Snag, Stump

snag [ snag ] noun: a standing dead or dying tree or part of a tree

stump [ stuhmp ] noun: the base of a tree still connected to the roots or the part of a limb that remains after the main part has been chopped or broken off

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The word snag is of Scandinavian origin and dates back to the late 1500s. It was commonly used to refer to a branch or tree projecting up from a waterway creating a threat to navigation. However, in the forest, snags today are recognized as an essential part of a healthy ecosystem. Forest managers may follow prescribed practices in locating, selecting, rotating, and harvesting snags. Although some residential landowners may view a dying tree—a hard snag with limbs and stable wood—or a dead tree—a soft snag without limbs and decayed wood—as a blot on the landscape, wildlife see a snag as a food store and potential home. 

In all stages of their life cycle, even in the various stages of decay, trees—especially indigenous species—play an important role in a myriad of wildlife activity. According to Oklahoma State Extension, about 20% (some sources say up to 25%) of forest animals depend on snags, including 20% to more than 60% of forest birds. A lack of snags can cause the decline of some animal species.

Snags are home to numerous insects. These insects attract birds, like woodpeckers who in turn help control damaging insect pest populations. Insects also serve as essential protein for bird hatchlings. Even adult birds that rely on a diet of mostly seeds and berries eat insects during breeding season and feed insects to their young. Additionally, small mammals like squirrels use natural cavities or those created and abandoned by woodpeckers to store their winter food. 

Snags provide a perching place for hunting, especially important for predatory birds on the lookout for prey, and for smaller birds to rest and court. They provide homes for cavity nesters like woodpeckers, owls, red-tailed hawks, wood ducks, wrens, nuthatches, chickadees, tufted titmice, and eastern bluebirds. Small mammals, such as bats, squirrels, chipmunks, opossums, rabbits, otters, foxes, shrews, and mice as well as a variety of amphibians and reptiles also use snags for shelter, dwelling, denning, or food. Pollinators like bees use the tunnels made by insect borers to make their nests and butterflies like mourning cloaks, eastern commas, and question marks hibernate in tree hollows and gaps in loose bark. Snags also provide support for climbing vines and for lichens, mosses, and mushrooms.

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Snags Support Fauna

Snags Support Flora

Left to right: Native Virginia-creeper climbing a snag (behind right) and a downed tree (left) at Green Spring Gardens in Alexandria, Virginia; lichens on a hard snag (a dying downy serviceberry) at Bon Air Park, Arlington, Virginia; flowers growing on a mossy snag along the Eastside Trail at Mount Rainier National Park, Washington; and fungus on a snag at Huntley Meadows Park in Alexandria, Virginia.

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Landowners wishing to create inviting habitats for pollinators and other wildlife should consider snags as an alternative to paying for dead tree removal, although an expert will probably be needed to cut down tall tree tops and branches. To support wildlife, snags should be at least 6 feet high and 10 inches in diameter at breast height (DBH is measured at 4.5 feet above the ground). Snags of large diameter last longer and those protected by nearby trees are less likely to suffer damage from wind. Those 20 feet or higher can accommodate the nests of large birds like owls and attract eagles as well as small birds. The size and location of a snag also affect the types of wildlife that seek it out. 

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Downed Trunks, Limbs, and Stumps Support Fauna and Flora

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If a snag is unstable or otherwise poses a hazard or violates local ordinances, it should be felled and landowners should consider allowing the trunk to remain on the ground as even then it is beneficial. Insects, like bumble and carpenter bees, wasps, ants, and beetles, that may take up residence in a downed log, can become food for reptiles, amphibians, and other animals. A trunk or limb that has fallen into a stream, pond, or like water body can provide shelter for fish and other aquatic life as well as a place for turtles to bask. It could become a nurse log—the moisture and nutrient content of its soft, decomposing wood “offers an ideal substrate” in which new trees can grow (Crafton, 2020). Unless another tree is to be planted in the place of a downed tree, the stump can remain to naturally decay. Like snags and logs, they can support insects, lichens, mushrooms, and mosses until they eventually rot into humus to replenish the soil. The stump could also be uprooted and used creatively elsewhere in the landscape to make a stumpery.

So, the next time you see a snag, think not of a useless carcass that should be removed from sight but rather the host, still, of many a forest life.

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References

Crafton L. 2020. Dead Trees “Snag” Lofty Praise as Habitat. Maryland Grows Blog. University of Maryland Extension.

Harris R, Laudenslayer B. 1998. Dead and dying trees: part of a healthy forest. Forestland Steward. California Forest Stewardship Coordinating Committee. Cooperative Extension University of California. 

Rafferty D, Masters R, Green C. 2017. Snags, Cavity Trees and Downed Logs. Wildlife Management Notes. Id: L-270.Oklahoma State Extension.