Regional patterns of riparian characteristics in the interior Columbia River basin, Northwestern USA: applications for restoration planning

Abstract

Recent declines in anadromous Pacific salmonids (Oncorhynchus spp.) have been attributed, in part, to degradation of freshwater habitat. Because riparian areas directly affect instream habitat, assessing riparian characteristics is essential for predicting salmon habitat quality and for prioritizing restoration projects. We quantified land use modification of anadromous fish-bearing streams in the interior Columbia River basin at multiple resolutions. We identified riparian areas in several land use and land cover classes using remotely sensed data. We then interpreted aerial photographs at random locations within each class to quantify riparian modifications at a local (stream reach) scale. Riparian areas in agricultural and urban areas were significantly narrower (~30 m, median) than those in forested or shrub/grass areas (~70 m). The largest proportion of modified riparian areas occurred in low-gradient streams with floodplains in semi-arid ecoregions. Riparian vegetation in these areas is unlikely to provide adequate in-stream functions, making these areas a natural starting point for restoration prioritization. We investigated how existing riparian restoration projects were spatially related to riparian land use and found that restoration effort varied among subwatersheds. Effective strategies for restoring high quality salmon habitat will be watershed-specific and must restore natural watershed processes. By using a hierarchical analysis to identify regional strategies, restoration or conservation activity can be focused in specific basins and thereby increase the likelihood that efforts will significantly improve habitat conditions for listed salmonids.