Short-term changes in-stream macroinvertebrate communities following a severe fire in the Lake Tahoe basin, California

Abstract

Large and severe wildfires can dramatically alter terrestrial and aquatic ecosystems. We documented changes in benthic macroinvertebrate communities and physical habitat at two sites along Angora Creek, CA, USA for 2 years following a severe fire. Although post-fire years had low precipitation, canopy cover and bank stability declined dramatically following the wildfire (canopy cover: 88% pre-fire, 22% post-fire; stable bank: 93% pre-fire, 11% post-fire). Substrate also changed substantially, with fine sediment 8× more abundant post-fire and cobble 7× less abundant post-fire. We found no consistent changes in taxonomic richness or diversity following the fire, but post-fire densities and percentage of sensitive taxa were significantly reduced. We observed large reductions in relative abundances of shredder and scraper taxa, while collector-gatherer abundances increased. Community composition shifted away from pre-fire configurations, and continued to diverge in the second year following the fire. Scores from a regionally derived index of biotic integrity (IBI) were variable but overall much lower in post-fire samples and did not show recovery after 2 years. Overall, our study demonstrated substantial post-fire effects to aquatic ecosystems even in the absence of large flooding or scouring events, and showed that these effects can be transmitted downstream into unburned reaches.