What can long-term monitoring data tell us about the influence of wildfire on stream habitat in the Pacific Northwest?
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Long-term monitoring datasets provide valuable opportunities to identify aquatic ecosystem responses to disturbance at broad spatial extents. The Aquatic and Riparian Effectiveness Monitoring Program (AREMP) is unique in this regard because the program re-surveys the same 1411 stream sites in the Pacific Northwest on an 8-year return interval. Regular return surveys provide snapshots of stream habitat conditions that bookend disturbance events, such as wildfire. We focus on pre- and post-fire changes for in-stream large wood at 84 sites, as large wood is a component of habitat complexity potentially impacted by wildfire. Post-fire change in large wood metrics was variable. Wood frequency increased at 40% of sites and decreased at 38% of sites; log jam occurrence increased at 11% of sites and decreased at 10% of sites. We use Random Forest models to assess large wood responses to burn severity and time since fire within context of initial wood availability, watershed drainage area, topography, forest age, and post-fire high flows. We highlight the utility of pre- and post-fire measurements to identify changes in stream habitat within the 8-year windows of AREMP surveys. Ongoing work will incorporate change-over-time for stream habitat metrics at sites where fire has not occurred in the recent past, facilitating understanding of fire effects within context of climate and anthropogenic disturbances in the Pacific Northwest.