The effects of grazing by sheep and wildlife on willow (Salix spp.) communities in the Greater Yellowstone Ecosystem were compared in this study. Willow communities grazed by wildlife (elk, Cervus elaphus, and bison, Bison bison) were on the northern range of Yellowstone National Park. Sheep-grazed areas were in the Centennial Mountains on the U.S. Sheep Experiment Station summer range. Canopy cover was similar in the Yellowstone exclosures and on the sheep range, and height was greater in the Yellowstone exclosures. Comparison of historic photos dating to the 1870's with recent photos showed that tall willows had disappeared in 41 of 44 Yellowstone sites, while tall willows remained in all 28 sites first photographed from 1871-1939 on the sheep range and even appeared to increase in some locations. The authors conclude that very heavy grazing by native ungulates has led to the sharp decline of willow in Yellowstone, while willow communities have persisted in the face of more moderate use by native and domestic ungulates on the U.S. Sheep Experiment Station.
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