The Value of Forested Buffers

[klingy]

Link

Should be required reading for our state lawmakers.

 

[Mike]

Good article. The observation that an appropriate forest buffer width starts at a minimum of 100 ft makes me wonder whether the original Pa buffer requirement of 150 ft was part of its downfall during the recent legislative session.

 

[duckfoot]

Good article. I have an entire day/chapter devoted to this in my environmental sciences lectures.

 

[troutbert]

Thinking about buffer widths of 100 feet or whatever width they decide is correct is interesting when it comes to streams with multiple channels.

It's pretty common to see 2 channels running parallel through the floodplain, and sometimes 3 or 4. I have seen as many as 5 parallel channels.

So, how do you go about figuring out your buffer widths in those cases?

Also, stream channels often move. If you create a riparian buffer a certain distance on both sides of a stream channel, and the channel jumps to the other side of the floodplain, then what?

 

[klingy]

The 100 feet (or so) designation is based off of what is the least amount necessary to have an appreciable percentage of benefit for the stream. Sure, an entirely 100% forested watershed might produce optimal water quality in a stream, but thats not a realistic option in most cases. I'm sure they'd love to recommend 2,000 foot buffers along the streams, but they know that aint happening. Any stream is going to meander through its floodplain, but having trees to help hold in soils, create habitat when undercut/fallen, filter sediment/nutrients, etc. (even if its 10 feet on one side, and 190 feet on the other side after the stream has meandered) is better than the alternative of no trees.

As far as the braided streams go, I would imagine that they would benefit highly from allowing trees to grow along the stream/in the braids. Less mass movement of sediment, etc. Not sure what else I would want to put in the middle of a couple stream channels on a braided stream besides trees.

 

[troutbert]

The article talks about large woody debris as being stabilizing, but it's a little more complicated than that.

LWD can deflect flow and cause bank erosion. Often this is balanced by deposition on the opposite side. It's a natural process, but most people tend to think that the banks are "supposed" to be ultra stable and not move.

LWD can also cause avulsions, i.e. channel jumping. This occurs during floods, and it is a radical change, where the main flow of the stream is diverted by a LWD jam into a completely different path flowing through a different part of the floodplain.

This is also a natural process and it's important ecologically in creating habitats for fish and other aquatic life, and for creating floodplain wetlands and influencing floodplain vegetation.

But few people recognize this channel jumping as natural, and commonly they use channel blocks to put the stream "back where it belongs."

If the full floodplain is forested, undeveloped, these channel avulsions create no problems, and should be left alone.

But where the stream just has strips of forest buffer along it, and the rest of the floodplain is used for other things, such as farmland, cabins, homes, roads, utility lines, etc., then channel avulsions create conflicts.

This is something that is not addressed in the article, but it will be something that will have to be addressed in regard to riparian forest buffers. People need to know this.

As the trees in forested riparian buffers mature, grow large, one of the benefits, as stated in the article, will be recruitment of LWD, which helps form pools and cover in the streams, with huge benefits to trout.

But LWD does also cause channel avulsions. And it also causes more flooding of the floodplain, because LWD obstructs flow, sending more water out across the floodplain. Also natural, also important ecologically.

But also something to deal with if you have uses of the floodplain.

Look at where streams flow through state park campgrounds, such as at Hyner Run SP, Sizerville SP, and Ole Bull SP.

See any LWD? No. If any gets in there, it's removed.

 

[sarce]

Great points Troutbert. I can think of many places where I've seen LWD jams cause channel avulsions. And as you mentioned, if the floodplain is forested it won't cause any long term issues.

 

[Chaz]

Mike wrote:
Good article. The observation that an appropriate forest buffer width starts at a minimum of 100 ft makes me wonder whether the original Pa buffer requirement of 150 ft was part of its downfall during the recent legislative session.

The original 150 feet was at best a guess at the time. No one really knows for sure. Certainly a narrower buffer may be all a small stream needs, but it may not be wide enough for a place the size of say Slate Run.