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The public is being misled about prescribed burning by certain researchers and the media

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    Low severity blazes burn up fine fuels like grass and seldom kill mature trees. Photo George Wuerthner

    This morning, Columbia University released a press release that proclaimed, “Low-intensity fires reduce wildfire risk by 60%, study finds.?  Fuel treatments may slow fire spread at strategic locations and facilitate fire suppression. However, like many of these studies, the story is more complicated than the research demonstrates.

    The study’s basic premise is that high-severity fires would be precluded and reduced if we only did more prescribed and cultural burning. Given the headline, one might assume that if agencies, tribal people, and others burned more of the landscape at low severity, we would not see large blazes.

    Low-severity burns typically burn fine fuels like grass and small trees while leaving mature trees intact and alive, while high-severity burns frequently kill a high percentage of vegetation.

    A high severity burn usually kills 75% or more of mature trees. Photo George Wuerthner

    However, only 1% of wildfires ever become large high-severity blazes. Most fires are low to moderate severity. Why is that significant? Nearly all fuel treatments aim to preclude the 1% of wildfires that reach large proportions—but the effectiveness of fuel treatments to prevent such blazes is questionable.

    Some 83% of wildfires occur on non-federal lands. Still, most of the Congressional appropriations and policy are directed towards reducing fire severity on federal lands while barely addressing wildfires that start and burn on non-federal lands.

    Here’s where you have to examine the study closely.

    The study was done by modeling. One must always look closely at any study using “modeling” because, as the story goes–garbage in results in garbage out. One always has to wonder if the parameters of the study are realistic. Putting that aside, we get to the other problems with the optimistic headline.

    Without going into too much detail, the authors used satellite imaging and “harmonized multiple state-wide datasets on fuel characteristics and fire behavior, including fire intensity (measured by the amount of energy released) and fire severity (measured by the ecosystem impacts of large fires).”

    The press release explained that the researchers used “a method that assembled unburned areas into a synthetic landscape closely resembling the burned landscapes’ attributes, such as weather patterns, elevation, vegetation type, and disturbance history.”

    And here is a crucial assumption of the study authors: “This approach allowed them to assess how these burned landscapes might have evolved had they not burned in that same year – and compare these counterfactuals to their actual evolution throughout time.”


    So here is one of the critical problems with the press release and media coverage. The vast majority of acreage burned by prescribed or cultural burning or even forest thinning treatments never encounters a blaze when they might effectively reduce fire severity, particularly the first year after a burn. So, the study findings do not apply to most fuel treatments, such as prescribed burns.

    In other words, if you burned an area the same year that fire encountered it, the blaze will likely burn at a lower severity.

    All prescribed fires require upkeep and reburning at regular interves to be effective. Photo George Wuerthner 

    However, beyond the low probability that a fire will encounter a “fuel treatment,” the authors admit that the effects last at most six years. Therefore, the “positive” outcomes are limited in time.

    To be effective, agencies or other authorities must do the “maintenance,” which is to say they have to burn the site frequently to maintain the fuel reductions due to the regrowth of fuels over time. This is something that seldom happens.

    You can imagine the problem that agencies have in doing the maintenance. You burn a site in year one, and by year six, if not sooner, you must return and reburn the first site. Then, in year 7, you are still burning new areas, but you must go back and return to year two and so forth. No agency has the human resources, funding, and time to do the upkeep.

    A further issue with the press release is that the results are specific to mixed conifer forests in California. This is important because most high-severity burns occur in plant communities that naturally burn at long and severe fire rotations in many other regions of the West. This includes sagebrush, chaparral, juniper/pinyon, lodgepole pine, spruce forests, fir forests, old-growth Douglas fir, western hemlock, and numerous other plant community types.

    In other words, the results of this study, even if it were accurate, do not apply to the bulk of plant community acreage in the West, yet this was never made clear in the press release.

    Politicians, agencies like the Forest Service, tribal advocates, and others latch on to the idea that if we only did more low-severity burns, we would not experience high-severity fires.

    Even in mixed conifer forests, high-severity blazes are not unknown and do occur at long rotations. In other words, you can have frequent fires every ten years for a century or two, then still get a high-severity blaze in these landscapes under the right conditions.

    An area of the Dixie Fire, one of the largest in California history, where fuel reductions did not effectively preclude high severity blazes. Photo George Wuerthner

    For instance, one study of Sierra Nevada mixed conifer forests found that 13-26% of historically mixed conifer forests had only low-severity fires, while mixed severity fires covered 43-48% and high severity fires burned 31-39% of the landscape.

    This gets to another issue. Most high-severity fires occur under extreme fire weather/climate conditions of severe drought, high temperatures, low humidity, and, most importantly, high winds. You need these specific conditions to get a sizeable high-severity blaze.

    Burn pattern after 1988 blaze in Yellowstone showing how the wind affected fire spread. Photo George Wuerthner

    An excellent example of this situation occurred in Yellowstone National Park. Between 1972 and 1987, the NPS did not suppress any backcountry wildfires. During this period, there were 235 blazes. All were self-extinguished without human suppression; most burned less than an acre.

    In 1988, a million acres were burned in the Greater Yellowstone ecosystem. What was different about 1988? Why didn’t a million acres burn  1986 or 1987? Can anyone suggest that there was suddenly more fuel in 1988?

    The difference had to do with climate/weather. Between the late 1930s and up until 1988, the West was dominated by cool, moist weather. Indeed, during this period, glaciers were growing in the Pacific Northwest. But in 1988, Yellowstone experienced the most severe drought in its history and some days of extremely high winds.

    The 235 fires that burned before 1988 did not halt or affect the spread of fire.

    A further issue with the study is that numerous examples of sizeable, high-severity blazes existed before the advent of fire suppression. The 1910 Big Burn that charred 3-3.5 million acres of Idaho and Montana occurred before any significant fire suppression but during extreme fire weather conditions.

    Other examples also exist in scientific literature. For instance, in the summer of 1710, an estimated 10 million acres burned in Washington state. There were no white settlers or anyone else to suppress fires, and there were plenty of Indians who presumably were setting cultural fires. How could we have had so many acres burning if low-severity cultural fires were occurring?

    Similar findings were documented for the Klamath Siskiyou region, where significant fire years occurred despite frequent cultural burning by Indians.

    Finally, the article’s premise is that high-severity fires are something to prevent. Indeed, in the majority of western ecosystems, high-severity blazes are the norm, and numerous plant and animal species depend on these blazes.

    The snag forests that occur after high-severity blazes contain the second highest biodiversity after old-growth forests. You find more bees, mushrooms, flowers, bird species, and so forth in the aftermath of high-severity blazes. Thus, in contrast to the common assertion that low-severity blazes produce “healthy” forest ecosystems, the truth is that without an occasional high-severity blaze, most plant communities in the West become ecologically degraded.


    All this goes to say that the media and many university researchers are misleading the public about the benefits of prescribed or cultural burning. That said, strategic burning on the perimeter of homes and communities that one can maintain with frequent repeat burns can enable firefighters to stop or at least direct a fire away from houses. But this is a very limited, though important use of prescribed burns.

    As a panacea for precluding large high-severity fires (assuming you even want to), these kinds of human-initiated low-severity burns are of limited use. Indeed, allowing high-severity fires to burn typically creates more acreage of low-severity burn.

    Home that survived the Thomas Fire by Santa Barbara, California. Photo George Wuerthner

    Even in most extreme fire weather conditions, usually 20-30%, if not less, of the burn perimeter is charred at high severity. However, if a fire burns a hundred thousand acreage, you might get 70,000 acres burned at low severity—something no agency or tribal burning program can emulate.

    All this goes to show that the media, politicians, agencies, and tribal advocates are all trying to suggest that we can preclude large fires through human management when the elephant in the room is human responsibility for climate warming.


    Plus, most fuel treatments, including prescribed burns, are often conducted far from communities. One study found that “only 3% of the area treated was within the Wildlands Urban Interface (WUI), and another 8% was in an additional 2.5-km buffer around the WUI, totaling 11%.”

    Another limitation is that only 17% of this buffered WUI is under federal ownership, which limits fire-risk reduction treatments near communities.

    If you could change the fire weather and climate conditions, we would not need to discuss how to reduce large, high-severity blazes.

    Home that survive the Cedar Fire in southern California. Photo George Wuerthner

    The most effective and efficient way to increase safety for humans is home hardening. By reducing the flammability of homes, we can survive the inevitable large fires. As a public policy program, home hardening is the best choice.


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