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.
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Vol. 57 • No. 6