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.
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 firstname.lastname@example.org or just phone it in by calling (936) 639-8180.
*This article was published in the June 2013 edition of the Texas Logger