Crop tree management is a very effective way to manage your trees. It basically concentrates all of your efforts to improve the growing conditions for the trees you want to harvest in the future. This is accomplished by providing more growing room for the crop trees by removing select neighboring trees. Studies show that growth rates of trees can as much as double, after a crop tree release.
The first step is to pick out your crop trees. Crop trees should be any trees that you want to see an increased growth response in. These trees may include trees with straight stems and few branches for timber production, wildlife mast producing trees (e.g. white oak for deer), or other species that are aesthetically pleasing (e.g. sugar maple for it's fall color).
Generally, crop trees should be selected when they are at least 4 inches in diameter; smaller trees can be ignored. Crop trees should also be selected that are young enough to benefit from the release. Trees at least 20 years younger than the mature tree age for a stand should be targeted. In most cases, there should be no more than 20 or 30 crop trees selected per acre and they should be spaced at a distance in feet of at least 1.5 x DBH [diameter of crop tree in inches at 4.5' from ground]. Example: two 20" dbh trees should be about 30' apart.
When you have chosen and marked your crop trees, then go back and thin out any of the trees that are interfering with (touching) the crown of your crop tree. After these trees are removed, there should not be any branches touching the crop tree's crown on any side. If, however, you have two really good looking trees close together, don't worry about keeping them both, as they will each still receive a release on three sides after the thinning. Just try and open up around them a little.
This process should be done with moderation in mind. If you get too much sun on the sides of the crop trees they will send out sprouts on the trunk of the tree in an attempt to shade itself. This will lower the quality of the timber and the value of the tree. If you are only removing the trees that are touching the crown, though, this should not be a concern.
It is OK to have only 5 crop trees per acre. Do not be concerned so much with the number of crop trees per acre as with the spacing. Part of managing your woodland is having some "filler" trees, as they will not all be "trophy" trees. The more crop trees per acre that you have the more brushy appearance the woods is going to have due to increased sunlight after their release. This is good for wildlife, however it may not be as aesthetically pleasing.
Economic Rotation The economic rotation of hardwoods in this region is between 20 and 24 inches DBH (diameter at breast height). This means that for maximum financial return on your woodlot, generally you should be harvesting your crop trees while they are in this diameter range. This does not mean that you can't harvest trees smaller than this, but rather that your best trees that are really going to make a good profit should be cut at this size. It also does not mean that you shouldn't have trees bigger than 24 inches; it is merely a rule of thumb.
Note: Economic rotation takes into account wind damage, lightning strikes and decay fungus that can work against you growing them any longer.
Washtenaw County Conservation District Copyright 2016