Conservation of riparian ecosystems in the United States

Riparian ecosystems include relatively mesic vegetative communities and associated faunas occurring between aquatic and more xeric upland sites.In eastern North America, these ecosystems often occur in broad zones and are referred to as floodplains or bottomlands.In the west, they are conspicuous as narrow belts of vegetation along ephemeral, intermittent, and perennial streams and rivers and are most obvious in steppe, shrubsteppe, and desert regions.Vegetation associated with streams has been referred to as the "aorta of an ecosystem" (Wilson 197932) because of its significance to the perpetuation of water, fish, wildlife, rangeland, and forest resources.Historically, riparian ecosystems have been subjected to both subtle and dramatic perturbations from water management practices (Carothers and Johnson 1975, Curtis and Ripley 1975) (Fig. l), agricultural conversions (Best et al. 1979, Conine et al. 1979), grazing (Cope 1979, Knopf and Cannon 1982), channelization (Barclay 1979, McCall and Knox 1979), and recreational development (Aitchison 1977, Schmidly and Ditton 1979, Johnson and Carothers 1982).Riparian systems represent areas of maximum potential conflict between users of timber, grazing, recreational, water, and wildlife resources (Thomas et al. 1979).Additionally, exotic woody species such as salt cedar (Tumavix pentandra) and Russian olive (Elaeagnus angustifolia) have naturalized extensively within western riparian ecosystems (Robinson 1965, Horton 1977, Olson and Knopf 1986b), displacing native woody species that provide valuable avian habitats but also providing additional habitats for selected species of wildlife (Knopf and Olson 1984, Hunter et al. 1985).Riparian ecosystems have recently attracted much attention, especially relative to the management of public lands in the west.Within the last