Hartnett et al. studied the effects of bison grazing in Kansas tallgrass prairie on plant species composition and diversity components in sites of contrasting fire frequency. Cover and frequency of cool-season graminoids and some forbs were consistently higher in sites grazed by bison than in ungrazed exclosures, whereas the dominant warm-season grasses and other forbs decreased in response to bison. Increased heterogeneity and mean species richness in grazed prairie to ungrazed prairie were likely a result of greater microsite diversity generated by bison, whereas preferential grazing of the dominant grasses and increases in subordinate species resulted in an increase in equitability of species abundances. Bison had a greater influence on species richness and heterogeneity of annually burned sites, which they have been observed using more than areas burned every 4 years. Results of this study indicate that bison grazing increases various components of floristic and spatial diversity in tallgrass prairie. Effects of native and domestic ungulate grazers on components of grassland biodiversity have important potential implications for grassland ecosystems and range management.
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