Log Jam Inquiry
Did you know that log jams make habitat for salmon, vegetation and other organisms? Aquatic log jams are those woody debris piles that provide habitat for life in the water. Some log jams don’t have to touch the water at all. These terrestrial log jams are upslope from the river and provide habitat for plants and other wildlife.
We’ve been studying the Elwha River because two dams are being removed. Land managers are helping to restore the river for salmon and for forest habitat. As the dams have been deconstructed, high quantities of sediment have been sent down the river toward the Strait of Juan de Fuca. Changes are occurring rapidly now that the lakes have almost completely disappeared.
New woody debris piles have created habitat for different types of organisms by providing shade from the sun. They slow water currents for fish and provide nutrients for plants to grow on, around and under. They also provide a living space for insects and other small creatures.
We classified the log jams into 4 categories: Class 1 (1-5 logs), Class 2 (6-10 logs), Class 3 (11-15 logs), and Class 4 (15+ logs). We also took pictures of each woody debris pile and located them with our GPS unit.
Our team documented five different log jams. They ranged from a small alder sapling to a single Douglas-fir, which was over two meters in circumference. We found various types of plants such as moss, small vegetation and mushrooms. The woody debris piles that are found away from water still make a home for vegetation and other creatures, such as insects or birds. The age of the log jam can be estimated by looking at the color, the condition of the logs and the level of decay. We were also able to find out which way the water flowed by looking at the angle of the log jam. Factors like old tree stumps, rocks and slopes help create a new log jam. We even saw some newly forming log jams at the sites.
The logs, trees and other woody debris found in the river on old reservoirs shores and dry riverbeds create a wealth of habitat for life. It provides a place for organisms to live. Plants and trees can grow on the decayed log jams. The log jams are perfect nurseries for trees and provide moisture like a sponge during dry summer conditions. In the river the log jams create a place for salmon to rest because the stream is slower than the rushing river, and the shade the log jams create provides cooler temperatures. The newly forming woody debris piles will help restore the Elwha River now that the dams are almost completely removed.