Dead Trees Give Life

Ken Bevis, DNR Stewardship Wildlife Biologist

Our grand trees reaching for the sky are really just skeletons and straws…

Tree cross sectionBut what is a tree? It is just a narrow layer of living tissue over a dead skeleton of fiber. Living cells only cover a very narrow outer layer of the conical cylinder(s) of wood. Some of that wood acts to move water upward and nutrients down, but most of the wood simply holds the tree in the sky.

The bark is dead too, protecting the fragile living cambium layers just beneath it. Here is where life resides. The vascular cambium layer grows in both directions creating xylem wood to the inside, and phloem towards the outside. The narrow phloem layer conducts nutrients down to the roots from the photosynthesis going on in the crown. The xylem moves water upwards from the roots. Another layer of living tissue, the cork (or bark) cambium, is just under the outer protective bark. It grows only outward, and produces the bark itself. The leaves (needles are leaves too) grow out of the living ends of branches and are supported by this miraculous stem system. That’s it.

But when something goes horribly wrong for the plant, and the living tree dies, all of this already dead tissue that has been

Loup Loup pass near Twisp, burned in 2014.
Loup Loup pass near Twisp, burned in 2014.

protected by plant functions (such as sap), begins to be fully acted upon by various biological agents. That sweet cambium goes first, eaten by insects and fungus right away. And patient fungi will work slowly on woody tissue to break it down into basic elements that cycle through the ecosystem. This takes time, and fungal action varies by climate and moisture. For example, wood decomposition rates for dry east Cascades forests are very different from those for wet, west side forests. Obviously some dead wood decay occurs on living trees (hollow stems for example), so the fungus is after the wood all of the time.

Dead wood, sometimes LOTS of dead wood, is foundational to forest ecosystems. The roles played by standing and lying dead wood include nutrient cycling, water retention, soil stability and habitat, among other functions. Our understanding of this complex set of ecological processes continues to grow.

Old fire scarred snag with Douglas squirrel cone cache.
Old fire scarred snag with Douglas squirrel cone cache.

Dead trees are created in pulses over time. Single or small groups of trees can die in mature forests, killed by fungus, wind, competition between trees, or insects. A root rot pocket, for example, can kill an expanding circle of susceptible trees. These small clusters of rotting stems can be a haven for many forest species. Pileated woodpeckers, with their distinctive oval excavations, and the flying squirrels that use their cavities or entrances to hollow trees, can have habitat havens in such places.

And what about fire? When forests burn, trees die. Sometimes large numbers of trees are killed all at once, sometimes across vast areas. It’s a fact. Particularly in hot fires in dense fuels; cambium cooks and needles fry. Conifers are particularly flammable and can go up in spectacular crown fire. This is not always bad news for wildlife. For example, some birds, such as the black-backed and three-toed woodpeckers are specifically adapted to utilize fire killed trees. Browse species usually recover and provide improved habitat for ungulates such as deer and moose in a few short years. But wood is left, and dead trees will stand for many decades. Blackened stems can be found in mature forests throughout Washington making us wonder, “When did this burn?”.

A burned sea of black, dead stems causes us to think we must DO something immediately. Not necessarily.

Post fire recovery is a complicated process that requires time and care to help the forest heal. Some trees will survive and

Twenty-year-old burn on Sherman Pass in NE Washington.
Twenty-year-old burn on Sherman Pass in northeast Washington.

form the core for the new stand. Dead trees have many important roles and are an integral component of the regenerative process after a fire. They offer some shade to seedlings trying to become established. Roots, although dead, provide soil stability. When the trees fall, (which can occur immediately, or much, much later), down logs help hold the soil in place, provide decaying organic material and habitat for many species such as chipmunks, small birds and snakes. Small mammals are particularly important to forest recovery due to their role in dispersal of colonizing plant seeds and fungal spores that inoculate soils with important microorganisms. Nutrients are released into the system as a result of chemical changes in vegetation and soil. Fire effects can be profound.

Dead trees are critical habitat for many wildlife species, providing nesting and feeding sites for woodpeckers and other cavity dependent species, as perches for song birds, and down logs for ground level habitat. This is true in for stands after fires and in recovered forests where old, burned snags and logs persist for many years.

Salvage logging, if done carefully, can recover lost value from timber crop trees, reduce future fuel loading and enable access to burned areas through roads and skid trails. But it can also damage fragile burned soils and accelerate erosion and weed infestation. Removing dead trees that could help stabilize the soil and provide habitat can sometimes actually inhibit long-term forest health and recovery. Removing dead trees may be necessary for protection of infrastructure such as buildings, or along roads where falling trees could pose safety hazards, or to gather monetary value from trees otherwise destined for harvest. However, dead trees generally do not need to be removed to help the forest recover. Overall, the forest often recovers best when the dead trees remain, especially the larger ones, and nature is allowed to take its course.

Dead trees are beautiful and stark reminders of the fury and healing properties of nature. Ponder their grandeur in the wake of fire and death. Leave them standing as functional landmarks to the power of nature and critical pieces in the puzzle of the forest ecosystem.

For information about forest stewardship on private lands, and opportunities for cost-share thinning projects in Eastern Washington to help protect property from the next fire event (it’s not if, but when), please visit the Department of Natural Resources Small Forest Landowner Office at www.dnr.wa.gov/sflo. And feel free to contact me with questions or observations about dead trees, or any other habitat issues at ken.bevis@dnr.wa.gov .