapped all areas where we the plot. We were not always able to distin- observed Russian olive density of at least 20 guish between 2 sedges, Carex aquatilis and plants ⋅ ha–1 and randomly selected 19 sites on C. lanuginosa, and so they were combined in the Marias and 15 sites on the Yellowstone for the analyses. sampling during mid-August and early Sep- In each sample plot we recorded the num- tember. At each site we subjectively located ber of Russian olive trees in each of 4 size sample plots to represent a recently deposited classes: seedling (<90 cm tall), sapling (>90 alluvial bar (when present) and all the distinct cm tall and <8 cm basal diameter [bd]), pole habitats that supported Russian olive. Each (>183 cm tall and 8–13 cm bd), and mature site had 2–4 sample plots, for a total of 38 (>13 cm bd). We obtained age estimates for 3 plots on the Marias and 42 plots on the Yel- plants in the 1–2 dominant (with the greatest lowstone. Sample plots were 500 m2 and cir- basal area) size classes and at least 1 plant in sub- cular or rectangular, depending on the shape ordinate size classes for cottonwood, Russian 4 WESTERN NORTH AMERICAN NATURALIST [Volume 61 olive, and green ash (Fraxinus pennsylvanica) environmental variables (Whitaker 1975:120, from cross sections or increment cores taken Gauch 1982). just above ground level (basal diameter). We Average growth rate was estimated as basal counted the number of annual rings using a diameter divided by age. We compared the 10× microscope. Age estimates of cottonwood growth rate of each recorded green ash tree taken from increment cores are likely to be with the Russian olive from the same plot with less than the actual age because ground level the most similar age within 10 years using a is not always the level of the establishment sur- paired-sample t test. For all other growth rate face (Bradley and Smith 1986, Scott et al. 1997). calculations, only Russian olive plants with In addition, some cottonwood trees had rotten unambiguous age determinations and 5–12 centers, resulting in underestimates of age. We years old were used. used the oldest measurement for cottonwood Recruitment rate is a measure of how quick- stand age, but this should be considered a ly the density of Russian olive trees increases minimum estimate. Many Russian olive branch in a stand. We estimated recruitment rate as at ground level, and root flare occurs just the number of seedling plus sapling plus pole below, so we often took increment cores or (if poles averaged <10 years old) plants divided ≥ cross sections from the base of the largest by the number of poles (if they averaged 10 leader. The largest leader was 1 year younger years old) plus mature plants multiplied by than the base in 5 of 6 juvenile plants where their mean age minus 10 (number of years to both were measured; thus, we added 1 year to maturity). In other words, recruitment rate is the estimated age of Russian olive when cores the number of recruits per mature tree per were taken from the largest leader. We mea- year since the stand was 10 years old. Plots sured basal diameter to the nearest 1 cm with without mature Russian olive were excluded a diameter tape and also recorded whether the from these analyses. This measure assumes no immigration of recruits and is only an approxi- sampled Russian olive trees had fruit. mate metric of how quickly Russian olive can We recorded the number of cottonwood and increase at a site. Seedling and sapling size Russian olive trees in each plot damaged by classes were considered juvenile because only beavers. We estimated ungulate browse use as 15% (N = 114) bore fruit, while 86% (N = the proportion of at least 25 two-year-old Russ- 128) of pole and mature classes bore fruit. ian olive or cottonwood twigs browsed. Twigs We used regression analysis to test for sig- with abruptly blunt ends and new shoots aris- nificant relationships between Russian olive ing from lateral buds were considered browsed growth and recruitment rates and age, tall- (Rutherford 1979). Only twigs easily available tree canopy cover, height above the river, and to native or domestic ungulates (1–5 ft high) vegetation. We used analysis of variance on vigorous plants were chosen haphazardly (ANOVA) to test for a difference in Russian on a random walk through the plot. olive growth rate between the 2 rivers with age Data Analysis of the trees as a covariate in the model. A t test was used to test for a difference in Russian We ordinated plot understory species by olive recruitment rate between the 2 rivers. percent cover with reciprocal averaging (RA). Two-way ANOVA was employed to assess dif- RA was chosen because it is an effective ferences in browse use between cottonwood method when the data set is structured by a and Russian olive between the 2 rivers. single predominant gradient (Gauch 1982, McCune and Mefford 1995). Species scores RESULTS indicated that the 1st axis represented a moisture continuum and was a metric of stand suc- Vegetation of Study Sites cessional age (see Results), a continuum that Vegetation on alluvial bars was sparse. Com- structures many Great Plains floodplain vege- mon plants included the annuals Xanthium tation mosaics (Johnson et al. 1976, Boggs strumarium on the Marias (n = 6 plots) and 1984). We used RA axis 1 plot scores to quan- Eragrostis hypnoides, Panicum capillare, and tify a successional continuum because vegeta- Chenopodium botrys on the Yellowstone (n = tion changes as represented by a multivariate 14). Cottonwood and Salix exigua seedlings gradient often integrate important correlated were common on both rivers. 2001] RUSSIAN OLIVE NATURAL HISTORY 5

TABLE 1. Understory plant species with highest and lowest scores on RA axis 1. Wetland indicator status estimates the probability of a species occurring in wetlands; obl = >99%, facw = 67–99%, fac = 34–66%, facu = 1–33% (Reed 1988). Species without a status generally do not occur in wetlands. Wetland indicator Species RA score status High scores (wet sites) Scirpus maritimus 447 obl Equisetum arvense/fluviatile 346 fac/obl Mentha arvensis 290 facw Phalaris arundinacea 285 facw+ Salix exigua 255 facw+ Carex aquatilis/lanuginosa 238 obl Solidago graminifolia 235 facw Muhlenbergia asperifolia 195 facw Spartina pectinata 192 facw Salix lutea 174 facw+

Low scores (moist sites) Medicago lupulina –170 facu Rhus trilobata –172 — Symphoricarpos occidentalis –201 — Poa pratensis –229 facu Agropyron smithii –269 facu Thermopsis rhombifolia –281 — Stipa viridula –296 — Elymus canadensis –316 facu Agropyron cristatum –319 — Calamovilfa longifolia –377 —

Terrace vegetation associated with Russian River. On the Yellowstone River, Russian olive olive was diverse. The 1st RA axis accounted varied from 20 to 5120 plants ⋅ ha–1 with a for 39% of variation among plots and clearly mean of 676 plants ⋅ ha–1. represented a moisture/successional gradient Russian olive in all size classes occurred spanning very wet low terraces to very dry along both rivers, and most stands were multi- upper terraces on both rivers. All 10 species ple-aged. The oldest Russian olives recorded with the highest RA scores are obligate or fac- were 36 and 40 years old on the Marias and ultative wetland plants, while 4 of the 10 low- Yellowstone rivers, respectively. Mean age of est scoring species are facultative upland plants, Russian olive stands (i.e., age of oldest tree in and the remainder are considered upland plot) was 15.3 years (x– = 1.2) on the Marias species (Table 1; Reed 1988). There was also a and 18.6 years (x– = 1.4) on the Yellowstone. strong correlation between cottonwood stand The oldest Russian olive tree was as old as or age (oldest tree) and RA plot scores (r = 0.59, older than the oldest cottonwood in 39% and P < 0.001). 14% of the stands on the Marias and Yellow- stone rivers, respectively. In many cases these Russian Olive Habitats were stands where cottonwoods appeared to Russian olive did not occur in alluvial bar have established in fresh alluvium deposited sample plots on the Marias River and was on existing terraces with established Russian found in only 2 alluvial bar plots (14%) on the olives. Yellowstone where density was <4 plants ⋅ 100 m–2. On young, moist terraces (high RA scores), Growth Russian olive occurred with and without a cot- Growth rate of Russian olive (diameter ⋅ tonwood canopy; however, it never occurred age–1) increased with age over all age classes outside a cottonwood canopy on the dry, high- (r2 = 0.10, P < 0.001, n = 153). This relation- est terraces. Density of Russian olive in ter- ship was significant for juvenile trees (5–10 race stands varied from 20 to 760 plants ⋅ ha–1 years; r2 = 0.11, P = 0.002, n = 91) but not with a mean of 186 plants ⋅ ha–1 on the Marias for mature trees (>10 years; r2 = 0.02, P = 6 WESTERN NORTH AMERICAN NATURALIST [Volume 61

0.31, n = 62). Growth varied between 0.1 and 2.7 cm ⋅ yr–1, with a mean of 0.80 cm ⋅ yr–1 (x– = 0.04) and was not different between the 2 rivers (F1,150 = 15.3, P = 0.61) when cor- rected for age. Growth rate was negatively associated with height above the September river level for both the Marias (r2 = 0.20, P = 0.028) and Yellowstone (r2 = 0.18, P = 0.012) rivers. There was no relationship between growth rate of Russian olive and understory vegetation as represented by the 1st RA axis (r2 = Fig. 2. Proportion of Russian olive trees producing fruit 0.01, P = 0.32, n = 153). There was a signifi- in 2-year age classes on the Marias and Yellowstone rivers. cant negative relationship between Russian olive growth rate and tall-tree (i.e., cottonwood) canopy cover (r2 = 0.06, P = 0.002, n = 153), which explained 21% of the variation relationship between recruitment rate and when age was included as a covariate in the tall-tree canopy cover (r2 = 0.006, P = 0.61). regression model (r2 = 0.21, P < 0.001). There was also no significant relationship be- Green ash occurred in 6 sample plots on tween Russian olive recruitment rate and asso- the Yellowstone River in the vicinity of Miles ciated understory vegetation as represented City. Mean density of green ash and Russian by RA axis 1 plot scores (r2 = 0.001, P = 0.87), olive juveniles (seedling + sapling) was 33 and there was no relationship between recruit- and 13 plants ⋅ plot–1 respectively, but this dif- ment rate and elevation above September ference was not significant (t = 0.74, P = river levels for either the Marias (r2 = 0.06, P 0.49). Sapling or larger green ash varied from = 0.28) or Yellowstone (r2 < 0.01, P = 0.86). 7 to 28 years old. Mean diameter growth rate Herbivory of green ash was 0.43 cm ⋅ year–1, while growth rate of paired Russian olive was 1.10 cm ⋅ year–1 Beaver damage occurred in 59% of the (paired sample t = 7.0, P < 0.001), nearly 3 Marias River terrace stands where an average – times as great. Mean ages of green ash and the of 57.1% (x = 9.4) of the cottonwood were – paired Russian olive were 16.5 and 16.6 years damaged by beaver, while only 14.6% (x = respectively. 5.2) of the Russian olive were damaged. Only 18% of sample plots on the Yellowstone showed Reproduction evidence of beaver, with 78% of cottonwood None of the Russian olive trees sampled on trees damaged, while none of the Russian the Marias River under age 5 produced fruit, olive in these plots were injured. Most beaver- while all trees over age 14 fruited (Fig. 2). On damaged cottonwood were felled at the base, the Yellowstone River only 1 of 38 plants ≤6 while damage to Russian olive was usually years old fruited in 1998. Fruiting generally confined to 1 or 2 basal limbs. began at 7–10 years, and 89% of Russian olive Ungulate browse use of 2nd-year branch >10 years old produced fruit (Fig. 2). These ends was 39% (x– = 5%) and 56% (x– = 5%) for results suggest the average age of 1st repro- Russian olive and cottonwood, respectively, on duction for Russian olive on both rivers is ca the Marias River and 57% (x– = 6%) and 48% 10 years. (x– = 6%) on the Yellowstone. There were no significant differences in overall browse use Recruitment between the 2 rivers (F1,54 = 1.19, P = 0.28) or Russian olive recruitment rate per mature between the 2 species when both rivers were tree in 46 stands varied from 0 to 4.07 recruits taken together (F1,54 = 0.57, P = 0.45). There ⋅ yr–1, with a mean of 0.69 recruits ⋅ yr–1 (x– = was a significant interaction between tree 0.15). There was no difference in recruitment species and river (F1,54 = 6.02, P = 0.02), rate between the Marias and Yellowstone rivers indicating different ungulate preferences be- (t = 0.51, P = 0.61). There was no significant tween the 2 rivers. 2001] RUSSIAN OLIVE NATURAL HISTORY 7

DISCUSSION flows. Here Russian olive could eventually preclude establishment of cottonwood’s shade- Vegetation of large riparian systems is dy- intolerant seedlings (Read 1958, Shafroth et al. namic. Cottonwood and willow usually establish 1995). from wind-borne seed on fresh, moist alluvium Cottonwood establishment and dominance deposited by floods or channel meandering will not be precluded by Russian olive on the (Braatne et al. 1996, Scott et al. 1996). Both upper reaches of the free-flowing Yellowstone native species are intolerant of shade and River where flooding and new channel devel- rarely reproduce in their own shade or that of opment continuously create new habitat for other species (Johnson et al. 1976, Rood and cottonwood establishment well beyond the Mahoney 1990). On the Marias and Yellow- zone of beaver activity. However, cottonwood stone rivers, terraces with an understory of may eventually be replaced by Russian olive willow and a ground layer of hydrophytic plants on the Marias River where flow regulation by (high RA scores) were dominated by relatively Tiber Dam has changed seasonal flow patterns young cottonwoods. As stands became older, and attenuated flood flows (Rood and Mahoney periodic deposition raised ground level higher 1995). Here riparian cottonwood forests will above the water table. These older stands sup- eventually be replaced by Russian olive as old ported an understory dominated by less hydric cottonwoods die on upper terraces and young shrubs and grasses (Johnson et al. 1976, Boggs cottonwoods on low terraces are removed by 1984). After 100–200 years cottonwoods die beaver or shaded by less palatable species and are replaced by sagebrush or shade-toler- (Lesica and Miles 1999). Absence of flooding ant green ash if it is present (Johnson et al. decreases alluvial deposition and cottonwood 1976, Boggs 1984, Hansen et al. 1995). Our recruitment on all but the lowest terraces results suggest that Russian olive may affect close to the river channel. Beaver damage to this successional riparian sequence in several cottonwood was usually severe on these lower ways. terraces, but Russian olives were little affected Russian olive was common along both rivers, and older stands generally had plants of many (Lesica and Miles 1999). Beaver damage ages, suggesting that recruitment occurs under occurred primarily close to the active channels established trees and does not require uncom- on both rivers probably for 2 reasons: beaver mon flood events. Russian olive has large seeds are more vulnerable to predators such as coy- that help allow establishment in the shade of a otes farther from the safety of water, and trans- cottonwood canopy and in the open on lower porting food material greater distances requires terraces and other relatively wet sites, such as more energy (Jenkins 1980, Belovsky 1984, banks of overflow channels (Shafroth et al. Easter-Pilcher 1987). Indeed, on both rivers 1995). Recruitment and growth were not sig- we observed that Russian olive often lined the nificantly affected by stand age as reflected by riverbank, with cottonwood becoming more understory vegetation; however, growth, but common farther away from the channel, sug- not recruitment, was greater on lower sites gesting that beaver can prevent cottonwood closer to alluvial ground water. from developing a mature canopy close to the Although Russian olive is capable of germi- river while having little effect on the contin- nating on bare, moist alluvium with cotton- ued invasion of Russian olive. woods (Shafroth et al. 1995), we rarely observed Cottonwood recruitment and growth can this in the study areas, and Russian olive was be adversely affected by livestock browsing younger than cottonwood in most stands. Both (Kauffman and Krueger 1984, Green and species grow quickly, but Russian olive does Kauffman 1995). Selective browsing could also not become as tall as cottonwood. On very favor one woody species over another; how- active river reaches where cottonwood estab- ever, we found no evidence of a preference for lishment occurs on new point bars or in flood cottonwood over Russian olive in our study channels, cottonwood will persist in the pres- reaches. We did not distinguish between wild- ence of Russian olive. However, on many life and livestock browsing, and we measured streams and entrenched rivers, cottonwood frequency but not quantity of browse damage. recruitment occurs primarily in alluvium de- However, our impression was that a higher pro- posited on existing vegetation by overbank portion of cottonwood than Russian olive twig 8 WESTERN NORTH AMERICAN NATURALIST [Volume 61 length was removed. This aspect of Russian should proceed slowly compared to many olive–cottonwood dynamics needs further study. aggressive herbaceous or shrubby weeds. The Russian olive did not appear to expand the average recruitment rate (mean number of aerial extent of riparian vegetation in our study recruits per mature tree per year) was 0.69. In areas, but it may allow tree-dominated habi- our simplified model of invasion dynamics, we tats to persist indefinitely in areas where cot- assume that a stand of Russian olive is initi- tonwoods have died or been killed by beaver. ated by a single plant with no density-depen- Knopf and Olson (1984) predicted that Russ- dent change in recruitment rate, no age- ian olive could increase the width of riparian dependent changes in fecundity, and no sub- corridors in some areas by establishing adja- sequent immigration. An average stand will cent to, but outside of, native woody riparian have 1 reproductive tree after 1 generation (10 vegetation. However, we found that Russian years) and a 2nd one after another generation olive did not establish on drier high terraces (20 yrs). An additional 0.69 mature trees will without a cottonwood overstory. The presence be recruited into this stand each year for the of Russian olive recruitment on upper terraces next 10 years, bringing the total to 8 mature only in riparian forests may be due to facilita- trees after 3 generations (30 years). After this tion by cottonwood. The overstory canopy point the number of mature trees begins to could be making the local microclimate cooler increase geometrically as increasingly more and more humid than in the adjacent steppe mature trees are recruited in each consecutive (Callaway 1992), and/or cottonwood may be year (Fig. 3). acting as a hydraulic pump, bringing water Our model is based on a mean annual from the water table to the upper rooting zone recruitment rate, and few stands will develop (Caldwell et al. 1998). However, once Russian exactly as predicted in Figure 3. Recruitment olive is present on these high terraces, it will be temporally sporadic, and the rate will appears to persist after overstory cottonwoods be higher in some sites but lower in others. have died. In the absence of Russian olive, Nonetheless, our model has heuristic value in many such sites would be dominated by sage- illustrating how low recruitment rate and late brush steppe (Boggs 1984). maturation age interact to damp the speed of In the riparian systems of eastern Montana, invasion. It also can provide guidelines for the Russian olive can fill the niche of late-succes- frequency of eradication treatments (see below). sional canopy dominant. It is ecologically sim- This model is consistent with our stand data, ilar to green ash and could replace it where indicating that Russian olive has been present both occur. Russian olive is shade tolerant for at least 36–40 years on both rivers, but den- (Campbell and Dick-Peddie 1964), capable of sity in many stands is low. In Montana, Russian reproducing beneath a cottonwood canopy or olive is near the northern limit of its natural- in other shaded sites. Older stands of Russian ized range in North American. It may be more olive generally have plants of many ages, indi- invasive in warmer parts of semiarid western cating that infrequent disturbance events are North America not required for recruitment. As cottonwoods decline with age and eventually disappear, MANAGEMENT IMPLICATIONS Russian olive can continue to reproduce and may become the canopy dominant (Lesica and Russian olive will continue to increase along Miles 1999). Green ash is also capable of Montana rivers and streams, at least partly due reproducing in the shade of cottonwood and is to relative immunity from beaver use and its the native late-successional dominant along tree-size stature and shade tolerance. Cotton- major rivers in much of the Northern Great wood successfully establishes on alluvial bars Plains and parts of eastern Montana (Johnson and in flood channels and will continue to be et al. 1976, Hansen et al. 1995). However, the dominant tree along many reaches of free- Russian olive is becoming more common in flowing rivers. However, we believe that Russ- Montana, and our data indicate that it grows 3 ian olive may replace cottonwood along reaches times faster in girth than green ash. of rivers and streams where overbank alluvial Russian olive has a low recruitment rate in deposition provides the only establishment sur- eastern Montana and requires ca 10 years to faces for cottonwood seedlings. Russian olive reach reproductive maturity; thus, invasion can become dominant along riverbanks, ditches, 2001] RUSSIAN OLIVE NATURAL HISTORY 9

ditches. Consequently, these are the places where control measures will have a more long- term benefit. Most, but not all, Russian olive invasions in eastern Montana occur over a period of several decades. Eradication of mature trees every 10 years or of all plants every 30 years may be effective strategies for controlling Russian olive.

ACKNOWLEDGMENTS

We thank Joe Frazier and Janet Henderson for help in the field and Steve Cooper, Dennis Flath, Louise de Montigny, John Malloy, Mike Merigliano, Jay Parks, Jody Peters, and Larry Rau for advise. Duncan Patten, Pat Shafroth, Stanley Smith, Linda Ulmer, and Helen Atthowe gave helpful comments on earlier drafts of the Fig. 3. Average number of mature Russian olive trees over time since colonization based on a model employing paper. Funding was provided by the Montana empirically derived values for mean recruitment rate and State Office of the Bureau of Land Management maturation age and assuming a single immigration and no (BLM) and the Montana Department of Fish, density-dependent effects. Wildlife and Parks.

LITERATURE CITED and overflow channels as well as in late-successional, declining cottonwood forests. Moist, ALT, D., AND D.W. HYNDMAN. 1986. Roadside geology of little-shaded channels and ditches where flood- Montana. Mountain Press, Missoula, MT. 427 pp. ing rarely occurs provide habitat conducive to BELOVSKY, G.E. 1984. Summer diet optimization by invasion. Russian olive may also increase its beaver. American Midland Naturalist 111:209–221. BOGGS, K.W. 1984. Succession in riparian communities of prevalence in the understory of many younger the lower Yellowstone River, Montana. Master’s the- riparian forests, possibly displacing native sis, Montana State University, Bozeman. shrubs and small trees such as green ash. BRAATNE, J.H., S.B. ROOD, AND P.E. HEILMAN. 1996. Life Russian olive does not establish well in dry, history, ecology, and conservation of riparian cottonwoods in North America. Pages 57–85 in R.F. Stettler upland habitats, and invasion of riparian com- et al., editors, Biology of Populus and its implications munities often depends on proximity to estab- for management and conservation. NRC Research lished, mature trees. Invasion in our study areas Press, Ottawa, ON, Canada. and presumably along most Montana rivers is BRADLEY, C.E., AND D.G. SMITH. 1986. Plains cottonwood recruitment and survival on a prairie meandering relatively recent and ongoing, receiving impor- river floodplain, Milk River, southern Alberta and tant impetus from domestic plantings (Lesica northern Montana. Canadian Journal of Botany 64: and Miles 1999). Russian olive should not be 1433–1442. planted close to riparian or overflow areas or BRINSON, M.M., B.L. SWIFT, R.C. PLANTICO, AND J.S. BAR- irrigation ditches if invasions are to be avoided. CLAY. 1981. Riparian ecosystems: their ecology and status. U.S. Fish and Wildlife Service, Biological Ser- Where a dynamic disturbance regime main- vices Program FWS/OBS-81/17, Washington, DC. tains most of the active floodplain in early-suc- CALDWELL, M.M., T.E. DAWSON, AND J.H. RICHARDS. 1998. cessional vegetation (i.e., young to middle-age Hydraulic lift: consequences of water efflux from the cottonwoods and willows), only a small pro- roots of plants. Oecologia 113:151–161. portion of the riparian zone will remain undis- CALLAWAY, R.M. 1992. Effect of shrubs on recruitment of Quercus douglasii and Quercus lobata in California. turbed long enough to become fully stocked Ecology 73:2118–2128. with Russian olive. Russian olive is more likely CAMPBELL, C.J., AND W.A. DICK-PEDDIE. 1964. Compari- to become dominant in reaches where the ripar- son of phreatophyte communities on the Rio Grande ian zone is less dynamic or where the stream in New Mexico. Ecology 45:492–502. CARMAN, J.G., AND J.D. BROTHERSON. 1982. Comparisons is more entrenched or has been artificially of sites infested and not infested with saltcedar channelized. These include regulated or en- (Tamarix pentantra) and Russian olive (Elaeagnus trenched rivers, smaller streams, and irrigation angustifolia). Weed Science 30:360–364. 10 WESTERN NORTH AMERICAN NATURALIST [Volume 61

CHRISTIANSEN, E.M. 1963. Naturalization of Russian olive north-central Montana. Canadian Journal of Botany (Elaeagnus angustifolia L.) in Utah. American Mid- 77:1077–1083. land Naturalist 70:133–137. LITTLE, E.L. 1961. Sixty trees from foreign lands. USDA CURRIER, P.J. 1982. The floodplain vegetation of the Platte Forest Service Agriculture Handbook 212, Washing- River: phytosociology, forest development, and seed- ton, DC. ling establishment. Doctoral dissertation, Iowa State MCCUNE, B., AND M.J. MEFFORD. 1995. PC-ORD. Multi- University, Ames. variate analysis of ecological data. Version 2.0. MjM DAUBENMIRE, R. 1959. A canopy-coverage method of veg- Software Design, Gleneden Beach, OR. etational analysis. Northwest Science 33:43–64. NAIMAN, R.J., H. DECAMPS, AND M. POLLOCK. 1993. The DEWAAL, L.C., L.E. CHILD, P.M. WADE, AND J.H. BOCK, role of riparian corridors in maintaining regional EDITORS. 1994. Ecology and management of invasive biodiversity. Ecological Applications 3:209–212. riverside plants. John Wiley and Sons, West Sussex, NATIONAL OCEANIC AND ATMOSPHERIC ASSOCIATION. 1982. England. 217 pp. Monthly normals of temperature, precipitation and DRAKE, J.A., H.A. MOONEY, F. DI CASTRI, R.H. GROVES, heating and cooling degree days. Montana, 1951–1980. F. J . K RUGER, M. REJMANEK, AND M. WILLIAMSON, National Climate Center, Asheville, NC. EDITORS. 1989. Biological invasions: a global perspec- OLSON, T.E., AND F.L. KNOPF. 1986a. Naturalization of tive. Wiley, Chichester, England. 525 pp. Russian-olive in the western United States. Western EASTER-PILCHER, A.L. 1987. Forage utilization, habitat Journal of Applied Forestry 1:65–69. selection and population indices of beaver in north- ______. 1986b. Agency subsidization of rapidly spreading western Montana. Master’s thesis, University of Mon- exotic. Wildlife Society Bulletin 14:492–493. tana, Missoula. PERRY, E.S. 1962. Montana in the geologic past. Montana ELIAS, T.S. 1980. The complete trees of North America. Bureau of Mines Bulletin 26, Butte. Field guide and natural history. Van Norstrand Rein- READ, R.A. 1958. Silvical characteristics of plains cotton- hold Co., New York. wood. USDA Forest Service Rocky Mountain Forest FINCH, D.M., AND L.F. RUGGIERO. 1993. Wildlife habitats and Range Experiment Station Paper 33, Fort and biological diversity in the Rocky Mountains and Collins, CO. Northern Great Plains. Natural Areas Journal 13: REED, P.B. 1988. National list of plant species that occur 191–203. in wetlands: North Plains (Region 4). USDI Fish and GAUCH, H.G. 1982. Multivariate analysis in community Wildlife Service Biological Report 88(26.4), Wash- ecology. Cambridge University Press, Cambridge. ington, DC. 298 pp. ROOD, S.B., AND J.M. MAHONEY. 1990. Collapse of riparian GREAT PLAINS FLORA ASSOCIATION. 1986. Flora of the poplar forests downstream from dams in western Great Plains. University Press of Kansas, Lawrence. prairies: probable causes and prospects for mitiga- GREEN, D.M., AND J.B. KAUFFMAN. 1995. Succession and tion. Environmental Management 14:451–464. livestock grazing in a northeastern Oregon riparian ______. 1995. River damming and riparian cottonwoods ecosystem. Journal of Range Management 48: along the Marias River, Montana. Rivers 5:195–207. 307–313. RUTHERFORD, M.C. 1979. Plant-based techniques for de- HANSEN, P., R. PFISTER, K. BOGGS, B.J. COOK, J. JOY, AND termining available browse and browse utilization: a D.K. HINKLEY. 1995. Classification and management review. Botanical Review 45:203–228. of Montana’s riparian and wetland sites. Montana SCOTT, M.L., G.T. AUBLE, AND J.M. FRIEDMAN. 1997. Flood Forest and Conservation Experiment Station Miscel- dependency of cottonwood establishment along the laneous Publication 54, Missoula. Missouri River, Montana, USA. Ecological Applica- HAYES, B. 1976. Planting the Elaeagnus Russian olive and tions 7:677–690. autumn olive for nectar. American Bee Journal 116: SCOTT, M.L., J.M. FRIEDMAN, AND G.T. AUBLE. 1996. Flu- 74–82. vial process and the establishment of bottomland HUSS-DANELL, K. 1997. Actinorhizal symbioses and their trees. Geomorphology 14:327–340. N2 fixation. New Phytologist 136:375–405. SHAFROTH, P.B., G.T. AUBLE, AND M.L. SCOTT. 1995. Ger- JENKINS, S.H. 1980. A size-distance relation in food selec- mination and establishment of the native plains cot- tion by beavers. Ecology 61:740–746. tonwood (Populus deltoides Marshall subsp. monilif- JOHNSON, W.C., R.L. BURGESS, AND W.R. KEAMMERER. era) and the exotic Russian-olive (Elaeagnus angusti- 1976. Forest overstory vegetation and environment folia L.). Conservation Biology 9:1169–1175. on the Missouri River floodplain in North Dakota. STOHLGREN, T.J., K.A. BULL, Y. OTSUKI, C.A. VILLA, AND M. Ecological Monographs 46:59–84. LEE. 1998. Riparian zones as havens for exotic plant KAUFFMAN, J.B., AND W.C. KRUEGER. 1984. Livestock species in the central grasslands. Plant Ecology 138: impacts on riparian ecosystems and streamside man- 113–125. agement implications . . . a review. Journal of Range WHITAKER, R.H. 1975. Communities and ecosystems. 2nd Management 37:430–437. edition. MacMillan Publishing, New York. KNOPF, F.L., AND T.E. OLSON. 1984. Naturalization of Russian-olive: implications to Rocky Mountain Received 14 July 1999 wildlife. Wildlife Society Bulletin 12:289–298. Accepted 13 March 2000 LESICA, P., AND S.L. MILES. 1999. Russian olive invasion into cottonwood forests along a regulated river in Western North American Naturalist 61(1), © 2001, pp. 11–18

BRANCHINECTA HIBERNA, A NEW SPECIES OF FAIRY SHRIMP (CRUSTACEA: ANOSTRACA) FROM WESTERN NORTH AMERICA

D. Christopher Rogers1 and Michael Fugate2

ABSTRACT.—Branchinecta hiberna, a new species of fairy shrimp, is described from temporary pools in the Great Basin region of south central Oregon, northeastern California, and adjacent Nevada. The new species shares several characters with Branchinecta cornigera Lynch, 1958: males bear a similar large patch of small spines on the basal segment of antenna 2, and females bear the similar robust antenna 2 with medial spur, brood pouch shape, and resting egg (cyst) morphology. The new species differs from B. cornigera in the shape of the distal segment of antenna 2 and the number and size of spines on the paired penis warts of males, and in the thoracic spine pattern and lack of dorsal cephalic projections in females. Observations on behavior and ecology of B. hiberna are discussed.

Key words: Branchinecta, new species, Branchinecta hiberna, Great Basin, fairy shrimp, Anostraca.

The following description presents a new METHODS species of Branchinecta. This is the 40th species described in this genus, which achieves its Dry soil samples were collected in October greatest diversity in the Americas. Most species 1993. Pieces of the top 2–5 cm of soil from the occur in vernal pools and other seasonal wet- bottoms of dry pools were collected and stored lands in the western United States and in in resealable plastic bags until samples were Argentina. One species is reported from the removed for hydration. Samples of approximate- Antarctic (Jurasz et al. 1983), and 6 are reported ly 75 mL dry soil were hydrated with deion- from Eurasia (Belk and Brtek 1995). This new ized water in 10-L glass aquaria. The aquaria species is the 24th anostracan reported from were placed in a 4°C walk-in cold room and California, the 8th from Oregon, and 6th from aerated vigorously for 24 hours, stirred, and Nevada. then gently aerated until the shrimp were fully We each discovered this new species inde- grown. After 24–48 hours, incandescent lights pendently. Fugate reared specimens from soil were used to raise the temperature to 13–15°C. samples collected from the Great Basin regions Hatching under these conditions normally of Oregon, and Rogers collected live animals occurred in 3–5 days. Shrimp were fed with from the Great Basin regions of California, baker’s yeast dissolved in deionized water. Oregon, and Nevada. Several biologists (Coopey We collected live animals from pools in 1946, Lynch 1972, C. Hunter personal com- February and March 1998 in the Great Basin munication) extensively sampled filled pools Desert regions of California, Oregon, and in this area, but none reported this species. Nevada from pools that were thawed, partially Fugate sampled filled pools in the area during covered with ice, or covered with a layer of ice May 1993 and returned in October to collect or ice and snow. Collections were made with a soil samples. Rogers collected from filled dip net. Where animals were collected from pools in the area between the end of March clear water, we stalked each specimen individ- and July 1987, 1989, 1990, and 1995 through ually due to the animal’s strong avoidance of 1999. Although numerous branchiopods were any disturbance in the water. present April through June, the species described in this paper was not found until soil MATERIAL EXAMINED samples were hydrated in the laboratory or surveys were performed during the final win- USA. CALIFORNIA, Lassen Co.: Tire ruts on ter months. Smoke Creek Road, 14 mi E of Hwy 395, 1700

1Jones & Stokes Associates, Inc., 2600 “V” Street, Sacramento CA 95818-1914. 2Wm. Keck Science Center, Claremont College, 925 N. Mills Avenue, Claremont CA 91711-5916.

11 12 WESTERN NORTH AMERICAN NATURALIST [Volume 61 m elev, 18 March 1999, 9 males, 11 females, Branchinecta hiberna n. sp. D.C. Rogers. Volcanic mud-flow vernal pool, (Figs. 1–3) 18 mi E of Hwy 395, 1750 m elev, 18 March 1999, 59 males, 43 females, D.C. Rogers. Modoc TYPES.—Holotype, male, data: CALIFORNIA, Co.: Railroad bed pool, Clear Lake Reservoir Modoc Co.: Modoc Plateau, volcanic mud-flow Road, 100 m E of Hwy 139, 1800 m elev, 9 temporary pool, 1530 m, 17 March 1998, D.C. March 1998, 18 males, 14 females, D.C. Rogers. Rogers, deposited: California Academy of Sci- Railroad bed pool, Clear Lake Reservoir Road, ences, San Francisco, CAS type no. CASIZ 100 m E of Hwy 139, 17 March 1998, 78 males, 119132. Allotype, female: same data as holo- 76 females, D.C. Rogers. Railroad bed pool, type. Paratypes: same data as holotype, 10 Clear Lake Reservoir Road, 100 m E of Hwy females, 10 males, deposited: California Acad- 139, 26 March 1998, 1 male, D.C. Rogers. Mud- emy of Sciences, San Francisco, CASIZ 119133. flow temporary pool along Harvey Buttes Road, Paratypes: same data as holotype, 2 females, 2 3 mi W of Harvey Lake, 1800 m elev, 17 March males, deposited: National Museum of Natural 1998, 39 males, 56 females, D.C. Rogers. Vol- History, Washington, D.C., USNM 268594; 10 canic mud-flow vernal pool, Harvey Buttes females, 10 males, deposited: DCR collection; Road, 3 mi W of Harvey Lake, 1800 m elev, 3 2 females, 3 males, deposited: collection of mi west of Harvey Lake, 17 March 1998, 23 Denton Belk; 10 females, 12 males, deposited: males, 34 females, D.C. Rogers. Volcanic mud- collection of Richard Hill; 2 females, 2 males, deposited: Bohart Museum of Entomology, flow vernal pool, Harvey Buttes Road, 2 mi E Davis, California. of Harvey Lake, 1800 m elev, 17 March 1998, TYPE LOCALITY.—The type locality is a vol- 13 males, 13 females, D.C. Rogers. Volcanic canic mud-flow temporary pool (sensu Hol- mud-flow vernal pool, Tucker Buttes Road, 3 land and Jain 1977) approximately 2 km north mi E of Harvey Lake, 1800 m elev, 17 March of Clear Lake Reservoir Road and 200 m east 1998, 32 males, 31 females, D.C. Rogers. Vol- of Harvey Buttes Road, Modoc County, Cali- canic mud-flow vernal pool, Tionesta Road, fornia. The area lies west of Clear Lake Reser- Perez, 0.25 mi W of Hwy 139, 1750 m elev, 17 voir, east of Hwy 139, and southeast of the March 1998, 12 males, 14 females, D.C. Rogers. community of Tule Lake. This pool is at an Volcanic mud-flow vernal pool, 2.5 mi N of altitude of 1530 m on the Modoc Plateau. The Big Sage Reservoir, 1750 m elev, 17 March pool, approximately 300 m2 in size, generally 1998, 2 males, 3 females, D.C. Rogers. NEVADA, inundates in November and dries in May. Washoe Co.: Vernal pool, SSR 8A (Hwy 299 in From the end of November through March California), Surprise Valley, near the base of the pool is frozen and under a few inches of Fortynine Mountain, 1850 m elev, 17 March snow. The pool has a grassy bottom with 1998, 3 males, 2 females, D.C. Rogers. OREGON, numerous volcanic rocks that project from the Harney Co.: Temporary pool 10 km S of Riley, water. Surrounding uplands are dominated by Hwy 395, 43°27′54″N, 119°33′39″W, 16 April Artemisia sp., annual grasses, and Juniperus 1999, 1 male, R.E. Hill. Temporary pool 15.6 occidentalis var. occidentalis. km S of Riley, Hwy 395, 16 April 1999, 1 male, ETYMOLOGY.—The species name is from R.E. Hill. Temporary pool 15.6 km S of Riley, the Latin word for winter, hibernum, and refers Hwy 395, 16 April 1999, 3 males, 2 females, to the animal’s late-winter activity period. R.E. Hill. Lake Co.: Temporary pool (~0.2 ha) Gender is masculine. on the south side of Squaw Butte, bisected DIAGNOSIS.—Male: Basal segment of 2nd by OR 31, 2 km N of Carlon Rd (43°02′N, antenna with a ventrally directed medial bulge 120°47′W), soil samples collected October bearing small, scattered spines at distal end 1994, M. Fugate. Temporary pool (0.02 ha), 13 (Fig. 1A). Basal segment directed anteroven- km W of US 395, 0.5 km N of XL Ranch Rd trally with distal half bent ventrally (Fig. 1B). (42°47′N, 120°21′W), soil samples collected Apophyses absent. Pulvilli ridgelike, lying at October 1994, M. Fugate. Large temporary bases of 2nd antennae and directed medially. pool (~0.2 ha), 5 km E of US 395, 0.2 km N of Distal 2nd antennal segment less than 1/3 Hogback Rd (42°43′N, 120°03′W), soil sam- length of basal segment. Distal segment flat- ples collected October 1994, elev, 1300–1500 tened laterally, directed medially, with apex m, M. Fugate. bent medially ∼30° (Fig. 1D). Medial surface 2001] NEW SPECIES OF BRANCHINECTA 13 of distal segment with patch of small spines. each. Endopodites ovate-triangular. Epipodite Anterior surface of base of distal 2nd antennal truncate (Fig. 2D). segment with patch of spines. Basal segments Female: Distal 1/3 of basal segment of 2nd of 2nd antennae and labrum covered with fine antenna bearing a stout, ventrally directed, spines. Genital segment with single ventrolat- medial spur. Thirty-three percent of females eral conical protuberance on each side. with an apical, anterolateral, hemispherical Everted penes elongated, extending to the 3rd bulge covered in small spines on 2nd antenna postgenital abdominal segment (Fig. 2A). Apices (Fig. 1C). Distal end stout, medially curved, and of everted penes bearing 2 dorsal wartlike apically acute. First antenna 60% length of 2nd mounds, each bearing 10–15 recurved spines antenna. Head without dorsal protuberances. about 1/3 as long as wartlike mound (Figs. 2B, Thorax with paired conical dorsolateral lobes C). Penes with a single medial basal spine on segments 3 and 5 or 6 through segments 10

Fig. 1. Branchinecta hiberna n. sp. types: A, male, left side of head, anterior view; B, male, left 2nd antenna, anterolateral view; C, female, left side of head, anterior view; D, distal segment of left 2nd antenna of male, from left to right: medial view, anterior view, lateral view, posterior view. 14 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Fig. 2. Branchinecta hiberna n. sp.: A, male, penes everted; B, detail of apex of left pene, lateral view; C, detail of apex of left pene, medial view; D, endopodite of male of thoracic segment 5 (setae not shown); E, endopodite of female of thoracic segment 5 (setae not shown); F, allotype, lateral view. or 11. Fourth thoracic segment bearing a sin- with angular, oval surface depressions, diame- gle conical dorsolateral lobe on each side. ter 20 µm, some depressions joined (Fig. 3). Thorax bearing lateral hemispherical lobes on COMPARISONS.—Male Branchinecta hiberna segments 3 through 9 or 11 (Fig. 2F). Ovisac are separated from all other reported Branch- fusiform, extending to postgenital abdominal inecta species by the presence of the ventrally segment 5 or 6. Endopodites ovate (Fig. 2E). directed medial bulge on the medial surface of Epipodite ovate. Seventeen percent of living the proximal segment of the 2nd antennae. females yellow-gold in color compared to typi- Male B. hiberna most closely resemble B. cor- cal off-white of other Branchinecta sp. and nigera Lynch, 1958; however, the distal seg- remaining 83%. ments of the 2nd antenna of B. cornigera males Resting egg: Desiccation-resistance cysts are nearly parallel sided and have acute apices. spherical, diameter approximately 250 µm, The everted penes of B. hiberna extend to the 2001] NEW SPECIES OF BRANCHINECTA 15

Fig. 3. Branchinecta hiberna n. sp.: A, cyst; cyst diameter = 250 µm; Squaw Butte, Lake County, OR; B, detail of cyst surface; polygonal depressions average width = 20 µm.

3rd postgenital segment, whereas in B. corni- Branchinecta hiberna and B. cornigera fe- gera the everted penes extend only to the 2nd males share the robust antenna 2 with medial postgenital segment. Similarly, the endopodites spur, brood pouch shape, and bright color- of B. cornigera are sickle shaped while those ation. Female B. hiberna are separated from B. of B. hiberna are triangular. Branchinecta cornigera Lynch, 1958 by the lack of trans- hiberna and B. cornigera share the large patch verse corneous projections at the sides of the of small spines on the proximal segment of head dorsal to the maxillary glands and by the antenna 2, and the abbreviated length of the arrangement of dorsolateral lobes. Female B. distal segment of antenna 2. cornigera have dorsolateral lobes on segments 16 WESTERN NORTH AMERICAN NATURALIST [Volume 61

6 through 11. Female B. hiberna are separable from B. pollicifera Harding, 1940 by the lack of dorsomedial cleft thoracic projections. Female B. hiberna are separated from all other reported Branchinecta species by the presence of the subapical, medial spur on the basal segment of the 2nd antennae. Many (33%) B. hiberna females also bear an apical, anterolateral spinose bulge on the basal segment of 2nd antenna as does B. cornigera; however, this bulge is many times larger in B. hiberna. The resting cysts of both B. cornigera and B. lynchi have angular surface depressions but tend to be more circular than oval and have larger diameters (30–60 µm). DISTRIBUTION AND HABITAT.—Branchinecta hiberna has been collected from south central Oregon, northeastern California, and adjacent Nevada (Fig. 4). Collection sites tend to be high-desert volcanic mud-flow vernal pools with clear or highly turbid water. Branchinecta hiberna was also collected from railroad bed toe-drains and roadside ditches, some as small as 0.15 m2. Populations were found throughout the Modoc Plateau from Lava Beds National Mon- ument to Clear Lake Reservoir, and from the city of Tule Lake to the Skedaddle Mountains, Fig. 4. Distribution of Branchinecta hiberna n. sp. Star indicates type locality. north of Honey Lake in Lassen County, Califor- nia. In some locations on the Modoc Plateau, B. hiberna was collected from pools covered with 0.5 to 2.5 cm of ice and 3.0 cm of snow. bottom. The animal would then swim quickly Pools ranged in size from 250 m2 to 500 m2. in a zig-zag pattern through the vegetation for Two of the Oregon populations are located another 0.5 m, always staying near the bottom. north of Lake Abert within the boundaries of If there were no further disturbances, the ani- Pleistocene Lake Chewaucan, which dried mal would rise to mid-water and swim nor- approximately 10,000 years ago. Summer Lake mally. In habitats that were covered with ice, and Lake Abert form the modern remains of the animals were slightly sluggish, yet still the previously 1200-km2 lake. A 3rd Oregon quickly swam from any disturbance. population was reared from soil collected DISCUSSION.—Hatching and rearing of below Squaw Butte, north of Summer Lake. branchiopod crustaceans from the dry soil of All collection locations in Oregon are from temporary pools often has been employed to Lake and Harney counties. reveal new species (e.g., Baird 1861, Brauer One population was found in Nevada on 1877, Sars 1896a, 1896b, 1898a, 1898b, Barnard the south side of SSR 8A (Highway 299 in Cal- 1928, Harding 1940). This technique is invalu- ifornia) in Surprise Valley at the base of Forty- able since pools are dry for most of the year nine Mountain in Washoe County. and are often inaccessible when filled due to BEHAVIOR.—Branchinecta hiberna displayed ice, mud, or snow. Barnard (1928) endorsed a strong predator-avoidance response in the this technique: “This is an extremely valuable field. In pools with low turbidity and without method of collecting, and no opportunity of ice, B. hiberna would quickly dart away from collecting samples of mud should be neglected.” any disturbance in the water or at the surface. Branchinecta hiberna hatches sometime dur- During the initial darting the animal would ing the winter. In culture, hatching occurred move as much as 1 m away and to the pool soon after cysts were hydrated at 4°C, giving 2001] NEW SPECIES OF BRANCHINECTA 17 no indication of a pre-hatching phase as Broch America suggests a relationship between these (1965) reported for Eubranchipus bundyi 3 species. Since B. pollicifera is quite morpho- Forbes, 1876. Branchinecta hiberna appears to logically distinct from other living Branchinecta be univoltine but may have successive emer- (female with large, cleft thoracic processes, gences in the event of subsequent thaws and male with 2 basal spines on the penes versus refreezings. One frozen-over railroad toe-drain 1, and an apophysis-like structure extending pool had no identifiable invertebrates on 28 posteriomedially from the distal end of the basal February 1998. On 9 March 1998 the same segment of the 2nd antenna [Harding 1940]) location had, under ice and snow, numerous and bears certain similarities to fossil Branch- immature B. hiberna co-occurring with imma- inecta (Belk and Schram in press), this 2nd ture Eubranchipus and calanoid copepods. By antennal spur may be pleisiomorphic. 17 March 1998, B. hiberna females were actively shedding their cysts, while Eubranchipus, now ACKNOWLEDGMENTS identifiable as E. serratus, did not yet have cysts in their brood pouches, and many imma- The authors thank Denton Belk, Richard ture B. dissimilis were present, as were some Hill, Robert Preston, Gerrit Platenkamp, and aquatic insects, calanoid copepods, cladocera, an anonymous reviewer for their comments; and small Lepidurus sp. On 27 March 1998, B. Richard Hill for additional material; and Tim dissimilis was present in large numbers, while Messick for generating the map. only a single male B. hiberna and 8 male and LITERATURE CITED female E. serratus were recovered after an hour of searching. On 10 April 1998 only B. BAIRD, W. 1861. Description of a new species of Branchi- dissimilis was present. pus (B. eximius) from the pool of Gihon in Jerusalem. Shorebirds and ducks were observed in Annals and Magazine of Natural History, Series 3, playas and sage flat wetlands near active 8:209–210 + plate 12. BARNARD, K.H. 1928. Contributions to the crustacean Branchinecta hiberna populations and may be fauna of South Africa. 10. A revision of the South predatory on B. hiberna. However, no birds African Branchiopoda. Annals of the South African were observed on any wetlands as small as Museum 29(1):181–272. BELK, D., AND J. BRTEK. 1995. Checklist of the Anostraca. those from which B. hiberna was collected. Pages 315–354 in D. Belk, H.J. Dumont, and G Maier, Predaceous diving beetles (Dytiscidae), water guest editors, Hydrobiologia: studies on large bran- scavenger beetles (Hydrophilidae), water crawl- chiopod biology and aquaculture II. Volume 298 ing beetles (Haliplidae), and backswimmers (1–5). BELK, D., AND F. R . S HRAM. In press. A new species of (Notonectidae) were all present in B. hiberna anostracan from the Miocene of California. Journal habitat in low numbers when females were of Crustacean Biology: In press. shedding their eggs and only appeared in larger BRAUER, F. 1877. Beitrge zur Kenntnis der Phyllopoden. numbers after B. hiberna had disappeared from Sitzungsberichte der mathematisch-naturwissenschaf- ten Classe der kaiserlichen Akademie der Wissen- the pools. Branchinecta hiberna was found co- schaften, Abteilung 1,75(1-5):583–614. occurring in pools with the fairy shrimps Eu- BROCH, E.S. 1965. Mechanism of adaptation of the fairy branchipus serratus Forbes, 1876, Branchinecta shrimp Chirocephalus bundyi Forbes to the temporary pond. Memoirs of the Cornell University Agri- gigas Lynch, 1937, and Branchinecta dissimilis cultural Experiment Station, No. 392. Lynch, 1972; the tadpole shrimp Lepidurus COOPEY, R.W. 1946. Phyllopods of southeastern Oregon. lemmoni (Holmes), 1952 and Lepidurus sp.; and Transactions of the American Microscopical Society the clam shrimp Lynceus brachyurus Müller, 65:338–345. HARDING, J.P. 1940. VIII. Crustacea: Anostraca and Con- 1776. chostraca. Transactions of the Linnaean Society, Branchinecta hiberna’s short life cycle, strong London (3), 1(2):149–152. disturbance-avoidance response, and activity HOLLAND, R.F., AND S.K. JAIN. 1977. Vernal pools. Pages period under ice may all serve as protection 515–533 in M.G. Barbour and J. Major, editors, Ter- restrial vegetation of California. Wiley-Interscience, from predators and competitors, and may also New York. explain why this species escaped detection for JURASZ, W., W. KITTEL, AND P. P RESLER. 1983. Life cycle of so long on the Modoc Plateau. Branchinecta gaini Daday, 1910, (Branchiopoda: The presence of a medial spur on the 2nd Anostraca) from King George Island, South Shetland Islands. Polish Polar Research 4:143–154. antennae of B. hiberna and B. cornigera in LYNCH, J.E. 1958. Branchinecta cornigera, a new species North America and B. pollicifera in South of anostracan phyllopod from the state of Washington. 18 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Proceedings of the United States National Museum ______. 1898a. On some South-African Phyllopoda raised 108:25–37. from dried mud. Archiv for Mathematik og Naturvi- ______. 1972. Branchinecta dissimilis n. sp., a new species denskab 20(4):1–43, 4 plates. of fairy shrimp, with a discussion of specific charac- ______. 1898b. Descriptions of two additional South- ters in the genus. Transactions of the American Micro- African Phyllopoda. Archiv for Mathematik og Natur- scopical Society 91:240–243. videnskab 20(6):1–23, 2 plates. SARS, G.O. 1896a. Descriptions of two new Phyllopoda from North Australia. Archiv for Mathematik og Naturvi- Received 21 September 1999 denskab 18(8):1–36, 6 plates. Accepted 11 January 2000 ______. 1896b. On some west Australian Entomostraca raised from dried sand. Archiv for Mathematik og Naturvidenskab 19(1):1–35, 4 plates. Western North American Naturalist 61(1), © 2001, pp. 19–24

SPRUCE BEETLE (DENDROCTONUS RUFIPENNIS) OUTBREAK IN ENGELMANN SPRUCE (PICEA ENGELMANNII) IN CENTRAL UTAH, 1986–1998

Alan D. Dymerski1, John A. Anhold2,3, and Allen S. Munson1

ABSTRACT.—Extensive Engelmann spruce (Picea engelmannii Parry ex Engelm.) mortality caused by the spruce beetle (Dendroctonus rufipennis Kirby) has been occurring at the southern end of the Wasatch Plateau in central Utah. This spruce beetle outbreak is the largest recorded in Utah history. An extensive ground survey was conducted in 1996 on the Manti-LaSal National Forest, Sanpete and Ferron Ranger Districts, to document mortality and impact of a major spruce beetle outbreak on post-outbreak forest composition. In 1998 the same sites were resurveyed. Survey results indicate Engelmann spruce basal area (BA) loss averaged 78% in trees ≥5 inches diameter breast height (DBH) in 1996. Ninety percent of BA ≥5 inches DBH was lost within the same sites by 1998. Tree mortality of spruce ≥5 inches DBH expressed in trees per acre (TPA) averaged 53% in 1996. In 1998 TPA ≥5 inches DBH mortality averaged 73%. Before the outbreak live Engelmann spruce BA ≥5 inches DBH averaged 99 square feet, and TPA ≥5 inches DBH averaged 97. In the sites surveyed in 1996 and resurveyed in 1998, Engelmann spruce BA ≥5 inches DBH averaged 21 and 9 square feet, and TPA ≥5 inches DBH averaged 43 and 25, respectively. Overstory tree species composition changed from stands dominated by spruce to subalpine fir. Stand ratings for potential spruce beetle outbreaks were high to mostly medium hazard pre-outbreak and medium to primarily low hazard by 1998, as a result of reduction in average spruce diameter, total basal area, and overstory spruce.

Key words: Dendroctonus rufipennis, bark beetles, insect outbreak, Scolytidae, Picea engelmannii.

The spruce beetle, Dendroctonus rufipennis National Forest. This represents the largest Kirby (Coleoptera: Scolytidae), is considered recorded outbreak in Utah. the most important natural mortality agent of Spruce beetle generally has a 2-year life mature Engelmann spruce (Picea engelmannii cycle. Adult beetles attack weakened and cur- Parry ex Engelm.; Holsten et al. 1999). Large- rently downed hosts in late spring and early scale outbreaks since the 1850s, affecting mil- summer. Eggs hatch through mid-October, lions of spruce from New Mexico and Arizona developing into 2nd through 4th instar larvae, through the Rocky Mountains and north to which is generally the overwintering life stage. British Columbia, have been documented by Approximately 1 year after attacking the host, Schmid and Frye (1977). Most outbreaks origi- larvae pupate, transforming into callow adult nate from disturbances such as windthrow, beetles. Following pupation, adult beetles over- avalanches, road building, landslides, and log- winter and emerge as mature adults the fol- ging residuals (Schmid 1981, Holsten et al. lowing summer to attack new host material. 1999). In the Manti-LaSal National Forest, a To document the vegetative effects of a spruce beetle outbreak began in 1986, primar- spruce beetle infestation across a large land- ily the result of a landslide that felled large scape, we conducted a ground survey over numbers of Engelmann spruce in the upper 4600 infested acres on the Manti-LaSal National southeastern portion of Twelvemile drainage. Forest (Fig. 1). Stands were selected because Since 1986, Forest Health Protection aerial beetle populations were declining on these sites. survey staff have annually monitored spread of the infestation. From 1987 through 1998, as a METHODS result of spruce beetle activity, 261,400 Engel- mann spruce trees have died on the Sanpete Fifteen stands totaling 4616 acres were sur- and Ferron Ranger Districts, Manti-LaSal veyed in 1996 based on access, topography,

1USDA Forest Service, Forest Health Protection, 4746 South 1900 East, Ogden, UT 84403. 2USDA Forest Service, Forest Health Protection, Arizona Zone Office, 2500 S. Pine Knoll Dr., Flagstaff, AZ 86001. 3Corresponding author.

19 20 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Fig. 1. Map of Wasatch Plateau, Manti-LaSal National Forest, Utah, showing Engelmann spruce stands surveyed to determine spruce beetle–caused impacts. Acres of each stand are also represented. and successive years of spruce beetle activity. adequately represent stand variability. Plot cen- Surveyed boundaries were digitized into a ters were systematically located at 10-chain geographic information system (ARC/INFO) (660-ft) intervals on transect lines spaced 10 to determine acreages and display stand loca- chains apart. A 20 basal area factor (BAF) was tions (Fig. 1). Populations were declining in all used to select sample trees. We measured all sample stands. Within these stands, 403 vari- sample trees ≥5 inches diameter breast height able-radius plots were measured. Thirteen of (DBH) and recorded the following character- fifteen original stands were resurveyed in 1998. istics for each: (1) DBH, (2) tree species, (3) We measured 272 plots encompassing 4110 tree condition as related to bark beetles (unat- acres. The 1998 plot centers were not the tacked, current attack, previous year’s attack, same as the 1996 centers; however, they were older attack, or strip attack), and (4) evidence in the general location. Uniform plot distribu- of other insect or disease activity. FINDIT, a tion throughout the stands was maintained to computer program for analyzing insect and 2001] DENDROCTONUS RUFIPENNIS OUTBREAK IN UTAH 21 disease populations from stand level surveys break BA and both 1996 and 1998 levels. (Bentz 2000), was used to compute average Spruce TPA mortality averaged 53% in 1996. DBH of spruce >10 inches, total basal area, In 1998 spruce TPA mortality increased to and proportion of spruce within a stand. Sum- 73% (Table 1). Again, there was a significant mary statistics were used in determining out- difference between pre-outbreak TPA and break potential hazard rating using the system both 1996 and 1998 levels. In addition, there developed by Schmid and Frye (1976.) The was a significant difference between 1996 and Schmid and Frye (1976) rating system for 1998 TPA levels. Table 1 shows that pre-out- spruce stands rates stand potential for spruce break average spruce DBH was 14.1 inches; beetle outbreak. We applied this rating scheme in 1996 and 1998, average DBH had decreased pre-outbreak and to surveyed stand data col- to 9.5 and 8.6 inches, respectively. Similar to lected in 1996 and 1998. To determine ratings the BA statistical findings, there was a signifi- for each stand, we examined 4 stand charac- cant difference between pre-outbreak DBH teristics: (1) average diameter of live spruce measurements and those determined in both >10 inches DBH, (2) stand basal area, (3) pro- 1996 and 1998. In all cases there was a trend portion of spruce in canopy, and (4) physio- within and among stands where stand DBH, graphic location. Physiographic location was TPA, and BA were reduced significantly dur- classified as well-drained creek bottoms or by ing this outbreak. site index (SI) obtained from ranger district Species composition pre-outbreak Engel- files. Calculated attributes were determined mann spruce averaged 74% of total live BA ≥5 for each parameter and assigned points. Points inches DBH. Spruce BA was reduced to 37% were summarized for each stand to determine in 1996 and 27% in 1998 (Fig. 2). Subalpine fir overall hazard. Mortality percentages were (Abies lasiocarpa [Hook.] Nutt.) comprised computed from FINDIT outputs. Weighted 22% of BA pre-outbreak, 51% in the 1996 sur- averages were calculated among stands using vey, and 60% in 1998. Other species recorded stand acres. Pre-outbreak stand averages were were quaking aspen (Populus tremuloides calculated using an average of both 1996 and Michx.), Douglas-fir (Pseudotsuga menziesii 1998 stand data. [Mirb.] Franco), and limber pine (Pinus flexilis We used 1-way analysis of variance with James). These species averaged 4% pre-out- Fisher’s multiple comparison procedures to break, 12% in 1996, and 13% in 1998. Engel- determine if there were any significant differ- mann spruce BA composition was 34–88% ences within sample periods: pre-outbreak, pre-outbreak, 15–56% in 1996, and 12–50% in 1996 survey, and 1998 survey. The F-test was 1998. used to test specific differences within live basal Physiographic locations for Schmid and area, trees per acre, and DBH for the sample Frye’s (1976) ratings for stands F, K, I, and M periods to 95% confidence levels (Table 1). were classified as well-drained creek bottoms; J has an SI of 86, and remaining stands have RESULTS indices between 40 and 80. Stand pre-outbreak ratings, along with 1996 and 1998 haz- In 1996, BA spruce mortality was 78% and ard ratings, are shown in Table 2. Before the increased to 90% by 1998 (Table 1). A signifi- outbreak all stands were classified as medium cant difference was found between pre-out- or high/intermediate hazard, with 2 rated high

± TABLE 1. Mean ( sx–) for stand variables measured pre-outbreak and as surveyed in 1996 and 1998, Manti-LaSal National Forest, Utah. Live spruce % BA spruce Live spruce % spruce Live spruce BA1 Range mortality TPA2 Range mortality DBH3 >5 Range Pre-outbreak 99 (9.9)a4 57–134 97 (12.3)a 43–149 14.1 (0.4)a 11.9–15.9 1996 survey 21 (3.4)b 5–36 78 (2.8) 43 (6.6)b 26–70 53 (4.1) 9.5 (0.5)b 7.7–11.8 1998 survey 9 (0.9)b 3–14 90 (1.2) 25 (3.8)c 8–41 73 (2.0) 8.6 (0.5)b 6.9–11.8

1BA = basal area per acre (sq ft). 2TPA = trees per acre >5 DBH. 3DBH = diameter at breast height >5. 4Means within columns followed by the same letter are not significantly different at the 0.05 level; Fisher’s least significant differences test. 22 WESTERN NORTH AMERICAN NATURALIST [Volume 61

overstory green spruce was, within a 5- to 6- year period, converted to a scene of grey, dead trees. Spruce beetle infestations reduce tree densities, sizes, and between-tree competition while increasing nutrient availability and accel- erating growth of residual trees (Schmid and Frye 1977, Veblen et al. 1991). Subcanopy trees can be expected to sustain high growth rates for 40–100+ years (Veblen et al. 1994). The result of this change is smaller and younger surviving spruce. Successional changes caused by spruce mortality result in long-term effects on water yield, forage production, wildlife, and fire hazard (Schmid and Frye 1977). In the absence of salvage logging or fire, succession will accelerate toward the shade-tolerant and non-host species subalpine fir (Schmid and Frye 1977, Veblen et al. 1991, Jenkins et Fig. 2. Percent species composition pre-outbreak, 1996, ± ± al. 1998). However, residual spruce seedlings and 1998, standard error of the means ( sx–). Other species includes aspen, Douglas-fir, and limber pine. will benefit more than fir seedlings from open- ing the overstory. Subcanopy trees of both fir and spruce will grow into the main canopy, hazard. Results from both surveys indicate a but spruce, with its greater maximum size and dramatic shift in stand hazard, with stands pri- longevity, will eventually attain basal area marily low and a few medium hazard. Stands dominance as the shorter-lived fir gives way to with pre-outbreak medium ratings exhibited disease and wind breakage. As the stand con- average spruce BA mortality of >76%; stands tinues to develop, it becomes increasingly sus- rated high/intermediate or high combined had ceptible to another major spruce beetle out- an average spruce BA mortality of >81%. break (Schmid and Hinds 1974, Veblen 1986, Alexander 1987, Jenkins et al. 1998). DISCUSSION Stand susceptibility to spruce beetles can be reduced through silvicultural thinning, Mortality of overstory Engelmann spruce thereby reducing potential impact of out- within the survey area verifies the significant breaks if compatible with management objec- loss of large-diameter spruce associated with tives. Through the use of stand rating schemes, landscape-scale spruce beetle outbreaks. Many forest managers can evaluate stand conditions, surveyed stands had pre-outbreak characteris- prioritize stand hazard, and initiate manage- tics that contribute to an increase in spruce ment practices to prevent or minimize out- beetle populations, i.e., large diameter, high break impacts. BA, and high proportion of spruce in the main Outbreak populations of spruce beetle are canopy. As a result, once a disturbance event occurring on 4 national forests in Utah (Table provides suitable downed host material and 3), suggesting widespread susceptibility to stands become infested, populations grow spruce beetle across many of Utah’s spruce rapidly. In stands where the majority of over- forests. Spruce beetle outbreaks will lead to ex- story vegetation is composed of Engelmann tensive structural changes within these spruce- spruce, visual effects of an outbreak can be fir forests as mature spruce are replaced by quite dramatic. Immediate effects of this spruce understory seedlings and advanced regenera- beetle outbreak are changes in vegetative tion. structure, species composition, and successional dynamics through the removal of large CONCLUSION overstory spruce. Our results mirror those of past studies by Massey and Wygant (1954), This investigation of the spruce beetle out- Schmid and Frye (1977), and Veblen et al. break on the Wasatch Plateau in central Utah (1991). A landscape once composed of large documents widespread, heavy spruce mortality 2001] DENDROCTONUS RUFIPENNIS OUTBREAK IN UTAH 23

TABLE 2. Pre-outbreak, 1996, and 1998 stand potential outbreak ratings. Hazard Pre-outbreak ratings 1996 ratings 1998 ratings High P,K None None High/Intermediate C,I,J,M,O None None Medium A,B,D,E,G,H,L,N A,F,I,K I,J,M Intermediate/Low None J,M H Low None B,C,D,E,G,H,L,N,O A,B,C,E,G,K,L,N,O

TABLE 3. Number of spruce trees killed by spruce beetles by national forest during 1997 as determined by aerial detections surveys. Number of spruce trees Forest Beetle population killed by spruce beetles Manti-LaSal Epidemic 37,400 Dixie Epidemic 23,800 Fishlake Epidemic 2,700 Wasatch-Cache Epidemic 1,400 Uinta Endemic 500 Ashley Endemic 200

and resultant changes in stand structure, species LITERATURE CITED composition, and forest succession. A disturbance event of this magnitude highlights large- ALEXANDER, R.R. 1987. Ecology, silviculture, and management of the Engelmann spruce–subalpine fir scale landscape changes and provides some type in the central and southern Rocky Mountains. insight regarding opportunities to minimize Agricultural Handbook 659, USDA Forest Service, future outbreak impacts within vegetatively Rocky Mountain Forest and Range Experiment Sta- managed sites. Landscapes composed of dense, tion, Fort Collins, CO. BENTZ, B.J. 2000. FINDIT forest insect and disease tally relatively even-aged, larger-diameter spruce system user manual. General Technical Report are susceptible to outbreaks of spruce beetle. RMRS-GTR-49, USDA Forest Service, Rocky Further impact assessments should be con- Mountain Forest and Range Experiment Station, ducted in other locations to capture the effects Fort Collins, CO. of this disturbance agent on Utah’s spruce-fir HOLSTEN, E.H., R.W. THEIR, A.S. MUNSON, AND K.E. GIBSON. 1999. The spruce beetle. USDA Forest forests. Insect and Disease Leaflet 127. JENKINS, M.J., C.A. DICUS, AND E.G. HEBERTSON. 1998. ACKNOWLEDGMENTS Postfire succession and disturbance interactions on an Intermountain subalpine spruce-fir forest. Pages 219–229 in T.L. Pruden and L.A. Brennan, editors, We thank the following people for invaluable Fire in ecosystems management: shifting the para- field-related assistance: Lynn Rasmussen, Dayle digm from suppression to prescription. Tall Timbers Bennett, Dawn Hansen, Valerie DeBlander, Fire Ecology Conference Proceedings 20, Tall Tim- Jason Johnson, Brian Gardner, Ben Meyerson, bers Research Station, Tallahassee, FL. MASSEY, C.L., AND N.D. WYGANT. 1954. Biology and con- and Phil Mocettini of USDA Forest Service; trol of the Engelmann spruce beetle in Colorado. Elizabeth Hebertson, Utah State University; U.S. Department of Agriculture Circular 944. 35 pp. Steve Deakins and Deborah Meyers, Utah SCHMID, J.M. 1981. Spruce beetles in blowdown. Research Department of Agriculture and Food. We also Note RM-411, USDA Forest Service, Rocky Moun- tain Forest and Range Experiment Station, Fort thank Dawn Hansen for digitizing stand bound- Collins, CO. aries into ARC/INFO and producing Figure 1 SCHMID, J.M., AND R.H. FRYE. 1976. Stand ratings for (map of Wasatch Plateau), and Greg Mont- spruce beetles. Research Note RM-309, USDA For- gomery and Diane Cote of the Manti-LaSal est Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO. National Forest for providing historical infor- ______. 1977. Spruce beetle in the Rockies. General Tech- mation and site index data. nical Report RM-49, USDA Forest Service, Rocky 24 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Mountain Forest and Range Experiment Station, VEBLEN, T.T., K.S. HADLEY, M.S. REID, AND A.J. REBERTUS. Fort Collins, CO. 1991. The response of subalpine forest to spruce SCHMID, J.M., AND T.E. HINDS. 1974. Development of beetle outbreak in Colorado. Ecology 72:213–221. spruce-fir stands following spruce beetle outbreaks. VEBLEN, T.T., K.S. HADLEY, E.M. NEL, R.T. KITZBERGER, Research Paper RM-131, USDA Forest Service, M. REID, AND R.VILLALBA. 1994. Disturbance regime Rocky Mountain Forest and Range Experiment Sta- and disturbance interactions in a Rocky Mountain tion, Fort Collins, CO. subalpine forest. Journal of Ecology 82:125–135. VEBLEN, T.T. 1986. Treefalls and the coexistence of conifers in subalpine forests of the central Rockies. Ecology Received 5 April 1999 67:644–649. Accepted 29 December 1999 Western North American Naturalist 61(1), © 2001, pp. 25–35

EXPERIMENTAL MANIPULATIONS OF FERTILE ISLANDS AND NURSE PLANT EFFECTS IN THE MOJAVE DESERT, USA

Lawrence R. Walker1, Daniel B. Thompson1, and Frederick H. Landau1

ABSTRACT.—In a mixed desert shrub community we removed and added shrub canopies to examine above- and belowground influences of 3 species of shrubs on islands of soil fertility and the survival of transplanted Ambrosia dumosa seedlings. Soils sampled under shrubs in the wet season had higher pH, water content, organic matter, and both total and mineralizable nitrogen than soils in adjacent open areas, confirming a widely established pattern in arid lands. However, we also found species differences in soil parameters. Soils under Coleogyne ramosissima had highest pH, soils under A. dumosa had highest water content and nitrogen mineralization rates, and soils under Larrea tridentata had lowest water content. Soils sampled under shrubs in the dry season, 7 months after experimental shrub removal, maintained higher organic matter and total and mineralizable nitrogen content than adjacent open soils, but pH and water were altered by shrub manipulations. Species differences persisted only in soil water levels (A. dumosa soils were driest). Over a 1-year period, transplanted A. dumosa seedlings had highest survivorship in shrub removal and open treatments and died most rapidly under control shrubs of all 3 species, suggesting that shrubs had a strong negative effect on seedling survival, even in the presence of higher organic matter, nutrients, and (initially) higher water content of fertile islands. Our results suggest that nurse plants and islands of soil fertility have the potential to facilitate growth of other species by nutrient additions, but that the net effect of nurse plants can be negative due to shading and/or root competition.

Key words: competition, facilitation, aridland soils, Ambrosia dumosa, Coleogyne ramosissima, Larrea tridentata.

The pattern of higher soil fertility under shrub roots may also compete with seedlings desert shrubs than in adjacent open areas is for available nutrients and water, and canopies well documented for arid lands (Charley and of established shrubs may reduce light levels West 1975, Virginia 1986, Franco and Nobel enough to limit primary productivity of under- 1989, Garner and Steinberger 1989, Schlesinger story seedlings (Charley and West 1975, Franco et al. 1996). Colonization of open areas (e.g., and Nobel 1989, Hunter 1989, Callaway et al. by species in the genus Ambrosia; McAuliffe 1996). The net effect of these potentially posi- 1988) apparently begins a cycle of habitat tive and negative attributes of desert shrubs amelioration in deserts in which organic mat- on recruitment of new seedlings can best be ter is built up from plant litter and entrapment examined with experimental manipulations of of wind-blown debris, and further enhanced fertile islands and associated shrubs. by secondary colonization of other shrubs and Fertile islands have important effects on the annuals. Animals presumably contribute to soil dynamics of desert ecosystems. Experimental nutrients, and their burrowing under shrubs studies of desert ecology have demonstrated increases soil aeration and water infiltration to that establishment and growth of dominant deeper soil layers (Garner and Steinberger shrub species are limited by nitrogen and 1989). These “fertile islands” under desert water (Fonteyn and Mahall 1981, Lajtha 1987, shrubs are therefore distinguished from adja- Smith et al. 1987, Fisher et al. 1988, Lajtha cent open areas between shrub canopies by and Whitford 1989). Thus, it is not surprising higher levels of organic matter and soil nutri- that there is strong evidence from arid lands of ents, higher rates of nutrient turnover, higher nurse plants that facilitate establishment of soil water content, higher productivity of other species (McAuliffe 1984, 1988, Franco annual plants, and increased soil microbe and and Nobel 1989). As the facilitated plant grows, vertebrate animal activity. Although these it may eventually out-compete the nurse plant. properties of fertile islands may enhance The fertile island can thus become the center recruitment of new seedlings under shrubs, of a centuries-long process of colonization and

1Department of Biological Sciences, Box 454004, University of Nevada–Las Vegas, Las Vegas, Nevada 89154-4004.

25 26 WESTERN NORTH AMERICAN NATURALIST [Volume 61 succession where nutrient cycling, plant productivity, and animal activities are all higher than in intershrub spaces. In this study we experimentally examined similarities and differences between above- and belowground influences of 3 species of desert shrubs on properties of fertile islands and transplanted seedlings by removing and adding shrub canopies. Species differences in fertile island characteristics were recognized Fig. 1. Diagram of natural pattern of islands of high soil by Charley and West (1975) but rarely have fertility under shrubs and less fertile spaces between been examined experimentally. We examined shrubs (top) and 5 treatments into which Ambrosia the effect of shrub canopy removal treatments dumosa seedlings were transplanted (bottom): S = control shrub, O = control open area, SR = removal of above- on survival of transplanted seedlings of ground shrub, OC = addition of cut shrub from SR to an Ambrosia dumosa, a species that may be criti- open area, SRC = removal followed by replacement of cal for establishing new fertile islands in the cut shrub in situ. Mojave Desert (cf. McAuliffe 1988). Our manipulations (Fig. 1) compared 5 treatments with various combinations of aboveground shade plots distributed along an elevational gradient effects, belowground nutrient effects, and be- from 1030 m to 1850 m in Lucky Strike Can- lowground root competition effects of desert yon. The study site is located on a 13-km-long shrubs. by 2-km-wide bajada with an average vertical slope of <5°. The slope lacks a central drainage METHODS channel but has multiple ephemeral channels scattered across the entire bajada that average Study Area 1–2 m deep; our study sites were only on the This study was conducted on a bajada (slope) broad, raised benches between washes. Soils in Lucky Strike Canyon (36°23′N, 115°28′W; of the canyon are limestone-derived with 1127 m elevation) on the east side of the cemented petrocalcic horizons (caliche) begin- Spring Mountain Range, 50 km northwest of ning at depths of 15–80 cm. Desert pavement Las Vegas, Nevada, in the Mojave Desert of and cryptobiotic crusts (cf. Evans and Belnap the southwestern United States. The study 1999) are moderately well developed at the area includes vegetation typical of regional site. Lucky Strike Canyon is characterized by desert bajadas and is located at the lower ele- hot summers above 35°C and cold winters vational boundary of the Coleogyne ramosis- below –10°C. Summer rainfall usually occurs sima Torr. (blackbrush) plant community (found during thunderstorms in July and August, but between 1100 and 2000 m elevation in the most precipitation comes as winter rains that Mojave Desert) and the upper boundary of a are widespread and may last several days. plant community dominated by Ambrosia du- Snow is occasional and not long lasting, and mosa (Gray) Payne (white bursage; Lei and mean annual precipitation at the site is <200 Walker 1997a, 1997b). Larrea tridentata Cov. mm. Precipitation increases with elevation and (creosote bush) is a co-dominant in the A. temperature decreases with elevation (Row- dumosa community. Shrub diversity is higher lands et al. 1982). During the study period at this ecotone than at any other elevation (March 1995–May 1996) total precipitation and on the bajada. Other common species include maximum and minimum temperatures were Krascheninnikovia lanata, Krameria erecta, 780 mm, 32°C, and –20°C at Kyle Canyon Ephedra nevadensis, E. viridis, and Acamp- (2135 m elevation) above Lucky Strike Canyon topappus shockleyi. For further descriptions of and 69 mm, 40°C, and –7°C at Corn Creek regional vegetation see Beatley (1975) or Run- (880 m elevation) at the base of Lucky Strike del and Gibson (1996). Nomenclature follows Canyon (National Climatic Data Center 1995, Hickman (1993). 1996). Relative humidity was typically low Experiments described here are part of a (<20%) and evaporation high during summer larger study of shrub dynamics on permanent months. 2001] EXPERIMENTS WITH FERTILE ISLANDS 27

Plot Designs, Treatments, at 550°C (Black 1965). We took care to avoid and Measurements higher temperatures that would cause loss of We examined responses of soil parameters carbonates. After oven-drying, a 0.4-g sample and of transplanted A. dumosa seedlings to of each soil was digested in sulfuric acid with experimental removals and additions of A. a mercuric oxide catalyst and then analyzed dumosa, L. tridentata, and C. ramosissima shrub colorimetrically for total Kjeldahl nitrogen canopies. In March 1995 we randomly selected using an automated salicylate procedure (Envi- 24 locations (8 sets of shrubs for each of 3 ronmental Protection Agency 1984). We mea- species) at approximately 15-m intervals along sured dry mass per volume and particle size a 360-m transect perpendicular to the slope of only in October. the bajada. At each location we selected In situ methods for assessing available nitro- (within a 10-m radius of the chosen point on gen are not suitable for desert soils because the transect) a set of 3 shrubs of the same water potentials fluctuate greatly between species and 2 open spaces and initiated the rainstorms and long dry periods (Lajtha and following treatments: unaltered shrub (S); Schlesinger 1986). Laboratory incubations removal of all aboveground portions of a shrub allowed us to compare potential mineraliza- (SR) by clipping stems at ground level; removal tion among treatments, but our values do not as in SR, followed immediately by replace- represent field conditions. The available nitro- ment of the cut shrub in situ with wire tie- gen pool was determined on 10 g of fresh soil downs (shrub removal plus shrub canopy addi- after extraction in 100 mL 2M KCl for 4 hours tion; SRC); open surface at least 50 cm from on a shaker. After the soil had settled, we ana- any shrub (O); and addition of SR shrub lyzed the supernatant for available N (Keeney canopy to an open site with tie-downs (OC; and Nelson 1982) using an automated Cd Fig. 1). Stump sprouts from the SR and SRC reduction procedure (NO2 and NO3) and an treatments were removed as needed during automated phenol procedure (NH4; Alpkem the experiment. Less than 15% of cut stumps 1991). An additional 10 g of fresh soil was sprouted. placed in a 40-mL tube that was then filled Immediately preceding the treatments with distilled water and placed in a 40°C oven (March 1995) and 7 months following treat- for 1 week, after which NH4 levels were again ment initiation (October 1995), surface soils determined. Water was added as needed to ensure an anaerobic environment. Nitrogen (0–8 cm deep; Ao and A1 horizons) were sampled in each treatment following removal of mineralization was then reported as the differ- any loose organic debris (O horizons). Trans- ence between post-incubation and pre-incu- planted seedlings were located on the east- bation NH4 + NO2 + NO3 concentrations northeast side of each shrub to minimize solar (Keeney 1982, Lober and Reeder 1993). radiation; soils were collected first (March) to Ambrosia dumosa seedlings were grown the south and subsequently (October) to the from locally collected seeds in 20-cm-deep north of focal shrubs in order not to disrupt cone-shaped containers (77.2 cm3) in a green- transplants. Soils were immediately passed house from December 1994 to March 1995. through a 2-mm sieve, then placed in air-tight Each potted plant was watered weekly as soil canisters and refrigerated at 5°C prior to needed to keep the soil moist until the final analysis within 72 hours of collection. month when watering was reduced. Nutrients After removal of 20 g of soil for analysis of were applied twice (12 mL Miracle Gro dis- nitrogen mineralization, soils were weighed, solved in 20 L of tap water) during the 4- dried at 105°C to a constant mass, and re- month period. In March 1995 the largest 252 weighed to determine soil moisture content seedlings (10–18 cm tall) were chosen. Twelve and dry mass of sieved fines per volume (an seedlings were removed for initial biomass approximation of bulk density). Soil pH was determination. To ensure survival of at least 1 determined with a glass electrode on a 2-g transplant per replicate, 2 seedlings were sample of dry soil saturated with 5 mL deion- planted at each of the 8 replicates of 5 treat- ized water (McLean 1982). We used the Bou- ments for the 3 species of shrubs (total = 240 youcos hydrometer method (Day 1982) to de- seedlings). Where both seedlings per replicate termine particle size. Organic matter content of survived transplanting, the smaller one was soils was determined by mass loss after ignition removed within 6 weeks of planting to ensure 28 WESTERN NORTH AMERICAN NATURALIST [Volume 61 survival of 1 seedling per replicate during the differences also emerged: soils under C. ramo- 60 weeks of the experiment. Seedlings at each sissima had higher pH and lower mineraliz- replicate were caged within a cylinder of 0.25- able nitrogen than soils under A. dumosa inch (0.63-cm) mesh hardware cloth, 15 cm in shrubs (Table 1, Fig. 2). Soils under L. triden- diameter and 15 cm (under shrubs) to 30 cm tata had pH levels similar to A. dumosa and (open sites) tall. Lower edges of the cages mineralizable nitrogen similar to C. ramosis- were buried and secured with nails to prevent sima. There were no species differences in soil rodent herbivory. Tops of the cages were left water and no significant treatment-by-species open. Only 2 incidents of herbivory were interactions in March. Dry mass per volume detected. Seedlings were watered (1 L plant–1 and particle size (measured only in October) week–1) for 3 weeks after planting. Seedling both varied between S and O treatments. Dry heights were measured 12 and 24 weeks after mass per volume was higher in open habitats planting. We compared treatment effects on (adjacent to L. tridentata: 1.22 ± 0.02 g cm–3; survivorship of seedlings (low survival after 60 C. ramosissima: 1.28 ± 0.03; A. dumosa: 1.29 ± weeks precluded destructive harvests). 0.03; P < 0.001) than in soils under shrubs (L. tridentata: 0.98 ± 0.04; C. ramosissima: 1.02 ± Statistical Analyses 0.04; A. dumosa: 0.96 ± 0.03). This difference Soils sampled in March (preceding shrub was due to lower sand and silt and higher clay manipulations) from the shrub and open envi- content (less air spaces) in open soils than in ronments were compared with a MANOVA soils beneath shrubs (data not shown; P < (SAS 1988), and significant differences between 0.01). Species differences were not found in treatments (shrub versus open) or species (A. dry mass per volume, or percent sand or silt, dumosa, L. tridentata, C. ramosissima) were but C. ramosissima soils had higher clay con- further examined with 2-way ANOVA fol- tent than the other 2 species (data not shown; lowed by Student-Newman-Keuls and Tukey P < 0.001). These soil results not only confirm tests for multiple comparisons. Soils from the presence of islands of fertility under October (28 weeks after treatment initiation) shrubs at the site but suggest that there are were also analyzed with MANOVA followed species differences in soil characteristics of fertile islands. by 2-way ANOVA to compare treatments (S, In October 1995 both treatment and species SR, SRC, O, and OC) and species. October effects were again significant in the overall values for dry mass per volume and particle MANOVA (Table 1). Soil organic matter, Kjel- size were compared with 2-way ANOVA. dahl nitrogen, and nitrogen mineralization Transplant heights were analyzed with 2-way were still higher in shrub-related treatments ANOVAs. Transplant survivorship was ana- (S, SR, SRC) than the open (O, OC), but ear- lyzed with a 2-way ANOVA (treatment and lier treatment differences in pH and water species), followed by Kruskall-Wallis 1-way content were no longer found (Table 1). Species ANOVAs on ranks (treatment, species) using differences were found only in soil water the number of weeks each seedling survived where soils associated with C. ramosissima (Sigma Stat 1995). Transplant survivorship was and L. tridentata were wetter than A. dumosa also analyzed by logistic regression of the soils (Tables 1, 2). number of seedlings alive or dead on the last sample date (Sigma Stat 1995). Significance Transplants was determined at P = 0.05. Mean heights of transplanted A. dumosa seedlings did not differ significantly by treat- RESULTS ment (P = 0.37) or shrub species (P = 0.86) 3 or 6 months after planting. Transplant sur- Soils vivorship (Fig. 3) did not differ among species Soils sampled in March (prior to our shrub (P = 0.67) but did differ among treatments (P manipulations) differed by both treatment and < 0.001) with the 2-way (parametric) ANOVA. species (Table 1). Soil pH, water, organic mat- There was no significant interaction between ter, Kjeldahl nitrogen, and nitrogen mineral- treatment and species (P = 0.77). However, ization were all higher under shrubs than in assumptions of normality and equality of vari- adjacent open areas (Tables 1, 2, Fig. 2). Species ances both failed on the 2-way ANOVA. 2001] EXPERIMENTS WITH FERTILE ISLANDS 29 Ambrosia dumosa, Larrea triden- = 0.15; df 8). P 0.39 0.32 0.04 0.08 0.05 0.04 0.06 ub) were compared. In October, 5 treat- ub) were compared. In October, ± ± ± ± ± ± ± = 8; treatments 3 species (SPP; 3 species (SPP; N ______, – x s ± = 0.56; df 8) or October ( P Organic Kjeldahl Mineralizable 0.350.380.040.040.040.060.04 12.88 13.39 0.17 0.27 0.19 0.21 0.27 ± ± ± ± ± ± ± ______0.250.320.010.030.010.030.04 11.83 13.36 0.16 0.19 0.16 0.21 0.15 ± ± ± ± ± ± ± dumosa tridentata ramosissima Ambrosia Larrea Coleogyne pH Water matter nitrogen nitrogen FP FP FP F P FP ______2. Gravimetric soil water content (percent) for March and October samples (mean ABLE T OSOSSRSRCOC 13.27 14.25 0.02 0.06 0.01 0.06 0.06 ARCH CTOBER Treatment M O are: O = open, S shrub, SR shrub removal, SRC removal and canopy replacement, OC 1. addition). Statistical comparisons are indicated in Table were compared. There no significant treatment-by-species interactions in March ( 1. Summary table of MANOVA of soil variables for March and October 1995 soil samples. In March, 2 treatments (TRT; open and shr of soil variables for March and October 1995 samples. In March, 2 treatments (TRT; 1. Summary table of MANOVA ABLE T TRTSPPTRT 0.0001SPP 0.0001 0.0001 1 0.0001 2 4 3.05 2 6.68 0.0200 1.19 0.0019 1.43 0.3181 12.2 0.2438 1.46 0.0007 1.07 0.2373 20.25 0.3776 31.75 0.0001 1.09 0.0001 15.39 0.3407 2.93 0.0001 29.62 0.0578 0.57 0.0001 20.87 0.5662 2.80 0.0001 3.55 0.0655 17.95 0.0093 6.35 0.0001 1.02 0.0001 0.3644 ARCH CTOBER ments were compared (open, shrub, shrub removal, shrub removal plus shrub canopy addition, and canopy addition). For both dates ments were compared (open, shrub, shrub removal, removal plus canopy addition, and addition). For tata, Coleogyne ramosissima) SourceM MANOVAO df 30 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Fig. 2. Values of 4 soil parameters (A: pH; B: organic matter; C: total Kjeldahl nitrogen; D: nitrogen mineralization) for shrub (S) and open (O) treatments associated with 3 shrub species (Ambrosia dumosa, Larrea tridentata, Coleogyne ± ramosissima) from March 1995 samples (prior to treatment initiation; mean sx–, N = 8). All shrub-versus-open comparisons were significantly different. See text for species differences.

Therefore, we performed subsequent 1-way DISCUSSION (nonparametric) ANOVAs on ranks that yielded similar results (species: P = 0.56; treatments: The establishment of desert plants is often P < 0.001). Survival was always highest (P < facilitated by nurse plants that provide shade, 0.05; Tukey and Student-Newman-Keuls mul- fertile soils, and perhaps protection from her- tiple comparisons following 2-way ANOVA) in bivores for new seedlings (McAuliffe 1984, the SR treatment (fertile island but no canopy) Franco and Nobel 1989, Callaway and Walker followed by the O treatment (neither fertile 1997). Ambrosia dumosa is able to become island nor canopy). Survival was also relatively established in open desert soils without the high in the SRC treatment (fertile island and aid of a nurse plant canopy (McAuliffe 1988) canopy but no root competition) for A. dumosa and may be a critical species for the establish- and C. ramosissima. Survival was lowest (P < ment of other common desert plants such as 0.05) in the S treatment for A. dumosa and C. L. tridentata. Understanding what limits estab- ramosissima and relatively low for L. triden- lishment and growth of A. dumosa seedlings tata. Shrub canopy therefore had the most can provide insights into why and how A. negative effect (O > OC, SR > SRC), even dumosa can begin a new cycle of fertile island overriding apparent positive effects of fertile islands (O > SRC). The logistic regression development. Canopy removal experiments in model was rejected, indicating that species this study not only confirmed the common and treatment were not good predictors of pattern of fertile islands under desert shrubs, transplant survivorship. but also detected differences in soil character- The influence of soil characteristics on istics beneath different species of shrubs. individual seedlings was tested by regressing Transplant responses to treatments indicated total weeks of survival against all soil variables the positive influence of increased soil nutri- and against principal components constructed ents under shrubs but the overall net negative from combined soil variables. None of these impact of shrubs on A. dumosa seedlings multiple regressions was significant either through competition (for nutrients, light, and within or across treatments (P > 0.20). water). These negative impacts may partly 2001] EXPERIMENTS WITH FERTILE ISLANDS 31

Fig. 3. Survival of transplanted Ambrosia dumosa seedlings associated with Ambrosia dumosa shrubs (A), Larrea tridentata shrubs (B), and Coleogyne ramosissima shrubs (C) in the S, O, SR, SRC, and OC treatments described in Figure 1. 32 WESTERN NORTH AMERICAN NATURALIST [Volume 61 explain why A. dumosa establishment occurs results suggest that survival is affected by vari- primarily in open spaces between shrub cano- ables or combinations of variables more pies. important than individual soil variables. High- All 7 measured soil variables (pH, water, est survivorship was in the SR treatment for organic matter, dry mass per volume, particle all shrub species, suggesting benefits of the size, total and mineralizable nitrogen) were fertile island soil environment (higher nutrients, more favorable for plant growth under existing water, and organic matter) and a high light shrubs than in adjacent open spaces. These environment. The fact that A. dumosa survivor- results support conclusions from other studies ship was better in SR and SRC than under of fertile islands (e.g., Garcia-Moya and intact shrubs (S) further suggests a lack of root McKell 1970, Charley and West 1975, Klem- competition may be important to seedling sur- medson and Barth 1975, Virginia 1986, Hal- vivorship (Fig. 4). The next highest survivor- vorson et al. 1994, Schlesinger et al. 1996) that ship was in the O treatment for all species, have found abundant evidence of spatial het- suggesting that any of the remaining treat- erogeneity in soil properties of arid lands. Our ments (S, OC, SRC), each of which includes a values for soil organic matter under shrubs are shrub canopy, was worse for A. dumosa seed- comparable to another study from Lucky lings than the high light but low nutrient envi- Strike Canyon (2–6%, Lei and Walker 1997b) ronment in the open. The S treatment had but higher than other Mojave Desert studies lowest A. dumosa survivorship, probably due (2–3%, Bolling and Walker 2000; 1.5–4.1%, to combined negative effects of shrub canopy Rundel and Gibson 1996) where surface organic and root competition. soils (Ao horizon) were removed. Our values Only 39.2% of all transplanted seedlings from the open spaces are also higher than gen- survived the 60-week period. However, differ- erally reported, perhaps due to the high cover ences in timing of mortality among treatments (25%, D. Thompson personal observation) of are likely to have important consequences for cryptobiotic crusts in our open sites. seedling establishment. The Mojave Desert is Species differences in soil characteristics characterized by infrequent and spatially patchy were detected among soils collected under- rainfall (Smith et al. 1997). Nearly dry seedlings neath 3 shrub species. These differences may are able to recover and sprout leaves within cause differential survival of A. dumosa seed- days following rainfall (F. Landau personal lings, although such differences were not seen observation). On average, the longer a seed- in this experiment (see below). In March, soils ling can survive through a dry period, the under A. dumosa shrubs had higher rates of more likely that it will experience rains and nitrogen mineralization than soils under C. survive to become a mature shrub. ramosissima or L. tridentata. Considering the Interactions between the effects of light (or additional allelopathic effect that has been presence of shrub canopy) and fertile island demonstrated for L. tridentata roots (Mahall soil conditions, and the relative importance of and Callaway 1992), L. tridentata shrubs may light, nutrients, and root competition, can be provide the least favorable environment for inferred from survivorship patterns of the A. seedlings. During the drier period in October, dumosa transplants. Light appeared to be a soils under C. ramosissima were wettest, per- limiting factor whether nutrients were low (O haps reflecting moisture retention of higher > OC) or high (SR > SRC, S). In contrast, nu- clay values under C. ramosissima. Organic mat- trients were not limiting at low light (OC > S, ter and Kjeldahl nitrogen tended (nonsignifi- no pattern for OC and SRC) but were limiting cantly) to be different among species in Octo- at high light (SR > O). These patterns suggest ber. Analyses of a larger data set including the most important factor is the negative effect other elevations (Thompson et al. unpublished of shrub canopy presence (Miriti et al. 1998), data) indicate that soils under A. dumosa followed by the positive effect of fertile island shrubs have lower organic matter levels than nutrients. Root competition (or the presence soils beneath L. tridentata and C. ramosissima of live roots) appears to be a 3rd variable that shrubs. also had a negative effect (SRC > S). Compe- Survivorship of A. dumosa transplants did tition for water by nearby adult plants can not differ among nurse plant species, despite reduce seedling growth (Fonteyn and Mahall differences in soil characteristics. These 1981, Fowler, 1986, Nobel and Franco 1986). 2001] EXPERIMENTS WITH FERTILE ISLANDS 33

in late May (10 weeks after transplanting), there was a 28-week drought. During this drought most A. dumosa transplant mortality occurred. There was no significant correlation between October gravimetric soil moisture at each transplant and individual transplant survivorship (P-values ranged between 0.30 and 0.70). More detailed measurements might have helped explain survivorship in terms of soil moisture because gravimetric soil content may not closely reflect water available for plant growth. Nevertheless, driest habitats (SR, O) had highest survivorship and the wettest habitat (S) had lowest survivorship, suggesting that in a drought water is not as limiting as light (or Fig. 4. Summary of how the 5 treatments (S, SR, SRC, absence of shade). Therefore, our results dur- OC, O) altered above- (shade and other canopy effects) and belowground (nutrients, roots) environments for ing a drought may be typical of the dynamics transplanted Ambrosia dumosa seedlings. Asterisk implies of seedling establishment in more mesic peri- addition or subtraction of not only nutrients but other soil ods as well. Alternatively, shrub roots may properties of fertile islands. have been so efficient at removing available water (Fonteyn and Mahall 1981, Hunter 1989) that the below-shrub environment was actu- Shade is normally considered advantageous to ally too dry for seedlings during our study. In seedling establishment in deserts because it wetter years root competition from the shrub reduces temperature extremes and water loss. may be less detrimental to seedling establish- Although we took no light measurements in ment. this study, we did measure photosynthetic Species differences in soil water were pre- photon flux density (using a Licor 1000) 5 sent only in the dry (October) sampling period months after initiation of identical treatments (C. ramosissima = L. tridentata > A. dumosa). with A. dumosa in a later experiment at the Canopy architecture might help explain why same site (May 1998). Despite leaf loss, the L. tridentata soils were wetter than A. dumosa ± ± –2 SRC (mean sx–: 398 43 micromoles m soils in the dry season. The canopy of L. tri- –1 ± sec ; N = 30) and OC (414 42) treatments dentata is shaped like an inverted cone (Lud- remained as shaded as the intact shrubs (S wig et al. 1975), and this shape may maximize ± treatment: 492 42) and all 3 “shrub” treat- condensation of water vapor and stem flow ments were significantly more shaded than from its relatively tall, spreading branches. open treatments (O: 1009 ± 42; SR: 1004 ± However, this shape also allows soil surface 42). Branches of A. dumosa (and equally dense evaporation because of the openness of the branches of C. ramosissima) apparently pro- surface beneath it; A. dumosa and C. ramosis- vided nearly as much shade as leaves and sima are hemispherical in shape with foliage branches combined. In contrast, L. tridentata almost to the ground, reducing loss from sur- has a very low leaf area index (Chew and Chew face evaporation. Therefore, other explanations 1965, Smith et al. 1997), so leaf loss presum- such as more efficient water extraction by A. ably does not markedly increase light trans- dumosa roots (D. Neuman personal communi- mission to the ground. cation) must also be considered. Soil moisture is considered to be a critical Ambrosia dumosa seedlings survived better environmental variable affecting establishment in the open (O) than under shrubs (S), support- and growth of desert plants and may affect ing McAuliffe’s (1988) assertion that Ambrosia nutrient availability (e.g., nitrogen is limiting is a colonizer of open habitats. When it does only when water is plentiful; Fisher et al. 1988, colonize under shrubs (or in exposed fertile Sharifi et al. 1988, Lajtha and Whitford 1989). islands caused by shrub mortality), it has a dif- This experiment was initiated during a wet ferent set of environmental characteristics to spring, and the March soil samples were col- cope with under each shrub species. For exam- lected 2 days after a rainstorm. Following rains ple, Smith et al. (1987) found that artificial 34 WESTERN NORTH AMERICAN NATURALIST [Volume 61 shade in the Sonoran Desert increased soil Dean, T. Keller, and S. Vrooman helped with nutrients in both shrub canopies and open lab analyses. Further welcome advice was desert, but patterns of increase differed be- provided by J. Brown, J. Cole, P. Medica, J. tween A. deltoidea and L. tridentata shrubs. McAuliffe, M. McGill, and W. Whitford. Par- Differential responses to these variations in tial funding was provided by NSF grant EPS- microsite ultimately impact distribution and 93-53227 and a grant from the University of zonation of desert shrub species. Our study Nevada, Las Vegas Grants and Fellowship Com- site, at the ecotone between A. dumosa– and mittee. The manuscript was improved by com- C. ramosissima–dominated communities, is ments from K. Lajtha, K. Owens, S. Smith, J. the type of environment where shrub species Titus, and an anonymous reviewer. replacements are most likely to lead to shifts in community composition along the eleva- LITERATURE CITED tional gradient. For example, the lower boundary of C. ramosissima in the Mojave Desert ALPKEM. 1991. Total Kjeldahl nitrogen. The flow solution has shifted at least 100 m several times in the methodology. Wilsonville, OR. BEATLEY, J.C. 1975. Climates and vegetation pattern across last 1000 years (Cole and Webb 1985, Hunter the Mojave/Great Basin Desert transition of south- and McAuliffe 1994). Current studies are ern Nevada. American Midland Naturalist 93:53–70. addressing how responses to shrub removals BLACK, C.A., EDITOR. 1965. Methods of soil analysis. Part vary at different elevations in Lucky Strike I. Physical and mineralogical properties. American Society of Agronomy, Madison, WI. Canyon and how episodic recruitment of L. BOLLING, J.D., AND L.R. WALKER. 2000. Plant and soil tridentata and C. ramossisima seedlings is recovery along a series of abandoned desert roads. affected by shrub species and shrub-induced Journal of Arid Environments 46:1–24. microsites. CALLAWAY, R.M., E.H. DELUCIA, D. MOORE, R., NOWAK, AND W.H. SCHLESINGER. 1996. Competition and facil- McAuliffe (1988) proposed that the estab- itation: contrasting effects of Artemisia tridentata on lishment of seedlings of A. dumosa in open desert vs. montane pines. Ecology 77:2130–2141. areas may initiate fertile island development CALLAWAY, R.M., AND L.R. WALKER. 1997. Competition where this species occurs in arid regions of and facilitation: a synthetic approach to interactions southwestern United States. We have demon- in plant communities. Ecology 78:1958–1965. CHARLEY, J.L., AND N.E. WEST. 1975. Plant-induced soil strated that 3 interacting variables (shade, chemical patterns in some shrub-dominated semi- nutrients, roots; Fig. 4) affect the initial sur- desert ecosystems of Utah. Journal of Ecology 63: vival of A. dumosa seedlings. However, shrubs 945–964. differ in their soil chemistry and may provide CHEW, R.M., AND A.E. CHEW. 1965. The primary produc- unique habitats for seedling establishment. tivity of a desert-shrub (Larrea tridentata) community. Ecological Monographs 35:355–375. Removal of a shrub with retention of the fer- COLE, K.L., AND R.H. WEBB. 1985. Late Holocene vege- tile island beneath it provided the best envi- tation changes in Greenwater Valley, Mojave Desert, ronment for A. dumosa seedling establishment California. Quaternary Research 23:227–235. (light and nutrient addition), followed by open DAY, P.R. 1982. Particle fractionation and particle size analysis. Pages 545–567 in C.A. Black, editor, Meth- habitats (light addition). Shaded habitats with ods of soil analysis. American Society of Agronomy, or without nutrients were poorer habitats for Madison, WI. establishment, and the intact shrub environ- ENVIRONMENTAL PROTECTION AGENCY. 1984. Nitrogen, ment (minus light, nutrient addition, root com- Kjeldahl, total. Method number 351.2. Methods for petition) was the worst environment. These chemical analysis of water and wastes. EPA-600/4- 79-020. results provide a mechanistic explanation for EVANS, R.D., AND J. BELNAP. 1999. Long-term consequences McAuliffe’s hypothesis and suggest A. dumosa of disturbance on nitrogen dynamics in an arid eco- establishment will be most likely to occur in system. Ecology 80:150–160. open habitats that have some nutrient enrich- FISHER, F., J. ZAK, G. CUNNINGHAM, AND W. W HITFORD. 1988. Water and nitrogen effects on growth and allo- ment. cation patterns of creosotebush in the northern Chi- huahuan Desert. Journal of Range Management 41: ACKNOWLEDGMENTS 387–391. FONTEYN, P.J., AND B.E. MAHALL. 1981. An experimental We thank our numerous field assistants, analysis structure in a desert plant community. Jour- including J. Alexander, C. Brundy, J. Cleverly, nal of Ecology 63:883–896. FOWLER, N. 1986. The role of competition in plant com- C. Heyne, T. Keller, S. Lei, F. Martin, J. Pior- munities in arid and semiarid regions. Annual kowski, L. Stark, and M. Turner. J. Bolling, D. Review of Ecology and Systematics 17:89–110. 2001] EXPERIMENTS WITH FERTILE ISLANDS 35

FRANCO, A.C., AND P. S . N OBEL. 1989. Effect of nurse plants MAHALL, B.E., AND R.M. CALLAWAY. 1992. Root communi- on the microhabitat and growth of cacti. Journal of cation mechanisms and intracommunity distributions Ecology 77:870–886. of two Mojave Desert shrubs. Ecology 73:2145–2151. GARCIA-MOYA, E., AND C.M. MCKELL. 1970. Contribution MCAULIFFE, J.R. 1984. Saguaro–nurse tree associations in of shrubs to the nitrogen economy of a desert-wash the Sonoran Desert: competitive effects of saguaros. plant community. Ecology 51:81–88. Oecologia 64:319–321. GARNER, W., AND Y. S TEINBERGER. 1989. A proposed mech- ______. 1988. Markovian dynamics of simple and complex anism for the formation of “fertile islands” in the desert plant communities. American Naturalist desert ecosystem. Journal of Arid Environments 16: 131:459–490. 257–262. MCLEAN, E.O. 1982. Soil pH and lime requirement. HALVORSON, J.J., H. BOLTON, JR., J.L. SMITH, AND R.E. Pages 199–209 in C.A. Black, editor, Methods of soil ROSSI. 1994. Geostatistical analysis of resource islands analysis. American Society of Agronomy, Madison, under Artemisia tridentata in the shrub-steppe. WI. Great Basin Naturalist 54:313–328. MIRITI, M.N., H.F. HOWE, AND S.J. WRIGHT. 1998. Spatial HICKMAN, J.C. 1993. Jepson manual: higher plants of Cali- patterns of mortality in a Colorado desert plant com- fornia. University of California Press, Berkeley. munity. Plant Ecology 136:41–51. HUNTER, K.L., AND J.R. MCAULIFFE. 1994. Elevational NATIONAL CLIMATIC DATA CENTER. 1995. Climatological shifts of Coleogyne ramosissima in the Mojave Desert data, Nevada 110:3–12. during the Little Ice Age. Quaternary Research ______. 1996. Climatological data, Nevada 111:1–5. 42:216–221. NOBEL, P.S., AND A.C. FRANCO. 1986. Annual root growth HUNTER, R. 1989. Competition between adult and and intraspecific competition for a desert bunchgrass. seedling shrubs of Ambrosia dumosa in the Mojave Journal of Ecology 74:1119–1126. Desert, Nevada. Great Basin Naturalist 49:79–84. ROWLANDS, P., H. JOHNSON, E. RITTER, AND A. ENDO. 1982. KEENEY, D.R. 1982. Nitrogen-availability indices. Pages Pages 103–162 in G.L. Bender, The Mojave Desert. 711–733 in C.A. Black, editor, Methods of soil analy- Reference handbook on the deserts of North Amer- sis. American Society of Agronomy, Madison, WI. ica. Greenwood Press, Westport, CT. KEENEY, D.R., AND D.W. NELSON. 1982. Nitrogen—inor- RUNDEL, P.W., AND A.C. GIBSON. 1996. Ecological com- ganic forms. Pages 643–698 in C.A. Black, editor, munities and processes in a Mojave Desert ecosys- Methods of soil analysis. American Society of Agron- tem: Rock Valley Nevada. Cambridge University omy, Madison, WI. Press, Cambridge, England. KLEMMEDSON, J.O., AND R.C. BARTH. 1975. Distribution SAS INSTITUTE, INC. 1988. SAS/STAT user’s guide, release and balance of biomass and nutrients in desert shrub 6.12 edition. Cary, NC. ecosystems. US/IBP Desert Biome Research Memo, SCHLESINGER, W.H., J.A. RAIKES, A.E. HARTLEY, AND A.F. 75-5. Utah State University Press, Logan. CROSS. 1996. On the spatial pattern of soil nutrients LAJTHA, K. 1987. Nutrient reabsorption efficiency and the in desert ecosystems. Ecology 77:364–374. response to phosphorus fertilization in the desert SHARIFI, M.R., F.C. MEINZER., E.T. NILSEN., P.W. RUNDEL, shrub Larrea tridentata (D.C.) Cov. Biogeochemistry R.A. VIRGINIA, W.M. JARRELL, D.J. HERMAN, AND 4:265–276. P.C. CLARK. 1988. Effect of manipulation of water LAJTHA, K., AND W.H. SCHLESINGER. 1986. Plant response and nitrogen supplies on the quantitative phenology to variations in nitrogen availability in a desert shrub- of Larrea tridentata (creosote bush) in the Sonoran land community. Biogeochemistry 2:29–37. Desert of California. American Journal of Botany LAJTHA, K., AND W. G. W HITFORD. 1989. The effect of water 75:1163–1174. and nitrogen amendments on photosynthesis, leaf SIGMA STAT. 1995. Sigma Stat statistical software. Jandel demography, and resource-use efficiency in Larrea Corporation, San Rafael, CA. tridentata, a desert evergreen shrub. Oecologia 80: SMITH, S.D., W.E. SMITH, AND D.T. PATTEN. 1987. Effects 341–348. of artificially imposed shade on a Sonoran Desert LEI, S.A., AND L.R. WALKER. 1997a. Classification and ecosystem: arthropod and soil chemistry responses. ordination of Coleogyne communities in southern Journal of Arid Environments 13:245–257. Nevada. Great Basin Naturalist 57:155–162. SMITH, S.D., R.K. MONSON, AND J.E. ANDERSON. 1997. ______. 1997b. Biotic and abiotic factors influencing the Physiological ecology of North American desert distribution of Coleogyne communities in southern plants. Springer Verlag, Berlin. Nevada. Great Basin Naturalist 57:163–171. VIRGINIA, R.A. 1986. Soil development under legume tree LOBER, R.W., AND J.D. REEDER. 1993. Modified water- canopies. Forest Ecology and Management 16:69–79. logged incubation method for assessing nitrogen mineralization in soils and soil aggregates. Soil Sci- Received 20 September 1999 ence Society of America Journal 57:400–403. Accepted 7 January 2000 LUDWIG, J.A., J.F. REYNOLDS, AND P. D . W HITSON. 1975. Size- biomass relationships of several Chihuahuan Desert shrubs. American Midland Naturalist 94:451–461. Western North American Naturalist 61(1), © 2001, pp. 36–42

HABITAT CHARACTERISTICS OF LEATHERSIDE CHUB (GILA COPEI) AT TWO SPATIAL SCALES

Kristine W. Wilson1,2 and Mark C. Belk1

ABSTRACT.—Populations of leatherside chub (Gila copei), a little-known species native to the eastern Great Basin, have declined and their distribution has become fragmented. To determine habitat requirements and possible factors responsible for population decline, we quantified macrohabitats and microhabitats occupied by leatherside chub. Macrohabitat was surveyed at 59 sites in the Sevier River drainage of south central Utah, and microhabitats occupied by leatherside chub were measured at 3 locations spanning the species latitudinal range. Characteristics of points in the stream where leatherside chub occurred were compared to points where they did not occur. Abundance of brown trout (Salmo trutta) and elevation were weakly negatively correlated with leatherside chub distribution on a macrohabitat scale. Microhabitats occupied by leatherside chub were characterized by low water velocities (2.5–45 cm sec–1), intermediate water depths (25–65 cm), and low percent composition of sand-silt or gravel substrates. This study suggests that the presence of introduced brown trout may have led to the decline of leatherside chub.

Key words: microhabitat, macrohabitat, Great Basin fishes, leatherside chub, Gila copei.

The Bonneville Basin has been an endorheic Utah, leatherside chub now occupy only 58% basin, isolating aquatic organisms at least since of their original range in the Sevier River sys- the early Pleistocene (Blackwelder 1948). Fish tem and have been extirpated from the Beaver assemblages of streams and rivers of the Bon- River system (based on historical records neville Basin comprised species of Salmon- dated from 1872 to 1989; Wilson and Belk, idae, Catostomidae, Cyprinidae, and Cottidae Utah Division of Wildlife Resources Final (Hubbs and Miller 1948, Hubbs et al. 1974, Report 93-0870, Salt Lake City, unpublished, Behnke 1992). Recent destruction of aquatic 1996). Only 2 small populations of leatherside habitat and introduction of many nonnative chub remain in Goose Creek drainage and fishes in this region by humans (Minckley and portions of Raft River drainage, Cassia County, Douglas 1991) have resulted in extinctions Idaho (Wilson and Belk, Idaho Department of (e.g., Utah Lake sculpin, Cottus echinatus; Fish and Game Final Report 5517410, SEPA Miller et al. 1989) and population declines (e.g., 4238, Boise, unpublished, 1996). Because of Bonneville cutthroat trout, Oncorhynchus clarki these substantial decreases in distribution and utah; June sucker, Chasmistes liorus; and least abundance, the leatherside chub is considered chub, Iotichthys phlegethontis [Behnke 1992]) a species of special concern (Utah Sensitive of native fish species. To prevent further de- Species List, Utah Division of Wildlife Re- clines in this unique fauna, we must understand sources, Salt Lake City, 1997; Idaho Depart- the ecological requirements of native species ment of Fish and Game personal communica- and their interactions with other species. tion). Conservation efforts in behalf of leather- The leatherside chub, Gila copei, is a small side chub are hampered by a lack of under- cyprinid native to streams and rivers of the standing of basic ecological requirements of eastern and southern Bonneville Basin of Utah, the species (Johnson et al. 1995). Idaho, and Wyoming; to the Wood and Raft The objective of this study was to identify rivers of Idaho; and possibly to areas of the characteristics of habitat use by leatherside chub upper Snake River above Shoshone Falls, Idaho on 2 spatial scales: macrohabitat and micro- and Wyoming (Hubbs and Miller 1948, Baxter habitat. Quantifying macrohabitat characteristics and Simon 1970, Simpson and Wallace 1982). will help determine ecological tolerance limits In the Sevier Lake basin of south central and possible causes of population fragmentation

1Department of Zoology, Brigham Young University, Provo, UT 84602. 2Corresponding author. Present address: Utah Division of Wildlife Resources, 1115 North Main, Springville, UT 84663-1055.

36 2001] LEATHERSIDE CHUB HABITAT 37 and decline. Quantifying microhabitat characteristics will provide information about possible interactions with co-occurring species and the importance of various features of stream morphology.

STUDY SITE AND METHODS Macrohabitat In this paper macrohabitat refers to general habitat features (i.e., gradient, elevation, conductivity, pH, presence of other species) that are relatively constant throughout the stream reach. Macrohabitat data were collected at numerous locations in the Sevier Lake drainage basin (Sanpete, Piute, Iron, Garfield, and Beaver counties) in south central Utah (Fig. 1). This system appeared to support the largest populations of leatherside chub within their native range. Sevier Lake drainage basin is an endorheic basin in a region of north–south trending mountains with broad, sediment-filled valleys. Mean annual precipitation is 33 cm, with high mountain elevations receiving up to 250 cm of snowfall annually (Greer 1981). Streams are often ice-covered during winter. High runoff Fig. 1. Macrohabitat survey locations in the Sevier and from mountain snowpack occurs during spring, Beaver river drainages in south central Utah, 1995. Sym- bols indicate presence or absence of leatherside chub at followed by low flows during July, August, and each location. September. Dominant riparian vegetation consists of grasses (Poaceae), forbs (numerous families), sagebrush (Artemisia spp.), wild rose velocity (to the nearest 0.01 m sec–1) was mea- (Rosa woodsii), willow (Salix spp.), tamarisk sured at 0.6 of the depth from the water sur- (Tamarix pentandra), and stands of mature cot- face with a global flow probe. Substrate and tonwoods (Populus spp.). riparian vegetation were also measured on the Macrohabitat variables were measured 5 equally spaced transects. Substrate type was August through November 1995 (n = 59) in categorized as sand/silt (<2.50 mm), coarse the Sevier and Beaver River systems (Fig. 1). fines (2.50–6.24 mm), gravel (6.25–74 mm), At each site we electrofished approximately rubble (75–149 mm), cobble (150–299 mm), 100 m of stream using a backpack electro- boulders (300–900 mm), large boulders (>900 shocker. Captured fish were identified to mm), or bedrock (including hard clay bottoms) species, enumerated, and standard length (SL) and measured as a percentage of the transect recorded to the nearest millimeter. line using the line intercept method (Bonham We measured the following macrohabitat 1989). Riparian variables categorized and variables: mean water depth, mean water veloc- measured were soil, rocks, grass, forbs, shrubs, ity, dominant substrate, riparian vegetation, sagebrush, tamarisk, willow saplings, cotton- water temperature, pH, dissolved oxygen (DO), wood saplings, and trees. Transect lines ex- water conductivity, stream gradient, and ele- tended 3 m from wetted stream on both right vation. Depth and velocity were calculated as and left banks. Riparian composition was the mean of measurements taken at 0.25, 0.5, recorded as a percentage of the 3-m transect and 0.75 stream-width intervals along 5 equally line using the line intercept method. Tempera- spaced transects established perpendicular to ture, pH, DO, and conductivity were mea- the stream. Depth was measured to the near- sured once on each 100-m station using the est centimeter with a meter stick, and water Hydrolab H20® multiparameter water quality 38 WESTERN NORTH AMERICAN NATURALIST [Volume 61 data transmitter. Gradient and elevation were brush has since been removed, and grasses obtained from appropriate United States Geo- now dominate the riparian vegetation. logical Survey (USGS) 7.5-minute series topo- The 3rd site, Salina Creek, Sevier County, graphical maps. Utah, is in the southern region of leatherside We used logistic regression analysis to de- chub distribution. It is a 3rd-order stream and termine the relationship between occurrence tributary to the Sevier River. Elevation ranges of leatherside chub and macrohabitat charac- from 2400 m at the headwaters to 1560 m teristics. Macrohabitat variables were selected where it joins the Sevier River. Gradients range for the logistic regression model using a step- from 5.0% at high elevations to 0.05% near the wise variable selection procedure (significance confluence of the Sevier River. At the survey level of P = 0.10, LOGIST procedure; SAS site the elevation and gradient are 1660 m and 1988). The 1st test compared sites where 1.3%, respectively. Salina Creek is canyon bound leatherside chub were present to sites where with dominant riparian vegetation consisting they were absent. The 2nd test compared sites of sagebrush, willow, wild rose, and grasses. where leatherside chub were abundant to sites To facilitate accurate sampling, we conducted where they were rare. Temperature and DO microhabitat measurement July through Octo- were ultimately removed from the macrohabi- ber 1995, when water flow was minimal (Imhof tat analysis because they varied with time of and Biette 1982). At each of the 3 microhabitat day and season. We analyzed the full data set study sites we established 100 transects spaced (n = 59) and a reduced data set (n = 44). Fif- 2 mean stream widths apart (Simonson et al. teen excised sites were areas where leather- 1994). Mean stream width was calculated as side chub were absent because of recent the average of 20 stream widths taken ran- chemical treatments or stream dewatering. domly along approximately 200 m of stream. Distance between each transect was measured Microhabitat along the thalweg, and the transect was estab- In this paper microhabitat refers to charac- lished perpendicular to flow. On each transect teristics of habitat experienced by individual a random point, constrained to 0.5-m intervals, leatherside chub within the stream (0.5-m was selected using a permutation table, located radius around the focal area). Microhabitats with a wooden stake driven into the right were measured at 3 sites where leatherside bank, and labeled with the location of the ran- chub were abundant. The 1st site, Trapper dom point measured as distance from the right Creek, Cassia County, Idaho, is on the north- bank. ern edge of the native range of leatherside Beginning on the initial transect, at the down- chub. A 3rd-order stream and tributary to stream end of the site, we shocked the first Goose Creek (determined from USGS 7.5- randomly selected point, identified species, minute series topographical maps, blue line number of fishes encountered, and measured information), it flows into Lower Goose Creek SL. Leatherside chub are a midwater species, Reservoir. Elevation ranges from 2375 m at and they may be pushed from one habitat to the headwaters to 1525 m where it flows into another by continuously pushing the electrode the reservoir. Streambed gradient is 2.5% at between survey points. To avoid startling the the survey site but ranges from 5.0% at the fish and biasing habitat measurements, we headwaters to 1.6% near the reservoir. Domi- slowly approached each sampling point with nant riparian vegetation consists of sagebrush, the electrode held out of the water. We then willow, wild rose, and birch. placed the electrode in the water and began The 2nd site is Thistle Creek, Utah County, electroshocking. Fish observed in the water Utah, located in the central part of the range column showed little response to electrode of leatherside chub. It is a 3rd-order stream placement prior to electroshocking (personal and tributary to the Spanish Fork River. Ele- observation). At Salina Creek and Trapper vation ranges from 2370 m at the headwaters Creek, turbidity was relatively high. Increased to 1550 m where it joins the Spanish Fork turbidity levels decrease reaction distances of River. Elevation at the survey site is 1735 m many fish (Miner and Stein 1996), further and streambed gradient is 0.5%. Historically, reducing the likelihood of startling the fish by riparian habitat was sagebrush steppe. Sage- placement of the electrode. The following 2001] LEATHERSIDE CHUB HABITAT 39 microhabitat variables were measured at each dance and microhabitat characteristics. All point: temperature, DO, depth, velocity, cov- variables were included in the model and sig- erage of aquatic vegetation, coverage of emer- nificance was evaluated at P = 0.05. gent rooted vegetation, coverage of undercut Juvenile fishes can occupy microhabitats that banks, coverage of dead woody debris (small differ significantly from habitat occupied by and large size classes), coverage of overhang- adults. To avoid mixing habitat characteristics ing vegetation, coverage of surface turbulence, of different life stages, we did not include and substrate class coverage (substrate classes young-of-year leatherside chub in this analy- were the same as those used for macrohabitat sis. These young-of-year are easily distinguished evaluation). Coverage was estimated as a per- from adults by size (Johnson et al. 1995). centage of a circle, 1 m in diameter, placed over the sampling point. RESULTS Logistic regression analysis was used to de- Macrohabitat termine the relationship between occurrence of leatherside chub and microhabitat character- Leatherside chub were found at 29 of 59 istics. To avoid spurious correlations, variables sites surveyed (Fig. 1), and they occupied with ≤10% nonzero values were excluded waters with a broad range of physical condi- from analyses. Temperature and DO were not tions (Table 1). Other native species were also included in final analyses because they varied found: cutthroat trout (Oncorhynchus clarki), temporally. Variables potentially included in mountain sucker (Catostomus platyrhynchus), all analyses were water depth, water velocity, Utah sucker (Catostomus ardens), speckled percent coverage of aquatic vegetation, per- dace (Rhinichthys osculus), Utah chub (Gila cent coverage of emergent rooted vegetation, atraria), redside shiner (Richardsonius baltea- percent coverage of overhanging vegetation, tus), and mottled sculpin (Cottus bairdi). Non- and percent coverage of 4 substrate classes native species encountered were brown trout (sand/silt, coarse fines, gravel, and rubble). (Salmo trutta), rainbow trout (Oncorhynchus Microhabitat variables were selected for the mykiss), brook trout (Salvelinus fontinalis), logistic regression model using a stepwise carp (Cyprinus carpio), fathead minnow (Pime- variable selection procedure (significance level phales promelas), and green sunfish (Lepomis of P = 0.05, LOGIST procedure; SAS 1988). cyanellus). Brown trout were the most wide- Points where leatherside chub were present spread introduced species, occurring at 43 were compared to points where they were sampling sites. absent. Each of the 3 sites was analyzed sepa- No variables were significantly associated rately followed by analysis of all sites com- with occurrence of leatherside chub when all bined. locations were included in the macrohabitat Because leatherside chub were abundant (n analysis (n = 59, all P > 0.1). After removing = 1–31 per occupied site) at Salina Creek, sites (n = 15) where leatherside chub were Utah, we used a Poisson regression model absent for reasons unrelated to availability of (GENMOD procedure; SAS 1993) to test for habitat, 2 of 12 variables were weakly nega- relationships between leatherside chub abun- tively associated with occurrence of leather- χ2 side chub: elevation ( 1 = 2.71, P = 0.0998) χ2 and number of brown trout ( 1 = 2.99, P = TABLE 1. Range of values of physical variables recorded 0.0840). Leatherside chub were not encoun- at locations occupied by leatherside chub in the Sevier tered at sites above 2195 m in elevation. As River drainage, Utah, 1995. the number of brown trout increased, the Variable Range probability of encountering leatherside chub decreased. Leatherside chub and brown trout elevation 1567–2195 m stream gradient 0.10–4.00% were sympatric at 14 sites, with a mean of 5 water temperature 1.01–25.87°C brown trout per site. Brown trout occurred at mean water velocity 6.0–77.0 cm sec–1 29 sites without leatherside chub, with a mean pH 8.0–9.9 of 12 brown trout per site. Comparison of sites conductivity 15.7–461.0 millimhos cm–1 where leatherside chub were abundant to sites dissolved oxygen 3.50–16.81 mg liter–1 where they were rare failed to yield significant 40 WESTERN NORTH AMERICAN NATURALIST [Volume 61 associations with macrohabitat variables (n = Abundance was negatively related to coverage χ2 29, all P > 0.1). of sand-silt substrate ( 1 = 46.79, P < χ2 0.0001; Fig. 3A) and gravel substrate ( 1 = Microhabitat 12.88, P < 0.0001; Fig. 3B). At Trapper Creek, Idaho (a high-gradient location), leatherside chub were found at 16 of DISCUSSION 100 sampling points. Water velocity was significantly negatively associated with the pres- Leatherside chub occupy a broad range of χ2 ence of leatherside chub ( 1 = 10.51, P = physical conditions, but none of the variables 0.0012). They were most likely to be found in designed to measure physical habitat associa- water velocities of 15.0–23.0 cm sec–1, and the tions were significantly associated with the probability of occurrence decreased at higher presence of this species. Small streams and velocities. At Thistle Creek, Utah (a low-gradi- rivers of the Bonneville Basin occupied by ent location), leatherside chub were found at leatherside chub exhibit extreme seasonal and 26 of 100 sampling points. Percent coverage of multi-year variation in physical conditions. sand-silt substrate was significantly negatively Water flow fluctuates seasonally with snowmelt, associated with the presence of leatherside resulting in turbid, high-water flows in late χ2 chub at this site ( 1 = 4.55, P = 0.0330). At winter and spring and clear, low-water flows Salina Creek, Utah (a medium-gradient loca- in summer and fall. Correspondingly, seasonal tion), leatherside chub were found at 31 of 100 fluctuations in water temperature range from sampling points. Both water velocity and per- near 0°C to above 25°C. Additionally, multi- cent coverage of sand-silt substrate were sig- year climatic fluctuations (e.g., El Nino south- nificantly negatively associated with presence ern oscillation events) result in periodic drought χ2 of leatherside chub (water velocity, 1 = 6.79, conditions followed by high precipitation peri- χ2 P = 0.0091; sand-silt substrate, 1 = 11.18, P ods. Small streams where leatherside chub are = 0.0008). When all 3 sites were combined particularly abundant are especially suscepti- and analyzed with logistic regression, only ble to drought-induced low water and conse- water velocity was significantly negatively quent environmental extremes. Given this wide associated with the presence of leatherside range in physical variation, it is not surprising χ2 chub ( 1 = 7.71, P = 0.0055). that there appear to be few physical limiting Using data from Salina Creek, Utah, in the factors at the macrohabitat scale. Poisson regression model, we determined that The weak negative relationship between water depth and coverage of coarse fines sub- presence of leatherside chub and elevation strate were significantly positively related to suggests an elevational limit to distribution, abundance of leatherside chub. Water velocity, but below this limit none of the physical para- percent coverage of sand-silt and gravel sub- meters measured appeared to limit distribu- strates, and coverage of overhanging vegetation. Thus, current variation in physical habi- tion were significantly negatively associated tat parameters that were measured cannot with abundance of leatherside chub. However, account for recent fragmentation of leather- 2 points where large numbers of leatherside side chub distribution in this drainage. Stream chub were found (n = 31 and 20, all other dewatering and chemical treatments were ob- occupied sites had 1 ≤ n ≤ 14) seemed to inor- vious contributors to the decline in occupied dinately affect the results (based on scatter- range, and it seems likely that these activities plots of the data). A reanalysis with the 2 may account for much of the fragmented dis- points removed demonstrated that leatherside tribution. chub abundance was not significantly related The only other variable related to occur- to coverage of coarse fines substrate or cover- rence of leatherside chub was abundance of age of overhanging vegetation. The significance brown trout. Presently, brown trout are widely level of all other variables in the reanalysis distributed in the Sevier River system. Brown was unchanged. Leatherside chub were more trout occur at lower elevations in warmer χ2 abundant at points with deeper water ( 1 = waters and feed more extensively on fish than 20.67, P < 0.0001; Fig. 2A) and lower water other species of trout (Sigler and Miller 1963). χ2 velocities ( 1 = 32.11, P < 0.0001; Fig. 2B). Leatherside chub occurred with brown trout 2001] LEATHERSIDE CHUB HABITAT 41

Fig. 3. Number of leatherside chub located at microhabitat survey points plotted against percent coverage of Fig. 2. Number of leatherside chub located at micro- sand-silt substrate (A) and gravel substrate (B). Data from habitat survey points plotted against water depth (A) and Salina Creek, Sevier County, Utah, 1995. Points with water velocity (B). Data from Salina Creek, Sevier County, equivalent values have been slightly offset to make them Utah, 1995. Points with equivalent values have been visible. slightly offset to make them visible.

cyprinids documented in other studies. In at 14 locations, but only in small numbers stream systems cyprinids have been shown to (<50 per 100 m reach). Brown trout were rare prefer intermediate water depths and lower or absent at those sites having highest densi- water velocities. They usually do not occur in ties of leatherside chub (>100 per 100-m areas with zero water velocity or with a high reach). This suggests that brown trout may percentage of silt (Moyle and Baltz 1985, Gross- negatively affect populations of leatherside man and Freeman 1987, Grossman and de chub, and fragmentation of leatherside chub Sostoa 1994). Use of low-velocity pockets in populations may be due to interaction with fast-flowing streams by leatherside chub is introduced brown trout. Further studies on similar to patterns of microhabitat use by the the interaction of brown trout and leatherside Virgin spinedace (Lepidomeda mollispinis mol- chub are needed to determine the nature and lispinis), a closely related species found in the magnitude of this possible negative effect. Virgin River basin of southwestern Utah and Leatherside chub were abundant and brown adjacent areas of Arizona and Nevada. Spine- trout rare or absent at all 3 locations where dace are reported to prefer swift streams and microhabitat characteristics were measured. utilize depths between 10 and 90 cm at veloci- Because of the possible interaction with brown ties between 10 and 100 cm sec–1 (Rinne trout, patterns of habitat use by leatherside 1971, Deacon et al. 1991). chub documented in this study may not coin- cide with patterns of habitat use in areas with ACKNOWLEDGMENTS brown trout (Walser et al. 1999). Microhabitats used by leatherside chub are Numerous individuals were involved in similar in general to microhabitats used by data collection: K. Wilson, D. Wilson, J. Belk, 42 WESTERN NORTH AMERICAN NATURALIST [Volume 61

C. Patillo, M. McGee, M. Whitney, P. Pixton, Great Basin. Memoirs of the California Academy of A. Young, K. Young, A. Heber, A. Hamblin, M. Sciences 7:1–259. IMHOF, J., AND R.M. BIETTE. 1982. Assessing fluvial trout Budge, M. Taylor, A. Buck, J. Shields, R. Heck- habitat in Ontario. Pages 197–209 in N.B. Armen- ert, D. Ward, C. Fechner, J. Caylor, C. Sexton, trout, editor, Aquistition and utilization of aquatic R. Evans, K. Hales, and C. Sperry. C. Patillo habitat inventory information. American Fisheries entered and edited data and A. Frank assisted Society, Western Division, Bethesda, MD. JOHNSON, J.B., M.C. BELK, AND D.K. SHIOZAWA. 1995. with mapping. We are deeply indebted to Age, growth, and reproduction of leatherside chub these individuals for their perseverance. This (Gila copei). Great Basin Naturalist 55:183–187. project was supported by the Bonneville MILLER, R.R., J.D. WILLIAMS, AND J.E. WILLIAMS. 1989. Chapter of the American Fisheries Society, Extinction in North American fishes during the past century. Fisheries 14:22–29, 31–38. Utah Division of Wildlife Resources, Utah MINCKLEY, W.L., AND M.E. DOUGLAS. 1991. Discovery Reclamation Mitigation and Conservation Com- and extinction of western fishes: a blink of the eye in mission, Idaho Department of Fish and Game, geologic time. Pages 7–17 in Battle against extinc- and the Department of Zoology, Brigham Young tion: native fish management in the American West. University. This research was conducted University of Arizona Press, Tucson. MINER, J.G., AND R.A. STEIN. 1996. Detection of predators under permit number 4COLL2003 from the and habitat choice by small bluegills: effects of tur- Utah Department of Natural Resources, and bidity and alternative prey. Transactions of the permit number F-96-94 from the Idaho Depart- American Fisheries Society 125:97–103. MOYLE, P.B., AND D.M. BALTZ. 1985. Microhabitat use by ment of Fish and Game. an assemblage of California stream fishes: developing criteria for instream flow determinations. Trans- LITERATURE CITED actions of the American Fisheries Society 114: 695–704. BAXTER, G.T., AND J.R. SIMON. 1970. Wyoming fishes. RINNE, W.E. 1971. The life history of Lepidomeda mol- Wyoming Game and Fish Department, Cheyenne. lispinis mollispinis (the Virgin River spinedace): a 129 pp. unique western cyprinid. Master’s thesis, University BEHNKE, R.J. 1992. Native trout of western North Amer- of Nevada, Las Vegas. 109 pp. ica. American Fisheries Society Monograph 6. SAS INSTITUTE INC. 1988. SAS user’s guide: release 6.03 Bethesda, MD. 275 pp. edition. Statistical Analysis Systems Institute Inc., BLACKWELDER, E. 1948. The geological background. Bul- Cary, NC. letin of the University of Utah 38:3–16. ______. 1993. SAS® technical report P-243. SASSTAT® BONHAM, C.D. 1989. Measurements for terrestrial vegeta- software: the GENMOD procedure, release 6.09. tion. John Wiley and Sons, New York. Statistical Analysis Systems Institute Inc., Cary, NC. DEACON, J.E., A. REBANE, AND T.B. H ARDY. 1991. Final SIGLER, W.F., AND R.R. MILLER. 1963. Fishes of Utah. report to National Park Service: a habitat preference Utah Department of Fish and Game, Salt Lake City. analysis of the Virgin spinedace in Zion National 203 pp. Park, Utah. University of Nevada, Las Vegas. 85 pp. SIMONSON, T.D., J. LYONS, AND P. D . K ANEHL. 1994. Quan- GREER, D.C. 1981. Atlas of Utah. Weber State College, tifying fish habitat in streams: transect spacing, sam- Ogden, UT. ple size, and a proposed framework. North American GROSSMAN, G.D., AND M.C. FREEMAN. 1987. Microhabitat Journal of Fisheries Management 14:607–615. use in a stream fish assemblage. Journal of Zoology SIMPSON, J.C., AND R.L. WALLACE. 1982. Fishes of Idaho. 212:151–176. University Press of Idaho, Moscow. 237 pp. GROSSMAN, G.D., AND A. DE SOSTOA. 1994. Microhabitat WALSER, C.A., M.C. BELK, AND D.K. SHIOZAWA. 1999. use by fish in the upper Rio Matarraña, Spain, Habitat use of leatherside chub (Gila copei) in the 1984–1987. Ecology of Freshwater Fishes 3:141–152. presence of predatory brown trout (Salmo trutta). HUBBS, C.L., AND R.R. MILLER. 1948. The zoological evi- Great Basin Naturalist 59: 272–277. dence: correlation between fish distribution and hydrographic history in the desert basins of western Received 7 January 1999 United States. Bulletin of the University of Utah Accepted 25 January 2000 38:17–166. HUBBS, C.L., R.R. MILLER, AND L.C. HUBBS. 1974. Hydro- graphic history and relict fishes of the north-central Western North American Naturalist 61(1), © 2001, pp. 43–49

RELATIONSHIPS BETWEEN CENTAUREA MACULOSA AND INDIGENOUS PLANT ASSEMBLAGES

Susan A. Kedzie-Webb1, Roger L. Sheley1, John J. Borkowski2, and James S. Jacobs1,3

ABSTRACT.—Ecological impacts of invasive plants include displacement of indigenous species and declines in species richness and diversity. The objective of this study was to characterize the functional relationship between plant community composition and Centaurea maculosa Lam. (spotted knapweed) within a Festuca idahoensis / Pseudoroegneria spicatum habitat type in Montana. Density, cover, and biomass of all species were collected along a gradient of spotted knapweed cover ranging from 0% to about 100%. Step-down regression was used to determine the relationship among C. maculosa, indigenous species, species richness, and Shannon-Weaver’s diversity index. Regressions showed that indigenous perennial grass cover, species richness, and species diversity were inversely related to C. maculosa cover. There was no relationship between C. maculosa and indigenous forbs. While this study does not imply a causal relationship, the literature suggests that C. maculosa displaces indigenous species and/or invades areas of reduced indigenous plant cover, low diversity, or low species richness. Knowing levels of indigenous perennial grass cover will help managers predict the outcome of weed management on rangelands that are vulnerable to weed infestation.

Key words: spotted knapweed, noxious rangeland weeds, species richness, species diversity, invasive plants.

Ecological impacts associated with non- by 56% and sediment yield by 192% when indigenous weed invasions include displace- compared with Pseudoroegneria spicatum ment of indigenous species, degradation of (Pursh.) Löve–dominated rangeland under ecosystem function, and declines in biodiver- simulated rain events (Lacey et al.1989). sity (Vitousek 1986, Randall 1996). Invasive Indigenous plant populations are thought species can alter nutrient cycles, fire regimes, to decline following invasion by nonindige- hydrologic cycles, and energy flow, and thus nous weeds. For example, Euphorbia esula L. pose serious threats to ecosystem structure (leafy spurge) is a perennial weed that invades and function (Vitousek 1986, Vitousek et al. northern grasslands and displaces indigenous 1987, Vitousek and Walker 1989, Whisenant vegetation (Belcher and Wilson 1989). Simi- 1990). For example, Bromus tectorum L. (cheat- larly, Nuzzo (1993) reported that the cover of grass) is a winter annual that alters ecosystem the indigenous ephemeral Cardamina concate- processes. Bromus tectorum dominates millions nata (Michx.) Sw. (toothwort) declined from an of hectares in the Great Basin and has increased average of 80% to 30% following invasion by fire frequency from once every 60 to 110 years the nonindigenous Alliaria petiolata (Bieb) to once every 3 to 5 years (Mack 1981, Cavara and Grande (garlic mustard). Studies Whisenant 1990). Indigenous shrubs of the that address displacement of indigenous by Great Basin, which are not adapted to fre- nonindigenous species often allude to subsequent fires, have been reduced in abundance quent declines in biodiversity (Thompson et al. or eliminated. Billings (1990) suggested that 1987, Webb and Kaunzinger 1993). However, B. tectorum may reduce biotic and genetic di- few studies have quantified the functional versity of Artemisia-dominated biomes by relationship between indigenous plant assem- eliminating plant and animal species. This in- blages and nonindigenous weed invasions. vasion has probably altered entire ecosystems. The objective of this study was to charac- Like cheatgrass, Centaurea maculosa Lam. terize the functional relationship between plant (spotted knapweed) is an important invasive community composition and C. maculosa with- plant in the Intermountain West. In a single, in a Festuca idahoensis / Pseudoroegneria spica- cursory study, C. maculosa increased erosion tum habitat type (Mueggler and Stewart 1980).

1Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717. 2Department of Mathematics, Montana State University, Bozeman, MT 59717. 3Corresponding author.

43 44 WESTERN NORTH AMERICAN NATURALIST [Volume 61

We hypothesized that indigenous species cover, mm in diameter) from each plot using a tulip species richness, and species diversity are bulb planter. Soil samples were dried at 60°C negatively related to C. maculosa cover. This to constant mass and weighed. Two 100-cm3 hypothesis does not imply a causal relationship. subsamples were taken from each sample, Knowledge of these relationships is essential mixed, and sieved (0.5 mm) to separate seeds to predict plant community changes resulting from soil and debris. Seeds were identified from weed invasions. and counted. Additional 65 × 80-mm soil samples were collected from each plot to deter- METHODS mine whether the C. maculosa gradient was related to differences in soil nutrients. Using a This study was conducted on 2 sites within standardized extraction process (Page and a Festuca idahoensis / Pseudoroegneria spicatum Klute 1982), we tested soil samples for avail- habitat type (Mueggler and Stewart 1980) able nitrogen, phosphorus, and potassium. dominated by F. idahoensis with patchy infes- There were no differences in available soil tations of C. maculosa. Site 1 is located in nutrients; therefore, the data are not presented. Story Hills (45°42′N, 111°01′W), 4 km north- To test whether C. maculosa invasion was a east of Bozeman, Montana. Elevation at this function of seed availability only, we harvested site is 1478 m and average annual precipita- 1 mature C. maculosa plant adjacent to each tion is 432 mm. Soils are clayey-skeletal, permanent plot (1 plant per plot), dissected it mixed Typic Argiborolls. Site 2 is located at at root crown, and aged it by counting annual Beartrap Canyon, about 45 km east of Norris, growth rings (Boggs and Story 1987). This Montana (45°36′N, 111°34′W). Elevation at procedure was used to test the assumption this site is 788 m with an average annual pre- that invasion by C. maculosa is associated with cipitation of 305 mm. Soils at site 2 are loamy- availability of seeds rather than differences in skeletal, mixed Aridic Argiborolls. soil and vegetation characteristics along the One C. maculosa patch, approximately 0.25 transects. Adult C. maculosa ranged in age ha, was randomly selected at each site. We from 1 to 7 years, but there were no differences randomly located 5 transects, each 20 m long, in age and distance along transect. Therefore, within each patch. Transects radiated from data again are not presented. dense C. maculosa in the center of each patch to an area of low or no C. maculosa occurrence Statistical Analysis on the outside of the patch. All transects radi- Data were compiled into tables showing ated from the center of the same patch. The number of transects (maximum of 5) along the plant community at each transect origin was C. maculosa gradient in which individual dominated by C. maculosa with few or no re- species were present for each site to character- sidual indigenous species in the understory. ize their presence and distribution. Plant den- Transects ended in areas dominated by F. ida- sity, cover, and biomass data were analyzed hoensis with a diverse understory. Twenty per- using a multi-step process. Covariance analy- manent plots (20 × 50 cm, spacing between sis was conducted to test for sample indepen- plots ranged from 0.5 to 2 m) were placed dence within transects. Because analysis indi- along each transect. Centaurea maculosa cover cated independence among all plots, we used in the permanent plots ranged from 0% to a step-down linear regression procedure to nearly 100% (about every 5%). Density and identify the best model (Neter et al. 1985). A cover of all species were sampled in each plot. combination of P-value, model simplicity, and To avoid the effect of destructive sampling R2 values was used to identify the best model on permanent plots, we randomly selected 30 for each step-down procedure. Scatter plots of temporary plots (20 × 50 cm) along the C. residuals versus standardized predicted values maculosa gradient to sample biomass, seed were used to evaluate heterogeneity of vari- bank, and soil nutrients at each site. We sam- ance for each model. Data transformations pled biomass during August 1996 for all species were conducted where necessary on predicted by clipping plants to ground level. Clipped variables using square-root transformations. samples were dried at 60°C to a constant mass Inverse, quadratic, and log transformations were and weighed. The soil seed bank was sampled tested but did not improve the models. Colin- by extracting a soil core (65 mm deep and 80 earity was evaluated using a SAS tolerance 2001] CENTAUREA MACULOSA AND INDIGENOUS PLANTS 45 procedure to test for relatedness of predictors [Hook.] Scribn., K. macrantha, Poa compressa (SAS 1990). Colinearity was not a problem in L., P. secunda, and S. comata), 2 nonindige- this analysis. Linear regression models were nous grasses (B. tectorum and P. pratensis), 10 fit using density, cover, and biomass of F. ida- indigenous forbs (Arabis holboellii Hornem., hoensis, indigenous perennial grass, indige- Artemisia frigida Willd., A. falcatus, B. sagit- nous forbs, indigenous species richness, and tata, Coryphantha missouriensis [Sweet] Britt. indigenous species diversity as predicted vari- & Rose, Gaillardia aristata Pursh, H. villosa, ables. Regressor variables used were density, L. punctata, Lupinus spp, and Opuntia polya- cover, and biomass of C. maculosa. For example, cantha Haw.), and 3 nonindigenous forbs (A. C. maculosa density, cover, and biomass were alyssoides, Berteroa incana [L.] DC., and T. used to predict F. idahoensis density, cover, and dubius) were present at site 2. Pseudoroegne- biomass, respectively. Based upon the design ria spicatum and F. idahoensis were present of this observational study, regressions should along most of the gradient. All other indige- not be interpreted to imply causality. Diver- nous grasses were limited in presence where sity was estimated using Shannon-Weaver’s C. maculosa cover was greater than 50%. Bro- diversity index (Shannon and Weaver 1949). mus tectorum was present at all levels of C. Means and standard deviations were calcu- maculosa cover and occurred in 3 or more lated for soil seed bank samples. transects, except at 70% and 100% cover, where it occurred in 2 and 1 transects, respectively. RESULTS The most abundant indigenous forbs included H. villosa and Lupinus spp. Nonindigenous A. Presence and Distribution alyssoides and B. incana were well repre- Eleven indigenous grasses (P. spicatum, F. sented along the gradient at site 2. idahoensis, Pascopyrum smithii [Rydberg] Löve, Aristida purpurea Nutt., Bouteloua gracilis Density [H.B.K.] Lag., Danthonia unispicta [Thurb.] We generated general linear models to pre- Munro, Koeleria macrantha [Ledeb.], Oryzop- dict density of indigenous species (predicted sis hymenoides [R.&S.] Ricker, Poa secunda variables) using C. maculosa density (regressor Presl, Stipa comata Trin. & Rupr., and Stipa variable). For each increase in C. maculosa viridula Trin.), 2 nonindigenous grasses (Bro- density (plants m–2), perennial grasses decreased mus japonicus Thunb. and Poa pratensis L.), linearly by about 0.07 tillers m–2 at both sites 12 indigenous forbs (Achillea millefolium L., (Fig. 1). Festuca idahoensis tiller density Artemisia ludoviciana Nutt., Aster falcatus tended to decline rapidly as C. maculosa den- Lindl., Antenarea spp., Balsamorhiza sagittata sity approached 300 plants m–2, and then con- [Pursh] Nutt., Heterotheca villosa [Pursh] tinued to decrease, but less steeply at both Shinners, Collomia linearis Nutt., Delphinium bicolor Nutt., Liatris punctata Hook., Linum lewisii Pursh, Lomatium dissectum [Nutt.] Math. & Const., and Lupinus spp), and 3 nonindigenous forbs (Alyssum alyssoides L., Comandra umbellata [L.] Nutt., and Trago- pogon dubius Scop.) were present at site 1. Of the indigenous grasses, P. spicatum was found in 2 or more transects along the gradient. All other indigenous grasses were limited in presence where C. maculosa cover was greater than 45%. Both nonindigenous grass species were present along the entire gradient. The most abundant indigenous forbs included H. villosa (hairy goldenaster) and Lupinus spp. The nonindigenous A. alyssoides was well represented along the gradient at site 1. Fig. 1. Relationship between indigenous perennial Eight indigenous grasses (P. spicatum, F. grass (IPG) density and C. maculosa density. Sites were idahoensis, B. gracilis, Calamovilfa longifolia similar; regression models represent combined data. 46 WESTERN NORTH AMERICAN NATURALIST [Volume 61

a a

b b

Fig. 3. Relationship between (a) species richness, (b) Shannon-Weaver’s diversity index, and C. maculosa based Fig. 2. Relationship between (a) indigenous perennial on cover. Sites were similar; regression models represent grass (IPG), (b) F. idahoensis, and C. maculosa cover. Sites combined data. were similar; regression models represent combined data.

ly increased (Fig. 2b). Indigenous forb cover sites (R2 = 0.55). Indigenous forb density was not associated with C. maculosa density at was not associated with C. maculosa cover either site (P ≥ 0.1). (data not shown). Indigenous species richness was negatively A negative relationship between indige- related to C. maculosa density (plants m–2) at nous species richness and C. maculosa cover site 2 (R2 = 0.39). At site 1 species richness was quantified at both sites. For each 1% intended to decline until C. maculosa densities crease in C. maculosa cover, species richness reached about 350 plants m–2. Species diver- decreased by about 3% (Fig. 3a). At both sites sity tended to increase slightly from about 1 to the prediction of plant diversity resulted in a × 2 Shannon-Weaver’s diversity index units quadratic model with a C. maculosa C. mac- based on C. maculosa density, and then began ulosa interaction (Fig. 3b). However, the qua- to decrease after reaching approximately 400 dratic component was so small that plant plants m–2 (R2 = 0.30). species diversity decreased nearly linearly based on C. maculosa cover. Cover Biomass General linear models indicated a negative relationship between indigenous grass cover Indigenous perennial grass biomass was and C. maculosa cover at both sites. For each negatively related to C. maculosa biomass at 1% increase in C. maculosa cover, indigenous both sites (Fig. 4a). Indigenous perennial grass perennial grass cover decreased by about 2% biomass tended to decline quickly as C. macu- (Fig. 2a). However, F. idahoensis cover declined losa biomass increased from 0 to 800 g m–2, with increasing C. maculosa cover until about after which no further decrease in grass 75% C. maculosa, after which this grass slight- occurred. Festuca idahoensis biomass followed 2001] CENTAUREA MACULOSA AND INDIGENOUS PLANTS 47

Fig. 5. Relationship between Shannon-Weaver’s diversity index and C. maculosa based on biomass. Sites were similar; regression models represent combined data.

DISCUSSION

The invasion of semiarid rangeland by nonindigenous species is often associated with changes in plant community composition through the displacement of indigenous species (Randall 1996). This study showed species richness and diversity were inversely related to C. maculosa cover and biomass (Figs. 1, 5). Fig. 4. Relationship between (a) indigenous perennial grass (IPG), (b) F. idahoensis, and C. maculosa and a C. Two plausible hypotheses explain this relation- maculosa quadratic component based on biomass. Sites ship: C. maculosa may displace indigenous were similar; regression models represent combined data. species, or it may invade areas of low diversity and low species richness. Tyser and Key (1988) suggested that C. maculosa is capable of modi- a trend similar to indigenous perennial grasses fying plant community composition by chang- (Fig. 4b). Indigenous forb biomass was not ≥ ing species frequency. Conversely, it has been associated with C. maculosa biomass (P 0.1). hypothesized that areas of poor species diver- The regression predicting species richness sity result in incomplete use of limiting based on C. maculosa biomass was y = 4.619 – resources, thereby increasing invasibility by 2 (0.015)X – (1.434)Y, R = 0.38 (X = C. macu- aggressive species (McNaughton 1993, Robin- losa biomass, Y = average of transect within son et al. 1995). Tilman’s (1997) observations site). Differences among transects within site of midwestern grasslands, that community occurred at both sites. For each increase in C. invasibility is greater in species-poor plant maculosa biomass, Shannon-Weaver indices communities, support this hypothesis. How- decreased by 0.007 (Fig. 5). ever, Stohlgren et al. (1999) found that, on Soil Seed Bank central grasslands, patterns of exotic invasions are more closely related to degree of resources There were no statistical differences among available and are independent of species rich- species found in the seed bank at either site. ness. Individual exotic species such as C. mac- Centaurea maculosa and B. japonicus were ulosa may behave differently from exotic prevalent species in the seed bank at site 1 species considered as a group. Studies are (Fig. 6a). Bromus tectorum was the prevalent needed to determine the cause of the relation- species in the seed bank at site 2. Seeds of ship between C. maculosa and species rich- perennial grasses either were not present or ness and diversity. were present at very low densities. Few indige- We also found that occurrences of C. macu- nous forb seeds were present (Fig. 6b). losa and indigenous perennial grasses are 48 WESTERN NORTH AMERICAN NATURALIST [Volume 61

occupy available niches left unfilled by indigenous species. Based on temporal and spatial similarities among forbs, some cursory evidence suggests that C. maculosa directly competes with indigenous forbs (Jacobs and Sheley 1999). In our study no relationship was detected between C. maculosa density, cover, or biomass, and forb density, cover, or biomass. In a study to assess herbicide impacts on nontarget species, Rice and Toney (1996) reported that forb (e.g., A. holboellii, B. sagittata, H. villosa) cover in control plots remained constant over time for 3 of 4 important species in areas of early to intermediate stages of C. maculosa invasion. Some indigenous rangeland forbs may not occupy the same niche as C. maculosa. This is surprising, because Sheley and Larson (1996) indicated that Centaurea diffusa Lam. can occupy all available niches by developing a hierarchy of age classes. These results may not apply to spring ephemeral forbs, which this study did not consider. Models predicting F. idahoensis density, cover, and biomass based on C. maculosa density, cover (Fig. 2), and biomass (Fig. 4), respectively, demonstrated a sharp decline in Fig. 6. Seed bank present in a 200-cm3 soil sample at (a) F. idahoensis followed by its low-level persis- site 1 and (b) site 2. tence at higher levels of C. maculosa (>350 plants m–2, >55% cover, and >550 g m–2). One objective of land managers in treating C. inversely related (Figs. 1, 2, 4). Watson and maculosa infestations with herbicides includes Renney (1974) reported that declines in P. spi- returning rangeland to pre-invasion levels of catum biomass are associated with increases in desirable grass species. It is recommended C. maculosa biomass. Invasive success of C. that land managers consider the understory of maculosa is attributed to rapid growth rate, residual grass species that is available to re- prolific seed production, and high biomass spond to management before weed management (Watson and Renney 1974, Sheley et al. 1998). decisions are made (Sheley and Jacobs 1997). Seedling studies have found C. maculosa to be This knowledge could potentially help land more competitive than grasses (Sheley and managers predict levels of perennial grasses Jacobs 1997, Velagala et al. 1997) and indicate necessary to return a C. maculosa–infested area to a desired perennial grass–dominated com- that C. maculosa’s competitive ability may allow munity. it to dominate and displace indigenous perennial grass in some situations. LITERATURE CITED Alternatively, C. maculosa establishment and the apparent decline in indigenous peren- BELCHER, J.W., AND S.D. WILSON. 1989. Leafy spurge and nial grasses may occur in areas of low grass the species composition of a mixed grass prairie. abundance (recruitment and dispersal) where Journal of Range Management 42:172–175. BILLINGS, W.D. 1990. Bromus tectorum, a biotic cause of open niches exist. Tilman (1997) demonstrated ecosystem impoverishment in the Great Basin. Pages that native undisturbed grasslands contain 301–322 in G.W. Woodwell, editor, Earth in transi- many available niches which invasive species tion: patterns and processes of biotic impoverish- may exploit and occupy. The lack of indige- ment. Cambridge University Press, New York. BOGGS, K.W., AND J.M. STORY. 1987. The population age nous species found in the seed bank (Fig. 6) structure of spotted knapweed (Centaurea maculosa) supports the hypothesis that C. maculosa may in Montana. Weed Science 35:194–198. 2001] CENTAUREA MACULOSA AND INDIGENOUS PLANTS 49

JACOBS, J.S., AND R.L. SHELEY. 1999. Competition and STOHLGREN, T.J., D. BINKLEY, G.W. CHONG, M.A. KALKHAN, niche partitioning among Pseudoroegneria spicata, L.D. SCHELL, K.A. BULL, Y. OTSUKI, ET AL. 1999. Hedysarum boreale, and Centaurea maculosa. Great Exotic plant species invade hot spots of native plant Basin Naturalist 59:175–181. diversity. Ecological Monographs 69:25–46. LACEY, J.R., C.B. MARLOW, AND J.R. LANE. 1989. Influence THOMPSON, D.Q., R.L. STUCKEY, AND E.B. THOMPSON. 1987. of spotted knapweed (Centaurea maculosa) on surface Spread, impact and control of purple loosestrife runoff and sediment yield. Weed Technology 3: (Lythrum salicaria) in North American wetlands. 627–631. U.S. Fish and Wildlife Service Research Report 2. MACK, R.N. 1981. Invasion of Bromus tectorum L. into Cornell University, Ithaca, NY. western North America: an ecological chronicle. TILMAN, D. 1997. Community invasibility, recruitment lim- Agroecosystems 7:145–165. itation, and grassland biodiversity. Ecology 78:81–92. MCNAUGHTON, S.J. 1993. Biodiversity and function of TYSER, R.W., AND C.H. KEY. 1988. Spotted knapweed in grazing ecosystems. Pages 361–383 in E.D. Schulze natural area fescue grasslands: an ecological assess- and H.A. Mooney, editors, Biodiversity and ecosys- ment. Northwest Science 62:151–159. tem function. Springer-Verlag, Berlin, Germany. VELAGALA, R.P., R.L. SHELEY, AND J.S. JACOBS. 1997. Influ- MUEGGLER, W.F., AND W.L. STEWART. 1980. Grassland and ence of density on intermediate wheatgrass and shrubland habitat types of western Montana. USDA spotted knapweed interference. Journal of Range Forest Service, Intermountain Forest and Range Management 50:523–529. Experiment Station, Ogden, UT. VITOUSEK, P.M. 1986. Biological invasions and ecosystem NETER, J., W. WASSERMAN, AND M.H. KUTNER. 1985. properties: can species make a difference? Pages Applied linear statistical models. 2nd edition. Richard 163–176 in H.A. Mooney and J.A. Drake, editors, D. Irwin, Inc., Homewood, IL. Ecology of biological invasions of North America NUZZO, V.A. 1993. Current and historic distribution of gar- and Hawaii. Springer-Verlag, New York. lic mustard (Alliaria petiolata) in Illinois. Michigan VITOUSEK, P.M., AND L.R. WALKER. 1989. Biological inva- Botanical Club 32:23–33. sion by Myrica faya in Hawaii: plant demography, PAGE, A.L., AND A. KLUTE. 1982. Methods of soils analy- nitrogen fixation, ecosystem effects. Ecological Mono- sis: part 2. Agronomy 9:228–262. graphs 59:247–265. RANDALL, J.M. 1996. Weed control for the preservation of VITOUSEK, P.M., L.R. WALKER, L.D. WHITEAKER, D. biological diversity. Weed Technology 10:370–383. MUELLER-DUMBOIS, AND P.A. MATSON. 1987. Biolog- RICE, P.M., AND J.C. TONEY. 1996. Plant population re- ical invasion by Myrica faya alters ecosystem devel- sponses to broadcast herbicide applications for spot- opment in Hawaii. Science 238:802–804. ted knapweed control. Down to Earth 51:14–18. WATSON, A.K., AND A.J. RENNEY. 1974. The biology of ROBINSON, G.R., J.F. QUINN, AND M.L. STANTON. 1995. Canadian weeds: Centaurea diffusa and C. maculosa. Invasibility of experimental habitat islands in Cali- Canadian Journal of Plant Science 54:687–701. fornia winter annual grassland. Ecology 76:786–794. WEBB, S.L., AND C.K. KAUNZINGER. 1993. Biological inva- SAS Institute Inc. 1990. SAS/STAT user’s guide, version sions of the Drew University (New Jersey) forest 6, volume 2. Cary, NC. preserve by the Norway maple (Acer platanoides L.). SHANNON, C.E., AND W. W EAVER. 1949. The mathematical Bulletin of the Torrey Botanical Club 120:343–349. theory of communication. University of Illinois Press, WHISENANT, S.G. 1990. Changing fire frequencies on Urbana. Idaho’s Snake River Plains: ecological and manage- SHELEY, R.L., AND J.S. JACOBS. 1997. Response of spotted ment implications. Pages 4–10 in E.D. McArthur, knapweed and grass to picloram and fertilizer com- E.V. Romney, S.D. Smith, and P.T. Tueller, editors, binations. Journal of Range Management 50: Proceedings of the Symposium on Cheatgrass Inva- 263–267. sion, Shrub Die-off, and Other Aspects of Shrub SHELEY, R.L., AND L.L. LARSON. 1996. Emergence date Biology and Management. Intermountain Research effects on resource partitioning between diffuse Station General Technical Report INT-276, USDA knapweed seedlings. Journal of Range Management Forest Service, Logan, UT. 50:39–43. SHELEY, R.L., J.S. JACOBS, AND M.F. CARPINELLI. 1998. Received 26 March 1999 Distribution, biology, and management of diffuse Accepted 28 December 1999 knapweed (Centaurea diffusa) and spotted knapweed (Centaurea maculosa). Weed Technology12:353–362. Western North American Naturalist 61(1), © 2001, pp. 50–56

MOURNING DOVE NUMBERS ON DIFFERENT SERAL COMMUNITIES IN THE CHIHUAHUAN DESERT

Lewis Saiwana1, Jerry L. Holechek1,4, Raul Valdez2, and Manuel Cardenas3

ABSTRACT.—Mourning Doves are the most commonly hunted game bird in New Mexico based on hunter harvest data collected by New Mexico Department of Game and Fish. Research is limited on the influence of rangeland ecological condition on Mourning Dove (Zenaida macroura) populations in the Chihuahuan Desert of New Mexico. Mourning Dove numbers were evaluated periodically (1988–1989) on ranges in late- and mid-seral conditions in south central New Mexico based on the Dyksterhuis quantitative climax procedure. Strip transect procedures were used to estimate Mourning Dove populations. Concurrently, vegetation canopy cover was determined by line intercept. On the basis of percent cover, grasses were the most abundant group on late-seral range while shrubs dominated mid-seral range. Mourning Dove sightings did not differ (P > 0.05) between late- and mid-seral ranges, nor did they differ (P > 0.05) among grassland, shrubland, and shrub-grass mosaic communities. Mourning Dove populations showed seasonal differences (P < 0.05), with numbers highest in summer and fall and lowest in winter and spring. Data from our study indicate that Chihuahuan Desert ranges in either mid- or late-seral stages provide equally suitable habitat for Mourning Doves.

Key words: arid lands, Zenaida macroura, rangeland, grazing, Mourning Dove, wildlife.

Mourning Doves (Zenaida macroura) are permit range and wildlife managers to inte- important game birds in the southwestern grate the needs of Mourning Doves into pro- United States and Mexico (Sadler 1993). grams involving grazing and brush manage- Because of high interest in hunting this game ment. For example, Smith et al. (1996) found bird, it has considerable economic and recre- higher numbers of Mourning Doves on sites ational importance to New Mexico and other in late-seral versus climax ecological condi- southwestern states (Sadler 1993). Mourning tions, but data are lacking on Mourning Dove Doves occur throughout New Mexico. Data populations on late-seral versus earlier seral collected by the U.S. Fish and Wildlife Service classes. The objective of this study was to indicate New Mexico Mourning Dove popula- determine the influence of late- and mid-seral tions were fairly stable in the 1989–1998 period upland sandy sites on Mourning Dove num- (Dolton and Smith 1998). However, because of bers in the Chihuahuan Desert of south cen- their economic importance, many managers tral New Mexico. About 32% of rangelands in on public and private lands would like to have southern New Mexico are in late-seral condi- better information on specific Mourning Dove tion, and 47% are in mid-seral condition (U.S. habitat requirements so they can maintain Department of Interior 1993). Rangelands in and/or possibly increase populations. early-seral condition account for 14% of south- New Mexico is characterized by >85% ern New Mexico rangelands, while only 2% rangeland, with cattle grazing being the pri- are in climax condition. mary land use. Generally, New Mexico rangelands are managed extensively, with little use STUDY AREA of herbicides or pesticides (McCormick and Galt 1993). Information is limited on how dif- We conducted the study on the Chihuahuan ferent seral classes of vegetation meet the Desert Rangeland Research Center (CDRRC) habitat requirements of Mourning Doves in the and adjacent Bureau of Land Management Chihuahuan Desert. This information would (BLM) rangeland in Doña Ana County, New

1Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003. 2Department of Fishery and Wildlife Sciences, New Mexico State University, Las Cruces, NM 88003. 3Department of Experimental Statistics, New Mexico State University, Las Cruces, NM 88003. 4Corresponding author.

50 2001] MOURNING DOVES IN THE CHIHUAHUAN DESERT 51

Mexico, 37 km north of Las Cruces. The on the CDRRC range and 35–40% on the CDRRC and BLM study areas are 12,993 ha BLM range (Tembo 1990). On a long-term basis and 10,342 ha, respectively, in the southern (1968–1990), the CDRRC range has been Jornada del Muerto Plain between the San stocked with cattle only for an average utiliza- Andres Mountains and the Rio Grande. Eleva- tion level of about 30% of the key forage tion of the study area varies from 1330 to 1348 species compared with about 50% on the BLM m above sea level (Wood 1969, Valentine 1970). range (Holechek et al. 1994). Between 1982 The area is arid, with no permanent water and 1991 a stocking rate reduction of nearly except for the Rio Grande and stock watering 50% was made on the BLM range. From 1982 points supplied by wells and temporary ponds. to 1990 forage utilization on the BLM range Annual precipitation during the study varied was 20–40% of current year’s growth. During from 190 to 296 mm, with a 30-year (1961 to 1986–1990 actual stocking rates on the CDRRC 1989) average of 248 mm. About half of the and BLM ranges averaged 48 ha and 67 ha per annual precipitation occurs between July and animal unit, respectively. September, with the greatest precipitation Several detailed vegetation inventories have amount in August. Wood (1969) described the been made on both the CDRRC and BLM climate of the area as semidesert with temper- study areas since 1981 (Holechek et al. 1994). atures varying from –23°C to 42°C and extreme Forage production and range condition scores daily fluctuations of 30°C. June is the warmest increased between 1982 and 1990 on both month, January the coldest. ranges as a result of above-average rainfall and Soils of the CDRRC and BLM study areas conservative stocking. Grazing management are mainly sandy loams underlain by calcium on the BLM range has involved a yearlong carbonate hardpan (caliche) at depths varying grazing scheme. On the CDRRC range 45% of from a few centimeters to 1 m or more (Valen- the area has been yearlong grazed and 55% tine 1970, Tembo 1990). They are classified as has been grazed under a best pasture grazing fine, loamy, mixed, thermic Typic Haplargids system since 1967 (McNeely 1983, Tembo and are in the Simona-Cruces associations 1990). (SCS 1980). In areas where groundcover is sparse, sandy dunes are formed around invad- METHODS AND MATERIALS ing honey mesquite plants (Prosopis glandu- We delineated 2 sites each on the CDRRC losa Torr.; Wood 1969). Over most of the and BLM study areas. Each of the 4 sites is CDRRC range, the soil profile is relatively about 1600 ha in size, with a livestock water- well preserved and stable. ing point near the center that was considered Study area vegetation is characterized as available to Mourning Doves. The 4 study Chihuahuan Desert grassland with scattered sites, arranged linearly from north (BLM) to shrubs. Much of the BLM site has been south (CDRRC), are 1.0–1.4 km east of Inter- invaded by honey mesquite. On the CDRRC state 25; total length of the study area from vegetation consists largely of black grama north to south is 12 km. The CDRRC and (Bouteloua eriopoda Torr.), mesa dropseed BLM study areas adjoin and are separately (Sporobolus flexuosus [Thurb] Rybd.), and fenced. The 2 study sites on the CDRRC (45% spike dropseed (S. contractus A. Hitch.). Broom yearlong, 55% best pasture grazing) were in snakeweed (Gutierrezia sarothrae Greene) late-seral ecological condition, and the 2 study dominates a few small, poor-condition areas. sites on the BLM area (yearlong grazing) were Detailed descriptions of vegetation on the in mid-seral ecological condition (Dyksterhuis CDRRC are provided by McNeely (1983) and 1949). To count Mourning Doves within each Tembo (1990). of the 4 study sites, we used 4 transects (6.4 The CDRRC and BLM study areas were km in length) spaced 500 m apart. All tran- classified into late-seral and mid-seral ecologi- sects were at least 500 m from watering cal conditions, respectively (Dyksterhuis 1949, points. To reduce boundary effects where the Tembo 1990), using the USDA Natural CDRRC and BLM areas adjoined, transects Resources Conservation Service procedure. were 500 m from the division fence. We Remaining climax vegetation during the study marked all transects with brightly colored period (1988–1989) was approximately 65–70% plastic flagging at intervals of 200 m. 52 WESTERN NORTH AMERICAN NATURALIST [Volume 61

We counted Mourning Doves once per sea- consisted mainly of black grama and mesa son from July 1988 through October 1989. dropseed; (2) shrub-grass (mid-seral) mosaic, Counts began approximately 30 minutes after which consisted primarily of a mix of honey local sunrise and continued for 2 hours. To mesquite, mesa dropseed, and broom snake- minimize the possibility of bird movements weed; and (3) shrubland (low-seral) commu- confounding counts, 2 different observers (1 per nity, which consisted mostly of honey mesquite ecological condition category) conducted sur- and broom snakeweed. The percentage of veys on the same day and at the same time. Mourning Doves recorded for each plant com- Because each transect was 6.4 km long, each munity was divided by the percentage area of observer was limited to 1 transect per day. each plant community to obtain relative obser- Observers rotated between ecological condi- vation values. A certified range consultant was tion classes to avoid confounding biases that used to determine the percentage area of each may result from survey techniques of individ- plant community on each study pasture. Ocular ual observers. We recorded only Mourning estimates and aerial photos were used for these Doves observed within approximately 50 m on determinations. either side of the observer. Mourning Doves Vegetation Inventories in flight that were observed but not flushed were omitted from counts, as were those that Vegetation inventories were made once per were heard but not seen. White-winged Doves season along the same transects used for (Zenaida asiatica) occur on the study area, but Mourning Dove counts between October 1988 only 2 were observed during enumerations. and October 1989 (Saiwana 1990). Percent- They were omitted from our tabular and sta- ages of herbaceous and woody canopy cover tistical analyses. were sampled by the line intercept procedure Our enumeration technique for Mourning (Canfield 1941), as modified by Holechek and Doves involved tabulating birds seen along Stephenson (1983). Cover measurements using 100 × 6.4-km transects. We acknowledge that a meter stick were collected every 64 m along this procedure involves a certain amount of the 6.4-km transects. Because the meter stick subjectivity by the observer as to whether was divided into 100-cm units, vegetational birds are in the census corridor. To minimize intercepts were expressed as percentages of this source of error and distribute it evenly the meter stick. In each transect the percent among transects, 2 well-trained, experienced intercept of each plant species was summed observers did all enumerations. Another poten- and divided by the total number of sampling tial problem with the technique is that some points (64) to obtain the percent cover per birds previously counted can move ahead of sampling unit (transect). the observer and potentially be counted again. Standing crop of Mourning Dove food plants The low level of Mourning Dove encounters (Davis and Anderson 1973) was determined in relative to distance traveled, the sparse nature October 1988 and 1989. Primary dove food of the vegetation, and the relatively flat terrain plants in the Chihuahuan Desert are redroot minimized this problem, and we considered pigweed (Amaeanthus pubescens [Uline and this source of error to be evenly distributed Bray] Rybd), leather leaf croton (Croton pottsii among transects in our study. Lam.), and Russian thistle (Salsola iberica L.; Brush cover was generally below the shoul- Davis and Anderson 1973). These data were der and of similar height on both late- and collected by clipping the standing crop of mid-seral pastures. However, visibility on individual plant species at ground level in 0.5- shrubland compared to grassland areas was m2 quadrats. Eighty quadrats (10 per transect) impaired to some extent and could have were clipped in each study area during each caused underestimation of Mourning Doves sampling period. All estimates are expressed on brushier areas. Nevertheless, we believe our on a dry matter basis. methods provided a reasonable estimation of Statistical Analysis relative dove numbers among transects, study sites, and plant communities. We summarized Mourning Dove numbers We recorded 1 of 3 plant communities for by ecological condition class and season. Using each Mourning Dove sighting. These included a randomized factorial analysis of variance, we (1) grassland (high-seral) community, which compared vegetation cover and dove numbers 2001] MOURNING DOVES IN THE CHIHUAHUAN DESERT 53 among ecological condition classes and seasons > 0.23; Table 1). Differences occurred among (Steel and Torrie 1980). Following procedures periods (P = 0.04) within each seral stage. of Saiwana et al. (1998), we estimated dove Mourning Dove sightings were highest in fall densities in different habitat types. We used 1989 and lowest in winter 1989. The absence the 16 transects on late-seral and mid-seral of Mourning Doves on both ranges in winter sites (4 per site × 4 per site) as sampling units 1989 is attributed to the fact that Mourning (replicates). The least significant difference Doves in southern New Mexico are migratory (LSD) test was performed at the 5% level for and generally have vacated the area by early determination of ecological condition effects, November. They begin moving back into the season effects, and ecological condition × sea- area in March and April. The interaction son interactions on Mourning Dove sightings between condition classes and periods was not (Steel and Torrie 1980). We divided percent significant (P = 0.78). Mourning Dove observations on grassland, Mourning Dove observations in grassland, shrubland, and shrub-grass communities by shrub-grass, and shrubland communities did the percent total area each of these communi- not differ from expectation (χ2 = 5.64, P = ties occupied. These values were then sub- 0.69; Table 2). These data indicate Mourning jected to chi-square goodness-of-fit analysis Doves had no definite preference for any of (Steel and Torrie 1980) to determine if more the 3 vegetation types. Mourning Doves were observed than would Total vegetation cover did not differ be- be expected if doves were randomly choosing tween mid- and late-seral study sites (P = 0.28; community types. Table 3). However, grass cover was higher on the late-seral sites (P = 0.04). Both broom RESULTS snakeweed and honey mesquite had higher cover on mid-seral sites. Mourning Dove sightings pooled across Standing crop of dove food plants differed seasons averaged 14.8 per 6.4-km transect on between mid- and late-seral sites for leather- the mid-seral site and 17.3 per 6.4-km transect leaf croton (P = 0.04; Table 4). However, red- on the late-seral site and were not different (P root pigweed (P = 0.39) and Russian thistle (P

TABLE 1. Mourning Dove sightings (sightings ⋅ km–2) on late-seral and mid-seral study areas in the Chihuahuan Desert of south central New Mexico (summer 1988–fall 1989).

______Mid-seral stage ______Late-seral stage – – Time x sx– x sx– Summer 1988 17 6.8 33 14.2 Fall 1988 20 8.9 13 2.7 Winter 1989 0 0 0 0 Spring 1989 8 4.3 11 3.7 Summer 1989 22 7.9 22 6.1 Fall 1989 22 8.2 25 13.1

TABLE 2. Relative observations of Mourning Doves on different vegetation types (% of birds sighted ⋅ % plant community area) for upland sites on south central New Mexico (summer 1988–fall 1989).

a,b ______Plant community Season Year Shrub-grass Shrubland Grassland Summer 1988 1.54 1.49 0.36 Fall 1988 0.05 0.97 1.47 Spring 1989 0.25 1.21 1.18 Summer 1989 1.23 1.27 0.68 Fall 1989 1.74 1.77 0.05 MEAN 0.96 1.34 0.75 aGrassland was 44%, shrubland was 35%, and shrub-grass was 21% of the area. bChi-square analysis (χ2 = 5.64, P = 0.69) indicated Mourning Dove sightings were not different from expected for the plant communities. 54 WESTERN NORTH AMERICAN NATURALIST [Volume 61

TABLE 3. Percent vegetation cover on late-seral and mid-seral Chihuahuan Desert rangeland in south central New Mexico for data pooled across periods (fall 1988–summer 1989).

______Fall 1988 ______Winter 1988 ______Spring 1989 ______Summer 1989 Late- Mid- Late- Mid- Late- Mid- Late- Mid- Species serala seral seral seral seral seral seral seral

GRASSES Sporobolus flexuosus 13.1 9.2 8.0 5.9A 5.9A 1.3B 7.3 5.7 Aristida spp. 4.7A 5.4B 5.0A 1.4B 3.4A 2.1A 5.7A 1.4B Boutelous criopoda 2.1A 0.5B 7.4A 0.8B 5.2B 0.6B 3.5A 0.3B Erioneuron pulchellum 1.4 0.9 2.0 2.1 1.2 2.0 1.5 1.4 Sporobolus airoides 0.2 0.0 0.0 0.0 0.1 0.7 0.0 0.0 Bouteloua gracilis 0.1 0.4 0.0 0.0 0.0 0.1 0.0 0.0 Bouteloua curtipendula 0.0 0.1 0.0 0.0 0.0 0.1 0.0 0.0 TOTAL GRASSES 21.6A 13.5B 22.4A 10.2B 15.8A 6.9B 18.0A 8.8B

FORBS-SHRUBS Gutierrezia sarothrae 12.5 15.9 8.8A 15.5B 8.5A 14.5B 7.7A 14.0B Prosopis glandulosa 2.4A 23.8B 2.4A 11.4B 3.2A 9.7B 6.0A 17.1B Croton pottsii 3.0A 0.1B 0.0 0.0 0.0 0.0 2.1A 0.0B Yucca elata 0.6 0.5 0.8A 1.7B 0.1A 1.2B 0.2A 3.4B TOTAL FORB-SHRUBS 18.5A 40.3B 12.0A 28.6B 11.8A 25.4B 16.0A 34.5B

TOTAL COVER 40.1 53.8 34.4 38.8 27.6 32.3 34.0 43.3 aRow means within periods with different letters differ (P > 0.05).

TABLE 4. Standing crop (g ⋅ m–2) of forbs on late-seral (LS) and mid-seral (MS) rangelands in south central New Mexico.

______September 1988______April 1988 September______1989 ______Mean Species LS1 MS LS MS LS MS LS MS Croton pottsii 2.0A 0.8B2 2.9A 0.0B3 1.9A 0.8B 2.3A 0.5B Salsola iberica 0.1 0.5 0.0 0.1 0.4 0.1 0.1 0.2 Amaranthus pubescens 0.1 0.4 0.1 0.2 0.1 0.3 0.1 0.2

1LS = late-seral area, MS = mid-seral area. 2Row means with different letters are significantly different (P < 0.05) for different ranges within sampling periods using least significant difference (LSD) tests. 3A trace amount (<0.1 g ⋅ m–2) occurred in samples.

= 0.29) standing crop did not differ between honey mesquite cover was higher on mid-seral sites. range (Table 3). It is also possible that adequate honey mesquite cover was available on DISCUSSION the late-seral rangeland to meet Mourning Dove nesting cover needs. Mourning Doves had no definite prefer- There is other evidence that honey mesquite ence (P = 0.69) for shrubland, shrub-grass, or is an important component of Mourning Dove grassland communities based on results of chi- nesting habitat in the Chihuahuan Desert. square analysis (Table 2). Jackson (1940) and Smith et al. (1996) reported that Mourning Clark (1969) reported that mesquite is impor- Doves were nearly absent (1.6 sightings ⋅ km–2) tant to nesting Mourning Doves. However, from climax Chihuahuan Desert grassland in Soutiere and Bolen (1976) found that Mourn- New Mexico with <1% honey mesquite cover, ing Doves in Texas compensated for the loss of but observations were common (22.3 sightings mesquite trees as nesting sites by nesting on ⋅ km–2) on late-seral rangelands where honey the ground. In their study nesting success was mesquite cover was about 7%. In this study actually higher for ground than tree nests. availability of Mourning Dove foods, primarily This may explain why Mourning Dove num- leatherleaf croton, was similar on both range- bers were similar on the late- and mid-seral land condition classes. If Smith et al. (1996) condition ranges in our study even though are correct, it appears that at some point a lack 2001] MOURNING DOVES IN THE CHIHUAHUAN DESERT 55 of shrubs, particularly honey mesquite, will approach for maximizing abundance of Mourn- limit Mourning Dove populations on Chihua- ing Doves in the Chihuahuan Desert may be huan Desert rangelands. to maintain a mixture of late- and mid-seral Mourning Doves seem to avoid densely veg- plant communities. A checkerboard pattern of etated areas for nesting and feeding (Soutiere mid-seral and late-seral pastures 1000 to 3000 and Bolen 1976, Baker and Guthery 1990). In ha in size may be ideal, but this needs study. studies by Bock et al. (1984) and Baker and We believe this mixture should maximize diver- Guthery (1990), Mourning Dove densities were sity in vegetation composition and structure. higher on moderately to heavily grazed areas Mid-seral communities are favored by moder- with a dispersion of bare ground than on un- ate grazing intensities that involve removal of grazed or densely vegetated areas. Nelson et al. 40–50% of current year growth of key forage (1997) found no difference (P > 0.10) in species (black grama, mesa dropseed, three- Mourning Dove sightings between moderately awn; Paulsen and Ares 1962). Late-seral com- and conservatively grazed Chihuahuan Desert munities are favored by conservative grazing rangelands although the data suggested there intensities (30–40% removal of key forages; was a tendency toward higher sightings on the Paulsen and Ares 1962, Holechek et al. 1994). moderately grazed areas. Our findings regarding Mourning Dove habi- Leatherleaf croton (also known as dove- tat in the Chihuahuan Desert may not apply to weed) standing crop was higher (P < 0.05) on other ecosystems, such as the shortgrass prairie late-seral than mid-seral areas (Table 4). and southern high plains of eastern New Mex- Another study found that Russian thistle and ico and western Texas, because of differences redroot pigweed were more available in areas in climatic conditions and vegetation composi- within 500 m of livestock watering points than tion. However, we consider this study some- in areas 500–1700 m from water (Tembo 1990). what exploratory. Long-term research is needed Moderate retrogression in ecological condi- to better evaluate Mourning Dove population tion from the climax caused by livestock graz- responses to livestock grazing and plant com- ing appears to favor these plants. From the munities in the Chihuahuan Desert. standpoint of optimizing cover and food for Mourning Doves, a mix of mid-seral and late- ACKNOWLEDGMENTS seral stages may be ideal. All 4 of our experimental sites are located Funding for this research was provided by within the home range of a Mourning Dove. the New Mexico Agricultural Experiment Sta- They are surrounded by large areas of range- tion and was part of project 1-5-27417. land in mid-seral or late-seral conditions. Therefore, we believe that Mourning Doves LITERATURE CITED had opportunity to readily display habitat preferences. Our selection of study areas sur- BAKER, D.L., AND F. S . G UTHERY. 1990. Effects of continu- rounded by large tracts of native rangelands ous grazing on habitat and density of ground-foraging birds in south Texas. Journal of Range Manage- also minimized potential confounding from ment 43:2–5. outside influences, such as agricultural lands, BOCK, C.E., J.H. BOCK, W.R. KENNY, AND V. M . H AW- roads, water points, and trees, whose locations THORNE. 1984. Responses of birds, rodents, and veg- could have caused doves to use one seral stage etation to livestock exclosure in a semidesert grass- differently compared with another. land site. Journal of Range Management 37:239–243. CANFIELD, R.H. 1941. Application of the line interception method in sampling range vegetation. Journal of MANAGEMENT IMPLICATIONS Forestry 39:388–394. CLARK, T.L. 1969. Nesting and production. State-wide During 2 years of study, Mourning Dove Mourning Dove research. Federal Aid Project W-95- R-3, Texas Parks and Wildlife Department, Austin. numbers were similar on late- and mid-seral 29 pp. Mimeo. Chihuahuan Desert upland sites. Another Chi- DAVIS, C.A., AND M.W. ANDERSON. 1973. Seasonal food huahuan Desert study (Smith et al. 1996) indi- use by Mourning Doves in the Mesilla Valley, south- cates higher Mourning Dove numbers on sites central New Mexico. New Mexico Agricultural in late-seral compared to near-climax condition Experiment Station Bulletin 612. 22 pp. DOLTON, D.D., AND G.W. SMITH. 1998. Mourning Dove as judged by the quantitative climax approach breeding population status, 1998. U.S. Department developed by Dyksterhuis (1949). The best of Interior, Fish and Wildlife Service. 56 WESTERN NORTH AMERICAN NATURALIST [Volume 61

DYKSTERHUIS, E.J. 1949. Condition and management of dissertation, New Mexico State Univeristy, Las rangeland based on quantitative ecology. Journal of Cruces. Range Management 2:104–115. SAIWANA, L., J.L. HOLECHEK, A. TEMBO, R. VALDEZ, AND HOLECHEK, J.L., AND T. S TEPHENSON. 1983. Comparison M. CARDENAS. 1998. Scaled quail use of different of big sagebrush range in northcentral New Mexico seral stages in the Chihuahuan Desert. Journal of under moderately grazed and grazing excluded con- Wildlife Management 62:550–556. ditions. Journal of Range Management 36:455–456. SCS. 1980. Soil survey of Doña Ana County area. United HOLECHEK, J.L., A. TEMBO, A. DANIEL, M.J. FUSCO, AND States Department of Agriculture, Soil Conservation M. CARDENAS. 1994. Long-term grazing influences Service, Las Cruces, NM. on Chihuahuan Desert rangeland. Southwestern SMITH, G., J.L. HOLECHEK, AND M. CARDENAS. 1996. Naturalist 39:342–349. Wildlife numbers on excellent and good condition JACKSON, A.S. 1940. Preliminary report on the status of Chihuahuan Desert rangelands: an observation. the Mourning Dove in Throckmorton County, Texas. Journal of Range Management 49:489–493. Unpublished master’s thesis, North Texas State SOUTIERE, B.C., AND E.G. BOLEN. 1976. Mourning Dove Teachers College, Denton. 136 pp. nesting on tobosa grass–mesquite rangeland sprayed MCCORMICK, J.C., AND H.D. GALT. 1993. Forty years of with herbicide and burned. Journal of Range Man- vegetational trend in southwestern New Mexico. agement 29:226–231. Pages 184–207 in Vegetation management of hot STEEL, R.G.D., AND J.H. TORRIE. 1980. Principles and desert rangeland ecosystem symposium. University procedures of statistics. McGraw-Hill Book Co., of Arizona, Tucson. New York. 481 pp. MCNEELY, R.P. 1983. Influence of mesquite on vegeta- TEMBO, A. 1990. Influence of watering and range condi- tional changes under two grazing strategies in south- tion on vegetation of Chihuahuan desert. Unpub- ern New Mexico. Unpublished master’s thesis, New lished doctoral dissertation, New Mexico State Uni- Mexico State University, Las Cruces. 61 pp. versity, Las Cruces. 127 pp. NELSON, T., J.L. HOLECHEK, R. VALDEZ, AND M. CARDENAS. UNITED STATES DEPARTMENT OF INTERIOR (USDI). 1993 1997. Wildlife numbers on late- and mid-seral Chi- Public land statistics. U.S. Department of Interior, huahuan Desert rangelands. Journal of Range Man- Bureau of Land Management, Washington, DC. agement 50:593–599. VALENTINE, K.A. 1970. Influence of grazing intensity on PAULSEN, H.A., AND F. N . A RES. 1962. Grazing values and improvement of deteriorated black grama range. management of black grama and tobosa grasslands New Mexico Agricultural Experiment Station Bul- and associated shrub ranges of the Southwest. U.S. letin 553. 21 pp. Department of Agriculture Technical Bulletin 1270. WOOD, J.E. 1969. Rodent populations and their impact on SADLER, K.C. 1993. Mourning Dove harvest. Pages 449–458 desert rangelands. New Mexico Agricultural Experi- in T.S. Baskett, M.W. Sayer, R.E. Tomlinson, and R.E. ment Station Bulletin 555. 16 pp. Mirarchi, editors, Ecology and management of the Mourning Dove. Stackpole Books, Harrisburg, PA. Received 27 July 1999 SAIWANA, L. 1990. Range condition effects on scaled quail Accepted 12 April 2000 in southcentral New Mexico. Unpublished doctoral Western North American Naturalist 61(1), © 2001, pp. 57–63

THE ROLE OF DIETARY FIBER IN DUNG SIZE OF BUSHY-TAILED WOODRATS, NEOTOMA CINEREA: ITS POTENTIAL APPLICATION TO PALEOCLIMATIC INTERPRETATION

Jennifer C. Hallett1 and Peter E. Wigand2

ABSTRACT.—A laboratory study was conducted to examine causes underlying variation in woodrat dung size. Eight bushy-tailed woodrats, Neotoma cinerea, were captured and sequentially fed 2 diets of 46% and 63% neutral detergent fiber (NDF). Dung pellets were collected for 2 days following 7 days of acclimation to each diet. Length and width of oven-dried pellets ranged, respectively, from 8.3 to 10.2 mm and 3.2 to 4.9 mm for diet 1, and 8.9 to 12.4 mm and 3.6 to 4.7 mm for diet 2. Body weight ranged from 232.0 to 504.5 g and did not significantly affect dung size. A series of 2-factor analyses of variance with repeated measures and sequential Bonferroni tests was used to assess the effect of dietary fiber consumption on dung size. An increase in fiber intake led to a significant increase in dung length and dry dung weight but not dung width or body weight. Results suggest a relationship between dung length in prehistoric woodrat middens and changing climate, although the relationship is not clearly understood and needs further evaluation.

Key words: dung size variation, Neotoma cinerea, fiber consumption, body size, paleoclimate proxy data.

Woodrat dung collected from prehistoric The study of prehistoric woodrat middens woodrat middens fluctuates significantly in as climate change indicators has recently led size. Incremental changes observed in average to the use of woodrat dung as a potential width of dung, from samples either within or research tool (Smith et al. 1995, Smith and between midden strata, appear to follow a pat- Betancourt 1998). However, not all factors that tern (Smith and Betancourt 1998). This pat- affect dung size have been clearly elucidated. tern of change seems to mirror late Quater- Therefore, its utility as an indicator of prehis- nary temperatures in the southwestern United toric climates remains unclear. States (Smith et al. 1995). Dung-size variation may reflect changes in Since the 1960s, plant remains collected genotypic or phenotypic traits of the woodrat from prehistoric woodrat middens have been in response to environmental change. One of used as a source of proxy data to characterize these traits, body size, would be expected to prehistoric climates (Wells and Jorgensen 1964, fluctuate over many generations. Two geneti- Spaulding 1985, Mehringer and Wigand 1990, cally similar rats might grow to different sizes Thompson 1990, Wigand and Nowak 1992). depending upon food availability (Holter and Urine-encrusted strata from middens have been Hayes 1977, Case 1978). Different body sizes disaggregated to recover encased vegetation may also reflect adult/juvenile and male/female fragments that are then taxonomically identi- differences in body size (e.g., male N. cinerea fied and radiocarbon dated. Once these data may weigh up to 130 g more than females are grouped with vegetational data collected [Escherich 1981]). In using prehistoric dung from other analyzed midden strata, they are samples to address body size, researchers used to reconstruct past distributional ranges have derived conclusions from dung measure- of plant species and changes in species distri- ment that may reflect shifts in gender of the butions through time. Ultimately, using modern woodrat occupying the nest, the presence of plant ecology, temporal and spatial distribution- juvenile rats, and/or environmental factors. al ranges of plant species are used to reconstruct Longer-term changes in body size may be prehistoric climate dynamics. the result of environmental conditions, such as

1Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512. 2Great Basin and Mohave Paleoenvironmental Consulting, 2210 Seneca Drive, Reno, NV 89506.

57 58 WESTERN NORTH AMERICAN NATURALIST [Volume 61 temperature. A biogeographical hypothesis size, and address the link between these fac- presented by Bergmann (1847) states that in tors and climate. colder climates populations of similar or the same animal species are larger bodied than in METHODS warmer climates. Changes in temperatures have been linked to altitudinal and latitudinal clinal We trapped 8 adult bushy-tailed woodrats trends in body size in many animal species in the Granite Hills, approximately 25 km (Boyce 1978, Burnett 1983, Benton and Uetz northwest of Reno, Nevada, between Febru- 1986, Bogdanowicz 1990). Perhaps the most ary and March 1993 and subjected them to a important issue connected to body size change series of feeding trials analyzing the relation- is how quickly it may occur. ships among dung size, body size, and dietary Modern Neotoma spp. show substantial fiber intake. The study animals were housed interspecific and intraspecific variation in body at the University of Nevada, Reno, Biology size (Hooper 1940, Hall 1946, Finley 1958, Department Animal Room and represented Brown 1968). Brown and Lee (1968) found the range of adult body sizes typically re- body size of N. cinerea to be inversely corre- corded for the species. Variables selected to lated with temperature, concluding that popu- characterize body size were body length and lations followed Bergmann’s rule. Harris (1984) body mass. These variables were selected noted that structural traits in the teeth and jaw based upon a correlation matrix comprising of prehistoric N. cinerea skeletal remains, col- numerous body size variables measured after lected from middens between 11,000 and captivity. Strongly correlated variables were eliminated to reduce the number of variables 33,000 years old, show morphology similar to in subsequent statistical analyses. We mea- modern N. cinerea; however, he does not sured daily body weights for each diet. Mean describe changes in body size. body weight for each woodrat for each diet Dung-size variation may also reflect wood- was used for statistical purposes. rat diets. Woodrat dung is composed primarily Woodrats were housed for 1.5 to 2 months of undigested food particles (structural carbo- prior to feeding trials and were fed a diet of hydrates) and metabolic products (bacteria Purina rat chow and water from gravity- and endogenous wastes; Van Soest 1982). demand bottles. Woodrats were kept in indi- Undigested food particles consist primarily of vidual cages with raised wire screens to avoid plant cell walls (cellulose, lignin, and hemicel- contact with fecal pellets. During feeding tri- lulose), which make up most fiber components als woodrats were provided, ad libitum, 2 nat- in the diet and cannot be broken down into ural-grain pelleted diets of differing levels of nutrients (Van Soest 1982). fiber. Diet 1 contained 14% acid detergent Since dung contains a large percentage of fiber (ADF), representing a higher-quality diet undigested fiber, the amount of fiber con- and, diet 2 contained 35% ADF. Feeding trials sumed in the diet and the ability to digest it began after a 7-day acclimation period to diet should affect dung composition and, conse- 1 to completely void previously consumed quently, dung size. In one study Neotoma spp. food after Smith et al. (1995). Following accli- dung contained 67% fiber produced on a 40% mation each woodrat was given a preweighed fiber diet (Justice and Smith 1992). The amount daily portion of diet 1 for 2 days. All dung and of fiber in forage relates to quality of the diet; orts (uneaten food particles) were collected high-fiber diets have lower nutritional value every 24 hours. The same procedure was fol- than low-fiber diets (Salisbury and Ross 1978, lowed for diet 2. Van Soest 1982, Demment and Van Soest To test for homogeneity in dung length and 1985). The ability to digest fiber varies; some width variances, we performed a Hartleys Fmax herbivores can select diets higher in fiber than test for gender and diet combinations. A sig- those with less efficient digestive systems nificant result would indicate that the data (Demment and Van Soest 1985). Diet selec- needed to be transformed. Following transfor- tion, though, is ultimately restricted by avail- mation (if necessary), diet effects were ana- ability of forage. lyzed in a series of 2-factor (diet and gender) In this study we assess the relationships analyses of variance (ANOVA) with repeated among dietary fiber levels, body size, and dung measures on diet since individual woodrats 2001] DIETARY FIBER AND WOODRAT DUNG SIZE 59 were observed under both diet conditions significant result would eliminate the need to (PROC GLM; SAS Institute Inc. 1988). Mean use body size variables (the continuous vari- dung widths and lengths were analyzed in ables) in the statistical tests. separate ANOVAs. Carryover effects of ingest- ing the 2 diets in the same order were mini- RESULTS mized by allowing sufficient time to elapse between the introduction of different diets so No statistically significant relationship could that the woodrats could acclimate. This reduced be detected between the independent variables, the need to randomize the sequence of feed- body length and body weight, and the depen- ing trials for each woodrat. dent variables, dung width and dung length Three ANOVAs were also conducted to test (Table 1). Only dung length data needed to be for differences in average food intake, average transformed, which was conducted by calcu- number of fecal pellets excreted, and average lating the inverse of the mean dung length. dry weight of dung produced per day between For the ANOVA comparing diet 1 to diet 2, the 2 diets. For all ANOVAs and regressions, dung length for diet 2 was significantly longer we used a sequential Bonferroni test to control (F = 31.66, df = 1,6, P < 0.0013). Remaining the probability of committing a type I error ANOVAs yielded nonsignificant results. and to detect more than 1 false null hypothesis Woodrats consuming diet 2 produced a sig- among tests. nificantly heavier amount of dung than wood- Fiber assays were conducted on diets 1 and rats consuming diet 1 (F = 8.19, df = 7, P < 2 at the Animal Nutrition Laboratory, Univer- 0.002); however, mean number of pellets pro- sity of Nevada, Reno. Neutral detergent fiber duced per diet was not significantly different (NDF) analyses were conducted so other stud- between experimental diets (Table 2). Mean ies using NDF could be referenced. For statis- amount of food (g) consumed per diet did not differ significantly between the 2 diets. NDF tical analysis fecal pellets representing each analyses resulted in 46% fiber for diet 1 and woodrat and diet were measured to assess the 63% fiber for diet 2 (ADF content for diet 1 effects of fiber level intake on dung size. For was 14% and 35% for diet 2). those woodrats producing over 80 pellets per diet, we randomly selected a minimum of 80 DISCUSSION dung pellets for measurement. The dung was oven-dried for 48 hours (to ensure that it was Dung length appeared to increase due to comparable to dung analyzed in prehistoric the greater amount of fiber in the dung during woodrat midden studies). Using digimatic the feeding of diet 2. Lee (1992) indicates that calipers, we measured dung length and width as fiber consumption increases, more excreta and then calculated means representing each (dry weight) is produced. Our study showed woodrat and diet. Relative precision for dung that total dry weight of dung produced per measurements was calculated (2% for dung day for each diet significantly increased for width and 1% for dung length). Oven-dried the higher-fiber diet. Even though a weak dung was counted for each woodrat and diet relationship exists between mean number of and also weighed to assess differences in dung pellets produced per day by each woodrat and density between diets. the experimental diets, an increase in fiber The relationship between body size and intake leads predominantly to longer, or possi- dung size was analyzed using simple linear bly denser, fecal pellets rather than an increase regressions (PROC GLM; SAS Institute Inc. in number of pellets produced. 1988). Eight linear regressions were conducted The direct physical influence of the diges- using dung length and width for each diet as tive tract on fecal material might control dung individual dependent variables, and body length and width. Contractile waves in the length and weight as individual independent colon form individual fecal pellets (Ruckebusch variables. Results from regressions dictated 1989); the material is forced out by lateral, the type of statistical test to be conducted on outward compressions to create the length of diet effects. They determined the functional fecal pellets. Larger amounts of material in relationship between diet and dung length the digestive tract from a higher-fiber diet and width and whether or not dung length might contribute to increased elongation of and width could be used as covariates. A non- fecal pellets. 60 WESTERN NORTH AMERICAN NATURALIST [Volume 61

TABLE 1. Differences in mean dung width and dung length between diets 1 and 2 produced by woodrats of distinct lengths and mean body masses. Mean body massa Mean dung width Mean dung length Woodrat (g) Body (mm) (mm) identification ______length ______number Diet 1 Diet 2 (cm) Diet 1 sx– Diet 2 sx– Diet 1 sx– Diet 2 sx– 8 440.0 ± 2.8 440.3 ± 0.5 18.8 3.35 .026 4.03 .030 9.42 .158 11.33 .124 9 261.3 ± 1.3 232.0 ± 0.8 17.3 3.43 .025 3.70 .040 8.31 .153 9.5 .211 10 327.6 ± 2.1 314.5 ± 6.5 19.7 3.28 .019 3.57 .023 10.15 .145 11.37 .247 11 256.8 ± 1.6 255.7 ± 2.2 18.5 3.40 .054 3.67 .040 8.30 .216 11.69 .215 13 295.3 ± 0.8 278.7 ± 3.2 17.8 3.22 .031 4.01 .037 8.43 .159 9.31 .170 14 400.2 ± 3.5 396.7 ± 1.1 17.5 3.58 .032 3.70 .036 8.50 .126 8.89 .153 15 504.5 ± 5.8 487.0 ± 3.9 18.0 4.87 .038 4.59 .035 10.08 .178 12.44 .116 16 272.7 ± 3.5 295.2 ± 8.0 15.6 4.35 .026 4.72 .030 8.47 .117 10.61 .118 OVERALL MEAN 344.8 ± 89.7 337.5 ± 89.5 17.9 3.69 4.00 8.96 10.64 a ± Values represent mean sx–.

The amount of material in the digestive plain the nonsignificant finding for dung width tract, and ultimately in the dung, is the result and fiber intake. of fiber digestibility. Digestion of fiber varies Other studies have found that dung size due to several factors, including body size and varies directly with body size (Murie 1974, passage rate through the gut (Demment and Luckenbach 1982, Smith et al. 1995). Smith et Van Soest 1985, Hammond and Wunder 1991, al. (1995) conducted a systematic evaluation of Justice and Smith 1992). In woodrats digesti- the relationship between dung size and body bility of fiber increases with increased body size. Their study analyzed only dung width and size (Justice and Smith 1992). Body size can pellets wider than 4 mm for 3 woodrat species. also affect the amount of fiber consumed by a In our experimental design we included the woodrat in its natural environment. Woodrats controlled testing of dietary fiber intake as have been shown to select foods with greater well as body size on a single species to analyze nutritional content, which would lead to a re- causal relationships. Thus, although our study jection of foods with lower nutritive value such and that of Smith et al. (1995) are not directly as those containing high fiber levels (Atsatt and comparable, results from each study illustrate Ingram 1983, Karasov 1989, Post 1993). For a different general trend between dung width example, the smaller-bodied N. lepida selects and body size. The different outcomes from foods with lower fiber content and as a result the 2 studies emphasize the need for addi- digests less fiber (Justice and Smith 1992). tional studies that combine elements from both Therefore, dung size variability would be experimental designs. expected to fluctuate within interspecific (and The significant relationship shown between potentially intraspecific) natural woodrat popu- dietary fiber and dung length is statistically lations because of the regulation of fiber selec- more powerful when using a small number of tion and digestion primarily through body size woodrats. On the other hand, the lack of evi- differences. Our study did not indicate any dence of a relationship between body size and effect of body size on dung width or length. dung size might have been a function of the This may be explained partially by the uni- small number of experimental woodrats used form fiber levels given woodrats in the experi- in the study. mental diets, disallowing them to select the Paleoecological Application amount of fiber. Regulation of fiber levels in our study combined with the digestive abili- of Woodrat Dung Size ties of larger-bodied woodrats may have mini- This study has documented that fiber intake mized any effect of body size on dung length affects dung length; however, a relationship and dung width. Variable digestive abilities between dung length and changing climate might also make the relationship between fiber needs to be established. To quantify this rela- intake and dung size less obvious and may ex- tionship, the interactions between climatic 2001] DIETARY FIBER AND WOODRAT DUNG SIZE 61

TABLE 2. Differences in mean number of dung pellets, mean weight of food consumed, and mean weight of dung pellets between diets 1 and 2. Mean number of Mean mass of food Mean mass of dung Woodrat pellets produced consumed per diet produced per diet identification ______per diet ______(g) ______(g) number Diet 1 Diet 2 Diet 1 Diet 2 Diet 1 Diet 2 8 107 118 14.4 17.5 4.5 8.8 9 66 78 8.2 —a 2.6 3.7 10 86 103 8.3 20.7 4.3 7.1 11 51 61 10.2 10.4 2.9 4.7 13 101 125 15.5 14.6 4.2 8.7 14 79 109 21.6 —a 6.9 4.7 15 63 126 18.7 14.6 6.4 12.4 16 63 69 10.8 15.9 4.6 6.6 OVERALL MEAN 77 99 13.5 15.6 4.6 7.1 aUnable to measure

change, woodrat behavior, and plant commu- makes it likely that N. cinerea, due to habitat nity dynamics need to be studied in a modern adaptability to mesic sites uninhabitated by setting. Such findings would be used to infer other woodrat species (Finley 1958), was the the amount and variation of fiber ingested in only woodrat species present in the northern different plant communities (and nutrient avail- Great Basin. Additionally, the fiber content ability) at various rainfall and temperature re- found in some of these plant species spans the gimes observed in prehistory. Ultimately, dung- range of fiber levels used in this study (Duke length measurements taken from ancient wood- and Atchley 1986). Thus, the Great Basin may rat middens may be exploited as a proxy for be a good candidate for studying variation in climate change. plant communities and climate change in rela- Fluctuation in fiber content is evident in tion to variation in fiber intake. individual plants due to seasonal influences Plant community changes in composition and plant structure, and among and within vege- within the northwestern Great Basin have been tation communities (Demment and Van Soest documented since 30,000 years BP, including 1985, Barboza and Hume 1992). These fluctu- variations in numbers of herbaceous, shrubby, ations, compounded with the ability of wood- and arboreal species (Wigand and Nowak 1992, rats to select forage that meets nutritional Nowak et al. 1994b). These variations reflect requirements, imply that fiber intake varies shifts between mesic and xeric species in the significantly throughout the lifespan of a sin- cold, wet late Pleistocene, 10,000–30,000 years gle woodrat and for populations living in dif- BP, and between mesic and xeric species in the ferent plant communities (Brown et al. 1972, warm Holocene, since 10,000 BP. Resulting Meserve 1974, Atsatt and Ingram 1983, Dial shifts in plant species along elevational and 1988, Justice and Smith 1992, Post 1993). latitudinal gradients in response to changing Dung-size variation from Neotoma cinerea climatic conditions must have influenced wood- in the Great Basin would be most indicative of rat diet quality and resultant fiber intake. climate change for several reasons. During the The Great Basin has abundant woodrat nests past 3200 years, populations of N. cinerea have that contain clearly distinguishable strata that not been particularly sensitive to habitat pref- can be sampled for woodrat dung and plant erences, implying that they adapted (within macrofossils ranging in age from modern to the range of habitat preference) to different tens of thousands of years. Currently, data are habitats, mesic and xeric, rather than shifting being evaluated for dung width and length their distribution (Barnosky 1994, Hadly 1996). measurements from a single woodrat midden During the Pleistocene the northern Great with multiple strata. This woodrat midden Basin was dominated by plant species typically provides one of the best records of terrestrial present within the current range of habitats of history currently available for the northern N. cinerea (Wigand and Nowak 1992). This Great Basin (Wigand and Nowak 1992, Nowak 62 WESTERN NORTH AMERICAN NATURALIST [Volume 61 et al. 1994a, 1994b). Also, carbon isotopic analy- LITERATURE CITED ses of plant materials from midden strata provide information regarding environmental ATSATT, P.R., AND T. I NGRAM. 1983. Adaption to oak and other fibrous, phenolic-rich foliage by a small mam- stress, in particular drought- and cold-related mal, Neotoma fuscipes. Oecologia 60:135–142. water stress (Wigand et al. 1994). Additionally, BARBOZA, P.S., AND I.D. HUME. 1992. Digestive tract mor- measurements of juniper seed length provide phology and digestion in the wombats (Marsupialia: a measure of effective moisture. Vombatidae). Journal of Comparative Physiology 162:552–560. Smith et al. (1995) have implied that a rela- BARNOSKY, E.H. 1994. Ecosystem dynamics through the tionship exists among woodrat body size, dung past 2000 years as revealed by fossil mammals from width, and climate change; this finding needs Lamar Cave in Yellowstone National Park, USA. to be addressed when analyzing the relation- Historical Biology 8:71–90. BENTON, M.J., AND G.W. UETZ. 1986. Variation in life-his- ships among fiber intake, dung length, and tory characteristics over a clinal gradient in three climate change. Since modern populations of populations of a communal orb-weaving spider. woodrats show a tendency to follow Berg- Oecologia 68:395–399. mann’s rule, it seems plausible that prehistoric BERGMANN, C. 1847. Uber die verhaltnisse der warme- okonomie der thiere zu ihren grosse. Göttingerstu- populations of woodrats would respond simi- dien 3(1):595–708. larly. In periods of drought or cold tempera- BOGDANOWICZ, W. 1990. Geographic variation and taxon- tures, as the woodrat’s body size increases, omy of Daubenton’s bat Myotis daubentoni in populations could be forced to consume higher- Europe. Journal of Mammalogy 71:205–218. BOYCE, M.S. 1978. Climatic variability and body size vari- fiber forage. The cumulative effect of an in- ation in the muskrats (Ondatra zibethicus) of North crease in body size and fiber intake might America. Oecologia 36:1–19. potentially amplify dung size and be mistak- BROWN, J.H. 1968. Adaptation to temperature in woodrats. enly attributed solely to body size. Body size Michigan University of Zoology, Miscellaneous Pub- lications No. 134–138. and fiber intake may vary on different time BROWN, J.H., AND A.K. LEE. 1968. Bergmann’s rule and scales. Fiber intake might influence dung-size climatic adaptation in woodrats (Neotoma). Evolu- variation more immediately and dramatically tion 23:329–338. over the short term. Body size changes might BROWN, J.H., G.A. LIEBERMAN, AND W. F. D ENGLER. 1972. Woodrats and cholla: dependence of a small mammal occur more slowly and would be reflected in population on the density of cacti. Ecology 53: longer-term changes in dung size. 310–314. The purpose of this and similar studies is to BURNETT, C.D. 1983. Geographic and climate correlates of understand how experimental findings relate morphological variation in Eptesicus fucus. Journal of Mammalogy 64:437–444. to prehistoric woodrat response and climate CASE, T.J. 1978. A general explanation for insular body change. A relationship between dung length size trends in terrestrial vertebrates. Ecology 59:1–18. and changing climate most likely exists; how- DEMMENT, M.W., AND P. J . V AN SOEST. 1985. A nutritional ever, before dung length can be used to indi- explanation for body-size patterns of ruminant and nonruminant herbivores. American Naturalist 125: cate paleoecological changes, underlying prin- 641–672. ciples and interactions need to be clearly DIAL, K.P. 1988. Three sympatric species of Neotoma: assessed. dietary specialization and coexistence. Oecologia 76: 531–537. DUKE, J.A., AND A. ATCHLEY. 1986. CRC handbook of ACKNOWLEGMENTS proximate analysis tables of higher plants. CRC Press, Boca Raton, FL. 389 pp. We thank the Desert Research Institute for ESCHERICH, P.C. 1981. Social biology of the bushy-tailed partial support of the study. We are grateful to woodrat, Neotoma cinerea. University of California Publications in Zoology 110:1–132. Debbie Palmquist, USDA Forest Service, FINLEY, R. 1958. The woodrats of Colorado: distribution Intermountain Forest and Range Experiment and ecology. University of Kansas, Museum of Nat- Station, for valuable assistance with statistical ural History Publications 10:213–552. analyses. The work reported here fulfilled in HADLY, E.A. 1996. Influence of late-Holocene climate on northern Rocky Mountain mammals. Quaternary part a master’s degree in the Environmental Research 46:298–310. and Resource Sciences Department as a thesis HALL, R. 1946. Mammals of Nevada. University of Cali- titled, “The effects of dietary fiber and body fornia Press, Berkeley. 710 pp. size on dung size of the bushy-tailed woodrat, HAMMOND, K.A., AND B.A. WUNDER. 1991. The role of diet quality and energy need in the nutritional ecol- Neotoma cinerea,” conducted at the Univer- ogy of a small herbivore, Microtus ochrogaster. Phys- sity of Nevada, Reno. iological Zoology 64:541–567. 2001] DIETARY FIBER AND WOODRAT DUNG SIZE 63

HARRIS, A.H. 1984. Neotoma in the late Pleistocene of RUCKEBUSCH, Y. 1989. Gastrointestinal motor functions in New Mexico and Chihuahua. Pages 164–178 in H.H. ruminants. Chapter 34, pages 1225–1282 in S.G. Genoways and M.R. Dawson, editors, Contributions Schultz, J.D. Wood, and B.B. Brauner, editors, Hand- in Quaternary vertebrate paleontology: a volume in book of physiology, section 6: the gastrointestinal memorial to John E. Guilday. Special Publications of system; volume 1: motility and circulation, part 2. the Carnegie Museum of Natural History 8:1–538. Bethesda, MD. HOLTER, J.B., AND H.H. HAYES. 1977. Growth in white- SALISBURY, F.B., AND C.W. ROSS. 1978. Plant physiology. tailed deer fawns fed varying energy and constant Wadsworth, Belmont, CA. 397 pp. protein. Journal of Wildlife Management 41:506–510. SAS INSTITUTE, INC. 1988. SAS/STAT user’s guide, release HOOPER, E.T. 1940. Geographic variation in bushy-tailed 6.03 edition. SAS Institute, Inc., Cary, NC. 1028 pp. woodrats. University of California Publications in SMITH, F.A., AND J.L. BETANCOURT. 1998. Response of Zoology 42:407–424. bushy-tailed woodrats (Neotoma cinerea) to late JUSTICE, K.E., AND F.A. SMITH. 1992. A model of dietary Quaternary climatic change in the Colorado Plateau. fiber utilization by small mammalian herbivores, Quaternary Research 50:1–11. with empirical results for Neotoma. American Natu- SMITH, F.A., J.L. BETANCOURT, AND J.H. BROWN. 1995. ralist 139:398–416. Evolution of body size in the woodrat over the past KARASOV, W.H. 1989. Nutritional bottleneck in a herbivore, 25,000 years of climate change. Science 270: the desert wood rat (Neotoma lepida). Physiological 2012–2014. Zoology 62:1351–1382. SPAULDING, W.G. 1985. Vegetation and climates of the last LEE, B.H. 1992. The effects of wheat bran supplemented 45,000 years in the vicinity of the Nevada test site, diets on fecal fiber excretion in omnivores and her- south-central Nevada. United States Geological Sur- bivores. Korean Journal of Animal Nutrition and vey Professional Paper 1329. Feedstuffs 16:300–308. THOMPSON, R.S. 1990. Late Quaternary vegetation and LUCKENBACH, R.A. 1982. Ecology and management of the climate in the Great Basin. Pages 200–240 in J. desert tortoise (Gopherus agassizii) in California. Betancourt, T.R Van Devender, P.S. Martin, editors, Pages 1–37 in R.B. Bury, editor, North American tor- Packrat middens: the last 40,000 years of biotic toise and conservation and ecology. U.S. Department change. University of Arizona Press, Tucson. of Interior, Fish and Wildlife Service, Wildlife VAN SOEST, P.J. 1982. The nutritional ecology of the rumi- Research Report 12. nant. Cornell University Press. Ithaca, NY. 476 pp. MEHRINGER, P.J., AND P. E . W IGAND. 1990. Comparison of WELLS, P.V., AND C.D. JORGENSEN. 1964. Pleistocene late Holocene environments from woodrat middens wood rat middens and climatic change in the Mohave and pollen: Diamond Craters, Oregon. Pages 294–325 Desert—a record of juniper woodlands. Science 143: in J. Betancourt, T.R. Van Devender, P.S. Martin, edi- 1171–74. tors, Packrat middens: the last 40,000 years of biotic WIGAND, P.E., AND C.L. NOWAK. 1992. Dynamics of north- change. University of Arizona Press, Tucson. west Nevada plant communities during the past MESERVE, P.L. 1974. Ecological relationships of two sym- 30,000 years. Pages 42–60 in C.A. Hall, V. Doyle- patric woodrats in a California coastal sage scrub Jones, B. Widawski, editors, The history of water, community. Journal of Mammalogy 55:442–447. eastern Sierra Nevada, Owens Valley, White-Inyo MURIE, O.J. 1974. Animal tracks. 2nd edition. Houghton Mountain Research Station. Symposium, Volume 4. Mifflin Company, New York. 375 pp. University of California, Los Angeles. NOWAK, C.L., R.S. NOWAK, R.J. TAUSCH, AND P.E. WIGAND. WIGAND, P.E., M.L. HEMPHILL, AND S. (MANNA) PATRA. 1994a. A 30,000 year record of vegetation dynamics 1994. Late Holocene climate derived from vegeta- at a semi-arid locale in the Great Basin. Journal of tion history and plant cellulose stable isotope records Vegetation Science 5:579–590. from the Great Basin of western North America. ______. 1994b. Tree and shrub dynamics in northwestern Pages 2574–2583 in Proceedings of the Fifth Annual Great Basin woodland and shrub steppe during the International High-Level Radioactive Waste Man- Late-Pleistocene and Holocene. American Journal of agement Conference and Exposition, 22–26 May Botany 81:265–277. 1994. POST, D.M. 1993. Detection of differences in nutrient concentrations by eastern woodrats (Neotoma floridana). Received 1 October 1997 Journal of Mammalogy 74: 493–497. Accepted 12 April 2000 Western North American Naturalist 61(1), © 2001, pp. 64–77

TAPHONOMY AND SIGNIFICANCE OF JEFFERSON’S GROUND SLOTH (XENARTHRA: MEGALONYCHIDAE) FROM UTAH

H. Gregory McDonald1, Wade E. Miller2, and Thomas H. Morris2

ABSTRACT.—While a variety of mammalian megafauna have been recovered from sediments associated with Lake Bonneville, Utah, sloths have been notably rare. Three species of ground sloth, Megalonyx jeffersonii, Paramylodon harlani, and Nothrotheriops shastensis, are known from the western United States during the Pleistocene. Yet all 3 are rare in the Great Basin, and the few existing records are from localities on the basin margin. The recent discovery of a partial skeleton of Megalonyx jeffersonii at Point-of-the-Mountain, Salt Lake County, Utah, fits this pattern and adds to our understanding of the distribution and ecology of this extinct species. Its occurrence in Lake Bonneville shoreline deposits permits a reasonable age determination of between 22 and 13 ka.

Key words: Megalonyx, Paramylodon, ground sloth, Great Basin, Lake Bonneville, Sangamon, Pleistocene, spit.

Records of the sloths Megalonyx jeffersonii, The partial Megalonyx skeleton described Paramylodon harlani, and Nothrotheriops shas- here was recovered from Lake Bonneville tensis in the Great Basin are rare. All currently shoreline sediments in the southernmost part known records for sloths are located around of Salt Lake County. Equipment operator Joe the region’s periphery. This scant record is also Miller, who works for Geneva Rock Products reflected in Utah, which has a very limited Company, made its discovery in the summer representation of Pleistocene ground sloths. of 1996. With the kind permission of that com- The first reporting of a sloth, the mylodont pany’s management, he presented the fossil Paramylodon, from Utah was based on 2 teeth material to the Earth Science Museum at and a partial vertebra (Miller 1976), presumably Brigham Young University, Provo, Utah, where from the same individual, in the Silver Creek it has been accessioned. local fauna. The site yielding this fauna is about The ground sloth bone-bearing unit lies 48 km northeast and 568 m higher in elevation within Pleistocene-age Lake Bonneville shore- than the sloth from Point-of-the-Mountain line deposits in the Jordan River cut of the (hereafter referred to as PM). Nothrotheriops, Traverse Range (Fig. 1). A Trimble TDC1 GPS the smallest of the 3 ground sloths, has been unit was used to calculate the elevation of the identified from cave sites in the southwestern bone-bearing unit at 1381.7 m (Fig. 2). The part of Utah based solely on dung samples bone-bearing unit lies approximately 10 m (Mead et al. 1984, Mead and Agenbroad 1992). below the present land surface. Machette The first Utah discovery of Megalonyx was (1992) mapped the surface sediments of the only recently made (Gillette et al. 1999) and study area as upper Pleistocene lacustrine was based on several bones of a single individ- gravels that were deposited during the Provo ual found near the city of Orem, about 26 km regressive phase of the Bonneville lake cycle. southeast of PM. The material described here These data broadly bracket the time of bone represents a substantial amount of a single, deposition from the maximum transgressive very large individual and is only the 2nd known phase of the Stansbury Level at approximately record of Megalonyx from the entire Great 22 ka (thousands of years before present) to Basin. It seems appropriate to provide as much the Provo regression at approximately 13 ka information as possible about this specimen (Currey et al. 1984, Currey 1990). and the depositional setting from which it was Research has shown that pre-Bonneville recovered and the inferences that can be made lakes occupied the lower parts of the north- regarding the ecology of this extinct species. eastern portion of the Great Basin back to a

1Hagerman Fossil Beds National Monument, Box 570, Hagerman, ID 83332. Present address: National Park Service, Geologic Resources Division, Science and Technical Services Branch, Box 25287, Denver, CO 80225-0287. 2Department of Geology, Brigham Young University, Provo, UT 84602.

64 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 65

Point-of-the-Mountain Megalonyx site

Fig. 1. Index map of the north central portion of Utah where Megalonyx jeffersonii fossils were collected.

Fig. 2. Topographic profile and location of key beds and lake levels at Point-of-the-Mountain. Elevations of the Bonne- ville and Provo Benches are taken from the Jordan Narrows 7.5-minute topographic map. Elevations of the Stansbury Level and of all ages are from Currey et al. (1984). 66 WESTERN NORTH AMERICAN NATURALIST [Volume 61 date of possibly 200 ka (Scott et al. 1983, McCoy ery of the sloth, excavation by the gravel pit 1987). Lake Bonneville, as generally under- operator resulted in the bed being completely stood, appears to have had its beginning some- covered. The currently exposed (1999) stratal time between 26.5 and 30.0 ka (Oviatt et al. unit above the bone-bearing bed is composed 1992, Oviatt et al. 1994, Lemons et al. 1996). of sand and gravel. The stratal unit below the Maximum lake depth, as viewed elsewhere in bed is primarily composed of sand as viewed the Great Basin, reportedly was 320 m about elsewhere in the pit. 14.5–15.0 ka (Jarrett and Malde 1987, Oviatt The ferruginous bone-bearing bed is over- et al. 1992) when the Bonneville Level devel- lain by high-angled (31°), NW dipping fore- oped at 1554 m above mean sea level. A well- sets of large-scale, sigmoidal, cross-stratified documented flood of gigantic proportions then beds (Fig. 3). The unit containing the bone- occurred, quickly lowering the lake to the bearing beds is approximately 10 m thick and Provo Level. Interstate Highway 15, which is composed of sand and gravel. Foreset beds runs immediately east of the fossil site, is situ- can be traced laterally and upward into gravel- ated on the resulting wave-built bench in this rich topset beds, which are largely low-angle area (Fig. 2). (12°) to planar beds. Measurements taken The Megalonyx skeleton reported here was from bedforms laterally to the south of topset recovered at 1381.7 m elevation, approximately beds indicate an azimuth direction of approxi- 10 m above the Stansbury Level. According to mately 260°. Grain-size distribution of 5 sam- Currey et al. (1984), this places the unit be- ples from the base to top of the unit indicates tween the Stansbury (approximately 1371.6 m) a coarsening upward trend (Fig. 4). Gravel- and Provo Level (1463 m) at PM. The Stans- and pebble-sized lithoclasts are subangular to bury Level probably formed before any other subrounded and are composed of limestone, levels between 20 and 23 ka (Currey et al. quartzite, and granite. Mica is a common com- 1984). The lowest Bonneville shoreline is the ponent of the sand. The unit is extremely fri- Gilbert Level at 1310 m, and it is significantly able to nearly unlithified, as grains can be dis- lower than the fossil occurrence. This shore- aggregrated by rubbing. A thin (0.6 m) soil line developed during the latest part of the horizon is presently developing on the top of Pleistocene, probably 10–11 ka. the unit in the study area. The bone-bearing unit is underlain by an LOCALITY DESCRIPTION 11.6-m-thick, sand-dominated unit that displays low-angle planar to undulating beds as seen in The sand and gravel quarry owned by more deeply excavated pit areas. This unit is Geneva Rock Products Company in which the also extremely friable. The lower portion of the sloth was found is in SW1/4, NE1/4, Sec. 23, unit displays soft sediment deformation in the T4S, R1W, Jordan Narrows 7.5′ Quadrangle, form of convolute bedding. The scale of con- Salt Lake County, Utah, at 111°55′W longitude, volute bedding is on the order of 2 m. 40°27′30″N latitude. This is BYU locality num- There is a sharp contact at the base of this ber 802. Sediments from which the sloth was lower sand with a relatively thick (1 m) gray- recovered were deposited on the north flank green clay. Within the excavated pits, this clay of the Traverse Mountains of the Wasatch layer acts as a permeability barrier and locally Range that forms PM. This range marks the ponds water (Fig. 5). Elevation of this clay layer easternmost boundary of late Pleistocene Lake (1370 m) is within 1.5 m of the Stansbury Level Bonneville. elevation (Currey et al. 1984) and is approximately 12.2 m above the elevation of the Jor- SEDIMENTOLOGY AND dan River. DEPOSITIONAL HISTORY The stratal unit overlying the bone-bearing bed is interpreted to represent progradation of Sedimentology a large spit developing at the PM on the north- Bone was found on and within an oxidized, ern flank of the Traverse Range. Perennial winds poorly sorted, sandy siltstone bed. Thickness from the west and northwest working on the and lateral extent of this ferruginous bed are extensive fetch of Lake Bonneville would have unknown. Detailed study of the bone-bearing produced strong southwest-oriented longshore bed is incomplete because shortly after recov- currents. Similar spits at Rocky Ridge and Little 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 67

Fig. 3. Topset and foreset sand and gravel beds in the stratal unit directly above the sloth bone-bearing unit. These beds are interpreted to have been deposited by a prograding spit during the Provo regressive phase of the Bonneville lake cycle.

Fig. 4. 3-D histogram displaying grain-size distributions of 5 beds within the sigmoidal cross-stratified unit above the ground sloth bone-bearing unit. Bed 1 is at the base of the unit and represents foreset to bottomset beds. Sample 5 represents topset beds. The diagram illustrates the coarsening upward trend typical of a prograding spit.

Mountain near the town of Payson to the south that time. Sediments here were shed from the and Stockton Bar to the west have been iden- nearby Wasatch Front as indicated by granite tified elsewhere in Lake Bonneville deposits and limestone lithoclasts that match the lithol- (Bissell 1968). Longshore currents were able ogy there. This spit built a relatively shallow to entrain large gravel-sized clasts and push a terrace where the strong currents were con- large quantity of sediment toward and around centrated. Sediments were pushed along the PM, which projected into Lake Bonneville at top of this terrace until they avalanched into 68 WESTERN NORTH AMERICAN NATURALIST [Volume 61

represents the simplest explanation and is preferred by the authors. Sedimentologic and taphonomic data suggest that the sloth carcass may have washed into Lake Bonneville relatively intact. The carcass was transported some distance along the Wasatch Front by longshore drift. As the carcass continued to be transported toward PM, it made its way to the edge of the wave-built terrace of a large spit. The spit would be migrating to the west, but the longshore current and direction of the spit would have produced foreset beds oriented to the northwest. The carcass eventually fell off the wave-built terrace of the spit and settled into deeper water (approximately 10 m) that had been receiving only suspended-load, hemi- pelagic sediments. Eventually, foreset lamina- tion from spit progradation buried the carcass, thus preventing scavenging and disassociation of the skeleton. With continued regression of Lake Bonneville, the bone and associated siltstone entered the vadose zone. The combination of atmospheric oxygen penetrating the large pore spaces of the coarse-grained sediment and occasional meteoric water that Fig. 5. Clay layer at 1370 m elevation. This unit is very close to the Stansbury Level (Currey et al. 1984). Note the perched on the impermeable siltstone upon water associated with this relatively impermeable clay. The which the skeleton lay, altered the siltstone ferruginous siltstone bed within which the Megalonyx was into a groundwater laterite. discovered may have been oxidized post-depositionally by A 2nd possible scenario involves deposition a perched water table such as this. of the sloth during Stansbury time and burial either by spit migration during the Bonneville transgressive phase or much later burial by deeper water. Once deposited as foreset beds spit migration during the Provo regressive within water as deep as 10 m, longshore cur- phase. This more complicated scenario sug- rents no longer entrained the sediments. gests that the ferruginous siltstone developed The ferruginous bone-bearing siltstone is under subaerial conditions resulting in a soil interpreted as either a deeper water hemi- horizon. The paleosol developed during the pelagic deposit that developed slightly basin- short regression that followed the Stansbury ward of the prograding spit, or possibly as a highstand. The animal died on dry land and paleosol. The underlying unit is interpreted to became iron-stained during soil-forming pro- represent shoreline deposits developed basin- cesses. Sometime later it was buried, either ward of strong longshore currents. Convolute during the Bonneville transgressive phase or bedding indicates fast sedimentation rates and/ the Provo regressive phase of the Bonneville or quick burial or possibly fluctuations in the lake cycle. Taphonomic observations, includ- groundwater table after subaerial exposure. ing the lack of bite or gnaw marks on bones, the absence of any indication of weathering of Depositional History the bone such as described by Behrensmeyer The above interpretations lead to 2 possible (1978), the lack of scattering of bones, and scenarios concerning the depositional history enough bones to produce both an articulated of the ground sloth bones. The 1st scenario left and right manus (Figs. 6A, B), suggest that involves deposition and burial by spit progra- scavenging must not have been a significant dation during the Provo regressive phase of factor. These observations weaken this 2nd the Bonneville lake cycle (Machette 1992). It scenario. 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 69

C D

Fig. 6. Selected bones of the especially large Megalonyx jeffersonii (BYU 13610) from Point-of-the-Mountain, Salt Lake County, Utah: A, dorsal view of articulated partial left manus; B, dorsal view of articulated partial right manus; C, proximal view of left navicular; D, proximal view of left astragalus; E, lateral view of left radius. 70 WESTERN NORTH AMERICAN NATURALIST [Volume 61

SPECIMEN AGE prevented any observation of the specimen in situ, recovery of most bones of the manus on Since no collagen was present in the Mega- both sides, as well as numerous other small lonyx bones (Austin Long, personal communi- bones, makes it reasonable to infer that the cation, 1998) a carbon-14 age could not be animal was buried as a fully intact or reason- obtained. Therefore, its age needs to be esti- ably complete carcass. Fresh fracture surfaces mated based on Bonneville lake levels that on several bones indicate significant breakage have been dated (Oviatt et al. 1992, 1994). The and probable loss of some skeleton during bull- age of the bone can be bracketed between dozing operations. Examination of recovered approximately 22 ka and 13 ka based on lake parts of the skeleton did not reveal any evi- level ages previously derived (Currey et al. dence of tooth marks caused by scavenging by 1984, Currey 1990). Assuming the bone was predators or gnawing by rodents, also suggest- deposited subaqueously and quickly buried, as ing rapid burial. in the 1st scenario discussed above, the age While we postulate that burial of the car- would be approximately 13 ka. This interpreta- cass may have occurred following some trans- tion concurs with Machette (1992), who mapped port in the lake by longshore currents, transit surface exposures in the study area as being time must have been minimal. Schaefer (1972) deposited during the Provo regressive phase noted that both whales and seals tend to sink of the Bonneville lake cycle. If the sloth was at death unless the animal has a high fat con- deposited subaerially, as in the 2nd scenario tent, in which case it may float longer before discussed above, the age would be approxi- sinking. Submerged carcasses may later become mately 22 ka. buoyant and float following gas buildup in the The large size of the specimen would sug- body cavity due to decomposition. This occurs gest the younger of the 2 alternative interpre- only if the animal does not sink into anaerobic tations for the age of the sloth. As discussed waters where conditions are unfavorable for below, there was a trend of size increase in bacterial activity so that insufficient gases are Megalonyx from its first appearance in the late produced to cause the carcass to surface. Our Hemphillian ca 5.2 ma (Hirschfeld and Webb postulated water depth of 14 m for the final 1968) through the Tertiary and Quaternary, resting place of the carcass was probably too with the largest specimens being latest Pleis- shallow to produce anaerobic conditions. If tocene in age. the original location where the animal died was on a shallower wave-built terrace of the SPECIMEN DESCRIPTION spit, then the carcass may have become par- Preserved portions of the partial skeleton of tially bloated and been able to float a short Megalonyx jeffersonii (BYU 802/13610) from distance before sinking into deeper water on PM include the following elements: left the face of the prograding spit. It is possible scapula, portions of both humeri, left radius that some parts of the skeleton had already (Fig. 6E), left manus: scaphoid, lunar, mag- separated from the carcass prior to this sec- num, unciform, metacarpal II, metacarpal III, ondary transport. As noted by Schaefer (1972), metacarpal IV, metacarpal V (Fig. 6A), partial the jaw and then skull are among the first right radius, right manus: scaphoid, lunar, parts to separate from the carcass in a floating ulnare, trapezoid, magnum, unciform, meta- animal. While the skull and jaw of the PM carpal I, metacarpal II, metacarpal III, proxi- specimen were not recovered, their absence mal and second phalanges of digit III (Fig. may reflect either their separation from the 6B), parts of left tibia, left astragalus (Fig. 6D), carcass prior to its transport to its final resting left navicular (Fig. 6C), left partial cuboid, place or destruction by heavy equipment before fragment of calcaneum, right fibula minus dis- recognition of the existence of the specimen. tal end. However, no traces of teeth or skull bones Bone preservation is excellent despite the were found after careful picking of all the complete depletion of collagen. None of the bone material. bones show any signs of weathering as described While all preserved bones of the PM speci- by Behrensmeyer (1978), suggesting immedi- men can be readily referred to the genus ate burial following death of the animal. While Megalonyx, none of the available material the mode of discovery by heavy equipment actually includes those portions of the skeleton 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 71 that provide diagnostic features used in identi- ity that exists within the species. A compari- fying the species as M. jeffersonii (McDonald son of relative lengths of metacarpals of the 1977). The Orem specimen described by Utah specimen with an articulated hand from Gillette et al. (1999) included the co-ossified American Falls Reservoir (IMNH 23034) and proximal and second phalanges of the third the 3 associated metacarpals of the type of M. digit of the pes, one of the features used by jeffersonii from West Virginia (ANSP 12508; McDonald (1977) to distinguish M. jeffersonii Fig. 11) indicates that despite differences in from all earlier species of Megalonyx. In ear- size, relative proportions of this segment of lier species of the genus the 2 bones are sepa- the hand remain constant. Figure 11 also pro- rate. Other features such as dentition and vides an indication of the relative size range skull features, parts absent in the PM speci- that existed in M. jeffersonii with regard to the men, can also be used to distinguish M. jeffer- range of metacarpal lengths. It must be re- sonii from other species. Currently, only a sin- membered that samples for each metacarpal gle late Pleistocene species of Megalonyx, M. represent a span of time and are not from con- jeffersonii, is recognized. The extremely large temporaneous individuals. Since there was a size of the individual (with caveats discussed size increase in M. jeffersonii from its initial below), the age of the deposits from which it appearance in the late Irvingtonian land mam- was recovered, and the geographic proximity mal age (McDonald 1977) until its extinction of the new specimen to other Megalonyx that at the end of the Rancholabrean, this produces can be securely referred to the species make it a considerable range of size for the species. reasonable to refer the PM sloth to Megalonyx This is best illustrated by comparing the jeffersonii. largest and smallest adult fifth metacarpals in One of the evolutionary trends of Mega- Figure 11. The largest specimen, from the lonyx has been an increase in overall body size Darke County, Ohio, individual, has a length of through time. The PM specimen is among the 135.8 mm, which is 154% larger than the small- largest individuals known of M. jeffersonii est individual at 88.1 mm from San Josecito (Fig. 6, Table 1). The only other known speci- Cave, Nuevo Leon, Mexico. The age of the San men of M. jeffersonii similar in size to the PM Josecito fauna has been recently dated between individual is from Darke County, Ohio (Mills 27 and 11 ka (Arroyo-Cabrales et al. 1995), 1975). The Ohio specimen is dated at 12,190 ± which makes it roughly contemporaneous with 215 BP, and so it is close to the younger of the both the Point-of-the-Mountain and Darke 2 possible ages for the PM specimen. The 2 County Megalonyx. skeletons have 4 bones in common, the radius Most known specimens of M. jeffersonii do (Fig. 7), second metacarpal (Fig. 8), third meta- not have associated absolute dates. Therefore carpal (Fig. 9), and navicular (Fig. 10), which it is not possible to quantify precisely the rate permit direct comparison of their size and of size increase through time for the species. dimensions. These bones and their measure- Size may be useful in a biostratigraphic con- ments are given in Table 1. The Megalonyx text but only in a generalized way. An added from Orem is also a large individual, but problem is that the overall sample size for each because it does not share any bones with the bone is so small that it is not possible to take PM specimen, a direct comparison cannot be into account size differences that may reflect made. differences in latitude or other environmental The closest sample of Megalonyx outside gradients that might affect the size of a local the Bonneville Basin is on the Snake River population. Size differences between the larger plain, the possible source area for dispersal of specimens from the north, PM (40.5°N) and Megalonyx into the basin (Gillette et al. 1999). Darke County (40°N), and the individuals from The PM specimen is larger than Megalonyx San Josecito Cave (24°N) suggest that a posi- from American Falls Reservoir, Idaho, consid- tive Bergmann’s response may exist in Mega- ered to be Sangamon in age, ca 100,000 years lonyx. Confirmation of this pattern will require (Pinsof 1998), and thus considerably older a larger sample than is presently available. than the PM individual. While precise quantification of size versus Since so few articulated specimens of M. time is not presently possible, there is no jeffersonii are available, this new specimen question that within the Megalonyx lineage permits an evaluation of the range of variabil- there was a trend toward an overall size in- 72 WESTERN NORTH AMERICAN NATURALIST [Volume 61

TABLE 1. Measurements of specimens of Megalonyx jeffersonii from Point-of-the-Mountain, Salt Lake County, Utah. All measurements in mm. Numbers in parentheses ( ) are approximate. BYU = Brigham Young University Earth Sci- ence Museum 802/13610 from Point-of-the-Mountain, Salt Lake County, Utah; DMNH = Dayton Museum of Natural History G-25748 from Darke County, Ohio. Bone BYU DMNH Left radius Length (center of proximal articular surface to center of distal articular surface) (435) (450) Anteroposterior width proximal end 66.8 76.4 Mediolateral width proximal end 66.7 64.0 Anteroposterior width distal shaft 102.7 — Mediolateral width distal shaft 35.3 — Mediolateral width distal end 86.2 (79) Anteroposterior width distal end 122.5 (107) Right scaphoid Mediolateral width 77.5 — Dorsoventral depth (medial side) 71.5 — Anteroposterior length 52.5 — Right lunar Mediolateral width 36.9 — Dorsoventral depth 50.1 — Anteroposterior length 63.3 — Right ulnare Mediolateral width 80.8 — Dorsoventral depth 52.4 — Anteroposterior length 62.1 — Left unciform Mediolateral width 64.5 — Dorsoventral depth 61.9 — Anteroposterior length 54.1 — Right first metacarpal Length 63.8 — Mediolateral width proximal end 41.8 — Dorsoventral height distal end 30.5 — Mediolateral width distal end 26.9 — Left second metacarpal Length 98.2 98.4 Width lateral side proximal end 60.1 58.2 Width dorsal side proximal end 48.2 44.9 Width ventral side proximal end 58.7 48.7 Width of distal end 38.8 43.2 Length of carina 58.5 59.4

crease through time. This is clearly indicated in the different samples is based on discrete for a variety of bones: radius (Fig. 7), second morphological criteria and not size. In all metacarpal (Fig. 8), third metacarpal (Fig. 9), cases the PM specimen is the largest individ- navicular (Fig. 10), and astragalus (Fig. 12). As ual within the M. jeffersonii sample, which can be seen in most cases, specimens identi- most likely reflects its relatively young age. fied as M. jeffersonii are larger than the ances- tral species, M. wheatleyi, based on samples DISCUSSION from Port Kennedy Cave, Pennsylvania, and the McLeod Limerock Mine in Florida. While While Megalonyx was widely distributed the large sample size of the second metacarpal across North America and is present in numer- (Fig. 8) does result in slight overlap in size ous Rancholabrean faunas in the western United between the 2 species, this would be expected States (Gillette et al. 1999), until recently it in an evolving population. Largest individuals was not known from Utah. This is surprising of M. wheatleyi are from younger populations given the number of localities in the state that of the species, while smallest M. jeffersonii are have produced remains of Pleistocene verte- from older populations. Identification to species brates (Jefferson et al. 1994). McDonald (1996) 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 73

TABLE 1. Continued. Bone BYU DMNH Left third metacarpal Length 114.6 — Dorsoventral length proximal end 62.4 — Mediolateral width proximal end 77.7 — Length of distal carina 71.0 — Mediolateral width distal end 45.1 — Left fourth metacarpal Length 128.4 — Dorsoventral length proximal end 59.6 — Mediolateral width proximal end 55.3 — Length of distal carina 69.2 — Mediolateral width distal end 48.2 — Left fifth metacarpal Length 122.6 135.8 Dorsoventral length proximal end 47.3 49.9 Mediolateral width proximal end 53.0 49.2 Dorsoventral length distal end 54.3 57.6 Mediolateral width distal end 29.1 31.7 Left astragalus Width posterior end of trochlea 120.5 — Width anterior end of trochlea (80) — Dorsoventral height navicular process 102.8 — Anteroposterior length 92.9 — Dorsoventral height of trochlea on lateral side 105.9 — Mediolateral width navicular process 70.7 — Left navicular Dorsoventral length 91.4 90.2 Mediolateral width 85.8 81.3 Anteroposterior thickness 49.6 45.2 Length of ectocuneiform facet 72.3 85.5 Length of meso and entocuneiform facets 76.1 76.3

noted that the 3 species of ground sloths found along the eastern margin of Lake Bonneville, in the western United States tended to utilize it may be that Megalonyx was restricted to different habitats, thus reducing the probabil- riparian habitat closely associated with the ity of association with each other in faunas. lake margin. These nearshore deposits of sands While this is also true of the Utah record, the and gravels (see above discussion on sedimen- extremely small sample size is not a valid test tology) form a narrow band along the eastern of this hypothesis. However, the rarity of all 3 shore of the lake at the Wasatch Front, which sloths in Utah, compared to other large herbi- acted as a sediment source. vores, suggests either that suitable habitats that Most vertebrate remains recovered from could support these animals were marginal and sands and gravels of Lake Bonneville consist may have supported only small populations or of isolated bones, many of which are tumbled that we have not yet sampled their preferred and abraded (Nelson and Madsen 1980). This habitats within the state. suggests that most vertebrate remains pre- Paramylodon harlani is known from only one served in sand and gravels associated with locality, Silver Creek (Miller 1976), at higher Lake Bonneville were transported as bones and elevations away from the Bonneville Basin. not as carcasses. While the entire skeleton of Nothrotheriops shastensis is reported from the sloth was not saved, the presence of most Cowboy Cave and Bechan Cave on the Col- bones of each manus suggests that, prior to orado Plateau based on dung (Mead et al. disturbance by heavy equipment, the PM was 1984, Mead and Agenbroad 1992) and is also probably still articulated and at least repre- absent from the Bonneville Basin. Since the sented a partial carcass. This was also the case only 2 records of Megalonyx found in Utah are of the Megalonyx found at Orem in which many associated with deposits that accumulated of the recovered bones were still articulated 74 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Fig. 7. Scatter diagram of the length of the radius against Fig. 8. Scatter diagram of the length of the second meta- the anteroposterior length of its distal end in Megalonyx carpal against the mediolateral width of the proximal end jeffersonii and Megalonyx wheatleyi. G = Point-of-the- in Megalonyx jeffersonii and Megalonyx wheatleyi. G = Mountain Megalonyx jeffersonii, I = Megalonyx jeffer- Point-of-the-Mountain Megalonyx jeffersonii, I = Mega- sonii, L = Megalonyx wheatleyi. lonyx jeffersonii, L = Megalonyx wheatleyi.

Fig. 9. Scatter diagram of the length of the third meta- Fig. 10. Scatter diagram of the dorsoplantar length of carpal against mediolateral width of the proximal end in the navicular against its mediolateral width in Megalonyx Megalonyx jeffersonii and Megalonyx wheatleyi. G = Point- jeffersonii, Megalonyx wheatleyi, and Megalonyx leptosto- of-the-Mountain Megalonyx jeffersonii, I = Megalonyx mus. G = Point-of-the-Mountain Megalonyx jeffersonii, I jeffersonii, L = Megalonyx wheatleyi. = Megalonyx jeffersonii, L = Megalonyx wheatleyi, ✳ = Megalonyx leptostomus.

(Gillette et al. 1999). Burial and preservation Odocoileus (deer), Camelops (camel), Boother- of at least a reasonably complete carcass sug- ium (musk ox), and Bison (buffalo), with the gest minimal transport and also indicate that musk ox being best represented. Similar taxa the animal may have been living close to the along with several others have been found in shoreline and deposition site. None of the re- Lake Bonneville deposits along the Wasatch mains of either of the 2 most common species Front, both north and south of the present found in these gravel deposits, Ovis canaden- locality (Nelson and Madsen 1978, McDonald sis (mountain sheep) or Bootherium bom- and Ray 1989, Jefferson et al. 1994, Gillette bifrons (musk ox), have been found as partial and Miller, 1999, Miller in press). skeletons. A majority of the species recovered are Due to the alertness of workers at Geneva grazers. Besides Megalonyx the only other Rock Products sand and gravel pits at PM, browsers recovered are Odocoileus (deer) and especially Richard Trotter, a number of Pleis- Bootherium (musk ox). Bootherium appears to tocene vertebrates have been discovered and have been an eclectic feeder capable of feed- donated to the BYU Earth Science Museum ing in woodlands but also able to use more over the past 15 years. These include speci- xeric grassland vegetation, including Agropyon- mens of Mammuthus (mammoth), Equus (horse), like, Bromus-like, and Poa-like grasses (Guthrie 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 75

Fig. 11. Graph showing relative lengths of metacarpals Fig. 12. Scatter diagram of anteroposterior length of in Megalonyx jeffersonii. Solid symbols are from articu- astragalus against mediolateral width of the posterior edge lated hands. Open symbols indicate isolated specimens of the trochlea in Megalonyx jeffersonii and Megalonyx and provide an indication of the size range of each bone. wheatleyi. G = Point-of-the-Mountain Megalonyx jeffer- G I = Point-of-the-Mountain, Utah (BYU 13610), = sonii, I = Megalonyx jeffersonii, L = Megalonyx wheat- L American Falls Reservoir, Idaho (IMNH 23034), = leyi. Cromer Cave, West Virginia (ANSP 12508, holotype of Megalonyx jeffersonii). As previously noted, while Pleistocene vertebrates (almost exclusively mammals), espe- 1992). Any attempt to reconstruct an integrated cially large ones, are not rare in Bonneville ecology of the Bonneville shoreline 13,000 deposits along the Wasatch Front, neither are years ago is hampered by a distinct preserva- they abundant. Extensive excavations have tional bias. While the majority of vertebrate taken place along the Wasatch Front, especially remains are from the eastern side of Lake in the past decade. It might therefore be Bonneville (Nelson and Madsen 1980), the assumed that larger quantities of fossils should documented paleobotanical record is primar- be uncovered than is the case. However, con- ily from the western margin of the lake (Rhode sidering that the eastern shore of Lake Bon- and Madsen 1995). neville at all its levels lapped up against the Rhode and Madsen (1995) recognized 3 steep Wasatch Front, only limited habitat sequential vegetation formations in the region would have been available to animals living in during the Pleistocene–Holocene transition: this restricted zone. With this consideration, cold montane steppe from 14,000 to 13,000 fossils would not be expected to be abundant years ago, limber pine woodlands from 13,000 even though preservational conditions were to 10,800 years ago, and woodland/steppe favorable. The one exception is Ovis canadensis mosaic and xeric desert scrub after 11,000 (Stokes and Condie 1961, Stock and Stokes years. The paleobotanical record indicates that 1969, Nelson and Madsen 1980), one of the montane shrub vegetation covered altitudes most common species preserved in Lake Bon- up to at least 2000 m in the western Bon- neville–related sediments in this area. The rel- neville Basin. The remains of wood recovered ative abundance of mountain sheep compared from lacustrine sediments in the northeastern to other species probably reflects their ability Bonneville Basin (Scott et al. 1983) indicate to utilize the steep habitat of the Wasatch Front, that the Wasatch Front east of the basin may certainly not a habitat that would be conducive have supported coniferous forests. Rhode and to the success of a ground sloth. Madsen (1995) suggest that differences in veg- While admittedly the 2 Utah records pro- etation on the eastern and western sides of the vide only a limited sample upon which to base Bonneville Basin may have resulted from more any broad conclusions concerning the ecology mesic effects and enhanced precipitation from of Megalonyx, the strong similarity in the lake effects. This in turn possibly would have occurrence of both does suggest a pattern. limited the distribution of Megalonyx within Despite the recovery of numerous mammalian the Bonneville Basin to the eastern margin of taxa represented by a reasonable number of the lake where some type of woodland habitat samples from sediments associated with Lake existed. Bonneville (Nelson and Madsen 1980, Miller 76 WESTERN NORTH AMERICAN NATURALIST [Volume 61

1982, Jefferson et al. 1994), only 2 records of LITERATURE CITED sloth, both Megalonyx, have been found. Both were recovered from deposits associated with ARROYO-CABRALES, J., E. JOHNSON, H. HAAS, M. DE LOS RIOS PAREDES, R.W. RALPH, AND W. T. H ARTWELL. the Provo Level of Lake Bonneville. In marked 1995. First radiocarbon dates for San Josecito Cave, contrast to other mammalian records, which Nuevo Leon, Mexico. Quaternary Research 43: consist of isolated bones, both sloth specimens 255–258. are partial, articulated skeletons, suggesting BEHRENSMEYER, A.K. 1978. Taphonomic and ecological information from bone weathering. Paleobiology 4: rapid burial. It can be inferred that Megalonyx 150–162. was restricted to a habitat closely associated BISSELL, H.J. 1968. Bonneville—an Ice-Age lake. Brigham with the margin of Lake Bonneville and that Young University Geology Studies 15. 66 pp. its absence in other Pleistocene faunas in the CURREY, D.A. 1990. Quaternary paleolakes in the evolu- area reflects this habitat preference. tion of semidesert basins, with special emphasis on Lake Bonneville and the Great Basin, U.S.A. Palaeo- geography, Palaeoclimatology, and Palaeoecology 76: ACKNOWLEDGMENTS 189–214. CURREY, D.A., G. ATWOOD, AND D.R. MAYBE. 1984. Major Special appreciation is given to Joe Miller levels of Great Salt Lake and Lake Bonneville. Utah Geological and Mineral Survey, Map 73. of Geneva Rock Products Company for dis- GILLETTE, D.D., H.G. MCDONALD, AND M.C. HAYDEN. covering the partial Megalonyx skeleton dis- 1999. The first record of Jefferson’s ground sloth, cussed in this paper and his wife, Kristina, for Megalonyx jeffersonii, in Utah (Pleistocene, Rancho- kindly bringing this very important specimen labrean land mammal age). Pages 509–521 in D.D. Gillette, editor, Vertebrate paleontology in Utah. to the Earth Science Museum at Brigham Young Utah Geological and Mineral Survey Miscellaneous University (BYU). Deep gratitude is also ex- Publication 99-1. pressed to the management of the above com- GILLETTE, D.D., AND W.E. MILLER. 1999. Catalogue of pany for their part in the acquisition of this new Pleistocene mammalian sites and recovered fos- fossil and other specimens that were earlier sils from Utah. Pages 523–530 in D.D. Gillette, editor, Vertebrate paleontology in Utah. Utah Geologi- recovered from their PM gravel pit. Richard cal and Mineral Survey Miscellaneous Publication Trotter, especially, and other co-workers at 99-1. Geneva have also provided important fossils GUTHRIE, R.D. 1992. New paleoecological and paleoetho- from this site over the years. Their thoughtful- logical information on the extinct helmeted muskoxen from Alaska. Annales Zoologici Fennici 28: ness and kindness in bringing them to the 175–186. above museum for scientific study is greatly HIRSCHFELD, S.E., AND S.D. WEBB. 1968. Plio-Pleistocene appreciated. John Chiles of Geneva Rock Prod- megalonychid sloths of North America. Bulletin of ucts is thanked for permitting the authors of the Florida State Museum, Biological Sciences 12: this paper access to the gravel pit to study 213–296. JARRETT, R.D., AND H.E. MALDE. 1987. Paleodischarge of deposits there and photograph relevant areas. the late Pleistocene Bonneville flood, Snake River, Ken Stadtman of the BYU Earth Science Idaho, computed from new evidence. Geological Museum did the necessary preparation of the Society of America Bulletin 99:127–134. sloth bones. Appreciation is extended to him JEFFERSON, G.T., W.E. MILLER, M.E. NELSON, AND J.H. MADSEN, JR. 1994. Catalogue of late Quaternary ver- for this. We also thank James Miller of the tebrates from Utah. Natural History Museum of Los Geology Department at Brigham Young Uni- Angeles County Technical Report 9. 34 pp. versity for helping produce Figure 1. Donald LEMONS, D.R., M.R. MILLIGAN, AND M.A. CHAN. 1996. Currey of the University of Utah provided use- Paleoclimate implications of late Pleistocene sediment yield rates for the Bonneville Basin, northern ful information, for which he is kindly acknowl- Utah. Palaeogeography, Palaeoclimatology, and Palaeo- edged. Austin Long at the University of Ari- ecology 123:147–159. zona is thanked for his attempts to obtain a MACHETTE, M.N. 1992. Surficial geologic map of the carbon-14 age based on bone samples of the Wasatch Fault Zone, eastern part of Utah Valley, Utah County and parts of Salt Lake and Juab coun- present specimen. We also thank Ginger Cooley ties, Utah. U.S. Geological Survey, Miscellaneous of BYU for the sedimentological processing of Investigations Series, Map I-2095. material used for analysis. We would like to MCCOY, W.D. 1987. Quaternary aminostratigraphy of the extend our appreciation and thanks to Drs. Bonneville Basin, western United States. Geological Jim Mead and Dave Gillette for their thought- Society of America Bulletin 98:99–112. MCDONALD, H.G. 1977. Description of the osteology of ful reviews of the manuscript and suggestions the extinct gravigrade edentate, Megalonyx, with for its improvement. observations on its ontogeny, phylogeny and func- 2001] JEFFERSON’S GROUND SLOTH TAPHONOMY 77

tional anatomy. Master’s thesis, Department of Zool- OVIATT, C.G., D.R. CURREY, AND D. SACK. 1992. Radiocar- ogy, University of Florida, Gainesville. 328 pp. bon chronology of Lake Bonneville, eastern Great ______. 1996. Biogeography and paleoecology of ground Basin, U.S.A. Palaeogeography, Palaeoclimatology, sloths in California, Arizona and Nevada. San Ber- and Palaeoecology 99:225–241. nardino County Museum Association Quarterly 43: OVIATT, C.G., G.D. HABIGER, AND J.E. HAY. 1994. Varia- 61–65. tion in the composition of Lake Bonneville marl: a MCDONALD, J.N., AND C.E. RAY. 1989. The autochthonous potential key to lake-level fluctuations and paleocli- North American muskoxen Bootherium, Symbos, and mate. Journal of Paleolimnology 11:19–30. Gidleya (Mammalia: Artiodactyla: Bovidae). Smith- PINSOF, J.D. 1998. The American Falls local fauna: late sonian Contributions to Paleobiology 66:1–77. Pleistocene (Sangamonian) vertebrates from south- MEAD, J.I., AND L.D. AGENBROAD. 1992. Isotope dating of eastern Idaho. Pages 121–145 in W.A. Akersten, Pleistocene dung deposits from the Colorado Plateau, H.G. McDonald, D.J. Meldrum, and M.E.T. Flint, Arizona and Utah. Radiocarbon 34:1–19. editors, And whereas . . . papers on the vertebrate MEAD, J.I., L.D. AGENBROAD, P.S. MARTIN, AND O.K. DAVIS. paleontology of Idaho honoring John A. White. Vol- 1984. The mammoth and sloth dung from Bechan ume 1. Idaho Museum of Natural History Occa- Cave in southern Utah. Current Research in the sional Paper 36. Pleistocene 1:79–80. RHODE, D., AND D.B. MADSEN. 1995. Late Wisconsin/early MILLER, W.E. 1976. Late Pleistocene vertebrates of the Holocene vegetation in the Bonneville Basin. Qua- Silver Creek local fauna from north central Utah. ternary Research 44:246–256. Great Basin Naturalist 36:387–424. SCHAEFER, W. 1972. Ecology and paleoecology of marine ______. 1982. Pleistocene vertebrates from deposits of environments. University of Chicago Press, Chicago, Lake Bonneville, Utah. National Geographic Society IL. 568 pp. Research Reports 14:473–478. SCOTT, W.E., W.D. MCCOY, R.R. SHROBA, AND M. RUBIN. ______. In press. Quaternary vertebrates of the northeast- 1983. Reinterpretation of the exposed record of the ern Bonneville Basin and vicinity of Utah. In: J.W. last two cycles of Lake Bonneville, western United Gwynn, editor, Great Salt Lake 2000: an overview of States. Quaternary Research 20:261–285. change. Utah Geological and Mineral Survey Mis- STOCK, A.D., AND W.L. STOKES. 1969. A re-evaluation of cellaneous Publication. Pleistocene bighorn sheep from the Great Basin and MILLS, R. 1975. A ground sloth, Megalonyx, from a Pleis- their relationship to living members of the genus tocene site in Darke County, Ohio. Ohio Journal of Ovis. Journal of Mammalogy 50:805–807. Science 75:147–155. STOKES, W.L., AND K.C. CONDIE. 1961. Pleistocene bighorn NELSON, M.E., AND J.H. MADSEN, JR. 1978. Late Pleis- sheep from the Great Basin. Journal of Paleontology tocene musk oxen from Utah. Transactions of the 35:598–609. Kansas Academy of Science 81:277–295. ______. 1980. A summary of Pleistocene fossil vertebrates Received 8 September 1999 in the northern Bonneville Basin of Utah. Pages Accepted 13 March 2000 97–113 in J.W. Gwynn, editor, Great Salt Lake, a scientific, historical, and economic overview. Utah Geological and Mineral Survey Bulletin 116. Western North American Naturalist 61(1), © 2001, pp. 78–84

SURVIVAL AND DEVELOPMENT OF PHORADENDRON CALIFORNICUM AND ACACIA GREGGII DURING A DROUGHT

Simon A. Lei1

ABSTRACT.—Survival and development of parasitic and autoparasitic Phoradendron californicum (desert mistletoe) and their Acacia greggii (catclaw) hosts were quantitatively investigated during the 1997 drought in southern Nevada. Phoradendron californicum was parasitic on other individuals of the same species (autoparasitic), and these in turn were parasitic on A. greggii hosts. An extensive drought from February 1995 to mid-July 1997 was characterized by extremely low seasonal rainfall and high summer air temperatures. Extensively mistletoe-infested hosts had significantly less canopy volume and produced significantly fewer leaves, flowers, and fruits than uninfested (control) or lightly infested hosts. Mistletoe plants on A. greggii hosts with fewer infections produced significantly more leaves and fruits and survived better than mistletoe plants on A. greggii hosts with extensive infestations. Autoparasites had significantly less canopy volume and fruit production than their parasitic hosts and parasites on hosts with fewer infections. Severity of infestation was significantly negatively correlated with A. greggii and P. californicum survival, as it was with leaf, flower, and fruit development of A. greggii and parasitic and autoparasitic P. californicum during the 1997 drought in southern Nevada.

Key words: host, parasite, autoparasite, Acacia greggii, Phoradendron californicum, drought, survival, development, Las Vegas valley, southern Nevada.

Phoradendron californicum (desert mistle- have been such an extreme. In general, pre- toe) is an autotrophic hemiparasite, surviving cipitation during this 2.5-year period was well at the expense of its higher vascular plant hosts below average. From casual observations, it (Kuijt 1969, Holland et al. 1977, Calder and appears that some P. californicum individuals Bernhardt 1983, Ehleringer et al. 1985, 1986). and their A. greggii hosts may be killed or Branches of these host plants often swell dur- damaged by drought alone. ing infection by this leafy mistletoe (Holland Autoparasitism is a condition in which a et al. 1977). Phoradendron californicum taps its parasite occurs facultatively on another indi- host xylem only to obtain water and mineral vidual of the same species. Phoradendron cali- nutrients within xylem fluids (Leonard and fornicum parasitizes A. greggii and Cercidium Hull 1965, Raven 1983, Ehleringer et al. 1986, floridum (blue palo verde) hosts and established Holland et al. 1977). P. californicum infestations in northwestern Acacia greggii (catclaw) is often covered Arizona (Schulze and Ehleringer 1984) and with thick masses of P. californicum, which may southeastern California (Lei 1999). However, reduce host growth and reproductive success Schulze and Ehleringer (1984) note that auto- through time (Knute and Faber 1991). Serious parasitism involving Phoradendron species long-term damage to host plants is largely occurs infrequently. caused by a combination of environmental and Schulze and Ehleringer (1984) and Ehler- Phoradendron-induced physiological (water inger and Schulze (1985) have greatly increased and nutrient) stress (Glatzel 1983, Hollinger our knowledge regarding the water and nutri- 1983, Schulze and Ehleringer 1984, Schulze ent status of P. californicum and its A. greggii et al. 1984, Ehleringer et al. 1986). Weather hosts in northwestern Arizona. Yet, the response extremes are an important environmental fac- of parasites, autoparasites, and their hosts to tor influencing survival and development of severe drought remains poorly understood. woody desert plants. Insufficient rainfall and The objective of this study was to describe above-average air temperatures during winter survival and development of leaves, flowers, and 1995–summer 1997 in southern Nevada may fruits of a complex host-parasite-autoparasite

1Department of Biology, WDB, Community College of Southern Nevada, 6375 West Charleston Boulevard, Las Vegas, NV 89146-1139.

78 2001] SURVIVAL AND DEVELOPMENT DURING A DROUGHT 79 pathosystem. Specifically, 2 questions are addressed in this study: (1) Does the severity of P. californicum infestation affect the survival and development of A. greggii hosts under drought stress? (2) Does the severity of infestation affect the survival and development of parasitic and autoparasitic P. californicum under drought conditions?

METHODS Study Site Field studies were conducted in Las Vegas, Nevada (roughly 36°10′N, 115°05′W; elevation 780 m), from spring through fall 1997. The Tropicana Wash lies across the southern part of the Las Vegas valley. Although this intermittent wash remains dry throughout much of the year, it often collects excess running water Fig. 1. Comparison of mean monthly precipitation from during and shortly after major storms. February 1995 through July 1997 with mean monthly precipitation of Las Vegas valley (NOAA, Las Vegas) in south- Las Vegas valley has experienced 3 episodes ern Nevada based on 1936–1997 data. of extreme drought since 1985, with precipitation falling well below annual means in some years. The most recent drought in Las Vegas sites. Once a host dies, all P. californicum indi- valley of southern Nevada occurred over a viduals parasitizing it also die. The condition period of 2.5 years, February 1995 through of each A. greggii host was recorded as live mid-July 1997, with precipitation generally without any dead branches (1), live with single falling well below monthly averages (Fig. 1). or multiple dead branches (2), or dead (3). Each An average reduction of 72.9% in precipitation P. californicum was recorded as live with green occurred during the 1995–1997 drought com- foliage (1), live with reddish brown foliage (2), pared to a normal, non-drought period (NOAA, or dead (3). Host plants having completely bare Las Vegas). Mean annual air temperatures, branches and lacking leaves, flowers, or fruits however, did not vary considerably despite the (without phenophases) through the 1997 grow- erratic precipitation pattern occurring during ing season were assumed dead. Similarly, par- this period. The 1995–1997 years generally asites and autoparasites with dark brown foliage had above-average air temperatures (Fig. 2). and extremely brittle stems, and without pheno- Field Surveys and phases, were also assumed dead. Laboratory Analyses Development of P. californicum (parasitic The sample included hosts with parasites and autoparasitic) and its A. greggii hosts was only, and with both parasites and autopara- assessed by examining vegetative and repro- sites; also included were adjacent individuals ductive characteristics. Thirty-two A. greggii without any visible parasites (control). A total trees were randomly selected and were evenly of 16 autoparasitic P. californicum individuals distributed among the 4 levels of P. califor- each infested another P. californicum, which in nicum infestation (control, light, moderate, turn parasitized 8 A. greggii hosts. severe). Light, moderate, and severe infections Within my study site, 1017 P. californicum implied fewer than 20, between 20 and 40, (parasitic and autoparasitic) individuals and 76 and more than 40 P. californicum individuals A. greggii (infested and uninfested) trees were per host tree, respectively. Due to the paucity surveyed for evidence of mortality. Because 13 of autoparasites, all 16 autoparasites were host trees were not infested by parasites (con- found on 8 severely parasitized host trees. trol), 1017 P. californicum individuals, includ- For each tree, volume of host canopies con- ing 16 autoparasites, were found on 63 hosts. taining green leaves was computed by first Phoradendron californicum are obligate para- assuming A. greggii architecture resembled an 80 WESTERN NORTH AMERICAN NATURALIST [Volume 61

were not arranged in a perfect elliptical cylinder, calculated volumes are likely to be over- estimates. Fruit production was determined by counting the number of berries from individual P. californicum canopies. Statistical Analyses Total numbers of live and dead A. greggii hosts with 4 levels of P. californicum infestation (control, light, moderate, and severe) were expressed in percentages. Similarly, total numbers of live and dead P. californicum individuals on A. greggii hosts with 4 levels of infestation (light, moderate, severe, and autoparasite) were also expressed in percentages. Thirty-two A. greggii hosts were randomly selected and evenly distributed among the 4 levels of P. c a l - ifornicum infestation to calculate the volume Fig. 2. Comparison of mean monthly air temperature of A. greggii and P. californicum foliage and to from February 1995 through July 1997 with mean month- determine fruit production of P. californicum. ly air temperature of Las Vegas valley (NOAA, Las Vegas) in southern Nevada based on 1936–1997 data. The remaining 44 A. greggii hosts were not selected in order to conduct appropriate statistical analyses using identical sample sizes. elliptical cylinder and then calculating the vol- One-way analysis of variance (ANOVA; Ana- ume using the following equation: (πab)h, lytical Software 1994) was used to detect sig- where a and b are radii and h is height of the nificant differences in leaf, flower, and fruit elliptical cylinder (Larson et al. 1994). Since production among uninfested hosts (control) A. greggii canopies had small open spaces with- and among hosts with 3 levels of infestation. in the cylindrical shape, measured volumes Tukey’s multiple comparison test (Analytical are likely overestimated. Total number of leaflet Software 1994) was then performed to com- pairs in each group of 100 compound leaves pare means of vegetative, floral, and fruit char- was counted. A compound leaf possesses 2 or acteristics when a significant infestation effect was detected. more separate leaflets, with 2 relatively sym- Pearson’s correlation analysis (Analytical metrical leaflets making up a leaflet pair. The Software 1994) was conducted to correlate total number of leaflet pairs was then divided severity of infestation with host and parasite by 100 to determine average number of leaflet survival, as well as severity of infestation with pairs per compound leaf. Flower and fruit pro- host and parasite development. Mean volume duction was determined by counting the num- of and number of fruits on P. californicum ber of floral spikes and pods (fruits) from indi- canopies were presented with standard errors; vidual host canopies, respectively. However, P-values less than or equal to (≤) 0.05 were flower and fruit production of hosts was not reported as statistically significant. compared because not all flowers will mature into fruits regardless of parasite severity. RESULTS Because only 8 autoparasitic P. californicum individuals were detected, only 8 parasitic P. Compared to adjacent unparasitized A. californicum individuals in each of 3 levels of greggii hosts (Fig. 3), more severely parasitized infestation (light, moderate, and severe) were hosts were either dead or had multiple dead randomly selected and measured, for a total of branches. Substantial insect damage was found 32 individuals. Foliage of mistletoe plants also on dead and dying A. greggii hosts. Insects, resembled an elliptical cylinder, and so the including bark beetles, invaded many weak- same formula (πabh) was used to calculate vol- ened A. greggii hosts. However, all unpara- ume (Larson et al. 1994). Again, since P. cali- sitized hosts and a majority of lightly to mod- fornicum canopies had small open spaces and erately parasitized hosts survived the 1997 2001] SURVIVAL AND DEVELOPMENT DURING A DROUGHT 81

Fig. 3. Condition (live and dead, n = 76) of uninfected Fig. 4. Condition (live and dead, n = 1017) of P. califor- A. greggii hosts (control) and hosts with various levels of P. nicum growing on A. greggii hosts with various levels of californicum infection in southern Nevada. Total numbers infection in southern Nevada. Total numbers of live and of live and dead A. greggii trees are expressed in percent- dead P. californicum individuals are expressed in percentages. Total number of trees in each infection class: control, ages. Total number of individuals in each infection class: n = 13; light, n = 27; moderate, n = 28; and severe, n = 8. light, n = 130; moderate, n = 562; severe, n = 309; autoparasite, n = 16.

TABLE 1. Vegetative, floral, and fruit characteristics of uninfected A. greggii hosts (control) and hosts with various levels of P. californicum infestation in southern Nevada (n = 100 in each infection class). Mean values in columns followed by different letters are statistically significant at P ≤ 0.05. Infection Leaflet pairs Green canopy Number Seeds Pods class per leaf volume (m3) of spikes per pod per tree Control 5.2a 7.0a 389.7a 6.9a 234.2a Light 5.2a 7.2a 374.1a 6.7a 223.1a Moderate 5.0a 4.9b 334.6b 6.4a 201.3b Severe 4.9a 2.8c 296.0c 6.3a 175.5c

drought and produced abundant flowers or Moderate to heavy infestation, with or with- fruits (Table 1) despite some dead branches. out autoparasites, significantly (P ≤ 0.001) de- Mortality of P. californicum was consider- creased host canopy volume and flower and ably greater (Fig. 4) on severely parasitized fruit production (Table 1) compared to unin- hosts than on adjacent unparasitized hosts and fested or lightly infested hosts. Conversely, hosts with light to moderate infestation. Regard- total number of leaflet pairs per leaf and total less of the extent of infestation, a large per- number of seeds per pod did not differ signifi- centage of P. californicum plants had reddish cantly (P > 0.05; Table 1). Mistletoe plants on brown foliage with relatively low flower or hosts with more infections produced signifi- fruit production throughout the 1997 growing cantly (P ≤ 0.001) less canopy volume (Fig. 5) season. All 16 autoparasites were found on 8 and had lower fruit production (Fig. 6) than heavily parasitized A. greggii hosts; 6 auto- mistletoe plants on hosts with fewer infec- parasites were dead, as were their parasitic tions. Autoparasites exhibited significantly (P hosts. ≤ 0.001) less canopy volume (Fig. 5) and fruit 82 WESTERN NORTH AMERICAN NATURALIST [Volume 61

± ± Fig. 5. Canopy volume (mean sx–, n = 32) of P. califor- Fig. 6. Fruit production (mean sx–, n = 32) of P. californicum growing on A. greggii hosts with various levels of nicum growing on A. greggii hosts with various levels of infection in southern Nevada. Different letters at the tops infection in southern Nevada. Different letters at the tops of columns indicate significant differences at P ≤ 0.05. of columns indicate significant differences at P ≤ 0.05. production (Fig. 6) than their parasitic hosts soil temperatures. Although not investigated and parasites on hosts with fewer infections. in this study, active transpiration with soils of Severity of infestation was significantly neg- low available moisture during growing seasons atively (P ≤ 0.001; Table 2) correlated with (1) may result in substantial branch damage or host and parasite survival; (2) leaf, flower, and even mortality of A. greggii hosts that support fruit production of hosts; and (3) leaf and fruit abundant P. californicum individuals on their production of parasites and autoparasites. branches. Severely infested A. greggii hosts would be expected to exhibit greatest branch DISCUSSION damage or mortality compared to uninfested or lightly infested hosts in drought years. Mistle- Survival and development of parasitic and toe infestation greatly reduces host growth autoparasitic P. californicum and A. greggii hosts and the ability to survive drought and insect were compared during the severe drought of outbreak (Calder and Bernhardt 1983). How- 1995–1997 in southern Nevada. Phoradendron ever, uninfested A. greggii hosts appear to be californicum had adverse impacts on its A. fairly tolerant of extreme water and heat greggii hosts as well as on other P. californicum (drought) stress, and are more capable of grow- individuals. ing in periodically stressful desert environments Long-term climatically extreme conditions, than moderately or severely infested hosts. such as drought, tend to episodically lower Although comparative water relations were host, parasite, and autoparasite populations. not examined in this study, prolonged drought The drought in southern Nevada began in would result in widespread host-plant water February 1995 and reached its greatest inten- stress, which in turn could increase mortality sity during the first 6 months of 1997, followed of established parasitic and autoparasitic infec- by well above-average monsoonal rainfalls in tions. Phoradendron californicum, which is July and September (NOAA, Las Vegas). This characterized by low water-use efficiencies, prolonged drought was characterized by ex- must maintain more negative water potentials tremely low seasonal rainfall and high summer than its A. greggii hosts to obtain water (Jor- air temperatures. The well below-average sea- dan et al. 1997). Some P. californicum individ- sonal rainfall and above-average air tempera- uals are more vulnerable to water stress than tures during winter 1995–summer 1997 likely their hosts. Jordan et al. (1997) propose that resulted in low soil water content and high drought may have a greater detrimental effect 2001] SURVIVAL AND DEVELOPMENT DURING A DROUGHT 83

TABLE 2. Correlation (r-value) between parasite severity Relationships between severity of infestation and A. greggii survival (n = 76) and development (n = and host, parasite, and autoparasite survival, 100), and between parasite severity and P. californicum survival (n = 1017) and development (n = 32). Signifi- and between severity of infestation and host, cance levels: * ≤ 0.05; ** ≤ 0.01; *** ≤ 0.001; NS: non-sig- parasite, and autoparasite plant development, nificant. may have occurred in the absence of drought. Interaction r-value Perhaps these phenomena are normal patterns irrespective of drought stress. Host trees with Host survival × parasite severity –0.99*** Host leaflet pairs/leaf × parasite severity –0.94*** severe leafy mistletoe infestations are slowly Host canopy volume × parasite severity –0.93*** declining and will eventually die long before Host flower production × parasite severity –0.98*** similar trees without infestation. This decline Host fruit production × parasite severity –0.98*** will occur over many years if not several × Host seeds/pod parasite severity –0.98*** decades. Reductions in canopy volume of Parasite survival × parasite severity –0.96*** Parasite canopy volume × parasite severity –0.99*** A. greggii likely occurred long before the Parasite fruit production × parasite severity –0.98*** 1995–1997 drought. The severe drought in 1997 may have accentuated or accelerated detrimental effects of mistletoe infestation on A. greggii hosts. Severely infested hosts are on P. californicum than on its hosts because expected to be the first to die during periods some P. californicum individuals die although of drought. A. greggii trees are already under their host branches do not. Extremely low infestation stress, and additional drought stress host-plant water potentials appear to result in will weaken them enough that insects, includ- substantial mortality of established P. califor- ing bark beetles, can successfully attack and nicum infections and may limit long-term P. kill them. Under extreme conditions in south- californicum infection success under severe ern Nevada, A. greggii hosts supported abun- drought conditions in southeastern California dant P. californicum before P. californicum ex- (Jordan et al. 1997). The final cause of mortality perienced autoparasitic- and drought-induced in mistletoe-infested A. greggii during drought mortality that killed parasites, autoparasites, in southern California was bark beetle infesta- and their hosts. tion. Jordan et al. (1997) observed extensive insect damage on mistletoe-infested A. greggii. ACKNOWLEDGMENTS This could be the main cause of mortality under drought stress. David Valenzuela and Shevaun Valenzuela In this study Acacia greggii experiencing provided valuable field assistance. Steven Lei moderate to massive infestations had a signifi- assisted with statistical analyses. Dean Jordan cant reduction in canopy volume and flower provided stimulating discussions. Critical re- and fruit production. Large clumps of P. cali- views by David Charlet greatly improved this fornicum were visible on host branches and manuscript. The Department of Biology of the canopies. Within a single, heavily infested host, Community College of Southern Nevada live branches supported abundant parasites, (CCSN) provided logistical support. while dead branches revealed dead and dying parasites and autoparasites. Despite infrequent LITERATURE CITED host-parasite-autoparasite interactions, infec- ANALYTICAL SOFTWARE. 1994. Statistix 4.1, an interactive tion and reproduction of autoparasitic P. cali- statistical program for microcomputers. Analytical fornicum were successful as evidenced by Software, St. Paul, MN. 329 pp. abundant green canopy and fruit production, CALDER, M., AND P. B ERNHARDT, EDITORS. 1983. The biol- respectively, at the expense of parasitic and ogy of mistletoes. Academic Press, New York. nonparasitic hosts. Under extreme moisture EHLERINGER, J.R., AND E.D. SCHULTZ. 1985. Mineral concentrations in an autoparasitic Phoradendron califor- stresses, A. greggii hosts died, as did their par- nicum growing on a parasitic P. californicum and its asites and autoparasites. host, Cercidium floridum. American Journal of Botany A very limited number of autoparasitic P. 72:568–571. californicum can be found in Las Vegas valley EHLERINGER, J.R., C.S. COOK, AND L.L. TIESZEN. 1986. of southern Nevada. Host, parasite, and auto- Comparative water use and nitrogen relationships in a mistletoe and its host. Oecologia 68:279–284. parasite survival and development are a func- EHLERINGER, J.R., E.D. SCHULZE, H. ZIEGLER, O.L. LANGE, tion of parasite severity and drought stress. G.D. FARQUHAR, AND I.R. COWAN. 1985. Xylem 84 WESTERN NORTH AMERICAN NATURALIST [Volume 61

mistletoes: water or nutrient parasites? Science 227: LARSON, R.E., R.P. HOSTETLER, AND B.H. EDWARDS. 1994. 1479–1481. Calculus. 5th edition. D.C. Heath and Company, Lex- GLATZEL, G. 1983. Mineral nutrition and water relations ington, MA. 1256 pp. of hemiparasitic mistletoes: a question of partition- LEI, S.A. 2000. Age and size of Acacia and Cercidium in- ing experiments with Loranthus europaeus on Quer- fluencing the infection success of parasitic and auto- cus petraea and Quercus robur. Ecologia 56:193–201. parasitic Phoradendron. Southern California Academy HOLLAND, J.S., R.K. GRATER, AND D.H. HUNTZINGER. of Sciences 99:45–54. 1977. Flowering plants of the Lake Mead region. LEONARD, O.A., AND R.J. HULL. 1965. Translocation rela- Southwest Parks and Monuments Association, Popu- tionships in and between mistletoes and their hosts. lar Series 23. 49 pp. Hilgardia 37:115–153. HOLLINGER, D.Y. 1983. Photosynthesis and water rela- RAVEN, J.A. 1983. Phytophages of xylem and phloem: a tions of the mistletoe, Phoradendron villosum, and comparison of animal and plant sap-feeders. Advanced its host, the California valley oak, Quercus lobata. Ecological Research 13:136–234. Oecologia 60:396–400. SCHULZE, E.D., AND J.R. EHLERINGER. 1984. The effect of JORDAN, L.A., D.N. JORDAN, F.L. LANDAU, AND S.D. SMITH. nitrogen supply on growth and water-use efficiency 1997. Parasitism of two codominant desert plant of xylem-tapping mistletoes. Planta 162: 268–275. hosts: low host-plant water potentials may limit long- SCHULZE, E.D., N.C. TURNER, AND G. GLATZEL. 1984. Car- term infection success. Abstract of the 1997 Ecologi- bon, water and nutrient relations of two mistletoes cal Society of America Annual Meeting, Albuquerque, and their hosts: a hypothesis. Plant, Cell and Envi- NM. 336 pp. ronment 7:293–299. KNUTE, A., AND C. FABER. 1991. Plants of the East Mojave. Wide Horizon Press, Cima, CA. Received 8 February 1999 KUIJT, J. 1969. The biology of parasitic flowering plants. Accepted 30 January 2000 University of California Press, Berkeley. 246 p. Western North American Naturalist 61(1), © 2001, pp. 85–92

SEED BANKS OF BROMUS TECTORUM–DOMINATED COMMUNITIES IN THE GREAT BASIN

L. David Humphrey1 and Eugene W. Schupp1

ABSTRACT.—Many shrub-steppe communities of the Great Basin have been converted to Bromus tectorum–dominated communities. Seed production and seed bank traits of native perennials may be poorly suited to conditions of communities dominated by this introduced annual, and native perennials may be lost from the seed banks. Seed banks of former shrub-steppe communities now dominated by annuals were quantified on 3 sites in western Utah to determine if seeds of native perennials were present and to track changes in Bromus tectorum seed densities and species composition of seed banks after fire. Burned and unburned plots on 1 site were sampled for 3 years after a wildfire. Plots consisted of grids of 5.2-cm-diameter soil cores. Seeds were quantified by monitoring seedling emergence from these cores over an extended period of time in the greenhouse. On unburned plots introduced annuals, mainly Bromus tectorum, constituted >99% of the seed bank, with Bromus densities of 4800–12,800 seeds m–2. Immediately after the fire, Bromus seed density was <3% of unburned plots, but its seed bank density recovered in 2 years. The major change in species composition of the seed bank following fire was a shift in proportional abundance between Bromus and 2 other introduced annuals immediately after the fire. One native annual and a native annual/perennial (Oenothera pallida) increased in the seed bank the 1st year after the fire. Of all samples, only 4 perennial-plant seeds representing 3 species (excluding Oenothera) were found, for a total perennial-plant seed bank of 2–3 seeds m–2. Lack of perennial-plant seeds in annual-dominated communities impairs the reestablishment of native perennials. Because perennial-plant seeds are so few, the reduction of Bromus seed banks by fire provides no opportunity for reestablishment of native species.

Key words: seed bank, Bromus tectorum, Great Basin, shrub-steppe, seed dormancy, annuals, perennials.

Unlike warm-desert plant communities, which seeds persist in the habitat in a viable native Great Basin shrub-steppe plant com- condition for longer than 1 year, or a transient munities usually have a low diversity of annu- seed bank in which none of the seeds persist als (Kemp 1989). Perennial-plant seeds are a in the habitat in a viable condition for more greater component of the seed bank, and total than 1 year (Thompson and Grime 1979). Seed seed densities are lower overall than in warm longevity is generally less important to persis- deserts (e.g., Hassan and West 1986). When tence of the species on the site for perennials annuals are a major component of plant com- than for annuals in deserts (Noy-Meir 1973, munities in the Great Basin, they are usually Kemp 1989) and in grasslands (Major and Pyott spring-growing introduced Eurasian species. 1966, Rice 1989). Consistent with this, some These invaded Great Basin plant communities important native shrubs and perennial grasses have seed bank characteristics more like those of semiarid Great Basin communities (Artem- of warm deserts, with annual-plant seeds as a isia tridentata, Young and Evans 1989; Chryso- major component of the seed bank, greater thamnus nauseosus, Meyer and McArthur 1987; overall seed densities, and greater temporal Leymus cinereus, Meyer et al. 1995; and variability of the seed bank (Kemp 1989). Pseudoroegneria spicata, Kitchen and Monsen Currently, otherwise similar semiarid Great 1994, Humphrey and Schupp 2001) form no Basin sites can support either communities persistent seed bank. However, others (Achna- dominated by native shrubs and bunchgrasses therum hymenoides, Jones 1990; Sporobolus or communities dominated by the introduced cryptandrus, Lippert and Hopkins 1950; most annual grass Bromus tectorum (Young and species of Stipa, Young 1988; Atriplex canescens, Evans 1973, Pellant 1990). The seed bank of a Meyer et al. 1987; and A. confertifolia, Meyer et site is the storage of viable seeds in litter or al. 1998) do form persistent seed banks. Species soil. Individual species can be characterized with transient seed banks can be completely as producing either a persistent seed bank in extirpated from local areas if disturbances

1Department of Rangeland Resources and the Ecology Center, Utah State University, Logan, UT 84322-5230.

85 86 WESTERN NORTH AMERICAN NATURALIST [Volume 61 remove seed-bearing individuals (O’Connor bank. We asked the following questions: (1) Are 1991). Native perennials have been greatly seed banks of native perennials present in these depleted on sites in the Great Basin now dom- annual-dominated communities? (2) How much inated by Bromus tectorum (hereafter referred are Bromus seed numbers reduced by fire, to as Bromus) through a combination of past and how quickly do they recover? (3) What overgrazing and wildfires. Wildfires occur changes in species composition of the seed much more frequently in Bromus-dominated bank occur after fire? Our main experiment communities than in native shrub-steppe com- followed seed bank dynamics on burned and munities (Whisenant 1990). Some perennials unburned plots for 3 years after a wildfire. We that resprout after fire may remain in annual- augmented information from this experiment dominated communities. However, because with seed bank data for 1 year from 2 other Bromus dries and is prone to burn before nearby sites. these perennials set seed, fires frequently prevent them from producing seeds. Although METHODS some native perennial species appear to have effective seed dispersal mechanisms, dispersal All 3 sites are at the U.S. Army Dugway onto sites where the species do not occur is Proving Ground, Tooele County, Utah, USA. apparently very limited (Marlette and Ander- The Long-Term site, where seed banks avail- son 1986). With seed input thus curtailed, able for the 1996, 1997, and 1998 growing sea- perennial-plant seeds may become very rare in sons were described, is in a nearly level area below the southeastern foothills of the Cedar annual-dominated communities, contributing Mountains at 1480 m elevation (40°14′30″N, to the inability of native perennials to reestab- 112°50′10″W). The other 2 sites, where seed lish (West 1983). This would be true especially banks available for growth only in 1996 were of species with only a transient seed bank. sampled, are a nearly level site 0.5 km from Although most Bromus seeds are destroyed the Long-Term site and at the same elevation, by wildfires, high seed production from the and a gently sloping higher-elevation site (1620 proportion that remains can quickly replenish m) at the southeastern end of the Cedar Moun- the seed bank (Young and Evans 1978, Hassan tains about 5 km northeast of the Long-Term and West 1986). Most seeds of Bromus germi- site (40°16′00″N, 112°49′40″W). All 3 sites nate soon after they are released (autumn– have deep (>1 m) sand to loamy fine sand soils spring after release in summer), but often some (Humphrey and Schupp 1999). Mean annual are exposed to environmental conditions that precipitation for the nearest weather station, cause them to become physiologically dormant about 8 km southwest of the Long-Term site in (induced dormancy; Young and Evans 1975, an open flat, is 20 cm (U.S. Army Dugway Kelrick 1991, Pyke and Novak 1994). Seeds Proving Ground, Meteorological Operations with no dormancy mechanisms can also remain Office), but our sites are in a topographic posi- viable in the soil for more than 1 year if they tion that is likely to receive more precipitation do not encounter conditions that allow germi- than this. During the study all 3 sites were nation (Young et al. 1969). Thus, Bromus can dominated by Bromus with 2 other introduced persist in the seed bank through years when annual species common, Sisymbrium altissimum seed input is lacking. and Salsola iberica. Native perennial species Seed banks of sagebrush-steppe communi- were almost completely absent from the sites, ties (Goodall et al. 1972, Parmenter and but a few were present 100–200 m away. MacMahon 1983, Hassan and West 1986) and Native vegetation was probably transitional transitional annual-perennial communities between sagebrush-steppe and salt-desert shrub (Young and Evans 1975) have been described, communities. Major native species remaining but seed banks of Great Basin communities on surrounding areas with similar soils and dominated by introduced annuals have not topography were Artemisia tridentata, Sarco- been described. We quantified soil seed banks batus vermiculatus, Atriplex canescens, Ephedra of 3 Bromus-dominated communities in west- nevadensis, Achnatherum hymenoides, Stipa ern Utah. Sampling was timed to include all comata, and Pleuraphis jamesii. the transient seed bank (produced in summer At the Long-Term site, burned and unburned and autumn), as well as any persistent seed plots were paired about 20 m apart on opposite 2001] BROMUS TECTORUM–DOMINATED SEED BANKS 87 sides of a dirt road that stopped a wildfire in of estimates and likelihood of encountering rare late summer 1995. There were 2 replicates of species. As a grid of core samples, each plot these burned-unburned pairs. The seed bank was intended to give a representation of the on burned and unburned plots was sampled seed bank for that treatment that takes into (1) after the wildfire and before any plant account heterogeneity of the seed bank. Our ex- growth, (2) after the 1st growing season fol- perimental design was not, however, intended lowing the fire, and (3) after the 2nd growing to quantify within-plot heterogeneity. season following the fire (March 1996, March Similarly, timing of sampling was not in- 1997, and February 1998, respectively). At the tended to address seasonal variation in the higher-elevation site, termed the Hill site, 2 seed bank. Instead, we took soil core samples replicate burned and unburned plots were once each year in winter (mid-March 1996, all located on opposite sides of the border where sites; 8 March 1997 and 19 February 1998, firefighters had extinguished a wildfire in July Long-Term site) to quantify the total yearly 1994. After 1 growing season all plots on this seed bank, which consisted of seeds produced site were burned by another wildfire (the late- in summer through autumn plus any persistent summer 1995 fire that burned the Long-Term seed bank. Taking samples at this time also site). Thus, for the March 1996 sampling time, allowed cold-stratification of seeds to occur in the 2 treatments represented the seed bank (1) the field. Seeds were quantified by monitoring immediately after 1 fire, and (2) immediately emergence in the greenhouse. Quantifying after the 2nd of 2 fires that occurred in con- germination after cold-stratification has been secutive years. The site near the Long-Term described as a preferred method for identify- site, referred to as the Near-Dune site, was ing species present in seed banks (Gross 1979). only lightly burned by the 1995 fire, with Bro- However, species with dormancy that is difficult mus stubble and seeds on the soil surface to break may be underestimated. After identify- remaining. On this site only 2 plots, consid- ing and counting field-emerged seedlings, we ered to be 2 replicates of a single burn condi- spread each soil core, along with its associated tion, were sampled. surface litter, over a base of sand in a 14-cm- On each site a plot consisted of a grid of diameter pot with the soil core sample form- 5.2-cm-diameter (21.2 cm2 surface area) soil ing a layer about 1 cm thick. Pots were placed cores taken to a depth of 4 cm with a steel in a heated greenhouse and watered as needed cylinder. On the Long-Term site in 1996, plots (every 2–4 days). Seedlings emerging through consisted of 30 core samples in a 6 × 5 grid with 2.5-m spacings between samples. Because spring were identified and counted. In addi- it was apparent from the 1996 data that seeds tion, we left the pots dry during summer and of perennial species were extremely rare, we monitored emergence again through autumn increased numbers of core samples to 40 per to identify previously dormant autumn-germi- plot in an 8 × 5 grid with 2 × 2.5-m spacing nating seeds. For the samples from all 3 sites between samples in 1997 and 1998 to increase in 1996, greenhouse emergence was censused the likelihood of finding perennial-plant seeds. on 9 April, 8 June, and 22 December 1996. (About 36 cores per plot were used in 1997 For the 2nd- and 3rd-year samples from the because some were later damaged.) At the Hill Long-Term site, emergence was censused on site each plot consisted of 25 cores taken in a 5 10–11 May, 20 June, and 10 December 1997; × 5 grid with 6-m spacing between samples. and 13 April, 5 May, and 19 December 1998. At the Near-Dune site, 24 cores per plot were The quantified soil seed bank consisted of all collected in a 6 × 4 grid with 6 × 3-m spacing seedlings that either existed in the core sam- between samples. We designed the areas occu- ples at the time they were taken or emerged pied by the grids of samples on these 2 sites to in the greenhouse. Seed density per plot for characterize the seed banks of plots used in a each species was the total number of seeds of revegetation experiment, and thus they were that species in all cores of the plot divided by larger than plots at the Long-Term site. These the total area of all cores of the plot. Inasmuch differences in plot sizes should not affect the as number of cores per plot differed between estimates of seed banks. However, greater num- years and sites, we standardized density esti- bers of core samples could increase precision mates to seeds m–2. 88 WESTERN NORTH AMERICAN NATURALIST [Volume 61

RESULTS Oenothera pallida) had a density of 1.9 seeds m–2 and made up 0.02% of the seed bank, or As expected, Bromus strongly dominated about 1 seed in 5000. The burned plots might the seed bank on all plots. Although much less be considered less likely to contain perennial- abundant than seeds of Bromus, seeds of 2 plant seeds because part of the seed bank was other annuals, Sisymbrium altissimum and Sal- destroyed by fire. However, of the few peren- sola iberica, greatly outnumbered seeds of any nial-plant seeds that occurred, more were on other species overall (Tables 1, 2). Only on the burned plots. With all burned and unburned burned plots of the Long-Term site after the plots included (564 cores), perennial-plant seed 1st growing season following the fire (1997 density was 3.3 seeds m–2, or 0.05% of the sampling) was the abundance of any native seed bank. species in the seed bank greater than 10 seeds After the 1995 fire, abundance of Bromus –2 m (Table 1). These species were an annual, seeds on burned plots of the Long-Term site Mentzelia albicaulis, and an annual to short- was <3% of that found on unburned plots lived perennial, Oenothera pallida. Although (Fig. 1). Abundance of Bromus seeds on the not previously observed on the plots, these 2 plots of the Hill site that were burned only in species formed a substantial part of the vege- 1995 was similar to that of burned plots of the tation in the 1st growing season following the Long-Term site after the fire, while Hill site fire on burned plots of the Long-Term site. It plots that were burned in both 1994 and 1995 was apparently seeds from these plants that had Bromus seed densities that were lower appeared in the 1997 seed bank. Despite the than on the once-burned plots (Table 2). On increased availability of seeds for 1997, these the lightly burned Near-Dune site, densities species were not prominent in 1997 vegeta- of Bromus seeds were much higher than on tion and their seeds were not found in the 1998 seed bank (Table 1). Except for these 2 the Hill site (Table 2), but considerably lower species in 1997, species other than the 3 major than on unburned plots of the Long-Term site species comprised ≥1% of the seed bank only in the same year. on burned plots immediately after fire where Seed banks were quantified for more than 1 Bromus seed densities were greatly reduced year following fire only on the Long-Term site. (burned plots of the Long Term site in 1996, Except for the 1-year pulse of Mentzelia and Table 1; and the Hill site, Table 2). Other Oenothera on burned plots after the 1st grow- species found in the seed bank were another ing season (Table 1), all species except the 3 native annual found on the Hill site (Table 2), dominant annuals occurred only occasionally 4 other introduced annual species, and 3 native in the seed banks and played no role in seed perennial shrub-steppe species (Tables 1, 2). bank dynamics. As with Bromus, seed banks of Each of these perennials was found only once the other 2 major annuals were reduced by or twice throughout all the samples. fire, but less drastically (Table 1). Thus, Bromus Seeds of these perennial species are obvi- made up a smaller proportion of the seed bank ously rare, but the 24–40 core samples per on the burned plots in 1996 (Table 1). From plot give a rather crude estimate of seed abun- very low numbers after the fire, the Bromus dance of species that occur extremely rarely. seed bank increased to almost 5000 seeds m–2 (One seed occurring throughout 30 cores after just a single growing season, and increased amounts to 15 seeds m–2, and the presence or further in the 2nd year (Fig. 1). Densities of absence of a species on a plot may be partly Bromus seeds on unburned plots were >12,000 due to chance.) A more accurate estimate of m–2 in 1996 and 1997 but, for reasons that are the abundance of these perennial-plant seeds unclear, declined greatly in 1998 to levels lower involves total number of cores taken across than those of the burned plots in that year sites and years. The samples from unburned (Fig. 1). Seed banks of the other 2 abundant plots of the Long-Term site for each of the 3 annuals also increased on the burned plots years and from the lightly burned Near-Dune through the first 2 growing seasons following site can be combined to represent seed banks the fire, but more modestly (Fig. 1). After 2 of recently unburned Bromus-dominated sites. growing seasons, the proportional composition Based on this larger data set (254 core sam- of the seed bank was similar on burned and ples), native perennials as a group (excluding unburned plots (Table 1). 2001] BROMUS TECTORUM–DOMINATED SEED BANKS 89 6 (0.1) d plots and on burned in late summer nuals, native annuals, and perennials. Unknown 7 (0.1) 90 (1.3) 27 (0.4) 24 (0.2) 103 (1.5) ______, is presented. The percent of the seed bank occupied by each species –2 8 (1.3) 8 (1.7) 1996 1997 1998 8 (0.1) Unburned Burned Unburned Burned Unburned Burned 854244 (5.9) (1.8) 130 38 (23.1) (6.9) 496 129 (3.7) (1.0) 598 256 (10.7) (4.5) 932 (11.0) 387 (4.8) 1197 (11.3) 749 (7.0) 12,817 (92.3) 333 (65.7) 12,806 (95.3) 4874 (81.5) 6755 (84.1) 8650 (81.4) ______?) 8 (1.3) b a . C. viscidiflorus. sp species was not identified. was 1. Occurrence of the 3 major species and of species infrequently represented in the seed bank for the Long-Term site on unburne 1. Occurrence of the 3 major species and infrequently represented in seed bank for Long-Term Amaranthus ABLE T Bromus tectorum Lactuca serriola Mentzelia albicaulis Oenothera pallida Sporobolus cryptandrus Chrysothamnus Sisymbrium altissimum Salsola iberica Cirsium (Cincus Amaranthus AJOR SPECIES ATIVE ANNUALS ATIVE PERENNIALS THER ALIEN ANNUALS NKNOWN Chrysothamnus The 1995. Seed banks in the years 1996, 1997, and 1998 are presented. Three groups of infrequent species listed: other alien an each species, mean number of seeds per plot, standardized to m species are also listed. For listed in parentheses. M N a b O U Species represented ______in the seed bank No. Percent No. Percent No. Percent No. Percent No. Percent No. Percent N 90 WESTERN NORTH AMERICAN NATURALIST [Volume 61

TABLE 2. Occurrence of the 3 major species and of species infrequently represented in the seed bank for the Hill site and the Near-Dune site for 1996 only. On the Hill site burn treatments were burned once or twice, as indicated. Three groups of infrequent species are listed: other alien annuals, native annuals, and native perennials. For each species, mean number of seeds per plot, standardized to number of seeds m–2, is presented. The percent of the seed bank occupied by each species is listed in parentheses.

______Hill site ______Near-Dune site Species represented ______Burned 1995 ______Burned 1994, 1995 Lightly______burned 1995 in the seed bank No. Percent No. Percent No. Percent

MAJOR SPECIES Bromus tectorum 289 (71.0) 132 (54.2) 4827 (97.1) Sisymbrium altissimum 81 (20.7) 95 (38.1) 79 (1.5) Salsola iberica 0 (0) 0 (0) 59 (1.2) OTHER ALIEN ANNUALS Lactuca serriola 10 (3.6) Erodium cicutarium 21 (5.6) NATIVE ANNUAL Gilia spp.a 10 (2.8) NATIVE PERENNIALS Sporobolus cryptandrus 1 (0.2) Sphaeralcea munroana 9 (4.2) aThe Gilia species was either G. leptomeria or G. inconspicua.

DISCUSSION (Meyer and McArthur 1987) but has wind-dispersed achenes, so the seed found apparently This study indicates that an extremely sparse entered the plot from plants near the site. perennial-plant seed bank occurs in Bromus- Germination trials were less likely to underes- dominated communities. Individual perennial timate densities of nondormant seeds such as species often have seed banks of only 1–5 those of Chrysothamnus. The virtual absence seeds m–2 in perennial-dominated shrub-steppe of these formerly dominant species from the communities (Hassan and West 1986), although seed bank is a major obstacle to their reestab- seed banks of some perennial species may be lishment. Similarly, reestablishment of late- considerably larger at some times of year (e.g., successional grasses of savannahs of the Chrysothamnus viscidiflorus in autumn; Young Edwards Plateau of Texas was impaired by and Evans 1975). However, the total perennial- absence of these species from the seed bank plant seed bank in our experiment, 2–3 seeds (Kinucan and Smeins 1992). m–2 with only 3 species represented, contrasts Except on plots where fire had recently with the perennial-plant seed bank of an un- consumed most seeds, densities of Bromus burned shrub-steppe community described by seeds were similar to or higher than those Hassan and West (1986): 25–27 seeds m–2 rep- reported by others (5900 m–2, Stewart and resenting 8–13 perennial species. Two of the 4 Hull 1949; 2400–8300 m–2, Young and Evans perennial plant seeds we identified were of the 1975; 10,000–15,000 m–2, Young and Evans grass Sporobolus cryptandrus, which is known 1985). Hassan and West (1986) reported a 3.5- to form a persistent seed bank (Lippert and fold increase in the Bromus seed bank after 1 Hopkins 1950) that would allow it to remain growing season following a fire. The increase longer in the seed bank of Bromus-dominated in Bromus seed bank after fire in this study communities after Sporobolus plants were gone. was even greater. The amount of the Bromus A 2nd perennial in the seed bank, Sphaeralcea seed bank destroyed by fire varies depending munroana, probably also forms a persistent on the intensity of the fire. The fire on the seed bank (see Roth et al. 1987). Since some Long-Term site consumed almost all litter on seeds of such species could have remained the plots, and the Bromus seed bank that dormant through our germination trials, den- remained was <3% that of unburned plots. Yet, sity of this persistent seed bank could be higher even after this great reduction, the Bromus than the extremely low levels indicated by our seed bank recovered to high levels after only 1 data. The 3rd perennial, Chrysothamnus vis- growing season. Young and Evans (1985) re- cidiflorus, forms no persistent seed bank ported that Bromus can recover to high densities 2001] BROMUS TECTORUM–DOMINATED SEED BANKS 91

perennials that form a persistent seed bank remained in the Bromus-dominated communities, and dispersal of perennial-plant seeds onto the site appeared extremely rare. Despite the reduction in abundance of Bromus seeds after fire, seeds of perennials were so few that seeds of Bromus and other introduced annuals still outnumbered seeds of perennial plants by orders of magnitude, and no opportunities for changes in species composition to perennial plants were created.

ACKNOWLEDGMENTS

We thank J. Martin and the Conservation and Preservation Division of the Environmen- tal Program Office, U.S. Army Dugway Proving Grounds, for their cooperation. This research was supported by the U.S. Department of Fig. 1. Number of seeds m–2 (means of the 2 plots and Defense Legacy Resource Management Pro- standard errors) of each of the 3 major species, Bromus gram (Project No. 94-0095), Utah Agricultural tectorum, Sisymbrium altissimum, and Salsola iberica, on Experiment Station (UAES), and Ecology Cen- plots burned (B) and unburned (UB) in 1995 on the Long- Term site in each of the 3 years of the experiment. Filled ter, Utah State University, Logan UT. The symbols represent burned plots; open symbols represent National Research Initiative Competitive Grants unburned plots. Program/U.S. Department of Agriculture (Award No. 97-35315-4926) supported data analysis and manuscript preparation. Approved as UAES within 3 years following fire. On the Long-Term journal paper 7149. site Bromus seed banks recovered to essen- tially pre-burn levels in the same amount of LITERATURE CITED time. GOODALL, D.W., S. CHILDS, AND H.H. WIEBE. 1972. Although fire reduced abundance of Bro- Methodological and validation study of seed reserves mus seeds for 1 year, Bromus never lost domi- in desert soils. US/IBP Desert Biome Research nance of the seed bank. Its dominance was Memorandum 72–78. Utah State University, Logan. somewhat decreased immediately after the GROSS, K.L. 1990. A comparison of methods for estimat- ing seed numbers in the soil. Journal of Ecology fire, with seeds of Sisymbrium and Salsola 78:1079–1093. becoming proportionally more abundant, but HASSAN, M.A., AND N.E. WEST. 1986. Dynamics of soil Bromus quickly returned to its previous level seed pools in burned and unburned sagebrush semi- of dominance. The fire and resulting reduction deserts. Ecology 67:269–272. HENDERSON, C.B., K.E. PETERSEN, AND R.A. REDAK. in abundance of Bromus seeds on the Long- 1988. Spatial and temporal patterns in the seed bank Term site appeared to provide some opportu- and vegetation of a desert grassland community. nity for 2 native species, Mentzelia (annual) Journal of Ecology 76:717–728. and Oenothera (annual to short-lived peren- HUMPHREY, L.D., AND E.W. SCHUPP. 1999. Temporal patterns of seedling emergence and early survival of nial), to establish, but they were only transitory Great Basin perennial plant species. Great Basin as a substantial component of the seed bank. Naturalist 59:35–49. Mentzelia apparently can form a persistent seed ______. 2001. Seedling survival from locally and commer- bank (Henderson et al. 1988). A small persis- cially obtained seeds on two semiarid sites. Restora- tent seed bank of these species may have been tion Ecology: In press. JONES, T.A. 1990. A viewpoint on Indian ricegrass research: present at the time of the fire, although none its present status and future prospects. Journal of was detected in the 1996 samples. Range Management 43:416–420. There were too few perennial-plant seeds KELRICK, M.I. 1991. Factors affecting seeds in a sage- to determine differences in their abundances brush-steppe ecosystem and implications for the dispersion of an annual plant species, cheatgrass (Bro- between burn treatments or years. Apparently, mus tectorum L.). Unpublished doctoral dissertation, only very small numbers of seeds of native Utah State University, Logan. 92 WESTERN NORTH AMERICAN NATURALIST [Volume 61

KEMP, P.R. 1989. Seed banks and vegetation processes in and S.G. Kitchen, editors, Proceedings—Ecology deserts. Pages 257–282 in M.A. Leck, V.T. Parker, and Management of Annual Rangelands. USDA Gen- and R.L. Simpson, editors, Ecology of soil seed banks. eral Technical Report INT-GTR-313, Ogden, UT. Academic Press, New York. RICE, K.J. 1989. Impacts of seed banks on grassland com- KINUCAN, R.J., AND F.E. SMEINS. 1992. Soil seed bank of a munity structure and population dynamics. Pages semiarid Texas grassland under three long-term (36 211–230 in M.A. Leck, V.T. Parker, and R.L. Simp- years) grazing regimes. American Midland Natural- son, editors, Ecology of soil seed banks. Academic ist 128:11–21. Press, San Diego, CA. KITCHEN, S.G., AND S.B. MONSEN. 1994. Germination rate ROTH, T.E., J.L. HOLECHEK, AND M.Y. HUSSAIN. 1987. and emergence success in bluebunch wheatgrass. Germination response of three globemallow species Journal of Range Management 47:145–150. to chemical treatment. Journal of Range Manage- LIPPERT, R.D, AND H.H. HOPKINS. 1950. Study of viable ment 40: 173–175. seeds in various habitats in mixed prairies. Transac- STEWART, G., AND A.C. HULL. 1949. Cheatgrass (Bromus tions of Kansas Academy of Science 53:355–364. tectorum L.)—an ecological intruder in southern MAJOR, J., AND W. T. P YOTT. 1966. Buried, viable seeds in Idaho. Ecology 30:58–74. two California bunchgrass sites and their bearing on THOMPSON, K., AND J.P. GRIME. 1979. Seasonal variation in the definition of flora. Vegetatio 13:253–282. the seed banks of herbaceous species in ten contrast- MARLETTE, G.M., AND J.E. ANDERSON. 1986. Seed banks ing habitats. Journal of Ecology 67:893–921. and propagule dispersal in crested wheatgrass WEST, N.E. 1983. Great Basin–Colorado Plateau sagebrush stands. Journal of Applied Ecology 23:161–175. semi-deserts. Pages 331–369 in N.E. West, editor, MEYER, S.E., AND E.D. MCARTHUR. 1987. Studies on the Temperate deserts and semi-deserts. Volume 5 in seed germination biology of rubber rabbitbrush. Ecosystems of the world. Elsevier, Amsterdam, Pages 19–25 in K.L. Johnson, editor, Proceedings of Netherlands. the Fourth Utah Shrub Ecology Workshop. Utah WHISENANT, S.G. 1990. Changing fire frequencies on State University, Logan. Idaho’s Snake River plains: ecological and manage- MEYER, S.E., J. BECKSTEAD, P.S. ALLEN, AND H. PULLMAN. ment considerations. Pages 4–10 in E.D. McArthur, 1995. Germination ecophysiology of Lemus cinereus E.M. Romney, S.D. Smith, and P.T. Tueller, editors, (Poaceae). International Journal of Plant Science Proceedings—Symposium on Cheatgrass Invasion, 156:206–215. Shrub Die-off, and Other Aspects of Shrub Biology MEYER, S.E., S.L. CARLSON, AND S.C. GARVIN. 1998. Seed and Management. USDA General Technical Report germination regulation and field seed bank carry- INT-276, Ogden, UT. over in shadscale (Atriplex confertifolia: Chenopodi- YOUNG, J.A. 1988. Seedbeds as selective factors in the aceae). Journal of Arid Environments 38: 255–267. species composition of rangeland communities. Pages MEYER, S.E., E.D. MCARTHUR, AND S.B. MONSEN. 1987. 171–188 in P.T. Tueller, editor, Vegetation science Intraspecific variation in germination patterns of applications for rangeland analysis and management. rangeland shrubs and its relationship to seeding suc- Kluwer Academic Publishers, Dordrecht, Nether- cess. Pages 82–92 in G.W. Frasier and R.A. Evans, lands. editors, Proceedings—Symposium on Seed and Seed- YOUNG, J.A., AND R.A. EVANS. 1973. Downey brome— bed Ecology of Rangeland Plants. USDA-ARS, Wash- intruder in the plant succession of big sagebrush ington, DC. communities in the Great Basin. Journal of Range NOY-MEIR, I. 1973. Desert ecosystems: environment and Management 26:410–415. producers. Annual Review of Ecology and Systemat- ______. 1975. Germinability of seed reserves in a big ics 4:25–51. sagebrush community. Weed Science 23:358–364. O’CONNOR, T.G. 1991. Local extinction in perennial grass- ______. 1978. Population dynamics after wildfires in sage- lands: a life-history approach. American Naturalist brush grasslands. Journal of Range Management 31: 137:753–773. 283–289. PARMENTER, R.R., AND J.A. MACMAHON. 1983. Factors de- ______. 1985. Demography of Bromus tectorum in Arte- termining the abundance and distribution of rodents misia communities. Pages 489–502 in J. White, editor, in a shrub-steppe ecosystem: the role of shrubs. The population structure of vegetation. Dr. W. Junk Oecologia 59:145–156. Publishers, Dordrecht, Netherlands. PELLANT, M. 1990. The cheatgrass-wildfire cycle—are ______. 1989. Dispersal and germination of big sagebrush there any solutions? Pages 11–18 in E.D. McArthur, (Artemisia tridentata) seeds. Weed Science 37: E.M. Romney, S.D. Smith, and P.T. Tueller, editors, 201–206. Proceedings—Symposium on Cheatgrass Invasion, YOUNG, J.A., R.A. EVANS, AND R.E. ECKERT. 1969. Popula- Shrub Die-off, and Other Aspects of Shrub Biology tion dynamics of downey brome. Weed Science 17: and Management. USDA General Technical Report 20–26. INT-276, Ogden, UT. PYKE, D.A., AND S.J. NOVAK. 1994. Cheatgrass demogra- Received 10 March 1999 phy—establishment attributes, recruitment, ecotypes, Accepted 29 December 1999 and genetic variability. Pages 12–21 in S.B. Monsen Western North American Naturalist 61(1), © 2001, pp. 93–102

NITROGEN ACQUISITION FROM DIFFERENT SPATIAL DISTRIBUTIONS BY SIX GREAT BASIN PLANT SPECIES

Sara E. Duke1 and Martyn M. Caldwell1,2

ABSTRACT.—Plants of different growth form may utilize soil nutrients in various spatial distributions through different scales of foraging. In this study we evaluated the ability of 6 species commonly found in the Great Basin to utilize nitrogen (N) distributed in different patterns. Three growth forms were represented by these 6 species. We applied 15N-labeled nitrogen in concentrated patches and over broader uniform areas (at approximately 1% the concentration of the patches) in large, outdoor sand-culture plots. Six weeks after N was applied, 2 plants adjacent to the patch (Patch Treatment) and 2 plants within the uniform application (Uniform Treatment) were harvested. One plant 35–45 cm from both applications (Distant Treatment) was also harvested. The proportion of application-derived N in the leaf N pool was calculated and the mass of N this represented was estimated. Winter annual species Aegilops cylindrica and Bromus tectorum utilized the concentrated patches to a greater extent than did perennial species. The mass of N acquired by Patch-Treatment annual plants was significantly greater than by Uniform- and Distant-Treatment plants. Annual plants in the Distant Treatment had very little application-derived N in their leaf tissue. The perennial tussock grasses Agropyron desertorum and Pseudoroegneria spicata differed in utilization of the N applications. Agropyron acquired a greater quantity of N from patches than from uniform applications, and Dis- tant-Treatment plants acquired very little from treatment applications. On the other hand, Pseudoroegneria utilized N in the 3 treatments equally. The shrub species Artemisia tridentata ssp. vaseyana and Chrysothamnus nauseosus also differed in their pattern of N acquisition. There were no differences in quantity of N acquired by plants from different treatments for Chrysothamnus; all treatment plants acquired appreciable amounts of N from the applications. In contrast, Artemisia tridentata was very effective at acquiring large quantities of N from patches relative to Uniform- and Distant-Treatment plants, and yet there was still appreciable acquisition of applied N by Distant-Treatment Artemisia plants. We compared our results for these species in utilizing N patches with their ability to utilize N pulses (Bilbrough and Caldwell 1997). The annual grasses, Artemisia, and Agropyron were capable of effectively acquiring N from both pulses and patches, whereas Pseudoroegneria was effective in exploiting pulses but not patches. Chrysothamnus was generally not responsive to either patches or pulses. Our results suggest that the 2 shrubs and 2 perennial grasses differed in the scale at which they foraged for nutrients. Some species exhibited a coarse-scale utilization of nutrients while others were clearly capable of fine-scale utilization of spatially distributed nutrient sources. This suggests the potential for at least some spatial niche separation among these species.

Key words: spatial heterogeneity, soil nitrogen distribution, sagebrush steppe, Great Basin, Aegilops cylindrica, Agropyron desertorum, Artemisia tridentata, Bromus tectorum, Chrysothamnus nauseosus, Pseudoroegneria spicata.

Supplies of soil resources to plants are Campbell et al. 1991). Utilization of a nutrient- characterized by spatial heterogeneity and enriched soil patch is commonly associated with temporal variation in many natural environ- the ability of a plant to elevate root physiologi- ments (Grime 1994). Plant characteristics that cal uptake capacity and proliferate roots in allow plants to acquire resources from spa- these local zones (Drew and Saker 1975, Jack- tially or temporally variable nutrient supplies son and Caldwell 1989). Plant communities can differ among species and likely depend on composed of species that vary in growth form the evolutionary history of the species (Grime and size have been postulated to exhibit dif- 1977, Chapin 1980, 1988, Aarssen 1983, Tilman ferent strategies for acquiring nutrients when 1986). Rapid acquisition of nutrients from resources are not uniform in space or time pulses requires the presence of an active root (Campbell and Grime 1989, Grime 1994). system to take up nutrients when they first Coexisting species that potentially compete for become available (Campbell and Grime 1989, the same resources are thought to segregate

1Department of Rangeland Resources and the Ecology Center, Utah State University, Logan, Utah 84322-5230. 2Corresponding author.

93 94 WESTERN NORTH AMERICAN NATURALIST [Volume 61 resource use both spatially and temporally geneity (Charley and West 1977, Crawford and (Aarssen 1983, Veresoglou and Fitter 1984, Gosz 1982, Jackson and Caldwell 1993, Halvor- Fitter 1986, McKane et al. 1990). son et al. 1995, Schlesinger et al. 1996). Spa- Sagebrush-steppe communities of the semi- tially variable nutrient distribution occurs due arid Intermountain West receive moisture pri- to redistribution of resources by perennial marily from late fall through spring. Summers species (Charley and West 1977, Hook et al. are warm and dry. Plant nutrient availability 1991), animal defecation, urination, and death, corresponds with soil moisture in fall and spring as well as microbial activity (Stark 1994). Root and is greatly reduced in summer months as proliferation and changes in nutrient uptake soils dry (Nye and Tinker 1977, Crawford and kinetics are thought to contribute significantly Gosz 1982, Barber 1995). to plant acquisition of nutrients from enriched Phenological differences among species can soil patches (Jackson and Caldwell 1989, Jack- result in different degrees of temporal cou- son et al. 1990, Robinson 1994). pling between nutrient uptake and its use for Our objective was to evaluate the ability of growth and reproduction. For example, in the 6 Great Basin species representing 3 life forms sagebrush-steppe, perennial tussock grasses to acquire N from different spatial distributions. and winter annuals initiate growth in early The relative capability of species for coarse- spring from overwintered tillers that began scale and fine-scale foraging of nutrients is growth in the fall (Nowak and Caldwell 1984). one aspect of potential spatial niche separation Tiller growth accelerates and seed production among coexisting species (Campbell et al. occurs in late spring and early summer, fol- 1991, Grime 1994). We evaluated this poten- lowed by death of annuals or dormancy of tial by comparing the ability of these species perennials in early to midsummer. The shrubs to acquire N from (1) locally enriched patches, Artemisia tridentata and Chrysothamnus nau- (2) a uniform distribution surrounding the plant, seosus initiate belowground growth early in and (3) enriched areas at a distance of 35–45 the spring (Fernandez and Caldwell 1975), but cm. Due to phenological differences among vegetative growth first begins in early summer the selected species, it was necessary to create and flowering occurs in late summer (Bilbrough spatial patterns of N that would persist over a and Caldwell 1997). Thus, within a sagebrush- sufficiently long period of time in the spring steppe community the timing of nutrient acqui- such that all species would have the opportu- sition in spring and its subsequent use by dif- nity to experience N applications when they ferent species can vary considerably. were active. We used an 15N-labeled ammo- Recently, Bilbrough and Caldwell (1997) nium-loaded clinoptilolite zeolite as a slow- investigated the ability of 6 species common releasing N source (Ming and Mumpton 1989). to the Great Basin to procure nitrogen (N) The 6-week experimental period overlapped from nitrogen-rich pulses at different times active growth stages of all 6 species (Bilbrough during the spring growing season. Plant growth and Caldwell 1997). We focused on total quan- was monitored throughout the growing season tity of N acquired from zeolite applications for each species. They concluded that most and translocated to current year’s leaf and the species exhibited a greater growth advantage proportion of the leaf N pool that this newly by the onset of summer when they received a gained N represented. single 4-day pulse of N in the spring than when they received the same quantity of nitrogen METHODS applied over 10 weeks in the spring. The species differed as to how effectively they The research was conducted in spring 1995 acquired N from the pulses, but there were at Utah State University Green Canyon only small differences in the timing when Research Center, located approximately 4 km pulses were best utilized among the species. northeast of Logan, Utah (41°45′N, 111°48′W, Therefore, temporal niche separation of N 1460 m elevation). Annual precipitation in acquisition among the species during spring Logan comes largely as snow in the winter, was apparently limited (McKane et al. 1990, but spring months receive 44 mm of rain on Bilbrough and Caldwell 1997). average. Superimposed upon temporal variability in Our experiment was conducted in large, un- nutrient resource distribution is spatial hetero- lined, sand-filled plots (5 m × 18 m, 1 m deep) 2001] NITROGEN ACQUISITION BY GREAT BASIN PLANTS 95 where plants were exposed to field conditions. There were 4 sand pits each planted with 6 species common to the Great Basin of the Intermountain West and used in earlier studies (Bilbrough and Caldwell 1997). The 4 perennial species were planted in 1992 as monoculture subplots within each sand plot. Subplots with perennial species were ~15 m × 1.5 m and were arranged parallel to each other along the length of the sand plots. Sub- plots with annual species were located at the end of each sand plot. Within each species subplot were 4 separate experimental units (approximately 1.5 m2 for perennials and 0.5 m2 for annuals; Fig. 1). Experimental treatments had been applied to the perennial species’ experimental units in previous years. Each species had received N (but no 15N) in the form of a pulse the previous 2 years, and these N pulses were applied to various experimental units at different times during the spring (Bilbrough and Caldwell 1997). For each species, we used 2 prior experimental units from each subplot in each sand plot (i.e., n = 8 experimental units). Prior treatments were included in the ANOVA as an experiment factor. The ANOVA factor PRIOR and all interaction terms with this factor were not statistically significant for any response variable for any species. Further- more, N tissue concentrations between plants Fig. 1. Diagram of plant location and N-amendment from different prior treatment experimental placement in experimental units (EU). Represented here units were not statistically different. Therefore, are (A) a perennial grass EU, and (B) an annual grass EU. we believe our N acquisition results were not Spacing among shrub plants was 25 cm, 20 cm among strongly influenced or confounded by these perennial grass plants, and 5 cm among annual grass plants. Each dot represents an individual plant. Solid-line prior N applications. circles represent patch applications and solid-line rectan- Perennial shrubs were transplanted as small gles represent uniform applications; dashed circles repre- seedlings and perennial tussock grasses as sent potential target plants to be harvested. Shrub EUs clumps of tillers in 6 parallel rows within each were similar in layout and treatment application to perennial grass EUs. The Uniform Treatment in the shrub EU subplot. We staggered plants in adjacent rows covered 2 plants in adjacent rows; otherwise treatment with consistent spacing between all plants, cre- coverage was the same as in perennial grass EUs. ating a uniform distribution (Fig. 1). Spacing between plants necessarily varied because of size differences of the growth forms. The introduced exotic annual grasses Bromus tec- indigenous shrubs Artemisia tridentata ssp. torum (L.) and Aegilops cylindrica Host. were vaseyana (Rydb.) Beetle and Chrysothamnus planted at 5-cm spacing in two 0.5-m2 experi- nauseosus (Pallas) Britt. were planted at an mental units within each sand plot (Fig. 1B). interplant distance of 25 cm. The introduced Because plants were growing in sand, they and indigenous perennial tussock grasses required light watering daily. To maintain Agropyron desertorum (Fisch. ex Link) Schult some background nutrient availability in these and Pseudoroegneria spicata ([Pursh] A. Löve), sand cultures, we applied a 20% Hoaglands respectively, were planted at 20-cm spacing. solution (with 5% N) through the drip irriga- After 2 years, however, the interplant distance tion system which was positioned between was approximately 15 cm in perennial grass plant rows. After a 45-minute watering period, subplots. In early March 1995 seeds of the the entire surface of the sand was wetted. 96 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Plants showed no signs of nutrient stress this uniform treatments, respectively. Patches in year or in previous years. annual plots were 4.5 cm in diameter and uni- We utilized the mineral clinoptilolite zeo- form applications were 300 cm2, each with 0.55 lite to create local areas of increased nitrogen g zeolite, corresponding to application rates of availability. Clinoptilolite zeolite is composed 8.0 g N m–2 and 0.042 g N m–2, respectively of a crystalline lattice with a very high surface (Fig. 1B). area that is negatively charged with an affinity Patch and uniform zeolite applications were + for NH4 (Ming and Mumpton 1989). Pulver- created within each experimental unit on 3 + ized zeolite can easily be “loaded” with NH4 May 1995. Plants were harvested 14–20 June. by soaking in concentrated NH4Cl solution, This experimental period was long enough for allowing the internal sites to become occupied zeolite to release much of the 15N-labeled + by the cation NH4 . We soaked 200 g of ammonium (J.L. Boettinger unpublished) and crushed zeolite for 7 days on a shaker table in overlapped the growth period of all 6 species 15 a 2% NH4Cl-labeled 1-M NH4Cl solution. (Bilbrough and Caldwell 1997). In each peren- We then repeatedly rinsed the zeolite with nial species experimental unit, 2 plants adjacent deionized distilled water to remove the chlo- to the patch (Patch Treatment), 2 plants within ride. Zeolite was oven-dried for 3 days and the uniform area (Uniform Treatment), and 1 stored in a desiccator. Following the “loading” plant 35–45 cm away from both applications + process, 1 g of dry NH4 -loaded zeolite con- (Distant Treatment) were harvested. Tissues + tained 2.3 mg of N. Zeolite released the NH4 for the 2 individuals harvested from Patch and 15 + + NH4 in exchange for other cations, such Uniform Treatments were not pooled for N as Ca2+, K+, and Mg2+ in our diluted Hoag- analysis. Two or 3 plants were between the lands solution; thus, it was effective in creat- Distant Treatment plant and zeolite applica- ing a long-term nutrient patch in this sand sys- tions in each experimental unit (Fig. 1). Imme- tem, since zeolite would release N slowly over diately following harvest, aboveground tissue time and remain localized. for shrubs was partitioned into current year’s Due to plant size differences (e.g., 3-year- growth and prior years’ growth. Perennial old shrubs versus 3-week-old annual seedlings), grasses were separated into living tiller mater- + we used different quantities of NH4 -loaded ial and seed. For the annual grasses there was zeolite and created different size application only leaf tissue. areas for each growth form. The quantity of Soil cores were taken from the interspace zeolite used for each growth form was based among plants in the Patch and Uniform Treat- on the spacing of plants such that uniform ments and adjacent to the single distant plant applications were approximately equal to pre- to assess local root morphological parameters. vious years’ background nitrogen fertilization Cores for shrubs and perennial grasses were (0.043 g N m–2). Patches for shrubs were 10 and 7.5 cm in diameter, respectively, slightly applied to 9.5-cm-diameter circular areas with larger than the diameter of patch treatments. 1.65 g zeolite placed on the surface in the All soil cores were 20 cm deep. Roots were space equidistant between 3 plants (Fig. 1A). separated from the soil cores and washed free Uniform applications were 900 cm2 with the of sand and other debris. All plant material same quantity of zeolite covering the soil sur- was processed immediately, frozen in liquid face; this included 2 shrubs in separate rows N2 in the field, and kept on dry ice until pro- (modification of uniform application in Fig. 1A). cessing. These application rates correspond to 5.3 g N Plant material was freeze-dried for 48 hours m–2 and 0.042 g N m–2 for the patch and uni- and then weighed. A subsample of roots was form treatments, respectively. Perennial grass rehydrated overnight and root length for each circular patches were 7 cm in diameter to which sample was assessed using a Comair root length 1.1 g of zeolite was applied over the soil sur- scanner (Melbourne, Australia). The current face in the space equidistant between 3 plants. year’s leaf material was then finely ground. Uniform applications were 600 cm2 with the Total nitrogen content and 15N enrichment of same amount of zeolite and encompassed 3 leaf and root tissues were determined by a plants in 2 adjacent rows (Fig. 1A). Application continuous flow direct combustion mass-spec- rates for perennial grasses corresponded to 6.6 trometer (ANCA 2020 system, Europa Scien- g N m–2 and 0.042 g N m–2 for the patch and tific Inc., Cincinnati, OH). Nitrogen acquired 2001] NITROGEN ACQUISITION BY GREAT BASIN PLANTS 97 by plants from the experimental treatments lyzed this new variable in the same manner as was determined based on 15N enrichment in described above. the leaf tissue in excess of background 15N (which we assumed to be constant at 0.36599 RESULTS atomic %). Total N in the tissue was estimated based on total tissue mass and tissue concen- All 6 species acquired N from patch and tration. Since zeolite was 2% enriched with uniform applications. The proportion of N in 15N, we could calculate the proportion of total leaf tissue derived from zeolite applications tissue N derived from our treatments. Mass of was greater for annual species (Figs. 2a, b) N acquired from treatments and translocated than for perennials (Figs. 3a, b, 4a, b). The into current year’s growth was calculated as proportion was significantly greater for both the proportion of treatment-derived N multi- species of annual plants adjacent to patches plied by total tissue N for each plant. (0.20 and 0.28 for Aegilops and Bromus, respectively, P = 0.0001) than for these annuals Statistical Analysis within the uniform distribution (0.06 and 0.12, Statistical analyses were performed at the respectively, P = 0.0001, Figs. 2a, b). For the species level to test for differences among N annual species, nitrogen acquired by plants levels in treatment plants. Comparisons among adjacent to patches and within uniform appli- species and growth forms were qualitative. We cations was significantly greater than N performed all analyses as a randomized block acquired by Distant-Treatment plants (P ≤ design with prior pulse treatments and distri- 0.03). A similar pattern was apparent for the bution treatments (Patch, Uniform, and Dis- mass of N procured. Aegilops and Bromus tant) as fixed effects in the model. Tests for plants both acquired a greater quantity of N normality were performed on each response from localized patches than from the uniform variable. Proportion data were transformed with application (P = 0.0001, Figs. 2c, d). Distant- a modified log transformation, and amounts of Treatment plants did acquire N from the total N acquired were transformed with a applications (P = 0.001), although significantly square root transformation to approximate less than Patch- and Uniform-Treatment plants normality. ANOVA analyses were performed (P = 0.0001). on transformed variables using a mixed-model For the perennial grasses, Agropyron Patch- analysis (Proc Mixed; SAS 1993) for the vari- Treatment plants exhibited a significantly ables proportion of N acquired, mass of N greater proportion of new N in leaf tissues and acquired, and specific root length. P-values also a greater mass of acquired N than Uniform- presented for explicit comparisons of means and Distant-Treatment plants (P = 0.002 and among treatments were Bonferroni adjusted. P = 0.001, Figs. 3a, c, respectively). However, Means and standard errors for each variable proportions of N in the leaf tissue and mass of were back-transformed for graphical presenta- N acquired from applications were not signifi- tion of the data. Statistical power was low for cantly different among the 3 treatments for this experiment because of small sample sizes; Pseudoroegneria (P = 0.25 and P > 0.26, Figs. therefore, we did not adhere to a strict inter- 3b, d, respectively). This suggests that zeolite- pretation of statistical significance for P-values N applications were utilized with equal effec- ≤ 0.05. P-values are presented in the results, tiveness by all Pseudoroegneria plants within allowing readers to form their own conclusions. the experimental unit regardless of their prox- There was high variability in the quantity imity to the application area. of N acquired between the 2 Artemisia plants The 2 shrubs also differed in their acquisi- within each experimental unit of our Patch tion of N from the treatments. There were no Treatments, and this contributed to large stan- differences in average mass of leaf N acquired dard errors for this variable. We therefore by plants from the 3 treatments for Chrysotham- defined a new variable, total N acquired by nus (P = 0.64, Fig. 4d). Artemisia exhibited the 2 plants harvested for each treatment, by significant differences among treatments for summing the mass of N acquired from the both the proportion of N and the quantity of N treatment applications for the 2 plants in the derived from zeolite applications (P = 0.05 Patch and the 2 plants in the Uniform Treat- and P = 0.06, Figs. 4a, c, respectively). Patch- ments within each experimental unit. We ana- Treatment plants acquired a greater mean 98 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Fig. 2. Mean proportion of leaf N pool (a, b) and mean Fig. 3. Mean proportion of leaf N pool (a, b) and mean mass of N (c, d) derived from zeolite-N application mass of N (c, d) derived from zeolite-N applications appear- appearing in leaf tissues for Aegilops and Bromus. Open ing in leaf tissues for Agropyron and Pseudoroegneria. bars represent plants adjacent to the patch application, Open bars represent plants adjacent to the patch applica- solid bars represent plants in the uniform application, and tion, solid bars represent plants in the uniform applica- hatched bars represent plants 35–45 cm from the application, and hatched bars represent plants 35–45 cm from tion. Vertical bars are standard errors based on n = 8 the application (n = 8). Vertical bars are standard errors EUs. Differences among means (P < 0.05) are indicated based on n = 8 EUs. Differences among means (P < 0.05) by different letters. are indicated by different letters. quantity of N than did Uniform- or Distant- among treatments for one species. Artemisia Treatment plants (P = 0.12, Fig. 4c). But Dis- was the only species that showed a significant tant-Treatment plants for both shrub species increase in SRL in the Patch Treatment com- had a significant quantity of application- pared with the Distant (P = 0.01) and Uni- derived N in their leaf tissues (Figs. 4c, d). form Treatments (P = 0.08, Fig. 5). In the Artemisia data plant-to-plant variability within treatments was particularly large. DISCUSSION Of the 2 plants harvested in Patch Treatments, one often acquired a much greater quantity of At least one species of each growth form N than its neighbor. Analysis performed on obtained a greater quantity of N from patches total N acquired by the 2 plants revealed that than from the uniform distribution: Artemisia, Artemisia procured more N from the Patch Agropyron, and both annual grass species than from the Uniform Treatment (P = 0.005). (Figs. 2, 3, 4, 6). The shrub Artemisia and the Such high plant-to-plant variability within tussock grass Agropyron both utilized the con- treatment pairs was not apparent for any other centrated patch better than the uniform appli- species; therefore, the same analysis was not cation (ratio of N acquired from patch:uniform warranted. > 2, Fig. 6), whereas the shrub Chrysotham- nus and the tussock grass Pseudoroegneria uti- Root Proliferation lized N from the patch and uniform applica- There were no differences in root mass tions equally (ratio of N acquired from patch: within soil cores between the patch- or uni- uniform ~1, Fig. 6). Thus, for the perennial form-application areas and the unamended soil species, effective acquisition of a localized for any of the species. However, specific root source of N did not simply correspond with length (SRL), root length per mass, did differ growth form (Campbell et al. 1991). 2001] NITROGEN ACQUISITION BY GREAT BASIN PLANTS 99

Fig. 5. Mean specific root length (SRL), root length per mass, for the 4 perennial species for the Patch, Uniform, and Distant Treatments. Means represent 8 soil cores. Vertical bars are standard errors based on n = 8 EUs. Dif- ferences among means (P < 0.05) are indicated by different letters.

Fig. 4. Mean proportion of leaf N pool (a, b) and mean mass of N (c, d) derived from zeolite-N applications appear- therum, behaved similarly to Bromus in effec- ing in leaf tissues for Artemisia and Chrysothamnus. Open tively acquiring N from patches and pulses, bars represent plants adjacent to the patch application, respectively. These 3 exotic annual grasses solid bars represent plants in the uniform application, and have similar growth habit and phenology and hatched bars represent plants 35–45 cm from the application (n = 8). Vertical bars are standard errors based on n are common aggressive weeds in agricultural = 8 EUs. Differences among means (P < 0.05) are indi- fields and rangelands (Donald and Ogg 1991, cated by different letters. Young 1992, Billings 1994). Their flexibility in effectively using patches and early pulses of N may contribute to their effectiveness in com- Root characteristics that provide the capac- peting with Great Basin perennials. ity to utilize spatially concentrated N patches Both perennial grasses appeared capable of may not necessarily be the same as those that translating N acquisition from spring pulses enable effective utilization of an N pulse. Our into a significant growth advantage (Fig. 7); study and that of Bilbrough and Caldwell however, these 2 grass species differed in their (1997) conducted in the same sand-plot sys- capacity to procure N from patches, as men- tem provide the opportunity to compare the tioned above (Fig. 6). Agropyron proved to be ability of these species to utilize patches and facile in exploiting patches while Pseudoroeg- pulses of N. Five of 6 species we tested were neria did not respond to patches, but appeared common to both studies. Bilbrough and Cald- to possess a more broadly distributed active well (1997) used another aggressive exotic root system (Fig. 3). It was better able to take annual grass, Teaniatherum caput-medusae, for advantage of N in distant patches than was their N-pulse study rather than Aegilops cylin- Agropyron. Shrub species behaved differently drica as used in our study. Of the species in their ability to utilize both N pulses and tested for capacity to utilize N pulses here, all patches. Artemisia responded well to both except Chrysothamnus exhibited a growth pulses and patches, while Chrysothamnus advantage when they received a 4-day con- acquired little N from different spatial distri- centrated pulse of N compared to a 10-week butions and did not respond to pulses. In a continuous-control N application; however, similar vein, Chrysothamnus was not able to this varied in degree (Fig. 7). It appears from utilize soil moisture in upper soil layers derived our results and those of Bilbrough and Cald- from summer precipitation events (Ehleringer well (1997) that Bromus has the ability to et al. 1991, Lin et al. 1996). In general, it effectively procure N from both concentrated appears this species is rather unresponsive to pulses and patches. The 2 annual grasses not resource opportunities in upper soil layers. In common to both studies, Aegilops and Teania- contrast, Artemisia effectively utilized N pulses 100 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Fig. 7. Greatest growth exhibited from 1 of 3 spring N pulses expressed as an increase in plant biomass relative to control plants. Data were extracted from Bilbrough and Caldwell (1997). Fig. 6. Ratio of mean mass of N in leaf tissues acquired by plants adjacent to patches to mean mass of N in leaf tissues acquired by plants in the uniform applications. grasses and Artemisia, exhibited a high precision in foraging in that they clearly acquired in the spring (Bilbrough and Caldwell 1997), the greatest proportion of N from enriched and roots in upper soil layers remained re- patches. Also, both perennial grasses in our sponsive to pulses of moisture following peri- study have similar growth rates (Caldwell et ods of drought (Ehleringer et al. 1991, Lin et al. 1991, Bilbrough and Caldwell 1997) but al. 1996). Based on its ability to obtain N effec- differ strikingly in their precision of foraging. tively from all 3 distributions, Artemisia appar- Results from our large, outdoor sand-cul- ently has a broad distribution of roots capable ture experiment allow us to identify potential of both coarse- and broad-scale nutrient forag- patterns of spatial soil resource use by these ing. Although the 2 shrub species occur in co-occurring Great Basin species. We do not similar habitats and have a generally similar suggest that these are necessarily the tactics general growth form and phenological progres- employed by these species in nature. How- sion, they appear to be functionally different ever, our results do identify differences among in use of shallow soil resources (Ehleringer et species use of localized nutrient patches and al. 1991, Donovan and Ehleringer 1994, Lin et precision of foraging. Differences in spatial use al. 1996, Bilbrough and Caldwell 1997). of mineral resources may contribute to spatial The ability to allocate a large proportion of niche separation in Great Basin communities. actively absorbing roots in nutrient-rich soil However, temporal niche separation expressed volumes should be of advantage in acquiring in the ability of these species to utilize pulses N from such patches. Campbell et al. (1991) of N through time is not necessarily correlated found that dominant species that captured the with spatial foraging patterns. most mineral resources were those exhibiting high belowground potential growth rates. These ACKNOWLEDGMENTS fast-growing species were not, however, particularly precise in allocating roots to resource- This research was supported by the National rich patches. Grime (1994) maintained that Science Foundation (DEB 9208212, DEB slower-growing species with high precision in 9807097) and the Utah Agricultural Experi- allocating roots to resource-rich patches would ment Station. We greatly appreciate the field be subdominant species that retain their posi- and laboratory assistance of Tim Hudelson, tion in the community by their precision in Valerie Tinney, and Holly Wolsey. Further, we root foraging. However, in our study relative gratefully acknowledge the statistical advice of growth rates of the species were not inversely Susan Durham and Dr. Richard Cutler and correlated with precision in foraging. Fast-grow- comments on earlier drafts of this manuscript ing species in our study, such as the annual by Dr. Neil West. 2001] NITROGEN ACQUISITION BY GREAT BASIN PLANTS 101

LITERATURE CITED ical and evolutionary theory. American Naturalist 111:1169–1194. AARSSEN, L.W. 1983. Ecological combining ability and ______. 1994. The role of plasticity in exploiting environ- competitive combining ability in plants: toward a mental heterogeneity. Pages 1–19 in M.M. Caldwell general evolutionary theory of coexistence in system and R.W. Pearcy, editors, Exploitation of environ- of competition. American Naturalist 122:707–731. mental heterogeneity by plants. Academic Press, San BARBER, S.A. 1995. Soil nutrient availability. 2nd edition. Diego, CA. John Wiley and Sons, Inc, New York. HALVORSON, J.J., J.L. SMITH, J.H. BOLTON, AND R.E. ROSSI. BILBROUGH, C.J., AND M.M. CALDWELL. 1997. Exploitation 1995. Evaluating shrub-associated spatial patterns of of springtime ephemeral N pulses by six Great Basin soil properties in a shrub-steppe ecosystem using plant species. Ecology 78:231–243 multiple-variable geostatistics. Soil Science Society BILLINGS, W.D. 1994. Ecological impacts of cheatgrass and of America Journal 59:1476–1487. resultant fire on ecosystems in the western Great HOOK P.B., I.C. BURKE, AND W. K . L AUENROTH. 1991. Het- Basin. Pages 22–30 in S.B. Monsen and S.G. Kitchen, erogeneity of soil and plant N and C associated with editors, Proceedings—ecology and management of individual plants and openings in North American annual rangelands. General Technical Report INT- shortgrass steppe. Plant and Soil 138:247–256. 313, Intermountain Research Station, Ogden, UT. JACKSON, R.B., AND M.M. CALDWELL. 1989. The timing CALDWELL, M.M., J.H. MANWARING, AND R.B. JACKSON. and degree of root proliferation in fertile-soil micro- 1991. Exploitation of phosphate from fertile soil sites for three cold-desert perennials. Oecologia 81: microsites by three Great Basin perennials when in 149–153. competition. Functional Ecology 5:757–764. ______. 1993. Geostatistical patterns of soil heterogeneity CAMPBELL, B.D., AND J.P. GRIME. 1989. A comparative around individual perennial plants. Journal of Ecol- study of plant responsiveness to the duration of ogy 81:683–692. episodes of mineral nutrient enrichment. New Phy- JACKSON, R.B., J.H. MANWARING, AND M.M. CALDWELL. tologist 112:261–267. 1990. Rapid physiological adjustment of roots to CAMPBELL, B.D., J.P. GRIME, AND J.M.L. MACKEY. 1991. A localized soil enrichment. Nature 344: 58–60. trade-off between scale and precision in resource LIN, G., S.L. PHILLIPS, AND J.R. EHLERINGER. 1996. Mon- foraging. Oecologia 87:532–538. soonal precipitation responses of shrubs in a cold CHAPIN, F.S. 1988. Ecological aspects of plant mineral desert community on the Colorado Plateau. Oecolo- nutrition. Advances in Mineral Nutrition 3:161–191 gia 106:8–17. ______. 1980. The mineral nutrition of wild plants. Annual MCKANE, R.B., D.F. GRIGAL, AND M.P. RUSSELLE. 1990. Review of Ecology and Systematics 11:233–260. Spatiotemporal differences in 15N uptake and the CHARLEY, J.L., AND N.E. WEST. 1977. Micro-patterns of organization of an old-field plant community. Ecol- nitrogen mineralization activity in soils of some ogy 71:1126–1132. shrub-dominated semi-desert ecosystems of Utah. MING, D.W., AND F.A. MUMPTON. 1989. Zeolite in soils. Soil Biology and Biochemistry 9:357–365. Pages 873–911 in J.B. Dixon and S.B. Weed, editors, CRAWFORD, C.S., AND J.R. GOSZ. 1982. Desert ecosystems: Minerals in soil environments. 2nd edition. Soil Sci- their resources in space and time. Environmental ence Society of America, Madison,WI. Conservation 9:181–195. NOWAK, R.S., AND M.M. CALDWELL. 1984. Photosynthetic DONALD, W. W. , AND A.G. OGG. 1991. Biology and control activity and survival of foliage during winter for two of jointed goatgrass (Aegilops cylindrica), a review. bunchgrass species in a cold-winter steppe environ- Weed Technology 5:3–17. ment. Photosynthetica 18:192–200. DONOVAN, L.A., AND J.R. EHLERINGER. 1994. Water stress NYE, P.H., AND P. B . T INKER, EDITORS. 1977. Solute move- and use of summer precipitation by a Great Basin ment in the soil-root system. University of California shrub community. Functional Ecology 8: 289–297. Press, Los Angeles. DREW, M.C., AND L.R. SAKER. 1975. Nutrient supply and ROBINSON, D. 1994. Tansley review No. 73. The responses the growth of the seminal root system in barley II. of plants to non-uniform supplies of nutrients. New Localized, compensatory increases in lateral root Phytologist 127:635–674. growth and rates of nitrate uptake when nitrate sup- SAS INSTITUTE INC. 1993. SAS system for mixed models, ply is restricted to only part of the root system. Jour- version 6.11. SAS Institute, Cary, NC. nal of Experimental Botany 26:79–90. SCHLESINGER, W.H., J.A. RAIKES, A.E. HARTLEY, AND A.F. EHLERINGER, J.R., S.L. PHILLIPS, W.S.F. SCHUSTER, D.R. CROSS. 1996. On the spatial pattern of soil nutrients SANDQUIST. 1991. Differential utilization of summer in desert ecosystems. Ecology 77:364–374. rains by desert plants. Oecologia 88:430–434. STARK, J.M. 1994. Causes of soil nutrient heterogeneity at FERNANDEZ, O.A., AND M.M. CALDWELL. 1975. Phenology different scales. Pages 255–284 in M.M. Caldwell and dynamics of root growth of three cool semi- and R.W. Pearcy, editors, Exploitation of environ- desert shrubs under field conditions. Journal of mental heterogeneity by plants. Academic Press, San Ecology 63:703–714. Diego, CA. FITTER, A.H. 1986. Spatial and temporal patterns of root TILMAN, D. 1986. Evolution and differentiation in terres- activity in a species-rich alluvial grassland. Oecolo- trial plant communities: the importance of the soil gia 69:594–599. resource: light gradient. Pages 359–380 in J. Diamond GRIME, J.P. 1977. Evidence for the existence of three pri- and T.J. Case, editors, Community ecology. Harper mary strategies in plants and its relevance to ecolog- & Row Publishers, New York. 102 WESTERN NORTH AMERICAN NATURALIST [Volume 61

VERESOGLOU, D.A., AND A.H. FITTER. 1984. Spatial and YOUNG, J.A. 1992. Ecology and management of medusa- temporal patterns of growth and nutrient uptake of head (Taeniatherum caput-medusae ssp. asperum five co-existing grasses. Journal of Ecology 72: [Simk] Melderis). Great Basin Naturalist 52:245–252. 259–272. Received 7 July 1999 Accepted 7 January 2000 Western North American Naturalist 61(1), © 2001, pp. 103–108

SHREWS OF THE LA SAL MOUNTAINS, SOUTHEASTERN UTAH

Eric A. Rickart1 and Lawrence R. Heaney2

ABSTRACT.—We conducted a trapping survey of small mammals along an elevational gradient in the La Sal Moun- tains and documented 4 species of shrews (Sorex), the largest number inhabiting any mountain range in Utah. Sorex palustris was restricted to very moist microhabitats near open water at mid- to high elevations where it was relatively common. Occurring in nearly all habitats across the entire sampling gradient, S. monticolus was the numerically dominant small mammal at many sites. Sorex nanus, a new record for the La Sals, was found in areas of rockfall at high elevations and in a rocky wash at mid-elevation. Sorex cinereus, a new record for southeastern Utah, was recorded at a single high-elevation locality. Most localities had 2 syntopic species of shrews, and at 1 site in and around a rockslide we recorded all 4 species. Despite their current isolation, the La Sal Mountains support a remarkably diverse shrew fauna. Their proximity to the main southern Rocky Mountains as a rich faunal source and the presence of abundant rockfall microhabitat appear to be important causal factors.

Key words: shrews, Sorex, new records, La Sal Mountains, elevational gradients, syntopic species, zoogeography.

The mountain ranges of western North This paper summarizes information on the America support unique local mammal faunas elevational distribution, habitat affinities, and that have been shaped by regional geography relative abundance of shrews occurring in the and history. These areas have been instrumen- La Sal Mountains of southeastern Utah. Rising tal in developing and testing ideas on histori- more than 2000 m above surrounding low- cal biogeography and community structure of lands, the La Sals are a relatively large, iso- mammals (Brown 1971, Patterson and Atmar lated range on the Colorado Plateau. Earlier 1986, Lomolino et al. 1989, Cutler 1991, Gray- work in the La Sals provided basic informa- son 1993, Lawlor 1998, Rickart 2001). Nonethe- tion on the mammal fauna and demonstrated less, information on many aspects of the distri- faunal affinities with the southern Rocky Moun- bution of mammals in this region is still sur- tain region (Kelson 1951, Lee 1960). This report prisingly incomplete, and the faunas of many stems from a more detailed survey of the non- mountain ranges remain poorly known. These volant mammals along an elevational gradient limitations have influenced research efforts. conducted during 1997 and 1998. For example, discoveries of previously over- STUDY AREA looked taxa on isolated mountain ranges in the Great Basin have greatly altered estimates of The La Sal Mountains, centered at 38°30′N colonization and extinction rates of montane latitude, 109°15′W longitude, constitute the mammals in this region (Grayson and Living- largest of several isolated mountain ranges in ston 1993, Grayson et al. 1996, Lawlor 1998). southeastern Utah that were formed during For small mammals, the quality of available the mid-Tertiary through laccolithic intrusion data varies among taxonomic or ecological (Hunt 1958). The range encompasses more groups. Shrews (Soricidae) are important com- than 800 km2 of land area above 2300 m (7500 ponents of local small mammal communities ft) elevation and includes several peaks that throughout western North America. However, exceed 3650 m (12,000 ft) elevation. Isolated information on their distribution and local to the west, north, and east by deep canyons of abundance is particularly incomplete because the Colorado and Dolores rivers, the La Sals many species are notoriously difficult to sur- are separated from mountains to the south by vey using conventional methods (Kirkland intervening low elevations. The nearest high- 1991, Kirkland and Sheppard 1994). land areas are the Uncompahgre Plateau, ca

1Utah Museum of Natural History, University of Utah, 1390 E. Presidents Circle, Salt Lake City, UT 84112. 2Field Museum of Natural History, Roosevelt Road at Lake Shore Drive, Chicago, IL 60605.

103 104 WESTERN NORTH AMERICAN NATURALIST [Volume 61

50 km to the east in Colorado, and the Abajo RESULTS Mountains located 60 km further south in Utah. From the standpoint of historical biogeogra- Four species of shrews have been recorded phy, the most significant highland association from the La Sal Mountains. The following is to the southeast with the San Miguel, San species accounts summarize information on Juan, and Rico Mountains of southwestern elevational range, habitat associations, and rel- Colorado (Lee 1960). ative abundance. We list the number of specimens from collecting localities in our survey, METHODS as well as other known records of occurrence within the mountain range. Fieldwork was conducted during August Sorex cinereus 1997 and 1998. We trapped shrews at sites along an elevational gradient extending from Specimens of the masked shrew were iden- 1775 to 3200 m elevation using a combination tified on the basis of relative size of the uni- of Museum Special snap-traps and pitfall traps cuspid teeth (U3 larger than U4) and relatively constructed by removing the tops from 350- small body size (adult mass <5 g, condylo- mL aluminum beverage cans. Snap-traps were basal length <17 mm). The species is distin- baited with rolled oats combined with either guished from the closely related S. preblei by peanut butter or canned cat food. Pitfall traps its larger size (condylobasal length >15 mm) were set without drift fences in runways, and inflated as opposed to relatively flat cra- along the margins of boulders or fallen logs, or nium (Junge and Hoffmann 1981). In August near natural openings. We placed a small 1998 we trapped 3 individuals at 2850 m ele- amount of water in each pitfall to facilitate vation at a site near Warner Lake. All were capture, and although they were not baited, taken in pitfall traps in a grove of small aspen they normally accumulated small invertebrates (Populus tremuloides) along the margin of a after several hours. Traps were checked at talus slope (260 trap nights; 1.2% trap suc- least twice daily and were set for 2 to 4 nights cess). At the time of the survey, this locality and occasionally longer periods. Total number was relatively dry, with no permanent surface of trap nights ranged from 75 to 300 at each water. Sorex monticolus and S. nanus also were locality. Percent trap success (number of indi- taken at this site. The specimens include a viduals captured in 100 trap nights) was used young male (UMNH 29935), an adult male to estimate relative abundance of species. At with scrotal testes but without prominent flank localities where both pitfalls and snap-traps glands (UMNH 29936), and an adult female were used, we based these calculations only with prominent mammae (FMNH 162898). on those types of traps that actually captured These represent the first records for S. the species in question. Sex and reproductive cinereus from southeastern Utah. The closest condition were determined through necropsy, known records are from Grand Mesa (ca 120 but these data often were obtainable only for km NE) and the San Juan Mountains (ca 150 very fresh specimens. Voucher specimens and km SE) in western Colorado (Armstrong 1972), field notes were deposited at the Utah Museum and from the Aquarius, Fishlake and Wasatch of Natural History, University of Utah, Salt plateaus (ca 200 km W) in Utah (Durrant and Lake City (UMNH), and the Field Museum of Newey 1953, Lee 1960, unpublished UMNH Natural History, Chicago (FMNH). Earlier and FMNH specimen records). records of shrews from the La Sal Mountains SURVEY SPECIMENS.—Total 3. Grand County: were obtained from collections at the Utah 0.7 km N, 0.4 km W Warner Lake, 2850 m ele- Museum of Natural History; the Monte L. vation (1 FMNH, 2 UMNH). Bean Museum, Brigham Young University, Sorex monticolus Provo, Utah (BYU); and the Carnegie Museum of Natural History, Pittsburgh (CMNH). Spec- The dusky shrew was recorded over the imens were identified on the basis of charac- entire sampling transect from 1775 to 3200 m ters used by Junge and Hoffmann (1981) and elevation. At lower elevations it was taken through comparison with other specimens at only in riparian habitat. It was relatively UMNH. uncommon (ca 2% trap success) at 1775 m in 2001] SHREWS OF THE LA SAL MOUNTAINS 105 streamside habitat dominated by Frémont cot- Creek, 2715 m elevation (2 BYU); T27S, tonwood (Populus fremontii) and willow (Salix R25E, sec 3NE, 2700 m (3 BYU). sp.), and with adjacent dry habitat dominated Sorex nanus by piñon (Pinus edulis), juniper ( Juniperus osteosperma), and sagebrush (Artemisia triden- The dwarf shrew is identified on the basis tata). The species was common (9% trap suc- of its small body size (adult mass <4 g, condy- cess) at 2350 m elevation in streamside habitat lobasal length <15 mm), relative size of the dominated by aspen, Douglas fir (Pseudotsuga unicuspid teeth (U3 smaller than U4), and menziesii), and low shrub cover, with sur- dorsoventrally flattened cranium (Junge and rounding vegetation including mixed piñon, Hoffmann 1981). On 31 July and 1 August juniper, scrub oak (Quercus gambelli), and 1997, we trapped a subadult female (UMNH mountain mahogany (Cercocarpus ledifolius). 29808) and an old adult male (UMNH 29810) It also was common in relatively dry scrub oak at 3200 m elevation at the head of Dark habitat at 2700 m (8% trap success). Sorex Canyon on the north flank of Mount Peale. monticolus was common or abundant at sites Both specimens were taken in pitfall traps (36 between 2800 and 3200 m elevation, where it trap nights; 5.6% trap success) placed in deep, was trapped along stream margins, in wet moist soil at the lower margin of an actively meadows, aspen woodland, mixed stands of moving talus field or “rock glacier” (Nicholas Engelmann spruce (Picea engelmannii) and 1991). Surrounding vegetation included open subalpine fir (Abies lasiocarpa), and in talus meadow with grasses and forbs, and mixed fields. It was the most frequently captured small stands of Engelmann spruce and subalpine fir. mammal species in most of these habitats Snap-traps at this locality failed to capture S. (5–15% trap success). Specimens taken during nanus. Sorex monticolus and S. palustris also August included recently weaned young, were taken at this site. In August 1998 we reproductively active females, and adult males caught 2 adult-sized S. nanus of undetermined with scrotal testes and prominent flank glands. sex (FMNH 162958, 162959) in pitfall traps in Nearly half of all individuals were caught dur- an aspen grove along the lateral margin of a ing daylight hours. The nearest regional talus slope near Warner Lake at 2850 m eleva- records for this species are from the Abajo tion (260 trap nights; 0.8% trap success). Sorex Mountains in Utah (Lee 1960) and the cinereus, S. monticolus, and S. palustris also Uncompahgre Plateau in Colorado (Armstrong were taken at or near this site. Another speci- 1972). men of S. nanus (an adult of undetermined SURVEY SPECIMENS.—Total 123. Grand sex, FMNH 162960) was snap-trapped in a County: 0.4 km S, 2.4 km W Warner Lake, deep crevice within a rock outcrop in the bot- 2700 m (8 FMNH); vicinity of Warner Lake, tom of a steep, dry wash located north of 2800–2865 m (39 FMNH; 30 UMNH). San Brumley Creek at 2165 m elevation in an area Juan County: Brumley Creek near confluence dominated by piñon and juniper. This was the with Pack Creek, 1775 m (2 UMNH); Horse only shrew recorded at this locality (225 trap Creek, 2350 m (9 UMNH); 0.4 km S, 1.0 km nights; 0.4% trap success). These represent W Geyser Pass, 3125 m (6 FMNH; 6 UMNH); the first records for this species in the La Sal 0.6 km S, 0.5 km E Geyser Pass, 3200 m (11 Mountains. Previous records for this species FMNH); 0.4 km S, 0.4 km W Geyser Pass, in Utah are from Elk Ridge on the west flank 3200 m (7 FMNH); head of Dark Canyon, N of the Abajo Mountains, ca 75 km SW of the of Mt. Peale, 3200 m (5 UMNH). La Sals (Durrant and Lee 1955), and the west- OTHER RECORDS.—Grand County: Beaver ern Uinta Mountains, ca 250 km N (Kirkland Creek, 2 mi NE Mt. Waas, 2660 m (4 UMNH); 1981). The nearest records in Colorado are Beaver Creek, 1.5 mi E La Sal Peak, 2740 m from Mesa Verde, ca 150 km SE of the La Sals (14 UMNH); Beaver Creek, 0.5 mi E Beaver (Hoffmeister 1967, Spencer 1975). Basin, 2900 m (2 UMNH); Beaver Basin, NW SURVEY SPECIMENS.—Total 5. Grand County: of Manns Peak, 3170 m (7 UMNH); 2.5 mi NE 0.7 km N, 0.4 km W Warner Lake, 2850 m (2 La Sal Peak, 2590 m (8 UMNH); Warner FMNH). San Juan County: tributary N of Ranger Station, 2960 m (2 UMNH). San Juan Brumley Creek, 2165 m (1 FMNH); head of County: Geyser Pass (1 BYU; 5 CMNH); Dark Canyon, N of Mt. Peale, 3200 m (2 T27S, R24E, sec 5NE, 2720 m (2 BYU); Horse UMNH). 106 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Sorex palustris the mountains of southwestern Colorado (Arm- The water shrew has been recorded over a strong 1972). Within Utah, the Uintas are the broad range of elevations in the La Sal Moun- only other mountain range known to support tains. We encountered it only in very wet these 4 species (Rickart 2001). This situation is areas, almost always in close proximity to flow- in stark contrast to that seen in the Henry ing water. At 2350 m, the lowest elevation Mountains, another laccolithic range located where the species has been documented in ca 150 km further west on the Colorado Pla- the La Sals, it was common in streamside habi- teau. The Henry Mountains are more isolated tat dominated by aspen and Douglas fir (ca 7% and also more arid than the La Sals, and they trap success). It probably occurs at somewhat support an extremely depauperate mammal lower elevations in the mountain range, al- fauna that does not include any shrews (Rickart though it was not recorded at our lowest ripar- 2001). ian site at 1775 m. The species was most com- The 4 species of Sorex inhabiting the La Sal mon at sites in the vicinity of Warner Lake Mountains differ with respect to habitat affini- (2800–2865 m elevation) where it was trapped ties and relative abundance. Sorex monticolus around ponds, along streams, near springs, occupies a wide spectrum of habitats across a and in wet meadows (8–10% trap success in broad elevational range. In our survey this these habitats). It was less common in stream- species was nearly ubiquitous. Recorded in all side habitat at 3200 m elevation near stream but the driest localities, it was the numerically headwaters (ca 3% trap success). The nearest dominant small mammal at nearly all sites where regional records for S. palustris are from the it occurred. Sorex palustris has narrow habitat Abajo Mountains in Utah (Lee 1960) and the requirements, occurring only in areas adjacent Uncompahgre Plateau in Colorado (Armstrong to water. We found it to be abundant in appro- 1972). priate habitat at mid-elevations, but less com- SURVEY SPECIMENS.—Total 32. Grand mon at high-elevation sites near stream head- County: vicinity of Warner Lake, 2800–2865 waters and probably absent from low eleva- m (13 FMNH; 9 UMNH). San Juan County: tions. S. cinereus was taken at only one locality head of Dark Canyon, N of Mt. Peale, 3200 m in our survey, but based on what is known of (1 UMNH); 0.4 km S, 0.4 km W Geyser Pass, the habits of this species in the region (Zevel- 3200 m elevation (2 FMNH); Horse Creek, off 1988, Fitzgerald et al. 1994), it probably 2350 m elevation (7 UMNH). occurs at relatively low abundance in a variety OTHER RECORDS.—Grand County: Warner of high-elevation habitats throughout the La Ranger Station, 2960 m (5 UMNH); Oowah Sals. We recorded S. nanus within (or immedi- Lake, 2680 m (2 UMNH); Beaver Creek, 1.5 ately adjacent to) talus or rock outcrops at mi E La Sal Peak, 2740 m (4 UMNH). San mid- to high elevations in the La Sals. This Juan County: Geyser Pass (1 CMNH). corroborates other studies that have documented broad elevational range and a prefer- DISCUSSION ence for talus and other rocky microhabitats (Hoffmann and Owen 1980). As an outlying mountain range on the Col- We found 2 or more species of shrews at orado Plateau, the La Sal Mountains support most localities we surveyed in the La Sal Moun- only a portion of the extensive montane mam- tains. At a site near Warner Lake, we found 3 mal fauna found in the “continental” Rocky species (S. cinereus, S. monticolus, and S. nanus) Mountains (Lee 1960, Lomolino et al. 1989, occurring together in talus habitat, and a 4th Rickart 2001). Although a few montane species species (S. palustris) in streamside habitat may yet remain undetected in the La Sals, immediately adjacent to the talus. High levels most if not all of the missing taxa either failed of species richness and local syntopy are not at to colonize in the first place or became locally all uncommon for North American shrew extinct since the end of the Pleistocene. In communities (Spencer and Pettus 1966, Brown light of this general pattern, the shrew fauna 1967, Williams 1984, Bury and Corn 1987, of the La Sal Mountains is surprisingly rich. Kirkland et al. 1997). However, the basis for Rather than being depauperate, it includes all coexistence of species that have such similar 4 species known to occur at high elevations in trophic requirements is not entirely clear. 2001] SHREWS OF THE LA SAL MOUNTAINS 107

Syntopic species of shrews generally differ in LITERATURE CITED body size and relative abundance, which may promote trophic separation and different pat- ARMSTRONG, D.M. 1972. Distribution of mammals in Colo- rado. Monograph of the Museum of Natural History, terns of habitat utilization (Kirkland 1991, University of Kansas 3:1–415. Hanski 1994). With a more than threefold dif- BROWN, J.H. 1971. Mammals on mountaintops: nonequi- ference in mean body mass between S. nanus librium insular biogeography. American Naturalist (<4 g) and S. palustris (>12 g), the La Sal 105:467–478. BROWN, L.N. 1967. Ecological distribution of six species assemblage exhibits the broadest size range of shrews and comparison of sampling methods in possible among North American Sorex. Species- the central Rocky Mountains. Journal of Mammal- rich shrew assemblages typically involve a mix ogy 48:617–623. of habitat generalists and specialists occurring BURY, R.B., AND P. S . C ORN. 1987. Evaluation of pitfall in structurally complex habitats, with actual trapping in northwestern forests: trap arrays with drift fences. Journal of Wildlife Management 51: syntopy confined to specific microhabitats 112–119. (Kirkland 1991). These features characterize CUTLER, A. 1991. Nested faunas and extinctions in frag- the situation in the La Sal Mountains. mented habitats. Conservation Biology 5:496–505. The fact that this small outlying mountain DURRANT, S.D., AND M.R. LEE. 1955. Rare shrews from Utah and Wyoming. Journal of Mammalogy 36: range on the Colorado Plateau supports such a 560–561. remarkably rich shrew fauna is less surprising DURRANT, S.D., AND J.P. NEWEY. 1953. Masked shrew, in light of local geography and geology. Sorex cinereus, in Utah. Journal of Mammalogy 34: Although the La Sal Mountains are currently 116–117. FITZGERALD, J.P., C.A. MEANEY, AND D.M. ARMSTRONG. isolated, they are in close proximity to the 1994. Mammals of Colorado. Denver Museum of main southern Rocky Mountain faunal region. Natural History and University of Colorado Press. Undoubtedly, this has allowed intermittent 467 pp. colonization of shrews, along with other mon- GRAYSON, D.K. 1993. The desert’s past: a natural prehistory of the Great Basin. Smithsonian Institution Press, tane taxa such as pikas (Ochotona princeps) Washington, DC. and red squirrels (Tamiasciurus hudsonicus), GRAYSON, D.K., AND S.D. LIVINGSTON. 1993. Missing during more mesic periods (Lee 1960). Fur- mammals on Great Basin mountains: Holocene thermore, the very extensive rockfall zones extinctions and inadequate knowledge. Conservation that characterize this laccolithic range (Nicholas Biology 7:527–532. GRAYSON, D.K., S.D. LIVINGSTON, E. RICKART, AND M.W. 1991) have created abundant areas of micro- SHAVER. 1996. Biogeographic significance of low- habitat particularly suitable for shrews. Fur- elevation records for Neotoma cinerea from the ther studies on other isolated mountain ranges northern Bonneville Basin, Utah. Great Basin Natu- in this region are needed to determine if the ralist 56:191–196. HANSKI, I. 1994. Population biological consequences of La Sal Mountains are truly unique in this body size in Sorex. Pages 15–26 in J.F. Merritt, G.L. respect, or merely appear to be due to inade- Kirkland, Jr., and R.K. Rose, editors, Advances in the quate knowledge elsewhere. biology of shrews. Special Publication of Carnegie Museum of Natural History 18:1–458. HOFFMANN, R.S., AND J.G. OWEN. 1980. Sorex tenellus and ACKNOWLEDGMENTS Sorex nanus. Mammalian Species 131:1–4. HOFFMEISTER, D.F. 1967. An unusual concentration of We thank Terry Horton, Stephanie Linde, shrews. Journal of Mammalogy 48:462–464. Rob McIntyre, Shannen Robson, Kate Walker, HUNT, C.B. 1958. Structural and igneous geology of the La Sal Mountains, Utah. Pages 305–354 in Geological and Mike Windham for assistance with field- Survey Professional Papers 294–1. U.S. Government work. Additional records from museum collec- Printing Office, Washington, DC. tions were provided by Sue McLaren (CMNH) JUNGE, J.A., AND R.S. HOFFMANN. 1981. An annotated key and Duke Rogers (BYU). Comments from Jim to the long-tailed shrews (genus Sorex) of the United Findley, Duke Rogers, and an anonymous re- States and Canada, with notes on Middle American Sorex. Occasional Papers of the Museum of Natural viewer helped to improve the paper. Collect- History, University of Kansas 94:1–48. ing permits were provided by the Utah Divi- KELSON, K.R. 1951. Speciation in rodents of the Colorado sion of Wildlife Resources. Partial funding was River drainage of eastern Utah. University of Utah provided by the Marshall Field, Ellen Thorne Biological Series 11(3):1–125. KIRKLAND, G.L., JR. 1981. The zoogeography of the mam- Smith, and Barbara Brown funds of the Field mals of the Uinta Mountains region. Southwestern Museum. Naturalist 26:325–339. 108 WESTERN NORTH AMERICAN NATURALIST [Volume 61

______. 1991. Competition and coexistence in shrews Unpublished doctoral dissertation, Department of (Insectivora: Soricidae). Pages 15–22 in J.S. Findley Geology, University of Georgia, Athens. 196 pp. and T.L. Yates, editors, The biology of the Soricidae. PATTERSON, B.D., AND W. A TMAR. 1986. Nested subsets Special Publication, The Museum of Southwestern and the structure of insular mammalian faunas and Biology 1:1–91. archipelagos. Biological Journal of the Linnean Soci- KIRKLAND, G.L., JR., AND P.K. SHEPPARD. 1994. Proposed ety 28:65–82. standard protocol for sampling small mammal com- RICKART, E.A. 2001. Elevational diversity gradients, bio- munities. Pages 277–281 in J.F. Merritt, G.L. Kirk- geography, and the structure of montane mammal land, Jr., and R.K. Rose, editors, Advances in the communities in the intermountain region of North biology of shrews. Special Publication of Carnegie America. Global Ecology and Biogeography 10: In Museum of Natural History 18:1–458. press. KIRKLAND, G.L., JR., R.P. PARMENTER, AND R.E. SKOOG. SPENCER, A.W. 1975. Additional records of Sorex nanus 1997. A five-species assemblage of shrews from the and Sorex merriami in Colorado. Journal of the Col- sagebrush-steppe of Wyoming. Journal of Mammal- orado-Wyoming Academy of Science 7:48. ogy 78:83–89. SPENCER, A.W., AND D. PETTUS. 1966. Habitat preferences LAWLOR, T.E. 1998. Biogeography of Great Basin mammals: of five sympatric species of long-tailed shrews. Ecol- paradigm lost? Journal of Mammalogy 79:1111–1130. ogy 47:677–683. LEE, M.R. 1960. Montane mammals of southeastern Utah— WILLIAMS, D.F. 1984. Habitat associations of some rare with emphasis on the effects of past climates upon shrews (Sorex) from California. Journal of Mammal- occurrence and differentiation. Unpublished doc- ogy 65:325–328. toral dissertation, Department of Zoology and Ento- ZEVELOFF, S.I. 1988. Mammals of the Intermountain West. mology, University of Utah, Salt Lake City. 199 pp. University of Utah Press, Salt Lake City. 365 pp. LOMOLINO, M.V., J.H. BROWN, AND R. DAVIS. 1989. Island biogeography of montane mammals in the American Received 24 May 1999 Southwest. Ecology 70:180–194. Accepted 29 December 1999 NICHOLAS, J.W. 1991. Rock glaciers and the Holocene paleoclimatic record of the La Sal Mountains, Utah. Western North American Naturalist 61(1), © 2001, pp. 109–113

SCATTER-HOARDING BEHAVIOR OF DEER MICE (PEROMYSCUS MANICULATUS)

Stephen B. Vander Wall1, Theodore C. Thayer1, Jennifer S. Hodge1, Maurie J. Beck1, and Julie K. Roth1

ABSTRACT.––Deer mice (Peromyscus maniculatus) are known to larder hoard food, but their scatter-hoarding behavior is poorly documented. Eleven deer mice were each presented with 150 Jeffrey pine (Pinus jeffreyi) seeds in 10 × 10- m enclosures in Jeffrey pine forests on the east slope of the Sierra Nevada. Subjects made a mean ± 1 s of 31.2 ± 30.0 caches per trial. Caches were shallow (most 2–12 mm deep) and usually contained only 1 or 2 seeds. Most caches were made at the edge of antelope bitterbrush (Purshia tridentata) shrubs in mineral soil or in thin layers of plant litter. These results suggest that deer mice might make a significant contribution to the dispersal of Jeffrey pine.

Key words: caching behavior, granivory, Jeffrey pine, mutualism, Pinus jeffreyi, seed dispersal, Sierra Nevada, Per- omyscus maniculatus, deer mice.

Deer mice (Peromyscus maniculatus) store behavior of deer mice will allow us to appreci- a variety of food items in larders in and near ate better the role of food storing in the lives their nests. These larders may contain more of deer mice and potential influences of deer than a liter of food, which is often segregated mice on animal and plant communities. Results by plant species (Howard and Evans 1961, reported here were gathered as part of a larger Eisenberg 1968). Frequently reported items study on interactions of deer mice and yellow include acorns, Prunus stones, and seeds of pine chipmunks (Tamias amoenus) over cached grasses and forbs (Criddle 1950, Howard and pine seeds (Vander Wall 2000). Evans 1961). Deer mice usually gather and store seeds and nuts in autumn (Cogshall STUDY AREA 1928, Criddle 1950, Howard and Evans 1961, Barry 1976, Tadlock and Klein 1979, Jaeger We conducted this study at the Whittell 1982), and the larder probably serves as an Forest and Wildlife Area, Washoe County, important food reserve for the mice during Nevada, in the Carson Range of extreme western Nevada about 30 km south of Reno, winter. However, deer mice have seldom been Nevada (39°15′10″N, 119°52′35″W). Elevation reported to scatter hoard seeds. Eisenberg is 1975 m. Experimental enclosures were (1962, 1968) briefly described the preparation located in antelope bitterbrush (Purshia tri- of small surface caches by captive members of dentata) shrubland openings in Jeffrey pine the genus. Abbott and Quink (1970) found that (Pinus jeffreyi) forest. Soils consist of decom- white-footed mice (Peromyscus leucopus), close posed granite. relatives of deer mice, scatter hoarded white pine (Pinus strobus) seeds under pine needle METHODS litter. Sullivan (1978), however, reported that deer mice did not scatter hoard conifer seeds We conducted caching trials inside five 10 at a site in coastal British Columbia. × 10-m rodent-proof enclosures. Enclosure The purpose of this report is to describe walls extended ≈75 cm aboveground and ≈45 scatter-hoarding behavior of deer mice, includ- cm belowground and consisted of 6-mm harding cache sizes, depths, and placement of ware cloth supported on a wooden frame. Tops caches in different microhabitats and substrates. of the walls had 20-cm-wide aluminum flashing We conducted the study in large enclosures on the inside and outside to prevent rodents in the field. Understanding scatter-hoarding from leaving and entering the enclosures.

1Department of Biology and the Program in Ecology, Evolution, and Conservation Biology, University of Nevada–Reno, Reno, NV 89557.

109 110 WESTERN NORTH AMERICAN NATURALIST [Volume 61

In each enclosure we buried a plastic 20-L >10 cm from the shrub canopy edge). We nest bucket in the ground such that the lid recorded data on the substrate (mineral soil, was level with the ground surface. Horizontal plant litter <1 cm deep, or plant litter >1 cm plywood dividers partitioned the nest bucket deep) at each cache site. into 3 levels. Mice could move freely between We tested whether deer mice preferred levels through holes 4 cm in diameter in the certain microhabitats or substrates for caching. partitions. The bottom level contained soil ≈2 For each cache made by a deer mouse, we cm deep and sufficient cotton for subjects to selected a random site (x and y coordinates make nests. A nearly horizontal segment of taken from a random numbers table) within PVC pipe (25 mm diameter, ≈50 cm long) con- the enclosure and determined its substrate nected the side of the upper level of the nest and microhabitat as described in the preced- with the ground surface, permitting mice to ing paragraph. All random sites were in por- enter and exit the nest bucket. We positioned tions of the enclosure that had actually been a 2.5-cm-thick piece of Styrofoam® insulation used by deer mice for caching. We compared just below the bucket lid to keep the nest use of substrates and microhabitats by 7 deer bucket cool. This nest design permitted us to mice that made sufficiently large numbers of isolate and remove mice as needed. Most sub- caches for analysis (n > 18) to the randomly jects readily accepted the buckets as nest sites. selected sites using chi-square tests for good- We placed a wooden feeder box measuring ness of fit (Zar 1996). We tested for hetero- 40 × 30 × 10 cm near the center of each enclo- geneity and combined all data sets for an over- sure. The design (bottom, top, and 2 sides) all chi-square test where appropriate. excluded birds but permitted mice to enter along 2 sides to remove seeds. We placed a tin RESULTS can containing water several meters from the Deer mice took 66% of the seeds from the feeder. feeder during trials that lasted an average of Between 2 July and 13 August 1997 and 2.6 days. Mice ate 29% and cached 71% of the 1998, we conducted 11 caching trials. To begin seeds taken. Deer mice made an average (± 1 s) a caching trial, we captured a deer mouse near of 31.2 ± 30.0 surface caches during 11 trials, the enclosure, weighed it, determined its gen- with a range of 1 to 109 caches per trial. der, marked it with a numbered ear tag, and re- Caches were generally small. Most (71%) con- leased it into the entrance of the nest bucket. tained only 1 seed, and 1- and 2-seed caches The next day we placed 150 color-marked, accounted for nearly 96% of all caches (Fig. 1). radioactively labeled Jeffrey pine seeds (see Jeffrey pine seeds are relatively large (mean Vander Wall 1992b for labeling procedure) in ±1 s = 157 ± 27 mg), and in laboratory studies the feeder. We checked the feeder daily for 3 (Thayer and Vander Wall unpublished data) days, and if all or nearly all seeds had been deer mice typically carried only 1 or 2 seeds, removed from the feeder, we terminated the suggesting that most surface caches in this trial. Two caching trials lasted 1 day, 1 lasted 2 field study were from single loads. Of the 7 days, and 8 lasted 3 days. At the end of each largest surface caches, 4 contained 4 seeds, 2 trial, we removed the deer mouse from the contained 5 seeds, and 1 contained 10 seeds. nest bucket and searched the bucket for larder- These large caches were presumably made in hoarded seeds and hulls of eaten seeds. We re- 2 or more loads. One subject made the 4 largest moved any unharvested seeds from the feeder caches. box and counted them. Then we searched the In 2 trials deer mice larder hoarded seeds enclosure with a Geiger counter to locate scat- in the nest bucket. One mouse cached 70 ter-hoarded seeds and hulls of eaten seeds. seeds in its nest (and made 14 surface caches), We carefully excavated each cache to deter- and the other mouse stored 40 intact seeds mine cache depth and number of seeds per and also ate 25 seeds in its nest (in addition to cache. We also collected data on the microsite making 1 surface cache). in which mice made caches. Cache locations Deer mice scatter hoarded most seeds at were described as “open” (>10 cm from a depths ranging from 2 mm to about 12 mm (Fig. shrub), “shrub edge” (within 10 cm of the shrub 2). Many cached seeds (30%) were partially canopy edge), or “shrub interior” (under a shrub exposed or beneath <1 mm of plant litter. Most 2001] SCATTER HOARDING BY DEER MICE 111

Fig. 2. Cache depth profile for deer mice storing Jeffrey pine seeds (n = 296 caches). Relative number of seeds buried at a given depth is proportional to the width of the profile. Fig. 1. Number of seeds in caches of 11 deer mice (n = ± 378 caches). Vertical lines represent 1 sx–.

cantly in microhabitat selection. The com- subjects spaced caches widely throughout the bined chi square showed a significantly non- χ2 enclosures with distances between caches typ- random use of microhabitats ( = 27.400, df ically ranging from 25 to 100 cm. However, we = 2, P < 0.001). did not analyze spacing patterns because caching behavior of subjects was probably DISCUSSION constrained by enclosure walls. These caching trials demonstrate that deer Deer mice (11 subjects combined) placed mice actively scatter hoard pine seeds. How- most caches in mineral soil and in light plant ever, their tendency to scatter hoard is consid- litter (175 caches in each substrate) and only a erably less pronounced than that of yellow few caches in heavy litter (Fig. 3A). The het- pine chipmunks. Under identical experimen- erogeneity chi-square test for the 7 mice with tal conditions, chipmunks invariably took and χ2 n > 18 caches was significant ( = 29.603, df cached nearly all seeds from the feeder in 1 = 12, P < 0.01), indicating that individuals day. At the end of this experiment (2.6 days), differed in their substrate use. Two subjects deer mice still had not harvested 34% of the used mineral soil extensively for caching (73% seeds. Also, deer mice larder hoarded less than of 19 cache sites and 56% of 34 cache sites; P we anticipated based on published accounts. < 0.005 for both). When we dropped these 2 This may have been because the subjects were subjects from analysis, the 5 remaining sub- not sufficiently familiar with the artificial nests jects did not differ significantly in substrate that we provided. In natural settings where use (heterogeneity chi square: χ2 = 13.518, df mice are accustomed to their surroundings = 8, P > 0.05), and they demonstrated no sig- and have a home nest and burrow system, they nificant preferences for caching in certain sub- may prefer to larder hoard in their burrows. strates (pooled chi square: χ2 = 2.071, df = 2, However, nearly all subjects appeared to accept P > 0.25). and use the nests, and other studies (Barry Deer mice cached seeds near edges of bit- 1976, Tadlock and Klein 1979, Sanchez and terbrush shrubs more than expected and Reichman 1987, Tannenbaum and Pivorum appeared to avoid open areas (Fig. 3B). The 1987) have shown that Peromyscus larder heterogeneity chi-square test for 7 mice was hoarded in artificial nests in laboratory set- not significant (χ2 = 8.214, df = 12, P > 0.50), tings. Another possible explanation is that we indicating that subjects did not differ signifi- tested subjects at a season (midsummer) when 112 WESTERN NORTH AMERICAN NATURALIST [Volume 61

white-footed mice (Abbott and Quink 1970). Second, other caches might be recovered by the hoarder and moved to the winter burrow later in autumn. Third, some caches are often pilfered by chipmunks and other rodents (Van- der Wall 2000). Finally, some seeds may escape detection and germinate the following spring. Abbott and Quink (1970) observed that some eastern white pine seeds cached by white-footed mice germinated in spring, but because the mice ate many of the seedlings, they concluded that the rodent’s net contribution to forest regeneration was probably minor. Unlike eastern white pine, which establishes almost exclusively as a direct result of wind dispersal, a large proportion of Jeffrey pine seedlings establish from caches made by rodents following initial wind dispersal. Most dispersal and establishment of Jeffrey pine in this region of the Sierra Nevada has been attributed to actions of yellow pine chipmunks Fig. 3. A, Frequency of caches made by 11 deer mice in (Vander Wall 1992a, 1992b, 1993b). However, 3 substrates (shaded bars) compared to relative abun- ways in which deer mice cache Jeffrey pine dance of those substrates (open bars) in enclosures (n = 373 caches); B, frequency of caches made by 11 deer mice seeds suggest that they also may be effective in 3 microhabitats (shaded bars) compared to relative dispersers of Jeffrey pine. abundance of those microhabitats in enclosures (n = 374 It is difficult at this time to assess the im- ± caches). Vertical lines represent 1 sx–. See Methods for portance of cache-site selection (substrate and definitions of substrate and microhabitat categories. microhabitat) in the effectiveness of deer mice as dispersers of pine seeds. Emerging pine seedlings generally have higher chances of they larder hoard little food (e.g., Criddle 1950, establishing when seeds germinate in mineral Howard and Evans 1961, Barry 1976). soil, a substrate that some mice seem to prefer Deer mice in this study usually made small and which is found in open areas between caches (1 or 2 seeds). In contrast, caches made shrubs. However, pine seedlings survive bet- by white-footed mice contained 20–30 eastern ter when under shrub nurse plants (Vander white pine seeds (Abbott and Quink 1970). Wall 1992a, Callaway and Walker 1997). Deer This discrepancy is partially because eastern mice cached seeds under shrubs <30% of the white pine seeds are much smaller than Jef- time. frey pine seeds. Most subjects in this study Under natural conditions, deer mice in these distributed caches widely within the enclosure semiarid, eastern Sierra Nevada forests proba- and covered seeds with relatively little soil or bly scatter hoard hundreds of seeds within plant litter. Except for the tendency of sub- their home ranges each year. Although they jects to cache at the periphery of shrubs (and bury some seeds at depths too shallow to permit avoid open areas), deer mice in this study ex- effective establishment of the seedling, many hibited no strong, consistent patterns in cache other seeds are buried more deeply, closer to site selection. optimum depth for germination and establish- The fate of seeds scatter hoarded by deer ment (Vander Wall 1993a). Deer mice are usu- mice under natural conditions has not been ally considered to have a detrimental effect on studied. Several alternatives seem plausible. regeneration of conifers (e.g., Abbott 1961, First, some scatter-hoarded seeds are probably Black 1969, Gashwiler 1970), but the manner recovered later in summer by foraging deer in which they scatter hoarded pine seeds in mice and are either eaten or recached else- this study suggests that they may, in fact, play where. This seemed to be the most common a positive role in the regeneration of some fate of eastern white pine seeds cached by forests. 2001] SCATTER HOARDING BY DEER MICE 113

ACKNOWLEDGMENTS GASHWILER, J.S. 1970. Further study of conifer seed survival in a western Oregon clearcut. Ecology 51:849–854. We thank Jennifer Armstrong, Lisa Cramp- HOWARD, W.E., AND F.C. EVANS. 1961. Seeds stored by prairie deer mice. Journal of Mammalogy 42:260–263. ton, Matthew Johnson, and Erin Vander Wall JAEGER, M.M. 1982. Feeding pattern in Peromyscus man- for their assistance in the field. This research iculatus: the response to periodic food deprivation. was supported by National Science Founda- Physiology and Behavior 28:83–88. tion grants DEB-9707098 and DEB-9708155 SANCHEZ, J.C., AND O.J. REICHMAN. 1987. The effects of conspecifics on caching behavior of Peromyscus leu- to the senior author. We thank the Whittell copus. Journal of Mammalogy 68:695–697. Board of Control for permission to conduct SULLIVAN, T.P. 1978. Lack of caching of direct-seeded the research at the Whittell Forest and Wild- Douglas fir seeds by deer mice. Canadian Journal of life Area. Zoology 56:1214–1216. TADLOCK, C.C., AND H.G. KLEIN. 1979. Nesting and food- storage behavior of Peromyscus maniculatus gracilis LITERATURE CITED and P. leucopus noveboracensis. Canadian Field-Nat- uralist 93:239–242. ABBOTT, H.G. 1961. White pine seed consumption by TANNENBAUM, M.G., AND E.B. PIVORUM. 1987. Variation in small mammals. Journal of Forestry 59:197–201. hoarding behaviour in southeastern Peromyscus. ABBOTT, H.G., AND T.F. Q UINK. 1970. Ecology of eastern Animal Behaviour 35:297–299. white pine seed caches made by small forest mam- VANDER WALL, S.B. 1992a. Establishment of Jeffrey pine mals. Ecology 51:271–278. seedlings from animal caches. Western Journal of BARRY, W.J. 1976. Environmental effects on food hoarding Applied Forestry 7:14–20. in deer mice (Peromyscus). Journal of Mammalogy ______. 1992b. The role of animals in dispersing a ‘wind- 57:731–746. dispersed’ pine. Ecology 73:614–621. BLACK, H.C. 1969. Fate of sown or naturally seeded conif- ______. 1993a. A model of caching depth: implications for erous seeds. Pages 42–52 in H.C. Black, editor, Pro- scatter hoarders and plant dispersal. American Natu- ceedings of the symposium on wildlife and reforesta- ralist 141:217–232. tion in the Pacific Northwest. School of Forestry, ______. 1993b. Cache site selection by chipmunks (Tamias Oregon State University, Corvallis. spp.) and its influence on the effectiveness of seed CALLAWAY, R.M., AND L.R. WALKER. 1997. Competition and dispersal in Jeffrey pine (Pinus jeffreyi). Oecologia facilitation: a synthetic approach to interaction in 96:246–252. plant communities. Ecology 78:1958–1965. ______. 2000. The influence of environmental conditions COGSHALL, A.S. 1928. Food habits of deer mice of the on cache recovery and cache pilferage by yellow genus Peromyscus in captivity. Journal of Mammal- pine chipmunks (Tamias amoenus) and deer mice ogy 9:217–221. (Peromyscus maniculatus). Behavioral Ecology 11: CRIDDLE, S. 1950. The Peromyscus maniculatus bairdii 544–549. complex in Manitoba. Canadian Field-Naturalist 64: ZAR, J.H. 1996. Biostatistical analysis. Prentice Hall, Upper 169–177. Saddle River, NJ. 662 pp. EISENBERG, J.F. 1962. Studies on the behavior of Per- omyscus maniculatus gambelii and Peromyscus cali- Received 18 November 1999 fornicus parasiticus. Behaviour 19:177–207. Accepted 10 April 2000 ______. 1968. Behavior patterns. Pages 451–495 in J.A. King, editor, Biology of Peromyscus (Rodentia). Amer- ican Society of Mammalogists, Lawrence, KS. Western North American Naturalist 61(1), © 2001, pp. 114–118

MICROHABITAT PARTITIONING BY TWO CHIPMUNK SPECIES (TAMIAS) IN WESTERN COLORADO

J. Jeffrey Root1, Charles H. Calisher1, and Barry J. Beaty1

ABSTRACT.—We examined microhabitat use of sympatrically occurring Tamias minimus (least chipmunk) and T. rufus (Hopi chipmunk) in a piñon-juniper/sagebrush vegetative community near Molina, western Colorado, from October 1994 to June 1999. This community is dominated by 2 major microhabitat types: shrub (sage; Artemisia spp.) and tree (pine and juniper; Pinus edulis and Juniperus scopulorum). Small mammals were live-trapped, marked, and released throughout this study. When it was the most abundant Tamias species on the study plots (1994–1997), Tamias minimus captures were associated with trees. Tamias rufus also exhibited this association but was captured at very low abundances during this period. Tamias rufus abundance was much greater, on average, than that of T. minimus between 1998 and 1999. During this time T. minimus captures were not associated with trees, but T. rufus captures remained associated with trees. As has been previously reported for other Tamias species, the greater abundance of 1 of 2 coexisting congeners in select areas may play a role in the microhabitat use of these 2 chipmunk species.

Key words: microhabitat, sympatric species, Tamias minimus, Tamias rufus, Mesa County, Colorado.

Microhabitat partitioning has long been energy chasing interspecifics out of its primary thought to contribute to the capacity of sym- habitat (Brown 1971). patric species of rodents to coexist, particu- Most microhabitat studies of rodents have larly in desert ecosystems (Price 1978). How- concentrated on open specialists vs. shrub ever, microhabitat associations have not been specialists (e.g., Price 1978), which appear to universally detected. For example, Thompson be the 2 most dominant microhabitat associa- (1982), Bowers (1988), and Jorgensen et al. tions for structurally simple desert ecosystems. (1995) failed to detect microhabitat associa- However, in more complex vegetative commu- tions (open specialists [i.e., primarily using nities, variations of the latter may exist. For ex- microhabitat with low-growing or no vegeta- ample, if one considers a community dominated tion] vs. shrub specialists) by certain species in by both shrubs and trees and arboreal and/or select vegetation types. semiarboreal/semiterrestrial mammal species, Competition may cause interspecific differ- microhabitat partitioning may be strikingly ences in selection of microhabitat in some different. rodent assemblages (Price 1978, Brown and We investigated the influence of growth Munger 1985) and may affect the home range forms of microhabitats on habitat patch use of size of some Tamias species (Trombulak 1985). coexisting T. minimus (least chipmunk) and T. Additionally, predation risk may affect forag- rufus (Hopi chipmunk) in a sagebrush/piñon- ing behavior of rodents (Pierce et al. 1992, juniper community in western Colorado. The Otter 1994) and may influence species compo- objectives of this study were to quantify cap- sition of communities of prey when risk differs ture rates of both species throughout the study among habitats (Kotler 1984). For example, plots, to quantify microhabitat types in which Otter (1994) found Tamias striatus to have these captures occurred, and to relate this in- shorter approach times to feed trays in the formation to the longitudinal coexistence of the open than to trays among forest cover. Further, 2 species. an interspecific dominance hierarchy may exist in Tamias communities (Chappell 1978, STUDY SITE AND METHODS Bergstrom 1992), and this can cause a dominant, aggressive species to waste time and A study site was established near Molina in

1Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523.

114 2001] MICROHABITAT PARTITIONING BY CHIPMUNKS 115 west central Colorado (Mesa County, 39°09′ even-numbered trap lines (i.e., 2, 4, 6, 8, 10, 45.8″N, 108°03′18.4″W). Calisher et al. (1999) and 12) were not utilized for microhabitat analy- provides a detailed summary of the natural ses. Therefore, only 230 of the total 290 trap history of this area. In general, sagebrush (Arte- stations were used for microhabitat analyses. misia spp.), piñon pine (Pinus edulis), and Rocky Mountain juniper ( Juniperus scopulo- RESULTS rum) dominate the vegetative community. Two trapping webs (Anderson et al. 1983) In 17,400 trap-nights from October 1994 to were established more than 500 m apart and June 1999, we recorded 320 Tamias captures were separated by an irrigation ditch. Each (T. minimus, n = 231; T. rufus, n = 89). Results trapping web consisted of 12 trap lines and 12 are presented for interspecific capture associa- trap stations per trap line. Trapping webs of tions, microhabitat associations, and relative this design are centered on a single trap sta- abundances. tion. Twelve 100-m trap lines radiated from We observed a difference in captures of the the central trap station at 30° angles from one 2 Tamias species by trap station. Of 230 total another. The first 4 trap stations were spaced 5 trap stations (i.e., trap stations used for micro- m apart, the remaining 8 trap stations 10 m habitat analyses), 118 captured chipmunks (all apart. We placed a single Sherman nonfolding, years). Eighty-six (73%) of the 118 trap sta- aluminum live-trap (23 × 8 × 9 cm) at each tions captured only a single chipmunk species. trap station. Traps were baited with a mixture Sixty-four trap stations captured only T. min- of rolled oats, cracked corn, and peanut butter imus, and 22 stations captured only T. rufus. and were sampled for 3, rarely 2, consecutive The remaining 32 trap stations captured both days and nights. species. Tamias minimus, the smaller species, Every 6 weeks from October 1994 to June tended to be captured at trap stations where T. rufus was absent more than expected (χ2 = 1999, rodents were trapped, sampled, and 7.9, P < 0.01, df = 1). released. However, trapping efforts generally Captures of T. minimus tended to be associ- ceased from December to March. Small mam- ated with trees more than expected (P < 0.01, mal processing was conducted according to Table 1) from 1994 to 1997; captures of T. rufus published protocols (Mills et al. 1995). The showed a similar pattern during that period (P minimum number known alive (MNA) was < 0.02, Table 1). However, when respective tabulated for both chipmunk species on each abundances of the 2 species shifted to a T. sampling occasion to estimate relative abun- rufus–dominated community (1998–1999, Fig. dances. These data were summarized with 1), T. minimus captures were no longer associ- SAS (SAS Institute 1988). ated with trees (P > 0.50, Table 1). Tamias rufus We characterized microhabitat into tree or captures remained associated with trees dur- nontree (generally shrub) categories. A trap ing this time (P < 0.01, Table 1). station was considered to fall within the tree Of 230 (2 webs with 115 utilized trap stations category if its radius was within 5 m of the each) trap stations, 114 had tree-covered micro- trunk or canopy of a tree that was a minimum habitat (Table 1). Most of the 116 nontree trap of 2.5 m in height. Trap stations in the nontree stations had shrub-covered microhabitats. category had no trees associated with them. However, a few (<10) trap stations had open These data were analyzed with chi-square tests, or grass-covered microhabitats. which were conducted with EPI 6.02 Software The mean MNA of T. minimus was greater (Centers for Disease Control and Prevention than that of T. rufus from 1994 through 1997 1997). Trap stations were densely positioned (Table 2). During 1998–1999 the MNA of T. within the center of the trapping web design rufus was greater, on average, than that of T. we utilized (i.e., the first 4 trap stations in each minimus (Table 2). Wide fluctuations of abun- trap line). Thus, in this small area multiple dances of both species were observed during trap stations could be classified potentially as the study (Fig. 1). tree sites from the occurrence of a single tree. To minimize this and to promote indepen- DISCUSSION dence of observations, the 1st and 3rd trap stations in odd-numbered trap lines (i.e., 1, 3, 5, Use and avoidance of microhabitats by 7, 9, and 11) and the first 3 trap stations in rodents are thought to be associated with many 116 WESTERN NORTH AMERICAN NATURALIST [Volume 61

TABLE 1. Association of captures of Tamias minimus and T. rufus (+ = species present, – = species absent) and trap- site microhabitat (+ = tree present, – = tree absent) in western Colorado.

Comparison/ ______Species vs. microhabitat time period Tree+ Tree– χ2 P T. minimus vs. microhabitata 1994–1997 T. minimus+ 59 26 20.0 <0.01 T. minimus–5590 1998–1999 T. minimus+ 9 6 0.3 >0.50 T. minimus– 105 110

T. rufus vs. microhabitata 1994–1997 T. rufus+ 7 0 5.4 <0.02 T. rufus– 107 116 <0.01b 1998–1999 T. rufus+ 33 14 9.0 <0.01 T. rufus– 81 102 aTest figures tabulated from number of trap stations with trees, number of trap stations without trees, number of T. minimus / T. rufus captures at trap sites with trees, and number of T. minimus / T. rufus captures at trap sites without trees. Multiple captures at the same trap site were not included in analyses. bFisher’s exact test P-value is furnished because a small expected cell size was observed in this comparison.

Fig. 1. Minimum number known alive (MNA; average of both sites) of Tamias minimus and T. rufus sampled within a sagebrush/piñon-juniper vegetation association in western Colorado, 1994–1999. factors, including risk of predation, inter- and In our study during 1998–1999, T. minimus intraspecific interactions, and differential re- showed no significant association with trees. source availability (Brown 1988, Kotler and Competition may have affected habitat use by Brown 1988, Bowers 1995). Thus, it is con- T. minimus once T. rufus became the more ceivable that the habitat used by a species may abundant species. Sheppard (1971) concluded not be the preferred habitat, especially if a that aggressive behavior of T. amoenus enabled superior competitor occupies the preferred it to exclude T. minimus from forested habitat. habitat type (Meredith 1976). Similarly, T. umbrinus may force T. minimus, Some habitat attributes (e.g., grassy areas at least partially, into open-overstory habitats and farmland away from wooded areas) have in north central Colorado (Bergstrom 1992). been thought to be inhospitable habitat for Thus, when T. rufus was relatively rare within certain chipmunk species (Bennett et al. 1994). the sagebrush/piñon-juniper community we 2001] MICROHABITAT PARTITIONING BY CHIPMUNKS 117

TABLE 2. Minimum number known alive of Tamias minimus and T. rufus sampled within a sagebrush/piñon-juniper vegetation association in western Colorado, 1994–1999.

______Species ______T. minimus ______T. rufus – – Time period x sx– range x sx– range 1994–1997 5.5 0.98 0–15 0.4 0.16 0–3 1998–1999 2.3 0.64 0–5 6.1 2.02 0–18 sampled, T. minimus may have been able to (Brown 1971, Bergstrom 1992). For example, exploit tree-covered portions of our study site foraging collection times of eastern chipmunks, more exclusively. However, the small, presum- T. striatus, increased in the presence of com- ably less aggressive T. minimus may have been petitors, due primarily to time spent alert or forced out of at least a portion of the trees dur- engaged in interactions with other individuals ing and after the increase in abundance of T. (Giraldeau et al. 1994). Brown (1971) noted rufus. Notably, Trombulak (1985) found that that when T. umbrinus was found in higher when T. townsendii was experimentally removed abundance than T. dorsalis, the situation actu- from his study area, the home range size of T. ally became disadvantageous for T. dorsalis amoenus increased considerably, but the 2 (the more dominant species) because it wasted species did not partition the environment based a great deal of time and energy on fruitless on any measured habitat attributes. chases of interspecifics. The low abundance of Tamias minimus is known to occur sym- T. rufus we observed from 1994 to 1997 may patrically with other species that occur only have allowed T. minimus to exploit tree-cov- parapatrically with one another (e.g., T. quad- ered microhabitats, but the increase in abun- rivittatus and T. umbrinus; Bergstrom and dance of T. rufus in 1998–1999 may have forced Hoffman 1991). Additionally, T. umbrinus and at least some T. minimus out of tree-covered T. dorsalis have been shown to occur together microhabitats. Tamias minimus, which range only in a very narrow strip of intermediate over more habitat types than any chipmunk in habitat (e.g., Brown 1971). Similarly, Sheppard Colorado, typically occupy areas on the edge (1971) determined that T. minimus was largely of escape cover (Fitzgerald et al.1994). Thus, confined to alpine habitat but also ranged into the seemingly better escape cover on the wooded portions of our study plots, compared subalpine forest, where its distribution nar- with open sagebrush areas, leads us to believe rowly overlapped that of T. amoenus. Heller that wooded portions of our study plots may and Poulson (1972) found that T. minimus be the most suitable habitat for both Tamias could be active in areas of hot, arid sagebrush species. However, the habitat used by a species by minimizing water loss and tolerating in- may not be its preferred habitat, especially if a creased body heat content through hyperther- superior competitor occupies the preferred mia and use of its burrows (Heller and Gates habitat type (Meredith 1976). This may be 1971). The aggressively dominant T. amoenus directly related to the relative abundance of a could exploit these areas only when patches of congener. shade were available from trees. Thus, the line of contact between T. amoenus and T. min- ACKNOWLEDGMENTS imus coincided with the lower limits of distribution of piñon pine (Heller and Poulson We thank R. Carns, E. Kuhn, S. Nabity, M. 1972). Aggression has not been selected for in Patterson, W.P. Sweeney, and many others for T. minimus because it is not metabolically fea- their assistance in our fieldwork, and Mr. and sible to engage in aggressive interactions in Mrs. R. Szczecinski for logistical support. the hot sagebrush desert (Heller 1971). Thus, Reviews and suggestions from B. Bergstrom when both T. minimus and T. rufus are well and 2 anonymous reviewers helped to improve represented within a given community, their earlier drafts of this paper. Funding for this sympatry may be limited to edges. work was provided by the U.S. Centers for Interspecific territoriality appears to be Disease Control and Prevention, Atlanta, GA, common among many chipmunk species under cooperative agreement U50/CCU81342D 118 WESTERN NORTH AMERICAN NATURALIST [Volume 61

-02-1. LITERATURE CITED HELLER, H.C. 1971. Altitudinal zonation of chipmunks (Eutamias): interspecific aggression. Ecology 52: 312–319. ANDERSON, D.R., K P. BURNHAM, G.C. WHITE, AND D.L. HELLER, H.C., AND D.M. GATES. 1971. Altitudinal zona- OTIS. 1983. Density estimation of small-mammal tion of chipmunks (Eutamias): energy budgets. Ecol- populations using a trapping web and distance sam- ogy 52:424–433. pling methods. Ecology 64:674–680. HELLER, H.C., AND T. P OULSON. 1972. Altitudinal zonation BENNETT, A.F., K. HENEIN, AND G. MERRIAM. 1994. Corri- of chipmunks (Eutamias): adaptations to aridity and dor use and the elements of corridor quality: chip- high temperature. American Midland Naturalist 87: munks and fencerows in a farmland mosaic. Biologi- 296–313. cal Conservation 68:155–165. JORGENSEN, E.E., S. DEMARAIS, AND S. NEFF. 1995. Rodent BERGSTROM, B.J., AND R.S. HOFFMANN. 1991. Distribution use of microhabitat patches in desert arroyos. Amer- and diagnosis of three species of chipmunks (Tamias) ican Midland Naturalist 134:193–199. in the Front Range of Colorado. Southwestern Natu- KOTLER, B.P. 1984. Risk of predation and the structure of ralist 36:14–28. desert rodent communities. Ecology 65:689–701. BERGSTROM, B.J. 1992. Parapatry and encounter competi- KOTLER, B.P., AND J.S. BROWN. 1988. Environmental het- tion between chipmunk (Tamias) species and the erogeneity and the coexistence of desert rodents. hypothesized role of parasitism. American Midland Annual Review of Ecology and Systematics 19: Naturalist 128:168–179. 281–307. BOWERS, M.A. 1988. Seed removal experiments on desert MEREDITH, D.H. 1976. Habitat selection by two para- rodents: the microhabitat by moonlight effect. Jour- patric species of chipmunks (Eutamias). Canadian nal of Mammalogy 69:201–204. Journal of Zoology 54:536–543. ______. 1995. Use of space and habitats by the eastern MILLS, J.N., J.E. CHILDS, T.G. KSIAZEK, C.J. PETERS, AND chipmunk, Tamias striatus. Journal of Mammalogy W. M. V ELLECA. 1995. Methods for trapping and 76:12–21. sampling small mammals for virologic testing. U.S. BROWN, J.H. 1971. Mechanisms of competitive exclusion Centers for Disease Control and Prevention, Atlanta, between two species of chipmunks. Ecology 52: GA. 61 pp. 305–311. OTTER, K. 1994. The impact of potential predation upon BROWN, J.H., AND J.C. MUNGER. 1985. Experimental the foraging behaviour of eastern chipmunks. Cana- manipulation of a desert rodent community: food dian Journal of Zoology 72:1858–1861. addition and species removal. Ecology 66:1545–1563. PIERCE, B.M., W.S. LONGLAND, AND S.H. JENKINS. 1992. BROWN, J.S. 1988. Patch use as an indicator of habitat Rattlesnake predation on desert rodents: microhabi- preference, predation risk, and competition. Behav- tat and species-specific effects on risk. Journal of ioral Ecology and Sociobiology 22:37–47. Mammalogy 73:859–865. CALISHER, C.H., W. SWEENEY, J.N. MILLS, AND B.J. BEATY. PRICE, M.V. 1978. The role of microhabitat in structuring 1999. Natural history of Sin Nombre virus in western desert rodent communities. Ecology 59:910–921. Colorado. Emerging Infectious Diseases 5:126–134. SAS INSTITUTE. 1988. SAS/STAT user’s guide. Release 6.0. CENTERS FOR DISEASE CONTROL AND PREVENTION. 1997. SAS Institute, Cary, NC. 378 pp. Epi Info 6: Version 6.02b. Atlanta, GA. 576 pp. SHEPPARD, D.H. 1971. Competition between two chip- CHAPPELL, M.A. 1978. Behavioral factors in the altitudinal munk species (Eutamias). Ecology 52:320–329. zonation of chipmunks (Eutamias). Ecology 59: THOMPSON, S.D. 1982. Microhabitat utilization and forag- 565–579. ing behavior of bipedal and quadrupedal heteromyid FITZGERALD, J.P., C.A. MEANEY, AND D.M. ARMSTRONG. rodents. Ecology 63:1303–1312. 1994. Mammals of Colorado. University Press of Col- TROMBULAK, S.C. 1985. The influence of interspecific com- orado, Niwot. 467 pp. petition on home range size in chipmunks (Eutamias). GIRALDEAU, L.A., D.L. KRAMER, I. DESLANDES, AND H. Journal of Mammalogy 66:329–337. LAIR. 1994. The effect of competitors and distance on central place foraging eastern chipmunks, Tamias Received 12 August 1999 striatus. Animal Behaviour 47:621–632. Accepted 17 March 2000 Western North American Naturalist 61(1), © 2001, pp. 119–123

POST-BREEDING SEASON MOVEMENTS OF COLUMBIA SPOTTED FROGS (RANA LUTEIVENTRIS) IN NORTHEASTERN OREGON

Evelyn L. Bull1 and Marc P. Hayes2

ABSTRACT.—Movements of Columbia spotted frogs (Rana luteiventris) were determined after breeding to provide managers with information on habitat requirements. We radio-tagged 47 adults and observed movements occurring with 22 frogs. Eleven frogs remained in breeding ponds, and 11 moved to other ponds or river stretches during spring and summer 1998. Distances frogs traveled to other water bodies ranged from 15 to 560 m. Movements appeared to be influenced by availability of habitat and aquatic conditions. Eleven of 16 frogs located within 100 m of other permanent water sources moved, while no frogs at an isolated breeding pond moved. Frogs moved to river stretches in July where water temperatures averaged 5.6°C cooler than ponds. Knowledge of Columbia spotted frog movements and habitat use in summer enables land managers to make decisions on activities that affect aquatic sites, vegetation, and stream structures that may influence frog populations.

Key words: Columbia spotted frog, movements, northeastern Oregon, Rana luteiventris, ranid.

The global decline of many amphibians has grazing, mining, and stream-altering activities created a crucial need for a comprehensive (Bull and Hayes 2000). Without knowledge of understanding of their ecology. For the Colum- R. luteiventris movements, unintentional dam- bia spotted frog (Rana luteiventris), informa- age can be done to important habitat through tion on habitat requirements, movements, and these management activities. For this reason activities during summer and overwintering is we focused on determining movements and especially sparse, and no data are available for the pattern of habitat use of R. luteiventris any population in Oregon. Considerable data during spring and summer in northeastern exist for breeding sites of some R. luteiventris Oregon. populations (Morris and Tanner 1969, Nuss- baum et al. 1983, Hovingh 1993), but few of METHODS these data provide insights about activities We monitored movements of radio-tagged outside the breeding season. In a classic mark- R. luteiventris between April and November recapture study, Turner (1960) reported sea- 1998 in northeastern Oregon. Frogs were cap- sonal movements of marked R. luteiventris in tured during egg deposition, or shortly after, Yellowstone National Park. In an unpublished in 6 permanent ponds used as breeding sites. study with radio-tagged spotted frogs in Idaho, All 6 ponds are in the upper Grande Ronde movements of substantial distances (>1 km) River watershed and are within 20 km of each away from breeding sites in summer, particu- other. Two ponds (ponds 1 and 2) are spring- larly by females, have been observed (David fed and are surrounded by grassland grazed Pilliod, Idaho State University, Pocatello, per- by cattle. Three of the ponds (ponds 3–5) were sonal communication). A further complication formed by mine tailings, are supplied with of determining movements is that despite the water from the hyporheic zone, have no graz- recent partitioning of spotted frogs into 2 ing, and have little ground vegetation sur- species, R. luteiventris may conceal as many as rounding them because of cobble from the 3 cryptic species (Green et al. 1997), which tailings. The last pond (pond 6), a spring-fed may exhibit different movement patterns. reservoir constructed for placer mining, is on a Rana luteiventris in northeastern Oregon ridge with sparse ground vegetation surround- exists in ecosystems influenced by a suite of ing the pond; no livestock grazing occurred management activities including timber harvest, here. Characteristics of the ponds vary (Table 1).

1Pacific Northwest Research Station, 1401 Gekeler Lane, La Grande, OR 97850. 2Washington Department of Wildlife, Olympia, WA 98501-1091.

119 120 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Pond depth changes by <25 cm during sum- 13% in other permanent ponds, 9% in river mer. Dates of egg deposition are variable, with stretches, and 6% in temporary ponds. Twenty- deposition at higher-elevation ponds occur- six females ranged from 59 to 91 mm SVL and ring at later dates (Table 1). The ponds are in, from 35 to 84 g; 21 males ranged from 58 to 74 or adjacent to, mixed-coniferous forest habi- mm SVL and from 22 to 41 g. Twenty-two (16 tats in Union County, and 5 ponds (ponds 1–5) females, 6 males) of 47 frogs were monitored are within 100 m of the Grande Ronde River for at least 28 days and up to 215 days, with a (Table 1). No ponds contain fish, although rain- mean of 83 days. Of the remaining frogs, 2 bow trout (Oncorhynchus mykiss) occur in the were not detected after initial capture, 1 died, Grande Ronde River. 1 was killed by a predator, 5 had transmitters Ponds were surveyed for frogs and egg removed due to abrasions, and 16 slipped their masses twice a week for a month following transmitters. Predominance of females being ice-melt. Number of egg masses was recorded monitored resulted from more males slipping and, when possible, adult frogs were captured. transmitters or having their transmitters re- Thirty-eight frogs were captured during the moved because of abrasions. breeding season, and 9 were captured after. A portion of the frogs left each of the 5 Frogs were sexed, measured (snout-vent length breeding ponds that were within 100 m of [SVL]), weighed, and fitted with a radio trans- other permanent ponds or the river (ponds mitter (model BD-2G, Holohil Systems Inc., 1–5), while no frogs left pond 6. Pond 6 was Ontario, Canada). Each frog was identified by isolated from other permanent water and was a 3-digit number preceded by M or F desig- larger than the other ponds (Table 1). Of 22 nating sex. Transmitters weighed 1.8 g, lasted frogs monitored 28 days or longer, 11 (8 females, 6 months, and had a range of 200–300 m. 3 males) remained in breeding ponds for the Each transmitter was glued to a 6-mm-wide summer, and 11 (8 females, 3 males) moved to satin ribbon that was fitted around the waist of other sites. Of the frogs that left breeding the frog (Bull 2000). ponds, 3 females moved to permanent ponds, We located the frogs once a week from April 4 females moved to the Grande Ronde River until November 1998, or until a frog slipped or a tributary, 1 male moved to both ponds the harness, the signal could not be detected, and the river, and 3 frogs (1 female, 2 males) or the harness was removed because of abra- moved to temporary ponds. All frogs that sions. We recorded date, type of site (tempo- moved to temporary ponds slipped transmit- rary or permanent pond or river), water tem- ters before the ponds dried, so their final loca- perature, and vegetation at each frog location. tions were unknown (Table 2). A higher pro- Each frog location was mapped to determine portion of radio-tagged frogs left the smaller the distance it traveled between successive breeding ponds (and left sooner after egg locations. Pond size or river/stream width, max- deposition) than left the larger ones (Table 1), imum water depth, elevation, distance to the although the relationship was not statistically river, distance to the nearest permanent pond, significant. and dominant vegetation were recorded at Six of 7 frogs that moved left ponds 3–5 and each pond or river stretch where frogs were traveled 22–434 m to 5 other ponds. Four of located. these 5 ponds were formed by mine tailings Paired t tests (Snedecor and Cochran 1980) and did not appear to have been used for were used to compare water temperatures at breeding based on an absence of eggs in the frog locations between the river and adjacent spring and of larvae in July as determined in a ponds. Using a Spearman’s rank correlation previous study by Bull and Hayes (2000). Ponds (Conover 1980), we determined the relation- to which the frogs moved were 100–250 m2 in ship between pond size and percent of frogs size and 40–100 cm deep, which was within leaving the breeding ponds. A significance level the size range of ponds they left (Table 1). of P < 0.05 was used. However, breeding sites were dominated by duckweed (Lemna minor), pondweed (Pota- RESULTS mogeton sp.), and buttercup (Ranunculus sp.), while ponds to which the frogs moved were We obtained 353 locations of 47 radio-tagged dominated by sedge (Carex spp.), mare’s-tail frogs, 72% of which were in breeding ponds, (Hippuris vulgaris), or cattail (Typha sp.). Ponds 2001] SPOTTED FROG MOVEMENTS 121

TABLE 1. Characteristics of 6 breeding ponds where Rana luteiventris were radio-tagged in northeastern Oregon, 1998. Characteristic Pond 1 Pond 2 Pond 3 Pond 4 Pond 5 Pond 6 Pond size (m2) 4132 630 86 224 264 28,526 Pond depth (m) 0.9 0.9 1.0 0.6 2.0 3.0 Vegetationa L L,P L R L P,T,E Distance to river (m) 90 27 12 30 55 1600 Distance to pond (m)b 720 2240 16 18 13 3600 Elevation (m) 1001 1240 1380 1380 1380 1810 Number of egg masses 39 843825 Egg laying initiation 30 Mar 18Apr 18 Apr 27 Apr 18 Apr 11 May Number of femalesc 521034 Number of malesc 101122 % females left pondd 40 100 100 — 100 0 % males left pondd 0 — 100 100 50 0 % all frogs left pondd 33 100 100 100 80 0 aDominant vegetation at the ponds was duckweed (L), pondweed (P), buttercup (R), cattail (T), and spike-rush (Eleocharis palustris) (E). bDistance between breeding ponds and nearest adjacent permanent pond. cNumber of female and male frogs monitored for ≥28 days at each pond. dPercent of radio-tagged females, males, and all frogs that left the breeding ponds.

to which the frogs moved lacked shallow water moved back toward their respective breeding sites with high solar radiation used as oviposi- ponds on 10 August, 31 August, and 28 Sep- tion sites. tember and were within 200 m of the breed- The 5 frogs that went to the Grande Ronde ing ponds when their transmitters failed. Only River or a tributary traveled 60–560 m from 1 frog that left the breeding pond was moni- ponds 1–5. Sites to which frogs moved along tored into November, and she did not return the river and tributary had cobble substrates, to that pond. no aquatic vegetation, and rapid water flow. All these sites were 8–15 m wide and 30–100 DISCUSSION cm deep, while the tributary was <1 m wide and 5–30 cm deep. Water temperatures at frog In this study frog movement appeared to locations on the river from July until Septem- be associated with proximity to the river or ber were significantly lower (x– = 14.8, s = 3.66) the nearest permanent pond, and with pond than those in the nearest breeding ponds at size. Frogs in ponds 3–5 were within 55 m of the same time (x– = 20.4, s = 4.28; t = –10.30, both the river and other permanent ponds, 22 df, P < 0.01). and we observed these frogs moving to the Frogs that left ponds 2–5 could travel along river and other ponds. The frogs at ponds 1 a riparian corridor. One frog that left pond 1 and 2 were within 90 m of the river but >600 traveled overland 400 m through relatively m from other permanent ponds; thus, these dry land in the floodplain covered in grasses frogs moved to the river or stayed in the breed- that had been grazed. Areas surrounding all ing pond. The largest ponds (ponds 1 and 6) breeding ponds had low ground vegetation, so had highest percentages of frogs remaining in frog movement was probably unhindered. the breeding pond. However, opportunities Timing of movements away from breeding for dispersal in pond 6 were limited because ponds varied with respect to the pond and the nearest body of permanent water was 1600 final frog location (Table 2). Frogs that went to m away through dense forest with an elevation other ponds typically left breeding ponds drop of 280 m. Larger ponds may provide ade- between late April and late May. Four of 5 quate resources for frogs to remain all year. frogs that went to the river did so between 7 Movements away from breeding sites may and 16 July. One frog went to a terrestrial result because conditions at breeding sites bank site next to the river in April for 2 weeks; become unfavorable or conditions away from her signal was not detected again. breeding sites become more favorable. Rea- Only 1 frog that left a breeding pond re- sons for leaving the breeding site may include turned to that pond (in mid-July). Three frogs elevated water temperatures, abundance of or 122 WESTERN NORTH AMERICAN NATURALIST [Volume 61

TABLE 2. Date that 11 Rana luteiventris moved from their breeding ponds, distance traveled, ultimate site to which frogs traveled, and number of days each frog was monitored in northeastern Oregon, 1998. Date frog left Distancea Number of days Pond/frog pond (m) Ultimate site monitored

POND 1 F260 23–26 Apr 480 Temporary pond 28 F320 28 Apr–5 May 183 River 48 POND 2 F242 30 Jun–6 Jul 60 River 109 F460 30 Jun–6 Jul 110 River 131 POND 3 F420 20–21 Apr 172 Permanent pond 53 M301 28 Apr–3 May 65 Temporary pond 73 POND 4 M118 28 Apr–3 May 15 Temporary pond 53 POND 5 F280 20–27 May 24 Permanent pond 215 F220 20–27 May 24 Permanent pond 115 F100 7–15 Jul 560 Tributary of river 140 M380 4–10 May 400 Ponds and river 108 aStraight-line distance between breeding site and the ultimate site to which frogs traveled.

vulnerability to predators, or food supply. Frogs response to drying of meadows and temporary that went to other ponds rather than the river ponds. Distances we reported were exceeded within a month of breeding encountered only by an individual R. luteiventris in Nevada warmer water than they would have in the that was recaptured 5 km from the original river. Frogs that left ponds in July all went to capture site 1 year later (Reaser 1996). Licht rivers, which had cooler water temperatures (1969) observed that female western spotted (averaged 5.6°C cooler than ponds). frogs (R. pretiosa) moved near breeding sites Movement away from breeding sites could during fall before winter hibernation in British provide frogs with a survival advantage if new Columbia. Three frogs in our study moved sites had fewer predators, better protection back near breeding ponds in fall, but we sus- from predators, more abundant food, or less pect at least some of them moved to breeding competition for food resources. Breeding ponds sites in spring as reported by Turner (1960). had a predominance of duckweed and sub- Movements of R. luteiventris that we ob- merged vegetation (pondweed and buttercup), served exemplify the need to protect permanent while 4 of 5 ponds to which frogs moved had a ponds and river and stream habitat within at predominance of emergent vegetation (sedges least 500 m of breeding ponds. We deter- and cattails). Emergent vegetation may have mined that pond size, proximity to other per- provided more cover from predators (mam- manent water, and water temperature were associated with frog movements. In particular, malian, avian, and reptilian) or better food additional research is needed to address the resources than submerged vegetation in breed- importance of predation or food supply in ing ponds. Quantification of predator abun- directing post-breeding movements of R. dance or food supply would be required to luteiventris. In addition, the effects of vegeta- address these hypotheses. tion manipulation and stream structures Distances we observed frogs traveling were (through livestock grazing, beaver [Castor similar to those reported for Rana luteiventris canadensis] activity, and human activity) on by Hollenbeck (1974) in south central Mon- use of these ponds and streams by R. luteiven- tana (41–553 m) and by Turner (1960) in Yel- tris during the summer warrant investigation. lowstone National Park (360–450 m). Turner (1960) observed 2 periods of movement: one ACKNOWLEDGMENTS in May that involved movements to breeding ponds, and another in July when frogs migrated David Pilliod and Kelly McAlister reviewed to a creek and other permanent water in an earlier draft of the manuscript. 2001] SPOTTED FROG MOVEMENTS 123

LITERATURE CITED LICHT, L.E. 1969. Comparative breeding behavior of the red-legged frog (Rana aurora aurora) and the west- BULL, E.L. 2000. Comparison of two radio transmitter ern spotted frog (Rana pretiosa pretiosa) in south- attachments on anurans. Herpetological Review 31: western British Columbia. Canadian Journal of Zool- 26–28. ogy 47:1287–1299. BULL, E.L., AND M.P. HAYES. 2000. The effects of livestock MORRIS, R.L., AND W. W. T ANNER. 1969. The ecology of the on reproduction of the Columbia spotted frog. Jour- western spotted frog, Rana pretiosa pretiosa Baird nal of Range Management 53:291–294. and Girard, a life history study. Great Basin Natural- CONOVER, W.J. 1980. Practical nonparametric statistics. ist 29:45–81. John Wiley & Sons, New York. NUSSBAUM, R.A., E.D. BRODIE, AND R.M. STORM. 1983. Amphibians and reptiles of the Pacific Northwest. GREEN, D.M., H. KAISER, T.F. SHARBEL, J. KEARSLEY, AND University of Idaho Press, Moscow. K.R. MCALLISTER. 1997. Cryptic species of spotted frogs, Rana pretiosa complex, in western North Amer- REASER, J.K. 1996. Rana pretiosa (spotted frog). Vagility. ica. Copeia 1997:1–8. Herpetological Review 27:196–197. SNEDECOR, G.W., AND W. G. C OCHRAN. 1980. Statistical HOLLENBECK, R.R. 1974. Growth rates and movements within a population of Rana pretiosa pretiosa Baird methods. 7th edition. Iowa State University, Ames. and Girard in south central Montana. Master’s thesis, TURNER, F.B. 1960. Population structure and dynamics of the western spotted frog, Rana p. pretiosa Baird & Montana State University, Bozeman. Girard, in Yellowstone Park, Wyoming. Ecological HOVINGH, P. 1993. Aquatic habitats, live history observa- Monograph 30:251–278. tions, and zoogeographic considerations of the spotted frog (Rana pretiosa) in Tule Valley, Utah. Great Received 2 August 1999 Basin Naturalist 53:168–179. Accepted 10 April 2000 Western North American Naturalist 61(1), © 2001, pp. 124–125

ACCIDENTAL MASS MORTALITY OF MIGRATING MULE DEER

Vernon C. Bleich1,2 and Becky M. Pierce1,2

Key words: accident, California, mule deer, mortality, Odocoileus hemionus.

Accidental deaths of mule deer (Odocoileus Jones (1954) speculated that fresh snow, hemionus) associated with anthropogenic causes which can mask glare ice, contributed to the are commonplace. Indeed, the literature is mortalities he reported; no fresh snow had replete with references to deer mortality asso- fallen prior to discovery of the deer carcasses ciated with roads and highways (Longhurst et during 1995. Snow, which is transformed to al. 1976, Pierce et al. 2000), fences (Papez ice by frequent thawing and freezing, occa- 1976), canals (Busch et al. 1984), and reser- sionally lasts through autumn at high elevations voirs (Reed 1981). Nevertheless, accidental (Jones 1954), and such would be expected deaths of deer from natural causes seldom are following winters of heavy snowfall. During identified or reported. Moreover, published 1952–1999 mean snow depth at Bishop Pass accounts of death assemblages of contempo- was 227 cm (s = 92 cm). In April 1952, prior rary large mammals are uncommon (Berger to the incident described by Jones (1954), 1983; see, for example, Jones 1954 and Swift snow depth was 297 cm, or 131% of the long- et al. 2000). term mean. Depth of snow at Bishop Pass in Jones (1954) described a situation near April 1995 (399 cm) was 176% of the long- Bishop Pass, Inyo County, California, in which term mean, consistent with the notion that ≥26 mule deer lost their footing and slid down snow that fell the preceding winter contribu- a snow-covered ice field to their deaths. ted to the deaths by persisting through fall Bishop Pass (elevation 3680 m) is a primary migration. From 1952 to 1999, April snow depth migration route used annually by mule deer was ≥297 cm during 12 years, suggesting that that spend summers west of the Sierra Crest accidental deaths of migrating deer may occur and winters east of the crest in Round Valley at Bishop Pass with some regularity. (Kucera 1992), Inyo and Mono counties, a The dead deer were reported to us over sev- major deer winter range typical of the western eral days by numerous individuals, all of whom Great Basin (Pierce et al. in press). On 25 expressed concern about population-level im- November 1995 we received a report of pacts should additional deaths occur. Because “numerous dead deer” just below Bishop Pass, of strong public interest and the potential for Inyo County. Upon investigation, we discov- additional losses, we proposed using hand ered the remains of 16 recently dead mule tools to enhance the trail across the ice and deer (12 males, 4 females) and observed 1 then covering the trail with sand to increase injured female in the same location described traction for other deer migrating to Round by Jones (1954). The carcasses were on a talus Valley. Permission to implement this strategy slope at the bottom of a steep, ice-covered was denied by wilderness staff from the Inyo hillside (Fig. 1). The deer apparently lost their National Forest because it would conflict with footing on the ice, which had repeatedly “natural processes” in wilderness. thawed and frozen in the summer sun, and slid to their deaths on the sharp rocks below. We thank J. Ostergard, J. Davis, and D. Based on differential levels of scavenging, it Racine for providing assistance in the field, and appeared that the dead animals were from ≥2 J. Berger for discussions of death assemblages groups. of contemporary large mammals. Funding for

1California Department of Fish and Game, 407 W. Line St., Bishop, CA 93514. 2Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK 99775.

124 2001] NOTES 125

Fig. 1. Remains of migratory mule deer that fell to their deaths when they slipped while crossing an ice-covered hillside near Bishop Pass, Inyo County, California, November 1995.

research on migratory mule deer in Round JONES, F.L. 1954. An unusual cause of deer mortality. Valley was provided by the California Depart- Journal of Wildlife Management 18:142. KUCERA, T.E. 1992. Influences of sex and weather on ment of Fish and Game (CDFG), Safari Club migration of mule deer in California. Great Basin International, Mule Deer Foundation, Califor- Naturalist 52:122–130. nia Deer Association, National Rifle Associa- LONGHURST, W.M., E.O. GARTON, H.F. HEADY, AND G.E. tion, Friends of the National Rifle Association, CONNOLLY. 1976. The California deer decline and Fish and Game Advisory Committee of Inyo possibilities for restoration. Proceedings of the West- ern Section of the Wildlife Society 18:74–103. and Mono Counties, University of Alaska Fair- PAPEZ, N.J. 1976. The Ruby-Butte deer herd. Nevada banks, and the University of California White Department of Wildlife Biological Bulletin 5:1–61. Mountain Research Station. This is a contribu- PIERCE, B.M., V.C. BLEICH, AND R.T. BOWYER. 2000. Prey tion from the CDFG Deer Herd Management selection by mountain lions and coyotes on mule Plan Implementation Program and is Profes- deer: effects of hunting style, body size, and reproductive status. Journal of Mammalogy 81:462–472. sional Paper 019 from the Eastern Sierra Cen- PIERCE, B.M., R.T. BOWYER, AND V.C. BLEICH. In press. ter for Applied Population Ecology. Habitat selection by mule deer: forage benefits or risk of predation by mountain lions? Journal of Wild- LITERATURE CITED life Research. REED, D.F. 1981. Conflicts with civilization. Pages 509–535 in O.C. Wallmo, editor, Mule and black-tailed deer of BERGER, J. 1983. Ecology and catastrophic mortality in wild horses: implications for sociality in fossil assem- North America. University of Nebraska Press, Lincoln. blages. Science 220:1403–1404. SWIFT, P.K., J.D. WEHAUSEN, H.B. ERNEST, R.S. SINGER, AULI INDE OCKE AND LEICH BUSCH, D.E., J.C. RORABAUGH, AND K.R. RAUTENSTRAUCH. A.M. P , H. K , T.E. R , V.C. B . 1984. Deer entrapment in canals of the western 2000. Bighorn sheep die-off due to suspected type C United States: a review of the problem and attempted botulism in southern California. Journal of Wildlife solutions. Pages 95–100 in P.R. Krausman and N.S. Diseases 36:184–189. Smith, editors, Deer in the Southwest: a workshop. Arizona Cooperative Wildlife Research Unit and Received 29 November 1999 School of Renewable Natural Resources, University Accepted 28 December 1999 of Arizona, Tucson. Western North American Naturalist 61(1), © 2001, pp. 126–127

BOOK REVIEW

Biology and Management of Noxious Range- the West according to land ownership. Chap- land Weeds. Roger L. Sheley and Janet K. ter 2 adequately discusses basic principles of Petroff, editors. Oregon State University noxious weed mapping and explains why accu- Press, Corvallis. 1999. $32.95, softcover; rate maps are critical in developing a success- 438 pages. ISBN 0-87071-461-9. ful weed management plan. Coordinated weed management planning is the topic of Chapter Invasive plant species (aka noxious weeds) 3, which provides a satisfactory discussion of have been described as one of the most seri- why human behavior and attitudes are more ous threats to the integrity and productivity of often barriers to developing and implementing our nation’s landscape. Successful manage- weed management plans than lack of technical ment of noxious weeds is an extremely com- expertise. Chapter 4, a discussion of economic plex process due to numerous biological and procedures for evaluating weed management anthropogenic constraints. This book provides actions, is directly related to Chapter 6 (Pre- a thorough overview of our current knowledge vention) and Chapter 7 (Early Detection and concerning the biology and management of Eradication), primarily because the most eco- noxious rangeland weeds. The book’s geo- nomical (and ecologically efficient) way to deal graphic range is stated as encompassing 15 with noxious weeds is to apply prevention and states and 4 Canadian provinces in western early eradication measures. Chapter 5 outlines North America. It is co-authored by 52 indi- 4 phases of an integrated weed management viduals from universities, private industry, and program, discusses the rationale behind main- state, federal, and county agencies or organi- taining “weed resistant” plant communities, zations. Twenty-nine of the contributors are and features 2 ecologically based models that employed in the northwestern U.S. (Idaho, predict outcomes of various integrated weed Montana, Oregon, Washington), which proba- management strategies. Apt discussions on bly reflects the editors’ regional collegial net- several weed management tools (i.e., grazing work. The authors and editors are to be com- management, biological control, herbicides, and mended for making diversity in writing style revegetation techniques on disturbed land) are and content a strength rather than a weakness covered in the final 4 chapters (8–11) of Sec- of the book. tion I. Mechanical or physical control as a weed The book is divided into 2 main sections. management tool apparently did not warrant a Section I, titled “Theory and Practice of Weed separate chapter in Section I, but it is dis- Management,” provides a primer on the general cussed where appropriate in Section II, which principles of weed management and includes covers individual weed species. Adequate ref- 11 chapters that should assist managers in erences appear at the end of most chapters in developing weed management plans. Chapter Section I for those who want to delve deeper 1 takes a systems approach in explaining the into the area under discussion; exceptions are ecologic (i.e., ecosystem structure, function, Chapter 3 (Coordinated Planning, where only and organization) and economic (micro- and 6 references are cited), Chapter 4 (Economics, macro-) impacts of noxious weeds. It may be only 3 references cited), and Chapter 6 (Preven- the most intriguing chapter of the book except tion, no references cited). for a confusing statement about cattle num- Section II, “The Weeds,” consists of 25 bers presently being at “close to record highs on chapters that cover individual weed species many western rangelands.” The phrase, “many characterized by the editors as “. . . the most western rangelands,” needs to be defined be- serious noxious weed species in the western cause trends in cattle numbers vary throughout United States.” Section II actually covers at

126 2000] BOOK REVIEW 127 least 32 species when you consider that 2 presented in the middle of the chapter on species of “snakeweed” (i.e., Gutierrezia saroth- biennial thistles. More logical locations for the rae and G. microcephala) and 3 species of photos would have been either immediately “whitetop” (i.e., Cardaria pubescens, C. chalapa, before (or immediately after) Section II, or and C. draba) are discussed in those respec- within the appropriate chapters on the indi- tive chapters. Each of Section II’s chapters vidual weed species. Photos of the individual typically provides a concise, yet informative species vary greatly in quality and are pre- review of a plant’s origin, history, identifying sented as a mixed assortment of close-up and features, biology, ecology, impacts, invasion landscape views. Scientific names are not potential, specific management options, and listed under each photo, only common names, distribution in the western U.S. The manage- which is an unfortunate omission because ment options section of each chapter will be common names are often used to refer to any especially useful in helping land managers number of plant species (e.g., whitetop). determine species- and site-specific manage- Third, although the back cover indicates that 4 ment tactics and strategies for weed species provinces are included in the book’s geo- that may occur in their area. Distribution maps graphic range, Canadians will be disappointed in each chapter will be especially useful to to find only 15 western U.S. states shown on U.S. managers because the maps provide a each weed distribution map. Finally, chapters county-by-county snapshot of weed distribu- in Section II are arranged alphabetically; I tion across 15 western states and show the would have preferred botanical organization. imminent potential for invasion throughout These problems aside, the 1st edition of the region. Most figures, tables, and illustra- this book will undoubtedly serve as a baseline tions are comprehensible and easy to read. An from which to evaluate “the way we were” ample reference section is provided at the end near the end of the 20th century with regard of each chapter in Section II for those who to noxious weed distributions in the western want to learn more about a particular weed U.S., and our state of knowledge of invasive species. plant management. Hopefully, there will be Section II is not completely without prob- additional editions forthcoming that will build lems, however. First, including a chapter on on the material presented in this original work. “snakeweeds” seems inappropriate when one Subsequent editions could serve as a steady considers the 3 ways that noxious weeds are source of new knowledge on invasive plant classified in the introductory chapter. To wit, issues, a topic that will surely continue to noxious weeds are (1) . . . foreign organisms— receive considerable attention for many years the invaders—of forest and rangeland; (2) to come. The book’s back cover hits the mark legally, . . . any plant designated by a federal, in describing the current effort: “An invaluable state, or county government to be injurious to resource for land managers, resource special- public health, agriculture, recreation, wildlife, ists, and students of natural resource manage- or any public or private property; or (3) . . . ment.” With regard to the last point, I recently those weeds that have invasive characteristics, used this book as a text in a capstone indepen- regardless of whether they have been legally dent study course designed for a senior level designated “noxious” at some government level. undergraduate student. I also plan to use it for Only the last classification appears to fit the 2 a graduate seminar course and as an important snakeweed species discussed in the book, and resource for developing extension and out- even then, these native species do not seem to reach programs. I recommend this book to all have near the invasive potential of the other who are interested in learning more about the nonnative species covered in Section II. Sev- Biology and Management of Noxious Range- eral invasive plant species that occur primarily land Weeds. or exclusively in the southwestern U.S. (e.g., African rue, buffalograss, camelthorn, Lehmann Larry D. Howery lovegrass, malta starthistle, red brome, salt 325 Biological Sciences East Building cedar, sweet resin bush) could have effectively School of Renewable Natural Resources replaced the snakeweed chapter. Second, color University of Arizona photographs of 29 noxious weed species are Tucson, Arizona 85721 Announcement and Call for Papers and Posters

GICAL RESEA LO RC IO H B C N O GREAT BASIN BIOLOGICAL I N S F A E B R RESEARCH CONFERENCE T E A N E C R E October 11–13, 2001 G

O Brigham Young University

T A

O Provo, Utah T

V 1

O Brigham Young University will host

3 P

- the Great Basin Biological Research Con-

Y 0

T 1 I

R ference on October 11–13, 2001. The con-

G V

M G Y N O U ference will feature contributed presentations and posters, keynote speakers, and round- table discussions related to the biological study and management of the Great Basin biota. Scientists, students, and professionals working on research relating to the Great Basin are invited to attend. Acceptance of submitted posters and presentations will be based on technical and scientific merit, as well as their contribution to present knowledge of biological systems, processes, and management practices in the Great Basin. Abstracts must be fewer than 250 words and submitted by July 13, 2001. Electronic submissions are encouraged via the conference website: bioag.byu.edu/mlbean/gbbrc. Papers will be allotted 12 minutes each, with an additional 3 minutes for questions (15 minutes total). Presentations may use a variety of media: 2 × 2 slides, overhead projection, and Microsoft PowerPoint. Posters are allotted 5′× 6′ maximum size. Registration Early registration (until August 17, 2001) $65 Late registration $85 Early student registration $40 Late student registration $55

Make registration checks payable to Great Basin Biological Research Con- ference. Credit card payments (VISA and MasterCard only) are also accept- able. For further information, contact Great Basin Biological Research Confer- ence, 290 MLBM, Brigham Young University, Provo, UT 84602 (phone 801- 378-5052, FAX 801-378-3733); also, Douglas C. Cox (801-378-6355 or e-mail: [email protected]).

Remember, abstract deadline for papers and posters is July 13, and early registration deadline is August 17, 2001.