Date of Award

5-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Wildlife and Fisheries Biology

Committee Member

David S. Jachowski, Committee Chair

Committee Member

Donald L. Hagan

Committee Member

Kyran E. Kunkel

Abstract

In western North America, the rapid loss of native grazers, abiotic disturbance processes (e.g., fire), and human-driven land conversion or degradation have resulted in steadily declining biodiversity and rangeland health. Keystone species restoration and their potential to increase rangeland health are common justifications for bison (Bison bison L.) reintroduction projects throughout North America's Great Plains. Similarly, many other conservation groups also justify the removal of livestock from traditionally cattle-grazed rangelands by citing potential increases in rangeland health or community dynamics following years of heavy use by cattle. Our objective was to assess how ten-years of bison reintroduction and livestock removal influence plant community dynamics in the mixed-grass prairie compared to cattle-grazed rangeland. We compared our treatments to each other, and to a predicted historic climax plant community (HCPC) by collecting plant species incidence, abundance, height, and bare ground data at 10 different sampling sites across each of our treatments, all within a common ecological site. We found that bison exhibited mixed keystone effects ten-years post-reintroduction. In support of their keystone role, we observed higher species richness and compositional heterogeneity (beta-diversity) in our bison-grazed treatment than either our cattle-grazed (p = 0.01 and p = 0.03 respectively) or livestock removal (p = 0.007 and p = 0.002 respectively) treatments. We also found that bison reintroduction outperformed cattle-grazing or livestock removal in moving plant communities toward a predicted HCPC-state, being not significantly different in forb composition (bootstrap resampling, p < 0.0001, nboot = 1,000) and abundance (LSM, t = 1.80, p = 1.80, df = 19), bare ground cover (t = -0.36, p = 0.73, df = 4), and abundance of grasses and sedges (t = -1.73, p = 0.12, df = 19). Bison reintroduction areas were also lower in noxious weed abundance compared to cattle-grazed (t = 1.80, p = 0.042, df = 27) and livestock removal (t = 2.88, p = 0.0039, df = 27). Bison may show some of their predicted keystone effects after ten-years, and we suggest that their reintroduction may be a useful to restoring and conserving the Northern Great Plains mixed-grass prairie ecosystem.

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