Diet and Vegetation Impacts of a Reintroduced Bison Herd

摘要

To redress prairie loss, managers seed former agricultural lands and reinstate key ecosystem processes with prescribed fires and reintroduction of native grazers to create restored prairies. Bison (Bison bison) were almost hunted to extinction in the late 1800's but are recovering and have recently been reintroduced to restored prairies for their ecosystem-engineering roles. The effects bison and fire have on remnant (never-plowed) prairie vegetation are well documented. However, there is little known about how bison will affect and shape vegetation patterns in restored prairies. These effects may be largely driven by bison's dietary preference to forage primarily on grasses. This study aims to quantify both bison diet and their effects on vegetation in a chronosequence of restored prairie with varied burning regimes. We used stable isotope analysis to quantify delta13C and delta15N in plants and bison hair to estimate the probability distributions for the proportional spread of bison diet constituents. Plant composition was measured across a chronosequence of restored prairie with varied grazing and fire regimes. We found that bison primarily grazed on C4 grass species throughout the late spring and early summer. However, bison foraged more on wetland species and high delta15N forbs in the late summer and fall. Plant diversity decreased with restoration age and did not differ among either grazing or fire treatments. However, grazed sites displayed a wider range of variation between plant communities. Older restorations tended to be more similar in species and functional group composition in comparison to the younger sites. The high contribution of wetland species in bison diet may be dampening their impacts on plant communities in the tallgrass prairie sites. Even though bison and fire did not have as important of a role as we predicted, changes in composition hint at bison impacts beginning to occur within these restored tallgrass prairies after three years of reintroduction.