POSTFIRE RESPONSES OF LOTIC ECOSYSTEMS IN YELLOWSTONE-NATIONAL-PARK, USA

Wildfire is a major large-scale disturbance affecting terrestrial land scapes and lotic ecosystems in many regions of the world. We examined environmental and biological responses of 20 streams in Yellowstone Na tional Park, U.S.A., over 5 years following extensive wildfires in 198 8. Streams of burned catchments displayed increases in dissolved nitra te-nitrogen following the fires. Summer water temperatures often excee ded 20 degrees C in small (first-and second-order) streams of burned c atchments compared with <15 degrees C in their unburned counterparts. Habitat heterogeneity decreased in streams of burned watersheds as dem onstrated by changes in substrate embeddedness and near-bed velocities . Substantial alteration of channels and major restructuring and movem ent of large woody debris occurred in fire-impacted but not reference streams. Transported and benthic organic matter, mostly charcoal, incr eased in burned sites. No major changes were found in macroinvertebrat e density, biomass, or richness, although significant changes occurred in relative abundances of miners, gatherers, and scrapers of burned s ites. Chironomidae abundance was greater initially (postfire years 1-3 ), followed by later increases (postfire years 3-5) by the mayfly Baet is bicaudatus in burned sites compared with reference streams. Our fin dings demonstrate an integral relationship over time between a stream and its catchment, following large-scale disturbances such as wildfire .