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 and biomass. To investigate the effects of wildfire on streams, we collected aquatic invertebrates from Cub and Little Cub Creeks on the east side of Yellowstone Lake before and after the East Fire (Figure 1.). The timing of our study was serendipitous with the fire burning after our first year of collecting samples. Therefore, we collected samples prior to the wildfire (2003), and 1 (2004), 2 (2005), and 9 years post fire (2012). The East Fire was a crown fire that set ablaze >17,000 acres and burned ≥95% of the watersheds of these streams. Working in Yellowstone National Park was opportune, because few other perturbations existed and the effects of wildfire can be easily studied. We analyzed the samples to understand how wildfire altered stream invertebrates. Our specific questions were: 1.) What affect did wildfire have on the density and biomass 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 and many birds (i.e., aquatic invertebrates) changes after wildfire.