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Stohlgren et al. compared 26 long-term grazing exclosure sites with adjacent grazed plots and examined the differences between native species richness, frequency and foliar cover. No significant differences were found in species diversity, evenness, cover, soil texture, or percentage of N and C at the 1000 square meter plot scale between grazed and ungrazed sites. The authors conclude that at the landscape level, grazing probably has little effect on native species richness and rate of exotic species spreading. Grazing has less of an affect on plant species diversity than other factors such as variable soil characteristics and climate.

Large scale (1000 m2) plots inside and outside 26 long-term (31.5 years on average) exclosures, within National Parks, Wildlife Refuges and other management areas, subjected to moderate to heavy grazing in four Rocky Mountain states, did not differ substantially in species diversity, evenness, percent cover by life form, soil texture, soil nitrogen or soil carbon. Yet, 1 m2 subplots demonstrated greater richness in grazed areas. Grazing accounted for about 10% of species richness, foliar and life form cover, plant diversity and some soil characteristics in the large scale plots, leading Stohlgren et al. to conclude that other factors play a larger role. The authors research led to five broad generalizations about current levels of grazing in these Rocky Mountain grasslands: (1) grazing probably has little effect on native species richness at landscape scales; (2) grazing probably has little effect on the accelerated spread of most exotic plant species at landscape levels; (3) grazing affects local plant species and life-form composition and cover, but spatial variation is considerable; (4) soil characteristics, climate, and disturbances may have a greater effect on plant species diversity than do current levels of grazing; and (5) few plant species show consistent, directional responses to grazing or cessation of grazing.