Living forests need dead wood

What’s wrong with this picture? The serene park-like setting near Lake Chelan in central Washington looks great but it is anything but natural. Why? Overly aggressive forest thinning has left it without the snags (standing dead trees), fallen logs, scattered woody debris, open patches and other natural features that many wildlife species of the forest need for habitat.

thinned forest parcel with wildlife features
Crews thinning excessive wildfire fuels from this forest parcel left behind several snags, logs and other features attractive to wildlife. Photo: Ken Bevis/DNR.

It sounds like a conundrum but dead wood is one of the most important elements of a living forest. Insects of all kinds live in and feed on the fungi found in snags and downed logs as well as on the dead limbs of living trees. Feeding on these insects are woodpeckers, nuthatches, chickadees and many other birds. The tree cavities created by woodpeckers during nesting and courtship also can provide homes for other species, such as bluebirds or flying squirrels and other species that are voracious feeders on insects (including the insects we consider forest pests). These birds, small mammals and reptiles help keep the forest healthy but only if the habitat remains suitable for feeding and nesting.

When DNR thins forests or assists landowners with thinning, we aim to reduce the dangerous fuels that can feed wildfires. These are generally small tree stems of less than 3 inches in diameter. These smaller stems can carry flames up into the crowns of larger nearby trees. Larger tree and logs, which should be left for habitat and soil enrichment, will ignite more slowly and are less likely to flash into a hot fire that spreads from tree to tree.

Forest thinning should retain snags that are greater than 10 inches in diameter at breast height (dbh) of the average person. In addition to resisting flames better than smaller trees, large snags provide excellent opportunities for excavators, such as the hairy woodpecker or flicker, to create cavities.

Snags and other types of wildlife trees are so important to that Washington state’s forest practices rules require timber harvesters to leave behind several of these trees per acre.

DNR Landowner Assistance Wildlife Biologist Ken Bevis suggest going beyond the require minimums to retain more wildlife trees — 12 to 16 per acre if possible. Where there are no snags, they can be created by various techniques, including removing bark from a portion of the tree’s trunk or major side branches or topping the tree. See more about snags as habitat on the Washington Department of Fish and Wildlife website.

More Dead Wood

Other forms of dead wood that can aid forest wildlife include:

Legacy trees: Big trees are the backbones of forests, especially on the state’s dry eastern side. Bevis advises keeping the largest trees, including defective ones, during a thinning operation. These senior trees will produce more cones and branch surface area than younger one; they also can provide more perches and nest sites, and will eventually become dead wood.

Fallen logs: The largest downed logs should be kept in place when thinning. Additional ways to improve habitat while thinning is to scatter tree tops and large pieces of wood across the treated area.

Thinning and fuel reduction projects are crucial to help our forests survive the current rounds of drought and devastating wildfire. Including habitat elements in these projects is not only possible but will bring additional benefits to landowners and the other inhabitants of the forest.

(This post is an abbreviated version of an article that appeared recently in Forest Stewardship Notes, a free e-newsletter about forestland management published quarterly by DNR and Washington State University Extension)

See the full list of free e-newletters from DNR