Date of Award:

12-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Peter B. Adler

Committee

Peter B. Adler

Committee

Johan du Toit

Committee

Janis L. Boettinger

Abstract

The 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 the wildlife officials who manage the bison population, and Bureau of Land Management officials and local ranchers who manage the rangeland. At the heart of this conflict is the question of whether bison are negatively impacting the rangeland resource, potentially reducing the abundance of preferable plant species. Negative impacts could include reduced forage availability in the short-term and undesired changes in plant species composition in the long-term. The objectives of this study are to (i) determine whether bison have negatively altered the structure and composition of the grass-shrubland plant community in the cattle winter range, and (ii) 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, abundance of present plant species, and grazing intensity on three adjacent, mesas with the same plant communities to assess potential changes induced by recent bison use. Each mesa has a different grazing history, one being grazed by bison and cattle, the second being grazed by cattle only, and the third being ungrazed. I used 28-years of satellite imagery to detect possible shifts in vegetative productivity for each mesa.

During the fall on the bison plus cattle grazed mesa, before the cattle were turned out to winter pasture, I found higher grazing intensity on two important dietary plant species. Despite the different grazing histories of the three mesas, I found few differences in species composition and cover consistent with grazing-related degradation. There was also no difference in the satellite imagery estimations of plant productivity through time across the three grazing types. My 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.

This project was partially funded by the Berryman Institute, which is dedicated to improving human-wildlife relationships and resolving human-wildlife conflicts through teaching, research, and extension. My results may ease the tension of the present conflict by providing objective data to characterize the extent of bison impacts on the cattle winter range.

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