Paper: Fire suppression makes wildfires more severe

Open-access paper in Nature Communications, “Fire suppression makes wildfires more severe and accentuates impacts of climate change and fuel accumulation.”


Fire suppression is the primary management response to wildfires in many areas globally. By removing less-extreme wildfires, this approach ensures that remaining wildfires burn under more extreme conditions. Here, we term this the “suppression bias” and use a simulation model to highlight how this bias fundamentally impacts wildfire activity, independent of fuel accumulation and climate change. We illustrate how attempting to suppress all wildfires necessarily means that fires will burn with more severe and less diverse ecological impacts, with burned area increasing at faster rates than expected from fuel accumulation or climate change. Over a human lifespan, the modeled impacts of the suppression bias exceed those from fuel accumulation or climate change alone, suggesting that suppression may exert a significant and underappreciated influence on patterns of fire globally. Managing wildfires to safely burn under low and moderate conditions is thus a critical tool to address the growing wildfire crisis.

Thanks, Nick Smith, for adding this to your Healthy Forests news roundup today….

20 thoughts on “Paper: Fire suppression makes wildfires more severe”

  1. This was odd to me..
    “attempting to suppress all wildfires necessarily means that fires will burn with more severe and less diverse ecological impacts, with burned area increasing at faster rates than expected from fuel accumulation or climate change.” Whatever happened to understanding mechanisms? Why would that happen? It’s hard for me to imagine how “fire suppression” can be a factor independent from fuel loading as they are obviously deeply related.

    • My take is that there is less diversity in burn severity. That is, more high-intensity fire and less moderate and low intensity. Instead of patchworks of high, medium, and low severity, we’re seeing lots of high and less low. Not on every fire, of course.

      • Yes, but why is that? Some areas have.. high fuel loads which tends to lead to more intense fires on those acres.Fire suppression leads to … more trees.. with more fuel, which leads to more intensity. What mechanism does fire suppression work through that doesn’t involve more fuel?

        • Sharon, maybe I’m misunderstanding your question. More suppression = more fuel + warmer temps (etc.) = more high-severity fire. Areas where fires might have left a mosaic of burned conditions now have lots of high and less moderate severity and low severity, and fires are, on average, larger.

          • My point was that fire suppression in and of itself, conceivably works through the mechanism of impacting fuel loadings. Greater fuel loadings via vegetation, also work to reduce water available to trees and other plants, thereby conceivably making them drier and more easily burned, not to speak of weakened and susceptible to bug attacks.

            I guess we all knew that fire suppression leads to higher fuel loadings. Higher fuel loadings lead to more intense fires. What new piece of information, or potential cause of higher intensity, in this paper adds to our pre-existing knowledge?

        • Suppression of wildfire often involves using fire to fight fire, often during highly unfavorable weather conditions. This might be another reason why fire suppression leads to more intense fire.

          Also, while there may be trends toward more high severity fire in parts of the west, there is still a lot of diversity in fire effects and the majority of burned acres are still low and moderate severity.

          “We tested trends for WUS [western United States], each state, and each month. We found no significant trend in WUS high severity fire occurrence over 1984-2014, except for Colorado (table S1). While some studies have shown increasing fire season length, we saw no significant increase in high severity fire occurrence by month, May through October (figure S1). We found no correlation between fraction of high severity fire and total fire size, meaning increasing large fires does not necessarily increase fractional high severity fire area.”

          Alisa Keyser and Anthony Westerling, 2017. Climate drives inter-annual variability in probability of high severity fire occurrence in the western United States, Environmental Research Letters. Accepted Manuscript online 4 April 2017

          • “We found no correlation between fraction of high severity fire and total fire size, meaning increasing large fires does not necessarily increase fractional high severity fire area.”

            But is “fractional high severity fire” really the metric of interest? Wouldn’t it be the total acres of high severity fire? My question would be, do larger fires lead to more acres of high-severity.. not whether larger fires have a different proportion of high to other severity.

  2. Much of the intermountain west’s forests are infeasible to manage with timber harvest, yet most wildfires on these landscapes are still targeted for full suppression. Most of these same forests are also fire dependent. Without mixed severity fires, these landscapes trend toward continuous canopies with heavier fuels. The current results are commonly landscape sized crown fires with little diversity post fire.

    Moderate mixed severity fires normally carry some risk, and agencies remain fully risk adverse. And Congress also would rather fund full suppression rather well than be linked to a more balanced program with risk. Change is needed.

  3. Why is it always one extreme or another? The real world, the fire world, just does not work that way. Before fires are engaged, Line Officers and Fire Management Officers convene to determine if it will be suppress, or manage. The Line Officer is charged with that decision.

    This one sentence seems to sum up a monumental lack of understanding of how fire actually work. “ Managing wildfires to safely burn under low and moderate conditions is thus a critical tool to address the growing wildfire crisis.” How in the world can you imply that just by “managing” (?) conditions, you can manage the outcome of severity? It just doesn’t work that way. The parameters to manage low to moderate fire behavior/severity/effects are the sum of the conditions present.

    Weather, safety concerns and fuels determine how a fire will burn. Ain’t no managing two of those three conditions, so I just don’t buy the premise! However, aggressive fuels management, both mechanically and Rx fire can moderate fuels.

    Also, to take the current fire threats as a point in time, one must go back to pre-European settlement to see how fires behaved at landscape scale. There was a very good reason for the 10 AM policy; it was the best decision at the time. How much we (collectively) changed the landscape from pre-European, just by itself, does not now lend itself to successful, large managed fires without extreme consequences!

    • Jim, I think this paper should have had fire practitioners involved in the design and review. I too have trouble connecting this to helpful advice for practitioners.
      I get discouraged by academics who write papers saying “people in practice are doing it wrong” without actually talking to them or attempting to understand their perspective. I think this is especially difficult in Wildfire World as many practitioners are Feds and therefore not allowed to tell their story to the press, with some exceptions. Or are too busy err.. doing burning or suppression.

  4. Who were the authors? Affiliations? I’m always curious as knowing helps avoid the one-size-fits-all approach to wildfire management. Thanks.

  5. Perhaps we have a tiger by the nose. But, for NOW, I respectfully very much disagree with the notion presented in the “Paper: Fire Suppression Makes Wildfires More Severe.” And, this is coming from a supporter of fire as a forest maintenance tool [see “193 Million Acres: Toward a Healthier and More Resilient US Forest Service, page 129, “Restoring Fire as a Landscape Conservation Tool: Nontraditional Thoughts for a Traditional Organization”, 2018, The Society of American Foresters, Steve Wilent, Editor]. The following, from Appendix A.24, The Concept of Managed Wildfire [Expanded], from “America’s Forests in the Balance: A National Emergency [aka, “A Call to Action”] helps explain the position of 76, and counting, conservation leaders:
    In the October 2022 Smokejumper Quarterly Magazine [pages 10-14], I thought the article by Robert Hirning entitled “Forest Fires and National Defense Policy” was especially informative and instructional. I believe much of his piece coincides quite closely with the document entitled, “America’s Forests in the Balance: A National Emergency [A Call to Action]”– a continuing text developed by 76 [and counting] professionals over the last four years. The section in A Call to Action – The Concept of Managed Wildfire [pages 10-11] – is especially well-linked to Hirning’s contribution. Accordingly, it seems prudent to share The Concept of Managed Wildfire in the Smokejumper.

    Managed wildfires are natural ignitions [some refer to them as “unplanned”] which under suitable weather and soil moisture conditions are allowed to burn to meet desired ecological objectives where pre-planned and approved in Forest Plans for the National Forests. This allows fire to play a natural role in restoring the ecosystems by recycling nutrients into the soil and clearing the forest floor of excessive debris. The key is to identify the right kind of fire at the right time at the right place. However, relying on natural ignitions to instantly create an opportunity for a managed wildfire in a random location, without adequate planning and pre-positioning for resources is “…like playing a game of Russian Roulette” as a very respected colleague once concluded. This [managed wildfire] is not to be confused with “Prescribed Fire” which is conducted under very specific conditions.

    Action item No. 2 in the list of “Top 10 Action” in A Call to Action calls for – without exception – the elimination of managed wildfire for the foreseeable future. The reality is, with the clogged-up conditions of our forests; hard to predict weather events; and the extremely high level of expertise required to perfectly “herd” a wildfire, managed wildfire quickly becomes an escaped fire. Thus, for now, the notion of effectively directing a wildfire to help restore the forest has become largely an intellectual argument and puts others needlessly in harm’s way; causes deaths due to smoke inhalation; and, significantly increases fire suppression costs that continue to shift more funds away from badly needed traditional forest maintenance and the associated loss of critical habitat, wildlife, and soil stabilization from various plant growth. An expanded program in mechanical treatments is fundamental to the forest maintenance success.

    Further, with the risks associated with the COVID-19 pandemic, the notion of letting fires burn to help accrue forest restoration targets is unconscionable. There is a strong connection between smoke inhalation and the more dire effects of Covid-19. In addition, coronavirus cases in the United States have recently surged with the spread of the highly transmissible variants. The longer we allow a fire to burn, the more smoke, the more deaths. Pretty basic stuff.

    Messages on managed wildfire are mixed. This lack of clarity may be due to available budgets and candidly, less than contemporary science that promotes managed wildfire regardless of different times and conditions [read, promoting an intellectual narrative]. Please know that a steady flow of funding from fire suppression is being used to manage wildfires or in reality, attempt to manage a wildfire. The application of pre-approved and planned prescribed fire comes with a much more constrained budgetary account. Using an unplanned ignition as a de facto prescribed fire and claiming land restoration credits is not appropriate.

    As stated above, the practice of managed wildfire, especially in the western part of our country, is a huge gamble that can quickly accelerate to an “escaped fire.” This has become all too common in recent years, regardless of good intentions. And, regardless of weather and all the other “fire factors,” the practice of managed wildfire requires far too much knowledge and authority by the person making this immediate call; frankly, it’s not a fair fight. There are simply too many factors at risk. The unpredictability of the fire and its destruction in this current time and place will almost always win.

    The outcome of prescribed fire is much more predictable. In recent studies, prescribed fires have shown to be much safer and if deployed carefully and under the right conditions can significantly help reduce hazardous fuels. Increased appropriations by Congress for prescribed burning is a critical step in the right direction.

    The concept of managed wildfire must be halted, And the careful use of prescribed fire needs to be a key tool in a pragmatic forest maintenance regime. It is interesting to note that recently, an extremely well-respected former Forest Supervisor for the USDA Forest Service stated: “…If I were Chief, I would never allow managed wildfires; not this year, not EVER.”

    Or, as an anonymous Forest Service employee so clearly stated: “…I try to point out the fact that if you’re not out conducting Rx fire [prescribed fire] right now, why in the hell do you think you could manage a fire for resource benefit[s].”

    Managed wildfire seems to be, as many have suggested, an intellectual theory, that should never be applied, while prescribed fire is a great tool that needs much more application and funding.

    Here is the bottom line: It is time to declare that all wildfires will be promptly and aggressively extinguished, period; no exceptions — for NOW. Extremely clear direction is a must. And this direction must be corporately followed. For example, the word “manage” means: to handle or direct with a degree of skill: such as to exercise executive, administrative, and supervisory direction. To us, this means a very hands-on approach. Backing off to the “next best ridge”, while perhaps workable, can hardly be called a “hands on approach.”

    Some have called me out on my current stance regarding managed fire. That’s fair. Again, in 2018, my colleague Tom Harbour and myself wrote an essay entitled, “Restoring Fire as a Landscape Conservation Tool: Nontraditional Thoughts for a Traditional Organization.” From an intellectual point of view, I love this essay. But, NOT NOW. These are different times. With the current land conditions and the impacts of a changing climate, the notion of allowing a fire to burn anywhere, for whatever reason, for the foreseeable future, is unacceptable and must be stopped.

    In my view, for now, a dominant Forest Service goal in 2024 and ahead, should be to put out all unplanned wildfire ignitions within 24 hours, no exceptions. I beg you, please help make this a cornerstone of America’s Chief Forester’s annual Letter of Intent for the next decade, at least. The credibility this stance will afford the USDA Forest Service, if corporately deployed, will be immeasurable. We believe the American people expect this on their lands. The current landscape conditions will not enable “managed fires” or “beneficial fires” or a “let it burn” policy.

    Perhaps I should have used a different phrase than “intellectual argument” when referring to “manage” or “beneficial” fire. I do not believe that fire as a forest maintenance tool has always been an intellectual argument, in total. I refer you again to the essay with the iconic Tom Harbour.

    If you read the essay, you can clearly see that I believe in fire as a forest maintenance tool, when it is “…at the right time, at the right place and the fire is right.” Frankly, since I crafted the National Fire Plan more than twenty years ago, I have not seen too many of these situations [i.e., the three “rights”]. Thus, I conclude for NOW, it is not the time to “back off to the next best ridge.” The conditions won’t allow it. Let’s look at the facts. Over the last decade especially, when we manage fire with the current land conditions it has been largely a mess [Dixie, Caldor, Tamarack Fires, as examples].

    So, all I am saying is, for NOW, until the forests are in a better condition to accept fire as a maintenance tool, let us have an objective to put all fires out immediately. Then, when the forests [forests are more than just trees] are more accepting, we can and should use fire, under prescription, to meet resiliency objectives. Yes, this will take time. But like our former Chief, F. Dale Robertson often said, “…the Forest Service is in it for the long haul.” The Chief’s annual Letter of Intent for Wildfire for 2024 would be a grand step forward if the letter included the aforesaid objective.

  6. It’s intriguing to me to see so many of you jump on this like it’s news and that you disagree. The vast majority of fire starts are successfully suppressed (something like 98% or more). Most fires escape suppression because fire weather conditions are such that suppression efforts are ineffective or there are so many starts at once that the suppression response resources are overwhelmed (followed by a hot and/or windy period). If the only fires that are able to burn larger areas are those that occur under the worst fire weather conditions, why would one expect anything different than the worst fire effects?

    • An interesting corollary is that most (>50%) ignitions would go out on their own, i.e., remain < 300 acres (the FS standard for a successful initial attack) if no suppression action were taken. Early 20th century FS fire inventories in California support this thesis. Back then the Forest Service presence consisted of a single ranger on horseback. Obviously, he couldn't do much to put out fires across his hundreds of thousands of mostly unroaded acres. What he could do, and did, was inventory fires at the end of the season (the government likes to count stuff). Those inventories are fun to examine. They show most fires stayed small all on their own. Lightning does strike the same places repeatedly, each time creating a fuel break for the next ignition. Human ignitions (since time immemorial) likely created fuel breaks along ridgeline travel routes.Today, with most ignitions east of the Mississippi human-caused, the natural suppression agent is the east's summer high humidity and equal precipitation throughout the year. Georgia's 50 or so inches of rain annually is distributed evenly throughout year. Almost all of Eugene's 40 inches is condensed into winter and spring, with drought conditions during summer and fall. When the Forest Service reports a 98% rate of initial attack success, it includes all those damp eastern ignitions that are never going to go anywhere.

    • Letting fires burn almost always results in ‘bad fires’. The weather ALWAYS changes, especially at higher elevations. Again, we should not be allowing fires to burn for dubious “resource benefits”, during the peak of fire season.


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