Coppock, David Layne. 1980. Bison-Prairie Dog-Vegetation Interactions in Wind Cave National Park, South Dakota. M.S. Thesis. Colorado State University, Ft. Collins, CO. 145 p.
Studies were conducted to determine if prairie dog impacts were facilitating bison grazing efforts in Wind Cave National Park, South Dakota. Objectives included quantifying (1) sequential prairie dog effects on plant standing crop biomass, compostition, forage quality, and forage accessibility; (2) bison seasonal use of prairie dog colonies; and (3) bison selection for and utilization of dog town sites having different durations of prairie dog activity. The investigation was stratified to examine bison use of older colonies (63-247 ha) having core acreage dominated by forbs and bison use of young colonies (<35 ha) having core acreage dominated by climax graminoids.
Long-term (>12 years) prairie dog impact, 73% of older colony acreage, produced significant decreases in August total plant standing-crops (-57%, p < 0.10) and in total graminoids (-78%, p < 0.01), with no significant effects on absolute forb representation compared to off town sites. Plant composition went from 87% graminoids and 13% forbs off towns to 54% graminoids and 46% forbs. Short-term (<3 years) impacts at colony margins (27% of older colonies) also significantly reduced total vegetation (-58%, p < 0.01), with most of this decrease occurring in graminoids (-60%, p < 0.01). No clear effects on forb abundance or overall plant composition were evident in these areas.
Both long- and short-term impacts significantly increased forage accessibility compared to off town sites by decreasing (p < 0.01) standing-dead/live graminoid biomass ratios. Increases in forage crude protein concentration were evident in long-term (+56%, p < 0.025) and short-term (+30%, p < 0.005) impacts sites during the peak period of bison use.
Bison seasonal use of older prairie dog colonies strongly supported the hypothesis that the primary motivation was related to using colony core areas for rutting activities; however, herds also exerted a strong selection (p < 0.005) for graminoid-dominated colony margins and grazed more per unit of time there (p < 0.04) than on off town or colony core sites.
Bison use of and prairie dog impacts within a young colony were analyzed more intensively. Plant standing crop and forage quality dynamics were characterized for several prairie dog impact levels (0 years, 0-3 years, 3-8 years, and > 8 years) over the 1979 growing season. Prairie dogs reduced peak total live vegetation (p < 0.02) and sequentially reduced total graminoids (p < 0.01) with increasing duration of occupation. Total forbs did not dramatically increase (p < 0.01) until prairie dog impact exceeded eight years. Plant composition began to shift after 3-8 years of impact, and plant species diversity was increased in this impact level. Prairie dogs increased forage accessibility (p < 0.01), forage crude protein concentration (p < 0.005), and forage in vitro dry matter digestibility (p < 0.025).
Bison consistenty selected dog town acreage over adjacent off town prairie in all visits (p < 0.07) and used older colony areas for resting and short-term impacted sites for grazing and resting. Seasonal bison use of young colonies was greatest during the early and mid summer, largely unconfounded with their breeding season. This, in conjuction wiht the observataion that over 75% of all bison grazing occurred in short-term impacted areas of the colony (28% of the study area), makes this investigation the superior example of prairie dogs facilitating bison grazing efforts in Wind Cave National Park.
Implications of these results to current grazing facilitation theory and to wildlife and habitat management in Wind Cave National Park are discussed. Research recommendations are also presented.