Is human-caused climate change killing the great forests of the American West?

Montana entomologist on bark beetles: “A couple of degrees warmer could create multiple generations a year. If that happens, I expect it would be a disaster for all of our pine populations.”

beetle.jpgClimate change inherently favors invasive pests.  On the one hand, milder winters since 1994 have reduced the winter death rate of beetle larvae in places like Wyoming from 80% per year to under 10%.  On the other hand, hot-weather uber-droughts — aka  “global-change-type droughts” — have made trees weaker, less able to fight off beetles.

Forest Ecology and Management just published a major new study by 19 researchers around the word, “A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests.”  Its key conclusion — that human-caused climate change is already killing forests, releasing carbon, and amplifying warming — will be a shock only to the anti-science crowd:

… studies compiled here suggest that at least some of the world’s forested ecosystems already may be responding to climate change and raise concern that forests may become increasingly vulnerable to higher background tree mortality rates and die-off in response to future warming and drought, even in environments that are not normally considered water-limited. This further suggests risks to ecosystem services, including the loss of sequestered forest carbon and associated atmospheric feedbacks.

Indeed, a 2008 Nature study looked at the beetle’s warming-driven devastation in British Columbia and concluded, “This impact converted the forest from a small net carbon sink to a large net carbon source.

Much of the media has been covering only half the story, focusing on the devastation from the bark beetle but ignoring human-caused climate change (see “Signs of global warming are everywhere, but if the New York Times can’t tell the story (twice!), how will the public hear it?” and “NBC News ignores climate change, blows the bark beetle story“).

So, as part of the Climate Science Project, I’m reposting an excellent piece on the study by Montana journalist Jim Robbins in its entirety.  It was first published at Yale’s Environment 360 online magazine.

For many years, Diana Six, an entomologist at the University of Montana, planned her field season for the same two to three weeks in July. That’s when her quarry “” tiny, black, mountain pine beetles “” hatched from the tree they had just killed and swarmed to a new one to start their life cycle again.

Now, says Six, the field rules have changed. Instead of just two weeks, the beetles fly continually from May until October, attacking trees, burrowing in, and laying their eggs for half the year. And that’s not all. The beetles rarely attacked immature trees; now they do so all the time. What’s more, colder temperatures once kept the beetles away from high altitudes, yet now they swarm and kill trees on mountaintops. And in some high places where the beetles had a two-year life cycle because of cold temperatures, it’s decreased to one year.

Such shifts make it an exciting “” and unsettling “” time to be an entomologist. The growing swath of dead lodgepole and ponderosa pine forest is a grim omen, leaving Six “” and many other scientists and residents in the West “” concerned that as the climate continues to warm, these destructive changes will intensify.

“A couple of degrees warmer could create multiple generations a year,” she said, as she chopped off a piece of bark on a dead lodgepole pine to show the galleries of burrowing larvae. “If that happens, I expect it would be a disaster for all of our pine populations.”

Across western North America, from Mexico to Alaska, forest die-off is occurring on an extraordinary scale, unprecedented in at least the last century-and-a-half “” and perhaps much longer. All told, the Rocky Mountains in Canada and the United States have seen nearly 70,000 square miles of forest “” an area the size of Washington state “” die since 2000. For the most part, this massive die-off is being caused by outbreaks of tree-killing insects, from the ips beetle in the Southwest that has killed pinyon pine, to the spruce beetle, fir beetle, and the major pest “” the mountain pine beetle “” that has hammered forests in the north.

These large-scale forest deaths from beetle infestations are likely a symptom of a bigger problem, according to scientists: warming temperatures and increased stress, due to a changing climate. Although western North America has been hardest hit by insect infestations, sizeable areas of forest in Australia, Russia, France, and other countries have experienced die-offs, most of which appears to have been caused by drought, high temperatures, or both.

One recent study collected reports of large-scale forest mortality from around the world. Often, forest death is patchy, and research is difficult because of the large areas involved. But the paper, recently published in Forest Ecology and Management, reported that in a 20,000-square-mile savanna in Australia, nearly a third of the trees were dead. In Russia, there was significant die-off within 9,400 square miles of forest. Much of Siberia has warmed by several degrees Fahrenheit in the past half-century, and hot, dry conditions have led to extreme wildfire seasons in eight of the last 10 years. Russian researchers also are concerned that warmer, dryer conditions will lead to increased outbreaks of the Siberian moth, which can destroy large swaths of Russia’s boreal forest.

While people in some places have the luxury to doubt whether climate change is real, it’s harder to be a doubter in the Rocky Mountains. Glaciers in Glacier National Park and elsewhere are shrinking, winters are warmer and shorter, and the intensity of forest fires is increasing. But the most obvious sign is the red and dead forests that carpet the hills and mountains. They have transformed life in many parts of the Rockies.

It has hit home for me on a personal level. Virtually every one of the hundreds of old-growth ponderosa pines on the 15 acres of land where I live near Helena, Montana is dead, and we are surrounded by a valley of dead and dying forest. Most trees have been logged and taken to a pulp mill, where they were turned into cardboard for boxes.

University of Montana ecologist Steve Running says warmer temperatures in the Rockies bring spring earlier and fall later, each by about a week, yet precipitation has remained about the same. That translates into a drought, and stressed trees are highly susceptible to beetle infestations. Wintertime minimum temperatures in the 1950s, meanwhile, ranged from 40 F to 50 F below zero. That’s risen to the 30-below range, and there are fewer days when minimums are reached. It’s not getting cold enough anymore to kill the beetles, which over-winter in their larval stage and survive the milder temperatures because they are filled with glycol, a natural anti-freeze.

In addition, the past suppression of fire and the fact that many Western trees are reaching the age at which beetles target them “” 80 to 100 years “” are also factors in the widespread loss of forests.

So the forests across the West are dying, in such large numbers that U.S. Secretary of the Interior Ken Salazar called it the West’s Hurricane Katrina. In Colorado and southern Wyoming, the U.S. Forest Service has created an emergency management team to cut down dead trees around towns and along roads and power lines. Forest Service campgrounds and trails have been closed because of the hazard from dead trees, and communities surrounded by dead forests have drawn up emergency evacuation plans for residents.

Large-scale die-offs have occurred in the past. Mountain pine beetles are native to the West and are part of the ecosystem. Lodgepole forests regenerate through large-scale “stand replacing events,” which include fire and insects. The die-offs now, though, are on a scale unprecedented since the West was settled and are so big that they are having unusual impacts on ecosystems. The whitebark pine, once largely protected from the beetles because it grew at high altitudes and was shielded by cold, is functionally extinct and may no longer be able to feed grizzly bears and other species that love its high-fat nut. In Mexico, bark beetles are beginning to kill oyamel fir trees in a rare 139,000-acre biosphere preserve where the majority of North America’s monarch butterflies travel each fall to spend the winter. So far, about 100 acres in a core area of 33,000 acres have been killed by bark beetles.

Tree-killing bugs aren’t the only problem. In 2005 Colorado researchers noticed that aspens were suddenly dying in large numbers. That year they found 30,000 acres of dead aspen forest. The next year there were 150,000 acres, and in 2008 it had soared to 553,000. The die-off is called Sudden Aspen Death, or SAD. “It’s growing at an exponential rate,” said Wayne Shepperd, who researches aspen for the Forest Service. “It’s pretty sobering when you see a whole mountainside or whole drainage of aspen forest dead.”

Groves at low elevations and facing south are dying fastest, and scientists believe the cause is hotter temperatures and drier weather. It’s not only killing mature trees, but the root mass as well. An aspen grove is the offspring of a large single underground clonal mass, which sends up shoots. “The whole organism is disappearing and it has profound implications,” Shepperd said. “When the roots die, groves that are hundreds or thousands of years old aren’t going to be there anymore.”

If the die-offs continue, the loss of the aspen trees would be a blow to goshawks, songbirds, and a number of other species that find food and refuge in the groves.

Perhaps more than anyone, Craig Allen is familiar with these large-scale forest die-offs. A forest ecologist with the U.S. Geological Survey’s Jemez Mountain Field Station in New Mexico, not only are his office and home surrounded by a pinyon die-off, he also is the lead author of the paper “” with 19 other authors “”published in Forest Ecology and Management, which sought to document and begin to understand what is happening to forests in North America and around the world as the result of climate change.

Coming up with a definitive understanding at this point is impossible, Allen says. Forests are complex, and unfortunately, woefully understudied, and there isn’t nearly enough data to draw a conclusion about the reasons behind forest die-offs globally. “There’s huge information gaps and uncertainties,” says Allen.

What contributors were able to do in the paper is collect anecdotal reports of broad-scale forest mortality from around the world. “The point of this paper is to connect the dots, at least the ones we can connect,” says Allen. “We can’t even tell you for sure if there’s more forest mortality. There’s not consistent monitoring.”

In 2005 a strong El Nino caused a dramatic drought in the Amazon. It killed forest across the region and is extremely well documented because so many researchers had existing plots there. “The heart of the biggest rainforest in the world turned from a carbon sink to a carbon source,” said Allen. “If you have long-term drought you can bleed a lot carbon into the atmosphere.”

A lot of beetles can also turn vast tracks of forest from carbon sinks to carbon sources. Take British Columbia, which is ground zero for the mountain pine beetle infestation in North America. Some 53,000 square miles of mature pine forest is dead and the province is projected to lose 80 percent of its mature trees by 2013. The second largest known die-off there occurred in the 1980s and claimed just 2,300 square miles. Bill Wilson “” the province’s director of Industry, Trade and Economics Research “” said he has flown in a plane for hours over the province and seen nothing but dead forest the entire time.

In 2008, so much of British Columbia’s forests had died they also went from being a net carbon sink to carbon source.

Diana Six works in Africa where she has seen other die-offs first-hand. “In Africa where I work, suddenly whole hillsides are dropping dead,” she said. “It’s happening so fast people are in shock. It’s a tragedy.” Species include the quiver tree, camel-thorn, and the giant euphorbia, a 30-foot-tall succulent. The causes are not known, but the suspects are hotter and drier weather, or shifting rainfall patterns.

All told, the paper that Allen co-authored describes 88 well-documented forest die-offs around the world, going back as far as the 1960s and 1970s, although most are in the 1990s and 2000s.

If there was a way to predict die-offs, Allen said, land managers could take preemptive action, such as mechanical thinning or prescribed burning to increase the vigor of forests.

What gives researchers pause is that many of these large die-offs have occurred with minimal warming, in just a few years. In the West, for example, the average temperature has warmed on average 1.8 F over the past century. “This is before we put two to four degrees centigrade (3.6 F to 7.2 F) into the system,” said Allen, referring to forecasts for warming by the end of this century. Trees across the world are stressed already from fragmentation, air pollution, and other problems, he said. “I don’t know how much stress the forests of the world can take,” said Allen.

JR:  One final point:  This catastrophic climate change impact and its carbon-cycle feedback were not foreseen even a decade ago “” which suggests future climate impacts will bring other equally unpleasant surprises, especially if we don’t reverse our emissions path immediately.

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19 Responses to Is human-caused climate change killing the great forests of the American West?

  1. Wit's End says:

    Haha funny, I just sent this email to the California State Agricultural Secretary after reading that California vineyards are threatened by an invasive insect:

    Dear Secretary Kawamura, Ms. Putnam, and Mr. Fimrite,

    I am writing in reference to the article about the invasive European moth threatening California vineyards.

    I live on the East Coast (rural New Jersey) where our ecosystem is collapsing as trees of all species cannot tolerate the level of pollution in the atmosphere.

    In my attempt to document and research this phenomena, I came across studies being done at the FACE project in Wisconsin, investigating effects of elevated ozone and CO2 on vegetation. This article ( has the following quote:

    “The soil exhibits many abnormalities, from decreased nutrient levels to changes in the amount of water in the soil. Karnosky and his colleagues have also noticed the trees are showing much more insect damage, leading them to conclude that pests thrive in these conditions and the trees are now more vulnerable to the insects.”

    There is a link to a National Geographic video at this post ( on a blog I began to collect photographs and research on this topic, where one of the scientists interviewed calls insects the “sharks that smell blood in the water” when the health of vegetation is compromised by exposure to ozone.

    I have read many reports of unexplained oak and other tree decline in California and surmise that your ozone levels, like those of the East Coast, are the underlying cause of damage to trees – as well as any other plant that needs to photosynthesize and produce chlorophyll. At the top of my blog is the collection of links to scientific research that demonstrates this fact.

    Chasing the bugs won’t save the vines if the air is poisonous.

    Thank you for reading and please feel free to contact me if you have any questions.


    Gail Zawacki
    Oldwick, NJ

  2. Wit's End says:

    Here is a link to my correspondence with Craig Allen, the lead author of the Forest Ecology study:

    No wonder he didn’t want to consider any other cause for forest decine than warming and drying – he had a big paper ready for publication restricted to just that.

  3. The killing of our forests was clear to me last summer when my wife and I camped in the California Sierra Mountains. We camped in the same site the year before and barely saw any beetle infestation in the heavily wooded area we had our tent. This year it was sad to see how many trees were infested by a large number of beetles. Each tree had as many as twenty or more bores. The trees could not fight that many invasions.

    I spent many hours walking around the campground taking pictures of the infestation. It was striking how much change can occur in just one year.
    I estimated that about a quarter of all trees were infested in summer of 2009 in the total camp area.
    You can read more about that experience by going to my wesite: and selecting the story:
    Camping and the environment

  4. mike roddy says:

    Trees are early victims of climate change because, unlike beetles and fungi, they have long lives and evolve slowly.

    If this is what we’re seeing with a 1C increase, there’s no telling what double that will bring, especially since the rate of temperature increase is going up. The great forests of North America and the Amazon will be defenseless, and currently sequester many billions of tons of carbon.

    There is already great pressure to “harvest” dead trees, which would be a mistake. If beetle killed forests end up burning in forest fires, about 80% of the carbon remains on site, and nutrient cycling is improved through charcoal. If the stand is clearcut, 80% of the carbon is released in the near term via CO2 emissions, soil can become dehydrated, and erosion is increased. The effects of industrial logging on an insect consumed forest are worse than the beetle kills themselves. Unfortunately, science rarely prevails in these circumstances.

  5. dhogaza says:

    I have read many reports of unexplained oak and other tree decline in California and surmise that your ozone levels, like those of the East Coast, are the underlying cause of damage to trees – as well as any other plant that needs to photosynthesize and produce chlorophyll. At the top of my blog is the collection of links to scientific research that demonstrates this fact.

    I seriously doubt this. And the air in much of the intermountain west, where pine infestations have been rampant the last 20 or so years, is much less polluted than in the crowded northeast.

    And it’s certain that air pollution in the boreal forests of canada is very low. We know that populations of bark beetles have their northern range limited by the number of freeze days during winter. That’s changing. The northern range is changing. Their productivity elsewhere in their range is increasing.

    We don’t need to look for straws to grasp when clearly understood reasons lie at our feet.

  6. Wit's End says:

    Actually I think it’s the opposite, dhogaza. Nitrogen oxide, sulphur dioxide and aldehydes are clearly understood reasons right over our heads; also that they travel enormous distances. The Great Smoky Mountains in remote Tennessee have the dirtiest air of all our national parks. The pollution from California drifts east, into the mountains.

    More importantly, this explanation of warming and drying is one I believed ever since I realized trees are rapidly dying. But it doesn’t explain all the facts, which is that last summer young trees, trees watered in nurseries, irrigated in landscapes, annual plants in fresh potting soil, and most importantly, aquatic plants, all had the same foliar damage indicative of atmospheric toxins that big old trees had.

    Now how can aquatic plants that are happily ensconced in ponds be suffering from long-term climate change induced warming and drying?

    I don’t argue that long-term climate change induced warming and drying – and insects that don’t get killed off by cold temperatures – aren’t decimating tree populations. All I’m saying is there is a much worse and more immediate threat to ALL vegetation, including annual crops, that scientists for some reason, for the most part, stubbornly ignore.

  7. richard pauli says:

    You mentioned Dr Seven Running – I often share the link to his easy-to-understand science lecture. It is a nice summary of some climate science and the regional studies that make global warming directly observable. A bit dated, he presents simple history, data in a way that is easy to understand.

    Also Dr Running published
    Is Global Warming Causing More, Larger Wildfires?

  8. mark says:

    I have traveled regularly by car through the pine forests of British Columbia. It can not be missed, from the trans canada highway.

    The forest destruction is vast, advancing, and horrific.

    I avoid thinking about the effect on the creatures that live in the dead and dying forests. four or five years ago, the area was larger than Vancouver island.

    I am unable to grasp why and how our various “leaders” that regularly pass through and over this absolute catastrophe can twiddle their thumbs
    and go on doing nothing, or worse. and pretend that it’s not happening.

    British Columbia has had a very early, dry, warm spring.

    look out.

  9. George Ennis says:

    This summer could be very interesting in therms of the confluence of the large die-offs in vegetation coupled with extremely low snow packs in many (but not all areas). If we have any record heat waves it could be catastrophic.

  10. Raleigh L says:

    An interesting article on ways to kill scores of pine beetles, especially in smaller scale areas. Though this is only a bandaid for a massive wound.

  11. Steve Bloom says:

    A public-access copy of the paper can be found here.

  12. Rick_D says:

    Snowpack for the Rockies and Cascades looks below average to poor. Without significant late-season storms it seems likely to be another very hard year on the forests. Very disturbing, indeed.

    The Sierra Nevada will catch a break after three consecutive drought years, with a rather normal one.

  13. percetakan says:

    horrible, how now nature has looked very damaged :( world people should be aware of and repair the damage he has done.

  14. Lewis Cleverdon says:

    Can anyone provide a link to a credible set of data on the trend of global CO2e outputs from forest wildfire in the last few decades ?

    I know that it isn’t possible to assess the outputs accurately, not least because of the uncertain proportions of CO2, CH4, VHCs etc in the smoke. But even a rough assessment would be helpful in identifying the rate of acceleration of this most tragic of the feedback loops.

    As to the need to clear infested dead wood, the best outcome is very plain. If the dead wood (& any beetles) are pyrolized for biochar & energy, CO2e outputs will be minimized.



  15. Wonhyo says:

    If drought and warm temps are turning historically carbon sink forests into carbon sources, what are the prospects for using rapid reforestation as a way to naturally suck carbon out of the atmosphere?

    I’ve long felt that it’s not going to be enough to slow or even stop net human CO2 emissions. To win the race against time, I strongly suspect we have to achieve net negative CO2 emissions by increasing mechanisms of CO2 removal. While many so-called “geoengineering” methods simply try to reduce heating, without reducing CO2 emissions, reforestation seemed liked the best, lowest-risk way of removing CO2.

    I hope there are areas of forest that are still amenable to reforestation as a method of expanding carbon sinks. Perhaps the Amazon and other tropical rain forests that are not affected by the pine beetle and similar pests? How big is the potential carbon sink of reforestation? Will it be enough to make up for, and even exceed, the growing carbon sources in the northern forests suffering from drought and pests?

  16. John Mashey says:

    Can we assume that RP,jr is articulate in telling his fellow Colorado residents about the merits of adaptation to the beetles?

  17. Mike#22 says:

    “My stratospheric suflur pipeline could save these forests” –Polymath

  18. Peter Murtha says:

    I have seen some commentators on the mountain pine beetle suggest that these infestations are “cyclical” and that over the long-run it all balances out. Based on my personal observation I don’t buy this argument whatsoever — most recently a rafting trip down the beetle-denuded Middle Fork of the Salmon River in Idaho — but I have not seen qualitative (or even quantitative) comparisons of the ongoing infestations in the Rockies and the Pacific Northwest with historic events. Can anyone point me to a solid data source on the issue of how the current situation compares to past outbreaks in size and intensity?

  19. John Mashey says:

    re: #18
    1) Tell them to visit British Columbia, and tell that to lumbermen there … and be ready to run fast. Some of them carry axes. I’ve talked to a just a few, guys in their 50s, and they certainly had seen nothing like this before. BC is a place that takes forestry rather seriously.

    2) Wikipedia is not bad.

    3) BC has an extensive website, of which I’;m especially fond of the animated maps (towards end of)Historical Mountain Pine Beetle Activity. Those take a minute or so to run, and of course, should not be over-interpreted, as there are plenty of confounding factors. I.e., beetle infestations stop after they’ve killed all the mature trees they like in some area, forest management matters, droughts matter, etc.

    4) The US Forest service says this.