Does grazing affect regional climate?

Before European settlement, the Great Plains of the United States contained vast herds of bison. These bison altered the landscape through their grazi ng. Measurement data of the disturbance that such grazing could produce, wh en scaled for the large population of bison, were used with a coupled atmos pheric-ecosystem model to evaluate the likely effect that this grazing had on the growing season weather in the Great Plains. A dynamically coupled me teorological and plant growth model was used to investigate the regional at mospheric conditions over a single growing season. A 50-km horizontal mesh was implemented, covering the central plains of the United States. The mode ling system was then integrated, with a time step of 90 s, for a period cov ering 1 April 1989 through 31 August 1989 using boundary conditions obtaine d from an objective analysis of gridded archive data. This integration was performed with and without grazing to assess the effects on regional atmosp heric and biological processes. The grazing algorithm was employed to repre sent presettlement North American bison and was switched on and off for dif ferent simulations. The results indicated a cooling response in daily maxim um temperatures to removal of grazing. The opposite trends were found for t he minimum daily temperature. It was also found that grazing produced signi ficant perturbations in the hydrological cycle.