Leveraging stream and riparian monitoring data to evaluate linkages between wildfire and aquatic habitats in the Pacific Northwest
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Wildfire is a characteristic disturbance process affecting ecosystems of the Pacific Northwest (PNW). However, 150 years of intensive management and resource extraction across diverse PNW ecosystems complicates our understanding of how fire interacts with various ecological processes. Wildfire impacts on aquatic ecosystems are of particular interest as streams and riparian forests provide habitat for anadromous fish and other organisms, but the multiple and complex pathways by which wildfires impact aquatic ecosystems are poorly understood. We present an approach using causal models and large-scale aquatic monitoring data to examine the strength of linkages between fire, upslope and riparian habitat, in-stream large wood, fine sediments, nutrients, and benthic macroinvertebrate assemblages. Our data come from the Aquatic and Riparian Effectiveness Monitoring Program (AREMP) that was initiated in 2002 and collects long-term in-stream and upslope data at 1411 study sites across the PNW. Of these AREMP study sites, 582 of their contributing catchments (41%) have burned at least once since 1984, and 79 (6%) have experienced multiple wildfires, which provides a unique opportunity to examine legacy fire effects. We compare models quantifying fire extent and severity at three spatial scales: 1) the pour point catchment, 2) upstream 100m riparian buffer, and 3) reach-scale 100m riparian buffer. Aquatic ecosystem responses to fire vary with spatial analytical extent, legacy effects of forest management and disturbance, and bio-geo-climatic context. This study tests the applicability of large-scale monitoring datasets to evaluate mechanistic hypotheses of fire influences on stream ecosystems. Results will expand spatial and temporal understanding of wildfire-aquatic linkages across PNW ecosystems.