Effects of wildfire on streambed grain size distributions in the area of the Northwest Forest Plan
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The effect of wildfire on aquatic habitat over time is not well understood, especially in the Pacific Northwest, and relies on the collection of ongoing data over long time periods. In Western Washington, Oregon, and Northern California, the Aquatic and Riparian Effectiveness Monitoring Program (AREMP) has been collecting ongoing monitoring data to support management of forest lands under the Northwest Forest Plan (NWFP) (~99,000 km2 / 24.5 million acres). Data collection for this program began in 2002 and includes sites within 219 randomly selected watersheds with at least 25% federal ownership that are surveyed on an approximately 8-year return interval. During the operating time-period of this monitoring program, wildfire has increased in frequency, area, and severity throughout western states. Of the 219 total AREMP watersheds, 120 (55%) have burned at least once since 1984, and of these, 61 have experienced multiple wildfires. In this study, we examine how streambed surface grain size distributions (GSD) have changed pre- to post-fire for 119 AREMP sites whose contributing pour point catchments have burned since 2002. This analysis investigates which landscape characteristics exert the most control on post-fire streambed GSDs in the area of the NWFP. This study offers insight into methods for utilizing long-term monitoring programs to identify burned catchment vulnerability or resiliency to aquatic habitat changes post-fire.