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Chapter 4 -- Watershed Processes and Aquatic Ecosystems (continued)

Woody Debris and Habitat Diversity

Because riparian areas of the Smith River grow some of the largest trees in the world, large woody debris can accumulate in the streams and create habitat diversity. The resistant geology of the Smith River watershed also favors creation of habitat diversity. Because the Smith River system has relatively low sediment loads, there is a greater proportion of deep pools than in many other rivers in the region. Because of these factors, there is a high potential for habitat diversity in the Smith River watershed.

Large trees that fall into a stream increase stream habitat complexity, create offchannel habitats, and help connect the stream with its floodplain. The combined effect is to increase biological productivity and fish populations (Bryant and Sedell 1995). Interaction between streamflow and large woody debris forms complex habitat including woody debris jams, undercut banks, backwater areas, and secondary channels. These habitats provide an abundance of features important to fish such as pools, stream margins, areas of low water velocity, and spawning gravel. In the upper tributaries, large woody debris is important in the formation of a stepped stream profile which creates low gradient areas for deposition of gravel. These isolated gravel deposits can be used for spawning and may be important in the larger perspective.

Large woody debris and other factors help create instream cover complexity which increases the value of stream habitat for fish. The cover benefits fish by reducing risk of predation and providing contrasting water velocities where fish can easily maintain feeding positions. Instream cover also divides the habitat into more territory units and thereby reduces competition between fish. This can increase carrying capacity, especially for juveniles. Features that contribute to habitat diversity include instream logs, root wads, boulders, undercut banks, bubble curtains, and submerged vegetation (Flosi 1994).


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