The Living Dead of the Forest Snags and Nurse Logs

I sat and watched a pileated woodpecker build a nest for twenty minutes recently. Minutes I meant to be spending doing other things. These largest of Pacific Northwest woodpeckers can be heard from quite a distance — pecking, I suppose, though that word seems too small for the sound they make: a deep, hollow, echoing tone, rapid, but not as quick as some of their smaller cousins. This sound is often the first hint they are there, before they are spotted. It is impossible to ignore, impossible not to stop what you’re doing and look up for the accompanying motion and splash of red.

I’d almost walked by, having heard and spotted it, when it disappeared into the hole it had been building, and kept knocking. First just its head went in, its tail still sticking out of the hole, nearly upside-down, so it could peck at the tree from the inside, just below the hole. And then it disappeared fully inside, though I could still hear it working. It would pop its bright red head up periodically, throwing wood chips out of the hole to rain down on the ground below. It was the quietest of dramas unfolding in front of me, the kind with no real end, but from which I could not, did not want to, look away.

It was doing this maybe forty feet above the ground, in the trunk of a dead but still standing alder tree — dead trees that remain standing are called snags. The holes a pileated woodpecker makes on the surface of the tree are only about the size of a tennis ball, but inside the tree is a cavity large enough for two adults — each roughly the size of a crow — and their young. Pileated woodpeckers abandon their nests each year to excavate a new one, leaving the abandoned ones free for the taking by other birds. They are what’s known as primary cavity excavators. This behavior also makes them keystone species in pacific northwest forest ecosystem — one that helps shape or hold together an entire ecosystem. They can’t do this without snags.

I’m not shopping for real estate right now, but as seems to be a trend among so many of my age-mates, I spend a fair bit of time skimming real estate listings anyway. There’s something irresistible about seeing all the different ways there are to live and to make a home your own, even while knowing that real-estate listings are necessarily a home at its best, a home photographed in such a way that its awkward angles are craftily hidden, a time in a home’s life when “potential” is clearly not something to aspire to.

In the exurbs of Seattle, “park-like” has become one of those terms, like “potential,” that I’ve read so many times it’s become nearly meaningless. In areas where lots are large, sometimes multiple acres that were never intended for commercial agriculture, it’s not out of the question for them to be park-like. The phrase does inspire almost universally positive feelings, but it doesn’t mean anything. Or perhaps, it could mean so many different things, that it means nothing. But looking through the images of the grounds of these listings (it’s hard to call them “land” or “yards”), it’s clear that “park-like” is used to mean only a couple of things. Grassy expanses with some large trees interspersed here and there, perhaps a fire pit or other seating area. Grass lawns a rich, dark green, not a dandelion in sight.

Alternatively, some of these properties do look more forested. Only at first glance though, after which it becomes clear that they are manicured and managed, they only happen to be manicured to look like a forest. There are trees, probably with a path or two winding through them. Perhaps most confusingly, because even if it takes you a moment to figure out exactly what is discomfiting about the scene, it is clear there is something: there is no debris on the ground. Fallen leaves, perhaps, but no fallen trees or branches. Pristine. Have you ever seen a forest like that?

This bent toward park-like spaces may be evolutionary. Humans evolved in savannas, and so now we prefer that our landscapes look like that: wide open spaces, shorn grass, large trees or water features here and there. We have specific preferences around the coherence of a vista, about ground surface texture, depth, complexity. We even have a preference for some mystery, or the sense that we don’t know everything that there is to know about a landscape, that we could walk around the next corner of the path and not know what we might find, peek around the trunk of a tree and find something new. Not too much mystery though: it’s important that we feel like we could find out without too much effort or risk.

I wonder though: what do the owners of these park-like pieces of land think they will look like 50 or a hundred years from now? Removing alder trees that provide a critical source of nitrogen; mowing the lawn around the trees that were deemed good enough to remain surely mows down any non-grass thing that tries to sprout. There are no tree saplings, no young trees even. They never stood a chance. So once the existing trees die out: then what? A lawn, I suppose, without even the benefit of trees interspersed. Almost certainly different owners by then though, whose problem it will become.

The Andrews Forest is an experimental forest in Oregon managed jointly by Oregon State University and the United States Forest Service that is left entirely to its own devices. Scientists study natural ecosystems there, but they don’t intervene. Those scientists found that 25% of the surface area of the forest floor was covered by downed logs. That number doesn’t include snags of the type my woodpecker and insect friends call home.

A large tree, settled on the ground where it is consumed by fungi and bugs, and where it can sometimes nurse young plants, including trees, to new heights, can take two hundred years or more to fully break down. By mass, these well-decomposed trees can contain more living tissue than a living and thriving tree of similar size. What we see as life can be so narrow that we miss it sometimes. To call these downed trees “nurse logs” feels apt, though in the later phases where the more recent additions have grown large themselves, they seem nearly to have consumed the original. The ones not called nurse logs because they host only bugs, fungi, bacteria: these are less dramatic but hosting no less life. They could just as accurately be called nurseries, if only humans had sufficient appreciation for the microscopic.

That dead things — snags, fallen logs, fallen leaves — are necessary to continue propagating new life is not a new insight. But that we might, as inhabitants of pieces of land, no matter how small, contribute to this circle of life just by leaving a dead thing be, may be one it’s time to start accepting. A chance to celebrate small moments of untidiness, and the new life that they harbor.

Sources

Falk, John H. & Balling, John D. Evolutionary Influence on Human Landscape Preference (Environment and Behavior 42(4):479–493, 2010)

Luoma, Jon R. The Hidden Forest: The Biography of an Ecosystem (New York: Henry Holt and Company, 1999)

Tallamy, Doug, Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard (Timber Press, 2020)

Wing-Chi Poon, CC BY-SA 2.5 , via Wikimedia Commons