Date of Award
Master of Science (MS)
Dr. Mitchell Greer
Purple threeawn (Aristida purpurea Nutt.) is a native warm-season bunchgrass found in western Kansas on The Nature Conservancy’s Smoky Valley Ranch and across rangelands of western North America. Upon reaching maturity, grazing/clipping pressure decreases for this bunchgrass due to poor forage quality and extreme unpalatability for cattle (Bos taurus) and Black-tailed prairie dogs (Cynomys ludovicianus). This decrease in grazing/clipping has led to development of near monocultures which cause negative impacts to the prairie ecosystem including decreases in rangeland quality and suitable habitat for prairie dogs, a keystone species. This decrease in prairie dog habitat directly affects many species on the ranch that rely on prairie dogs for habitat, including the Black-footed ferret (Mustela nigripes), North America’s most endangered mammal. This study aimed to determine a large-scale management strategy using natural processes such as fire and grazing to decrease purple threeawn cover and reproductive effort. Treatments investigated the effects of high intensity grazing by cattle, at short duration and season long, as well as the effects of clipping by prairie dogs, post burn. Through two grazing seasons, purple threeawn percent cover did not changed. However, reproductive ability decreased in both short and long duration grazing treatments, by means of decreased live purple threeawn crowns and increased dead purple threeawn crowns, as well as decreased purple threeawn seedstalk densities. A larger decline was seen in the short duration grazing treatment from 2017 to 2018 than in the long duration grazing treatment. With this decrease in purple threeawn reproductive ability, prairie dog densities increased within both short and long duration grazing treatment plots, with the greatest increase in the short duration treatment. These results will help inform management of purple threeawn to increase forage and associated economic benefits, while creating better quality habitat for prairie dogs and the organisms that rely on them.
Copyright 2019 Justin Roemer
Roemer, Justin, "The Purple Plague: Effect Of High Intensity Grazing Post Fire On Purple Threeawn Cover And Reproductive Effort And Prairie Dog Responses" (2019). Master's Theses. 3134.