Considering Wildlife Trees During Tree Marking

By Thembi Borras

Wildlife occupies every layer of a tree. In a light intensity single tree selection, during tree marking, you have the opportunity to evaluate each tree individually for wildlife value. Trees that provide preferred habitat to wildlife include goose pens, trees with broken tops and decadent trees.

Goose pen is the name given to a basal tree cavity, which during the homestead era could provide shelter for a goose or a gaggle of geese, depending on the size of the cavity. Goose pen is now used to describe any tree with a basal cavity, most often created by fire. Species that use goose pens include bats for roosting and birds for nesting.

Trees with broken tops facilitate fungal entry causing rot in the stem, which allows primary cavity nesters to begin excavation. Secondary cavity nesters follow. Flat tops provide nesting platforms and are preferred by several owl species if they are concave; meaning the top breaks off below the remaining canopy. Ospreys, a fish eating raptor, will nest in exposed flat tops. Portions of broken tops that stick above the rest of the canopy may be used by birds for roosting and perching.

Decadent trees, trees in a condition of decline, may possess oversized limbs and exfoliating bark, dense clusters of branches caused by a mistletoe infection and rotten cavities caused by some physical damage such as lightening or wind. Large limbs are platforms that support wildlife, the larger the limb the wider the range of species able to use the platform. Exfoliating bark is used by birds and bats to nest and roost. Dense clusters of branches may be used as cover or rest sites for animals including martens, fishers and squirrels. Northern spotted owls have used them as locations to nest. Decaying wood provides the medium in which woodpeckers forage and cavity nesters build nests.

Goose pens and decadent trees are not easily recreated given fire has been suppressed and stand age has been lowered. There is often an inverse relationship between the economic value and the wildlife value of a tree, which facilitates the decision to retain trees with high wildlife value and low economic value.