August BMP Q&A

By: Shane Harrington, BMP Forester (Ret.), Texas Forest Service

Q:   Recently a landowner asked me why I left trees along the stream bank and why the trees I cut were directionally felled away from the stream.  I really did not have a good answer for him because this is the way that I was always taught.  A friend of mine told me that I should send this question in to get an answer as to why we do this.  Can you give me a good answer for these questions so next time, I will be able to give the landowner a better answer?

A:   This is a very good question and thanks to your friend for recommending that you send this in.  Many people may be like you and only do this because that is what they grew up doing or was taught.

First of all lets look at why trees should be felled away from a stream.  The reason we recommend doing this is to minimize the chance or amount of logging debris that can enter a stream during a harvest operation within a Streamside Management Zone (SMZ).  The problem with debris entering a stream is that if enough of it is deposited, a dam can form.  When a stream becomes blocked the water has nowhere to go, so it begins to back up on itself.  This can cause flooding of the surrounding land and eventually the stream will create a new channel around the dam.  Now not only do you have logging debris in the stream but also a large amount of dirt from the newly formed channel. The sedimentation that has occurred not only impacts aquatic wildlife, but also raises treatment costs to make the water suitable for human consumption.  The Bluebook recommends that trees that can only be felled across a stream or into a stream should not be harvested. 

Why should trees be left along the stream bank?  The answer to this question is much like the answer to the previous question.  When trees along a stream bank are harvested, the bank may become unstable.  When the root system of the tree dies the bank will begin to sluff off or erode into the stream channel.  Before removing the trees from the stream bank the soil was held in place by the root system of the trees.  The excessive amount of sedimentation will have an immediate impact on the stream.  The soil moving into the stream could potentially dam up the stream much like logging debris can with the result being the same. 

Not only does the removal of bank trees cause the stream bank to become unstable but it also reduces the amount of shade that once covered the stream channel.  This increases the water temperature of the stream, making it hard for fish and other aquatic species to live in the stream.  The removal of bank trees will also increase the flood plain of that particular stream.  A stream that was unlikely to flood during the winter months will probably now flood covering a greater area of the surrounding lands.  The Bluebook recommends that trees found along the stream bank should be left to provide shade and to stabilize the stream bank.

Remember that harvesting within an SMZ is acceptable as long as 50ft² of basal area is left in the SMZ.  If you are not familiar with basal area the Texas Forest Service has a chart on its website that will aid you in determining basal area or you can leave 50% crown cover and achieve the 50ft² of basal area.  If you need a copy of the Bluebook you can get one from your local TFS office or view it online at http://txforestservice.tamu.edu/water.  If you have any questions or comments regarding BMPs please call me at (936) 639-8180.

* This article was published in the August 2004 issue of the Texas Logger