ECOLOGICAL DIFFERENCES BETWEEN LOGGING AND WILDFIRE

GEORGE WUERTHNER

Though many may perceive there to be no difference between a tree killed by a fire or a tree killed by a chainsaw as part of a logging operation, there are vast ecological differences. Furthermore, logging based upon the presumption that reduction in fuels will reduce or eliminate large blazes is based upon flawed premises. We need big fires.

Across many landscapes, intensive timber cutting has replaced fire in ecological significance, but not in ecological effect. Because of some commonalities between effects of logging and fire, there is a perception held by many people is that logging emulates natural disturbances like wildfire. For instance, the draft legislation for the Beaverhead Deerlodge Partnership, suggests that logging can mimic wildfires. There are, however, substantial ecological differences between logging and wildfire.

A second assumption inherent in many assertions made by timber industry proponents is that logging can reduce large blazes. As a corollary to this assumption, most proponents of fire control believe suppression of large blazes is desirable. Such assertions are self-serving and play upon ecological ignorance and nuances in the ecological literature to create what appears on first review to be a plausible argument in favor of logging––an argument, however, that ignores many ecological realities.

Wildfire, whether from natural sources like lightning or a result of human ignition, has been a major influence on many ecosystems around the world. One mapping of presettlement fire patterns found that more than half of the United States burned on a fire return interval of between 1 and 12 years. Though much of this was grasslands as well as forests, particularly in the Southeast, it nevertheless, demonstrates the ecological importance of fires in many regions of the country. In the native plant communities of the western United States, fires have probably played a more critical role in shaping ecosystems than any other ecological factor.

Fire affects both forest structure and ecosystem processes. How a tree dies and is ultimately utilized is critically important to the long-term health of a forest. A tree removed by logging has a different effect on soils, watersheds, wildlife habitat, and, ultimately, biodiversity than one killed by fire and left on-site.

Superficially, logging and wildfire have some gross similarities; however, fire differs from logging in many ways. Fires vary in intensity thus create many small, and occasional very large, burn patches in a shifting mosaic across the landscape. For instance, in Yellowstone National Park, 83 percent of all natural fires are less than 1.2 acres in size, and 94 percent of all natural fires burn less than 100 acres, but the occasional large blazes––such as those in 1988––burn hundreds of thousands of acres. For this reason, fires tend to have a landscape-scale diversifying influence. Logging tends to create more evenly spaced, evenly sized habitat patches and does not alter all forest stands—particularly lands dominated by noncommercial forest species.

Fire alters an ecosystem by chemical processes; logging, by the mechanical process of tree removal. Fire rapidly recycles nutrients, kills pathogens, and selectively favors fire-adapted species. Logging leads to the loss of soil nutrients and organic matter and increases soil compaction, thereby reducing water infiltration. Fires do not leave a large road network in place (assuming the blaze was not suppressed otherwise there may be dozer lines, etc.). Logging creates roads that fragment habitat and generally increase human access, both of which affect the use of the land by wildlife. Moreover, roads and logging equipment can become vectors for the dispersal of weeds.

It is widely recognized in the scientific community that past commercial logging, road building, livestock grazing, and aggressive firefighting are the sources of many “forest health” problems, including unnaturally severe wildfires. According to the Sierra Nevada Ecosystem Project’s final report to Congress, a government report that reviewed the ecosystem health of California’s Sierra Nevada mountains: “Timber harvest, through its effects on forest structure, local microclimate, and fuels accumulation, has increased fire severity more than any other recent human activity.”

Impacts Associated with Logging
Logging is more than the removal of trees. It typically involves a road network, which has a substantial and diverse array of impacts on the land. Since most areas are not logged all at one time and are repeatedly cut over a century, logging has many additional effects, including periodic human invasion and disturbance from human activities. Soil erosion from logging roads is a major impact, particularly on aquatic ecosystems. Logging also significantly increases debris slides. One northern California study, for example, found that 61 percent of the soil displacement (erosion) resulted from logging roads.

Structural changes in the forest are obvious effects of logging, particularly with clearcutting. Timber harvest tends to leave few or no snags (standing dead trees). Even when logging leaves snags behind, the usual prescription is to have only one or two per acre which is considerably fewer than needed for cavity-nesting animals. Plus snags as they rot provide a long-term nutrient supply so there removal short circuits nutrient cycling on the site.. Even selective cutting can radically alter forest stand dynamics since most commercial logging selects for larger-diameter trees—the very individuals that under a natural fire regime are most likely to survive a blaze and persist on the site.

Commercial logging tends to remove the larger trees—exactly the ones most resistant to fire. By contrast, fires tend to kill the smaller trees, reducing competition for water and light among remaining trees. In addition, the process of logging takes away the least flammable portion of trees––their main stems––and leaves behind the most flammable parts of the tree, the limbs and needles.

In addition, partially buried and buried wood debris can make up as much as 50 percent of all surface organic matter in old-growth forests and remain for centuries. Logging eliminates the potential for creating additional soil wood.

The activities associated with logging, including the coming and going of workers and vehicles, can displace wildlife sensitive to human presence. Because of this human activity, the impacts of logging-created fragmentation are worsened by human access, reducing the effectiveness of remaining habitat patches for wildlife sensitive to human intrusions. This disturbance may be semi-permanent, since logging roads often remain open for subsequent timber harvest or public access. Human activity along roads has been shown to reduce habitat use by elk for up to a half mile on either side.

A recent study by the Montana Department of Fish, Wildlife and Parks found that grizzly bears avoid roaded areas, often for years after timber activities ceased. A severe loss of suitable habitat may occur even if the amount of land that is directly disturbed is quite small. Increased access for human trappers and hunters also changes or reduces population structure in species sought. Poaching may increase. Road closures can mitigate some, but usually not all, of these impacts. Research has demonstrated no road is better than a closed road.

The physical impact of logging upon site topography and soil profile is another difference between timber harvest and fires. Heavy logging equipment compacts soils. Studies done by the Forest Service have demonstrated that compaction inhibits forest regeneration and slows growth of tree seedlings that do manage to emerge. Fires, on the other hand, often provide ideal seedbeds for the reestablishment of plant cover.

Weed invasion is another problem often associated with timber harvest, particularly because roads serve as vectors for weed dispersal. Seeds of spotted knapweed and many other invasive exotic species are carried on the chassis of logging trucks to new locations. If the logging roads are left open for public access after a logging operation, other vehicles may also disperse weed seed. And the disturbed soils along bulldozed roads provide ideal habitat for the proliferation of weed species.

Wildfire mosaics maintain natural curves and lines, while logging introduces abrupt edges and scars from logging roads and skid trails that take decades to heal. Edge effects are generally more severe with logging than with fire.

The timing of stand-destroying fires differs substantially from the timing of stand-destroying clearcuts. In many managed forests, the goal is to eliminate older trees to favor faster-growing younger ones. The loss of old-growth structural features in a managed forest has many ecological ramifications, including changes in nutrient flows and storage, and in wildlife habitat parameters. Though fires do occasionally burn up substantial acreages of old growth, in many ecosystems, the old-growth stands are relatively fireproof except under extreme conditions, such as severe drought. Since standard forestry management practice is to cut trees at or shortly after they reach peak wood production efficiency, most managed timber stands will never possess old-growth features.

Some of the above negative features associated with logging can perhaps be mitigated or reduced by changing timber harvest methods, but one factor that almost certainly cannot be emulated by foresters is the randomness of fire disturbance. Though fire ecologists make predictions about fire frequency and “average” size, wildfires are essentially unpredictable. Logging does not emulate this randomness, and we do know how important it may be to ecosystem integrity and function.

Finally, fire performs many of the above ecological services at no economic cost––unless, of course, it threatens human life or habitation. Foresters claim that timber harvest can achieve the same ends, but frequently it costs far more to taxpayers per treated acre––particularly in places like the Rocky Mountains, where the value of timber is low––than can be recouped from the timber sales. In contrast, a prescribed-natural-burn policy, particularly if there are no fire suppression costs, is very cost-effective––no more than pennies per acre burned in monitoring costs.

Large Fires Are Necessary

There is an inherent assumption by many people, including those who support wildfires in general, that large blazes are somehow abnormal or destructive. Yet it is large fires, not the ordinary small blaze, which set the ecological parameters of western ecosystems. Large blazes are usually weather-driven—favored by drought and wind. Furthermore, since fuels are not the driving force behind most large blazes, small prescribed burns, and even “salvage” logging and/or mechanical thinning to reduce fuel loading, generally do not have an effect on large fires, nor would this be desirable. In most ecosystems, we should be encouraging, not discouraging, large fires. Current forestry policies of fire suppression, road building to facilitate suppression, fuel reduction, and so on, all contribute to the fragmentation of fire habitat, distorting natural fire regimes. Big fires are as ecologically important to functioning and healthy ecosystems as large predators are to wildlife populations. Just as large predators are “top-down” regulators of other species, fire serves a similar ecological function for ecosystems.

This is why we need large, protected nature sanctuaries such as large national parks, wilderness areas, and other preserves. Large natural areas are necessary so that big blazes can “roam” freely across the landscape, just as preserving habitat for wide-ranging species like grizzlies and wolves is important to sustaining natural biodiversity.

Ecosystem Functions Performed by Fires

Most fires perform a variety of ecosystem services that are not normally associated with logging. For example, fires cleanse a forest. Heat from fires can kill forest pathogens in the soil, including root rots, as well as insects and fungi that may be found in fallen trees or snags.

Heating and subsequent rapid cooling of rocks and boulders cracks and breaks them apart. Repeated numerous times over the centuries, this is an important soil-building process. Logging, of course, provides no such benefits.

The influence of fires often extends beyond the blaze perimeter.

Laboratory studies have demonstrated that smoke from fires will kill certain arboreal forest pathogens, reducing, for a time, the influence of some tree diseases. Smoke also aids the germination of some plant species.
Fires also change nutrient flows. Dead litter burns and turns to ash. The heat and combustion change the chemical composition of soils. Depending on how hot they burn, fires can volatilize certain nutrients, like nitrogen, that are lost as gases into the atmosphere. However, the nitrogen pool available to plants is large relative to most fire-induced losses, plus nitrogen is quickly replaced in the soil through nitrogen fixation by bacteria, which usually increase significantly after a burn in most western U.S. ecosystems. Studies have shown that bacteria and other nitrogen fixers typically make up all the losses to volatilization within two years of a burn. Other important plant nutrients, including phosphorus and calcium, are released from litter by fires and leached into the top layers of the soil. Despite some losses to waterways and the atmosphere, the overall effect of all but the most intense fires is the redistribution of nutrients from the forest canopy and floor into the soil, thus increasing soil fertility. For instance, one study in a Southwest ponderosa pine forest found that ammonium nitrogen levels were 80 times greater after a recent burn than before.

In some forests, more than a third of the nitrogen-fixing capacity is provided by microorganisms responsible for decaying wood on the soil surface and in the soil itself, again emphasizing the importance of retaining wood debris even after a fire.
Nutrients may also wind up in waterways by directly washing into a stream or lake or settling as ash from the air. Periodic nutrient enrichment from fires may be necessary for the maintenance of aquatic ecosystems, particularly those at higher elevations, which tend to be low in nutrient inputs.

By contrast, timber harvest removes nutrients from the ecosystem since trees are transported out of the area. The severity of this removal depends on logging practices. In conifers, most nutrients are stored in the branches and needles; thus, the more slash left on site, the less actual nutrient removal. Nevertheless, to replace the nutrients lost, even when only the boles are extracted, takes longer than the timber rotation period (time between logging episodes) on many sites. As a result, over time, repeated timber harvest may gradually deplete a site of important nutrients.

By removing forest canopies and increasing sunlight, logging may stimulate the growth of nitrogen-fixing plants, but usually not enough to match the quantities that grow after a fire. Furthermore, foresters usually attempt to truncate such early successional stages in order to hasten the restocking of forests with commercial species. For instance, in the Pacific Northwest, where red alder is an important nitrogen-fixing species that colonizes burned or logged areas, it is standard practice to treat such sites with herbicides to kill off the hardwoods like alder so that commercially preferred conifers can quickly regenerate.

In many forests, another important source of nitrogen input is arboreal lichens. Nitrogen-fixing lichen species are common on the branches and bark of older, larger trees. Rainwater percolating through these lichen-covered branches leaches and transports nitrogen to the soil. Since the rotational age (age when trees are large enough to cut profitably) when trees are cut is usually far shorter than the age at which they might otherwise burn, the amount of old growth in managed forests is usually substantially less than in wild, natural forests, reducing the potential input of nitrogen from lichens. How important such contributions may be to forest productivity and health is unknown.

Logging may provide a temporary flush of nutrients, but this is often accompanied by a flush of sediment as well. True, fire-bared slopes will at times wash high sediment loads into river systems, particularly if heavy rains occur immediately after a burn. However, on most sites, within a year or two of a fire, vegetation covers the ground, since fires typically do not kill underground tubers or seeds that may be lodged in the soil. However, logging roads are seldom removed or decommissioned, and thus they are a long-term and unending source of sedimentation.

Also, the snags that are left on a burn site often fall across the slope, creating check dams that slow erosion and reduce sediment yield to streams. Again logging, particularly “salvage” logging, removes such snags, hence increasing sedimentation and its many negative effects.

In addition, the soil disturbance caused by logging and heavy equipment strips away soil and the buried seeds and roots that might otherwise sprout and quickly cover a slope. Logging roads are notorious for generating high sediment loads, even higher than typically found on the logged or burned slopes themselves.

Of course, the amount of sedimentation, whether because of fire or because of logging, is largely determined by such things as soil type, gradient, seasonality of runoff, and timing between periodic natural floods. Logging nearly always increases sedimentation over natural levels associated with most, but not all, burns. High sedimentation kills aquatic insects and fish, and changes stream channel patterns.
Fires may temporarily reduce the amount of organic matter in aquatic ecosystems, to the detriment of aquatic invertebrates, particularly in smaller streams. However, within a few years, the flush of new vegetation begins to compensate for these losses.

Unless the blaze is extremely hot, fires do not totally consume a forest. Typically, hundreds of snags per acre remain. These snags serve a number of important ecological functions. Woodpeckers carve cavities that provide an abundance of homes for many birds and mammal species, including bluebirds and nuthatches and flying squirrels. Snags offer perching sites for flycatchers, swallows, and raptors.
Furthermore, many of these standing fire-killed trees (snags) are invaded by wood-eating beetles and other insects. These in turn provide an abundant food source for woodpeckers and other insect feeders. Some species, like the black backed woodpecker, show tremendous increases for three or four years after a fire, then decline. The woodpecker is one of several species that may depend on fire-shaped landscapes to maintain adequate population levels. Populations of black backed woodpecker do not increase on logged sites since few standing dead trees are left after harvest.

Dead trees continue to play important ecological roles, even after they fall over. On the ground they provide habitat and hiding cover for a mostly different group of invertebrates, as well as rabbits, voles, shrews, and other small mammals. These animals in turn provide a food source for predators like pine marten and lynx. In addition, as these fallen snags molder and rot, they gradually add organic matter to the soil, which increases its fertility and water-holding capacity.

Trees that fall into waterways are important to aquatic ecosystems. Fallen logs create pools and riffles, which provide habitat for aquatic invertebrates and fish. Logs also help to stabilize stream banks, deflecting or reducing the erosive force of water. Furthermore, since submerged logs rot slowly, they are important long-term sources of nutrients for aquatic ecosystems.

Finally, though naturally a live forest provides more cover than the snags left after a blaze, dead tree boles still provide some thermal and hiding cover––much more than found in a clearcut. A burned area thus has far more value as security cover to big game and other hunted species than a logged area. Since snags typically remain for 50 to 100 years after a blaze, they commonly survive until the new forest has a chance to mature sufficiently to provide new hiding and thermal cover.


In sum, wildfire is an important ecological process not emulated by logging practices. Some kinds of timber harvest, such as selective cutting of young, small-diameter trees, may superficially mimic the structural influence of fire––creating, for example, open stands of large-diameter trees––but it fails to emulate the ecosystem processes associated with fires. Forest structure is just an outward manifestation of ecosystem processes. If we must husband anything, it should be ecosystem processes, not preconceived notions of “proper” structural appearance.
Maintaining fire as an ecosystem process is still an option. Acknowledging that many people have inappropriately built towns and homes in what is the fire equivalent of a floodplain does not necessarily lead to the conclusion that we have no choice but to suppress wildfires. Indeed, a wise course of action is to make a few areas defensible against wildfire by frequent prescribed burning and the surgical use of limited, selective logging around towns, and around other structures deemed worthy of protection. In the rest of forested areas, wildfires should be permitted to burn unsuppressed. Our goal should be ecosystem maintenance, not ecosystem management.
Large wildfires have many of the same characteristics as large carnivores. They range widely, occur in relatively small numbers, are often in conflict with human exploitation schemes, and thus can only exist in large wildlands. They contribute to the ecological processes that maintain ecosystems. A western wilderness without large, episodic wildfires is as ecologically bankrupt as one without grizzlies and wolves. Without them all, our wildlands are no longer truly wild, no longer ecologically intact.

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JOHN F. LEHMKUHL, 1 U.S. Forest Service, Pacific Northwest Research Station, 1133 North Western Avenue, Wenatchee, WA
98801, USA
RICHARD L. EVEREiT,2 U.S. Forest Service, Pacific Northwest Research Station, 1133 North Western Avenue, Wenatchee, WA
98801, USA

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