PARENT SESSION
Oral Session #99: Grazing.
Presiding: T. Arredondo
Friday, August 9. 9:00 AM to 12:00 PM. Graham Meeting Room, TCC.
Bison grazing response to landscape heterogeneity generated by fire.
CROSTHWAITE, KATE1, WALLACE, LINDA*,2, 1 Bureau of Land Management, Rawlins, WY2 University of Oklahoma, Norman, OK
ABSTRACT- To determine whether fire spatial and temporal scales affect foraging behavior and grazing intensity by bison (Bison bison), we burned three different spatial scales of fire (225 m2, 900 m2, and 3600 m2) across an otherwise homogeneous landscape. We then monitored grazing intensity for the succeeding fourteen months. During the first five months after the burn (August to January), the bison grazing intensity pattern was inversely related to plot size. During the next five months (January to June), the bison grazing intensity in the control plots was less than that in the burned plots. The grazing intensity was highest in the 900 m2 plots and lowest in the 3600 m2 plots. The final four months (June to October), the bison grazing intensity was higher in the control plots compared to the burn plots except in the 3600 m2 plots. The pattern displayed within the first five months after the burn is congruent with the expectations of optimal foraging theory with overmatching in the smallest plot size of 225 m2. The next two sampling periods displayed a matching aggregate response to plot size relative to biomass availability. The temporal shift that we found in bison response to burn patch size is, to our knowledge, the first such examination of both spatial and temporal responses by bison to landscape heterogeneity. We now have quantitative evidence of how herbivores can alter their foraging responses to changes in landscape structure over time.
KEY WORDS: Bison bison, tall grass prairie, grazing, fire