Effects of Wildfire and Subsequent Hydrologic Events on Fish Distribution and Abundance in Tributaries of North Fork John Day River

Abstract

AbstractRecent large wildfires in western states have fueled increasing concerns of resource managers and the public about the effects of fire, including risks to fish, particularly endangered species. However, there are few empirical studies on the response of fish to fire and none that include anadromous species. The Tower Fire was one of four large fires in the upper John Day River basin in Oregon in 1996. Much of the area burned at moderate to high severity, consistent with the pattern of increasing fire severity and size projected for the region. Intense spring storms in 1997 and 1998 triggered large floods, landslides, and debris torrents that affected streams within and downstream of the fire. We investigated the effects of the fire and ensuing floods on fish distribution and abundance in three streams immediately after the fire through 2003. Immediately after the fire, no fish were found in moderate‐ and high‐intensity burn areas. Fish began to repopulate defaunated reaches the year after the fire, and within 4 years distribution of juvenile steelhead (anadromous rainbow trout Oncorhynchus mykiss) and resident rainbow trout was similar to that before the fire. Juvenile spring Chinook salmon O. tshawytscha also began to use lower reaches of one of the streams after the flood, which had eliminated a culvert near the mouth of the stream suspected to be a barrier. Densities in most burned reaches and in unburned reaches downstream of the fire have rebounded to levels similar to or greater than densities in reference streams outside of the fire. An isolated introduced population of brook trout Salvelinus fontinalis also recovered. Thus, despite the size and severity of the fire, postfire hydrologic events, and human‐induced changes to watersheds, fish populations were highly resilient.