The Life in Dead Trees

Image Gallery Tree roots grow around a fallen tree, or nurse log, in Olympic National Forest, in Washington state. DAVE SCHIEFELBEIN

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Young autumn’s shorter days and colder nights soon will do their work shutting down the chlorophyll factories in the woody landscape, and the skies will rain bright leaves. We humans will look up and watch admiringly even as we stand in our yards holding rakes in blistered hands, ever more leafy labor drifting to our feet.

Once shed of summer’s green and autumn’s multicolor, trees seem to us somber and lifeless. Nothing could be further from the truth — a leafless tree in fall and winter is near to popping with life, merely holding its vegetative breath. Nestled within its buds are thousands of miniature, fully formed infant leaves — all the foliage the tree will, at winter’s end, finally exhale in the great green gush we call spring.

That we see no life when we see no leaves is, in other words, only human foible. No tree, in fact, ever is lifeless — not even when the tree is long dead.

Life After Death

“Snag” is the traditional forestry word for a standing dead, or partially dead, tree. Recently, though, biologists have adopted a more descriptive and deserving term: wildlife tree.

With the exception of living plants, probably no other single component of the woodland environment supports more animal life. In North America, about 85 species of birds, at least 50 mammal species, and roughly a dozen reptiles and amphibians rely on snags for shelter, food, mating, resting, nesting and other critical functions. In addition, dozens of invertebrates — millipedes, beetles, spiders, worms, ants and more — also call snags “home” (or at least “snack bar”). In all, says the U.S. Forest Service, some 1,200 forms of fauna rely on dead, dying or rotted-hollow trees.

So much for the “dead wood” notion.

It’s the insects, naturally, that attract many of the higher creatures. Drawn largely by the easy pickings at snags, hungry insectivores help control insect pests in the forest overall.

But by far the greatest benefit of snags is the cavities — holes used for nests and shelter — that they foster. For many birds and animals, no better home exists than a hole in wood. Woodpeckers, chickadees, bluebirds, nuthatches, owls, wrens, tree swallows, raccoons, squirrels, bats, opossums, flying squirrels, porcupines — these are only a few of the species that require or prefer cavities. For them, a good snag is hole heaven.

Evolution Of A Snag

Often, ironically, it is a cavity or the beginning of one that causes a snag-to-be’s demise. What sugar is to teeth, forest fungi are to wounded trees. Maybe it’s a lightning strike, a broken limb, a climbing bear’s dotted claw-scratch (ascending) or long-lined scrawl (descending).

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