Black-Tailed Prairie Dog Effects on Montana's Mixed-Grass Prairie

Abstract

Forty paired sites were examined on the mixed-grass prairie of northeastern Montana to compare the effects of black-tailed prairie dog (Cynomys ludovicianus) colonies on native range vegetation. Thirty 0.25-m2 quadrats were placed on colonized and uncolonized locations and matched by environmental conditions. Cover and standing crop biomass of each plant species was estimated using a double sampling procedure where every third plot was clipped and estimated. A total of 2 400 quadrats were estimated, whereas 720 quadrats were clipped during the months of May-August of 2000 and 2001. Crude protein, digestibility, neutral detergent fiber, and acid detergent fiber were determined on the basis of vegetative classes (cool-season grasses, warm-season grasses, standing dead grass, forbs, and dwarf shrubs). Pairwise comparisons were made using paired t tests and differences were declared significant at the 0.05 level. Plant biomass of colonized sites was dominated by fringed sagewort (Artemisia frigida Willd.) (42%), blue grama (Bouteloua gracilis [HBK] Lag. ex Steud) (16%), and western wheatgrass (Agropyron smithii Rydb.) (16%). Uncolonized sites were dominated by Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) (36%), western wheatgrass (13%), and blue grama (12%). Standing crop biomass, plant species richness, litter, standing crop crude protein, sagebrush canopy cover, and density were greater (P < 0.05) on uncolonized areas compared to colonized areas. Bare ground and crude protein concentration were greater (P < 0.05) on areas colonized by prairie dogs compared to uncolonized areas. Digestibility and fiber content of both areas were not different (P > 0.05). Activities associated with prairie dog colonies reduced plant productivity and plant species richness of the mixed-grass prairie by reducing cool-season perennial grasses and litter, increasing bare ground, and eliminating big sagebrush.