Chapter 5 Grassland and Desert Scrub Authors: Corrine Dolan and Alix Rogstad

Cover photo: Prescribed burn conducted by the Apache-Sitgreaves National Forests, Clifton Ranger District. Courtesy of Tom Shafer.

Chapter 5 60 GRASSLANDS AND DESERT SCRUB

Description

in colder northern Arizona fall more towards the shrubby end of the continuum. This means there are a greater number of species such as sagebrush and blackbush. Many of these grasslands have undergone extensive vegetation change (Turner et al. 2003). Improper grazing management, nonnative species, fire exclusion, and altered climatic conditions have contributed to this change, although to what extent each factor is responsible is under much debate. Photo by Cori Dolan It is apparent, however, that fire is a driving force in these vegetation communities, shaping plant Picacho Peak State Park communities’ structure and function. Compared to forest communities, grassland communities are There are approximately 6 million acres of more flammable, can ignite and spread fire under a grasslands in Arizona (Figure 5.1) (USGS 2004) that wider range of conditions, and are able to recover contain almost 400 species of grasses (Hendricks more rapidly following a fire (D’Antonio and 1985). In Arizona, there are three types of grasslands Vitousek 1992). that differ by elevation, annual rainfall, and vegetation. Mountain meadow grassland is found The desert scrub vegetation community occupies at the highest elevations (7,000 to 10,000 feet) and approximately 41 million acres in Arizona (USGS receives the most precipitation (20 to 35 inches 2004) (Figure 5.1) and can be found at elevations annually). The most extensive mountain meadow ranging from 100 to 6,500 feet (Hendricks 1985). grasslands occur in the White Mountains and on the Desert scrub communities are characterized by Kaibab Plateau. They also occur in isolated areas open, patchy stands of plants scattered over bare in southeastern Arizona, such as the Pinaleño and ground. Compared to grasslands, desert scrub Chiricahua Mountains (Hendricks 1985). Plains communities receive less rainfall overall, between grassland is found at mid elevations (5,000 to 5 and 12 inches annually. Desert scrub in southern 7,000 feet) and receives slightly less precipitation Arizona contains fewer shrubs and more cacti (10 to 20 inches annually). Plains grasslands occur than in northern Arizona. Due to a colder climate, mostly east and north of Flagstaff, but also in northern Arizona desert scrub has a high shrub southern Apache County and in much of Yavapai content with very few cacti. Box 5.1 contains a list of County. Semi-desert grassland is found at the lowest elevations of all three types and receives the least amount of precipitation (3,000 to 5,000 feet elevation and 8 to 15 inches of rain annually). Desert grasslands occur mostly in southeastern Arizona where they extend from the U.S.-Mexico border to the north and east of Tucson, with a few patches north of Phoenix. Species composition varies across the geographic area (Abbott 1997). Southeastern Arizona, with hotter temperatures than northern regions, has more pure grasslands with little shrub component. However, these same

Photo by Tom Shafer; Apache-Sitgreaves National Shafer; Tom Photo by Forests, Clifton Ranger District grasslands also have a higher density of nonnative grass species, which can alter fire regimes (see Human Dimension section, this chapter). Grasslands Arizona desert scrub community.

Chapter 5 61 common plants found in desert scrub areas. While grasslands are adapted to periodic fire, desert scrub areas are typically the opposite. Alterations to the landscape, however, are leading to a convergence of these two different fire regimes. Desert scrub vegetation is encroaching on grasslands while nonnative grasses and shrubs are invading desert scrub areas. The result is an increase in the amount of fire in desert scrub. People value grasslands and desert scrub areas for a variety of reasons including livestock grazing, horseback riding, hiking, camping, and residential

Photo by Guy McPherson and commercial development. The grassland Garden Canyon, Fort Huachuca Military Reservation and desert scrub vegetation communities are experiencing rapid human population

The most common species associated with grassland and desert scrub vegetation communities are listed below. Species that are commonly found in both communities are in the Overlap Species column. Detailed PLANT FACT SHEETS with pictures of each species listed are located in Appendix C.

Box 5.1 Species Commonly Associated with Grasslands and Desert Scrub

Major Grassland Species Major Desert Scrub Species Overlap Species

Arizona fescue Barrel Cactus Mesquite (Festuca arizonica) (Ferocactus wislizenii) (Prosopis spp.) Black grama Blue Paloverde Ocotillo (Bouteloua eriopoda) (Parkinsonia florida) (Fouquieria splendens) Lehmann lovegrass Broom snakeweed (Eragrostis lehmanniana) (Gutierrezia sarothrae) Sagebrush Catclaw acacia (Artemisia spp.) (Acacia greggii) Sideoats grama Mormon tea (Bouteloua curtipendula) (Ephedra viridis) Three awns Saguaro (Aristida spp.) (Carnegiea gigantea) Tobosa Yellow Paloverde (Hilaria mutica) (Parkinsonia microphylla)

Chapter 5 62 Desert Scrub and Grassland in Arizona

Figure 5.1. Desert Scrub and Grasslands in Arizona

Chapter 5 63 Historic Fire Regime

Woody plants, such as mesquite and sagebrush, were almost nonexistent in grasslands prior to 1880 (McPherson 1995). Fire most likely prevented shrub establishment because most shrubs in this type are not fire resistant, especially as seedlings. Therefore, fire was a significant factor in keeping grasslands from turning into shrublands (Humphrey 1958; Wright and Bailey 1982). Fire history in desert scrub is much harder to describe than in grasslands due to the lack of research. Historical accounts suggest that fires did not significantly impact desert scrub areas prior to the 1880s (Humphrey 1974). Although wildland fires were never frequent in desert scrub communities,

Photo courtesy of the Bureau Land Management they may have been more common in the 19th Fire in grasslands prevented shrub encroachment. century due to greater grassland continuity (Bahre 1985). Throughout the Southwest, shrubs have Historically, wildland fire was common in the invaded former grasslands that historically may grassland vegetation communities of Arizona. It is have had frequent fires (Wooten 1916, Leopold 1924, difficult to determine exact historic fire frequencies Humphrey 1958, Turner et al. 2003). When fire did because grasslands lack large trees that could occur, recovery of the burned area was slow due to contain fire scars. Historical accounts dating back to low water availability (Brown and Smith 2000). 1528, however, suggest that fires were large in size and occurred frequently (Humphrey 1958; Bahre 1991). The historic fire return interval for grasslands Grasslands are inherently fire-adapted is thought to be around every 4 to10 years (Kaib et vegetation communities, while desert al. 1996), which is about the same frequency as the ponderosa pine forests, but much more frequent scrub is not. than the neighboring desert scrub areas.

Current Fire Regime

The grassland and desert scrub vegetation communities in Arizona are significantly different from what they were prior to major European- American settlement. There are now fewer native plants, more woody plants, and a more fragmented landscape. Perhaps the most significant factor affecting grasslands is the reduction in continuous fuel required to carry a fire (McPherson 1995). The result is that fires do not occur as often as they once did and are smaller in size (Bahre 1985). On the other hand, the most significant factor affecting desert scrub is the increase in nonnative grasses, which increases fire occurrence in locations where it once was rare. The

result is that common desert scrub plants and animals Photo courtesy of the Bureau Land Management that are not adapted to fire can be severely harmed Cave Creek Fire, 2005 when fire occurs frequently.

Chapter 5 64 In grasslands, improper livestock grazing and are more tolerant of periodic fires. Increasingly management allowed much of the fine, grassy fuels frequent fires, however, even those of low-intensity, to be removed over time. Additionally, roads and are devastating to the plants in this vegetation trails broke up the continuity of fuels and further community because they are poorly adapted to contributed to reductions in fire frequency and survive the passage of a fire. In addition, desert scrub size. Furthermore, humans actively suppressed fire may take centuries to fully recover from a severe fire when they could. The natural fire return interval (Esque and Schwalbe 2002). for grasslands is long enough for grasses to recover but not long enough for woody plants to become established before the next fire comes through (Brown and Smith 2000). The result of fire exclusion and improper livestock grazing management, therefore, is that woody species such as mesquite (Prosopis spp.), acacia (Acacia spp.), and sagebrush (Artemisia spp.) are encroaching into the grasslands. Desert scrub vegetation communities have fewer fires than grasslands (Bahre 1991), although fires are occurring more frequently now than historically. Desert scrub vegetation communities most likely experienced some fire events, but did not evolve with recurrent fires. Of the four deserts in Arizona, the Chihuahuan Desert contains more grasses and more bare, rocky areas than the Sonoran, Mohave, Photo by Cori Dolan and Great Basin Deserts. The result is that some Fires are increasing in occurrence in desert scrub vegetation areas of the Chihuahuan Desert carry fire more easily types.

Fire Effects

Plants

The effects of fires are more consistent from site The impact of fire on individual species is largely to site in grasslands than in the other vegetation dependent on the growth form of the plant and the communities described in this publication. The amount of moisture available following the fire. For majority of plants in grasslands are considered fine example, black grama (Bouteloua eriopoda) is extreme- fuels that ignite and spread fire easily (DeBano et al. ly susceptible to fire damage because the growth 1998). Additionally, because of the fineness of the fuel, structures are above ground (Simonin 2000). If the fires are more likely to be low- to moderate-intensity with fewer negative impacts than in the forest or woodland vegetation communities. Fire may decrease plant cover in the short-term as the aboveground portions of individual plants are killed. In contrast, fire can reduce woody plants allowing grasses to expand coverage in the long- term. Additionally, fires can increase the rate of nutrient cycling. The impact of fire on grasslands is much more dependent on when and how often the fire occurs than on individual plant adaptations to fire (McPherson 1995). Fires that occur during the growing season (which varies depending on grassland type and location in the state) are much more damaging and the impacts last longer than fires that occur when plants are dormant. Photo courtesy of the Bureau Land Management The impact of fire on most desert scrub plants depends on frequency.

Chapter 5 65 Wildlife The numbers of individual animals in the grassland vegetation community killed by fire is low. Most animals can escape fire by moving out of the area or by staying underground. Aside from the direct effect that fire has on some individuals (i.e. death), the indirect impact of fire on animals is dependent on the plant communities’ response to the fire (McPherson 1995). Fires that remove large amounts of woody plants may have a negative impact on some birds and rodents that use those plants for food and shelter. Other animals like chipping sparrows (Spizella passerina) and mourning doves (Zenaidura macroura) thrive on the increase in grassy plants, while animals

Photo by Cori Dolan like the pronghorn (Antilocapra americana) experience advantages from burned sites where the view is cleared and predators can be seen more easily Impact of a fire in a Lehmann lovegrass dominated grassland. (McPherson 1995). stand was healthy prior to the fire, however, and there Animals common in desert scrub areas have not is adequate summer moisture in the first two growing evolved with frequent fire and therefore are not seasons, recovery can be good (Uchytil 1988). Tobosa adapted to survive fire. The invasion of nonnative grass (Pleuraphis mutica), however, comes back more grasses into desert scrub has increased fire frequency easily after a fire occurs because its growth structures where fire was rare. Animals, such as sage grouse are protected below ground and can recover fully (Centrocercus urophasianus) and desert tortoise after about 3 years if normal precipitation follows the (Gopherus agassizii), cannot survive frequent fires. burn (Uchytil 1988). The impact of fire on most desert scrub plants depends on its frequency. For example, one low- intensity burn may not kill cacti because hairs and spines usually protect the growth structures (McPherson 1995). Repeated fires at short intervals, however, can remove the structures that shield the plant and result in death. Spines also protect cacti from being eaten by herbivores. Frequent fires that remove leave the plant vulnerable to be eaten by animals. Some woody plants have protected buds that

will resprout after a fire, although these plants do not Photo courtesy of National Park Service possess the ability to resprout until after they reach several years of age. Pronghorn (Antilocapra americana)

Human Dimension

Fragmentation and Fire Suppression and other development. Fragmentation impacts Human presence and movement on the landscape the landscape by removing natural corridors, have significant impacts on fire regimes in the displacing animals, and decreasing gene flow among grassland and desert scrub vegetation communities populations. In addition, fragmentation impacts fire in Arizona. For example, the dramatic increase behavior by decreasing the continuity of fuels that in population (Appendix A) has led to exploding are available to burn. Increased development in both development. As a result, the landscape is fragmented grassland and desert scrub vegetation communities by expanding communities, businesses, roads, trails, also increases the need for fires to be suppressed.

Chapter 5 66 Photo by Cori Dolan

Photo courtesy of the Bureau Land Management

Livestock grazing can have significant impacts on grassland fire Prescribed fire in nonnative Lehmann lovegrass regimes.

Livestock Grazing

Cattle and other livestock were introduced into landscaping. Nonnative species can become invasive grasslands around 1500 when European explorers through high rates of reproduction, aggressively brought cows, goats, and sheep to North America competing with native species, and severely altering (Humphrey 1958). Large-scale cattle ranching in the habitat that they are introduced into. Specifically, Arizona began in the 1870s (Bahre 1991). One result nonnative species can alter the fire regime by of improper livestock grazing management is the changing the fuel characteristics at a given site. Many spread of mesquite and other woody shrubs into the invading grasses burn hotter than native plants and grasslands. Improper livestock grazing management can increase in density after a fire (D’Antonio and can lead to increased woody species in several ways. Vitousek 1992). In addition, nonnative species can First, animal droppings spread woody plant seeds like carry a fire through an area where fire is uncommon those of mesquite. Second, livestock grazing decreases and native plants are less adapted to tolerate fire, such the amount of grass in the area. Those grasses would as the case in desert scrub. Some of the more common otherwise interfere with woody plant establishment nonnative species that affect fire regimes in grassland by using nutrients and water required for shrubs to and desert scrub vegetation communities are listed in grow. Third, the removal of fine, grassy fuels that Box 5.2. would have carried fires allowed for the invasion of woody species into the grassland (Humphrey 1958; Nonnative species in grasslands and fire create a Bahre 1991). positive-feedback cycle. For example, nonnative plants colonize an area. The invasion increases an area’s susceptibility to potentially more intense fires. Nonnative Plants Nonnative plants then recover more quickly than natives and increase in density and/or spread out and Another alteration that humans make in vegetation the new increase in nonnative plants further increases communities is the purposeful or accidental the area’s susceptibility to fire (Box 5.3). introduction of nonnative species. A nonnative species is one that is introduced into a place outside of its natural range. Humans have brought many of these nonnative species from other sites. This is especially true for grasses that may have been brought from other places for cattle forage or ornamental

Chapter 5 67 Box 5.2 Common Nonnative Plants in 5.3 Fire-Grass Feedback Cycle Grasslands and Desert Scrub

African lovegrass (Eragrostis spp.)

Buffelgrass (Pennisetum ciliare)

Cheatgrass (Bromus tectorum)

Red brome (Bromus rubens)

Sahara mustard (Brassica tournefortii)

Photo credits top to bottom: U.S. Fish and Wildlife Service; National Park Service; Tom Huette, U.S. Forest Service; Cori Dolan; Desert Managers Group.

Chapter 5 68 Human Dimension

grasses, fragmentation due to housing developments and roads, and shrub invasions (Wright 1986, Bahre 1991, Bock and Bock 1992). Prescribed burning is used in grasslands to decrease woody encroachment. Grasslands are considered to be a low-volatility fuel, which makes them relatively safe to work with. Fire management activities in desert scrub are much more limited than in grasslands. Because fire is not a common occurrence in desert scrub, managers mainly use mechanical treatments to remove nonnative

Photo by Cori Dolan grasses.

Research fire in nonnative Lehmann lovegrass

Regular fire in grasslands keeps woody shrubs from taking over. The absence of fire and the subsequent establishment of woody shrubs in more and more grassland areas is a concern to fire managers. Once woody plants invade a grassland, it is not possible to remove them by simply adding fire back onto the landscape because there is not enough grassy fuel to carry a fire with enough intensity to kill the woody species (McPherson 1995). Managers must consider herbicides or mechanical controls in conjunction with fire to have an effect. The goal of many fire management activities in desert grasslands is to reduce or maintain exotic grasses at current levels. Fire frequency, structure,

Photo by Tom Shafer; Apache-Sitgreaves National Forests, Shafer; Tom Photo by Clifton Ranger District and function of many grasslands in the region have been altered by several factors including improper livestock grazing management (both historic and Rough Ridge prescribed burn current), fire suppression, introduction of nonnative

Chapter 5 69 Grasslands and Desert Scrub Literature Cited

Abbott, L. 1997. The ecological role of fire Humphrey, R. 1974. Fire in the deserts and in semidesert grassland ecosystems of desert grassland areas of North America. In: southeastern Arizona. Final Draft, Upper T. Kozlowski and C. Ahlgren, eds. Fire and San Pedro Ecosystem Program, The Nature Ecosystems. Acad. Press, New York. p. 365-401. Conservancy, Contract No. USPE050197. Kaib, M., C. Baisan, H. Grissino-Mayer, and T. Bahre, C. 1985. Wildfire in southeastern Arizona Swetnam. 1996. Fire history in the gallery between 1859 and 1890. Desert Plants. 7:190 pine-oak forests and adjacent grasslands of – 194. the Chiricahua Mountains of Arizona. P. 253- Bahre, C. 1991. A Legacy of Change: Historic -–264 in P. Ffolliott, L. DeBano, M. Baker, Jr., Human Impact on Vegetation in the Arizona G. Gottfried, G. Solis-Garza, C. Edminster, Borderlands. Tucson, AZ, The University of D. Neary, L. Allen, and R. Hamre, Technical Arizona Press. 231 p. Coordinators. Effects of Fire on Madrean Province Ecosystems. USDA Forest Service Bock, J. and C. Bock. 1992. Vegetation responses General Technical Report RM-GTR-289. Fort to wildfire in native versus exotic Arizona Collins, CO. grassland. Journal of Vegetation Science. 3: 439-446. Leopold, A. 1924. Grass, brush, and timber fire in Southern Arizona. Journal of Forestry. 22(6):1- Brown, J. and J. Smith, eds. 2000. Wildland fire 10. in ecosystems: effects of fire on flora. General Technical Report RMRS-GTR-42-vol. 2. Ogden, McPherson, G. 1995. The role of fire in the desert UT: U.S. Department of Agriculture, Forest grasslands. In: McClaren, M. and T. Van Service, Rocky Mountain Research Station. 257 Devender, eds. The Desert Grassland. The p. University of Arizona Press. Tucson, AZ. p. 130-151. D’Antonio, C. and P. Vitousek. 1992. Biological invasions by exotic grasses, the grass/fire Simonin, K. 2000. Bouteloua eriopoda. In: Fire cycle, and global change. Annual Review of Effects Information System, [Online]. U.S. Ecology and Systematics. 23: 63-87. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences DeBano, L., D. Neary, and P. Ffolliot. 1998. Fire’s Laboratory (Producer). Available: http://www. Effects on Ecosystems. John Wiley and Sons, fs.fed.us/database/feis. Inc., New York, NY. 333 p. Esque, T. and C. Schwalbe. 2002. Alien annual Turner, R., R. Webb, J. Bowers, and J. Hastings. grasses and their relationships to fire and 2003. The Changing Mile Revisited: an biotic change in Sonoran desertscrub. In: ecological study of vegetation change with Tellman, B., ed. Invasive Exotic Species in the time in the lower mile of an arid and semiarid Sonoran Region. University of Arizona Press region. Tucson, AZ: University of Arizona and Arizona-Sonora Desert Museum: Tucson. Press. 334 p. p.165-194. Hendricks, D. 1985. Arizona Soils. College of Uchytil, R. 1988. Pleuraphis mutica. In: Fire Effects Agriculture, University of Arizona: Tucson, Information System, [Online]. Arizona. 244 p. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Humphrey, R. 1958. The Desert Grassland: A Laboratory (Producer). Available: http://www. history of vegetational change and an analysis fs.fed.us/database/feis. of causes. Botanical Review. 24:193 -252.

Chapter 5 70 USGS National Gap Analysis Program. 2004. Provisional Digital Land Cover Map for the Southwestern United States. Version 1.0. RS/ GIS Laboratory, College of Natural Resources, Utah State University.

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Wright, H. and A. Bailey. 1982. Fire Ecology: United States and Southern Canada. John Wiley and Sons, Inc. 501 p. Wright, H. 1986. Effect of fire on arid and semi- arid ecosystems – North American continent. In: Rangelands! A resource under siege. Proceedings, 2nd International Rangeland Congress. Cambridge University Press: pp. 575-576.

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