Riparian Plants in the Southwestern United States

Phenology and Stand Composition of Woody Riparian Plants in the Southwestern United States

Item Type Article

Authors Brock, John H.

Publisher University of Arizona (Tucson, AZ)

Journal Desert Plants

Download date 07/10/2021 05:55:16

Link to Item http://hdl.handle.net/10150/554241 Brock Riparian Plants 23 species were observed monthly (bimonthly in summer) at six Phenology and Stand sites in eastern Arizona and New Mexico. Phenologi- cal events were placed into eight categories for data collection. Stand composition data was collected from four randomly lo- Composition of Woody cated macroplots at each site in the summer of 1983. Weather data for the period of study was summarized for the region. Riparian Plants in the Four general phenology groups were identified: 1) spring flowering and fruit dispersal as characterized by Fremont cotton- Southwestern United wood (Populus fremontii) and Goodding willow (Salix gooddingii), 2) Spring flowering/autumn -winter fruit dispersal characterized by box elder (Acer negundo var. interius), netleaf States hackberry (Celtis reticulata), Arizona sycamore (Plantanus wrightii), and velvet ash (Fraxinuspennsylvanica ssp. velutina), 3) Spring flowering and late summer fruit dispersal demon- strated by Arizona walnut (Juglans major), and 4) Multidate flowering and fruit dispersal displayed by velvet mesquite (Prosopis velutina). Fremont cottonwood and Goodding willow dominated the sites, while netleaf hackberry, box elder, velvet ash and Arizona walnut were minor components of the John H. Brock stands. Variation in phenology of the tree species reflected in- Professor dividual species adaptations to the particular environment. School of Agribusiness and Environmental INTRODUCTION Resources A riparian plant community is one that occurs in or adjacent to Arizona State University a stream and/or a stream's floodplain, or on a site where soil water is not limiting during most of the year, and is character- Tempe, Arizona 85287 -3306 ized by species and growth forms different than those of the surrounding uplands. Although riparian habitats represent about 1% of the lands in the western United States (U.S. GAO 1988), they are extremely important for ecosystems because they provide niches for wildlife (Johnson and Lowe, 1985; Thomas et al., 1979), maintain water quality (Lowrence et al., 1985), and contribute to landscape aesthetics.

Since the early 1800's, riparian habitats in the arid southwest United States have undergone significant biological and hydro- logic changes (Carothers, 1977). This occurred because agricultural expansion and electrical power generation were con- sidered necessary to develop the west. To achieve these goals, Funding was supplied in part by the U.S. Bureau of Reclama- river "taming" by reservoir construction was given high prior- tion through the U.S. Forest Service, Rocky Mountain Forest ity (Parker et al., 1985). As the result of many diverse land and Range Experiment Station in Tempe, AZ. During the study uses, riparian vegetation has declined since European man's the author carried an IPA arrangement with the Forest Service entry to the southwest (Almand and Krohn, 1978; Fox, 1977; and Arizona State University. I wish to thank students who Jones et al., 1977 and Brown, 1982). It is estimated by the Ari- helped in some stage of data collection; Dennis Pope, Richard zona Riparian Council, that only about 10% of the original Siegel, Anthony Moreland, Terry Dean, Lorenzo Espinosa, and Arizona riparian habitats remain in their natural form. Chris Brock. Appreciation also to Leonard DeBano, David Patton and Marty Jakel for peer review of the manuscript. The maintenance of a riparian plant community is dependent on the regeneration of desirable trees, shrubs and herbaceous Keywords: Ecology, cottonwood, willow, mesquite, sycamore plants. Successful regeneration is in turn, dependent on the phenology of major riparian species fitting environmental and ABSTRACT site conditions. Phenology has been described as being the study Knowledge of phenology is important for understanding the of the relationship between climatic factors and periodic growth autecology of a species. Information concerning flowering dates, events in organisms (Daubenmire, 1974). leaf development, seed/fruit dispersal, and aberrant weather effects on phenological status of a species should be well uti- It became clear that little was known about the phenology of lized by persons interested in the ecology, management and res- most of the woody riparian plants when a project was being toration of riparian communities. The phenology and stand com- developed to study the factors influencing the development and position of key woody species from selected riparian areas of maintenance of riparian plant communities in the desert south- the southwestern United States was studied. Eight riparian tree west. Limited information existed as to when some species may 24 Desert Plants 11(1) 1994 germinate and the number of seeds produced (USDA, Forest The tree species under study were arranged into groups having Service, 1974), but phenology information was lacking. The similar phenological development. Four groups resulted, includ- objective of this paper is to report on the phenology and stand ing: 1) spring flowering and fruit dispersal, 2) spring flower - composition of key woody riparian species common to the south- ing/autumn- winter fruit dispersal, 3) spring flowering and late western United States. summer fruit dispersal, and 4) multidate flowering and fruit dispersal. METHODS Study Site Locations Weather Data Three study locations were used to collect phenology data. One Weather data were summarized from U.S. Weather Service re- study location was near Clifton, Arizona on the San Francisco ports (USDC, National Oceanic and Atmospheric Administra- River. The other two locations were in western New Mexico on tion 1982, 1983, 1984) from reporting stations at Clifton, AZ the Gila River near the towns of Red Rock and Cliff/Gila (Fig- from Red Rock, and Silver City, NM. Precipitation, and tern - ure 1). Six specific study sites were established, two at each perature data were averaged to develop a characterization of location. At each location, one site was near a proposed reser- the regional weather. Average monthly normal precipitation were voir dam site with a similar upstream site which would have computed for the study locations and compared to the observed been inundated after construction. The potential reservoir sites monthly precipitation. Precipitation and air temperature data were known as the Quail Springs, Conner, and Hooker for the are reported beginning with January 1982 to provide informa- Clifton, AZ and the Red Rock and Cliff/Gila,NM locations re- tion about antecedent weather that could influence species phe- spectively. The Quail Springs sites were about 6.4 and 20.9 km nology as observed beginning in May 1982. Air temperature upstream from Clifton, AZ for the dam and inundation areas data were reported as average monthly maximums and mini- respectively. The Conner dam study site was 1.6 km from the mums for the three locations. Monthly maximum and mini- geographical location of Red Rock, NM. The inundation site mum air temperatures were also averaged to permit interpreta- was just north of the "Gila Box" and the "Bird Management tion of the duration or onset of significant phenological events Area" designated by the U.S. Forest Service, approximately 17.7 that could be altered, e.g., by freezes or uncharacteristically warm km upstream from Red Rock, NM. The Hooker dam and inun- weather. dation study sites were upstream approximately 9.6 and 14.1 km from the townsites of Cliff/Gila, NM (Figure 1). Approxi- RESULTS AND DISCUSSION mate elevations for the six study sites are: 1) Quail Springs Stand Composition dam site, 1067 m; inundation site, 1103 m; 2) Conner dam site, Fremont cottonwood and Goodding willow were the most com- 1219 m; inundation site, 1249 m; and 3) Hooker dam site, mon trees in the riparian gallery forests occupying the six study 1341m; inundation site, 1463 m. Average elevations were 1085, sites on the San Francisco and Gila rivers. Combined, these 1249 and 1402 m above sea level for the Quail Springs, Conner trees had an average relative density of 53.8% and a relative and Hooker study locations respectively. dominance of 61.1% (Table 1). Velvet mesquite and Arizona sycamore were also common having 16.8 and 13.1% relative Stand Composition density respectively. The importance of Arizona sycamore in Phenology data were collected from mature gallery forests along riparian forests is illustrated by its relative dominance of 16.1%, the perennial streams. At each study site, four randomly lo- compared to only 2.3% relative dominance for velvet mesquite. cated belt transects (25 x 4 m) provided macroplots in which This occurs because Arizona sycamore trees are large with a the number of trees were counted. Density (number/ha), rela- mean dbh of 24.9 cm compared to 3.4 cm dbh for the smaller tive density ( %), mean dbh (cm) and relative dominance ( %) velvet mesquite trees. (based on basal area) were calculated for the tree species. Plants with a diameter at breast height (dbh) of >1.0 cm were recorded Netleaf hackberry, box elder, velvet ash, and Arizona walnut as trees, those with a dbh of <1.0 cm as seedlings. were scarce on the study sites (Table 1). On three sites, very few of these species were present and did not occur within the belt Phenology Data Collection transects. However, all eight species were found at the sites used Data on phenological stages were collected monthly from Sep- to observe phenology. Alligator juniper (Juniperus deppeana), tember through April and biweekly from May through August catclaw (Acacia greggii), and soapberry (Sapindus saponaria from May 1982 to May 1984. Phenology was recorded into eight var. drummondi) occurred in some belt transects, but their corn - categories including: dormancy, bud break, leaf expansion, flow- bined relative density was less than 10 %. Alligator juniper was ering, mature leaves, fruit development, leaf senescence and a common understory species in stands dominated by mature fruit dispersal. Information was gathered to provide estimates Fremont cottonwood or Arizona sycamore probably because of the initiation and termination of phenological events. Phe- roosting birds disseminated the seeds. nology data were averaged for the three study locations and the six individual study sites. Phenological data were collected from There was no seedling reproduction in the gallery forests by the following trees: Fremont cottonwood (Populus fremontii), obligate riparian tree species, such as Fremont cottonwood, Arizona sycamore (Plantanus wrightii), Arizona walnut (Juglans Goodding willow, Arizona sycamore, and box elder. Seedling major), Goodding willow (Salix gooddingii), netleaf hackberry regeneration of obligate riparian tree species, such as velvet (Celtis reticulata), box elder (Acer negundo var. interius), vel- ash and Arizona walnut was observed in the gallery forests, vet mesquite (Prosopis velutina), and velvet ash (Fraxinus although they were not found in the belt transects. Seedling pennsylvanica ssp. velutina) (Lehr, 1978). regeneration of the obligate riparian trees occurred mainly on Brock Riparian Plants 25

ALMA

Ft*n6\sco ÇATRON_ COUNTY OuAIL SPRINGS s GRANT COUNTY HOOKER Q

1 CLIFTON l °4 94. CLIFF GILA

OI SAFFORD CONNER ,/ Silver City DUNCAN RED ROCK

STUDY SITE SYMBOLS: DAM wiI INUNDATION

Figure 1. Study site locations (6) in eastern Arizona and western New Mexico utilized in the study of the phenology of eight riparian tree species.

Density Relative dbh Relative Species (N/ha) Density ( %) (cm) Dominance( %)

Fremont Cottonwood 73 30.0 59.2 39.5 Goodding Willow 58 23.8 32.3 21.6 Velvet Mesquite 41 16.8 3.4 2.3 Arizona Sycamore 32 13.1 24.9 16.6 Netleaf Hackberry 23 9.4 2.6 1.7 Box Elder 8 3.2 11.4 7.6 Arizona Walnut 5 2.0 11.5 7.7 Velvet Ash 3 1.2 4.3 2.9

Total 99.5 99.9

Table 1. Mean density (number/ha), relative density( %), diameter at breast height [dbh(cm)], and relative dominance ( %) of woody riparian species in gallery forests on six study sites along the San Francisco and Gila Rivers of eastern Arizona and western New Mexico. 26 Desert Plants 11(1) 1994 nursery bars as has been reported by Brady et al. (1985) and Goodding willow broke bud approximately a month later than side channels within active streambeds (Brock, 1984). In the Fremont cottonwood, flowered rapidly, expanded its leaves and gallery forests, seedlings of facultative riparian species, velvet dispersed its seeds by late -May and early -June (Figure 5). Ma- mesquite and netleaf hackberry were found in the belt transects ture leaves remained on the trees until mid- October. Both Fre- where they occurred at mean densities of 240 and 38 plants/ha mont cottonwood and Goodding willow produce large numbers respectively. At three ofthe six study sites, no seedlings of these of seeds. Generally, seed viability for these two species is re- species were found in the belt transects. ported to be about six weeks under laboratory conditions (Fenner et al., 1984; Seigel and Brock, 1989) and is speculated to be less Weather under natural conditions. For successful regeneration of these Average monthly precipitation in 1982 was nearly normal, ex- species by seed, a moist seedbed must be available at the time of cept for October being very dry (Figure 2). Average monthly seed dispersal. precipitation, for the three study locations, in 1983 was above normal. The autumn of 1983 was unusually wet and most streams flooded in early October. Winter precipitation in 1984, FREMONT COTTONWOOD preceding the fmal phenology evaluations was below normal, Populus fremontii especially during the first three months.

Phenological stages, influenced by weather, are controlled mainly by air temperatures, especially freezing. Average normal air temperature varied about 20 °C from winter to summer (Figure 3). Monthly average maximum temperatures, over the study period, ranged from about 12 to 35 °C, for December to July 1982. Monthly average minimum air temperatures ranged from about -4 °C in February 1984 to 18.5 °C in August 1982. However, the phenology ofthe study trees were controlled mainly by the extremes in air temperature, especially freezing. Pheno- logical events were interrupted in late -April to early -May 1983 by a late spring frost. An average monthly minimum temperature for the three study locations was calculated to be -2.5 °C for April 1983 (Figure 4). Cold weather damaged the flowers and tender leaves of plants having early bud break dates which re- GOODDING WILLOW duced fruit/seed yield of those species in 1983. When compar- Saliipooddingii ing year differences, the average minimum temperatures for the winter of 1983 -84 were lower than those of 1982 -83. How- ever, low temperatures did not effect the phenology of the trees because they were dormant.

Phenology Phenological events for the eight riparian tree species had a one to two week variation from starting to ending date depending on weather conditions and elevation. Generally, phenological events for riparian trees on the San Francisco River in Ari- zona were earlier than those at higher elevations on the Gila River. Variations of air temperature and/or precipitation was believed responsible for the difference in plant responses.

Spring Flowering and Fruit Dispersal LEAF SENESCENCE DORMANCY Fremont cottonwood and Goodding willow were placed in the BUD BREAK category of spring flowering and fruit dispersal. Fremont cot- LEAF EXPANSION tonwood initiated bud break between late -February and early - onMATURE LEAVES March (Figure 5). Following bud break, flowering and leaf expan- FLOWERING sion began with mature leaves by late -May as indicated by a FRUIT DEVELOPMENT color change from light to dark green. Seed dispersal followed MI SEED DISPERSAL flowering within about two weeks, ranging from late -April to late -May depending on the elevation. Mature leaves began Figure 5.Sequence and duration of phenological stages senescing in late- September and began abscission in mid -Octo- throughout the yearfor spring flowering and fruit dispersal ber when minimum air temperatures of 0 °C are approached. plants: Fremont cottonwood and Goodding willow, averaged for three locations in eastern Arizona and western New Mexico. Brock Riparian Plants 27

Average Precipitation (3 Locations) - - - .Average Normal Precipitation (3 Locations) 8-

1 1 1 1 1 I I I I 1 I 1 1 I II 1 I I I 1 1 1 1 I I I 1 JF M A MJ JA S ON D¡J F MA MJ J A SO ND F M A M

1982 1983 1984 Figure 2. Average normal and average monthly precipitation (cm) (1982, 1983 and through May 1984) for study sites of phenology of riparian tree species on the San Francisco and Gila rivers in eastern Arizona and western New Mexico.

Avian. Maximum T.mpaaur.s Manna Maximum Tanpaatums Awning Minimum Temperatures Ave.'s' Norma Tarlp.ruwrue - - Malaga Minimum Tanp.raursa 40

40 -

30 -

i " `, , / ', i ,¡ 20 / It . / - / 1t // ' ; ' / /'i / 1 / 1 ; t 1 i , / / 1 10 1 :/ 1 ; / 11 / \ / t i / 1 ." ' I 1 ' / 1 / / 1 / 1 / T T 7 Ì i- // \\ 1 / -I / \ / i1 \/'/ \L- 1 / 1 0 \ \ / \L /f- \/ \ i ///

-5 ,/ 10 J F M A M J J A S O N O Ì J F M A M J J A S O N D¡ J F M A M J F M A M J J A S O N M A M J J A S O N D J F M A M

1982 1983 1984 1982 1983 1984

Figure 3. Monthly average maximum and minimum air tern- Figure 4.Average temperature (C) extremes (maximum and peratures (C) for three riparian woody plant phenology study minimum) per month for three riparian plant phenology study locations in eastern Arizona and western New Mexico. locations in eastern Arizona and western New Mexico. 28 Desert Plants 11(1) 1994 Spring Flowering /Autumn -Winter Fruit Dispersal ARIZONA WALNUT Four of the species studied fit this category (Group 2): box el- JugLi smajor der, netleaf hackberry, Arizona sycamore, and velvet ash. Of these four species, box elder was the first to break bud in the spring (March) (Figure 6). Flowering was rapid with staminate and pistillate flowers borne on separate trees (Sargent, 1965). Fruit development of box elder was evident by early -May and the fruit attained nearly full size by mid -June. The fruit remained green during the summer than slowly ripened into the autumn. Fruit dispersal began slowly in October and fruit was released over the winter months. Some of the previous year's fruit remained on the trees until the next spring.

Netleaf hackberry emerged from dormancy early in the spring and simultaneously flowered and produced leaves. The fruit of LEAF SENESCENCE I I this plant grows slowly, attaining mature size by early June. DORMANCY The fruit matures by late summer indicated by a color change FM BUD BREAK from green to an orange -red (Figure 6). Fruits of netleaf hack - ® LEAF EXPANSION berry are dispersed slowly over the winter and spring. A por- MATURE LEAVES FLOWERING tion of the seed persist on the trees into the next year. I »;: i'1FRUIT DEVELOPMENT SEED DISPERSAL Arizona sycamore trees are important aesthetically in the ripar- Figure 7. Sequence and duration of phenological stages through- ian community. The exfoliating bark exposes smooth white out the year for Arizona walnut with spring flowering and late - trunks and branches support arrays of leaves and the ball- shaped summer fruit dispersal, averaged for three locations in eastern fruit. The trees retain senescent leaves into the winter period Arizona and western New Mexico. providing reddish -brown color spots throughout the winter landscape. Flowering and leaf expansion occurred simultaneously Multidate Flowering and Fruit Dispersal in late -March or early -April (Figure 6). Ball- shaped flower heads Velvet mesquite flowered and initiated spring growth at approxi- emerge from the flower buds. Fruits attained full size in the early mately the same time or with a slight lag in flowering (Figure summer and matured by autumn. The fruit (achenes) begin to 8,page 30). Velvet mesquite can produce several flower and fruit disperse following frost. The whole fruit falls, or individual crops each year. In 1982 and 1983, two fruit crops were produced achenes tipped with a fringe of bristle -like hairs (which aids wind at nearly all sites, one following the initial spring flowering and dispersion), fall with increased rapidity in February and March. the other after summer rains. Three fruit crops were observed in one stand of velvet mesquite in 1982, with the last resulting from Velvet ash remains dormant a week or two longer than the other a flowering event in September. The fruit of velvet mesquite are three species in the spring flowering/autumn -winter fruit dis- pods that drop rapidly from the trees, usually within two weeks persal group. The average data for bud break for velvet ash was following maturity. Velvet mesquite pods and seed provide food early -April (Figure 6). Flowering of this dioecious species imme- for many animals utilizing riparian habitats including domestic diately followed bud break coinciding with leaf expansion. Imma- livestock. ture fruit was present within two to three weeks after flower initiation and attained full size by late -May and early -June. During Velvet mesquite's strategy for reproduction is different than the the summer months the fruit remained green. By September the more typical riparian tree species, although, it was the major fruits began to mature, turning a straw color. The seeds dis- seedling species found in the gallery forests. This plant is of persed rapidly in autumn and most of the seeds were deposited concern to riparian ecologists and habitat managers because it on the soil surface by late November. has the potential to become more prevalent in riparian habitats over time. This may be especially true if the normal regimen of Spring Flowering and Late -Summer Fruit Dispersal river flow decreases, or if land management is not changed to Arizona walnut flowers prior to and/or simultaneously with leaf favor development of riparian habitats dominated by obligate development in about mid -March depending on individual trees (Figure 7). Arizona walnut rapidly drops its fruit in the late riparian species. summer (August). The fruit maintained a green color during CONCLUSION the summer which rapidly turned a very dark brown or black upon dispersal. Monsoonal storms were observed to accelerate Variation in phenology for the eight tree species studied reflect fruit dispersal with nearly an entire crop being shed in one storm. individual species adaptations to a particular environment. The fruit is important food for many riparian animals, espe- Variation in timing of phenological events, was also triggered cially squirrels (Brown, 1984; Theobald, 1983). by weather events such as freezing temperatures. Generally, phenological events of the species at the lower elevation location on the San Francisco River in Arizona preceded those at higher elevations on the Gila River by one to two weeks. Brock Riparian Plants 29

BOX ELDER NETLEAF HACKBERRY Acernegundo var interius Celtisreticulata

ARIZONA SYCAMORE VELVET ASH Platanus wrightii Fraxinus pennsylvanica ssp, velutina

LEAF SENESCENCE DORMANCY

;: t:`. ; jBUD BREAK LEAF EXPANSION EN MATURE LEAVES FLOWERING FRUIT DEVELOPMENT ® SEED DISPERSAL

Figure 6. Sequence and duration of phenological stages throughout the year for spring flowering/autumn -winter fruit dispersal plants: box elder, netleaf hackberry, Arizona sycamore and velvet ash, averaged for three locations in eastern Arizona and western New Mexico. 3 0 Desert Plants 11(1) 1994 Carothers, S. W. 1977. Importance, preservation, and management of riparian habitats: An overview. p. 2-4. In: R. R. Johnson and D. A. Jones (eds.) Importance, Preservation, and VELVET MESQUITE Managment of Riparian Habitats. USDA Forest Service. GTR - Prosopisvelutina RM-43. Fort Collins, CO.

Daubenmire, R. F. 1974. Plants and environment: a text- book of autecology. John Wiley and Sons. New York.

Fenner, P., W. W. Brady, and D. R. Patton. 1984. Observations on seeds and seedlings of Fremont cottonwood. Desert Plants. 6:55 -58.

Fox, K. M. 1977. Importance of riparian ecosystems: economic considerations. p 19 -22. In: R. R. Johnson and D. A. Jones (eds.) Importance, Preservation, and Managment of Ripar- ian Habitats. USDA Forest Service. GTR- RM -43. Fort Collins, n LEAF SENESCENCE CO. DORMANCY BUD BREAK Johnson, R. D., and C. H. Lowe. 1985. On the develop- ® LEAF EXPANSION ment of riparian ecology. p.112 -116. In: R. R. Johnson, C. MI MATURE LEAVES FLOWERING D. Ziebell, D. R. Patton, P. F. Folliott and R. H. Hamre (eds.) FRUIT DEVELOPMENT V>:::::>::1 Riparian Ecosystems and Their Management: Reconciling Mi SEED DISPERSAL Conflicting Uses.First North American Riparian Confer- ence, USDA Forest Service. GTR -RM -120. Fort Collins, CO.

Figure 8. Sequence and duration ofphenological stages through- Jones, A. R., F. P. Sharpe, P. Strauss, and W. D. Deason. 1977. out the year for velvet mesquite with multidate flowering and Interaction of water management and riparian ecosystems: fruit development, averaged for three study locations in eastern attitudes, practices, and effects. p. 284 -288. In: R. R. Johnson Arizona and western New Mexico. and D. A. Jones (eds.) Importance, Preservation, and Man- agement of Riparian Habitats. USDA Forest Service. GTR - RM-43. Fort Collins, CO. LITERATURE CITED Lehr, J. H. 1978. A catalogue of the flora of Arizona. Desert Almand, J. D., and W. B. Krohn. 1978. The position of the Botanical Garden. Phoenix, AZ. Bureau of Land Management on the protection and management of forest ecosystems.p. 359 -361. In: R. Lowrance, R., R. Leonard, and J. Sheridan. 1985. Managing R. Johnson and J. F. McCormick (eds.) Strategies for riparian ecosystems to control non point pollution. Journal Protection and Management of FloodplainWetlands of Soil and Water Conservation. 40: 87 -91 and Other Riparian Ecosystems. USDA Forest Service. GTR - RM-43. Fort Collins, CO. Parker, M. F.., F. J. Wood, B. H. Smith, and R. G. Elder. 1985. Erosional downcutting in lower order riparian ecosys- Brady, W. W., D. R. Patton, and J. Paxson. 1985. The tems: Have historical changes been caused by removal of development of southwestern riparian gallery forests. beaver? p. 35 -38.In: Johnson, R. R., C. D., Zieball, P. R. p. 39 -43. In: R. R. Johnson, C. D. Ziebell, D. R. Patton, Patton, P. F. Ffolliott,and R. H. Hamre. (eds.)Riparian P. F. Ffolliot and R. H. Hamre (eds.) Riparian Ecosys- Ecosystems and Their Management: Reconciling Conflict- tems and Their Management: Reconciling Conflicting ing Uses. First North American Riparian Conference, USDA Uses.First North American Riparian Conference, USDA Forest Service. GTR -RM -120 Fort Collins, CO. Forest Service. GTR -RM -120. Fort Collins, CO. Sargent, C. S. 1965. Manual of the trees of North America. Vol. Brock, J. H.1984. Some autecological studies on regen- Two. Dover Publications, Inc., New York. eration and maintenance of selected riparian species. Final Report. Bureau of Reclamation. Seigel, R. S., and J. H. Brock. 1990. Germination requirements of key southwestern woody riparian species. Desert Plants. Brown, D. E. 1982. Biotic communities of the American 10: 3 -8. Southwest - United States and Mexico. Desert Plants. 4:1 -342. Theobald, D. P. 1983. Studies on the biology and habitat of the Arizona gray squirrel. MS. Thesis. Arizona State University, Brown, D. E. 1984. Arizona's tree squirrels. Arizona Game and Tempe, AZ. Fish Department. Phoenix, AZ. Brock Riparian Plants 31

Thomas, J. W., C. Masser, and J. E. Rodiek. 1979. Riparian Zones. USDC National Oceanic and Atmospheric Administration. 1983. p. 40 -75. In: Wildlife Habitats in Managed Forest of the Blue Climatological data: Arizona -New Mexico. 87:(1 -12). Mountain of Oregon and Washington. J. W. Thomas (tech. ed.) USDA Forest Service, Agricultural Handbook 553, Wash- USDC National Oceanic and Atmospheric Administration. 1984. ington, D.C. Climatological data: Arizona - New Mexico. 88:(1-5).

USDA Forest Service. 1974. Seeds of woody plants in the United States General Accounting office (US GAO). 1988. Pub- United States. Agr. Handbook. 450. lic rangelands: some riparian areas restored but widespread improvement will be slow. United States General Accounting USDC National Oceanic and Atmospheric Administration. 1982. Office, Report to Congressional Requesters. GAO /RCED -88- Climatological data: Arizona - New Mexico. 86:(1-12). 105.

Upcoming meetings

Society for Range Management: "Diversity of Land and People" 48th Annual International Meeting January 14- 21,1995 Phoenix Civic Center, Phoenix, Arizona General Managers: Jack Bohning (602) 445 -7816 John Brock (602) 965 -7036

The Ninth Wildland Shrub Symposium: Shrubland Ecosystem Dynamics in a Changing Environment May 23- 25,1995 Hilton Hotel, Las Cruces, New Mexico Sponsored by: Shrub Research Consortium New Mexico State University Jornada Experimental Range /Long Term Ecological Site Questions regarding paper submission: Dr. Jeny Barrow, (505) 646 -7015 Questions regarding registration: Diana Kovar, (505) 646 -3049