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1996 Flood/Woody Debris in Streams

Since there is no obvious connection between logs and stream health, people used to think logs made rivers "messy." Then, in 1982 scientists at the Andrews began a study to track logs for 200 years to monitor decay rates. Researchers found that logs play important roles in streams because they provide habitat for species throughout the food chain. They shelter insects in the decaying wood and create splash pools of cool water where fish can rest from the current. As it turns out, managers were harming the stream by removing logs! Policies have changed to keep logs in the stream, where they can benefit the ecosystem for hundreds of years after their death.

How do you think most of these logs get into the stream?

Trees can fall into the stream after they die of natural causes or when they are undercut by erosion. But many of these logs were deposited in the stream when Lookout Creek flooded in the winter of 1996. You can see the red high-water mark, the highest point since 1964, on the tree to your left (or right, etc). The flood was a valuable opportunity for the scientists of H.J. Andrews because they had years of prior stream habitat data which allowed them to compare the "before" and "after" pictures. After the flood, they were able to closely scrutinize the effects of the storm on the stream and forest habitat. They found that the overall structure of the stream is affected more by brief, large-scale events than by years of steady erosion. Gordon Grant, an H.J. Andrews scientist, described it this way: "Decades of boredom punctuated by hours of chaos do much of the physical work of the landscape so that the features we see.owe their origin to that 12 or 24 hour window during which these channels are in full flood." (Torrents of Change video)

While much of the rain that falls here feeds the stream, a lot of it is absorbed into the soil for plants to use.

How do you think the trees draw water from the roots all the way up to the leaves on the highest branches?

Click on the pictures below to enlarge them.

Stream Debris-1 Stream Debris-2 Stream Debris-3 Stream Debris-4 Stream Debris-5 Stream Debris-6

This is a thirteen minute interview between Nick Gillispie and Fred Swanson, Ph.D about large woody debris in streams and how research is valued in forest management. If you would like, you can download the mp3 version by right clicking here and pressing "save as."

Post 3-Disturbance Arrow Left   Arrow RightPost 5-Structual layers