Riparian corridors of Eastern Oregon and Washington: Functions and sustainability along lowland-arid to mountain gradients

Riparian corridors of eastern Oregon and Washington, like those in other regions, comprise small portions of river drainages but provide disproportionately important ecosystem functions. However, most riparian and fluvial ( streams and rivers) systems have been greatly altered. Degraded ecosystems commonly reflect influences of land-uses ( e. g., mining, logging, road construction, fire suppression, livestock grazing), hydro-developments ( e. g., dams, irrigation, flood control) and other human actions. Some important consequences include: degradation and fragmentation of habitats, changes in riparian plant associations, isolated fish populations, and altered flow and sediment regimes. This synthesis paper evaluates some major environmental factors that can influence the sustainability of riparian corridors and fluvial systems along lowland-arid to mountain gradients within river drainages of eastern Oregon and Washington. Four tributary rivers of the Columbia River, the Grande Ronde and John Day Rivers in northeastern Oregon, and the Yakima and Methow Rivers on the eastside of the Cascade Mountains in Washington, provide perspectives on environmental conditions. Factors evaluated include: a) dominant riparian plant associations and distributions in relation to differences in precipitation and temperature regimes along elevation gradients; b) ecological and physiochemical functions of riparian and fluvial systems along elevation gradients; c) long-term historical and contemporary cumulative impacts of human actions; and d) management provisions that could restore and sustain ecosystem functions. Ecological functions of riparian and fluvial systems are viewed as being closely coupled because of their dependence on hydrological ( surface and sub-surface) and sediment routing regimes. From a river landscape perspective, achieving greater connectivity can be a key objective for analyzing and integrating the management of riparian and fluvial ecosystems. Effective management should include ensuring the delineation of major limiting factors ( e. g., erosion, water shortages and temperatures) and identification of streamside and channel networks that link critical habitats at multiple landscape scales ( e. g., locations and spacing of refuge habitats for fish and wildlife). Management actions should encourage the connectivity of reaches and habitats and maintenance of riparian and fluvial functions so interactions can occur. Efforts should include renewal of natural flood and sediment routing regimes and the reestablishment of habitats adjacent to ecologically intact habitats.