The Secret Life of Dead Trees

The woods of summer draw us in with hues of green – the fully leafed trees glorying in the sunshine and offering cool shade to a hiker. In the fall, one gazes at the streaks and splashes of yellow and crimson. In winter, when the deciduous trees have shed their leaves, the evergreen conifers, hollies, and hemlocks bring the landscape to life. And in spring, in looking for nature’s rebirth, it’s often the green of wild onions or fiddlesticks that we notice first.

But while verdant woods delight the eye, one sometimes overlooks the dead trees that signal a healthy forest as well. Often burgeoning with life, dead trees, either fallen or still standing, are crucial to a rich ecology. It’s as if nature were following the motto of Mary, Queen of Scots: “In my end is my beginning.”

Standing dead trees, commonly called snags, provide important habitat to a wide variety of beings: bacteria, fungi, and lichens; insects and other invertebrates, birds and mammals. Snags can last up to 40 years. After they fall, becoming coarse woody debris, they often become nurseries for seedlings.^[1]

The life cycle of dead trees begins with their colonization by mosses and fungi, which break organic matter into vital nutrients for the soil. They are soon followed by insects. Explains ecologist Clive G. Jones: “Wood-boring insects are much more prevalent in dead trees.”^[2] The insects, in turn, attract birds such as woodpeckers. No wonder Kevin Krajick, writing for Science magazine, says some trees support more biodiversity dead than alive.^[3]

Woodpeckers are the primary excavators of nesting holes. Ecologists call these birds primary cavity nesters. Their hollows are later used by many others: bluebirds, wrens, chickadees, barred owls, and kestrels. These birds are known, naturally enough, as secondary cavity nesters.

Snags provide shelter, nesting, and foraging sites for many other animals as well, including mice, squirrels, flying squirrels, bats, raccoons, and tree frogs. This ecological cycle also supports raptors, who perch atop snags for a clear view when searching for prey.

If a log falls across a stream, it’s a bridge for animals. And “dead logs are like runways for small animals as they move around the forest,” says Jones. “They act as visual shelter from predators such as owls.”^[4]

Some researchers say removing dead material from a woody area can mean a loss of habitat for up to a fifth of the animals.^[5] A healthy habitat for woodland animals means leaving two to four snags per acre.^[6]

But snag and den trees are disappearing as forests are being intensively managed through cordword cutting, timber management, and land clearing.^[7] Dead wood is taken away from the forest floor in an attempt to control unwanted animals, to remove fungi, or for aesthetic reasons. The suppression of wildfires and the use of pesticides have also disrupted the natural lives and deaths of trees.

Those of us who are blessed with large yards or woodlots can leave snags to provide wildlife habitat. “Snags may not appear very attractive,” said Laurel Barnhill, wildlife biologist with the South Carolina Department of Natural Resources, “but their value to wildlife is clear.” We should, Barnhill urges, “take a second look at dead or dying trees” and include snags in our landscaping plans.^[8]

Once one understands their importance to forest health, snags begin to have a certain kind of beauty. It’s the beauty of nature’s ability to reduce, reuse, recycle – which it knew long before humans began to learn the lessons of conservation.

Footnotes