Arizona's Diverse Vegetation and Contributions to Plant Ecology Author(S): Mitchel P

Society for Range Management

Arizona's Diverse Vegetation and Contributions to Plant Ecology Author(s): Mitchel P. McClaran and Ward W. Brady Source: Rangelands, Vol. 16, No. 5 (Oct., 1994), pp. 208-217 Published by: Allen Press and Society for Range Management Stable URL: http://www.jstor.org/stable/4000982 Accessed: 21/05/2010 21:08

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http://www.jstor.org 208 RANGELANDS16(5),October 1994

Rrizona's Diuerse Vegetation and Contributions to Plant Ecology

Mitchel P. McClaran,and WardW. Brady

In the 1880's, Mr. and Mrs. J.C. at 2,600-4,900 feet elevation separat- the discrete approach has decided Lemmon were among the few ed by mountain ranges reaching advantages when the goal of classifi- botanists to collect plants in Arizona 8,200-10,800 feet. These sharply ris- cation is to improve communication during the conflict between Apaches ing mountain ranges are often referred about the general appearance and and European settlers. Unlike many to as sky islands surrounded by a sea location of vegetation. In this paper, settlers, the Lemmon's traveled safely. of desert. we use a discrete classification to Apparently the Apaches considered As expected, the elevation gradient communicate the variety and dynam- plant collecting a form of insanity and associated climate gradient pro- ics of nine plant communities in (Benson 1959). Many have continued vide the ingredients for a rich and Arizona: desert scrub, desert grass- collecting plants and studying vegeta- diverse flora. Over 3,400 vascular taxa land, chaparral, northerndesert scrub, tion in the groundbreaking and are recognized (Kearney et al. 1960), juniper-pinyon woodland, oak wood- unyielding tradition of the Lemmons. and an ongoing flora revision will land, ponderosa pine forest, mixed These subsequent contributions have increase that number (Vascular Plants conifer forest and riparian forest. By been at the forefront of plant ecology, of Arizona EditorialCommittee 1992). using the discrete approach for com- and their legacy spreads well beyond Plant taxa range from subtropical munication, we are not endorsing its the state borders. species with distributionaland genetic use for describing the factors that Arizona extends over 7 million acres affinities with taxa in Mexico and determine species distributions. between 31 and 360 north latitude, and Central America, Mediterranean about 80% of the area is state or fed- species with affinities in California,and Desert Scrub eral public land. The climate is gener- temperate and alpine species with 25 million ally arid, with a bimodal precipitation affinities to the north and east includ- Covering about acres in pattern of wet summer months (July- ing the Rocky Mountains. (Nichol 1937) southern and western September), moderately moist winter The biotic diversity and the dramatic Arizona, the desert scrub is a sparse, months (December-March) and a very elevation/climate gradients in Arizona low stature vegetation of shrubs, short hot and dry spring and early summer have provided important cases for a trees, cacti and scattered perennial (Green and Sellers 1964). The propor- rich discussion concerning the organi- herbs (Fig. 1). Conspicuous species tion of winter precipitationincreases to zation of plant communities. The life are saguaro (Carnegiea gigantea the north. Additionally,dramatic eleva- zone classification was developed by (Engelm.) Britt. & Rose), palo verde tional gradients in Arizona alter the Marriam(1898) while working around (Cercidium spp.) bursage (Ambrosia magnitude of the temperature and pre- Humphrey Peak north of Flagstaff. His spp.) and creosote (Larrea tridentata cipitation values. This elevational gra- approach described a series of dis- (D.C.) Coville). Generally, annual pre- dient ranges from 68 feet near the crete and sharply differentiated biotic cipitation does not exceed 10 inches, Colorado River in southwest to over communities. In contrast, Shreve and precipitation in this area has the 12,630 feet on Humphery Peak in the (1 915) and Whittaker and Niering greatest annual variation in the United north. The Mogollon Rim is a 1,600- (1965) applied a more gradual or con- States (Hidy and Klieforth1990). 2,300 foot escarpment that rises tinuum approach to describing the dis- The majorityof biomass productivity above the central desert regions. tributionof plant species along the ele- occurs in the spring following winter Rising above the Rim to greater than vation/climate gradients in the sky rains, but some significant growth can 9,800 feet are the White Mountains to islands of southeastern Arizona. They occur following summer rains. Spring the east, and San Francisco suggested that the abundance of wildflower displays are most common Mountains to the north. In the south- species along the gradients were when fall precipitation exceeding 1 east, a basin and range physiography dependent on the tolerance of individ- inch stimulates germination, and suffi- dominates the landscape with valleys ual species to the physical environ- cient winter and spring precipitation ment, and largely independent of other sustains growth until flowering in The authors are associate professor of Range plant species. March (Beatley 1974). Germination Management, University of Arizona, Tucson 85721 and survival of many species are more and professor of Environmental Resources, Arizona Although the debate focuses on the State University, Tempe 85287-2005. factors controlling species distribution, common under other plants than in RANGELANDS16(5), October 1994 209

Greene), snakeweed (Gutierrezia sarothrae (Pursh.) Britt. & Rusby), Arizona cottontop (Digitaria califomica (Benth.) Henr.), tobosa (Hilariamutica (Buckl.) Benth.), and grama grasses (Bouteloua spp.). Generally, annual precipitation is between 10-16 inches/yr. The majorityof herbaceous biomass production occurs in August and September, and total net annual productivity is usually less than 1,300 lb/acre (Schmutz et al. 1991). Woody species growth is most abundant in spring when winter moisture is utilized, and some growth occurs in summer with sufficient precipitation. The study of historic vegetation changes have been facilitated by the development of repeat photography Fig. 1. Hot Desert vegetation with saguaro, foothill palo verde (Cercidium microphyllum (Torrey) Rose & Johnson) and triangel leaf bursage (Ambrosia deltoidea (Torrey) Payne) in techniques and the establishment of Tucson Mountains. the Santa Rita Experimental Range in southern Arizona (Fig. 2). The open areas (McAuliffe 1988). This is ety of ecosystems worldwide. Changing Mile by Hastings and Turner commonly referred to as a nurse plant According to packrat midden analy- (1965) was one of the earliest and relationship. Bursage, living or dead, is ses, much of this area has changed most influential applications of repeat a common nurse plant while creosote from a juniper-oak woodland as the photography (comparing old and con- rarely serves as a nurse plant. warmer and drier post-Pleistocene cli- temporary photographs from the same In 1903, the Carnegie Institute mate developed over the last 11,000 location) to describe vegetation established the Desert Laboratory in years (Van Devender 1990b). The dynamics. Some of the original pho- Tucson as one of the first facilities recent increase in annual plants from tographs were taken on the Santa dedicated to the study of desert the Mediterranean region, including Rita, which was established as the ecosystems (Bowers 1990). The red brome (Bromus rubens L.) and red world's first range experiment station genus Carnegiea used for the saguaro filaree (Erodium cicutarium(L.) L'Her.) in 1903. Research initiallyfocused on cactus reflects the early involvement represent a vegetation change sustainable livestock production, but of the Carnegie Institute Desert (Burgess et al. 1991) equal to the geo- the focus quickly expanded and has Laboratory. The world's oldest, regu- logic time-frame changes because continued to include more general larly measured plots that monitor indi- these recent arrivals with increased plant ecology pursuits (Martin 1975). vidual plant size and mortality are biomass depress native wildflowers The Bureau of Plant Industry initially located on this facility (Goldberg and and promote wildfires. An increased administered the area. The Forest Turner 1986). This long term informa- frequency of wildfires may then lead to Service then administered the area tion has shaped the understanding furtherchanges in desert scrub includ- from 1915 until 1989, when it was and approach to studying desert vege- ing the loss of some fire sensitive transferred to the State of Arizona and tation dynamics worldwide. species such as some cacti. administration was assumed by the The development of packrat midden University of Arizona College of analysis in Arizona desert scrub facili- Desert Grassland Agriculture. tated the study of vegetation dynamics In the past 100 years, the abun- in arid environments over geologic Spread over nearly 15 million acres dance of woody species particularly time-frames. The middens include in southeastern Arizona, and scattered velvet mesquite has increased and plant material and various attractive areas in central Arizona, the desert grass has decreased. Hastings and objects collected by packrats grassland includes herbaceous, shrub- Turner's (1965) classic repeat photog- (Neotoma spp.) and preserved in a by and short tree species with at least raphy shows the magnitude of this matrix of crystallized urine in their 20-40% bareground. The ability of change and that while woody species latrine caverns (Betancourt et al. these diverse lifeforms to persist and were present 100 years ago their 1990). Analysis of the plant material co-exist has led some to suggest that abundance has clearly increased. and radiocarbon dating were originally mixed shrub savanna is a more accu- Several hypotheses have been pre- applied to describe changes in desert rate name. Conspicuous species are sented to interpret this vegetation vegetation over the last 40,000 years, velvet mesquite (Prosopis velutina change including shifts in seasonal but it has since been applied to a vari- Woot., burroweed (Isocoma tenuisecta 210 RANGELANDS16(5),October 1994

Fig. 2: Desert Grassland vegetation dynamics depicted with repeat photography from Santa precipitation toward winter months Rita Experimental Range. A livestock exclosure constructed in 1916 is visible on the right (Neilson 1986), decreased fire fre- side of the images, and the similarity of vegetation dynamics within and outside the exclo- quency from reduced fuels and fire sure suggest that livestock grazing is not necessary to produce dramatic vegetation suppression (Bahre and Shelton 1993; changes. Instead, weather pattems and the arival of new species can be more dominant in producing these vegetation changes than livestock grazing. Humphrey 1958), decreased grass cover from grazing (Glendenning and Paulson 1955) and wild hay harvesting (Bahre 1987), and seed dispersal by livestock (Glendenning and Paulson 1955). According to packrat midden analyses, the dominant woody species have changed from pine, juniper and oak to the more subtropical velvet mesquite

r-- and desert hackberry (Celtis pallida Torr.) over the last 1 1,000 years as the warmer and drier post-Pleistocene I _ climate developed (Van Devender 1990a,b). However, the dominant grass species are largely the same as during the Pleistocene. The recent increase and spread of the south African Lehmann lovegrass (Era- grostis lehmanniana Nees.) from isolated seedings (Anable et al. 1992) represents a vegetation change of a Fig. 2A: In December 1922, annual grama grasses (Boutelouaaristidoides (H.B.K. Griseb. and magnitude similar to the contemporary B. barbata Lag.) appear to be the dominant herbaceous species with scattered velvet woody species increase and the dis- mesquite and desert hackberry (Celtis pallida Torr.) small trees and shrubs. The 3 metal appearance of the pine, junipers and stakes at the bottom of the picture are the plot markers for a permanent plot where charting of individual plants was performed. oaks over the last 1 1,000 years. Because lovegrass spread does not require disturbance associated with livestock grazing (McClaran and Anable 1992), it appears that the spread will continue regardless of management actions.

Chaparral

_I ,, Chaparralvegetation occurs south of the Mogollon Rim on rough mountain- ous terrain between 3,000 and 9,800 feet (Fig. 3). The extent of the chaparral depends on definition and varies between 6 million acres (Nichol 1937) and 4 million acres (Cable 1975' i I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~IFfolliott and Thorud 1975). Dominant shrubby species are similar in appearance to the sclerophyllous species that dominate true chaparral vegetation (Plummer 1911). However, Arizona chaparral differs from "true"chaparral by having summer precipitation in addition to winter precipitation that occurs in both. Total annual precipita- Fig. 2B: In July 1970, the small shrub burroweed and chain fruitcholla cactus (Opuntia fulgida Engelm.) dominate the scene. Inside and outside the exclosure, the majonity of the bur- tion is between 15-27 inches, with roweed plants are dead, and they died within the previous 12 months. There are also a num- over 50% typically falling in the cooler ber of dead cacti. months. RANGELANDS 16(5), October 1994 211

laid important groundworkthat helped plant ecologists better understand dynamics of the hydrologic cycle in arid environments (Ffolliottand Thorud 1975). Conversion programs, however, were effectively suspended when the use of herbicides attracted interna- tional attention and resulted in recon- sideration of both the methods and 4A, desirability of conversion (Ffolliottand Thouud 1975, Shoecraft 1971).

Northern Desert Shrub

: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~t Most of the 4 million acres (Nichol 1937) of northern desert shrub occurs in Arizona north of the Colorado River: an area known locally as the "strip" which also includes Grand Canyon National Park. Shrubby species dominate this vegetation type which occurs between 2,300-5,900 feet. Annual precipitation is approximately 4-14 inches Fig. 2C: In September 1993, the south AfricanLehmann lovegrass dominates the scene both with approximately 50% falling in inside and outside the exclosure. The grass was aerially seeded in the area in the mid- 1970's. Burroweedis present beneath the grass canopy, but cactus plants are veryscarce. June-September when the majorityof herbaceous plant growth occurs Inter-Agency Range Tech- Numerous shrub species occur in Livestock were first introduced into (Arizona 1969; Judd 1962). Arizona chaparral, but rarely do more the Arizona chaparral in 1874 when nical Subcommittee of the northerndesert shrub is than two species co-dominate a partic- the first cattle were driven into Tonto Much stands of big sage- ular stand (Cable 1975). The most Basin in central Arizona (Croxen dominated by pure Pure common species is shrub live oak 1922). Cable (1975) suggested that brush (Artemisia tridentataNutt.). of blackbrush (Coleogyne (Quercus turbinelIa Greene). Other chaparral, at this time, had consider- stands also occurs in the important species include Emory and ably lower shrub cover and included ramossissima Torr.) state. Palmer oaks (0. emoryi Torr. and Q. good stands of interspersed grasses. northwestern portion of the shrubs are winterfat dunnii Kellog), species of mountain Peak stocking did not occur until 1900 Locally important Moq.) and four- mahogany (Cercocarpus spp.) and when stocking levels were estimated (Eurotialanata (Pursh) saltbush (Atriplex canescens several species of manzanita as being 15 to 20 times the carrying wing Nutt.). There is a diverse (Arctostaphylos spp.). Understory capacity of the range (Croxen 1926). A (Pursh) group of herbaceous understory species are typically scarce, highly major drought occurred in 1903-1904 common are variable and the same species found and resulted in the death of many cat- species, and species gracilis in adjacent vegetation types (which tle and a permanent reduction in blue grama, (Bouteloua Lag.), needle-and-thread includes ponderosa pine forest, stocking. Cable (1975) hypothesized (H.B.K.) grass (Stipa comata Trin. & Rupr.), juniper-pinyon woodland, oak wood- that this period of intense livestock Indian ricegrass (Oryzopsis land and desert grassland). Annual grazing and the continuing suppres- (Roem. & Schult.) production of understory species is sion of fire resulted in an increased hymenoides Ricker), squirreltail (Sitanion hystrix typicallyaround 175 lb/acre. density of overstory species and J.G. and western Like true chaparral, Arizona chapar- reduction in herbaceous species. (Nutt.) Smith), (Agropyronsmithii (Rydb.) ral is prone to fire. Many species, par- Chaparral research in the 1950's wheatgrass Nichol 1952). ticularly the oak-mountain mahogany began to emphasize the conversion of (Judd 1962; Understory production is highly vari- complex, are vigorous sprouters fol- chaparral to grass-forb cover to able from year to year and from stand lowing fire and rapidly reestablish increase water yield for downstream to stand and is inversely related to even after severe burns (Pase and users (Barr 1956). Calibrated water- cover of the shrub canopy. Most Lindemuth 1971; Pond and Cable sheds were established in four areas herbaceous production occurs in the 1960). Other species, such as the (Whitespar, Mingus, Threebar, and and biomass can manzanitas, do not sprout but germi- Natural Drainage watersheds) to eval- summer standing range from 350 to 1,000 lb/acre nate profusely following fire (Pase uate the effects of conversion on water and Throud 1975). 1965). yield. Studies on these watersheds (Ffolliott 212 RANGELANDS 16(5),October 1994

nas to dense woodlands (McClaranet al. 1992). Conspicuous species are Arizona white oak, Mexican blue oak, and Emory oak (Quercus arizonica Sarg., Q. oblongifolia Torr. and 0. emoryi Torr.), point leaf manzanita (Arctostaphylos pungens H.B.K.); and warm-season grasses including I I rz I gramas (Bouteloua spp.) and blue- stems (Andropogon spp.). Precipi- tation varies from 20-26 inches/yr and only rarely occurs as snow (McClaran et al. 1992). Spring is the primary period of tree growth following sufficient winter moisture, but during dry winters some trees become deciduous and resume growth with the onset of summer rain. In contrast, herbaceous growth is largely in summer, but some cool season species under tree canopies grow in the spring including pinyon rice- Fig. 3. Chaparralvegetation near Mayer,Arzona is dominatedby shrub live oak and other grass (Piptochaetium fibriatum small shrubs withvery little herbaceous biomass. (H.B.K.) Hitch.) and prairie junegrass (Koeleria pyramidata Lam.) Beauv. Decreased fire frequency from sup- Oak cover can reduce herbaceous pression and reduced fuels from live- biomass production from 140 lb/acre stock grazing is the generally accept- down to 80 (McPherson 1992). Juniper-pinyon Woodland ed interpretation of this increase. Disparate descriptions of historic Management efforts to reduce tree Covering about 12 million changes in lower boundary of oak acres in cover and density were most common northern, northeastern and woodland show an upslope retreat scattered between 1950-1970, but only about areas in southeastern (Hastings and Turner 1965) and rela- Arizona (Nichol 5% of the area ever experienced tree 1937), the juniper-pinyon woodland tively static boundaries (Bahre 1991). removal and less than 1% was ever varies from widely scattered From 1880-1940, extensive areas of trees and retreated (Dalen and Snyder 1987). shrubs in grasslands to dense oak were cut for domestic and smelt- wood- Current efforts to reintroduce fire are lands with little ing fuel, but much of the cut-over area herbaceous understo- hindered by the reduction of herba- ry. Conspicuous species are one again supports oak because the cut seed ceous biomass following the increased and trees produced stump sprouts that Utah junipers (Juniperus tree cover. monosperma (Engelm.) have matured (Bahre and Hutchinson Sarg. and J., Evidence from packrat midden osteosperma (Torr.) Little), 1985). pinyon analyses suggest that during the cool- pine, (Pinus edulis Engelm.), algerita, Recently, McPherson et al. (1993) er and wetter Pleistocene period more (Berberis fremontii Torr.) described the first application of new western than 18,000 years ago, this area sup- wheatgrass and blue grama. techniques in stable carbon isotope Annual ported mixed conifer vegetation, and precipitation ranges from analysis to describe a downslope 12-20 inch- the junipers and pinyons arrived about es, and some winter movement of oaks. This technique is precipitation 8-10,000 years ago from areas to the occurs as snow (Springfield based on the differentconcentration of 1976). south and southeast (Betancourt Woody species growth is carbon isotopes in woody species (C3) most abun- 1987). It is possible that some part of dant in spring and and warm season grasses (C4), and early summer, the recent spread of these trees is a whereas herbaceous production is the concentration of the carbon iso- continued expression of this geologic greater in the topes in the soil will reflect the type of summer when warm time-frame expansion. season species are present vegetation growing above the soil. (Springfield 1976). Herbaceous pro- Oak Woodland Subsequent carbon14 analysis sug- duction ranges from 45-4501b/acre and gests that the downslope movement is inversely related to tree cover. Oak woodland covers about a million has occurred over the last 700-1,000 In the past 100 years, the extent and acres on the slopes of the sky islands years. This relatively recent, pre-his- density of the woodland has increased in southeastern Arizona, and its toric downslope movement is contrary dramatically (Springfield 1976). appearance ranges from open savan- to the general pattern of unslope RANGELANDS 16(5), October 1994 213 retreat of oak since the Pleistocene seedling growth are enhanced as well Moore 1994). (Betancourt et al. 1990). as seedlings survival because fuel lev- Evidence from packrat middens sug- els are reduced. gest that this area supported mixed Ponderosa Pine Forest Tree ring analysis has been widely conifer vegetation more than 18,000 used to assess the frequency of pre- years ago, and that ponderosa pine Primarilyabove the Mogollon Rim in settlement fires and tree recruitment. arrived about 8-10,000 years ago from north and eastern Arizona and scat- The study of tree rngs was developed areas to the south and southeast tered areas on the sky islands in the at the Tree Ring Labatory, University (Thompson 1988). In fact, in the last southeast, the 4 million acre pon- of Arizona. Established in 1937, this is 10,000 years, the extent of ponderosa derosa pine forest (Nichol 1937) varies the world's foremost tree ring facility pine has increased from a very isolat- from dense, dog-hair thickets of pine, for climate reconstruction, fire history ed distributionto become of the most park-like stands of large trees with and stand age structure (Douglass widespread pines in North America. herbaceous understory. Conspicuous 1944). Recent tree ring analysis has species are ponderosa pine (Pinus identified variable weather patterns as Mixed Conifer Forest ponderosa Lawson), Gambel oak an additional variable leading to pine (Quercus gambelii Nutt.), blue grama increase. Workingwith tree rings from Mixed conifer forest occupy approxi- mountain muhly (Muhlenbergia mon- the Navajo Indian Reservation, mately 2.5 million acres above pon- tana (Nutt.) Hitch.), squirreltail and Savage and Swetnam (1990) showed derosa pine forests in northern and Arizona fescue (Festuca arizonica decreased fire frequencies following eastern Arizona (Fig. 5) and on the Vasey). Annual precipitation ranges increased livestock grazing beginning higher sky islands in the southeastern with a from 13-20 inches significant in 1980, but pine increase did not portion of the state (Spencer 1966). proportion occurring as snow (Clary occur until 1910-1930 when unusually One of these sky islands has achieved 1975). wet years coincided with the fire-free considerably notoriety as environmen- Tree growth and cool season herba- period. Current efforts to reintroduce talists and a University of Arizona-led ceous growth is primarily in the late fire are hindered because the consortium have clashed over the spring and early summer, and warm increased pine cover has created a effects of the under-construction Mt. season grass growth is generally later heavy, vertical stacking of fuel that will Graham Observatory and attendant in July-August (Clary 1975). Her- mixed conifer forest on the sur- result in serious crown fires rather loss of baceous growth declines from 890 isolated and endangered than the cooler ground fires than prob- vival of the lb/acre down to less than 175 as tree Mt. Graham red squirrel (Tamiasciurus ably existed before the increase in tree density and cover increases. hudsonicus grahamensis) population density and cover (Covington and Northern Arizona has been the site (Turbak 1993). Mixed conifer forests, of continuous observation of an increase in tree density and decreased grass cover over the last 100 years (Arnold 1950; Cooper 1960; White 1985). This long-term research utilized study areas that were established near the turn of the century and produced some of the most precise descriptions of vegetation change available in the western United States. The results of this impressive research suggest that decreased fire frequency from suppression and reduced fuels from livestock grazing was responsible for this vegetation change. Ponderosa pine germination requires bare mineral soil and grass reduces pine seedling growth (Elliot and White 1987). Cool season grasses reduce pine seedling growth more than warm season grasses because seedling growth coincides with the earlier season growth of the cool season tree species. Therefore, which occurred at much lower eleva- less grass will favor more trees Fig. 4. Ponderosa Pine Forest vegetation near Flagstaff, Arizona is dominated by pine trees grasses in the understory. because seed germination and with blue grama and squirreltail 214 RANGELANDS16(5),October 1994 tion as early as 10,000 years ago Mixed conifer forests are a valued and Fremont cottonwood (Populus fre- (Thompson1988), may not continueto resource for their recreational and montii Wats.) become major species. persist on some mountaintops if pro- wildlifevalues. These forests are used The lowest elevation ripariancommu- jections of warmerclimates are real- extensively for winter sports and also nities traverse desert vegetation and ized. support a large portion of Arizona's are dominated by mesquite, willows Annual precipitation in the mixed cold water fishery including several (Salix spp.), and the introduced salt conifer forest ranges between 12-16 streams supporting endangered native cedar (Tamarixpentanda Pall.). Other inches with half or more fallingduring Arizona trout. The Merriam elk riparian communities are dominated July through September. Because (Cervus elphus merriami)which once by shrubs including alders and willows mixed conifer forests occur at higher dominated the White Mountains of at the higher elevations and burro elevations,much of the winterprecipi- Arizona is now extinct. Populations of bush (Hymonoclea monogyra T. & G.) tationfalls as snow. These forests are Rocky Mountain elk (Cervus elphus), at the lower elevations. uniformlycold with nighttimefreezing which once were restricted to a much Because of the uniqueness of ripari- temperatures beginning mid- smaller range, have increased dramat- an vegetation, concern has arisen September and continuing into May ically (from 10,000 elk in 1980 to over concerning loss or degradation of (Brown1982). 30,000 in 1990) and now present a these ecosystems (Stromberg Higher elevation mixed conifer challenge to managers of this and 1993a,b). Ohmart et al. (1977) report- forests are dominatedby Engelmann adjacent ecosystems (Brown 1982, ed that over 90% of riparianvegetation spruce (Picea engelmanniiPerry), and Arizona Game and Fish Dept. 1992). along a small portion of the lower corkbarkfir (Abies lasiocarpavar. ari- Colorado river had been either lost or zonica (Merriam)Lemm.) (Embry and Riparian Forests degraded. While one cannot extrapo- Gottfried 1917). Douglas fir late this percentage to the remainder (Pseudotsuga menziesii (Mirb.) Riparian vegetation occurs on 0.25 of Arizona's ripariansystems, consid- Franco),and the largest nativetree in million acres in Arizona along erable habitat has been lost and/or Arizona (sometimes exceeding 51 drainages and/or floodplains that tra- degraded and plans once existed to inches in diameter and 170 feet in verse the entire state (Szaro 1989). remove riparian vegetation from very height, Little1950) occurs in mixtures The ecological and aesthetic impor- large portions of Arizona's rivers to with blue spruce (Picea pungens tance of this vegetation type is far out reduce evapotranspiration and Engelm.), southwestern white pine of proportionto its relative area, partic- increase water delivery downstream (Pinus strobiformisEngelm.), white fir ularly in arid and semi-arid habitats. (Pacific Southwest Inter-Agency (Abies concolor (Gord. & Glend.) Carothers and Johnson (1975), for Committee 1969). Lindl.),and ponderosapine. Firestim- instance demonstrated the importance Intensive livestock grazing has been ulates sprouting of quaking aspen of riparian vegetation as habitat for identified as a major factor in the (Populustremuloides Michx.) in mixed breeding birds. The discipline of land- degradation of western riparian sys- conifer forests and repeated fires scape ecology has emphasized the tems (Ames 1977; Davis 1977; Martin resultin persistenceof quakingaspen importance of streams and their asso- 1979; Thomas et al. 1979). Szaro stands. ciated vegetation as corridors facilitat- (1989), in a study of southwestern Mixedconifer forests typicallyhave ing movement of terrestrialplants and riparianvegetation, reported that virtu- dense overstorycanopies with littleor animals across the landscape (For- ally all ripariansystems were grazed, no herbaceous vegetation occurring man and Gordon 1986). the only exception being unique topo- beneath the canopy (Pase 1966). Szaro (1989) provided a detailed graphic or ownership situations. Many Exceptionsoccur where disturbances classification of riparian communities studies have reported adverse effects have opened the canopy(fire or timber in the Southwest. Forest communities of cattle grazing and recovery when harvest), beneath quaking aspen above 6,500 feet in elevation are dom- grazing is modified (Ames 1977; Knopf stands, or where soils favorthe dense inated by mixed conifer species includ- and Cannon 1982; Taylor 1986; herbaceous of mountain meadows. ing big tooth maple (Acer grandidenta- Winegar 1977). The Environmental Among the species that do occur in tum Nuft), white fir, blue spruce, and Protection Agency (Chaney et al. the mixed conifer type are pine narrow-leaf cottonwood (Populus 1993) recently described management dropseed, several bromes, and fes- angustifolia James). In the ponderosa to mitigate the effects of livestock. cues (Bromusspp. and Festucaspp.), pine zone, riparian forests are often However, the most serious challenge rushes, sedges, (Juncus spp. and dominated by box elder (Acer negun- to grazing may come from proposals do L. Carex spp.) pine dropseed (Blephar- var. interius (Britt.) Sarg.) and to protect the habitat of the endan- oneuron tricholepis (Torr.) Nash), alder (Alnus oblingofolia Torr.). Below gered willow flycatcher (Empidonax numerousforbs, and shrubs such as this, extending through chaparral and trailliiextimus) (Endangered Species Fendler ceanothus (Ceanothus fend- grassland into the desert, black walnut Technical Bulletin 1993). These pro- leri Gray), and bearberrymanzanita (Juglans major (Torr.) Heller), Arizona posals, if enacted, will potentiallyelimi- (Arctostaphylosuva-ursi (L.) Spreng.). sycamore (Platanus wrightii Wats.), nate grazing on many southwestern velvet ash (Fraxinus velutinaTorr.), RANGELANDS16(5), October 1994 215 ranges adjacent to riparianforests pro- ue to provide fertile ground for ecolo- Brown, D.E. (ed.). 1982. Biotic communities viding habitat for this neotropical gists to work in the Lemmon's resolute of the AmericanSouthwest-United States and Mexico.Desert Plains 4(1-4):1-287. species. tradition. Burgess, T.L., J.E. Bowers and R.M. Riparian forests, however, have Turner. 1991. Exotic plants at the Desert been influenced by several factors in LiteratureCited Laboratory, Tumamoc Hill, Tucson, addition to grazing. These forests Arizona.Madrono 38:96-114. orig- Ames, C.R. 1977. Wildlife conflicts in riparian Cable, D.R. 1975. Range Management for inally developed along free-flowing management: Grazing. In, R.R. Johnson the chaparraltype and its ecological basis: streams under the seasonal influence and D.A. Jones (tech. coords.). Importance, The status of our knowledge. U.S. Forest of flooding (Brady et al. 1985; Fenner Preservation, and Management of Riparian Service Research Paper RM-115. Habitats: a Symposium. U.S. For. Ser. Carothers, S.W. and R.R. Johnson. 1975. et al. 1985; Stromberg et al. 1991). General Tech. R.M.-43. p.49-52. Water management practices and their The construction of dams and regula- Anable, M.E., M.P. McClaran, and G.B. effects on nongame birdsin range habitats. tion of downstream flows have signifi- Ruyle. 1992. Spread of introduced In: Proceedings Symposium on cantly changed the riparian environ- Lehmann lovegrass Eragrostis lehmanni- Managementof Forest and Range Habitats ana Ness. in southern Arizona, USA. for Nongame Birds.U.S. For. Serv. General ment leading to inevitable long-term Biological Conservation 61:181-188. Tech. Rpt.WO-1. p. 210-222. and possible major changes in the Arizona Inter-Agency Range Technical Chaney, E., W. Elmore and W.S. Platts. associated riparianvegetation (Nilsson Subcommittee. 1969. Guide to improve- 1993. Managing Change. Livestock ment of Arizona rangeland. of 1982; Petts 1984; Stromberg et al. University Grazing on Western Riparian Areas. Arizona Agric. Sta. Bull. A-58, Tucson, Ariz. Environmental Protection Agency, 1991; Warner 1984). Arnold, J.F. 1950. Changes in ponderosa Northwest Resource InformationCenter, Recreation has also proven to be a pine bunchgrass ranges in northern Arizona Inc. Eagle, Idaho. significant factor affecting both riparian resulting from pine regeneration and graz- Clary, W.P. 1975. Range management and ing. J. of Forestry 48:118-126. its ecological basis in the ponderosa pine vegetation and soils (Manning 1979). Bahre, C.J. 1987. Wild hay harvesting in type of Arizona: the status of our know- Off-road vehicles have been particu- southern Arizona: a casualty of the march ledge. U.S. Forest Service Research Paper larly implicated in degradation of of progress. J. of Arizona History, Spring: RM-158. streambanks as well as the stream 69-78. Cooper, C.F. 1960. Changes in vegetation, Bahre, C.J. 1991. A Legacy of Change: structure,and growthof southwesternpine channel itself (Johnson and Carothers Historic Human Impact on Vegetation in the forests since white settlement. Ecological 1982). These disturbance factors, Arizona Borderlands. University of Arizona Monographs30:129-164. along with the outright elimination of Press, Tucson, Ariz. Covington, W.W., and M.M.Moore. 1994. Bahre, C.J., and C.F. Hutchinson. 1985. riparian communities for homesites Southwestern ponderosa forest structure: The impact of historic fuelwood cutting on changes since Euro-Americansettlement. and agriculturehave made this one of the semi-desert woodlands of southeastern J. of Forestry92:39-47. the most intensely impacted Arizona Arizona. J. Forest History 29:175-186. Croxen, F.W. 1926. Historyof grazingon the ecosystems. Bahre, C.J., and M.L. Shelton. 1993. Tonto.Tonto GrazingConference, Phoenix, Historic vegetation change, mesquite Arizona,November 1926. 12 p. Arizona continues to provide ecolo- increases, and climate in southeastern Dalen, R.S., and W.R. Snyder. 1987. gists with an incredibility rich and Arizona. J. of Biogeography 20:489-504. Economic and social aspects of pinyon- diverse laboratory for understanding Barr, G.W. 1956. Recovering rainfall. Report juniper. In: R.L. Everett (compiler). of the Arizona Watershed ecosystem dynamics. The work of pio- Program. Proceeding- Pinyon-JuniperConference. University of Arizona Department of U.S. Forest. Serv. GeneralTech. Rep. INT- neer ecologists including Merriamand Agricultural Economics. Part 1, Tucson, 215. p. 343-350. Shreve, the establishment of some of Ariz. Davis, G.A. 1977. Managementalternatives the world's earliest long-term research Beatley, J.C. 1974. Phenological events and for the riparianhabitat in the Southwest. In their environmental triggers in the Mojave areas, and the development of sophis- R.R. Johnson and D.A. Jones (tech. desert ecosystem. Ecology 55:856-863. coords.). Importance, Preservation, and ticated methods for documenting eco- Benson, L. 1959. Plant Classification. D.C. Management of Riparian Habitats: a logical change, including packrat mid- Heath and Company. Symposium.U.S. For. Serv. GeneralTech. den analysis, dendrochronology, and Betancourt, J.L. 1987. Paleoecology of pin- Rep. RM-43.p.56-67. yon-juniper woodlands: summary. In: R.L. Douglass, A.E. 1944. Laboratory of Tree stable isotope carbon analysis has Everett (compiler). Proceedings- Pinyon- Ring Research. Phi Kappa Phi Journal given the ecological community a Juniper Conference. U.S. For. Ser. General 24:86-87. unique and important window for Tech. Rep. INT-215. p. 129-139. Elliot, K.J. and A.S. White. 1987. Betancourt, J.L., T.R. Van Devender, and observing ecosystem change over Competitiveeffects of various grasses and P.S. Martin (eds.) 1990. Packrat Middens: forbs on ponderosa pine seedlings. Forest time. Arizona's ecosystems have not The Last 40,000 Years of Biotic Change. Science 33:356-366. only shown dramatic change since the University of Arizona Press, Tucson, Ariz. Embry, R.S., and G.J. Gottfried. 1971. Pleistocene, they continue to illustrate Bowers, J.E. 1990. A debt to the future: sci- Basal area growthof Arizonamixed conifer entific achievements of the Desert the change species. U.S. Forest Service Research inherent in ecosystem Laboratory, Tumamoc Hill, Tucson, Note RM-198. dynamics. A plethora of factors from Arizona. Desert Plants 10:9-12,35-47. Endangered Species Technical Bulletin. introduction of exotic species in Brady, W., D.R. Patton, and J. Paxson, 1993. Southwestern Willow Flycatcher Arizona's deserts and grasslands to 1985. The development of southwestern (Empidonax traillii extimus). June-Oct riparian forest. In: R.R. Johnson, C.D. XVIII:3USDI Fish and WildlifeService. the challenges of fire management in Ziebel, D.R. Patton, P.F. Ffolliott, and R.H. Fenner, P., W.W. Brady, and D.R. Patton. shrublands and forests to the manage- Hamre (tech. coords). Riparian Ecosystems 1985. Effects of regulated water flows on ment of endangered species and habi- and Their Management: Reconciling regeneration of Fremont cottonwood. J. tats (including riparian Conflicting Uses. First North American Range Manage.38:135-138. forests) contin- Riparian Conference. U.S. For. Serv. Ffolliott, P.F., and D.B. Thorud. 1975. Water General Tech. Rep. RM-120. p. 39-43. 216 RANGELANDS 16(5),October 1994

Yield Improvement by Vegetation cattle grazing on riparian habitats in the RM-56. Management: Focus on Arizona. Final national forest of Arizona and New Mexico. Pase, C.P. 1966. Grazing and watershed val- report for Rocky Mountain Forest and In: O.B. Cope (ed.). Proceedings of the ues of native plants. In: Native plants and Range Experiment Station, Fort Collins, Forum-Grazing and Riparian/Stream animals as resources in arid lands of the Colo. and Arizona Water Commission, Ecosystems. Trout Unlimited Inc., Denver, southwestern United States. American Phoenix, Ariz. Colo. p.35-38. Association for Advancement of Science. Forman, R.T.T., and M. Gordon. 1986. McAuliffe, J.R. 1988. Markovian dynamics of Southwestern and Rocky Mountain Landscape Ecology. John Wiley and Sons, simple and complex desert plant communi- Division. Committee on Desert and Arid New York, N.Y. ties. American Naturalist 131:459-490. Zones Research .Contribution8:31-40. Glendenning, G.E., and H.A. Paulson, Jr. McClaran, M.P., L.S. Allen, and G.B. Ruyle. Pase, C.P., and W.W. Lindenmuth, Jr. 1955. Reproduction and establishment of 1992. Livestock production and grazing 1971. Effects of prescribed fire on vegeta- velvet mesquite as related to invasion of management in the encinal oak woodlands tion and sediment in oak-mountain semidesert grasslands. U.S.D.A. Technical of Arizona. In: P.F.. Ffoliott, G.J. Gottfried, mahogany chaparral. Journal of Forestry Bulletin No. 1127. D.A. Bennett, V.M. Hernandez-C,A. Ortega- 69:800-805. Goldberg, D.E., and R.M. Turner. 1986. Rubio and R.H Harme (tech. coords.). Petts, G.E. 1984. Impounded Rivers: Vegetation change and plant demography Ecology and management oak and associ- Perspective for Ecological Management. in permanent plots in the Sonoran Desert. ated woodlands: perspectives in the south- John Wiley and Sons, New York, N.Y. Ecology. 67:695-712. western United States and northern Plummer, F.G. 1911. Chaparral, studies in Green, C.R., and W.D. Sellers 1964. Arizona Mexico. U.S. For. Serv. General Tech. Rep. the dwarf forests, or elfinwood of southern Climate. University of Arizona Press, RM-218. p. 57-64. California. U.S. Forest Service Bulletin 85. Tucson, Ariz. McClaran, M.E. Anable. 1992. Spread of Pond, F.W., and D.R. Cable 1960. Effect of Hastings, J.R., and R.M. Turner. 1965. The introduced Lehmann lovegrass along a heat treatment on sprout production of Changing Mile. University of Arizona Press, grazing intensity gradient. J. of Applied some shrubs of the chaparral in central Tucson, Ariz. Ecology 29:92-98. Arizona. Journal of Range Management Hidy, G.M. and H.E. Klieforth. 1990. McPherson, G.R. 1992. Ecology of oak 13:313-317. Atmospheric processes affecting the cli- woodlands in Arizona. In: P.F. Ffolliott, G.J. Savage, M., and T.W. Swetnam. 1990. Early mate in the Great Basin. In: C.B. Osmond, Gottfired, D.A. Bennett, V.M. Hernandez-C, 19th-century fire decline following sheep L.F. Pitelka and G.M. Hidy (eds.). Plant A. Ortega-Rubio and R.H Harme (tech. pasturing in a Navajo ponderosa pine for- Biology of the Basin and Range. Springer. coords.). Ecology and management oak est. Ecology 71:2374-2378. Verlag. p. 17-45 and associated woodlands: perspectives in Schmutz, E.M., E.L. Smith, P.R. Ogden, Humphrey, R.R. 1958. The desert grassland: the southwestem United States and north- M.L. Cox, J.O. Klemmedson, J.J. Norris, a history of vegetational change and an ern Mexico. U.S. For. Serv. General Tech. and L.C. Fierro 1991. Desert grassland. In, analysis of cause. The Botanical Review Rep. RM-218. p. 24-33. R.T. Coupland (ed.). Natural Grasslands: 24:193-252. McPherson, G.R., T.W. Boutton, and A.T. Introduction and Western Hemisphere. Johnson, R.R., and S.W. Carothers. 1982. Midwood. 1993. Stable carbon isotope Elsevier Scientific Publishing Company. p. Riparian Habitats and Recreation: analysis of soil organic matter illustrates 337-362. Interrelationships and Impacts in the vegetation change at the grassland/wood- Shoecraft, B. 1971. Sue the bastards!" D. Southwest and Rocky Mountain Region. land boundary in southeastern Arizona, Franklin Press, Phoenix, Ariz. Eisenhower Consortium bulletin 12 U.S. USA. Oecologia 93:95-101. Shrove, F. 1915. The vegetation of a desert Forest Service, Rocky Mountain Forest and Merriam, C.H. 1898. Life zones and crop mountain range as conditioned by climate. Range Experiment Station. Fort Collins, zones of the United States. U.S. Carnegie Institute of Washington, D.C. Colo. p.31. Department of Agriculture, Division of Publication No. 217. Judd, B.I. 1962. Principal Forage Plants of Biology, Survey Bulletin 10. Spencer, H.S., Jr. 1966. Arizona's forests. Southwestem Ranges. U.S. Forest Service Neilson, R.P. 1986. High-resolution climatic U.S. Forest Service Intermountain Forest Rocky Mountain Forest and Range analysis and Southwest biogeography. and Range Experiment Station Bulletin 279. Experiment Station, Station Paper No. 69 Science 232:27-34. Springfield, H.W. 1976. Characteristics and Fort Collins, Colo. Nichol, A.A. 1937. The natural vegetation of management of southwestern pinyon- Kearney, T.H., R.H. Pebbles and collabora- Arizona. University of Arizona Agricultural juniper ranges: the status of our knowledge. tors, supplement by J.T. Howell, E. Experiment Station Technical Bulletin No. U.S. Forest Service Research Paper RM- McClintock and collaborators. 1960. 68, Tucson, Ariz. 160. Arizona Flora. Second Edition with Nichol, A.A. 1952. The natural vegetation of Stromberg, J.C., D.T. Patten and B.D. Supplement. University of California Press, Arizona. Arizona Agricultural Experiment Richter. 1991. Flood flows and dynamics of Berkeley, Calif. Station, Technical Bulletin 127 (revision of Sonoran riparian forests. Rivers 2:221-235. Knopf, E.L. and R.W. Cannon. 1982. Technical Bulletin 68), 230 p., Tucson Ariz. Stromberg, J.C. 1993a. Fremont cotton- Structural resilience of a Salix community to Nilsson, C. 1982. Effect of stream regulation wood-Goodding willow riparian forests: a changes in grazing practices. In: J.R. Peek on riparian vegetation. In: A. Lillehammer review of their ecology, threats, and recov- and P.D. Dalde (eds.). Wildlife-Livestock and S.J. Safveit (eds.). Regulated Rivers. ery potential. Journal of the Arizona- Relationships Symposium. Proceedings 10. Universitet Sforlaget As, Oslo. p. 993-1006. Nevada Academy of Sciences 27:97-1 10. University of Idaho, Forestry, Wildlife and Ohmart, R.D., W.D. Deason and C. Burke. Stromberg, J.C. 1993b. Riparian mesquite Range Experiment Station, Moscow, Ida. p. 1977. A riparian case history: the Colorado forests: a review of their ecology, threats, 398-307. River. In: R.R. Johnson and D.A. Jones and recovery potential. Journal of the Liftle, E.L., Jr. 1950. Southwestern trees-a (tech. coords.). Importance, Preservation, Arizona-Nevada Academy of Sciences guide to the native species of New Mexico and Management of Riparian habitats: a 27:111-124. and Arizona. U.S.D.A Handbook 9, Symposium. U.S. For. Serv. General Tech. Szaro, R.C. 1989. Riparian Forest and Washington, D.C. Rep. RM-43. p.35-46. Scrubland Community Types of Arizona Manning, R.E. 1979. Impacts of recreation on Pacific Southwest Inter-Agency Com- and New Mexico. Desert Plants 9(3-4):1- riparian soils and vegetation. Water mitee. 1969. Arizona phreatophyte treat- 138. Resources Bulletin 15:30-43. ment survey. Report of the Phreatophyte Taylor, D.M. 1986. Effects of cattle grazing Martin, S.C. 1975. Ecology and management Subcommittee. on passerine birds nesting in riparian habi- of southwestern semidesert grass-shrub Pase, C.P. 1965. Shrub seedling regenera- tat. Journal of Range Manage. 39:254-258. ranges: the status of our knowledge. U.S. tion after controlled burning and herbicidal Thomas, J.W., C. Maser, and J.E. Rodick. Forest Service Research Paper RM-156. treatmentof dense pringlemanzanita chap- 1979. 1979 Riparian zones in managed Martin,S.C. 1979. Evaluatingthe impacts of arral.U.S. ForestService Research Note rangelands-their importanceto wildlife.In, RANGELANDS16(5), October 1994 217

O.B. Cope (ed.). Proceedings of the Forum-Grazing and Vascular Plants of Arizona Editorial Committee. 1992. A new flora Riparian/Stream Ecosystems. Trout Unlimited Inc., Denver, CO. p. for Arizona in preparation. J. Arizona-Nevada Academy of Sciences 21-30. 26:1 Thompson, R.S. 1988. Vegetation dynamics in the western United Warner, R.E. 1984. Structural, floristic, and condition inventory of cen- States: modes of response to climatic fluctuations. In:, B. Huntley tral Valley Riparian Systems. In:, R.E. Warner and K.M. Hendrix and T. Webb Ill (eds.). Vegetation History. Kluwer Academic (eds.). California Riparian Systems: Ecology, Conservation, and Publishers. p.415-458. Productive Management. University of California Press, Berkeley, Turbak, Gray. 1993. Survivors in the shadows: threatened and endan- Calif. p. 356-374. gered mammals of the American west. Northwest Publishing. White, A.S. 1985. Presettlement regeneration patterns in a southwest- Flagstaff, Ariz. ern ponderosa pine stand. Ecology 66:589-594. Van Devender, T.R. 1990a. Quaternary vegetation and climate of the Whittaker, R.H., and W.A. Niering. 1965. Vegetation of the Santa Chihuahuan Desert, United States and Mexico. fn:, Betancourt, J.L., Catalina Mountains, Arizona. I. Gradient analysis of the south slope. T.R. Van Devender and P.S. Martin (eds.) 1990. Packrat Middens: Ecology 46:429-452. The Last 40,000 Years of Biotic Change. University of Arizona Winegar, H.H. 1977. Camp creek channel fencing- plant, wildlife, Press. p. 104-133, Tucson Ariz. and soil and water response. Rangeman's Journal 4:10-12. Van Devender, T.R. 1990b. Late Quaternary vegetation and climate of the Sonoran Desert, United States and Mexico. In, Betancourt, J.L., T.R. Van Devender and P.S. Martin (eds.) 1990. Packrat Middens: The Last 40,000 Years of Biotic Change. University of Arizona Press. p. 134-165, Tucson, Ariz.