Dead Trees “Snag” Lofty Praise as Habitat

A snag at Patuxent Wildlife Refuge, North Tract. Photo: N. Allred

Chad Hanson, a University of California-Davis researcher and Sierra Club board member observes, “We are trapped by an outdated cultural idea that a healthy forest is one with nothing but green trees. An ecologically healthy forest has dead trees, broken tops, and down logs.”

Over the last several years, you may have noticed an increase in dead and dying trees in our watershed, particularly oaks. There are a number of factors at play, including soil compaction from development, old trunk wounds, storm damage, environmental stressors such as heat and drought, opportunistic diseases and insects, and just plain old age. If you think the only response to a dead tree is to cut it down, think again!

chickadee explores a tree cavity
Insect-feeding songbirds like chickadees find food and shelter in snags. Photo: Christa R.

It has been estimated that dead trees, called snags when they are still upright, and trees with decaying wood provide important habitat for about 25 percent of the forest wildlife species in the northeastern United States. Add aquatic species and that number climbs even higher.

Did you know that more than eighty birds in North America are cavity-nesters, including 10 species of owls, 7 ducks, 2 falcons, all 21 woodpeckers, and about 40 songbirds? They raise their young in hollowed-out sections of dead and dying trees. In addition to providing a place for birds to nest, cavities also protect birds from predators and offer shelter from the elements. Dead branches serve as a perch from which birds can survey their surroundings, hunt, eat, and dry their wings and rest. If that weren’t enough, a dead tree offers a smorgasbord to insect-eating birds and other animals, with holes, depressions, and cracks that double as places to store seeds, nuts, and other food.

red-bellied woodpecker in a dead tree
Red-bellied woodpecker (Melanerpes carolinus). Photo: Lip Kee

Logs on the ground also provide a bounty of food and shelter for a range of critters. Hollow logs provide cover and protection for small mammals like foxes, rabbits, skunks, and raccoons. The wood itself may be home to ants, beetles, and carpenter bees that tunnel into it, while bark beetles build extensive chambers under the bark. These insect residents are, in turn, a good source of protein for turtles, toads, and lizards. No walk in the woods is complete without flipping over a log to see what lies beneath –
beetles, worms, centipedes, and, if you’re lucky, a salamander. Don’t forget to roll the log back over gently, lest you destroy someone’s happy home.

Dead logs and snags are also the major home for pollinating insects like wasps and bees. Solitary and colonial bees, of which hundreds of species reside in downed logs and/or snags, are among the major pollinators of flowers and berry-producing shrubs. More food in the making!

Decaying logs retain moisture and nutrients that aid in new plant growth too. Young trees may sprout from a single downed limb known as a nurse log. The soft wood tissue of a nurse log offers an ideal substrate for many young trees during their initial growth and development. Logs also store energy and fix nitrogen, and dead wood serves as a ground cover, lessening soil erosion and preventing animals such as deer from over-browsing plant seedlings.

tree seedling growing from an old log
Photo: Paul Bolstad, University of Minnesota,

It’s not just forests that benefit from dead trees, they are important in aquatic ecosystems as well. Logs in a stream cause the stream to meander or braid and the power of the water’s energy is dissipated so the flow becomes less destructive, reducing erosion. Logs are also important in trapping sediment. By slowing the velocity of the water, logs allow sediment to settle out. Dead trees and branches that fall into our creeks and rivers offer sanctuary for molting crabs and small fish, especially in areas where there is no submerged aquatic vegetation (SAV) to provide a safe haven. It’s also a place where insects breed, lay eggs and hatch into larvae. Those larvae are an important source of food for fish. Some will later molt into dragonflies and damselflies – predators in their own right. A single dragonfly can devour mosquitoes at the rate of 30-100 per day!

turtles on a log
Photo: Lottie/Flickr

The main problems some property owners have with dead trees and snags are their unattractiveness and the threat to people and property associated with their deterioration. Remember, as a rule, dead trees don’t come down in a hurry, particularly hardwoods. As long as safety isn’t a concern, consider letting nature take its course. If only the topmost branches pose a risk, you can ask your tree service to remove them, leaving the lower portion of the tree to deteriorate naturally. The tree will become a wildlife magnet and worth its weight in gold to our local critters whose natural habitat has been compromised by development.

Lise Crafton is a University of Maryland Extension Master Gardener in Anne Arundel County and member of the Magothy River Association

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