Postfire responses of lotic ecosystems in Yellowstone National Park, U.S.A.

Abstract: Wildfire is a major large-scale disturbance affecting terrestrial landscapes and lotic ecosystems in many regions of the world. We examined environmental and biological responses of 20 streams in Yellowstone National Park, U.S.A., over 5 years following extensive wildfires in 1988. Streams of burned catchments displayed increases in dissolved nitrate-nitrogen following the fires. Summer water temperatures often exceeded 20°C in small (first- and second-order) streams of burned catchments compared with <15°C in their unburned counterparts. Habitat heterogeneity decreased in streams of burned watersheds as demonstrated by changes in substrate embeddedness and near-bed velocities. Substantial alteration of channels and major restructuring and movement of large woody debris occurred in fire-impacted but not reference streams. Transported and benthic organic matter, mostly charcoal, increased in burned sites. No major changes were found in macroinvertebrate density, biomass, or richness, although significant changes occurred in relative abundances of miners, gatherers, and scrapers of burned sites. Chironomidae abundance was greater initially (postfire years 1–3), followed by later increases (postfire years 3–5) by the mayfly Baetis bicaudatus in burned sites compared with reference streams. Our findings demonstrate an integral relationship over time between a stream and its catchment, following large-scale disturbances such as wildfire. Résumé: Les incendies de forêts constituent une grave perturbation à grande échelle pour les paysages terrestres et écosystèmes lotiques de nombreuses régions du monde. Par suite d’importants incendies de forêts qui ont sévi en 1988 dans le Parc national Yellowstone aux États-Unis, nous avons examiné sur 5 ans les réactions environnementales et biologiques d