Snag Some Habitat

Standing dead wood has incredible value to living things across western Montana’s forests. As fall stretches on and wood stoves burn more frequently, standing dead wood has high wildlife habitat value in addition to providing heat for homes.

Forest snags provide denning, roosting and foraging habitat for hundreds of wildlife species. Often snags receive compounding use by forest vertebrates over time. Tall snags originally provide perching or nesting habitat while broken tops provide denning or resting for mammals. Cavities are continually excavated providing larger holes increasing opportunity for a larger suite of species. On your next walk in the woods, there are a few things to note about the value of snags for wildlife in our national forests.

Not every snag is equal as wildlife habitat. Western larch, cottonwood and cedar have the highest value for wildlife habitat in our forests, while other species like alpine fir, spruce and lodgepole pine snags often have less use by wildlife species in our forests.

Snags often provide unique features for wildlife security. Black bears have been found to be denning in broken-top cottonwood snags during the winter. Hollow cedar snags provide valuable denning and resting habitat for weasel species like the American marten. Martens spend high amounts of energy foraging for prey especially in the winter months.

Cavities provide important protection from predators, security from inclement weather and thermal insulation.

Large diameter, tall, robust larch and pine snags often provide important perch and launch sites for foraging forays by some raptors (hawks, owls, eagles) and flying squirrels. Some raptor species use the tops of large snags as a sentry post within their territory or for plucking posts for eating their captured prey. Woodpeckers are known to hammer or drum on hard snags as a form of territorial or mating communication.

A large number of bird species use snags as a food source. They glean insects and other invertebrates from dead wood, bark, fissures and cracks in dead and dying wood. A few species even use cavities and crevices in snags to cache their food for later use.

Snags may improve as habitat for an increasing number of species as time goes on. Western larch with heart rot decay is valuable to the pileated woodpecker. As undecayed western larch is dense, pileated woodpeckers select the softer decayed wood heart rot larch.

Pileated woodpeckers are considered a “pathfinder” species, as many other cavity nesters or small mammals use pileated created nesting, roosting or feeding excavations because they would otherwise be incapable of excavating the dense wood of western larch.

Larger diameter snags often have increased value to wildlife species. Generally though, the larger the snag, the less common it is. This is largely due to less trees living to an older age. As trees age, they grow slower. Few reach very-large diameters before mortality, due to various disturbance factors and the inability of forests to contain large old trees and snags due to various types of disturbance agents (human or ecological), which kills and removes them over time.

Across a landscape, the character of snags can vary dramatically over time and space, largely depending on recent disturbance history. Warmer and drier areas historically underwent more frequent, lower-intensity fires and typically supported fewer snags and large downed logs than cooler and moister environments that often reached climax conditions before having stand-replacing fires. Types and densities of snags often vary significantly at different elevations or in proximity to riparian areas due to the influence of different ecological factors like exposure to heavy winds, shallow or deep water tables and susceptibility to insect and disease outbreaks.

Many land management activities can reduce the presence of snags on the landscape. Research has shown that snag abundance is markedly different in harvested forest areas and along open roads. Utilization of dead wood for firewood cutting or sanitation, salvage and commercial timber sales often reduce snag abundance within harvested units or along open forest roads.

The Occupational Safety and Health Administration has imposed standards to fall snags that represent a danger to contractors in the woods or wildland firefighters. When considering all the multiple uses of our National Forests, it can be a challenge to maintain high quality snag habitat over time while considering the safety of loggers and firefighters or the utility of firewood or commercial timber. Consider that it may take 200 years to produce a hollowed 20-inch plus diameter snag.

The Forest Service has a long history of snag management and conservation. A Forest’s Land and Resource Management Plan or Forest Plan gives standards, guidelines and objectives for management. All the forest plans in the Northern Region recognize the value of snags and include various provisions for snag conservation. For instance, the Flathead Forest has standards to provide conservation of different size classes of snags by habitat type when designing and planning forest management projects. Firewood cutting provisions are often put in place, at least in part, for snag protections. Using Forest Inventory and Analysis data (FIA), Region 1 monitors snag densities across ownerships, inside Wilderness and out to evaluate trends and distribution of snag diameter classes to better inform management practices.

Understanding the ecological importance of snags and the processes that create them is important for management in our forests. As you are out for a walk with your rifle or just enjoying the fall, keep an eye out for the unique features standing dead trees provide for wildlife. If you’re paying attention, every snag has a story to tell.