The effects of fire on the plant community in a Chihuahuan Desert grassland

Background/Question/Methods

Disturbance from fire can affect the abundance and distribution of shrubs and grasses in arid ecosystems. Specifically, fire may increase grass and forb production while hindering shrub encroachment. Therefore, prescribed fires are a common management tool for maintaining grassland habitats in the southwest. However, Bouteloua eriopoda (black grama), a dominant species in Chihuahuan Desert grassland, is highly susceptible to fire resulting in death followed by slow recovery rates. A prescribed fire on the Sevilleta National Wildlife Refuge in central New Mexico in 2003 provided the opportunity to study the effects of infrequent fires on vegetation in this region. Our study was conducted along a transition zone where creosote bush (Larrea tridentata) are encroaching on black grama grassland. Before and after the fire, we monitored above ground plant productivity and composition from 2003 to present. Our questions were: 1) Does fire affect plant composition and productivity in this grassland? 2) How quickly do grasses recover from fire in this grassland? and 3) If fire does affect the plant community, does climate variability affect community response?

Results/Conclusions

Following the prescribed fire, there were fewer individual grass clumps and less above ground grass cover in burned areas compared to unburned areas. This decrease in productivity was primarily from a loss of B. eriopoda. Specifically, B. eriopoda density and cover were significantly lower following the fire with a slow recovery in the 5 years following the fire. Other grasses showed no such adverse response to burning. We found more species in burned areas than unburned areas for all years except 2006, when the area had exceptionally higher summer rainfall. Forb species showed a similar pattern across all years. Grass species composition, richness and abundance did not differ between burned and unburned areas or among years. Furthermore, forb cover for most years in both spring and fall was higher in the burned area. In 2006 and 2008, though, there was significantly less forb cover in the spring. Winter precipitation previous to these two springs was less than 15 mm. Therefore, fire negatively affects the dominant grass species while increasing forb cover and richness. However, extreme precipitation events decrease the effects of fire in this arid grassland.