Wildlife snag
Tree snag with decay and den hole. Not a hazard because there is no target. photo: Joseph O'Brien, USDA Forest Service, bugwood.org

Although not always practical or possible, there is a real value to keeping parts of a severely damaged or standing dead tree (snag) in the urban landscape. Proximity to “targets” (houses, picnic sites, fences, people, etc.) is the consideration here. Safety always comes first. But in the right setting, allowing a damaged tree or snag to remain is a great benefit to animals and birds who “make their living” and their homes in these trees.

Who uses these remnants of our urban forest?

Over one-fourth of forest dependent wildlife species use dead and dying trees for food, shelter, and cover. When coarse woody debris (downed trees, logs, decaying branches on the ground) is factored in to equation, that number rises to over one-third of forest wildlife species relying on the habitat structure within ‘defective’ trees.  There are five basic categories of these species:

  • Primary cavity excavators — Examples include woodpeckers, flickers, and nuthatches that make and use new cavities every year.
  • Secondary cavity users — Several species of small owls, bluebirds, kestrals (sparrow hawks), cavity nesting ducks, including wood ducks, flying squirrels, raccoons, martens, and deer mice, are examples of more than 100 species species who cannot excavate cavities by themselves, but use abandoned holes to nest and raise young.
  • Open nesters — Larger birds like eagles or osprey can use either dead or live trees, but they usually prefer trees with a broken top or flat crown to support their nest and provide a good view of the area.
  • Other mammals — Small mammals like bats, flying squirrels or mice look for shelter and nesting places under loose bark and other small cavities.
  • Amphibians — Many species of frogs and salamanders use dead and dying trees for habitat, especially once the wood is in an advanced stage of decay and laying on the ground (coarse woody debris). In general, decaying trees are also an important food source at all levels of the food chain.

Snags provide an incredibly diverse range of microhabitats, crucial to insects, invertebrates, cavity nesting birds and

Downy woodpecker
Downy woodpecker photo: David Cappaert, MI State Univ., bugwood.org

small mammals. Almost every part of a dead tree is used by wildlife. Various stages of decaying wood offer opportunities for animals, from providing habitat to insects that become the local diner for insect-eating animals, to softening up wood to allow cavity nesting birds to excavate their dream home.

Keeping snags in urban settings is crucial for these species survival. That’s not a rotten tree, that’s “Joe’s Diner!”

If you are planning to leave remnants of damaged trees, watch for trees that are too tall and unstable to retain, and then cut them to a height where they won’t be a hazard when they eventually fall over. It is a good idea to try to leave some limbs on the trunk and rough up the top to make it look natural for the birds that enjoy a room with a view.

Recruiting the services of a certified arborist will assure the safety of all while tree tops are carefully extracted. If requested, an arborist can bore a few holes in the trunk to speed up the natural process of decay. Couple habitat development with retention of existing trees and replanting of understory trees and plants, and you can rest assured that you have provided a wide variety of future wildlife habitat needs.

Broken branch
photo: Joseph O'Brien, USDA Forest Service, Bugwood.org

For more information about urban wildlife visit:

WSU Forest and Wildlife Extension’s:

Backyard Forest Stewardship in Eastern Washington

Backyard Forest Stewardship in Western Washington

National Wildlife Federation’s Making Wildlife Habitat at Home.

Reference: Wildlife Habitat in Urban Areas; Oregon Department of Forestry Urban and Community Forestry Assistance Program; www.oregon.gov/ODF

Thanks to DNR Wildlife Biologist Jim Bottorff for his editing assistance.