Author
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Drewa, Paul |
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Havstad, Kris |
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Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/11/2000 Publication Date: 8/1/2001 Citation: Drewa, P.B., Havstad, K.M. Effects of fire, grazing, and the presence of shrubs on Chihuahuan Desert grasslands. Journal of Arid Environments. 2001. v. 48(4). p. 429-443. Interpretive Summary: Southwestern desert grasslands were once characterized by lightning- initiated fires that are traced back to the early 1500s. During the late 1800s, heavy grazing by domestic livestock reduced perennial grass abundance and likely marked the advent of reduced fire occurrence. This period of overgrazing contributed to the expansion of shrub distributions and abundances and accelerated soil erosion. At present, there is renewed interest in the role of fire in the Southwest as vegetation abundance and fire intensities have increased following reductions in livestock activity. Little is known about the role of fire in grasslands of the northern Chihuahuan Desert, particularly in south central New Mexico. We examined the responses of non-woody plants to fire, livestock grazing and the presence of honey mesquite in northern Chihuahuan desert grasslands on the Jornada Experimental Range. After 4 years following June prescribed fires, perennial grass cover decreased 13% but increased 5% in unburned areas. In contrast, cover of perennial forbs was 4% greater after fire. Occurrence frequency of perennial grasses and forbs decreased 30% more and increased 10% more respectively in burned than unburned areas. Species diversity increased 225% more following burning. Light livestock grazing (<30% utilization) had similar effects as fire, and the presence of honey mesquite had no effect on responses of non-woody species. Fires were conducted during near drought conditions while grazing occurred during years of precipitation equivalent to long-term average. Precipitation immediately following fire may be critical for recovery of dominant perennial grasses in desert grasslands; relationships between fire and post-fire precipitation patterns require future investigation. Technical Abstract: Responses of herbaceous and suffrutescent species to fire, grazing, and presence of Prosopis glandulosa were examined in a Chihuahuan Desert grassland in south central New Mexico. Treatments were assigned randomly to eight, 12m x 8m plots within each of two blocks. Following fires in June 1995, unfenced plots were exposed to livestock grazing over four years. Plots were established that either included or excluded P. glandulosa. Species cover and frequency were estimated before and after treatments. Perennial grass cover, primarily Bouteloua eriopoda, decreased 13% in burned plots but increased 5% in unburned areas. Conversely, perennial forb cover was 4% greater after fire. Frequency of perennial grasses and forbs decreased 30% more and increased 10% more respectively in burned than unburned areas. Further, species diversity increased 225% more following burning and was attributed to increases in evenness. In general, ,grazing had similar effects as fire, and the presence of P. glandulosa had no effect on responses of non-shrub species. Fires were conducted during near drought conditions while grazing occurred during years of precipitation equivalent to the long-term average. Precipitation immediately following fire may be critical for recovery of B. eriopoda dominated desert grasslands; relationships between fire and post-fire precipitation patterns require future investigation. |
