Comparing Stream Invertebrate Assemblages Before and After Wildfire in Yellowstone National Park

Abstract

Warmer, dryer climate conditions during the past 3 decades are thought to have increased severe fires in the western United States. Severe fires may change food webs due to altered light levels, nutrient concentrations, and hydrology in streams. To measure how wildfire changes stream food webs, we collected aquatic invertebrates before and after a fire, and calculated their density. To investigate the effects of wildfire on streams, we collected aquatic invertebrates from Cub Creek on the east side of Yellowstone Lake before and after the East Fire. The timing of our study was serendipitous with the fire burning after our first year of collecting samples. Therefore, we collected one year of data prior to the wildfire (2003) and 2 years of data after the fire (2004 and 2005). The East Fire was a crown fire that set ablaze >9000 hectares and burned 95% of the watershed of this stream. Working in Yellowstone National Park is opportune, because few other perturbations exist and the effects of wildfire can be easily studied. We analyzed the samples to understand how wildfire alters stream invertebrates. Our specific questions are: 1.) What effect did wildfire have on the density of aquatic invertebrates? 2.) How did the composition of aquatic invertebrates change before and after wildfire? Results from our study will inform managers about how the food base for fish (i.e., aquatic invertebrates) changes after wildfire.