Why Thinning Forests is a Poor Wildfire Strategy

Much of the current political discussion about forest thinning and many of the efforts being implemented or proposed for federal forest lands are aimed at reducing large severe wildfires. It seems intuitively obvious to most people that reducing fuels will eliminate or minimize large fires that burn across large swaths of the West and occasionally threaten homes and communities.

But it is also intuitively obvious that the sun rises in the East and sets in the West, and thus must circle the Earth—yet we know that what seems intuitively obvious about the sun’s relationship to the Earth is false. Similarly while fuel reductions may appear to be a panacea for halting large fires, in reality they are not.

To evaluate thinning for fuel reduction effectiveness we need some context.  First there is the issue of how fires burn and don’t burn. Fires only ignite and spread when the weather/climatic conditions are appropriate to sustain a blaze. You can have all the fuel in the world, and not get a fire if the fuel is too moist or otherwise unable to sustain a flame. That is why there are few large fires in the old growth coastal forests of the Pacific Northwest even though there is tons of fuel per acre.

Because fires only burn when weather/climatic conditions are “ripe” for a fire, most ignitions go out whether we do anything or not. For instance, between 1972 and 1987 Yellowstone National Park decided to experimentally allow all natural fires to burn without suppression. There were 237 blazes during that period, and the vast majority burned only a few to a hundred acres, and no more.  Even more telling, all self-extinguished without any intervention.

Yet under normal fire policy on public lands, such fires would have been “put out” by fire fighters who would have claimed credit for extinguishing the flames. The vast majority of all wildfires are in this category—in that they would go out on their own with or without suppression and they will only char a small amount of forest.

On the other hand, there are a few blazes that are ignited under severe fire weather conditions of low humidity, high temperatures, drought and wind. Under these extreme conditions, fires are difficult to impossible to extinguish. They may burn hundreds of thousands of acres before they go out—usually on their own whether we do anything or not. These are the fires that everyone knows, such as the Yellowstone fires of 1988, the 2002 Hayman fire in Colorado, the Biscuit Fire of Oregon in 2002, the 2007 Murphy Fire in Idaho, the Rim Fire near Yosemite in 2013, and other well-known blazes that have charred millions of acres of the West in recent years.

There is a consistent theme to these fires. They all burned under extreme fire weather conditions—and often burned through thinned forests, clearcuts, overgrazed rangelands and previously burned acreage. In other words, fuel reductions did not appear to appreciably change the course of these blazes.

When you look at statistics it is these few well known fires that burn the vast majority of all acreage in the West. One study concluded that more than 96% of all acreage burned was the result of 2% of the blazes and, even more telling, half of all acreage burned was the result of less than 0.1% of all blazes. In other words, it is a few very rare, and very large, fires that burn the bulk of all forest acreage and, it should be noted, these do the bulk of all ecological work and provide most of the benefits associated with fire.

So it is these few fire that most fire-fighting policy and related thinning efforts are designed to halt or control. Yet it is never asked whether thinning can actually effectively halt such blazes.

There are good reasons to believe that thinning cannot and will not effectively halt such blazes.

First, most thinning projects are not done properly. A properly performed fuels reduction project would include not only mechanical removal of smaller trees and reduction of canopy density, but also broadcast prescribed burning to reduce ground fuels. In fact, mechanical thinning alone often INCREASES fire spread by putting more fine fuels on the ground.

Additionally, thinning in some instances can INCREASE fire spread by exposing the forest floor’s fuels to greater sun drying and greater penetration by wind through the open forest stands.  What is surprising to learn is that often the most dense forest stands (i.e. those with the most fuels) do not burn well because they retain moisture the longest, and wind is impeded from pushing flames through such dense forests.

Second, thinning by removing competition between trees and brush often increases rapid regrowth of vegetation. Therefore, any thinning/fuels reduction program must have follow-up maintenance in the form of recurring prescribed burns and/or thinning to be effective.  Yet most thinning projects do not even get the first prescribed burning, much less follow up burns.

There are several reasons for this. The first is that many thinning projects, although consistently money-losing affairs, do recoup some funds by the sale of wood to timber companies.  But once a site has been logged, it is decades before it can be logged again. So there is no financial incentive for follow-up maintenance work.

Also, prescribed burning is risky, and the opportunity for agencies to set fires is limited to short windows of time.  Many forest managers are loath to okay a prescribed burn unless conditions are ideal for containment.  No one wants to be the person who signed off on a prescribed burn and then had it get away and burn homes to the ground. However, when conditions are good for controlling a blaze, they are usually not good for fire spread.

In the last analysis, the politics of forest thinning promotes more logging. The timber industry has successfully sold the idea that fuel reductions work and it has great influence with politicians who buy into to its assurance that logging reduces large fires.

Due to rapid regrowth of vegetation released from competition from other trees and shrubs, the effectiveness of fuel reduction projects—even those done properly—is lost relatively quickly.

Since one cannot predict where and when fire will occur, the vast majority of fuel reduction projects are a waste of time and money because the probability that a fire will start or move into a thinned forest in any given time period that matters is exceedingly small.

Worse, all thinning projects have unintended ecological consequences. Nearly all require roads for forest access. Roads are a major cause of the spread of weeds. Roads also increase access for hunters, trappers, and poachers, reducing security for wildlife. Roads also are the major source of sediment flow into waterways, thus negatively impacting fish. Removal of biomass off-site also has impacts on forest ecosystems, eliminating nutrients and reducing wildlife habitat.

So even where fuel reductions are done and maintained properly, and happen to be in the path of a major fire, one must ask if the negative impacts associated with these thinning projects don’t outweigh the benefits—especially, since they all lose money.

And here’s the clincher. Even if thinning/fuel reductions did stop fires under moderate fire weather conditions, it would likely not matter because most of such fires self-extinguish anyway.

The fires that thinning is designed to halt are the very few large severe wildfires that are driven by drought, high temperatures, low humidity and, most importantly, wind. The fires that make the news stories across the country and are responsible for burning the vast majority of all acres in the West are exactly the fires thinning—even when done properly—cannot halt. The reason? Wind!

Wind blows burning embers several miles ahead of a fire front, easily hopping over thinned forest patches. Wind also increases the intensity of the blaze as anyone who has blown on a smoldering fire and seen it flare up can attest. All large fires around the West burn under high wind conditions and in those situations, fire fighters and their techniques are ineffective.   Indeed, under high winds, fires will jump highways, rivers, and lakes where there is no fuel. They will race across grass stubble on over-grazed rangelands. Fuels do not limit fires under such weather/climate conditions.

Even if it were possible to reduce large fires by thinning, one must ask whether it would be advisable to do so. It turns out that the severely burnt forests that result from large conflagrations are among the most biologically important habitats. The snag forests that result from severe stand replacement blazes have the second highest biodiversity of any forest habitat in the West. The dead trees that result are a long term biological legacy critical to forest ecosystem health.

So is there any place for forest thinning/fuel reductions?  There is.  But it should be limited to the areas immediately surrounding homes and communities. Since one can’t predict where a fire will start and burn, thinning forest willy-nilly is a waste of effort.  Not only are most thinning projects done improperly, most are done for the wrong reasons and lose taxpayer money to boot.

No one wants houses and towns to burn up.  Focusing thinning on the immediate area around structures is cost effective. It is also easier to maintain fuel reductions near homes because access is easy, and even though there are negatives with any logging operation, by focusing those impacts to the area immediately around homes and towns—places already impacted by human use—we minimize those negative ecological impacts.

Thinning trees/shrubs near homes, combined with a reduction in home flammability by installation of metal roofs, removal of flammable materials adjacent to homes, and other measures can virtually guarantee a home will survive even a severe high intensity forest fire.

Thinning forests for fuels reductions, unless strategically done, is a waste of taxpayer funds, and has significant ecological impacts. It is unwise forest policy.



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  1. Garry Rogers Avatar

    I agree with some of your arguments and suspect that some of your others are correct.

    Do you know if the original purpose for forest thinning was increased tree growth? I think thinning began long before fire ecology arguments popped up.

    If you can add some sort of forest picture to your post I can promote it on Pinterest, Twitter, and in my Scoop.It news. Thank you.


  2. mikepost Avatar

    George, I agree with most of your arguments but you did not comment on the value to wildlife associated with intelligent thinning. We have all been dense forest where the ground is nothing but a mixture of dead fall and barren ground. There are also these pathetic fir plantations that have been planted in priur fire sites that now produce 10′ pines whose needles touch each other and provide limited wildlife habitat.

    I love burns, they make the forest come alive 2-3 years later, (not to mention deadly as the unharvested dead trees start to fall) but until we fix the holistic forest problem I believe there times and places where thinning is appropriate.

  3. Nancie Mccormish Avatar
    Nancie Mccormish

    George, I’m excited I will get to meet you this semester, my prof said you are coming to speak at our campus!

    A couple of thoughts from one who has spent a lot of time (paid and otherwise) in various forests.

    First, I think you are spot on about the perception vs reality of thinning. I worked on beetle kill crews in the 1970s to limb and burn slash, then treat the cut up trunks with everything in the USFS arsenal at that time. Can’t see any big change in fire regimes in Colorado, in fact we have larger events when the woods do go up.

    Second, two runaway fires in Conifer, CO in recent years presented these truths: one was started by a prescribed burn that was supposedly “out” but high winds reignited within a day or so… and 3 people were burned alive in their homes though all were aware of it, they simply had no time to escape. One of the aerial copter shots showed a house whose owners had done everything to the max about fire protection for their newly constructed house. Cleared areas, thinned woods, debris removed, water tanks on site, fireproof stucco (or something similar) on the structure walls, metal roof, sprinkler system… etc. etc. etc. They spent a fortune on fireproofing from square one. When the smoke cleared, there was a faint trace of a foundation left, the fire was that hot.

    One last thing comes to mind, that being a photo graph I saw attached to a forestry article when I was working for a forestry education center back in the 1980s. The photo accompanied an article which referenced a poll of Americans asking them to select their ideal of a “forest” from a handful of supplied photos. These showed different amounts of undergrowth and canopy but similar types of climax trees. The overwhelming winner was a German plantation forest with large trunked conifers in neat shady rows, with nary a branch or shrub (or any wildlife) to be seen on the ground. Anything that fell had been picked up as tidily as if someone had vacuumed the place on a regular basis.

    I’ve done some thinning as selective cuts to improve woodlots but nothing as extreme as that German forest! This makes me wonder if we need to review what our image of a healthy forest is. The German photo was simply large scale woodcropping at the expense of anything like a fully functional ecosystem.

  4. rork Avatar

    I mostly agree, and very nice article in any case.
    I think we need more planned fire where I am (MI) – I help prepare and cleanup after. It does cool things in oak, and prairie.
    Second paragraph was a bit painful for me: Motion is relative. The educated avoid that analogy since about 1904 if not earlier.

    Nancie’s last point: yeah, we need more educated eyeballs. We have plantations in MI that we don’t call forests usually – they have only a handful of species, like a desert.

  5. Logan Avatar

    Great article, confirms what I have come to understand about wildfire. I agree that logging isn’t a complete substitute for fire and the roads required become problematic as access points unless rehabed to prevent vehicle passage. The fact that the Forest Service spends 43% of its 5.5 billion dollar budget fghting fires that will eventually put themselves out is a horrible waste of money. We should only perform fire prevention and suppression in the immediate area of towns. I say if you build your house 10 miles out into the forest you accept the risk of fire, why should we spend millions of dollars to protect your house. This goes for my parents too.

    1. rork Avatar

      I believe I’ve heard about houses being in “the stupid zone”.

      1. Nancie Mccormish Avatar
        Nancie Mccormish

        Rork, in a recent college science course I took we discussed this issue but it is problematic on many levels. Yes, houses built in forests may be at risk of burning (no matter your preparations) but where exactly IS a “safe” place to build? Coastlines, nope. Anyplace within hundreds of miles of Yellowstone, nope. Islands? Nope. High mountain valleys? Nope. Downstream of just about any human activity? Nope.

        There are any variety of natural disasters which are part and parcel of anyplace we choose to set down roots. Cyclones, hurricanes, earthquakes, floods (which kill by far the largest numbers of people), avalanches, mass wasting, sea level rise, etc. etc. etc.

        With over 7 Billion people now walking this earth the relativity about who is in an “approved” place and who isn’t seems pointless. My prof was leaning towards the idea that all humans should live in densely packed urban areas (as was his history)since that made more sense collectively.
        I think this approach divorces people even further from the natural world they share, and further turns nature into nothing but either a playground or a pantry.
        I think it better we figure out ways to (as Wes Jackson puts it) “meet the expectations of the land” in ways which enable it to recover from our disturbances.

        1. rork Avatar

          I am merely asking people to accept the risk and costs, without outside subsidy, in forest, New Orleans, Grand Rapids, beach front, river side, irrigated landscapes, and quake prone areas. Tornado flattened my place, Mar 15, 2012. Pigs, elephants, and hickory trees can fly – it’s easy.

          1. Nancie Mccormish Avatar
            Nancie Mccormish

            That’s why God invented insurance agents, right? I agree with you about not subsidizing (generally) but then you get into what threshold achieves the level of a disaster requiring outside assistance. Unfortunately, the poorer tend to not have insurance and live in areas more subject to major catastrophes (ala New Orleans)etc. If people can’t afford to insure, or move elsewhere, and suffer a major impact to a significant population size, what would you suggest?

            Sorry your place got hit. Did you rebuild in the same place?

  6. Ken Watts Avatar
    Ken Watts

    George, I am trying to learn more about you. I see that you have a wildlife management degree. Do you also have a degree in forestry or related field?

  7. Gary H. Avatar
    Gary H.

    Excellent information that as a forester and wildland firefighter I have known for years. Now, all we (FS, BLM, state, rural and urban agencies) need to do is use this information.

    I may be incorrect, but I believe some of the reasons that agencies are not willing to let wildfires burn without suppression efforts is for the fall out (politics) from the public. I know when Yellowstones Superintendant allowed the 1988 wildfires burn at first, he was wrongly critisized and may have been disciplined. As we now know, that ecosystem is healthier because of the fires.

    I will e-mail this information to the land management agencies that are partially promoting thinning to reduce fire intensity and severity and see what their response is.

  8. Nancy Avatar

    “I may be incorrect, but I believe some of the reasons that agencies are not willing to let wildfires burn without suppression efforts is for the fall out (politics) from the public”

    Gary H – it would be interesting also to know just how many of those ” who got a prime piece of property close to wilderness areas and don’t want it to burn” take advantage of that suppression 🙂

    1. Gary H. Avatar
      Gary H.


      As the author accurately stated, suppression efforts do little to affect wildfire behavior.

      One important factor is that wildfire suppression dollars go into the pockets of local businesses and to firefighters. When you work for an agency, pressure is put on the employees to go on fires because it saves the district where they work money. There is also a lack of urgency to suppress the fire, as firefighters typically earn 3 times the money working on a fire than their regular occupation. I do not have proof that these factor in whether fire suppression dollars are spent, but I do know as Logan stated above that firefighting costs are in the billions and its an industry that needs to be reformed (let fires burn and protect structures.

  9. Nancie Mccormish Avatar
    Nancie Mccormish

    As Gary points out, fire is a big business (and I remember some fat paychecks from fighting Federal fires in my youth), something described in the article below as the “fire industrial complex.”

    Then there are some significant questions about those fire suppression chemicals being dropped all over the woods and watershed:


  10. Ken Robinson Avatar
    Ken Robinson

    Not all forest are equal as your article might suggest. Forest in the northern Rockies and Pacific northwest have very long periods of time between large fires due to climatic conditions and are adapted to large, high-intensity fires every few hundred years. They also have relatively high fuel loads to support such fires due to such long intervals. However, forest in the southwestern US are not adapted to such conditions. There is evidence to suggest that burn cycles in the southwest US occurred on a much shorter time scale during pre-settlement conditions. There is also evidence to suggest that these frequent fires were low-intensity in nature, only burning the understory of the forest floor. This is due to the low density of trees and low fuel loads in the southwest US forest at that time. Also the bark of a mature ponderosa pine tree, which dominates most forest in the southwest, will peel off while burning at the base thereby not allowing fire to climb to the top of the tree canopy which limited wind driven, spot-fire ignitions, This type of fire activity also decreased the chances of a crown-type, high intensity fire. Now, due to over 100 years of active fire suppression, the forest fuel loads in the southwest are 10 times what they were during pre-settlement conditions. Large fires have become the norm in the last 30 years which are high intensity in nature. These high intensity fires, which are occurring in forest that are not adapted to such burning conditions, are decimating southwest forest and are sterilizing the soils making it difficult for these type of forest to recover. So in order to restore southwest forest to pre-settlement conditions, it make sense to thin and return fuel loads to what they once were over 100 years ago. This activity also restores low intensity fire activity which has been observed in areas where large, high-intensity wildfires have reached previously pre-treated, thinned areas. So while forest thinning would do nothing to return the forest in the Pacific northwest or northern Rockies to pre-settlement conditions, forest thinning in the southwest would likely go a long way towards returning health and vitality to these type of forest. Your really should take into consideration the type of forest that your trying to treat and restore instead of advocating for a total rejection forest thinning all together.

  11. A E Fletcher Avatar
    A E Fletcher

    While I agree with a number of your observations, you appear to be guilty of the same thing that many people are guilty of — believing that one size fits all. A pinyon-juniper forest is very different from a ponderosa pine forest, and both are very different from a lodgepole pine forest (which is designed for stand replacement following natural burning). Site conditions, as well as dominant tree species vary greatly, making some forests more prone to burning than others.

    Where trees are not thinned, or overly thinned, it stands to reason that trees will be dryer and more prone to catching fire and burning, whether from a lightning strike, or from an unattended campfire. However, n the Los Alamos fire, there were houses that burned to the ground, while an evergreen tree immediately next to the house, which had been watered along with the green lawn, remained green and very much alive. Soil moisture does make a difference in trees’ survival.

    However, it is a mistake to believe that the thinner a forest, the safer it is from burning. I believe you are correct that in some cases a thinned forest is more prone to soil drying. However, a forest that is thinned to that level which will reduce competition between trees for soil moisture, while maintaining a reasonable canopy cover (perhaps 60%) is less likely to suffer long-term drastic damage from a forest fire than one where trees have not been thinned at all.

    We already have evidence that trees that are too dense when they burn can result in fire temperatures that literally bake soils to ceramic (as occurred after the Los Alamos fire). A properly thinned forest contains less fuel, and in the case of ponderosa pines, can often survive a forest fire with loss of only part of its trees.

    Fires will occur anywhere something combustible exists. The question is not whether forest fires are inevitable; the question is can we limit the long-term damage through proper management and thinning? I believe the answer is yes, and that alone justifies many, if not most, forest thinning efforts. The answer is not to do nothing, as you seem to imply but to strive to manage forests so they will be resistant to very long term, perhaps irreversible damage when forest fires burn through.

George Wuerthner is an ecologist and writer who has published 38 books on various topics related to environmental and natural history. He has visited over 400 designated wilderness areas and over 200 national park units.

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George Wuerthner