Snags: Dead Trees are Nature’s Hottest Critter Condos

August 29, 2016
Dead Trees
S.H. LEEStanding dead trees provide a home to a wide range of critters.

When you’re out hiking this fall, you’re likely to see some stunning foliage. But in addition to the bristling evergreens and the maples just starting to shed their autumn colors, the careful observer will spot another set of trees: the ones whose branches are bare year-round. These trees may be dead, but they’re far from lifeless. Standing dead trees, called snags, are vital to the survival of dozens of bird species, among other woodland creatures. “They provide homes and food for a variety of wildlife,” says Jim Oehler, a habitat biologist with the New Hampshire Fish and Game Department. “Some people call them ‘critter condos.’”

Nature’s Smorgasbord
Insects colonize dead trees, hastening the process of decay. Some beetles and assorted bugs eat bark and dead wood, while others graze on the fungi and bacteria that grow on snags. Still others move into holes and tunnels left in the wood by earlier invaders. These burrows often lead straight to a tree’s interior, a veritable food court serving up smaller bugs. All of these insects attract mammals, including raccoons and black bears that dig deep into a snag’s heartwood, seeking edible insects. You might hear the pileated
woodpecker using its chisel-like bill to excavate holes in search of larvae, pupae, carpenter ants, and termites. Other birds—brown creepers, nuthatches, and a variety of woodpeckers— eat insects that stick closer to the surface, such as bark beetles, spiders, and ants. Snags can even help birds catch larger prey.
Open branches provide perches for hawks, eagles, and owls, yielding clear sight lines to small mammals below.

Home Sweet Hole
In addition to drilling for food, woodpeckers regularly hollow outnests in snags, excavating several holes a year. This leaves many spaces for secondary cavity nesters, such as chickadees, nuthatches, great crested flycatchers, wood ducks, owls, and bats—species that aren’t able to make their own holes. Hollow snags and large knotholes also provide homes for mammals as diverse as squirrels, martens, porcupines, weasels, fishers, raccoons, and bears. It isn’t only the holes in snags that provide shelter. Bats and the small songbirds known as brown creepers roost under loose bark.

Humans’ Role
Trees die from disease, lightning, fire, drought, animal damage, competition with other plants, and simple old age. If left undisturbed, the resulting snags can be a resource for decades. Dense hardwoods, such as sugar maples and beeches, tend to stand the longest after a tree has died, especially when their roots are anchored in deep soils, Oehler says. When trees do come down, artificial snags can provide some of the same benefits. Over the past 200 years, as much of the Northeast’s forests were cleared to make way
for farming and other development, human-erected bird boxes helped certain species survive near extinction. The first recorded use of artificial nesting structures for the brightly colored wood duck was in the 1930s, in an Illinois wildlife refuge. But bird boxes and nesting platforms don’t offset related hazards, such as hunting and deforestation. As Northeastern woods have rebounded during the last century, so have snags. Foresters now have a better understanding of the value of standing dead trees and try to leave at least six snags per acre. “The bigger, the better,” Oehler says, since a wood duck requires a trunk at least 20 inches in diameter. While snags aren’t as eye-catching as autumn maples, they’re doing their part to keep the forest full of life.

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Heather Stephenson

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