Identifying the drivers of aquatic ecosystem vulnerability to wildfires in the Pacific Northwest.
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Wildfires can have complex effects on aquatic ecosystems that vary widely depending on the characteristics of the fire and the ecological context of the watershed, making predictions of fire effects on species of social and conservation interest, like salmonid fishes (Oncorhynchus spp.), difficult. As fire regimes shift, resource managers want to predict where on the landscape wildfires pose a risk to fish and aquatic habitats. However, before we can effectively predict where aquatic systems will be vulnerable to wildfires and shifting fire regimes, we first need to understand how and why fires influence aquatic ecosystems. Here, we present two complementary modeling efforts that seek to synthesize the effects of fire on aquatic ecosystems, identify the drivers that can lead to aquatic ecosystem vulnerability, and develop a spatial risk index to predict where fires may pose a risk for fish and aquatic habitats. First, we adapted a food web system-dynamics model to explore how wildfires influence aquatic ecosystems at multiple trophic levels via the physical and biological processes that support them. Model simulations were then repeated to explore how variation in fire severity and ecological context influenced ecosystem responses and the associated pathways driving those responses. Second, we are leveraging the pathways identified by food web modeling to inform a spatial index of wildfire risk to predict the relative vulnerability and resilience of watersheds regionally across the Pacific Northwest. Taken together, these modeling approaches aim to contribute an improved understanding of the effects of fire on aquatic ecosystems that can help to develop new conceptual models, direct empirical studies, as well as guide management actions in the Pacific Northwest.