Date of this Version
Fire Science Brief, Issue 77, November 2009
Much of the previous research on wildfire’s effects on stream communities has examined biotic responses in burned versus unburned watersheds (catchments). But we know that fires burn in a mosaic pattern of differing severities across the landscape, depending on topography, aspect, vegetation, weather, and other factors. Scientists evaluated the gradient of burn severity among watersheds in a dry Intermountain West ponderosa pine forest in central Idaho to gauge the relative response of stream communities under a range of burn severities. They observed a gradient of both habitat and biotic effects correlated with a gradient of burn severity. Effects varied based on interactions of annual stream flow patterns and burn severity of the streamside forest. Macroinvertebrate communities in burned areas did not stabilize within 4 years after fire, nor did they become similar to communities in unburned areas. With this expanded knowledge of wildfire’s effects on streams, the scientists compared the stream ecosystem effects of a prescribed burn to only those watersheds that burned at low severity in wildfire. They found that the prescribed fire conducted in the spring when fuels were moist had negligible effects on stream communities. However, even the lowest severity wildfires produced changes in stream communities. They concluded that prescribed fire effects in these forests on stream communities are negligible, at least when the riparian forest is not burned.