Effects of spatially heterogeneous fire and grazing on butterfly communities in tallgrass prairie

Prior studies have demonstrated that fire and grazing can alter butterfly community composition in mixed grass and tallgrass prairies by decimating populations of prairie-specialist butterfly species.  However, those studies have typically involved prescribed fires that were extensive (they burned the entire study site) and grazing that was uniformly intensive.  In contrast, historic fire and grazing regimes in the Great Plains are believed to have been spatially heterogeneous, and many land managers are trying to restore that heterogeneity.  We sought to determine the effects of spatially heterogeneous fire and grazing on tallgrass prairie butterfly communities at 10 tallgrass prairies in southwestern Missouri, U.S.A.  One third of each prairie was burned each year, and five of the prairies were also grazed by cattle (moderately stocked) from mid-April to early August.  We assessed butterfly community composition on these sites from late spring to late summer via modified Pollard walk transects.  In late spring and early summer, recently burned, ungrazed sites had surprisingly large populations of prairie specialist as well as generalist butterfly species, whereas butterfly communities in recently burned, grazed sites were dominated by generalists, and had very low numbers of butterflies overall.  However, by late summer, recently burned, grazed sites fostered diverse butterfly communities and large populations of many species.  In our study, the effects of disturbance on butterfly communities appeared to be fairly short-lived.  We speculate that the close proximity of highly disturbed sites to less disturbed sites can permit specialists as well as generalists to recolonize habitat patches following disturbance.