Resumen de The effect of fire spatial scale on Bison grazing intensity
L. L. Wallace, K. A. Crosthwaite
To determine whether fire spatial and temporal scales affect foraging behavior and grazing intensity by Bison (Bison bison), we burned three different patch sizes (225, 900, and 3600 m2) across an otherwise homogeneous grassland landscape. We then monitored grazing intensity for the succeeding 14 months. During the first 5 months after the burn (August–January), the Bison grazing intensity pattern was affected by whether a plot was burned and only marginally affected by plot size. During the next 5 months (January–June), grazing intensity was unaffected by plot size, but was greatest in the unburned 225 and 3600-m2 plots. The final 4 months (June–October), grazing intensity was unaffected by treatments other than being higher in the unburned 3600-m2 plots. By the final sampling date, biomass was significantly greater in the burned plots and grazing intensity appeared to be responding to the amount of biomass present and the total amount of N present. The pattern displayed within the first 5 months after the burn is congruent with the expectations of optimal foraging theory with overmatching in the smallest plot size of 225 m2 (BioScience 37 (1987) 789–799). The next two sampling periods displayed a matching aggregate response relative to biomass availability (Oecologia 100 (1999) 107–117) and total nitrogen mass (g m−2). 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 native herbivores can alter their foraging responses to changes in landscape structure over time.
