by Colton Finch, Ph.D. Student Utah State University
During the summer of 2010, lightning ignited the Twitchell Fire in the Tushar Mountains of south-central Utah. Before fall rains extinguished the blaze, it burned 18,000 hectares of montane forest (Figure 1), including important high-quality stream habitat for Bonneville cutthroat trout, Oncorhynchus clarkii utah. Post-fire habitat conditions, especially debris flows and channel alterations, eliminated nearly all fishes from the burned area (Figure 2). The Twitchell Fire is not exceptional; wildland fire is occurring with increasing frequency in western North America. Despite the potential threat of fire to fish conservation, the effects of fire on stream fish habitats and populations has
only been qualitatively described. Researchers at Utah State University are enumerating the effects of wildland fire on coldwater stream ecosystems as part of a cooperative research project including Utah Division of Wildlife Resources, the U.S. Forest Service, and the USGS Utah Cooperative Fish and Wildlife Research Unit.
Utilizing data from both burned and adjacent unburned streams, the research team is describing the watershed effects of wildland fire in three principal ways,: (1) taking detailed measurements of pool depths, water velocities, stream widths, substrate size, overhead cover, and coarse woody debris within numerous 100-m index sites. These data will be complemented with aerial bathymetric lidar data to expand the description of physical habitat alteration to a watershed scale as part of a National Science Foundation grant, (2) measuring biological response to wildland fire as demonstrated by primary and secondary production, and selection of food and habitat by trout, and (3) construction of a metapopulation viability model to determine how the spatial structure of the watershed, including habitat alterations as a result of wildfire, affects persistence of Bonneville cutthroat trout (Figure 3).
Results of the Twitchell Fire study will help accelerate biological recovery of streams in the burned area, which will be the largest watershed in Utah devoid of exotic species. The restoration of this native fish community will be a large step forward in conservation of Bonneville cutthroat trout, as well as sensitive non-game species such as southern leatherside chub, Lepidomeda copei. As fire occurrence and scale continues to increase due to legacy fire suppression, climate change, or other factors, the opportunistic watershed restoration typified by Utah State University’s research offers a valuable conservation tool in increasingly challenged stream ecosystems.