Evaluating the Status and Trends of Physical Stream Habitat in Headwater Streams within the Interior Columbia River and Upper Missouri River Basins Using an Index Approach

—Identifying the overall status of freshwater streams is an important step in evaluating effects of land management and prioritizing restoration activities. To address these needs, we developed an index of physical habitat condition for headwater streams based on physical stream habitat data (2003–2007) and evaluated the condition status of 217 reference streams and 934 managed streams in the interior Columbia River and upper Missouri River basins. We used data collected from reference reaches to generate this index, which consisted of eight commonly collected metrics used in stream habitat monitoring. We incorporated landscape and climatic covariates into multiple linear regression analyses to control for inherent differences in physical habitat attributes among reaches, and we scored the overall condition of reaches with index values ranging from 0 to 100. Our results indicated that the condition index score of physical habitat was significantly higher in reference reaches (mean 6 SE 1⁄4 47.1 6 1.4) than in managed reaches (30.4 6 0.7); relative to reference reaches, a greater frequency of managed reaches had low habitat condition and a lower frequency of managed reaches had high habitat condition. Analyses evaluating the relationship between management activities and the condition of physical habitat in streams indicated a significant negative relationship with lower index scores in stream reaches within catchments containing higher densities of roads. When roads and livestock grazing occurred within catchments, we found the presence of grazing had an additional, significant negative effect on the relationship between road density and the condition of physical habitat of streams. Our results suggested that once natural variability and geoclimatic differences among reaches are accounted for, a multimetric index approach can provide managers with an easily interpretable tool to monitor the status of the overall condition of physical habitat. Stream habitat alteration, degradation, and loss related to forest and rangeland management have been identified as causes for the decline in the distribution and abundance of native salmonid fishes in the Pacific Northwest (Meehan 1991). The listing of resident and anadromous salmonids under the U.S. Endangered Species Act in the 1990s led to substantial changes in federal, state, and tribal land management activities (FEMAT 1993) as well as increased stream restoration efforts (Bernhardt et al. 2005; Katz et al. 2007). Determining whether changes in management or restoration efforts improve physical stream habitat, however, relies on the ability to consistently assess the status and trends of physical habitat. Efforts to understand how land management activities have affected the quality of stream habitat have largely focused on the status of individual stream attributes (Dose and Roper 1994; McIntosh et al. 2000) or separate assessments of multiple attributes (Woodsmith and Buffington 1996; Kershner et al. 2004b). Concomitantly, many land management and restoration efforts historically focused on specific stream attributes without consideration of the overall condition of the stream or the watershed (Roper et al. 1997). While these assessments have improved our understanding of how management affects individual stream attributes, overall assessments that incorporate multiple attributes into a single measure of the status of stream habitat are still needed (Rheinhardt et al. 2007). Multimetric indices of biotic integrity (IBIs) have been widely used in fisheries research and management to assess and define the health of stream systems (Karr and Chu 1999; Pont et al. 2006; Tejerina-Garro et al. 2006; Whittier et al. 2007; Roset et al. 2007; Stoddard et al. 2008). Ease of interpretation and effectiveness for monitoring the biotic condition of streams have led to the extensive use of IBIs at the local scale (Angermeier and Schlosser 1987; Lyons et al. 1996) and larger spatial scales (Oberdorff et al. 2002; Whittier et al. 2007). In the Pacific Northwest, IBIs developed for both coldwater fish (Mebane et al. 2003; Hughes et al. 2004) and macroinvertebrate (Herlihy et al. 2005) assemblages have been used to evaluate the effects of land management practices. Despite the importance of physical conditions for instream biological assemblages (Binns and Eiserman 1979; Minshall et al. 1983), there have been no * Corresponding author: [email protected] Received November 18, 2008; accepted February 13, 2010 Published online June 14, 201