[OPINION] Wildfire: Dead Trees Vital to Forests

[Read the opposing view to this opinion piece, “Wildfire: Thinning Forests for Biomass Energy Can Reduce Fire Severity,” by John Buckley, Executive Director, Central Sierra Environmental Resource Center]

– by George Wuerthner, Ecologist

Dead. Most of us have negative associations with the word. So it’s not surprising that most of us tend to view dead things as undesirable, unless we are talking about mosquitoes and rattlesnakes.

We impose this cultural bias about dead things to our forests as well. Public land management agencies spend billions annually trying to contain wildfire and insect outbreaks based upon the presumption that these natural processes are destroying the forest by killing trees.

And this bias feeds the biomass industry. After all if dead trees are a “wasted” resource, why not burn them to make “clean” energy? That is the prevailing idea behind many biomass proposals.

For example, throughout much of the West, advocates of biomass burning suggest that forest thinning projects, particularly removal of bark beetle-killed trees or the aftermath of a wildfire, could be used to accomplish two goals: making the forest “healthy” and producing power.

But the idea that removal of dead trees or reducing tree density to preclude wildfire and/or beetle outbreaks is based upon flawed ecological knowledge.

A new perspective is slowly taking root among forest managers, based on growing evidence that forest ecosystems have no waste or harvestable surplus. Rather, it seems that forests reinvest their biological capital back into the ecosystem, and removal of wood—whether dead or alive—can lead to biological impoverishment.

Large stand-replacement blazes and major insect outbreaks may be the ecological analogue to the forest ecosystem as the hundred-year flood is to a river. Scientists are discovering that dead trees and downed wood play an important role in ecosystems by providing wildlife habitat, cycling nutrients, aiding plant regeneration, decreasing erosion and influencing drainage and soil moisture and carbon storage.

Dead trees are important to wildlife. Think woodpeckers. But a lot more species than just woodpeckers depend on dead trees and downed wood for food and shelter.

But it’s not just the use of snags for nesting, or even feeding as with woodpeckers, that attracts birds and other wildlife to recently killed forests. Burned forests also are used extensively by seed-eating species that are attracted by the abundance of new seeds shed by cones and colonizing plants.

Some two-thirds of all wildlife species use dead trees or downed wood during some portion of their life cycle. Among Pacific Northwest vertebrates, sixty-nine species depend upon cavities for shelter or nesting, while forty-seven other species are strongly associated with downed wood.

It’s easy to identify an ecosystem for its most photogenic species, but there are dozens of small cogs that are of equal importance.

One of those is ants, and downed logs are their preferred home. Ants are among the most common invertebrate in forest ecosystems and, not surprisingly given their abundance, are critical elements in forest ecosystems. The most obvious value of ants is as food—from birds such as flickers to much larger animals like bears.

Dead logs and snags are also home to pollinating insects.

Healthy forest soils also require decomposing material. Below the litter layer in the soil is yet another layer of life that depends on dead wood.

People commonly assume that wildfire destroys trees and leaves a smoldering pile of ashes. In truth, some live trees and a lot of dead wood physically survive blazes. Beyond the value of dead trees as feeding, hiding and resting habitat for wildlife, downed logs play an important role in forest regeneration.

Snags and downed logs modify micro-sites that can affect seedling establishment. For instance, snags provide some shade and reduction of drying winds, creating more favorable conditions for tree seedling survival.

Trees heated and killed by fire create sapwood that resists rotting and lasts longer in the ecosystem. Trees dead prior to the fire tend to become blackened and charred. Charred trees are also resistant to decay. Thus, wildfire creates long-lasting biological legacies that can survive for a century or more.

Wildfires and/or insect outbreaks create downed logs that fall into streams and across slopes. Downed logs, by slowing the velocity of the water, allow sediment to settle out and help return sediment flows to pre-burn levels.

The loss of salmonids in many parts of the west can be attributed to the absence of wood in streams.

The criteria for healthy ecosystems can’t be easily defined or exhaustively listed. But healthy ecosystems have a full array of processes operating unimpaired, including hydrologic function, soil productivity, carbon sequestering, provision of wildlife habitats, and keystone disturbances such as fires, floods, storms and insect outbreaks.

One crucial element present in unmanaged, healthy systems is a significant amount of dead trees and downed wood.

George Wuerthner is an ecologist and publisher of 38 books on environmental subjects, including Wildfire: A Century of Failed Forest Policy.

2 comments

  • George said, “A new perspective is slowly taking root among forest managers, based on growing evidence that forest ecosystems have no waste or harvestable surplus.” Is George suggesting that no wood should be harvested?
    Joe

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  • Dr. Wuerthner’s opinion piece, DEAD TREES VITAL TO FORESTS, fails to mention probably the most important reason for not cutting down or removing beetle-killed or other dead trees. The standing dead trees play a key role in the normal succession process of the forest, promoting the growth of the next or likely climax species mix. Where conditions allow tree growth, the climax vegetation will usually be shade-tolerant tree species. Cutting down or removing dead trees may alter the conditions such that other sun-loving trees or brush will grow instead, setting the succession process back by up to hundreds of years.

    In the Central Rockies, where I live, the climax vegetation is sub-alpine fir and Engelmann spruce, We also, however, have large acreages of lodgepole pine, the result of past clear-cutting. In nature, the lodgepole would only grow following fires–which are rare and not part of the normal ecology at our 9,000+ foot altitude. Following fire or clear-cutting, the lodgepole grow very densely, to the exclusion of other vegetation (and wildlife) with foliage only in the canopy and maturing very slowly, perhaps after 100 years. At that point, nature’s succession process uses pine-bark beetles or other forces to kill and thin out enough of the trees that some new lodgepole, but much more so, the shade-tolerant spruce and fir can start growing up underneath, eventually leading to beautiful, flora and fauna-rich spruce-fir forest.

    If, however, man interferes by clear-cutting or anything more than minimally thinning the beetle-killed or other dead or live lodgepole, it sets the succession process hundreds of years, going back to grasses, shrubs, and new brier patches of lodgepole that love the sun. (Because spindly lodgepole have very shallow roots, they can stand only because of how densely they grow with their neighbors. Cut down the surrounding dead trees and all the live ones blow down, so significant cutting basically means clear-cutting.) One-hundred or more years later, you finally get back to maturing lodgepole being thinned by beetle kill and the chance to let nature take its course of succession to spruce-fir climax–or not and once again starting over.

    While spruce-fir climax, very slow forest growth and infrequent fire may be somewhat unique to very high elevation, lodgepole pine and other sun-loving, pre-climax species are certainly widespread at lower elevations. So the situation probably applies to many, if not most forest types. Cutting down or removing too many dead or live, sun-loving or climax species trees can totally disrupt the natural succession process and deprive man as well as nature of beautiful climax forests..

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