More science indicates pine beetle outbreaks do not lead to catastrophic fire

mountain pine beetle
Mountain pine beetle

Scientists continue to develop evidence showing that pine beetle outbreaks do not lead to catastrophic wildfires. This should not be a shocking development to those who have been keeping abreast of the studies on the subject, including one that Wildfire Today first covered in 2010 (Firefighters should calm down about beetle-killed forests).

In a soon to be published paper, University of Colorado Boulder researcher Sarah Hart determined, “The bottom line is that forests infested by the mountain pine beetle are not more likely to burn at a regional scale. We found that alterations in the forest infested by the mountain pine beetle are not as important in fires as overriding drivers like climate and topography.”

The CU-Boulder study authors looked at the three peak years of Western wildfires since 2002, using maps produced by federal land management agencies. The researchers superimposed maps of areas burned in the West in 2006, 2007 and 2012 on maps of areas identified as infested by mountain pine beetles.

Western U.S. forests killed by the mountain pine beetle epidemic are no more at risk to burn than healthy Western forests, she found. Results that fly in the face of both public perception and policy.

The area of forests burned during those three years combined were responsible for 46 percent of the total area burned in the West from 2002 to 2013.

Co-authors on the new study include CU-Boulder Research Scientist Tania Schoennagel of the Institute of Arctic and Alpine Research, CU-Boulder geography Professor Thomas Veblen and CU-Boulder doctoral student Teresa Chapman.

Sarah Hart CU Boulder
Sarah Hart

The impetus for the study was in part the severe and extensive native bark beetle outbreaks in response to warming temperatures and drought over the past 15 years that have caused dramatic tree mortality from Alaska to the American Southwest, said Hart. Mountain pine beetles killed more than 24,700 square miles of forest across the Western U.S. in that time period, an area nearly as large as Lake Superior.

“The question was still out there about whether bark beetle outbreaks really have affected subsequent fires,” Hart said. “We wanted to take a broad-scale, top-down approach and look at all of the fires across the Western U.S. and see the emergent effects of bark beetle kill on fires.”

Previous studies examining the effect of bark beetles on wildfire activity have been much smaller in scale, assessing the impact of the insects on one or only a few fires, said Hart. This is the first study to look at trends from multiple years across the entire Western U.S. While several of the small studies indicated bark beetle activity was not a significant factor, some computer modeling studies conclude the opposite.

The CU-Boulder team used ground, airplane and satellite data from the U.S. Forest Service and the U.S. Geological Survey to produce maps of both beetle infestation and the extent of wildfire burns across the West.

The two factors that appear to play the most important roles in larger Western forest fires include climate change — temperatures in the West have risen by about 2 degrees Fahrenheit since 1970 as a result of increasing greenhouse gases — and a prolonged Western drought, which has been ongoing since 2002.

“What we are seeing in this study is that at broad scales, fire does not necessarily follow mountain pine beetles,” said Schoennagel. “It’s well known, however, that fire does follow drought.”

The 2014 Farm Bill allocated $200 million to reduce the risk of insect outbreak, disease and subsequent wildfire across roughly 70,000 square miles of National Forest land in the West, said Hart. “We believe the government needs to be smart about how these funds are spent based on what the science is telling us,” she said. “If the money is spent on increasing the safety of firefighters, for example, or protecting homes at risk of burning from forest fires, we think that makes sense.”

Firefighting in forests that have been killed by mountain pine beetles will continue to be a big challenge, said Schoennagel. But thinning such forests in an attempt to mitigate the chance of burning is probably not an effective strategy.

“I think what is really powerful about our study is its broad scale,” said Hart. “It is pretty conclusive that we are not seeing an increase in areas burned even as we see an increase in the mountain pine beetle outbreaks,” she said.

“These results refute the assumption that increased bark beetle activity has increased area burned,” wrote the researchers in PNAS. “Therefore, policy discussions should focus on societal adaptation to the effect of the underlying drivers: warmer temperatures and increased drought.”

The entire paper can be downloaded (1MB).
Reports about other pine beetle studies, and general articles on the insects, are tagged beetles.

Typos, let us know HERE, and specify which article. Please keep in mind our commenting ground rules before you post a comment.

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Author: Bill Gabbert

After working full time in wildland fire for 33 years, he continues to learn, and strives to be a Student of Fire.

8 thoughts on “More science indicates pine beetle outbreaks do not lead to catastrophic fire”

  1. Let me be one of the first to point out that the data used (final fire perimeters) and its analysis without regard for temporal differences can hardly be expected to support the overriding conclusion of the Hart et al. study no matter what journal it is published in. Furthermore, the impetus for the article appears biased from the outset.

    Martin E. Alexander, PhD, RPF
    Leduc County, Alberta,

  2. Marty.. As a non-scientist, let me share empirical observations from our huge bug kill from a firefighter perspective.. After the short period 12-36 months of red needles, the severity of fire and the potential for crown fire was greatly reduced….. No ladder in snags and greater crown spacing…. Not rocket science.

  3. Ken: Couldn’t agree more with you on your observations. I’ve done a little work on the fire behavior potential – mountain pine beetle issue myself:

    Jenkins, M.J.; Page, W.G.; Hebertson, E.G.; Alexander, M.E. 2012. Fuels and fire behavior dynamics in bark-beetle attacked forests in western North America and implications for fire management. Forest Ecology and Management 275: 23-34.

    Page, W.G.; Jenkins, M.J.; Alexander, M.E. 2013. Foliar moisture content variations in lodgepole pine over the diurnal cycle during the red stage of mountain pine beetle attack. Environmental Modelling and Software 49: 98-102.

    Page, W.G.; Alexander, M.E.; Jenkins, M.J. 2013. Wildfire’s resistance to control in mountain pine beetle-attacked lodgepole pine stands. Forestry Chronicle 89: 783-794.

    Page, W.G.; Jenkins, M.J.; Alexander, M.E. 2014. Crown fire potential in lodgepole pine forests during the red stage of mountain pine beetle attack. Forestry 87: 347-361.

    Page, W.G.; Jenkins, M.J.; Alexander, M.E. 2015. Models to predict the moisture content of lodgepole pine foliage during the red stage of mountain pine beetle attack. Forest Science 61: 128-134.

    I nevertheless stand by my comment of March 27, 2015.

    Martin E. Alexander, PhD, RPF
    Leduc County, Alberta,

  4. Good day Bill. I don’t see any “resistance to control curve” in the graph.

    Martin E. Alexander, PhD, RPF
    Leduc County, Alberta,

  5. Bill:

    Got you. Thanks.

    Martin E. Alexander, PhD, RPF
    Leduc County, Alberta,

  6. I wonder if Sarah Hart has actually been on a wildfire fueled by bug killed timber? I have numerous times in the Northern Rockies and Central Sierras during my 34 year professional wildland fire career. When all that standing red and dead falls over a few years late, one has tons of dead and downed fuel that can ladder into the crowns. Just like a pile of matchsticks interlaced with Tinker Toys! Need to convey good science to the public!

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