The 99-Year-Old Grandmother Effect: How to View Fuel Reductions on the Bootleg Fire

Blackened stumps indicate this area was thinned prior to the Bootleg Fire but with no effect on fire severity. Photo George Wuerthner.

The basic theme of the Capital Press article is how thinning and prescribed burning reduced the Bootleg fire’s intensity and the mortality of trees in a thinned and prescribed burned area owned by TNC.  The article’s photos show treated areas with limited mortality and nearby untreated areas with blackened snags. Proponents of thinning have cited this article in favor of more forest manipulation. The article has been republished in other areas like the Deschutes River Conservancy website.

If one did not know much about wildfire ecology, the photos accompanying the article might persuade you that thinning and prescribed burning should be widely applied to our forests.

The blackened stumps are trees that were “thinned” prior to this fire in the Scratchgravel Hills near Helena, Montana. The density of the remaining trees is lower than most “thinning” projects, but still burned severely in this wind-driven blaze.”  George Wuerthner.

However, there is much unstated in the article. For instance, there is abundant evidence from numerous high severity blazes around the West that “fuel reductions” typically fail. Of course, not all fuel reductions fail, but most do not significantly alter the outcome of fires.

Like in nearly everything in science, there are anomalies, what I call the 99-year-old grandmother exception. Everyone has heard about people who might smoke three packs of cigarettes a day and live to be 99 years old. Some point to such people to “prove” that smoking cigarettes doesn’t cause cancer or reduce your life expectancy.

This map shows the perimeter of the Bootleg Fire, and all the bright colors indicate past “fuel reduction”. Map by Bryant Baker.

However, science is about statistical averages. And statistically, if you smoke, you are more likely to die from lung cancer than non-smokers.

And this is where the TNC “proof” needs context. I have no idea why the fuel treatments on TNC lands appeared to reduce fire severity, but I can say that it was an exception in the Bootleg Fire. A review and map of the Bootleg Fire Perimeter showed that nearly 75% of the area had previously been “treated” by various “fuel reductions.”

TNC logging advocates would likely respond and say not all “fuel treatments” are equal, which is true. The best treatments involve thinning smaller trees, followed by prescribed burns.

Nevertheless, I have visited dozens of large wildfires and seen many areas that had been thinned and treated by prescribed burn where the fire spread and tree mortality was unaffected by such fuel reductions. Nearly all large wildfires have burned through landscapes with significant acreage of “fuel reductions.”

For example, the Camp Fire, which charred the community of Paradise, California, was surrounded by clearcuts, hazardous fuel reductions (FS euphemism for logging), and even several recent wildfires—none of which prevented the rapid spread of the blaze.

Holiday Farm Fire burned the western slope of the Cascades in a region with extensive logging. Map Oregon WIld.

Similarly, the 2020 Holiday Farm Fire, which raced across the western slope of the Cascades in Oregon, burned through a landscape dominated by past commercial logging, including numerous clearcuts.

Map of the 2021 Dixie Fire in northern California where bright colors indicate past fuel reductions. Map Bryant Baker.

The 2021 900,000 acres Dixie Fire blazed across a heavily logged landscape in northern California also failed to alter the fire progress.

A previously thinned area on the Dixie Fire near Chester, California. Photo George Wuerthner.

A 2016 review of 1500 fire found that fire severity was higher in areas treated by fuel reductions compared to wilderness and parks where no logging is allowed, and presumably, fuels are higher.

All of these examples are robust because they don’t focus on the exceptions, but provide a statistical test of the idea that fuel reductions can reduce large blazes.


Some of the variability in fire burn patterns is due to weather, timing, and topography. For example, the wind has an enormous influence on fire spread. Wind effect is exponential. Wind gusts can push a fire through any fuel reduction or toss embers over any treatment. Conversely, if the wind dies down, fires will shift to the ground surface and often muddle along.

Slope also influences fires. A fire racing up a hill burns hotter because of the “preheating” of the fuels above by the fire below. Conversely, a fire “backing down” a slope tends to burn at a lower intensity.

Finally, most fires tend to burn at a lower intensity at night due to higher humidity and lower air temperatures.

Even to the degree that thinning/prescribed burning might reduce fire severity, its effectiveness wears off over time. Thus, any fuel reduction treatment must be continuously “maintained” by additional logging and burning—all of which is disruptive to the forest ecosystem, wildlife, and soils.

The people quoted in the Capital Press article attribute the larger fires across the West to “excess fuels.” However, nearly all studies show that climate/weather is the driving force in high severity large blazes. The West is experiencing one of the most severe droughts in a thousand years does not seem to enter the discussion with the “fuels are the problem, logging is the solution” crowd.

For one thing, the idea that “fire suppression” contributed to fuel build-up ignores the role of climate. Large blazes had always occurred with the right weather/climate conditions long before any “fire suppression” and even with Indian burning.

The decades in the middle of the last century (in blue) were cool and moist and the area burned was significantly less than the decades before or after which were warmer and drier. Nature was “effective” at fire suppression.

During the middle of the last century (approximately 1940-the 1980s), the Pacific Decadal Oscillation, a periodic shift in Pacific Ocean currents, brought cooler and moister weather to the West. During this period, there were far fewer ignitions and limited acreage burned.  Interestingly glaciers also grew in the PNW during this period due to the increased moisture and cool temperatures.

Fire suppression proponents point to this period as the time of “successful” fire suppression, but in reality, Nature was good at suppressing fires.

Then starting in the late 1980s and continuing to the present, the PDO shifted, and warmer, dryer weather has prevailed. That shift in climate, along with human Greenhouse Gas Emissions, has led to much warmer conditions, as well as extensive drought. It is these weather conditions that are the main factor in large blazes.

Proponents of logging like TNC and forestry professors tend to discount the harmful effects of logging on forest ecosystems. However, the snags resulting from high severity fires are not ecological disasters but critical to healthy forest ecosystems.

Dead trees killed by the Dixie Fire are critical to healthy forest ecosystems. They store carbon, provide habitat for many plants and animals. Photo George Wuerthner.

Therefore, high severity fires are essential for “healthy forest ecosystems. Some studies suggest that biodiversity in the snag forests resulting from high severity burns is the highest of any habitat type. For instance, nearly 50% of all birds depend on the snags resulting from high severity fires, whether for nesting, roosting, or feeding. In addition, down logs and snags store considerable amounts of carbon.

And many ecosystems depend on the periodic input of large dead trees for ecological stability. For instance, the input of large trees into rivers may only occur every couple of hundred years, but that input of large snags is critical to healthy aquatic ecosystems.

Another issue downplayed or ignored in the Capital Press piece is that even dead trees store carbon for significant amounts of time. While logging releases carbon immediately. Studies in Oregon show that 35% of the annual GHG emissions result from logging and wood processing. 

Other impacts associated with logging include sedimentation of streams resulting from logging roads, the spread of weeds, disturbance of wildlife, and changes in age and genetic structure of forest stand (resulting from thinning), compaction of soils, and other well-documented impacts associated with any logging operation are all typically ignored or dismissed.

I have often gone on field trips with thinning proponents and asked them to indicate which trees in the stand are genetically resistant to drought, fungi, mistletoe, or bark beetles. Thinning can reduce the genetic variability in a forest stand; all I get is bewildered stares as if my question is crazy.

Ironically, the proponents of massive thinning across the forested landscape are among the first to point out that the active “fire suppression” policy was a failure; few of them appear to question their promotion of a similar west-wide forest manipulation in the name of fire reduction.

An even more critical question seldom entertained is whether efforts to reduce fire severity and spread is even a wise policy. There are continued references by proponents of thinning that the forests are burning differently than in the historical past, without acknowledging that the current climate/weather conditions are different. We are experiencing one of the worse droughts in a thousand years. Under different climates, you would expect different responses by vegetation. Perhaps large blazes in some forested stands are a way for the planet to adjust to extreme drought and high temperatures.

TNC and the Forest Service’s response to wildfire is based on an Industrial Forestry Paradigm that sees dead trees as undesirable and failure to see the forest ecosystem through the trees. Even if thinning/prescribed fire reduced wildfires, translating that into a general policy of forest manipulation across the landscape might be a disaster for forest ecosystems.

Foundation of a burnt-out house near Fort Klamath. Treating the area from the home outward is the best way to protect communities. Photo George Wuerthner.

Promoting fuel reductions from the home outward for a hundred feet or so can help protect communities, but beyond this distance, fuel reductions typically have little influence when extreme fire weather conditions prevail.

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