Streamside forests provide travel corridors for large secretive animals like bear, cougar, and deer. Generally, the value of forest as a wildlife habitat increases with its width, degree of continuity along and across the stream, plant species diversity, and structural complexity. Plants rooted next to streams or on floodplains screen sediment out of passing water, slow flood velocities, and influence erosion. All of these actions impact disturbance in the streamside zone. For example, when plants screen sediment out of the water, it causes floodplain deposition and building.
Tree roots can also deflect water, leading to erosion and undercut banks.
The importance and magnitude of these general functions also vary depending on the size and complexity of the streamside forest. Terrestrial wildlife functions tend to be more important on larger streams with larger floodplains and extensive streamside communities. The actual size of functional large wood should be defined operationally, in relation to the size of the stream. Large woody debris affects streams in a number of ways. It directs streamflow, stores and distributes sediment, and creates pools, riffles, and waterfalls.