Erosion Control using Mats of Discarded Christmas Trees
Work with M-NCPPC staff to locate areas appropriate for Christmas tree revetments, the technical term for this form of bioengineering.
Obtain Christmas tree discards from tree sales lots after Christmas. Christmas trees discarded from homes following the Christmas season are not as desirable because they are dried out, the limbs are spread out and commonly have tinsel and light strings that must be removed before use. Trees that were unsold in tree lots are fresher and are usually bound in twine or netting that is easy to remove. However there may be reasons to use trees discarded from home. People appreciate being given a place to recycle their Christmas trees. Getting trees from a municipality is a way to make a friend for life.
Obtain anchors for the tree mat. It is preferable to use duckbill anchors ($4.95 a piece from Forestry Suppliers 800-647-5368). As an alternative one could use 5 ft and 7 ft metal medium duty fence posts. Street sign posts are free from local road departments and are sold as scrap. Using them also provides another way to make new friends.
Extract stones from area of repair and set aside.
Drive the duckbill anchors or fence posts into the ground in a 4 foot grid in the area of repair. Only a few inches of each post should remain above ground. One axis of the grid will be parallel to the stream flow and the other will be perpendicular. The longer fence post should be used in the row of posts closest to the stream.
Using cable clamps secure a 3/16 steel cable through each post of the axis perpendicular to the stream flow.
Lay trees in the gap between two cables perpendicular to the stream flow. If one has a mix of pine and fir trees, use pine trees for this layer. Firs should be used for the upper layers as they keep their needles longer and, with their fuller branches, trap more sediment. The fir trees should be saved for the upper layer.
Using a come-along, pull fir trees over the bottom layer
and below the cables so that the butt end of the tree
is upstream. The trees of this layer will be parallel
to the stream flow and perpendicular to the cables and
the bottom layer. Protect the come-along from dirt that
could foul the gears by resting it on a flat board.
Place two to four layers of trees under the cable until the space is compact and overfilled. The mat of trees should be about knee high or roughly 20 inches. To ensure that the mat completely fills with sediment, make sure that there are no air pockets left in the mat.
Continue using this technique until the space under all the cables is filled.
Cover the layers of trees with any available soil or mulch.
Lay the rocks that were set aside atop the trees and soil.
Insert willow, dogwood or black alder stakes (clipped during the winter prior to spring budding) into the soil below the Christmas tree mats. The stakes will take root and help to hold the bank and trees in place.
In a year or so stormwater and snow melt will transport sediments which will fill the gaps in the mat of trees. In 4-6 years the trees will decompose.
The mat of trees can be enhanced to two ways:
1. Duckbill anchors ($4.95 a piece for 24 or more from Forestry Suppliers (800-647-5368) with 5 foot length of half inch rebar as a driver OR five or seven foot medium duty fence post from hardware stores (the type that are shaped like an omega in cross section with a blade fixed close to the bottom of the post 2. 3/16 inch twisted wire cable (plastic coated) and 3/16 inch cable clamps with two lock washers 3. Rachet wrench with 7/16 socket. 4. Tools to drive duckbill anchors or fence posts - 4 lb hammer, 8 lb sledge hammer, fence post driver, posthole digger and/or air hammer 5. Come-along cable puller with two 6 foot lengths of rope and a 2 foot length of rebar used as an anchor 6. Two 6 ft inch steel poles sharpened at one end for levering 7. Shovel and pick for digging 8. Hand tools and supplies: lineman's pliers vise grips round file knife or box cutter folding saw 3/8 x 12 inch screwdriver for levering tape measure trowel electrical or duct tape 7 foot tamping bar WD-40 wire brush 1"x8"x6' board