Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources, and are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems. By recognizing the spatial differences in the capacities and potentials of ecosystems, ecoregions stratify the environment by its probable response to disturbance (Bryce et al., 1999). Ecoregions are directly applicable to the immediate needs of state agencies, including the development of biological criteria and water quality standards and the establishment of management goals for nonpoint-source pollution (Omernik and Griffith, 1991; Hughes et al., 1990; Whittier et al., 1988). Ecoregions are also relevant to integrated ecosystem management, an ultimate goal of many federal and state resource management agencies.
Oregon is ecologically diverse. The west side of the state has a marine-influenced climate and receives plentiful precipitation three seasons of the year. In contrast, eastern Oregon lies in the rain shadow of the Cascades and is much drier. The climatic gradient is evident in the state's landscapes: forested mountains, glaciated peaks, shrub- and grass-covered plains, agricultural valleys, beaches, desert playas, and wetlands. There are 65 level IV ecoregions in Oregon.