This study was designed to provide part of the framework for placing the aboriginal landscape-scale process of bison grazing within the context of contemporary prairie remnants. The specific objectives were: (1) determine the ineractions between fire and the spatial distribution patterns of bison grazing; and (2) identify the extent to which fire and range site constrain the bison utilization of the landscape. The study was conducted at the Niobrara Valley preserve (Nebraska) within a 2,812 ha pasture with a bison stocking rate of 1.0 AUM.ha-1.year-1. Thirteen percent of the pasture was burned each year (80% during the dormant and 20% during the growing seasons) with burn units selected with a weighted random system from areas with the highest fuel. Bison herd location and dispersion were recorded weekly from 1989 to 1996 within 16 ha grids. The data was incorporated into a GIS system with layers for burn patterns and range site location. There was a significant bison selection for burned areas during the growing seaason that lasted from 1-3 years but no departure from the null model during the non growing period. There was a significant under selection of choppy sands by bison during the growing season but no departure from null model predictions during the non-growing season. Fire was hierarchically dominant over range site (it overrode range site effects). Fire is a key ecosystem process in grazing behavior in sand hill grasslands and hierarchically constrain range site selection. The absence of fire alters bison grazing patterns and can significantly change the spatial distribution and landscape patterns of plant diversity.