Linking post-fire ecosystem responses to catchment characteristics to map wildfire vulnerability of aquatic ecosystems across the Pacific Northwest

Across the Pacific Northwest the size and frequency of wildfires has been steadily increasing over the last two decades, potentially further stressing the region’s aquatic ecosystems. However, aquatic ecosystems vary widely in their responses to wildfire, with some systems having muted responses while others appear to be highly sensitive. Importantly, understanding the causes of the variability is needed to inform the development and implementation of regional risk mitigation strategies. At a broad level there are two primary sources of variability in ecosystem responsiveness to wildfire disturbance; the ecological characteristics (food webs, population, etc) and the physical context (elevation, geology, climate) in which the ecosystem is embedded. Herein we focus on characterizing the physical drivers of differential responses to develop an index of catchment vulnerability to wildfire impacts. We present a bootstrapping approach to calculate a spatially explicit estimate of the mean vulnerability index for each catchment along with bounding estimates of uncertainty. We then use this approach to generate a map of the wildfire vulnerability and its associated uncertainty for the entire Pacific Northwest. To validate the usefulness of the vulnerability index we compare the aggregated values of the index from individual fire scars to post-fire synoptic observations of biological conditions in several streams across the region. The results of this work provide a new, regionally coherent tool for coordinating and implementing large-scale decision making by land management agencies. Finally, this work represents a significant first step toward developing the knowledge and tools needed for designing and enhancing ecosystem resilience in the face of environmental pressures.

Impact/Purpose

Across the Pacific Northwest, wildfires have been increasing in severity and frequency over the last two decades. It remains unknown how this increase in wildfire pressure will affect the region’s aquatic ecosystems. This uncertainty is due in part to the fact that an ecosystem’s response is governed by a complex interplay between the physical setting in which an ecosystem is embedded and the ecological capacity for resisting detrimental effects. This oral presentation to the Oregon Chapter of the American Fisheries Society will present a region-wide map of the catchment-level vulnerability to wildfire. Importantly, this talk will focus why vulnerability is predicated on the physical setting and how this data product might be used by regional land managers to strategically implement pre- and post-fire risk mitigation tactics. Finally, the talk will conclude with a frank and open discussion regarding the role of large-scale data products in trans-regional planning strategies.

Citation

Almquist, V., Joe L Ebersole, Ryan A Hill, AND M. Beyene. Linking post-fire ecosystem responses to catchment characteristics to map wildfire vulnerability of aquatic ecosystems across the Pacific Northwest. Oregon chapter of the American Fisheries Society Meeting, Bend, OR, March 02 - 06, 2020.