that hydrological factors do not account for the differences between plant communities inside and outside of exclosures. Lowering water tables from stream incision and loss of beaver ponds may reduce wetland habitat. There may be drying of wetland depressions but there are no long-term data on shallow groundwater levels in northern range locations where drying may be occurring to explain changes in these depressions. Some of the depressions may also be filling in, reducing the amount of area available for wetland species (committee observation, Yellowstone National Park northern range, June 1999). Wetlands in the northern range that support herbaceous vegetation may be grazed, but use of these areas probably is not as detrimental to their long-term sustainability as potential changes in groundwater availability. However, wetlands dominated by woody plants appear to be significantly degraded by browsing.



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