Ecological Responses of Stream Ecosystems Ten Years After Disturbance by Wildfire

Abstract

Wildfire is a major large-scale disturbance that profoundly influences stream ecosystems over broad spatial and temporal scales. Research has focused primarily on short-term effects, with most data collected within the first few months or years following wildfire. We determined the ecological conditions of 13 streams (10 burned, 3 unburned) 10 years after major fires in Yellowstone National Park (YNP), in order to determine the mid-term responses of stream ecosystems to wildfire. Information from this study is critical to the basic understanding of the role of wildfires in the flowing water systems of wilderness areas and national parks. In addition, this information will be helpful in the formulation of future fire policies and resource management approaches in public forests, wilderness areas, and parks and will provide educational and interpretive information to aid the public and its representatives in better understanding the importance of fire in natural ecosystems. Differences among burned streams in chemical properties were related to local geology and not to the effects of fire. Stream habitat measurements indicated that there was more fine sediment in the burned headwater streams compared to the reference streams and that burned mid-size streams were wider and shallower than the comparable sized reference stream. Benthic macroinvertebrate density was higher and percent Ephemeroptera-Plecoptera­Trichoptera was lower in the burned streams than in the reference. These changes were accompanied by an increase in the proportion of smaller, more vagile taxa, suggesting a shift in community structure from K- to r­ strategists. However, these differences did not exist for taxa richness or biomass, indicating that metabolic compensation accompanied the change in community structure. Mid-term recovery appears to be delayed in YNP streams as a result of increased precipitation and runoff in recent years. These results indicate that significant changes are still occurring in these streams ten years after the fires; these impacts and trends are expected to be even more apparent when the patterns over the whole ten years are examined.