In this study, Day and Detling evaluated the influence of natural and simulated urine deposition by a native herbivore, American bison (Bison bison), on plant biomass, species composition, and N concentrations in a northern, mixed-grass prairie in South Dakota. In particular, they examined the response of Schizachyrium scoparium (C4) and Poa pratensis (C3) to increased soil N levels via urine deposition. Total aboveground biomass on putative bison urine patches was significantly higher than on control areas, but amounts of standing dead were similar on the two areas. Species composition was reversed on treatment and control areas, with P. pratensis dominating urine patches and S. scoparium dominating adjacent areas. Nitrogen concentrations of P. pratensis and S. scoparium were significantly higher on urine patches. Although N concentrations of both grasses were similar on control areas, N concentrations of P. pratensis were higher than S. scoparium on urine patches. The relative proportion of P. pratensis on simulated and natural urine patches was significantly higher than on control areas, while S. scoparium was proportionately lower on both urine patch types. Aboveground herbivore utilization was greater on urine patches than on adjacent vegetation. Although urine patches only covered 2% of the study site, they provided 7% of the biomass and 14% of the N consumed by aboveground herbivores from June through August.
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