Wildfire and Native Fish

Native aquatic species are adapted to survive in the range of environmental conditions present in their natural habitats. This adaptation reflects past survival and reproduction by members of the population. In the Pacific Northwest, few species have behaviors as diverse as salmon and trout. Their complex genetic lineage allows them to survive in remarkably variable and dynamic stream conditions. These remarkable fish face changes in habitat at an unprecedented rate as global climate change interacts with land management and changing fire regimes. In this research, we investigated the effects of wildfire on the composition, juxtaposition, quality, and diversity of fish habitat at network extents.

Wildfire effects on aquatic ecosystems and species are complex and varied. Bayesian network models for the Wenatchee River basin predicted that wildfire can potentially improve habitat quality for adult and overwintering juvenile spring Chinook salmon (Oncorhynchus tshawytscha) through increased wood delivery, but fine sediments can temporarily degrade egg and fry habitat (Flitcroft et al. 2016).

Wildfire that follows historical wildfire-return intervals and intensities is a key disturbance processes affecting terrestrial and aquatic habitat complexity in the U.S. Pacific Northwest. Human land use, particularly long-term fire suppression, has altered the intensity and frequency of wildfires in forested upland and riparian areas in the western United States. Climate change is further exacerbating the trend toward larger and more intense wildfires, while also altering recovery of upland forest-stand composition. However, emerging research points to unexpected resilience mechanisms in native fish populations, even to intense wildfire and associated debris flows. A variety of adaptive strategies including movement, shifts in life-stage development timelines, and use of alternative habitats allows many native fish to thrive under dynamic landscape conditions. Our understanding of the effects of wildfire is enhanced by considering the natural patterns of wildfire disturbance and the adaptive mechanisms that may already be present in native species.

Photo Credit

USDA Forest Service photo by Jay Munyon.

Recent fires in the Clackamas River basin in the Mount Hood National Forest in western Oregon burned riparian areas in many places. Postfire landslides and debris flows spurred by winter storms over the next decade will deliver large wood and sediments that are critical components of stream-channel habitats for native fish.