Intermediate Term Response of Seasonal Habitat and Salmonid Distributions to Debris-Flow Deposits in Oregon Coast Range Streams.

With the decline of Pacific salmon, stream restoration has focused on constructing temporary habitat structures, often with little consideration for the geomorphic processes that create and maintain habitat.  Resilience and persistence of a diverse salmonid assemblage require habitat complexity sufficient to support a range of fish age-classes and life history strategies.  Debris-flow-prone headwater tributaries in mountainous areas may play a critical role in contributing materials needed to create complex habitat in fish-bearing systems.  Although debris flows are initially destructive, physical heterogeneity may be produced over time from large depositions of sediment and wood.  Widespread debris flows in the Oregon Coast Range during the winter storm season of 1996 provide an opportunity to assess the abiotic and biotic effects of debris flow deposits 15 years after occurrence.  I will use continuous habitat and snorkel surveys in previously surveyed streams to assess the effects of the presence and characteristics of 1996 debris flow deposits on seasonal variation in habitat and fish distribution.  Understanding the patterns of seasonal habitat availability and fish abundance and considering the trajectory of habitat development between survey years will provide a more complete assessment of the effects of debris-flow deposits, and inform management of the low-order streams that may be important to processes that generate high-quality fish habitat.