From August edition of Washington Department of Fish and Wildlife's Crossing Paths newsletter
As strange as it seems, some trees can actually provide more habitat for wildlife when they're dead than when they're alive. Standing dead and dying trees, called "snags" or "wildlife trees," are important for wildlife in both natural and landscaped settings.
Birds, small mammals, and other wildlife use snags for nests, nurseries, storage areas, foraging, roosting, and perching. Live trees with snag-like features, such as hollow trunks, excavated cavities, and dead branches can provide similar wildlife value. Snags occurring along streams eventually fall into the water, adding important woody debris habitat for fish and other aquatic life.
Snags can attract wildlife species to your property that you might not otherwise see.
More than 100 species of our birds, mammals, reptiles, and amphibians need snags for nesting, roosting, and denning. Hollow snags and large knot-holes are used by Douglas squirrels, northern flying squirrels, martens, porcupines, raccoons, and even black bears. Several species of owls and woodpeckers also use large cavities. Bluebirds, chickadees, swallows, wrens and other songbirds use smaller cavities. Brown creepers, nuthatches, bats, lizards, and mourning cloak butterflies will roost behind loose bark and bark slits for winter warmth and shelter.
Some 45 of our wildlife species forage for food in snags, which are often loaded with insects. Woodpeckers, sapsuckers, flickers, nuthatches, and a myriad of other insectivorous species regularly make snags their dining rooms. Mice, squirrels, jays, crows and other wildlife use snags more like kitchens, for food storage areas.
Some snags make ideal hunting perches for hawks, eagles, and owls. The more open resting perches that snags provide are preferred by swallows, band-tailed pigeons, mourning doves and other colonial birds. And of course the resonating surfaces of some snags are perfect for woodpeckers to announce their presence with their hammering bills during courtship season.
Snags of both deciduous and coniferous trees are used by wildlife. The most favored snag species east of the Cascades are ponderosa pine, western larch, quaking aspen, and paper birch; west of the Cascades, Douglas fir, western red cedar, big-leaf maple and cottonwood snags are highly used. Softwood trees such as fir tend to make better food foraging trees, while hardwood trees are sometimes better for nesting cavities.
Unfortunately, many of these dead or dying trees are cut down without much thought to their wildlife value and the management options that can safely prolong their existence. Of course if not managed properly, snags can pose a risk to people and structures. If a dead or dying tree threatens something that can be moved, such as a swing set or patio furniture, consider moving those items before cutting the tree down. An alternative to eliminating the entire tree is to remove only the dangerous sections.
Consulting with a certified arborist experienced in wildlife snags is recommended. These professionals can determine what part of a tree is a hazard and provide management options to reduce or eliminate any risk. Remaining parts can be removed over time. Often, once the unsafe limbs or portions of the trunk have been removed, the tree is safe.
Retain live trees and tall shrubs near a snag to protect it from wind and provide a more complete environment for wildlife. In urban areas, tall snags are best located away from high activity areas, where they won't pose a hazard if they fall. Trees that lean away or are downhill from structures and other areas of human activity present little or no risk.
When a tree must be cut down, maximize its habitat value by placing as much of the debris as possible near the area where the tree was removed. In hot, dry areas, move the material into the shade of nearby trees or large shrubs.
You can create a snag from trees that are hazardous or problematic, like ones with forked tops or disease or invasive roots threatening a drainage or septic system, or individual trees in a group that needs thinning. Like landscaping rocks and boulders, snags can add interesting, artistic angles to your property.
More information about snags, including details about how to safely create a snag, or enhance existing dead or dying trees, is available at http://wdfw.wa.gov/living/snags.