Loss of riparian forests from wildfire led to increased stream temperatures in summer, yet salmonid fish persisted

Native salmonid fishes-cutthroat trout (Oncorhynchus clarkii) and steelhead/rainbow trout (Oncorhynchus mykiss)-are ecologically, culturally, and economically important species distributed across western North America. These fish are generally considered cold-water adapted species. As such, recent studies have speculated about the potential effects of climate change on these native salmonids if stream temperature thresholds exceed 16-20 degrees C during the summer. However, the magnitude of stream thermal responses to the slow but steady increases in regional temperatures associated with climate change remains uncertain and hard to predict. Comparatively, abrupt disturbances, such as wildfire, may produce almost instantaneous and substantial increases in stream temperatures that may persist for multiple years until near-stream vegetation becomes re-established. In the first summer following a severe wildfire in western Oregon, we observed the initial persistence of populations of O. clarkii clarkii (coastal cutthroat trout) and O. mykiss (rainbow/steelhead trout). The fire burned the entire catchment, including the riparian area (similar to 76% of the watershed area burned at moderate or high severity), resulting in stream temperature that regularly exceeded 20 degrees C and represented increases of 6-7 degrees C relative to prefire conditions. However, the mechanisms enabling the persistence of cold-water fishes despite the dramatic increases in stream temperature remain unclear and require further investigation. Nevertheless, wildfires represent acute natural disturbances that can substantially alter stream thermal regimes and provide unique insights that allow us to better understand how native fishes in natural systems cope with projected increases in stream temperatures.

Automated summary

This study examines the impacts of climate change and abrupt disturbances such as wildfires on native salmonid fishes. It is found that wildfires can lead to substantial increases in stream temperature, yet populations of cold-water fishes are able to persist despite the drastic changes, with unclear mechanisms requiring further investigation.