Present effects of past wildfires on leaf litter breakdown in stream ecosystems

We investigated the present effect from a 10 year-old wildfire on leaf litter breakdown rates in three, central Idaho headwater streams. Based on soil instability and burn patterns, we identified three stream ‘conditions’: unburned, burned-only, and burned/scoured (these systems experienced a massive debris flow one year post-fire). We placed bags containing willow leaves (Salix sp.) in each stream. We removed bags at various time intervals until all bags were collected at 100 days. Leaves were dried, weighed and decay rate coefficients calculated.  Macroinvertebrates in bags were enumerated, identified, and selected taxa placed into trophic groups. The unburned stream had the fastest leaf litter breakdown rate, the lowest level of incident light and the largest amount of benthic organic matter.  The ‘burned /scoured’ stream was nearly opposite.  Two detritivore invertebrate taxa, Seratella tibialis and Zapada oregonesis, were highest in the unburned but lowest in burned/scoured stream. A third taxa, Baetis showed the opposite relationship. Predatory invertebrates did not affect detritivore abundance or decay rate.  Stream recovery response had not returned to pre-fire levels a decade after the initial wildfire. Stream recovery appears connected to the return of the riparian zone, though fire-induced debris flows can slow final recovery of the system.