June 2013 BMP Q&A

By: Todd Thomas, Water Resources Forester, Texas A&M Forest Service

Q: When harvesting trees within an SMZ I've always been told to keep tops and slash out of the stream, however, when you walk along a stream in the forest there are tons of limbs already in the stream. What is the big deal?  I know it is a guideline, but why is it so important to keep limbs out of the stream when there are already so many there naturally?

A: You bring up a good point, but since there are in fact lots of limbs and debris in the stream bed, there is no need to add any additional debris.  First and foremost, the more debris that gets added to a stream the greater the likelihood of the stream being dammed up and as a result causing flooding.  Flooding is going to happen from time to time with heavy rains, but the less floods in these forested streams the better.  With excessive flooding comes the potential for more erosion on a site, as well as the potential for nutrient loss in the soil.  As the flood waters recede, the eroded soil and nutrients are then carried to the stream, severely affecting water quality.  This flooding could also cause a reduction in the amount of water downstream, further affecting other bodies of water.

Build up of slash in an intermittent stream in East Texas

With the increase of limbs in the stream also comes more scouring or erosion of the stream bank itself.  Since this already occurs naturally, additional scouring can be problematic.  The first issue comes with more sediment in the stream.  More sediment traveling downstream has many negative effects on water quality as well as on aquatic plants and animals.   This increased scouring also releases nutrients that were once stored up in the soil of the stream banks.  As more nutrients travel downstream, they can accumulate and degrade water quality. 

Another benefit of keeping the slash out of the stream is being able to utilize the slash elsewhere on the tract.  Slash is an excellent tool for erosion prevention on closed out skid trails and temporary roads.  Why contribute to a problem when something can contribute to a solution? 

In conclusion, keep slash out of streams, the folks downstream will thank you, aquatic life will thank you, and the landowner will thank you.  Remember extra debris in the stream contributes to flooding and water quality degradation.  Remember to keep the questions coming, you can send them to me at tthomas@tfs.tamu.edu or just phone it in by calling (936) 639-8180.  

*This article was published in the June 2013 edition of the Texas Logger  

Utilization of logging residue or slash

Not this Slash.  

Today I would like to take some time to focus on logging residue, also known as “slash”.    All too often when someone passes by a timber harvest, they see the slash scattered about the area and think to themselves, “Look at all that wasted wood”.  There is no need for concern here, for that wood has not been wasted at all.  When it comes to reducing overland flow and the erosion that occurs as a result, slash does an excellent job.  Due to the nature of the operation, slash is in abundance, so why not utilize a material that is already on site and in bulk?  In addition to reducing erosion, slash contributes nutrients to the soil.  As it decomposes, the nutrients in the slash are returned to the soil.  So not only are the nutrients that are already there retained instead of washing away, more nutrients are deposited!

It is especially important for slash to be distributed in highly sensitive areas, or areas that are the most erosion prone.  Woods roads or skid trails that are going to be closed following the operation should have slash distributed down them in such a manner to keep them from washing out.  This entails putting down the finer slash first and running over it with a skidder to get it down into the soil, followed by larger slash.  The amount of slash put out depends on how much potential there is for erosion, however, it’s pretty hard to overdo it. 

Skid trail stabilized with slash

Skid trail in a clearcut stabilized with slash

Another sensitive area that can benefit from distributing slash on it is the approaches for stream crossings.  The slash should be put down just as you would when closing down a woods road to hold the soil in place and keep it from entering the stream.  It is important to take note that the slash is put down on the approaches to the crossing, but not down in the stream bed itself.  If excessive slash is left in the stream bed, then those excess nutrients will end up in the stream as the slash decomposes, posing water quality risks.  Even worse, slash in the stream bed will eventually dam up the stream creating issues both up and downstream.  A common approach to crossing streams where low water crossings are not practical is to use a bundle of slash in the stream so that equipment can drive over it.  These crossings should be removed immediately as soon as operations are complete to prevent negative impacts to water quality. 

Stream Crossing approaches stabilized with slash

Other sensitive areas such as steep slopes or areas with highly erodible soils can benefit from slash distribution as well.  The slash will keep these areas from eroding until vegetation can re-establish itself and continue to keep the soil intact.  In most cases the slash has more or less decomposed at this point, and vegetation has taken over and erosion is still kept to a minimum.