Effects of Fire Disturbance on Grasshopper (Orthoptera: Acrididae) Assemblages of the Comanche National Grasslands, Colorado

Abstract

We documented effects of spring burns on grasshopper assemblages of the shortgrass prairie at the Comanche National Grassland, Baca County, Colorado, in 1999 and 2000. We measured grasshopper density and diversity at each of four transects on both burned and unburned sites at three locations. We did not find consistent responses of these assemblages to fire in 1999 or 2000 due to site-specific assemblage dynamics. Specifically, grasshopper density exhibited three different trends between treatments at the three locations sampled: responses were similar between burned and unburned plots at Location 1, there were significantly more grasshoppers in the unburned pasture at Location 2, and there were significantly more grasshoppers in the burned pasture at Location 3. These site-specific trends were supported by species richness measurements. Furthermore, there were no significant differences in any of the subfamilies or guilds in the number of grasshoppers collected in the burned versus the unburned treatment pooled over location. The different trends between treatments at each location for the grasshopper assemblage as a whole were most likely the result of pre-existing differences among locations and sites. That the same three trends were seen in 2000, despite time for recovery, supports this explanation. The results suggest that spring burns in the shortgrass prairie do not affect the grasshopper assemblage beyond the natural variability occurring within the grasshopper assemblage.