In early spring of last year, the Instream Committee of the Au Sable River Watershed Restoration committee met to discuss and debate important issues affecting the river. Among those present were representatives of the Michigan DNR, The Anglers of the Au Sable, Trout Unlimited, the Au Sable River Property Owners Association, and the Au Sable Canoe Livery Association.
One of the subjects discussed at this meeting was large woody debris (LWD), an organic material derived from the riparian timber along the river. It gets into the river either from natural causes or by human activity.
(The riparian zone is usually defined as one or two mature tree lengths on each side of the river. On the Au Sable this is about seventy-five to 150 feet.)
The Importance of Large Woody Debris
LWD is important, if not absolutely essential, to the health of the river's ecosystem. It provides cover for trout - its most obvious function. For example, the recent telemetry study of large brown trout on the Mainstream Au Sable showed that large brown trout utilized logjam structures (otherwise known as LWD) during a significant part of the day.
LWD also produces places for twigs and leaves to collect and decompose rather than be flushed downstream and disappear. (In the headwaters of the Au Sable, with insufficient LWD, this debris is flushed to the Mio Pond. The debris is then collected and held, not passed downstream, and is lost to the river ecosystem, outside of the pond, illustrating one of the negative attributes of dams.) The decomposition of this organic matter provides a major energy source - and ultimately food for trout - to the river.
Large debris, including man-made structures, provides home for the beetles, the stoneflies, the mayflies, the caddis flies, and even the black flies. They form the small dams which block and collect the fine organic material where the invertebrates feed, the shredders shred, the collectors collect, and the predators (damselflies, dragonflies, and trout!) eat them all.
LWD decreases the channel slope, produces channel roughness, increases channel diversity (otherwise known as pools and riffles), stores and contains sediment, helps the stream retain organic matter (energy for trout), and deepens the water to both cool the water and provide protection for trout.
Large wood in our rivers is very good stuff indeed!
(If you want to know more about the value of the good stuff, I refer you to Riparian Systems and Management by Sandy S. Verry of the USDA - Forest Service.)
What Can We Do?
As riparian trees fall into the river we must balance the desire to keep the river navigable and retain the LWD in such a manner to maximize its benefit to the river. Aesthetics must also be considered; the river should remain as natural as possible.
The Committee had several opportunities this past year to address these concerns. As word of downfalls were received, we met at the sites. At each site, the first step was to obtain permission from the land owner to gain access to the downfall. Plans were then developed.
The following considerations helped to implement the plans:
(Steve Sendek, a biologist with the Michigan DNR, was very helpful in the formulation of these plans.)
With consensus, the land owner was informed and approval granted. The plan was then executed.
A brief description of a few of the many sites will illustrate these concerns.
1. White Pine Campground Early in the spring, both a red pine and a white pine fell across the river from the north sandbank because of its instability. Due to the nature of the stream flow, these trees were cut only at the top, leaving a passage of about four feet between the cut trunks and the south bank. The tops were cabled to swing downstream to provide additional cover.
Later in the summer, the clay bank gave way, the downsteam trees moved, and the passageway was almost closed. Two or three additional feet of tree trunk were then removed and cabled.
2. Upstream from Townline Road A large white pine on the south bank fell across the river. Because of the current, an existing logjam, and the very tight, narrow bends in the river, it was decided a wider channel was desirable. The top of the tree was cut after being cabled to a stake driven into the north bank and then swung in the current and positioned to provide cover along the north bank.
It should be noted that every attempt was made to hide the stakes and cables used in the repair. We worked hard to keep the river as natural as possible.
Additionally, the lower portion of the trunk was cabled, cut, and then swung parallel with the south bank. All cut limbs were positioned and secured as integral to the structure.
An interesting footnote: the property owners, though originally skeptical of the plan, were very enthusiastic when they saw the end result.
3. Upstream from Stephan's Bridge Two willows on the south bank fell into the river. Most of the limbs were then cut and positioned on an existing LWD structure. The trunks were cabled and cut to swing parallel with the current providing a new and imposing structure.
Subsequent to this repair, within three weeks, I had clients catch several trout feeding by the new structure, a location where I had never before seen feeding fish.
4. Downstream from Canoe Camp A red pine fell from the south bank across the river, with the root ball providing a secure anchor. We made a cut providing almost eight feet of clearance. The top was secured.
Our river is a wonderful, momentous, renewing resource. Its continuing vitality depends on many factors, ranging from environmental to human.
We are now attempting to address but one of these features in an informed, coordinated, and reasonable fashion. We welcome comments and suggestions.
I will report more about our efforts to protect the LWD in our river in future issues of The Riverwatch.
There will be a lot more about large woody debris in future Riverwatches. - Editor
RWOL
© Copyright 1997 - , Anglers of the Au Sable, Inc. All rights reserved. Last modified: January 20, 2005
