Tuesday, June 5, 2007 - 10:45 AM
137

The "Fire Pulse:" Effects of wildfire on periphyton, benthos, insect emergence, and riparian predators in a wilderness watershed

Rachel L. Wilkinson and Colden V. Baxter. Stream Ecology Center, Department of Biological Sciences, Idaho State University, Box 8007, Pocatello, ID 83209

Wildfire has the potential to alter many land-water connections, yet few studies have addressed its influences on stream-forest linkages.  Mid-term (5-10 years post-fire) effects of fire may lead to increased solar insolation and in-stream primary production, in turn leading to increases in benthic insect larvae, greater emergence of adult insects and greater numbers of terrestrial predators at burned versus unburned sites.  We tested these hypotheses in 2nd-3rd order stream reaches of three classes: unburned, low-intensity (canopy intact), and high-intensity (canopy lost) burned sites in the central Idaho wilderness.  We observed greater solar insolation and higher (though not significant) periphyton biomass at high-intensity burned sites.  Biomass of benthic macroinvertebrates and emerging adult insects were lowest at low-intensity and significantly higher at high-intensity burned sites, with unburned sites intermediate.  Tetragnathid spiders were most abundant at high-intensity sites, as were the echolocation calls of bats.  Our findings suggest that there may be a “fire pulse,” that stimulates productivity, and increases insect emergence and abundance of terrestrial predators.  Yet, our results also suggest that variation in wildfire intensity may determine both the strength and direction of this response, as removal or retention of the canopy appeared to trigger positive and negative effects, respectively.