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Yellowstone National Park Report

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The recovery of stream ecosystems in Yellowstone National Park following the fires of 1988 has been punctuated by disturbances caused by high flows in 1991 and again in 1992. In at least a third of the study sites, changes in channel conditions in 1992 were equal or greater than those documented in the preceding year. These impacts are expected to translate into reductions in primary production, benthic organic matter, and macroinvertebrate abundance and diversity over the next few years in most of streams draining burned watersheds in and adjacent to the Park. However, in Cache Creek and its tributaries the changes are so profound that recovery of biotic structure and function to prefire or reference stream conditions are unlikely to occur in succeeding decades or even centuries. Comparison of conditions in Cache Creek with those in other, less severely impacted watersheds in subsequent years could provide valuable insights into the differences in ecosystem response to severe versus moderate disturbance following fire or other comparable impacts such as overgrazing or climate change. The changes which occurred in Cache Creek in 1992 are expected to result in much reduced rates of recovery in ecosystem structure and function and possibly to the establishment of new (lowered) equilibrium conditions. Although such a possible outcome has been postulated (Minshall et al. 1989), the ideas have never been tested. Examination of additional streams, coupled with analysis using Geographical Information System (GIS), would permit determination of whether the adverse effects seen in Cache Creek are widespread or limited to only a f drainages and whether they are in the normal range of conditions or have been magnified as a result of fire suppression or other factors.