Abstract - Prairie Dog and Bison Grazing Effects on Maintenance of Attributes of a Prairie Dog Colony
Cid, Maria Silvia. 1987. Prairie Dog and Bison Grazing Effects on Maintenance of Attributes of a Prairie Dog Colony. PhD Dissertation. Colorado State University, Fort Collins, CO. 112+ p.
Simultaneous grazing by prairie dogs (Cynomys ludovicianus) and bison (Bison bison) produces, maintains and intensifies a series of well documented changes in the structure and function of prairie dog colonies in different grassland types. However as prairie dog and bison grazing regimens differ in frequency and intensity through time, their impacts in the maintenance of the properties of the prairie dog colonies may be different.
The main objective of this study was to determine the individual and combined influence of prairie dogs and bison grazing regimens in maintaining some selected plant and soil attributes of a prairie dog colony in a mixed-grass prairie at Wind Cave National Park, S.D. This was assessed by individual and simultaneous release from their grazing and monitoring the system responses during two years following grazing exclusion. A secondary objective was to determine whether prairie dogs modify their diets in response to these induced changes.
The tendency of the system to revert to its former state when prairie dogs or bison were removed, indicated that they played important individual roles in maintaining the structure and function of the prairie dog colony. However, different characteristics of soil and aboveground vegetation had different temporal patterns of response to grazing release. In a two year period, changes in biomass and shoot nitrogen concentration were clearly expressed, relative cover of differeft growth forms was only slightly affected, and plant species diversity and total soil nitrogen concentration remained unchanged. The different grazing patterns of prairie dogs and bison had similar effects in maintaining the system structure. Though not statistically significant, simultaneous release from both herbivores appeared to have some additive affect on graminoid biomass.
Climatic factors direct and indirectly controlled the structure and function of the plant community. Intensity and frequency of precipitation regulated not only vegetation responses but also bison use of the study area and prairie dog grazing pressure, thereby markedly affecting the response of shoot nitrogen concentration to grazing release.
In spite of lower nitrogen concentration in graminoids and perennial forbs when bison were excluded, prairie dogs did not modify their diets either qualitatively or quantitatively.