Plant species composition was monitored in watersheds receiving different prescribed burning and bison grazing regimes across a topographic gradient (lowlands, slopes, uplands) at Konza Prairie Research Natural Area, Kansas, USA for 8 years.  A combination of multivariate analyses were used to determine how individual species, life forms, and the plant community as a whole respond to fire and bison grazing over space and time.  Species diversity was maximized in watersheds that were infrequently burned and grazed by bison and at infrequently burned slope sites, while diversity was lowest on frequently burned ungrazed sites and on frequently burned slope sites.  In general, grass cover was highest in infrequently burned ungrazed watersheds and lowest on frequently burned grazed watersheds, while forb richness was highest in infrequently burned watersheds and grazed watersheds.  Woody plant cover was highest in infrequently burned watersheds and on slopes, while woody species richness was highest on infrequently burned grazed watersheds.  Community stability was positively correlated with species richness.  This study shows that overall, fire and grazing are the main determinants of the plant community in this grassland system, but that topography and year-to-year variability in climate mediate these effects.  A combination of bison grazing and infrequent fire are necessary to maximize diversity and community stability across the landscape.