Grazing results in the removal of natural vegetation, the alteration of plant community composition, and the modification of soil characteristics, which in turn affect hydrologic and erosional processes. Effects are particularly acute in the riparian zone, where livestock tend to congregate, attracted by water, shade, cooler temperatures, and an abundance of high-quality forage. Grazing results in the removal of vegetation and the change in the composition of the vegetation. East of the Cascade range, the willow, aspen, sedge, rush and grass communities have been reduced or eliminated and replaced with annual grasses and sagebrush. In general, grazed lands have less vegetation and litter cover than ungrazed lands and in many areas of the West, perennial grasses have been replaced by non-native annual grasses and weedy species.
Grazing also influences vegetation characteristics and soil permeability through compaction.
In addition, the hooves of grazing animals can also detach soil particles, making the land more susceptible to erosion. Grazing may also promote erosion along streambanks where animals have trampled the banks and eliminated riparian vegetation, decreasing bank stability as deep-rooted vegetation is lost. Downcutting effectively separates the stream channel from the floodplain, allowing flood waters to be quickly routed out of the system and leading to lowering of the water table. Grazing may affect stream temperatures through a number of mechanisms. Riparian vegetation shades streams, serving to help regulate stream temperatures.