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The influence of human activities on riparian zone vegetation differs markedly by ecoregion and stream size. Large rivers, dams and water diversions affect ecological processes more than local land uses do. However, for small streams, the reverse is generally true. Examples demonstrating these relationships include studies completed on the Missouri River in North Dakota, the Platte River in Nebraska, and Foster Creek in western South Dakota. On the Missouri River, damming has stopped river meandering and the regeneration of riparian forests in gaps between reservoirs. In contrast, on the Platte River, diversion of a large portion of the flow for cropland irrigation has contributed to the expansion of riparian forests. And on Foster Creek, the riparian zone was destroyed by homesteading early in this century; however, the creek is recovering because of improved land management. I conclude that restoration methods need to be tailored to deal with the large variation in stream response to human use.