Protecting Den Trees and Snags

Adult great horned owl and chick at entrance of nesting cavity in a tree

A woodland management plan for wildlife should include practices for protecting snags and den trees.

Den trees are live trees with a natural hollow in the trunk or limbs. A snag is a standing dead tree. Both are essential habitat for many kinds of woodland wildlife. The number of den trees and snags in an area has a direct effect on the amount of wildlife in that area.

Trees that make excellent den trees:

  • Best: White oaks, post oak, and other members of the long-lived white oak family
  • Ash, basswood, hickory, American elm, American sycamore, eastern cottonwood, black gum, sugar maple, and black or red oak

Preserving existing snags and den trees, as well as protecting potential den trees, helps the woodland become a productive wildlife area for many years to come.

How Many Den Trees Are Enough?

As a general rule, seven snags or living den trees per acre provide an adequate number of cavities.

  • Leave at least one snag and one den tree larger than 20 inches at diameter at breast height (DBH) for every acre of woodland.
  • Keep at least four snags ranging between 10 and 20 inches at DBH per acre.
  • Leave at least two snags and two den trees ranging between 6 and 10 inches at DBH.

How Can I Create Den Trees?

You can create den trees and snags by wounding selected trees. Open wounds allow fungi to enter the tree and begin the decay process. It may take several years for trees to develop cavities. This process can be hastened through these techniques:

  • Cut a limb (the larger the better) about 6 inches from the trunk of the tree. Ash, elm, cottonwood, sycamore, basswood, and silver maple are especially prone to develop natural cavities from cuts.
  • Chop a section of bark from the trunk of a suitable tree, preferably one that already shows signs of damage or decay. Select trees at about 100-foot intervals.
  • Drill a hole at least 2 inches in diameter and 3 inches deep into the trunk of a tree. If possible, make the hole under a limb that is 3 inches or more in diameter.

To create immediate nesting and denning sites, put up birdhouses to attract birds and boxes that can serve as dens for mammals or native pollinators.