Michigan Trout Unlimited
MICHIGAN Trout
The Critical Role of Wood in Michigan Rivers: Taking Action on the Upper Manistee
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by Kristin Thomas, Michigan TU Aquatic Ecologist
Fall/Winter 2021
The role of wood in Michigan rivers is an often discussed and debated topic among anglers and scientists alike. One thing is sure; wood is critical to the morphological and biological health of Michigan rivers. The morphological importance is especially pronounced in the sandy, low-gradient streams found in the Lower Peninsula. There is consensus that rivers were filled with wood before we chopped down all the trees and cleared the rivers for log drives—much more than we see in streams today. Clearcutting and driving logs not only removed all the wood in our rivers but also removed the source of new wood, interrupting recruitment for years to come. In addition, humans have continued to remove wood from streams and riparian areas, furthering the interruption in recruitment. The result is many streams which would benefit from more wood and more consistent recruitment of new wood. Wood is critical in Michigan streams not only as habitat for fish and aquatic insects, but also to the morphology or shape of the river. The structure that wood provides in our slow, sandy streams is what creates diversity of habitat. As water flows into a downed tree, it is forced to change direction and speed. These changes in the flow of water create deep pockets, areas of hard substrate, and slow areas for deposits of sand and silt.
and overhead cover. One big tree—all this habitat diversity. When these low gradients, sand-bed rivers lose their wood, and they lose their diversity. Water velocity is slow and monotonous, sand settles out, depth becomes uniform, and diversity decreases. We don’t have the big floods of higher gradient systems to flush out sand and create new habitats. Without these flushing flows, Michigan streams have a hard time repairing themselves. This is the scenario observed in much of the Upper Manistee River between Yellow Trees and CCC Bridge, especially between Yellow Trees and Rogers Landing. Wide, shallow, sandy stretches of the river. Corner pools that are deep but have minimal structure or cover. Old CCC structures were no longer doing their intended job. Every project partner who floated this stretch agreed there was not one spot that had too much wood. An increase would be of benefit just about everywhere. And so, a project was formed: a multi-tiered approach to adding wood to the Upper Manistee River. One of the project’s goals is to use a variety of techniques – hinge cuts, single whole trees, and groups of whole trees – to see which techniques work best. Which provide biological and morphological diversity? Which maintain themselves over time and look natural through time? Which will translate well to other low gradient sandy Michigan systems? A project with
Imagine a large tree has fallen into a stream you love to fish. The area where the tree fell was wide, sandy, and shallow. Typically, you would pass right by, thinking no fish here. But what do you think when you come to fish and see the new tree? Perhaps you think about the new pocket of deep water that will form downstream of that tree as water flows quickly over the tree, churning and moving sand on the downstream side. Maybe you also see slow water upstream of the tree and think of a new spot for sand, or perhaps silt to settle out—new Hex habitat. You might also look at the tip of the tree and see a bubble line. Notice that water is being pushed to the middle of the stream. Maybe that increase in velocity will move some sand and uncover gravel. The concentration of flow might create more depth towards the middle of the stream as well. You may also think of big fish hiding under the new structure, eating insects that colonize the Upper Manistee River hinge cuts, crisscrossed in pools to create diverse cover and wood, and enjoying the shade, deep water, habitat.
