Ecological Processes–Woody Debris

Woody debris within streams and rivers are both a habitat feature for many species and factors that can significantly change the physical and biological characteristics of streams. Debris dams or partial dams (deflectors) can create pools and scour holes, and change patterns of sediment deposition within the stream channel.

Organic debris ranging from leaf litter to large tree trunks provides substrates and shelter for invertebrates. In addition to their own inherent value, invertebrates are important components of river and stream ecosystem due to their role in nutrient processing and food chain support. Accumulations of debris (branches and tree trunks) provide underwater shelter for fish and wildlife, basking sites for turtles and snakes, and foraging areas for amphibians, minks, raccoons, and other predators.

Large woody debris (large branches and tree trunks) and debris dams are also important for their role in altering stream hydraulics and influencing local instream habitat conditions. Woody debris can dam up stream sections creating pools in areas that would otherwise lack them. Water plunging over woody debris may create plunge pools. Woody debris may also divert or constrict flows, changing patterns of scour and deposition and creating deep holes and fresh gravel beds that serve as important habitat for fish and wildlife.

Road-stream crossings tend to block the downstream movement of woody debris with the potential to create blockages at the structure entrance and reducing the amount of debris in downstream sections. Removal of woody debris from stream channels in order to help safeguard undersized structures robs the stream of these important elements of instream habitat.