Why Prescribed Burning May Not Prevent Large Wildfires

This site by Chester, California was treated by thinning and even clearcutting (seen in the background) and later burned in the Dixie Fire. Photo George Wuerthner.

A recent article in the Los Angeles Times on November 8th  (Prescribed burns are crucial to reducing wildfire risks) Los Angeles Times highlights a California study that advocates suggest demonstrates the effectiveness of fuel reductions as a result of prescribed burns and thinning.

In the study, plots were treated with thinning, thinning in combination with prescribed burning, and a control with no treatment. According to the Forest Service, the area treated with thinning and prescribed burning survived a recent blaze with the most negligible mortality.

While numerous other studies have confirmed the basic findings that thinning combined with prescribed burns is the most effective means of reducing fire spread and severity, there is more to the story than acknowledged in the article.

First, we must acknowledge that wildfire is a natural ecological process, so any efforts to reduce wildfire should be limited to the “structure ignition zone.”

The study zone, Goosenest Adaptive Management Area, is a patch of old timberland that was heavily logged before it was turned over to the Forest Service in the mid-1950s. Previously logged forests are not the same as natural forest stands. They tend to have a higher tree density. Fire tends to burn with higher severity in tree plantations.

The second problem is that the study results which may be accurate cannot be “scaled up” readily due to costs and personnel shortage. The thinned/prescribed burn sites in this study were five acres in size and experienced two rounds of broadcast burning in 2001 and 2010. To do this kind of fuel manipulation over millions of acres is simply not practical.

Most national forests have trouble treating more than a few thousand acres per year. To expand such fuel treatments presents many problems. One is the amount of smoke that would occur annually during the prescribed burning season that would be added to the smoke resulting from the normal natural summer/fall ignitions. Not to mention, scaling up also scales up the potential for prescribed fires to get out of control and inadvertently burn communities and lands.

Plus the effectiveness of any fuel reduction, but especially prescribed burning, lose their effectiveness over time.

Indeed, unless maintained (i.e., reburned on a frequent rotation), the prescribed burned areas are ultimately more explosive than before burning. One reason is that prescribed burning by removing or killing some vegetation and releasing nutrients permits the rapid regrowth of plants. However, this regrowth is dominated mainly by flashy fuels like grasses, shrubs, and small trees.

Secondly, think of the problem created by trying to maintain prescribed burning on a landscape scale. Since you can’t just burn an area once and expect it to remain effective, you must return over and over to re-burn sites. Over time, the more acreage treated, the more area you must re-burn.

The third issue not mentioned by the Forest Service researchers is that the likelihood of a fire encountering any treated area is small—most studies suggest a 1-2% probability. So most treated acres do not influence wildfires.

Fourth, no fuel treatment work under extreme fire weather conditions. Why is this important? Because the very fires that fuel reduction advocates are trying to influence are the larger blazes.  Thinning, or the combination of thinning and prescribed fire may work under low to moderate fire weather but fails under extreme fire conditions.

For instance, a study in Yellowstone National Park, which allowed 235 backcountry ignitions to burn without any suppression, found that 222 of them burned less than an acre of land, and even the few that grew larger all self-extinguished. The same statistics still dominate all fires—the vast majority are small whether we suppress them because they ignite when climatic/weather conditions are not conducive to fire spread.

We have lots of evidence that fuel reductions, mainly thinning/logging, are ineffective at controlling wildfire under extreme fire weather conditions. For example, the two largest fires of the summer of 2121, the Dixie Fire that spread across more than 900,000 acres in northern California and the Bootleg Fire that raced across 400,000 plus acres in southern Oregon, both burned through lands where the majority of the landscape had experienced significant logging/thinning. For instance, it is estimated that 75% of the Bootleg Fire burned through “fuel reductions.”

Therefore, the majority of all acreage experiencing wildfire annually results from a small percentage of blazes burning under extreme fire weather conditions characterized by low humidity, high temperatures, drought, and high winds. Unfortunately, these are the very conditions that now dominate the western landscape due to climate warming. And paleoclimate studies and fire show that we have always had large blazes under such conditions, so the fires today are not unusual nor unexpected.

Another issue seldom mentioned is that most of the wildfire acreage burning is not in ecosystems where wildfire was frequent. For instance, the Labor Day Fires that burned across Western Oregon Cascades in 2020 occurred in Douglas Fir forests where the normal fire rotation is 300 years or more. Similarly, much of the acreage burning in the Rockies is in higher elevation forests of spruce, fir, and lodgepole pine—all of which tend to have fire rotations of hundreds of years. Same for the range fires charring sagebrush where natural fire frequency is also often on the hundreds of years rotation.

Plus most of the “fuels are the problem” advocates are working under a flawed set of assumptions. One flaw is comparing the acreage burning today to fire acreage from the recent past when the climate was significantly different. This mistake is what some call a “sliding baseline.”

California and much of the rest of the West is experiencing the most severe drought in a thousand years. Does anyone seriously think that with such a severe drought, wildfires will respond the same way to fire ignitions they did when the climate is moist and cool, as was common between the 1940-s and 1980s?

Logging can also increase solar radiation drying vegetation and permits greater wind penetration increasing fire spread.

The entire emphasis of the study and current Forest Service policy is based on the Industrial Forestry Paradigm that sees large fires as somehow abnormal and chainsaw medicine as the cure. The current Infrastructure bill will fund logging and fuel treatments of more than 30 million acres of public lands. Thirty million acres is nearly the acreage of Maine, New Hampshire, and Vermont combined!

Logging is not benign.  Ecological impacts of logging/and fuel treatments include a reduction in carbon storage, the spread of weeds due to logging disturbance, impacts to aquatic ecosystems from the chronic sedimentation that results from logging roads, displacement of sensitive wildlife, and loss of genetic diversity in forests, and other effects. Treated areas are “sanitized” with low tree age class diversity and habitat diversity.

These ecological impacts are seldom considered or downplayed, in part, because many logging/thinning projects now occur under “Categorical Exclusions,” eliminating most environmental reviews.

The “fuel reduction” paradigm also downplays that increasingly larger blazes dominate current fire regimes due primarily to climate warming, not fuels. Thus, even if thinning/burning did reduce fire severity and spread, this is essentially a “fire suppression” mindset.

It is yet another example of human hubris that suggests humans know what is best for the forest and other plant communities, and we know enough to manipulate them for their “own” good.

Ironically, thinning/logging millions of acres of land, as fuel reduction advocates assert, will “cure” or “reduce” larger blazes ignores the fact that logging is a significant contributor to climate warming- the very factor responsible for larger wildfires. For instance, 35% of the Greenhouse Gas Emissions are due to logging and wood processing in Oregon. Thus, ramping up logging and thinning even more will only exacerbate climate warming.

A far better solution than more logging/thinning/and prescribed burning is to stop all logging on public lands, which will create carbon reserves that will reduce the climate warming that is propelling wildfires.

Instead of controlling the planet, we should focus on controlling the human behavior that is causing the problem. Ultimately this means a serious effort to reduce all sources of GHG emissions, from logging to the burning of fossil fuels.

Beyond that long-term goal, we can emphasize other measures that will reduce the negative impact of wildfire on humans, such as zoning to preclude more home construction in the Wildlands Urban Interface and reducing the flammability of homes. Such treatments more than 100 feet from structures provide no additional benefits.

George Wuerthner has published 36 books including Wildfire: A Century of Failed Forest Policy