Another new study titled “Does wildfire likelihood increase following insect outbreaks in conifer forests?”  by Garrent Meigs and co authors concludes that bark beetles outbreaks do not lead to greater likelihood of fires. This research joins a growing list of studies, all using different methods of evaluation, that finds that bark beetles are not a driving force in wildfire. Rather climate, terrain, and other factors are more important.

Yet the Forest Service continues to promote the idea that logging beetle kill trees will reduce future fires.


Lodgepole pine is one of the most common trees in the Northern Rockies. For instance, 80% of the trees in Yellowstone National Park are lodgepole pine. However, it is also a common tree in the Cascades, Sierra Nevada, and into British Columbia.

One of the important drivers in lodgepole pine ecology is periodic beetle kill from the mountain pine beetle.  Bark beetles are like wolves that thin an elk herd down to its carrying capacity. Typically only the older trees are suitable for attack, so mortality in lodgepole forests is usually less than 50% of trees. The remaining trees, freed up from competition grow much faster and for a while are able to resist any future beetle attacks.

Bark beetles lay their eggs in the inner layer of tree bark where larvae develop. The larvae eat the living layer. A fungi that enters the tree with the bark beetles. The two factors often kill the tree. Leading to a common sight of red-needled trees covering hillsides.

Since beetle mortality usually occurs in a mosaic with patches of dead trees and patches of live tree, the overall ecosystem biodiversity increases. Species dependent on dead trees like cavity nesting birds benefit from beetle kill, while those that might need some live trees—say thermal cover for elk in winter—also benefit.  Thus beetles can be thought of a “keystone species” that creates habitat for many other species.  Some research suggests that beetles create greater biodiversity overall as a consequence.


Bark beetle numbers surge during drought periods. Trees stressed by drought are unable to cast off beetles.  One of the common assumptions behind logging/thinning projects being promoted around the West is that beetle kill will increase fire risk. So the solution to this perception is to log forests to preclude beetle kill by reducing densities and/or to remove existing dead trees to reduce fuels.

However a host of studies demonstrate that beetle killed forests are no more likely to burn than green forests. Indeed, some studies suggest that for a period of time after a bark beetle outbreak, forests are less likely to burn.

This is easily explained by fuels. One of the big misconceptions about wildfire is that fuels drive them and the more biomass, so the thinking goes, the more likely you are to have a major fire. But the “fuels” that carry wildfires are the small flashy fine fuels like pine needles, cones, small branches, not the boles of trees. That is why there are “snags” left after a fire. Most of the tree is not consumed or burned in a wildfire. So once a beetle kill tree loses its needles and the small branches break off in winter storms, they are actually less flammable than live green trees.

In fact, green trees, due to their abundance of resin-filled needles and branches will burn more intensely than dead wood under extreme weather conditions of low humidity, high temperatures and high winds. These are the kind of weather conditions that drive large wildfires.

There is a nuance here, however. As the young trees unaffected by bark beetles grow up in the understory of remaining trees, they do provide more “ladder” fuel that can sometimes increase fire spread for a few decades until the canopy closes and fire risk is again reduced—assuming that conditions for fire spread exist at all during those decades and there are ignitions.

Of course, the other factor in the beetle/fire story has to do with timing of fires in lodgepole pine forests. Lodgepole pine tends to burn at long intervals of hundreds of years. That is because the right combination of wind, humidity, and ignition simply do not exist every year and often for decades or centuries. So while beetles may kill trees, the likelihood that those particular trees will be in the path of a fire is a low probability.


As a consequence a number of studies have demonstrated that there is no greater increase in fires in beetle kill area on average than other sites. In some cases, at least until the younger trees start to fill in the forest, fire risk is actually reduced.

Despite this evidence the Forest Service continues to advocate logging/thinning on the flawed assumption that a reduction in beetle kill trees, will preclude large wildfires. Not only is this not the case but in reality we need large wildfires for the ecological work they do. Even if it were possible to reduce fires we would not to do this.


Some 98% of all beetle outbreaks are in remote areas and the likelihood that they will encounter or threaten homes is extremely small. Nevertheless, it is well established the best way to protect homes from wildfire is not by thinning the forest, but by keeping homes from being built in the “fire plain” in the first place, and for those homes already in the fire plain, reducing the flammability in the home ignition zone (200 feet is all that is need) surrounding a home is the only proven way to safeguard homes.


  1. Area burned in the western United States is unaffected

by recent mountain pine beetle outbreaks

SarahJ. Harta,1, Tania Schoennagela,b, Thomas T. Veblena, and Teresa B. Chapmana


  1. The European spruce bark beetle Ips typographus

in a national park: from pest to keystone species

Jo¨rg Mu¨ ller Æ Heinz Bußler Æ Martin Goßner Æ

Thomas Rettelbach Æ Peter Duelli

Biodivers Conserv (2008) 17:2979–3001


DOI 10.1007/s10531-008-9409-01

  1. Does wildfire likelihood increase following

insect outbreaks in conifer forests?



AND ROBERT E. KENNEDY 2 July 2015 v Volume 6(7) v Article 118


  1. Don’t Blame the Beetles

By Cally Carswell


10 OCTOBER 2014 • VOL 346 ISSUE 6206

  1. Fire severity and tree regeneration following bark beetle outbreaks: the role

of outbreak stage and burning conditions


Brian J. Harvey 1a, Daniel C. Donato1, William H. Romme2, Monica G. Turner1

Ecological Society of America

  1. The influence of mountain pine beetle outbreaks and drought on severe wildfires

in northwestern Colorado and southern Wyoming: A look at the past century

Dominik Kulakowski ⇑, Daniel Jarvis

Forest Ecology and Management 262 (2011) 1686–1696


  1. Management for Mountain Pine Beetle Outbreak Suppression:

Does Relevant Science Support Current Policy?

Diana L. Six 1,*, Eric Biber 2 and Elisabeth Long 2

Forests 2014, 5, 103-133; doi:10.3390/f5010103

  1. Are density reduction treatments effective at managing for resistance

or resilience to spruce beetle disturbance in the southern Rocky


Christian Temperli a,⇑, Sarah J. Hart a, Thomas T. Veblen a, Dominik Kulakowski b, Julia J. Hicks a,

Robert Andrus a

Forest Ecology and Management 334 (2014) 53–63

  1. Bark Beetles and Fire;: Two Forces of Nature Transforming Western Forests


  1. Bark beetle outbreaks, wildfires and defensible space:

how much area do we need to treat to protect homes

and communities? Glen AronsonA and Dominik Kulakowski  International Journal of Wildland Fire 2013, 22, 256–265




About The Author

George Wuerthner

George Wuerthner is an ecologist and former hunting guide with a degree in wildlife biology

7 Responses to Beetle outbreaks do not increase fires

  1. Ralph Maughan says:


    This is just the kind of article the members of the anti-science party need to read, but they won’t. For the sake of the timber lobbyists they will ignore it. The same is true with scientific findings on pesticides, energy resources, grasslands, geologic hazards, liminology, economics, history, sexuality, evolution, aging, public health, effects of drugs, on and on.

    Don’t give up, some random event might bring them low, e.g., party chaos brought on by Donald Trump. People like you are the hope for the future of the Earth, even including the science deniers.

  2. Mike Bickley says:

    Thank you George!

    There was a time when I thought extinguishing all wildfire was a good thing. There was a time when I thought killing all bark beetles was a good thing. Could it be that every component of a healthy forest ecosystem has a part to play? Gee, imagine that!

    We have a lot to learn about Nature not the least of which is that it can function perfectly well without our intervention or micromanagement.

  3. Gary Humbard says:

    First, the top priority areas of federal fuels reduction projects (i.e. thinnings, prescribed fire, pile burning) are either within or near rural interface zones, where homes and property could be adversely impacted.

    Second, there are millions of acres of federal forests that are affected by mountain pine beetles and due to lawsuits, federal in-efficiencies (bureaucracy) and declining budgets, among others, a small fraction of these acres are receiving fuels reduction activities. From a landscape basis, the overall impacts due to fuels reduction projects are indiscernable.

    The author stated that “the “fuels that carry wildfires are the small flashy fine fuels like pine needles, cones, small branches, not the boles of trees. Most of the tree is not consumed or burned in a wildfire. So once a beetle kill tree loses its needles and the small branches break off in winter storms, they are actually less flammable than live green trees”. True, the 1988 Yellowstone fires (albeit an extreme example) had all of the right conditions for extreme fire behavior; beetle epidemic killing the majority of the trees thus creating a large buildup of fine ground fuels along with some live green trees for crowning fire; together with hot, dry, and windy weather. Inside a national park, absolutely appropriate; adjacent or near communities, what do you think?

    Lastly, when fuels reduction projects are proposed, the EA’s are prepared using numerous studies that are cited that either outright or partially contradict the sources George cited. It does not make his right and theirs wrong. Of course, one must presume the Forest Service is following management plans, best available science, laws and policies and is NOT in the bed with the timber industry.

  4. Ida Lupine says:

    I have to say this is another fascinating article from George, and Nancy’s link was good too – Beetlemania. 🙂

  5. Mike Post says:

    George, I buy into your argument with the exception that you do not address all the new invasive beetles that have arrived in the US in the last 2 decades. You may not see them, yet, in your neck of the woods but critters like the Polyphagous Shot Hole Borer from Asia and others of that ilk that are loose in the far west add a whole new dimension to this debate…they are not part of any natural cycle in our forests…


July 2015


‎"At some point we must draw a line across the ground of our home and our being, drive a spear into the land and say to the bulldozers, earthmovers, government and corporations, “thus far and no further.” If we do not, we shall later feel, instead of pride, the regret of Thoreau, that good but overly-bookish man, who wrote, near the end of his life, “If I repent of anything it is likely to be my good behaviour."

~ Edward Abbey