Response of Chihuahuan Desert Mountain Shrub Vegetation to Burning GARY M. AHLSTRAND Abstract The effects of fire on vegetation in the desert mountain shrub huan Desert. Bunting and Wright (1977) reported theeffectsof fire community were studied on 3 to 7-year-old burned sites near the on desert mountain shrub vegetation 2 years after burning in the northern limits of the Chihuahurn Desert. Coverage and fre- Texas Big Bend country. quency of redberry juniper (Juniipcruspinchotii) and frequency of Kittams (1973) noted that in burned desert mountain shrub whitebail acacia (Acacia texends) were lower, while frequencies of communities, catclaw mimosa (Mimosa biuncifera). skunkbush catclaw mimosa (Mimosa biunc~em) and skeleton goldeneye (Rhus aromatica), silver dalea (Dalea argyraea), skeleton golden- (Viguiera stenoloba) were higher on burned sites when_compared eye (Viguiera stenoloba). mountain mahogany (Cercocarpus mon- with unburned paired piants. Lechuguiiia (Agave lecheguil&, tanus), scrub oaks (Quercus spp.), redberry juniper (Juniperus sotoi (DasytYrion leiophylbun), and sacahuista (No&r spp.) suf- pinchotii) and alligator juniper (J. deppeana) usually recovered fered losses in excess of 50% on burned sites. With the exceptions through some form of vegetative sprouting. He observed that of sideoats grama (Bouteloua curtipendula) and bull muhiy lechuguilla (Agave lecheguilla), datil (Yucca baccata), and mature (Muhlenbergia emersleyi), ail grasses had recovered or showed soto (Dasylirion leiophyllum) were usually killed by fire. ,Bunting increases by the end of three growing seasons. Ail grasses had and Wright (1977) found that fire reduced shrub cover and total recovered or increased on 6 to 7-year-old bums. Recovery of grass cover 43% and 72% respectively in a desert mountain shrub burned piants was predominately by vegetative means, suggesting community 2 years after burning. Coverage of forbs and half that periodic fires can be used to maintain or even increase grass shrubs increased 650%. The fire significantly reduced the density or coverage at the expense of shrubs in this community. cover of sideoats grama (Bouteloua curtipendula), blue three-awn (Aristida glauca), sotol, and lechuguilla, whereas coverage contrib- The response of native vegetation to burning has been the sub- uted by skeleton goldeneye tripled through vigorous sprouting and ject of numerous papers, especially over the last 25 years. Little, seedling establishment on the burned area (Bunting and Wright however, has been reported concerning the effects of fire on vegeta- 1977). tion of the Chihuahuan Desert. Kittams (1973) observed the recov- Information pertaining to other species common to the Chihua- ery of vegetation I to 3 years after burning in desert mountain huan Desert is available from studies conducted elsewhere. Mor- shrub communities located near the northern limits of the Chihua- tality rates for cholla (Opuntia imbricata) and pricklypear (0. phaeacantha) two growing seasons after a prescribed burn on the Author. at the time of the research. was ecologist. National Park Service and Texas High Plains averaged 45% and 68%, respectively (Heirman adjunct professor of range management. Department of Rangeand Wildlife Manage- ment. Texas Tech University. His present address is National Park Service, Alaska and Wright 1973). Pricklypear mortality was 3270 the first year Regtonal Office, 549 W. 5th Avenue, Anchorage, Alaska 99501. following a prescribed burn (Cable 1967) and 28% the second This research resulted from a cooperative effort between the U.S. Department of Interior, National Park Service; and Texas Tech University. It is a contribution of growing season after an experimental tire (Reynolds and Bohning College of Agricultural Sciences, Publication No. T-9-235. Texas Tech University. 1956), in two separate studies conducted in the Arizona Sonoran Manuscript received March 28, 1980. Desert. Survival of ocotillo (Fouquieria splendens) following a 62 JOURNAL OF RANGE MANAGEMENT 35(l). January 1999 wildfire in the Sonoran Desert was 33Ycfor heavily damaged plants compared between burned and unburned sites using analysis of and 50% for plants only scorched (White 1969). Regeneration variance and Chi-square analyses, respectively. Student’s t-test was occurred primarily through basal sprouting. Algerita (Berberis used to determine differences in coverage by growth forms on trifoliolata) sprouted vigorously following a wildfire in south cen- burned and unburned sites. Differences were judged to be signifi- tral New Mexico (Dwyer and Pieper 1967). cant at the 0.05 level. The objective of this study was to document longer term effects Taxonomic nomenclature follows Correll and Johnston (1970). of fire on vegetation in the mountain shrub community of the Chihuahuan Desert by examining 3 to ‘I-year-old burned areas. Results and Discussion Of the 95 species sampled in the 7 paired sites, 47 were common Study Area to 2 or more of the paired sites. Because drought conditions prevailed throughout the sampling period, few annuals were pres- The study sites are in the Guadalupe Mountains of Eddy ent and perennial forbs were not abundant. Most grasses were County, New Mexico, and Culberson County, Texas. The moun- identified using vegetative characteristics. tains, primarily limestone, are part of a Permian reef complex Coverage and frequency of redberry juniper were less on burned termed the Capitan Barrier Reef. The area’s semiarid, continental than on unburned sites. Kittams (1973) observed that a considera- climate is characterized by mild winters, warm summers, and ble amount of heat is required to ignite this species, but once summer showers. The mean annual temperature is 19” C (63” F) at ignited it burns so vigorously that usually all the branches are 1,352 m (4,435 ft) in this community at Carlsbad Caverns National killed. Regeneration occurs slowly through crown sprouts. Burned Park, and annual frost-free days average 226 (U.S. Department of junipers in the present study regained up to 50% of their mature Commerce 1967). Mean annual precipitation is 36.6 cm (14.4. in), height during the 3- to 7-year recovery period, and the 25 to 50 but has ranged from less than 12 cm (4.6 in) to 110 cm (43.2 in)per years predicted by Kittams (1973) for top-killed plants to re- year. Nearly 90% of the annual precipitation occurs between May establish their prebum stature is a reasonable estimate. and October. The frequency of whiteball acacia (Acacia texensis) was greater Characteristic desert mountain shrub vegetation in the Guada- on unburned than on burned sites. Although this dwarf acacia is set lupe Mountains includes lechuguilla, sotol, and redberry juniper. back by fire, this effect may be only temporary until new colonies Prickly pear and sacahuista (Nolina spp.) are generally abundant, can form from rhizomes. and grama and three-awn grasses are common in the community. Burning induces vigorous crown sprouting in catclaw mimosa Vegetation of the area has been described by Gehlbach (1967), (Cable 1975, Carmichael et al. 1978). It may recover from burning Bunting (1978), and Northington and Burgess (1979). in as little time as 5 years (Kittams 1973). Although catclaw mimosa was not abundant on any of the sites in this study, its Methods frequency was greater on burned than on unburned sites. Seven sites that burned between 1967 and 1971 in the desert Skeleton goldeneye was more frequent on burned than on mountain shrub community of the Guadalupe Mountains were unburned sites. Kittams (1973) predicted this species would sampled during the summer of 1974. A similar unburned site was increase through root and crown sprouts 2 to 3 yearsafter burning. located near each burned site for comparison. Shrub intercepts An increase was evident on 3-year-old bums and it persisted were measured by species along ten 25-m (82 ft) lines placed at 5-m through to ‘I-year-old burned sites. (16.4 ft) intervals in each pair of sites. Fifty 20 X 50-cm (7.9 X 19.7 Coverage and frequency of sotol were 75% less on burned than in) plots were sampled at 5-m (16.4 ft) intervals along each inter- on unburned sites. The sheath of dead leaves surrounding the trunk cept line using a frame. Species included within or overlapping the makes this species especially susceptible to fire, and plants with plot frame were recorded according to one of six cover classes with fire-girdled trunks usually die. Sprouting occurs only from the midpoint cover percentages of 2.5, 15.0, 37.5,62.5, 85.0, and 97.5 terminal bud in lightly to moderately burned plants (White 1969, (Daubenmire 1968). Coverage was calculated for individual spe- Kittams 1973). The present study as well as that of Kittams (1973) cies from intercept and plot data, and frequency was determined found that surviving sotol regain most of their cover within 3 years, for species sampled with the plot frame. Sampling adequacy was but many more years will be required for plants to accumulate determined by a species area curve and by plotting cumulative shaggy bases of dead leaves. mean coverage (Mueller-Dombois and Ellenberg 1974). Sacahuista was less frequent on burned sites than on unburned. Burned sites were located using fire narrative records for Carls- Sprouting occurred from the outer portion of the caudex in most bad Caverns and Guadalupe Mountains National Parks. No infor- plants that survived burning. Kittams (1973) measured a 48% loss mation concerning fire intensity, defined as the product of fuel of sacahuista on a 197 I burn. This burn was studied 3 years later, as energy consumed and rate of fire spread (van Wagtendonk 1974), a part of the present study. Frequency and coverage for sacahuista was available, but fuels were estimated not to exceed 1.1 X 10s on the burned site were 53% and 47% respectively, of those present kg/ha (0.5 ton/acre) for litter and cured grasses and 1.6 X 104 on the unburned partner site.