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Seeing Red

Filed under: — Jim @ 24 October 2010

NOTE: The hijacking and spread of misinformation and slander by certain commenters has led to the closing of further comments on this article.  I am however, very thankful to those many who made good points, asked good questions and provided further references, thus contributing to better public education.  Jim.

Note: This is the first of two or more articles on the extensive tree mortality now being caused by bark beetles in western North America. The goal of this first post is simply to provide necessary background on the relevant biological/ecological processes involved, so that future articles discussing climatic and other possible influences, are more understandable.

It’s mid autumn in the northern hemisphere, whose deciduous forests annually provide one of earth’s great spectacles. When deciduous trees prepare for their seasonal cold dormancy they partially recycle important elemental components of chlorophyll and the associated photosynthetic machinery, such as nitrogen, phosphorous and magnesium. Other more minor leaf pigments, which vary in abundance and spectral properties from species to species, are then temporarily exposed on the tree before leaf drop. The timing of the chlorophyll loss varies between trees, and when combined with the presence of evergreen conifers, gives the flamboyant array witnessed, typically heavy in the yellow to red pigments.

New Hampshire, USA, in the autumn

If you’ve never seen it, consider putting it on your list of worthwhile things to do in your life, as did the guy from San Francisco I once met on the Appalachian Trail in Vermont. Never mind that he carried most of his gear in a plastic garbage bag slung over his shoulder and wondered why the bears were bothering him at night when he didn’t hang his food (mostly a large hunk of cheese in a paper bag). We were instantly friends when he told me he was on the trail just to see the colors, up close and personal for a few days, in response to a magazine article he’d read.

In western North America, true deciduous forests are strictly riparian and therefore limited. The vast majority of upland forests and woodlands are dominated by conifers, all but one of which are evergreen. However, one highly important deciduous species—quaking aspen (Populus tremuloides), which turns brilliant yellow—forms groves that range in size from a few trees to vast forested expanses, typically on mid to high elevation mountain slopes with decent groundwater supply through the summer. [The largest known organism in the world is a large aspen stand in the West Elk Mountains of Colorado, USA (aspen is highly clonal, connected by rhizomes).] The greens and yellows provide a poor man’s version of fall color compared to an eastern hemlock-hardwood forest perhaps, but when combined with often colorful rock exposures, blue skies and rivers, and montane topography, the sight usually has its own magnificence.

Red foliage however, is one thing you’re not supposed to see a lot of in western North America, any time of year.

In many places in the west–particularly through the central and northern Rocky Mountains and British Columbia–there is now a lot of red foliage, but unfortunately, it’s not just in autumn, and is occurring on non-deciduous species. The proximate causes of this are (1) Dendroctonus spp. (literally, “tree killer”), the most destructive of several destructive bark beetle genera, and (2) tree physiological stress. God’s “inordinate fondness for beetles”*, combined with certain human activities, is now causing some serious problems indeed. Here I’ll try to give background on the issues related to bark beetle outbreaks, working from proximate to ultimate causes, and focusing on the one beetle species currently doing by far the most damage, the mountain pine beetle (MPB), Dendroctonus ponderosae. The MPB is attacking a set of highly important pine species (Pinus spp.) over a very large area of western North America, especially lodgepole pine (Pinus contorta), ponderosa pine (Pinus ponderosa) and whitebark pine (Pinus albicaulis), but also some of the other five needle pines (esp. limber pine). Other species of beetles in the genera Dendroctonus and Ips are also doing some serious damage to these and other species, albeit at smaller spatial scales and/or less intensively, and represent so many variations on the theme illustrated by the MPB.

Not New Hampshire in autumn. MPB mortality on whitebark pine in western Wyoming’s Bridger-Teton National Forest. (Fig. 4 of Bentz et al, 2010)

Theological considerations aside, there are many hundreds of species of bark beetles worldwide, and the Curculionidae, or weevil family, of which bark beetles are a member, contains the largest number of species of any animal family. However, only a very small percentage of “aggressive” bark beetle species has the potential to cause extensive tree death during population outbreaks (“irruptions”). These species kill by overwhelming, with coordinated aggression and sheer numbers, a tree’s defenses, followed by a complete destruction of the tree’s ability to transport the products of photosynthesis (e.g. sucrose, amino acids, hormones, etc.) through its transport tissue, the phloem or inner bark. This is usually accompanied by an impaired ability to transport water to the leaves via the outer xylem (the sapwood), courtesy of blue stain fungi (e.g. Grosmannia or Ceratocystis spp.) carried and introduced by the beetles. As ecological systems go it’s very well studied, and contains the interesting wrinkles, non-linearities and feedbacks so typical of ecological systems, even relatively simple ones like this. Plant physiology and demography, insect population dynamics, insect-fungal symbioses, land management practices, and climate dynamics all play important roles in the overall outbreak process. Simplistic explanations of the causes of these dynamics are, as usual, to be avoided.

Whether or not an individual tree will survive a beetle attack is determined by its pre-attack nutritional and hydration states, and the number and timing of beetles that attack it. Conifers defend themselves with both pre-existing (“constitutive”) and de-novo (inducible) defense systems. In pines, resins–a large class of complex plant chemicals that function as antimicrobials, fungicides and insect toxins –are delivered primarily via a constitutive production/delivery system consisting of resin canals lined with resin-producing epithelial cells. Resins typically have strong and interesting odors (familiar to many in products like turpentine, a commercial resin derivative), and they cause the distinctive smell of a pine forest in the summer when they vaporize from leaves and bark. They are produced and delivered in solution, flowing through the ramifying canals in the outer sapwood (the mostly live, water conducting part of the wood) and phloem, which exist solely for that purpose. These solutions are typically highly viscous and sticky, not unlike the consistency of molasses or honey.

Adult mountain pine beetle, about 6 mm long.

Beetles attack by chewing straight through the outer bark into the phloem. If they sever a resin canal of a healthy, hydrated tree, there is an immediate and forceful flow of resin solution under hydrostatic pressure that often kills the beetle. This action represents a cost to the tree however, in both water and resin, the latter being metabolically highly expensive material. If the tree’s carbon balance has been suffering and/or the tree is not well hydrated–due to things such as drought stress, an extended beetle attack or low light levels–its ability to maintain resin solution pressure and/or chemical toxicity, is accordingly reduced. Inducible defenses are also important and involve gene activated cell death and a subsequent “walling off” of living cells/tissues via induced biochemical processes, to slow the beetles’ and fungus’ physical progress in the tree. Although many beetles will thus typically be killed or isolated during an attack, even a perfectly healthy tree can eventually have its defenses overcome by sheer beetle numbers. These trees then become breeding grounds for a repeat of the process on other, nearby trees. This leads directly to issues in beetle population dynamics, which are arguably the most critical element in the system’s dynamics.

Bark beetle population growth potential depends on forest structure and composition, tree vigor, and weather/climate. A key reason for the destructive potential of aggressive species like the MPB is plasticity in the number of generations produced per year, which correlates well with mean annual temperature. There are (at least) two direct temperature effects (and likely several other indirect ones) on beetle population processes. In the warm season, warmer temperatures accelerate development through several larval stages and pupation, and in the cold season they can reduce the kill of over-wintering larvae. In the MPB, two (or more) generations can be produced per year in warmer climates (“multivoltine” reproduction) while only one half generation per year may occur in more northerly or higher elevation populations. For equivalent food supply and fecundity rates, this variability in generation time will obviously have a very strong effect on the number of adult beetles emerging per unit time to attack new host trees (although the thermal requirements for the full developmental cycle can mitigate this somewhat). As a generalization, winter temperature controls are relatively more important in colder climates than in warm ones, so the thermal controls on population growth will vary with geography and physiography. Also, generation time has important implications for the potential rate of evolutionary adaptation to changing growth constraints (such as host defenses or climatic tolerances), via the total possible number of genetic recombination chances per unit time. Plants and their insect herbivores have been involved in this evolutionary battle for tens of millions of years, and have developed some fascinating defense and attack mechanisms in the process. It’s not at all easy being green.

Life cycle timing of the mountain pine beetle in British Columbia

Because a tree can recover from some limited number of beetle attacks–by restoring its carbon balance and/or hydration over time–aggressive species like the MPB do not allow this to happen. They do so by emerging from trees within a narrow window of time, roughly 2-3 weeks (also temperature dependent) and then coordinating their attacks using chemical communication (i.e. pheromones). For the MPB in southeast Wyoming’s Snowy Range for example, where there is currently one generation per year, emergence from lodgepole pine is typically in high summer (late July to early August) when trees are feeling the effects of summer water stress. The pheromones released by inititial colonizers signal to newly emerging beetles in flight that an attack is underway, drawing a critical mass of beetles into a coordinated attack on certain trees exceeding a minimum basal diameter. (Beetles reproduce far more effectively in larger trees and near the tree base, because the phloem food source is thicker there.) This creates an attack that would otherwise be far more diffuse and less effective, were beetles to just land randomly on potential hosts. Once tree defenses have been overwhelmed and the tree is certain to die, other pheromones are then produced which drive in-flight beetles away, thereby maximizing the food resource for the colonizing beetles and their coming offspring.

A tree under attack, with vigorous defense of resin exudate from entrance holes. This tree will not likely survive.

Tree physiological stress also plays a critical, climate-dependent role, especially in getting an outbreak started. A central tradeoff in all vascular plants is the unavoidable loss of water for a given gain of carbon dioxide, since both exchanges occur via stomatal pores on leaf surfaces. When plant water status drops below minimum levels required for cell functioning, stomates quickly close and carbon fixation thus stops. When light levels are low, carbon fixation also slows (albeit for different biochemical reasons). High tree densities can thus limit per-tree water and/or light availability, leading to lowered photosynthesis and consequent carbon balance problems that directly affect trees’ abilities to defend themselves from predation. An MPB population can very quickly irrupt in, and destroy, a stand of physiologically weakened trees. Healthy forest stands and landscapes, and mixed species and/or mixed size forests, stand a much better chance of at least slowing an outbreak down, especially at as the spatial scale increases. However, even then, large forested areas can eventually be overwhelmed by sheer beetle numbers, as is now happening in many places.

Much of western North America has elevated tree densities, relative to pre-settlement times, either for all trees, the largest tree classes thereof, or both. This is primarily due to active fire reduction/suppression policies over the last century or more by federal and state land managers, and/or timber harvesting practices. The resulting increased competition, without any increased climate stresses, would by itself increase tree physiological stress and affect beetle outbreak dynamics. The addition of warmer and/or dryer conditions simply magnifies this problem. Similarly, increased climatic stress unaccompanied by increased competition would also favor the beetles. Because natural fire regimes varied widely historically, and are complicated in many places by similar variability in logging practices and intensities, the effect of fire reductions on bark beetle outbreaks varies considerably and involves several issues of spatial and temporal scale variability. This makes the topic both interesting and difficult, and requires good information on past land management practices and forest stand dynamics. That topic however is fodder for another post.

*A famous quote, sometimes attributed to Charles Darwin, but formally attributed to evolutionary biologist J.B.S. Haldane (in: Hutchinson, G.E. (1959). Homage to Santa Rosalia, or why are there so many kinds of animals. American Naturalist 93 (870): 145-159): “There is a story, possibly apocryphal, of the distinguished British biologist, J.B.S. Haldane, who found himself in the company of a group of theologians. On being asked what one could conclude as to the nature of the Creator from a study of his creation, Haldane is said to have answered, “An inordinate fondness for beetles.””


The next article will discuss the geography and dynamics of the beetle outbreaks in relation to likely causative factors, including climate. I encourage those interested to read the following recent paper:

Bentz, B.J. et al. 2010. Climate change and bark beetles of the Western United States and Canada: Direct and indirect effects. BioScience 60(8):602–613:

General References:

Raffa, K.F. 1988. The mountain pine beetle in western North America, pp. 505-530 in: Dynamics of Forest Insect Populations., A.A. Berryman ed. Plenum Press, New York.

Gibson et al., 2009. Mountain Pine Beetle. USDA Forest Insect and Disease Leaflet 2

Leatherman et al., 2010. Mountain Pine Beetle (Colorado State University Extension Fact Sheet)

72 Responses to “Seeing Red”

  1. 1
    John Mashey says:

    Great post, thanks.
    We spend ~3 weeks/year in British Columbia, and I’ve sat in a ski lodge there with lumbermen, people to whom it would have been unwise to claim non-existence of global warming. Big guys who know how to use axes should not be messed with.
    B.C. takes this very seriously, and of course, they are chewing into ALberta, too.

    I certainly think the beetles are among the most obvious and unwanted early indicators of climate, as they show the Northward incursion of something with no benefits.

    I’ll look forward to the next installment

    [Response: Thanks much John. And excellent advice regarding big guys with axes.–Jim]

  2. 2
    Joe Pinto says:

    Although there has been little study done on this as far as I can see our midwesteren paper birch (Betula papyrifera) seems to be experiencing a similar fate. The once common and towering trees that were commonly used for making canoes are withering away.

  3. 3
    Mal Adapted says:

    Beetle attacks on drought- and heat-stressed trees are blamed for a massive die-off of pinyon pine (Pinus edulis) in northern New Mexico in the early 2000s. See e.g. Breshears et al. 2005.

    [Response: Good reference. I probably should have stated that forest insect irruptions have a long and reasonably well documented history going back into the 1800s. Major irruptions themselves are not new, although the intensity and geographic scale now being seen might well be.–Jim]

  4. 4
    David B. Benson says:

    Jim — minor typo in “variability in logging pactices”.

    Very clear.

    [Response: Thanks a lot David.–Jim]

  5. 5
    Doug says:

    I would like to get some information concerning the siege of a number of destructive beetles, including the emerald ash borer and the Asian longhorn beetle, in eastern forests and if these invasions are climate related. I know these beetles are invasive species, but there are a number of other pathogens that are taking severe tolls in the east.


    [Response: There will always be a climatic component when insects and trees are involved, but that doesn’t necessarily mean it’s well understood, nor that it’s the dominant force in a given irruption. The ash borer’s rapid spread right now is largely due to it’s invasiveness, i.e. lack of a coevolved defenses by N. American Fraxinus spp. There’s a lot of info available on it, given how serious it is. I’m not up on the longhorn.–Jim]

  6. 6
    caerbannog says:

    Here’s an anecdotal data-point.

    Three years ago (Early Oct 2007), I went out to Denver to visit family. While I was there, we took a trip up to Rocky Mountains National Park. Weather prevented us from getting over to the west-side, so we spent our time there exploring the east side.

    I kept my eyes open for signs of bark-beetle infestations — saw mostly healthy-looking lodgepoles; noted only a couple of small “dead-patches” in a sea of healthy-looking green lodgepole pines. Mind you, I was *looking hard* for beetle-killed trees, and I didn’t see any obvious evidence of major bark-beetle infestations then.

    Fast-forward three years, and the changes were breathtaking. Large swaths of dead/dying lodgepole pines were visible on the east side, especially on the south-facing slopes. The changes I noted in just three short years were, to put it mildly, stunning.

    [Response: Yes, exactly. It just so happens that I am just southeast of the park right now, between it and Boulder, comparing this area to mountains in SE Wyoming where I spent the summer. What you describe for 3 years ago in RMNP pretty much describes the situation here now, and what you describe now in RMNP’s east side is pretty much the standard all across the west side of the Divide, and all the high country of SE Wyoming (Snowy, Sierra Madre, and Laramie ranges). Furthermore the ponderosas are currently in much worse condition as you go north along the front range from Denver to Laramie, with obvious potential for southward spread all along it, which would be devastating.–Jim]

  7. 7
    Rick Brown says:

    Thanks Jim, nicely done. I look forward to the next post(s).

    For those who don’t have access the cited chapter by Raffa, the following article by Raffa and others provides a few more tidbits about the natural history of bark beetles (though they inexplicably use “eruption” rather than “irruption”).

    Raffa, K.F., et al., Cross-scale drivers of natural disturbances prone to anthropogenic amplification: the dynamics of bark beetle eruptions. BioScience, 2008. 58(6): p. 501-517.

    [Response: Thanks much Rick. Excellent reference! And eruption and irruption are used interchangeably by some–Jim]

  8. 8
    Thomas says:

    I can recall something similar I witnessed during the few years (early 80’s) that I spent in Los Alamos. The nearby Jemez mountains contained a lot of immature aspen trees. Every summer by about midsummer there would be a huge epidemic of tentworm catterpillers, and within a few weeks every aspen leaf was consumed. At the time my presumption was that the town (which borders on and continues into the forest) probably formed an environment for the winter survival of the worms (which I remember from my boyhood in New Jersey, but have never seen in any other location out west).

    [Response: Thanks Thomas. Forest insect outbreaks are varied and frequent. As for aspen, there’s concern right now with some serious things going on with aspen in W. CO over the last few years, which may have a climatic component.–Jim]

  9. 9
    KeenOn350 says:

    Nice post – very informative, and I look forward to the next instalment.
    One small point – in reference to coniferous “red foliage” you say:

    “Red foliage however, is one thing you’re not supposed to see a lot of in western North America, any time of year.
    In many places in the west -particularly through the central and northern Rocky Mountains and British Columbia- there is now a lot of red foliage, but unfortunately, it’s not just in autumn, and is occurring on non-deciduous species. ”

    You don’t specifically mention that, for coniferous (non-deciduous) trees, *red* means *dead* – which may need to be pointed out for some people in tropic climes…

    [Response: Thank you and good point–yes, red means dead (and also, the red typically shows in the year after the tree was killed).–Jim]

  10. 10
    Rattus Norvegicus says:

    Although a nice post overall, I have to disagree with the section detailing pheromones.

    Here in SW Montana at least, one of the preferred for curbing irruptions at a stand level is the application of pheromone packets to individual trees. This has been quite effective in areas usually visited by humans. It is expensive, but has (as far as my observations go) near 100% effectiveness in preventing infestations. One of my friends is the city forester of Bozeman, MT and he confirms this. The packets work (but they are expensive), so it may be related to the level of pheromones associated with an individual tree. Too much and it tells the MPB to go elsewhere.

    [Response: Not sure what you disagree with–I was just describing what happens during an attack. Anti-aggregation pheromone applications are fine for protecting small groups of trees of individual landowners. They’re no solution at the vast scales we’re discussing here–Jim]

    One “joke” we have around here is that there is a new species of pine around here, the “red pine”. If you drive between Deer Lodge and Helena over McDonald Pass the sight is appalling.

  11. 11
    Frank says:

    Below are some questions that you could addressed in your next post. I personally find information more persuasive (and less like propaganda), when obvious questions like these are address.

    Climate change has occurred many times in the past. From the end of the Little Ice Age in the mid 1800s until the late 1930s, the climate probably warmed about as much as it did in the late 1900’s. Was this warming experienced by Western forests? Did it cause massive outbreaks of insect borne disease? Are there any other periods of climate change that have been associated with outbreaks of insect borne disease?

    The linked paper suggested that insect borne disease could cross the country through forests in southern Canada, an area which may be made susceptible by warming. It is my understanding that the non-forested Great Plains extend fairly far north into Canada. How far north does one need to go to make a forested route to the East Coast and how much how much warming is needed at that location to make this possible? Don’t Western insects already have access to Eastern forests by being transported across the country in wood products by humans?

    Some massive outbreaks of destructive insects are controlled because the population of their predators increases (due to an abundant supply of food). Does this happen with these insects?

    [Response: Good questions. It’s hard to go back much before the late 1800s, although there are some studies that have attempted to, using dendro techniques. There are certainly many documented cases of major insect outbreaks before AGW became an issue. So it’s an important question as to how unique the current situation is, and what’s fundamentally driving it. That’s the topic for a future article(s). As for spread of the MPB, if it adds jack pine (closest extant relative to lodgepole) to it’s list of suitable hosts, that could potentially allow it to move from NW Alberta all the way across Canada. As for the last question, typically no–these large outbreaks seem to be limited more often by food supply than predator increases–Jim]

  12. 12
    Leo G says:

    Jim, thanx for this, very much appreciated. I live in B.C. and have property in the pine area. In our little valley we have a good mix of lodge pole, Bull (pondrosa), fir, aspen and birch. Unfortunately now, for the last 2 years we have been noticing that the firs are now being attacked by the spruce bud worm. About the only good thing that I can see from this latest outbreak is that our property seems to have a lot more birds then recently. As this is an issue that I have been following closely, I am very appreciative of your time on it.

    One last thing, I remeber reading in the Canadian Geographic some years back that at one time it was thought that the Rockies would be a barrier to the beetles entering Alberta. If I remember right, the author stated that when the beetle did eventually make the ascension over the Rockies, their numbers were so vast that you could see the “cloud” from satellites.
    I cannot find that specific issue anymore, so i am wondering if this tidbit has ever been substantiated?

    [Response: Thanks a lot Leo. Yes, almost certainly insectivorous bird increases. Don’t know about that specific event, but there are some phenomenal accounts of the number of beetles during outbreaks. I was just reading about one in the White River area of NW Colorado in 1949 that produced “a layer of beetles 6 in deep and 6 ft wide for over a mile”. And these beetles are pretty small. As for the crossing over the rockies, yes the MPB has done so and is in Alberta. There is concern that it might begin to infect jack pine and spread therefore, all the way across Canada and into the Great Lakes and NE USA.–Jim]

  13. 13
    Hunt Janin says:

    A very clear and very well written article. Keep ’em coming!

    [Response: Thanks Hunt, much appreciated.–Jim]

  14. 14
    Rattus Norvegicus says:

    Jim, I completely agree with you here. Just think you should have mentioned it. No real disagreement. Kind of an interesting and counter intuitive effect, often found in ecology…

    [Response: Thanks. Wasn’t able to work in even 1/5 of what I’d have like to have said, so I’m glad you mentioned it. Also, is that mostly lodgepole you’re seeing, do you know?–Jim]

  15. 15
    Edward Greisch says:

    John Mashey’s link says: “Recovering the greatest value from dead timber before it burns or decays, while respecting other forest values”
    I was wondering about that and I’m glad they are working on it.

    Will the lumbermens’ reaction on the GW issue result in their taking any action on GW? We need every ally we can get.

    Is there a different kind of tree that will grow there that the beetles don’t eat?

  16. 16
    George Robinson says:

    Most interesting. We too have the problem here in Sweden, but what i have seen for myself during the past 5 years, since moving close by a spruce and pine forest is the following.
    Every late spring, May time, when we get the first really warm day, we get swarms of beetles hatching out in the grass parts by the houses, this provides the birds with ample food for their young, and within a couple of days they are gone, that is what I thought. Now autumn has arrived, and blue jays and other larger birds are investigating these lawns AND finding larva. the birds can dig up several sq meters at one go. The locals tell me that its the larva that lies over the winter to become the new beetles next spring. A very interesting phenomenon

  17. 17
    Chris S says:

    A colleague of mine was at a conference earlier this year chatting to someone who wanted to study MPB 15 years ago but couldn’t get funded as their threat was thought to be limited. An illustration, perhaps, of quite how rapid an ecological change this has been.

    One wonders what the effect would be if the same thing happened to a pathogen of a food crop…

  18. 18
    Green Bug says:

    There is also this paper on climate and mountain pine beetle in BC and Alberta:

    [Response: Thank you, good reference.–Jim]

  19. 19
    is(de) says:

    Great article! Just one little quibble: aren’t the tracheids which transport water from the roots to the crown supposed to be dead cells even if they are located in the outer sapwood?

    [Response: Thanks much. Yes the mature tracheids are indeed dead as you state, but there are other living cells (parenchyma) in the sapwood, especially the outer parts thereof.–Jim]

  20. 20
    Phil. says:

    When reading your article it occurred to me that pheromone traps would be a way to go but that the vast areas and numbers would be a problem. I saw the results of the infestations when in BC last march, no way that new outbreaks could be contained by a cordon sanitaire? My personal experience of Asian longhorns occurred a year ago when investigating a sickly old maple in my back yard and finding these large white larvae in the tree. I photo’d them and emailed the pic to the university tree guy, within the hour I was descended upon by him, township and state people! Fortunately it wasn’t the Asian longhorn but the response impressed me with how seriously they took it.

  21. 21
    Alexandre says:

    Regional climate change. Great article. I think that’s something that people relate more easily to their immediate perception, and thus understand better what’s likely to come.


    [Response: Thanks for the complement Alexandre. I agree with your comment.–Jim]

  22. 22
    Jim Eager says:

    FranK @11, the plains grasslands don’t extend nearly as far north in Canada as you think. The infestation is already far enough north.
    See here:
    and here

  23. 23
    Mike Roddy says:

    Thanks, Jim, interesting details, but I wish you had been more direct about the effects of industrial logging. In 1994 or thereabouts, the Oregon Department of Forestry assembled a collection of over 200 scientific papers called “Cumulative Effects of Forest Practices in Oregon”. The conclusions and studies were so disruptive that it was suppressed almost as soon as it appeared, and I was only able to find one of several remaining copies via interlibrary lending- as far as I could tell, only a couple of libraries in Oregon still have copies. I alerted my friend Tim Hermach of Native Forest Council, who printed out a few dozen copies. I don’t have my copy handy, but here are a few conclusions (from memory):

    1. Industrial logging sends Oregon forest ecosystems into new trajectories, making return to prior species relationships very long term, if ever. This has implications for insect predator habitat and natural selection of trees, among other things.
    2. Microclimates are severely affected: streams below clearcuts can contain water that is 6 degrees warmer than upstream. Air temperature around clearcuts can be 10 degrees warmer or more.
    3. Clearcuts alter water’s ability to remain in the local forest atmosphere, due to reduced friction and transpiration. I saw temperature records of the Scott River, a tributary of the Klamath in northern California, showing that the logging caused change from a wet conifer area to deciduous scrub resulted in a much hotter local climate.

    Along with global warming and fire suppression, our penchant to clearcut Western forests is a huge contributor to MPB outbreaks, including in British Columbia. I urge you and readers to Google Earth the entire province sometime- dense, parched, and monotonic stands are perfect habitat for the beetles.

    Let’s call this rapacious and ignorant forest liquidation, not land use changes or logging practices. The purposes are to produce soft toilet paper and two by fours and chip board for houses. You touch on logging’s effects, but for this topic the intersection of logging practices and ecosystem health is rather stark. Forest biologists need to speak up more directly, because the public needs to be in on this conversation.

    [Response: This is not an article about–and certainly not an indictment on–logging practices Mike. This is an attempt to get folks on the same page so that we can understand the effects of climate change on bark beetle outbreaks. Nothing more.–Jim]

    Your colleague Chad Hanson, founder of the John Muir Project, is a great resource here. I hope he chips in on this thread.

  24. 24
    Hank Roberts says:

    Which birds eat the beetles? Migratory or local?
    What else do they eat and where, in addition to beetle outbreaks?
    Which trees do those birds prefer to nest in?
    What forest patterns suit them (unbroken, or patchwork with edges)?
    Were those trees protected in the past when areas were logged, or targeted for removal? Are those trees/forest patterns favored for nests when timber is salvaged now?

  25. 25
    Jim Metzger says:

    A very good article but some clarfication is in order. First of all a bark beetle attack does nothing to the plant water status; water in the xylem is under tension so when cut, water will move into xylem, not out. A resin duct cell while having a positive hydrostatic pressure does not contain enough cell sap to drown the insect. Resin duct cells do secrete resin when mechanically damaged, and seal wounds when resin components polymerize; this process does trap insects (amber is fossilized resin). This process costs the plant virtually nothing in terms of water, and is a small, but significant part of the overall carbon economy. When photosynthesis is reduced for any reason the plant will re-allocate even less of its carbon to defensive compounds. So from that perspective silviculture and logging practices may affect the vulnerability to insect attack. However, Dan Herms at Ohio State has shown that stressed trees can be actually more resistant to insect attack, at least at a whole forest level. Regardless many of the defensive mechanisms that plants have against insects and pathogens require that the plant recognize that it is being attacked. It could very well be that the insect has recently evolved mechanisms to elude detection or to circumvent the plant defenses. This especially an issue when the plant is exposed to a novel herbivore/pathogen. Probably the way a bark beetle or EAB kills the tree is by girdling the trunk such that the all phloem transport is stopped.
    Another factor that might come into play is atmospheric CO2 levels. Elevated CO2 levels would increase photosynthesis but this could lead to forests which could support higher numbers of insects. Apparently under highly productive conditions, the trees produce and store more digestible materials.

    [Response: I think you’ve misinterpreted some things. Beetle attacks certainly do affect plant water status–by both fungal disruption of xylem water flow, and loss of some water via resin solution exudation, which is obvious when you look at any tree under attack–unless that tree is so dehydrated already that it has so little water to exude. I didn’t say the resin exudate “drowns” them, just that it kills them, which it definitely does. Beetles are not eluding detection–this is obvious when you look at any tree under attack. Phloem translocation is definitely interfered with during attack, although the proportions of the eventual loss of function due to adult vs larval feeding is not clear to me. I would be interested in any refs you can provide showing that physiologically weakened trees are more resistant to attack, because this goes straight against common understanding–Jim]

  26. 26
    Mike Roddy says:

    Hank Roberts-

    The pileated woodpecker is the main pine beetle predator, and it nests only in snags (large standing dead trees). The small holes and cavities they make serve as protection from creatures such as hawks and martens that prey on them.

    Old trees are burned or removed during clearcutting, to create space for more planted saplings. Old trees are critical to forest ecosystem health, including after they topple, when they provide grub habitat and replenish the soil. Dozens of species live in standing and prone dead trees at various stages of their life cycles.

    The loggers don’t care anymore than the coal companies who are destroying the mountains of Appalachia.

  27. 27
    LH says:

    Like many New Englanders, we live surrounded by a dense mixed-species forests. White pines are the dominant conifer, but is there any evidence of lower risk from pine beetle infestations in forests that are half (or more) mixed deciduous? Of course, other species have their own pests to worry about, and the moths eat them all.

    [Response: I’m not up on any specifics related to eastern white pine (or e.g. red spruce etc), but I do like your question! Tree spatial patterns are a component in this thing and are one of the reasons that species like lodgepole, ponderosa and whitebark pine get hit so hard–they are all capable of forming single species stands, making contagious spread easier, especially given that pheromone signalling is involved.–Jim]

  28. 28
    Rattus Norvegicus says:

    Jim —

    Out here they’ll attack anything, even spruce sometimes, although not often (yet). Most of the pines at lower elevations here are ponderosa. Lodgepoles higher up.

    [Response: That sounds about right. I’d like to see what’s happening to the whitebarks and limbers in your area.–Jim]

    [Response: On second thought, no I wouldn’t… ]

  29. 29
    Robin D Johnson says:

    Fascinating. Thanks for the information!

    And points out something I have trouble getting through folks heads sometimes… Too many plants can produce just as much harm as too many animals in a given area. It seems ever so simple “too much of anything can be harmful” but humans routinely behave as though its not. Admittedly it is probably a natural instinct that requires discipline, training and education to overcome.

  30. 30
    CM says:


    Nice one, and good pictures! Looking forward to the rest.

    re #16 (Sweden),

    Were those bark beetle larvae? What were they doing in lawns??

    But yes, Scandinavia has reasons to worry too, though there hasn’t yet been an outbreak of spruce bark beetle (Ips typographus) as severe as the one caused by storm-felling and drought in the 1970s. (In Norway, where pheromone-baited traps were developed to control the pest, there was even a hit song called “Beetle Bark Boogie.”) Climate change could be changing the game already. 2006 saw the first double-generation summer for bark beetles recorded in Sweden, according to the NYT. Research in Norway (e.g. this) and Sweden (e.g. this) suggests bivoltinism could become the rule in the latter half of the century. Boogie on…

    [Response: Thanks for the comment and good references. Switches to multivoltinism are indeed real cause for concern–Jim]

  31. 31
    JCH says:

    I apologize if this was addressed, but what is going to replace them?

  32. 32
    Ibrahim says:

    An annotated list of the important North American forest insects (1909):

  33. 33

    What can be done with insecticides?

  34. 34

    24 Hank Roberts,

    Thank you for bringing up the kind of issues that need to be understood when we start creating standing forests.

    By the way though, an aquaduct with well designed irrigation systems does not mean flooding the land with water, as the hostile argument tends to portray the forestation concept.

  35. 35

    28 CM

    What the heck is pheromone? Whatever it is, the traps so baited seem to have controlled beetles. Why are we not using it?

    [Response: Insect communication chemicals (“semiochemicals”) There’s a lot of work being done on them, and they can definitely be effective, but there are very serious issues of scale.]

    It is my impression that the Norwegians are not given to careless use of chemicals. But I would be glad to hear more.

  36. 36
    Hank Roberts says:

    > insecticides

    Useful against the second wave plague of flickers and woodpeckers:
    Northern Flicker
    Of the 11 species of woodpeckers (including sapsuckers) that live in Washington …. Avoid using pesticides, especially insecticides. …. Flickers inspect tree trunks and branches for wood-boring beetles …

    Preventing Woodpecker Damage
    The northern flicker, responsible for most woodpecker damage to Colorado homes, …. Insecticides or wood preservatives may deter woodpeckers …
    Weinberg’s Second Law: “If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization.”

  37. 37
    Gail Zawacki says:

    I’m sure it’s some sort of glitch that caused my earlier comment to be erased, since it is on-topic and perfectly pleasant, so here it is again:

    [Response: No, it wasn’t a glitch and if you call: “Unfortunately this situation is so critical that we just can’t wait for scientists entrenched in old ways of thinking to save the ecosystem from total collapse”, perfectly pleasant, then I’d hate to see what you consider hostile. I deleted that comment. It’s full of nonsense such as “The trees on the east coast aren’t turning beautiful colors this year, nor did they last year.” and a bunch of other unsubstantiated general claims without reference. If you want to spout such things, you have your own website to do that. This article is about bark beetles killing trees and you’re welcome to discuss that if you want–Jim]

    [edit ]

  38. 38
    Andy Stahl says:

    Upon graduation from forestry school 30 years ago, I was handed a chainsaw, sent to Colorado, and told to thin lodgepole pine forests to beetle-proof them against the then on-going epidemic (how well did that work?). I’ve seen no compelling evidence that the current outbreak is different in some fundamental parameter (e.g., size, mortality) than past events. We humans tend to be subjectively poor at evaluating the relative magnitude of infrequent, large-scale events. If a remarkable event has happened only once in one’s lifetime (e.g., one’s first big snowstorm as a child), it makes a big impression.

    A nit-pick: “In western North America, true deciduous forests are strictly riparian and therefore limited.” The oak spp. forests of western Oregon and northwestern California are not riparian and were quite extensive before European cultivation and fire suppression.

    [Response: Valid questions and points Andy. I hope to address those issues in the next post. I will say however, that many people who work in this area feel that the combination of the geographic extent and spread, number of tree species being attacked, and intensity of the attacks, makes the current situation worse than any in recorded history. And you are definitely correct about the deciduous oak woodlands of CA and OR–Jim]

  39. 39
    Steve Bloom says:

    Jim, you might want to note in the next post this MPB news aggregator blog. It’s a great resource for anyone wanting to follow the issue on an ongoing basis.

    Also, I haven’t checked out the links Jim Eager provided in #22, although I will, but I recall finding a couple of obscure papers on a search ~6 months ago that indicated that jack pines are perfectly palatable to MPBs. IIRC the main evidence was that the beetles have already been found to be thriving on a hybrid of jacks and another pine species (possibly lodge poles). In any case there seemed to be no evidence that the beetles won’t find jacks as tasty as anything else. The factors that seem to have impeded the jump to the boreal so far are that the access to it is pretty far north (very cold winter temps) and forest cover is a bit spotty leading up to it. I suppose there’s some irony that this same general area is where the tar sands are located. Anyway, I’ll see if I can locate those papers again.

    [Response: I think you are right on there Steve, although I too need to read up some more on it. Going from memory I’m almost certain they hybridize, and even if they don’t the MPB is able to attack a wide number of pine species. I think there might well be spatial contiguity issues as you state.–Jim]

  40. 40
    Richard Simons says:

    Jim asks about using insecticides.

    Insecticides are not effective once the beetle lays its eggs in the tree, they have to be applied before the tree gets infected, but can be used to protect particular trees. Another problem is the vast areas that are infected – over 35 million acres in BC alone – that include prime salmon spawning grounds. I gather that in Alberta controlled burns are being tried as a control measure.

    BC had a crash program of harvesting dead trees but it seems that the logs are rotting in the stacks.

  41. 41
    Mike Roddy says:

    Andy Stahl, nice to hear from you. The last time I saw you I think was at a Sierra Club forest conference in Pasadena in 1993, featuring Martin Litton, Tim Hermach, and Chad Hanson, where you delivered an excellent speech (I made one myself that day).

    I appreciate your knowledge about the evils of fire suppression, but don’t agree that the current beetle infestation may not be unique or at least highly unusual. Yes, the NW drought of the 30’s was more severe, but it occurred without current warming conditions and before the western forests had been virtually liquidated. The result recently has been a larger beetle outbreak in spite of wetter overall conditions. I realize you’re in an awkward position with your organization, but would welcome a comment about the general issue of industrial logging. Maybe we should pretty much leave the woods alone for a while by reducing our wood products consumption to a minimum (we currently consume 25% of the global total), and substituting inert and durable materials.

    [edit–not going to get into that, thanks]

  42. 42
    w kensit says:

    25 Mike Roddy: I share your dislike of logging companies but however hard you try I will never believe them a significant cultivator of MPBB. BC loggers have been hard at it for over 125 years but it is only in the last few decades that beetles have come to be the great destroyer of forests. My most recent memory of sustained periods of -40 temperatures is about 1985 and that in the Rockies. Since then there has been no significant die back of the beetles. BC has been fighting MPBB in Tweedsmuir Prov park for 20 years and that is close to being a roadless wilderness, no logging at all. If the beetles develope an appetite for Spruce they’ll be at the tree line before I die and I’m 70.

  43. 43

    34 Mine re inline by moderator,

    Thanks for the clarification about pheromones, though the implications of ‘communications’ versus insecticides is not entirely obvious.

    [Response: The idea with pheromone treatments is to either lure them into traps where they die, or repel them away from trees, i.e. using highly targeted chemicals and thus avoiding the side effects of the less specific insecticides, as e.g. Richard describes above.]

    39 Richard Simons,

    Thanks for adding that about protecting particular trees. It sounds like we are talking about something that could be managed with adequate trained labor. Now we are getting somewhere; we have a lot of people needing real work.

    I mean of course that we are getting somewhere in the discussion. The next step is to get it into the political discourse.

  44. 44

    41 Mike Roddy,

    I suggest that it would be better to distinguish between different kinds of forest products, at least from the CO2 sequestering point of view.

  45. 45
    John E. Pearson says:

    38: MPB’s and jack pines. I’m out of my depth here but I live in the southern rockies. We call Ponderosa pines jack pines and they definitely get hit by what we call \bark beetles.\ Dunno if bark beetles = MPB’s and not sure if you include Ponderosa among \jack pine\ that’s just what we say around here. There are yellow jack and \black jac k\. The yellow ones tend to be bigger and older than the black ones.

    They definitely have been hit by bark beetles although I think that since about 2005 or 06 the drought has let up and the widespread death has stopped. (This is my own undocumented observation. Take it with a grain of salt.)

    [Response: That’s some sort of local usage. Jack pine = Pinus banksiana, primarily a Canadian and Great Lakes species, closely related to lodgepole pine.–Jim]

  46. 46
    Ray Ladbury says:

    Gail Zawacki,
    I realize that you are probably very frustrated that your posts have not been met with acclaim. I and most of the other posters understand and share your sense of urgency. It is important, though, that the science be done rigorously and conservatively, espeically given the microscope it is under. Denialists are eager to mine any quote from this site that could sound alarmist, even if they have to distort the context to do so. (Remember the UEA hack).

    My recommendation would be to read the blog entries and the quotes of the posters who are generally well received. There are ways of emphasizing urgency without giving fodder to the denialists. Don’t get discouraged, and don’t hold it against the moderators.

  47. 47
    David B. Benson says:

    Jim Bullis, Miastrada Co. — The political discourse b3elongs somewhere else other than RealClimate. Thank you.

  48. 48
    Gail Zawacki says:

    okay, since you had an objection to the sentence you quoted, here’s my comment WITHOUT the objectionable passage:

    The trees on the east coast aren’t turning beautiful colors this year, nor did they last year. They have holes, stippling, chlorosis, and are turning brown, shriveling up, and falling off prematurely. The conifers are turning bright yellow, and then their needles fall off. The bark is oozing, splitting, and falling of branches and trunks. Lethal cankers are prevalent, and lichen is spreading unnaturally quickly.

    Foresters are trained to look for disease, fungus, bacteria, and drought when trees die. This is analogous to blaming the death of an AIDS patient on pneumonia. There is a much broader force at work here than any collection of pathogens…and it is the composition of the atmosphere. It could be that we have reached a level of background tropospheric ozone that is intolerable to vegetation – or it could be the recently mandated addition of ethanol to gasoline, since trees are dying at a rapidly accelerating rate, annual crop yieldsare markedly reduced, and even ornamentals planted in good soil in pots with regular watering exhibit the characteristic damaged stomates on foliage indicative of exposure to ozone.

    Trees have natural defenses against native threats, but they lose the ability to deter attacks when they are weakened by ozone. The insects, fungus and disease that begin to thrive as ozone levels increase have been described by a researcher at the Aspen FACE research center as the “sharks in the water” circling an injured victim.

    Here is an article about their findings followed by an excerpt:

    “The trees of the future may be much more vulnerable to a variety of pests, say scientists studying greenhouse gases in northern Wisconsin forests. Their work is published in the Nov. 28 edition of the journal Nature.

    Researchers in the Aspen FACE (Free-Air Carbon Dioxide Enrichment) Experiment, based in Rhinelander, Wis., have been measuring the effects of elevated levels two greenhouse gases, carbon dioxide and ozone, on aspen forest ecosystems. While the trees, Populous tremuloides (trembling aspen), seem to do relatively well in a carbon dioxide-rich atmosphere, ozone is another story.

    Trees growing in an ozone-enriched atmosphere have been hit much harder by their traditional enemies: forest tent caterpillars, aphids and the rust fungus Melampsora.

    “This has been a surprise,” said Professor David Karnosky of Michigan Technological University’s School of Forest Resources and Environmental Science, a principal investigator on the Aspen FACE project. ‘Our experiment was never meant to look at pest occurrence. But it became obvious that the greenhouse gases were affecting the abundance of pests.'”

    This post from my own blog has excerpts from a course syllabus taught by Dr. Muir at Oregon State U: which addresses the issue of proof of causality, as well as this one:

    “What is actually killing many of the trees is bark beetles (western pine bark beetles), who are able to attack the O3-weakend trees. That is, beetles are the proximate cause of death, while O3 is ultimate – or is the ultimate factor high population density and use of fossil fuels? In addition, the trees’ weakened roots are vulnerable to attack by root rotting fungi which can cause death (recall that O3 decreases plant allocation of carbohydrate to roots…).”

    Also at the top of my blog is a page, Basic Premise, with an extensive list of links to scientific research about the impacts of ozone on vegetation, which has been recently supplemented by the heroic efforts of “Highschooler,’ a courageous teenage student who reads my blog and understands what is at stake. Maybe it helps to be young or an amateur to “think outside of the box”.

    [Response: Whatever you say.–Jim]

  49. 49
    Gail Zawacki says:


    I am not frustrated that my posts haven’t been met with acclaim. I am disgusted that they have been DELETED.

    We are in a f***ing emergency where we and everything else is in danger of going extinct.

    I’m bloody fed up with websites like real climate that are ostensibly reality-based but in actuality are just more propaganda for the fossil fuel industry profits that control science, media, universities, and government.

    I am disgusted with scientists, I say with deep regret.

    Print that, your climate real b*******s!

    [Response: Do please calm down. RC is not, has not been, and will not be, providing ‘propaganda for fossil fuel interests’ at any point. I would have thought that was obvious to anyone. That doesn’t mean we have to agree with everyone on what they think is going on, or what should be done. Let’s please try and maintain a little decorum and maintain at least the possibility of dialog. If you aren’t happy with that, I assure you that swearing at us is not going to help. – gavin]

  50. 50

    Jim, thanks for allowing Gail’s voice.

    Gail has never misrepresented herself as a scientist. She is an amateur – she even calls herself a provocateur. And she happened to point out some very current and needed studies on ozone damage to plants.

    While her blog is filled with lots of personal images and expressions of motherly pride, she gets serious about links and discussion on ozone research. Much seems right on target:
    and Holmes’ 1989 research notes discuss Ozone Risk

    Tropspheric ozone is a quite big deal and I hope that RealClimate can revisit that topic as you see fit.

    [Response: A quick comment to say that, yes, we are well aware of tropospheric ozone, and yes, it is an issue for trees. It is probably not the issue, but we will do a post on this at some point to try to clarify things. –eric]