Print PageThe American Bison in the Henry Mountains are one of the last free-roaming, genetically pure herds of bison remaining in North America. Over the last decade, the herd has used a cattle winter range during the summer and early fall, creating a conflict between wildlife officials, land managers, and local ranchers. At the heart of this conflict is the question of whether bison are negatively impacting the rangeland resource. The objectives of this study are to (i) determine whether bison have altered the structure of the salt desert plant community in the cattle winter range, (ii) use NDVI/remote sensing data to help us confirm that any spatial differences we document reflect temporal trends, and (iii) help resolve the conflict between wildlife managers and ranchers over the limited winter range resource by replacing perceptions with data. Vegetation surveys were conducted over two growing seasons to characterize plant species composition, cover, species richness, and grazing intensity on three adjacent, geomorphologically similar mesas, one bison and cattle grazed, one cattle only, the third un-grazed. We used a 25-year remote sensing time series to detect temporal shifts in the plant community vegetation.
Results/Conclusions
We found few differences in species composition on the three mesas despite their different grazing histories. There was also no difference in the NDVI time series across the three grazing types. However, we did find higher grazing intensity on the two dominant forage species, Achnatherum hymenoides and Pleuraphis jamesii, on the bison plus cattle grazed mesa in fall, before the cattle were turned out to winter pasture. Our results indicate that high intensity summer bison grazing has yet to significantly alter plant community composition. Shifts in community composition can take years to unfold and just as long to correct, therefore continued monitoring of the combined effects of cattle and bison is important.
phone 202-833-8773