Many species of woodland wildlife benefit from the presence of "den trees." Den trees are those large, standing trees that are used by animals for nesting, roosting, cover, food supply and other critical functions.
These trees are often over-mature trees with many defects and have no financial value. If a stand is being managed for timber, it may be advisable to kill den trees by girdling. This provides a couple of timber management benefits as well as protecting the den tree. When the tree dies, the leaves drop, and light is available to the smaller trees below, encouraging them to grow faster. Also, by leaving the tree standing, it will fall to the ground slowly, one branch at a time, reducing the amount of damage to the surrounding timber.
Girdling of large trees can be accomplished with a chainsaw or hatchet, at whatever height is convenient, by making two horizontal, parallel cuts, three inches apart, two inches into the wood, all the way around the tree. However, if timber is not a primary concern, den trees should be left alive, as they will remain in place longer, and in many cases provide a food source.
Following are recommendations for selecting den trees:
Select trees that will also provide food and have durable heartwood, for example, white oak, black walnut, chestnut oak, red gum, black gum, maple or basswood.
Select a live tree at least 15" in diameter and with a den entrance at least 20' from the ground.
Select a tree that is being used, as indicated by the cutting of bark and wood around the den entrance.
Select den trees that are well distributed throughout the area.
Generally, 2-3 den trees per acre are appropriate. Note: Girdling deeper than the recommended depth or on trees that show evidence of internal decay is not recommended as it could weaken the tree too much, and put it at risk of being blown down.
Washtenaw County Conservation District Copyright 2016