Global Warming is Doubling Bark Beetle Mating, Boosting Tree Attacks Up To 60-Fold, Study Finds

Long thought to produce only one generation of tree-killing offspring annually, some populations of mountain pine beetles now produce two generations per year, dramatically increasing the potential for the bugs.

Because of the extra annual generation of beetles, there could be up to 60 times as many beetles attacking trees in any given year, their study found. And in response to warmer temperatures at high elevations, pine beetles also are better able to survive and attack trees that haven’t previously developed defenses.

Pine beetle damage

That’s from the University of Colorado, Boulder news release for a new study in in The American Naturalist.

We’ve known that climate change  favors invasive species, but the mountain pine beetle infestation is far worse than anyone had imagined even a decade ago. This this new study, “Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming,” spells out the grim facts:

The current MPB epidemic is the largest in history, extending from the Yukon Territory, Canada, to southern California and New Mexico…. To date, more than 13 million ha [hectares] of trees have been killed in British Columbia. The MPB-killed trees in British Columbia alone will release 990 million tons of CO2 into the atmosphere, an amount equal to five times the annual emissions from all forms of transportation in the country. Forests affected by bark beetles also have altered hydrology and biogeochemical cycles. Thus, extensive beetle kill is altering forest ecology and tipping conifer forests from regional carbon sinks to carbon sources, thereby creating positive feedback for climate-change factors.

For more on the amplifying feedback, see “Nature: Beetle tree kill releases more carbon than fires.”

It turns out that there has been an “exponential increase in the beetle population.” Why has infestation been nonlinear? The study’s abstract explains:

The mountain pine beetle (MPB; Dendroctonus ponderosae) is native to western North America, attacks most trees of the genus Pinus, and periodically erupts in epidemics. The current epidemic of the MPB is an order of magnitude larger than any previously recorded, reaching trees at higher elevation and latitude than ever before. Here we show that after 2 decades of air-temperature increases in the Colorado Front Range, the MPB flight season begins more than 1 month earlier than and is approximately twice as long as the historically reported season. We also report, for the first time, that the life cycle in some broods has increased from one to two generations per year. Because MPBs do not diapause and their development is controlled by temperature, they are responding to climate change through faster development. The expansion of the MPB into previously inhospitable environments, combined with the measured ability to increase reproductive output in such locations, indicates that the MPB is tracking climate change, exacerbating the current epidemic.

[Read about diapause here. I welcome a simpler explanation from any biologist reading this.]

For more  background on the study, here is an extended excerpt from the news release:

This exponential increase in the beetle population might help to explain the scope of the current beetle epidemic, which is the largest in history and extends from the Sangre de Cristo Mountains in New Mexico to the Yukon Territory near Alaska.

“This thing is immense,” Mitton said. The duo’s research, conducted in 2009 and 2010 at CU’s Mountain Research Station, located about 25 miles west of Boulder, helps explain why.

“We followed them through the summer, and we saw something that had never been seen before,” Mitton said. “Adults that were newly laid eggs two months before were going out and attacking trees” — in the same year. Normally, mountain pine beetles spend a winter as larvae in trees before emerging as adults the following summer.

These effects may be particularly pronounced at higher elevations, where warmer temperatures have facilitated beetle attacks. In the last two decades at the Mountain Research Station, mean annual temperatures were 2.7 degrees Fahrenheit warmer than they were in the previous two decades.

Warmer temperatures gave the beetle larvae more spring days to grow to adulthood. The number of spring days above freezing temperatures increased by 15.1 in the last two decades, Mitton and Ferrenberg report. Also, the number of days that were warm enough for the beetles to grow increased by 44 percent since 1970.

The Mountain Research Station site is about 10,000 feet in elevation, 1,000 feet higher than the beetles have historically thrived. In their study, Mitton and Ferrenberg emphasize this anomaly.

“While our study is limited in area, it was completed in a site that was characterized as climatically unsuitable for (mountain pine beetle) development by the U.S. Forest Service only three decades ago,” they write.

But in 25 years, the beetles have expanded their range 2,000 feet higher in elevation and 240 miles north in latitude in Canada, Mitton said.

Ferrenberg had the idea to monitor the beetles at higher elevations partly because trees at lower elevations have been attacked by beetles for centuries and have developed some defenses.

Lodgepole pines at higher elevations tended to have a lower density of resin ducts, which transport resin, the sole defense against beetles. The number of resin ducts in a tree can be a “marker” for whether a tree has a higher or lower resistance to a beetle attack, Ferrenberg said.

The trees at higher elevations had not faced the same intensity of beetle attacks as those at lower elevations until temperatures warmed, and they have not faced pressures of natural selection exerted by attacking beetles. “The trees in that area are somewhat naïve in their response,” Ferrenberg said.

These data help explain why westbound motorists emerging from the Eisenhower Tunnel on I-70 can look up, from 11,000 feet in elevation, and see beetle-killed trees. “We think we see some of the reason for the fact that this epidemic is so widespread,” Mitton said.

And so the bark beetle is a major unexpected, nonlinear impact of manmade global warming with devastating economic and environmental consequences —  that is also an unexpected amplifying feedback of a warming.

And we’ve only warmed about a degree Fahrenheit in the last few decades. Imagine  the unexpected nonlinear impacts and feedbacks we face  when we warm 10 times that this century, as we are likely to do if we keep listening to the do nothing or do little crowd.

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33 Responses to Global Warming is Doubling Bark Beetle Mating, Boosting Tree Attacks Up To 60-Fold, Study Finds

  1. Mike Roddy says:

    Tree mortality in general has tripled in the US and Canada since 1970. This is a huge amount, and, combined with industrial logging, leads to classic deforestation.

    There are several mitigation strategies available- we could greatly reduce logging, ban clearcutting (which causes erosion and hotter microclimates), close ozone producing coal plants, and begin a program of beetle resistant reforestation.

    These are dreams at present. The timber industry’s power in DC is close to that of the oil companies.

  2. Paul Magnus says:

    It is also causing it seems explosions at saw mills…

    At least five explosions linked to wood dust have rocked B.C. wood manufacturing plants since 2009. None of the earlier explosions resulted in injuries, unlike the two fatal incidents this year at Lakeland Mills in Prince George and Babine Forest Products mill in Burns Lake, in which four workers were killed.

    The United Steelworkers’ Colville said pine-beetle killed wood is “really dusty. You can see it, you can smell it … it’s far worse than it used to be back when we harvested a lot more green wood.

    Read more:

  3. This is obvious, but worth mentioning: bark beetle is a good example of a positive feedback loop resulting from warming(warming means more beetles which means more tree death which means more carbon released meaning more warming) one that’s actually happening to join other amplifying feedback loops that are less in our faces, like concerns about ice sheet destabilization and arctic methane releases.

  4. Joan Savage says:

    A dead forest also alters the snow melt rate. Depending on the location of the beetle-damaged trees in a watershed, such as low or high altitude, or on south-facing versus north-facing slopes, the results can vary. Intact forest cover filters radiation to the snow pack, and slows water release, while denuded slopes can lead to faster melt, runoff and flooding. – Yet another feedback loop in the climate change process.

  5. Lore says:

    I commented on this sometime back in a previous post. Almost all of the N.A. forest Is in jeopardy or essentially ecologically dead. Much of the hardwood woodland where I live in Michigan is infected and dying from foreign invasive species all brought about by our careless introduction. The many billions of these absent CO2 filters will only add to what is already a desperate situation.

    Most urban dwellers are too insulated from what’s going on around them. You only have to open your eyes a bit the next time you take a drive to the country to see how ugly it’s really turning. I predict as our forested areas begin to start looking like a pile of pick-up-sticks you’re only then going to be hearing more about in in the MSM.

  6. Mulga Mumblebrain says:

    There is no chance that forests under capitalism will ever be treated as anything but ‘product’ to be mined for the greatest profit obtainable. Theoretically, in ‘capitalist democracies’ a sensible government, with social responsibility to maintain the biosphere for the use and survival of future generations, would impel corporations to act to protect the forests, or do it themselves. Unfortunately, in the age of Rightwing fundamentalist zealotry through which we are living, politicians are the servants of the economic power and nothing but money matters in the least. Governments, the supposed expression of the people’s will in democracy, are now regarded as evils that stand in the way of the billionaires exercising their ‘freedom’. Bye bye forests, bye bye humanity. The really creepy aspect is that these increasing horror stories seem to produce not an iota of alarm from the mentally obtunded populace, too busy being busy.

  7. Mulga Mumblebrain says:

    Beware the ‘unknown unknowns’. Lots of nasty surprises, dead ahead.

  8. Mulga Mumblebrain says:

    Once the ecosystem is assailed by sufficient destabilising phenomena, its resilience collapses, and the collapse is synergistic and accelerating. One thing leads to another, then several, then exponential unravelling, until a new stability is reached, at a lower state of diversity and complexity. Unforunately we are assaulting the biosphere with so many destabilisers, so rapidly, that the collapse will be deep and protracted. And it is plainly already too late, and has been for decades, to prevent it.

  9. Mulga Mumblebrain says:

    And landslides.

  10. Lou Grinzo says:

    And droughts during the summer when that water supply in the mountain snowpack has already melted.

  11. Jpeg says:

    Diapause: The halting of development in response to colder weather. Allows larva hatched to survive winter.

  12. Joan Savage says:

    I’m sure you are referring to the Emerald Ash Borer (EAB) which has been leap-frogging out of Michigan with yet more careless human activity. On Saturday, I helped distribute tree seedlings including Black Ash, but I really hope they are not planted in a monoculture. Tree planting needs to take a lesson from ecology and diversify the tree species, which helps cut down on how fast an invasive pest can spread. Under climate change conditions it is wise to diversify anyway, as extreme weather is one heck of a bunch of selection pressures.

  13. Joan Savage says:

    Over 10 million trees have died in Michigan from EAB – as Lore says, “you only have to open your eyes a bit..”

  14. DRT says:

    Would it make sense or is it feasible to convert the dead trees to biochar via pyrolisis on site or nearby, use the ‘wood gas’ to power the equipment, and return the biochar to the local soil.

  15. Timberline in Colorado, the altitude above which pines can not grow, is around 11,000 feet. Also, the surface area of mountains diminishes as you approach the peaks (like cones). So, in proportion to the overall forest, there is not that much forest area above 9,000 feet or so, and at this rate almost all of it will be wiped out in a decade.

    But a lot more will go with it, because the lower-altitude trees, which are somewhat more resistant to beetles, will be stressed by AGW driven drought and, therefore, less fire resistant. So when the forest fires get going among the dead and dying trees at the higher altitudes, where there is a lot of lightening in the summer, they will sweep right down the slopes taking out large swaths of the low-slope and valley pines as well.

    Recovery from said fires will be slower than it would normally be, due to the same conditions that caused the fires in the first place. Severe erosion can be expected to follow through much of the Rocky Mountain west.

    Erosion, in turn, clogs rivers and, as well as killing fish and wildlife, clogs hydroelectric dam reservoirs, making renewable energy less viable, exacerbating global warming.

    Down, down, down, in a burning ring of fire…

  16. Lore says:

    It’s not just the Ash trees due to the import of the EAB, but also the Beech and Oak are dying from a combination of imported insect and scale. This already follows the demise of all our American Chestnut, and Elm from similar pathogens. How long before the N.A. forest ecosystem completly collapses is the only question left?

  17. Mulga Mumblebrain says:

    One area in which stability is not just desirable, but essential, is climate. We might even have survived climate destabilisation if it occurred over centuries, but over decades-not a hope.

  18. Mulga Mumblebrain says:

    Not much ‘upside’ is there?

  19. I spent some time in Colorado during the two past summers and saw a lot of evidence of the beetle damage. In 2011, I revisited some of the areas around the Dillon Reservoir where I had seen the discolored trees that the beetles leave in their wake the previous year. By 2011 they were clear cutting large areas of those trees. When I asked one local resident if that was supposed to control the beetles, she said something like, “No, you can’t control them. The cutting is just because the damaged trees are so dry that they are a fire hazard.” I think they are expecting to lose much of the forests there soon.

    The U of Colorado story mentions beetle damage at the west end of the Eisenhower Tunnel, which is not far from Dillon. However, I also saw damage at the east end. It is easy to see from the Loveland Pass up above that area. AS you approach the Loveland Pass on US 6 from the west, you also see a lot of damage.

    I have a page on my web site ( with some of the pictures I got from 2010 and 2011. Just now I updated it to link to the U of Colorado news story and also the study by Mitton and Ferrenberg.

  20. Spike says:

    Interestingly there is evidence of increased insect activity in the PETM

  21. BillD says:

    Yes, diapause is simply the invertebrate equivalent of hibernation in vertebrates. It is usually a way to get through winter in an inactive stage that resists cold. However, some aquatic species diapause during summer to avoid predators and then are active in winter.

    As this study shows, diapause has to be timed so that adults can breed and produce diapausing eggs or larvae before hard times.

  22. Joan Savage says:

    Agreed about the risk. This is why I have long thought we need to plant many varieties of trees and place them northward or up-altitude from their former ecological niches. There is now an initiative in Europe to test out tree varieties for ACC adaptation.

    28 March 2012 “Climate change tree test begins” By Jeremy Cooke

  23. jyyh says:

    diapause – the normal method for a fast developing species to sync its development to the annual cycle (arrested development), if the annual cycle changes this may lead to problems in wintering of the species or in surviving the hot/dry season (aestivation). If favorable conditions for development during growth continue for longer period, the second generation may appear. Species that can overwinter in many phases of their development are likelier to produce massive outbreaks, and it appears this is the case here.

  24. mark t says:

    There is a very interesting little book on bark beetles, “The Insatiable Bark Beetle” by Reese Halter. This book is the Western equivalent of the earlier book on Eastern trees, “the Dying of the Trees” by Charles little. Neither book is very uplifting. Our forests are sequentially losing species to acid rain, disease, predation and introduced pests. Within decades both the Eastern and Western forests, what is left of them, will be very different ecosystems. I have been hiking Eastern and Western forests for over 40 years, and the changes in species composition is sobering and dismal.

  25. Joan Savage says:

    Let’s bear in mind that the Mountain Pine Beetle is a species that does NOT go into diapause.

    That means it is NOT restrained to a regular annual reproductive cycle. Like humans it can go on mating and reproducing opportunistically.
    Other insects which have diapause have constraints based on other factors such as day-length, which has not changed.

  26. Joan Savage says:

    Maybe I should leave this alone, but diapause can be driven by temperature, as well as day-length, moisture/dryness, biochemical signals, and maybe other factors.

    When the researchers say MPB doesn’t have diapause, that means that with higher temperatures, that leaves no factor in the beetle’s environment that would synchronize its reproductive clock to an annual cycle.

  27. Paul Magnus says:

    let’s cut it all down…
    A Shocking Glimpse of BC’s New Forest Plan
    For more than a quarter century, logging companies at the government’s blessing have been on a tear through British Columbia’s expansive interior forests.
    In the name of “salvaging” economic value from forests attacked by mountain pine beetles,
    A catastrophic “falldown” in future logging rates loomed because the industry was literally cutting out the ground from beneath its own feet. But the illusion of abundance was sustained as the beetle attacks spread and more timber became available on a one-time basis only to salvage log.
    So-called “reserves” of forest that would otherwise not have been logged — biologically rich remnant patches of old-growth trees, important forests for wildlife species, forests in visually stunning valleys or slopes near towns, economically more marginal tracts of trees, forests higher up on mountain slopes — are now all about to be placed on the chopping block. All in the name of buying a few more years of logging, which will in turn place an even higher burden on future generations.

  28. Paul Magnus says:

    yes interesting…

  29. john atcheson says:

    These kind of positive feedbacks are ubiquitous in the climate literature, but absent in nearly all climate modeling.

    The result is that we are underestimating the rate and extent of warming on a continuous basis.

    The history of climate change — if we have sufficient leisure to study history in the future — might well be titled, “Far Faster than Forecast.”

  30. Paul Klinkman says:

    A French shepherd planted 100 acorns a day and in his lifetime restored a huge swath of forest. This generation, as individual climate volunteers if not as a government priority, needs to replant much of the earth with somewhat more tropical trees. Because bugs are far more adaptive than trees, we must help the trees, or else we simply won’t have any carbon-eating forests.

  31. Gail Zawacki says:

    A COMPLETE explanation as to why trees are dying not just from bark beetles, but disease and fungus, all over the world.


    It’s not temperature, or precipitation, because those are still variable and in many cases, not outside the historical climatic record for the lifetime of trees, which is often in the several centuries or even thousands of years.

    HERE is what they share in common (as well as annual crops that are losing yield and quality:

    rising levels of persistant, background tropospheric ozone.

    Yeah – pollution. It’s poisonous and renders trees susceptible from insects, diseases and fungus they are naturally able to withstand.

    Ozone also causes plants to reduce allocation of C energy to their roots as they must repair damage to the foliage or needles that absorb the toxin. So they are more vulnerable to drought, winter damage and wind.

    WAKE UP PEOPLE. This really is as much as no-brainer as smoking causes cancer. We’ve put our trees on a 10-pack a day habit.

  32. Raul M. says:

    If a forest fire in the beetle blighted forests does sequester carbon if the fire only burns so much as when rain quells a fire does that have any significance?
    And does knowing the information put a researcher at risk of being a socitical problem?

  33. Ben C. says:

    Hi There
    The implications of this are just terrifying.

    For more background on what seems like a worldwide phenomena, There is a great short science clip that aired the other night on ABC (Australian TV). It covers tree deaths from around the world and also from an Australian perspective where we have our own homegrown mite that is proliferating abnormally due to warming temperatures and killing swathes of trees in certain areas:

    Enjoy (or not!)