Assessing the Effects of Local Plant Communities on Grazing Selection by American Bison (Bison bison) in the South Dakota Badlands

Abstract

The American Bison (Bison bison) is the largest land mammal in North America. Grazing in herds, they can clip large areas of prairie vegetation. Black-tailed prairie dogs (Cynomys ludovicianus) rely on short vegetation to see predators and provide crucial benefits as a prey source and tunnel architect for the endangered black-footed ferret (Mustela nigripes). An understanding of bison grazing selection could influence future studies intended to manipulate that selection and increase suitable habitat for prairie dogs, increasing suitable habitat for ferrets. We conducted vegetation surveys using a Daubenmire frame to assess plant diversity and ground coverage on twenty plots across Bouquet Table South, a nearly 4,300-acre pasture in Buffalo Gap National Grassland in southwestern South Dakota, from June 30, 2025 – July 2, 2025. We categorized each plot by the most abundant plant species. We then divided the pasture into 20 Thiessen Polygons in ArcGIS Pro, assigning each the nearest survey point. We also collected bison herd locations using a GPS unit, compass, and rangefinder from June 4, 2025 – June 28, 2025. Additionally, we collected location data from satellite ear tags on eight of the roughly 350 bison in the pasture from May 9, 2025 – July 2, 2025. Using observational and satellite tag data, we plotted bison locations across the pasture. We then assigned each bison location to the nearest sample plot and its associated vegetation community. We conducted a chi-squared test to compare actual bison distribution to the proportional area assigned to each vegetation community.