Large Woody Debris

Large pieces of wood in a stream are very important to fish.

We call large pieces of wood, such as logs and stumps, that are sitting in the stream Large Woody Debris. Wood must be over 10 cm in diameter and at least a couple of meters long to be classified as LWD. If this wood is anchored in the stream bank or in the stream bed, it serves several useful purposes for salmon.

SHELTER

Salmon stay under wood to be in the shade and to hide from predators.

First, woody debris is excellent shelter for salmon. Salmon often hide under these logs so predators such as birds cannot see them. Also, woody debris can be shelter from the hot sun which makes salmon uncomfortable and very visible.

COMPLEXING

Wood changes how the stream flows, giving salmon more habitat.

Secondly, logs and stumps that sit in the stream may change the stream's flow patterns, often benefiting salmon habitat. For example, a log that is crossing part of the stream may slow the water, creating a smooth deep pool upstream of it for salmon to live and grow in.

NUTRIENTS

Wood eventually becomes nutrients in the stream and ocean.

As this wood breaks down over time, it also adds nutrients to the watershed, encouraging the growth of many organisms in and around it.

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