Snags are standing dead or dying trees. In natural forests in the Pacific Northwest, there are usually a number of trees that have died from lack of light, overcrowding, competition and whatnot. Forests older than 150 years are heading into old growth status and by then some trees in these forests have been killed by fungi infecting the roots or trunk (the diseases they cause go by colorful names like stringy butt rot or laminated root rot). Wind is a big creator of snags. There may be some broken tops in trees with sound roots but weak trunks (windsnap) or if the roots are rotten or the ground soft from rain and snow, blow downs (windthrow).
In an old-growth west side conifer forest (250 – 1000+ yrs) diversity abounds: openings where giants have fallen let in light to allow shrubs and seedlings to grow better, there is wood on the ground, standing dead snags, trees growing out of nurse logs, a mossy zone with perennials and groundcovers, a shrub layer, a lower understory tree layer, intermediate to very tall trees. This is all great from an ecologist’s perspective.
An oak woodland has a different character. If a woodland or savanna was burned, it might have an open character. If no fire killed the young trees and brush, it will be crowded with skinny trees reaching over each other for the light, maybe one or two legacy giants that were seedlings 150 to 300 years ago, overtopped by douglas firs; dappled shade, poison oak shrubs, and vines climbing the trees, grasses, a few shrubs (serviceberry, snowberry) and flowering bulbs (camas) and perennials (checkermallow, strawberries) persist in the low light. There will be dead standing oaks in either case, many with dead branches and brittle broken limbs among the live ones. And lichens: many species and a great biomass of lichens.
In a managed forest, the forester does the thinning in order to grow fatter trees for market, like a row crop. When these trees – all the same age – are eventually cut, like giant broccoli, there will be some green trees left and some dead standing snags because the Oregon Department of Forestry requires it.
Why? Why do we value snags enough to write them – however few and inadequate in number – into the forestry regulations? Life. And diversity. A dead tree has arguably more life in it than a live tree. The diversity of fungi, bacteria, and wood decay organisms is enormous. Beetles, termites, ants, and others feed on the dead wood and fungi. These are the base of the food web, the decomposers and recyclers that return nutrients stored over decades or centuries, to the forest.
There are plenty of birds (woodpeckers, chickadees, nuthatches) who visit the snag to find food, and excavate nest cavities in the softening wood. Others (owls, bats) who can’t excavate a hole, use those made by woodpeckers, in a grand circle of beneficial re-use and mutual aid. A dead tree is a great place for a raptor like a hawk or osprey to nest or sit and watch for prey, possibly a douglas or flying squirrel. Snags are so important to wildlife that getting rid of them endangers species that rely on old growth and dead wood.
Next time you drive through the Oregon Coast Range on the way to the beach, observe the difference between a national forest and adjacent tree farms owned privately or by the BLM. Instantly the trees get bigger in the national forest, the ground level cooler and more diverse, the depth of the canopy is higher and the light changes. Streams look like real streams. This you can tell at 55 miles per hour.
We had a tree next to the house made into a snag. A dougfir that needed to be removed for safety. Our arborist Brian French (that’s him up the tree in photo below) took off the limbs, topped it and crafted a new jagged top – an outstanding fake lightning strike to accelerate fungal invasion. (Final touch was a birdhouse built by birdman Tom Brewster, volunteer with the Yamhill Conservation District, local woodworker, and possessor of the best Willamette Valley accent/drawl ever.) Brian also hollowed out a section of trunk behind a carefully cut piece of bark, then replaced the bark so the birds could move in right away without waiting for the snag to soften up.
Just in time for nesting season, a tree swallow pair scouted it and pronounced it livable. The rest of the flock looks on in envy. For the first time we have tree swallows careening over the house grabbing insects in the new, more sunny and open space. Yay snag.