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Technical Report

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Watersheds -- Research -- United States


We used two data sets to evaluate stream and watershed condition for sixth-field watersheds in each aquatic province within the Northwest Forest Plan (NWFP) area: stream data and upslope data. The stream evaluation was based on inchannel data (e.g., substrate, pieces of large wood, water temperature, pool frequency, and macroinvertebrates) we sampled from 2002 to 2009 (193 watersheds) as part of a repeating sample design. We just completed our first round of sampling, so only current condition was calculated for this data set. When condition scores for the inchannel data were grouped into categories, relatively few fell into the low (10 percent) and very low (1 percent) categories. The majority of inchannel attribute scores fell into the moderate (35 percent) and high (41 percent) condition ranges, with relatively few (12 percent) in the very high category. For low-scoring watersheds, water temperature was often the most influential factor. Aquatic invertebrate scores also appeared influential in producing the low scores. An evaluation of upslope and riparian (watershed-wide) conditions for all 1,379 sixth-field watersheds in the NWFP area with significant federal ownership was based on mapped data, including road metrics from U.S. Forest Service and Bureau of Land Management geographic information system road layers and vegetation metrics derived from satellite imagery. Watershed-wide condition scores were calculated for 1994 and 2008, and the difference between these scores was used to represent trend. Regarding status, the overall condition scores of the 1,379 watersheds mostly fell into the low (21 percent), moderate (27 percent), high (26 percent), and very high (22 percent) categories; relatively few watersheds scored in the very low (4 percent) category. The majority of watersheds (69 percent) had a positive change in condition scores (trend). Of those with larger positive changes, most were driven by both improvements in road (decommissioning) and vegetation (natural growth) scores. The greatest negative score changes were caused by the Biscuit Fire and other fires along the eastern side of the Cascades. Half of the fire-affected watersheds were in congressional reserves, 35 percent in late-successional reserves, and 15 percent in matrix (lands identified for timber production).


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