Large wood (LW) provides habitat to aquatic organisms and can significantly alter stream geomorphology. Sources of LW to stream ecosystem originate in riparian forests and are influenced by wildfire regimes. To quantify the relationship between burn severities and in-stream LW, we surveyed 15 low order streams effected by varying wildfire burn severities in a near-pristine watershed of the Frank Church River of No-Return Wilderness in Central Idaho. In the field and using remotely sensed imagery, burn severity was divided into four categories: “unburned,” “low,” “moderate,” and “high”. We hypothesized that burn severity would be positively correlated with in-stream LW. Alternatively, in areas with the highest burn severities, LW might be limited due to combustion. To test this hypothesis we used principal components analysis that indicated fire severity, recruitable LW, and pre-fire vegetation are the most important predictors of in-stream LW in landscapes with a natural wildfire regime. In particular, high category severity burns had significantly more LW than the other categories. An increase in burn severity is also correlated with increased average piece size. The comparison of fire severity maps to field data found a significant correlation locally but no correlation with fire severity of upstream reaches. Few studies have compared the interaction of in-stream LW and fire severity in a near-pristine stream ecosystem. The results of this study improve our understanding of LW dynamics in Intermountain West watersheds with a natural wildfire regime, and could inform post-fire salvage logging management practices.
Includes bibliographical references.