From The Native Trees of Colorado.

Information about the Mountain Pine Beetle and the Pine Beetle Epidemic.
April 18, 2012.

"Since 1997, bark beetles have collectively killed billions of trees across billions of acres of in western North America. The fact that so many regional bark beetle events are happening concurrently at such intensity across so many ecosystems is truly remarkable."

An outbreak of mountain pine beetle is spreading to an unprecedented extent in the western part of North America, including Colorado where a very large die-off of Lodgepole pine and other pines is occuring. Here are a variety of reports, including the most authoritative I know of. No one source has all the information about the mountain pine beetle and the pine beetle epidemic, but together these cover the topic very well. Excerpted quotations are to highlight some important facts and interpretations; they are not a summary.

Even in this situation which calls for scientific fact, views of the meaning of this event span a spectrum with extremes something like "beetles killing trees is normal" on one hand to "catastrophic" on the other. So any one source of information may not be a complete or balanced assesment of the situation.

Sometimes there seems to be a reluctance to state the obvious, that this beetle epidemic is significantly different than past events, and that it gives every sign of being another result of global warming. Beetle kill happens every year, but this event is far from normal. Similarly, sea ice melts in the arctic every year, but arctic summer melting in the past decade has been anything but normal. The behaviors of robins, marmots, mountain pine beetles and other organisms in the Rockies have diverged from historic norms during the past ten to twenty years, and all are what is expected from warming climate.

The Status of Our Scientific Understanding of Lodgepole Pine and Mountain Pine Beetles - A Focus on Forest Ecology and Fire Behavior
2008, The Nature Conservancy, Arlington, VA. GFI technical report 2008-2.
This report is an excellent overview of key points about lodgepole pine forest ecology and the pine beetle.
Authors and Affiliations: Merrill R. Kaufmann (science team leader), US Forest Service Rocky Mountain Research Station (emeritus) and The Nature Conservancy; Gregory H. Aplet, The Wilderness Society; Michael G. Babler (science team co-leader), The Nature Conservancy; William L. Baker, University of Wyoming; Barbara Bentz, US Forest Service Rocky Mountain Research Station; Michael Harrington, US Forest Service Rocky Mountain Research Station; Brad C. Hawkes, Natural Resources Canada, Canadian Forest Service Pacific Forestry Centre; Laurie Stroh Huckaby, US Forest Service Rocky Mountain Research Station; Michael J. Jenkins, Utah State University; Daniel M. Kashian, Wayne State University; Robert E. Keane, US Forest Service Rocky Mountain Research Station; Dominik Kulakowski, Clark University Ward McCaughey, US Forest Service Rocky Mountain Research Station; Charles McHugh, US Forest Service Rocky Mountain Research Station; Jose Negron, US Forest Service Rocky Mountain Research Station; John Popp, US Forest Service Rocky Mountain Research Station; William H. Romme, Colorado State University; Tania Schoennagel, University of Colorado; Wayne Shepperd, US Forest Service Rocky Mountain Research Station (retired); Frederick W. Smith, Colorado State University; Elaine Kennedy Sutherland, US Forest Service Rocky Mountain Research Station; Daniel Tinker, University of Wyoming; Thomas T. Veblen, University of Colorado.

    "A synthesis of our current knowledge about the effects of the mountain pine beetle epidemic on lodgepole pine forests and fire behavior, with a geographic focus on Colorado and southern Wyoming."

    "Regardless of whether or not the current mountain pine beetle epidemic and lodgepole pine mortality are within the historical range of variability at some time scale, the epidemic and associated tree mortality are large and are having immediate effects on forest structure and function over a vast area."

    "A high proportion of larger lodgepole pine trees (diameters greater than six inches) are dying, and in many places many smaller trees are being killed as well. Mortality may approach 100% in pure lodgepole pine stands having few small trees."

    "In forests killed by mountain pine beetles, future fires could be more likely than fires before the outbreak. Large intense fires with extreme fire behavior are again possible."

    "...surface fires in years following needle fall may not be intense and crown fires may be nearly impossible (assuming the forest is relatively pure lodgepole pine and most or all large trees are dead)."

    "Trees killed by mountain pine beetle may remain standing for a number of years, but as they progressively decay and fall to the ground (often aided by wind), the fuel structure changes once again. In this phase (typically 10-20 years or more after death), a large amount of biomass becomes available as fuel within flame heights that can be generated by the fine surface fuels."

    "The potential for erosion from wildfire still exists, however, if extensive fire occurs in the decades following the epidemic, when large amounts of fuel are on the ground. Thus while the mortality of trees does not increase erosion significantly, erosion remains a possibility if a post-beetle fire occurs with heavy fuel loading on the ground."

    "...we have seen a number of significant ecological events in the last decade, including the mountain pine beetle epidemic in lodgepole pine. All of them coincide with warmer climatic conditions than were typical for the past century or more for which we have records. Warming temperatures (especially winter minimum temperatures), longer growing seasons, and growing season drought may be playing major roles in the widespread bark beetle outbreaks in Colorado and southern Wyoming and elsewhere."

Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming
The American Naturalist, vol 179, No. 5, May 2012.
by Jeffry B. Mitton and Scott M. Ferrenberg. Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado.

This is a top scientific paper with current information in a broad view, including climate change indications.

    "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. "

    "...expansion of the MPB into previously inhospitable environments, combined with the measured ability to increase reproductive output in such locations..." (accessed April 18 2012)

Mountain Pine Beetle (pdf version)   (HTML version).
by D.A. Leatherman, I. Aguayo, and T.M. Mehall, Colorado State University Extension.

    "During early stages of an outbreak, attacks are limited largely to trees under stress from injury, poor site conditions, fire damage, overcrowding, root disease or old age. However, as beetle populations increase, MPB attacks may involve most large trees in the outbreak area."

    "Foliage turning yellowish to reddish ... usually occurs eight to 10 months after a successful MPB attack."

    "Extreme cold temperatures also can reduce MPB populations. For winter mortality to be a significant factor, a severe freeze is necessary ... For freezing temperatures to affect a large number of larvae during the middle of winter, temperatures of at least 30 degrees below zero (Fahrenheit) must be sustained for at least five days."

    "MPB prefers forests that are old and dense. Managing the forest by creating diversity in age and structure with result in a healthy forest that will be more resilient and, thus, less vulnerable to MPB. Most mature Colorado forests have about twice as many trees per acre as those forests which are more resistent to MPB."

The Northern Front Range Mountain Pine Beetle Working Group: Information, news, event schedules.
"A centralized source for mountain pine beetle-related information to the public."
2010 Colorado Front Range Mountain Pine Beetle Epidemic Map

Results of the 2011 Aerial Detection Survey in Region 2 (R2)
U.S. Forest Service, Rocky Mountain Region.

  • For all pine species (lodgepole pine, ponderosa pine, limber pine, whitebark, and bristlecone), mountain pine beetle has affected 3.3 million acres in Colorado, 3.3 million acres in Wyoming and 389,000 acres in South Dakota.
  • The epidemic has slowed down in many areas of Colorado and Wyoming as the availability of large pine trees to attack has been depleted.
  • The mountain pine beetle affected area in northern Colorado and southern Wyoming expanded by 140,000 acres in Colorado and 68,000 acres in southern Wyoming and has affected 4.2 million acres since 1996.
  • In Colorado, mountain pine beetle was active on 752,000 acres in 2011 and 275,000 of that was in ponderosa pine. This activity in ponderosa pine occurred primarily in the northern Front Range Counties of Larimer with 254,000 acres and Boulder with 18,000 acres.
  • In Wyoming, mountain pine beetle was active on 719,000 acres and epidemics expanded onto 167,000 previously uninfested acres statewide. Pine forests on the Bighorn National Forest showed the lowest levels of mountain pine beetle activity in Wyoming¿s National Forests.

Colorado's Forests and the Pine Beetle Epidemic (youtube video; 8 minutes; 1 June 2011)
by Professor Jeff Mitton and researchers Scott Ferrenberg and Teresa Chapman, University of Colorado.

Understanding the mountain pine beetle: Seven facts you need to know
by Greg Aplet. June 17, 2009.

    "5. Infrequent, large fires are the norm in lodgepole pine forests, and they are likely to be in the future ¿ with or without beetles. There is general agreement that as the dead needles fall from the trees, the probability of crown fire will diminish, but the probability of surface fire may increase.
    6. Because mountain pine beetle outbreaks do not disturb the soil, they are not likely to cause increased erosion, though they may increase water yield.
    7. Changes like we are observing in the current mountain pine beetle outbreak are not unlike the changes we should expect from climate change in the decades ahead."

Managing Forests To Manage Wildfires
NPR Radio interview, September 23, 2011, "Science Friday," Flagstaff, Arizona, with Wally Covington, Regents' Professor of Forest Ecology at Northern Arizona University, and the executive director of the university's Ecological Restoration Institute, and Mary Lata, a fire ecologist with the U.S. Forest Service in Flagstaff.

    Will the dead trees make forest fires worse?

    LATA: " the bark beetle has absolutely devastated parts of the Central Rockies, up in southern Wyoming and northern Colorado, the Black Hills where you literally have tens of thousands of acres of dead trees. They get the red needles on them. When the needles die at that point, they're particularly flammable. Then, the needles fall off, and you just got the big dead downed trunks. And once those start to fall, the resistance to control is huge. Putting out those big trees is really hard. You can't get in there. You can't just walk through them."

    Let me go to a question I've been wanting to ask - is it possible, Wally, after a big fire that a stream or a river system - I mean, I know that the soil is going to be affected. It - could it be totally changed, and what happens with the water in that forest area?

    COVINGTON: "Yeah. There's, you know, we see this time and again. The Schultz fire that you referred to here in Flagstaff is a classic example. That's a fire that burned last year about 15,000 acres, as you said. And what happens under these severe unnatural crown fires is you burn up and kill the vegetation. The roots die. There's nothing to hold the soil or to prevent flooding from occurring. So what happens with crown fire is there's, my old hydrologist at Yale used to call it the one-two punch.

    And the one punch is you kill a lot of the trees and the animals on an area. The two punch is the soils start marching inexorably toward the sea. And as - without cover, then the impact of the rain as the root systems decay over years, not just immediately after the fire, but over years that soil starts moving down slope. And if you happen to have a human community below that, it's devastating. That's what we have going on right now in the Flagstaff area. "

With Deaths of Forests, a Loss of Key Climate Protectors
By Justin Gillis, New York Times, October 1, 2011

The Truth about Pine Beetles: Ecologist Greg Aplet weighs in on the beetle epidemic
By Hali Young. September 1, 2011. The Wilderness Society.

Q and A: Forests and Climate
By Justin Gillis, New York Times, October 6, 2011

    "The beetle is now wiping out a whole ecosystem, high-elevation whitebark pine forests, that saw only limited beetle outbreaks during warm spells in the past. It has jumped into a new tree species, the jack pine, that could give it a path to spread across the continent in coming decades, into forests that have no defenses."

    "... Werner A. Kurz, a leading Canadian scientist, wrote back that while the beetle is indeed native to the region, it has experienced an expansion in range northward and to higher elevations as climate warming has allowed the species to occupy areas that were previously too cold."

Mountain Pine Beetles: Climate Change Disaster or Natural Phenomenon?
by Stephanie Rogers

    "That's not to say that the beetles aren't causing major damage, with the potential to do even more harm in the future. Bark beetles have destroyed 8 million acres of forest, a level of destruction not seen in 150 years. Once killed and vacated by the beetles, affected trees are at high risk of burning so hot in places that the fires could bake the soil, causing severe erosion and runoff. Moreover, many of the affected trees provide sustenance that species like grizzly bears rely on for survival.

    "Even the scientists who insist that the infestations are part of a natural process admit that, well, okay, maybe it's not entirely natural. Fire suppression efforts and large-scale clear cuts make forests more vulnerable.

    "Dr. Diana Six, who has studied the phenomenon and believes that it's a natural cycle that must play its course, says there's no foreseeable end to the outbreak and that if it's climate driven, we have to reverse climate change. "

Mountain pine beetle and climate change by Jacques Régnière1 and Barbara Bentz, 2009.
in McManus, Katherine A; Gottschalk, Kurt W., eds. Proceedings. 19th U.S. Department of Agriculture interagency research forum on invasive species; January 8-11 2008; Annapolis, MD. Gen. Tech. Rep. NRS-P-36. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 63-64.

    "Since the early to mid-1990s, an outbreak of MPB has reached unprecedented levels in terms of acreages and numbers of pine trees, in particular lodgepole pine, killed throughout its range, most notably in Colorado and British Columbia."

    "We know that cold winter temperature is the major mortality factor in MPB ecology...."

NASA Satellites Reveal Surprising Connection Between Beetle Attacks, Wildfire

    "... the naked trees left behind are essentially akin to large fire logs. However, just as you can't start a fire in a fireplace with just large logs and no kindling, wildfires are less likely to ignite and carry in a forest of dead tree trunks and low needle litter.

    "Forest ecologists noted this same phenomenon after the massive Yellowstone wildfires in 1988. As large crown fires swept quickly through the forest, many trees were killed and their needles burned off, but the standing dead tree trunks remained. In the ensuing years, new wildfires have tended to slow and sometimes even burn out when they reach standing dead forest. There simply aren't enough small fuels to propel the fire.

How the mountain pine beetle devastated B.C.'s forests. by David Suzuki and Faisal Moola. May 6, 2008. accessed March 25, 2012.

Mountain pine beetle and forest carbon feedback to climate change
W. A. Kurz1, C. C. Dymond1, G. Stinson1, G. J. Rampley1, E. T. Neilson1, A. L. Carroll1, T. Ebata2 & L. Safranyik
Nature 452, 987-990 (24 April 2008)

    "The current outbreak in British Columbia, Canada, is an order of magnitude larger in area and severity than all previous recorded outbreaks. ... Climate change has contributed to the unprecedented extent and severity of this outbreak. Insect outbreaks such as this represent an important mechanism by which climate change may undermine the ability of northern forests to take up and store atmospheric carbon, and such impacts should be accounted for in large-scale modelling analyses."

Deaths of trees 'catastrophic'
Todd Hartman, Rocky Mountain News January 15, 2008

    "Every large, mature lodgepole pine forest in Colorado and southern Wyoming will be dead within three to five years, killed in a mountain pine beetle infestation unprecedented in the state."

    State and federal foresters, calling the numbers "catastrophic," said recent aerial surveys reveal the dead and dying lodgepole acreage now has grown to 1.5 million since the first signs of outbreak in 1996.

    With 22 million acres of forest in Colorado, the beetles won't kill it all, but they could do away with most of the "pure lodgepole" stands as well as many of the trees within mixed systems of lodgepole, spruce, fir and ponderosa that cover several million acres in the state.

    It will take decades for the stands to return.

    Rick Cables, the U.S. Forest Service's regional supervisor described the die-off as "a huge, unprecedented event" with major social and economic implications.

    Perhaps most at stake are the state's water supplies. A lack of soil cover and the potential for forest fires as the dying trees dry out could leave reservoirs and rivers clogged with sediment more likely to pour off the landscape. ...

    "We were surprised by the spread into high-latitude forests - it was very uncharacteristic for the mountain pine beetle to go that high up in elevation," said Susan Gray, a specialist in forest health for the Forest Service.

    Colorado State Forester Jeff Jahnke blamed "an unprecedented combination of drought and warm winters" for stressing the trees and leaving them especially open to beetle-infiltration and too weak to ward off attacks.

    Indeed, other pine beetle outbreaks have collapsed after weeks-long cold spells with temperatures under 20 degrees below zero. But Gray said it hasn't been cold enough long enough, to kill the sturdy, rice-sized beetles.'

Bark Beetle Outbreaks in Western North America: Causes and Consequences .
Barbara Bentz, USFS, et al., 42 p., Bark Beetle Symposium, Snowbird, Utah, November 2005.

    "Since 1997, bark beetles have collectively killed billions of trees across billions of acres of in western North America. The fact that so many regional bark beetle events are happening concurrently at such intensity across so many ecosystems is truly remarkable and suggests common factors."


The Insatiable Bark Beetle. Reese Halter Rocky Mountain Books, 2011. 176 pp.

Empire of the Beetle: How Human Folly and a Tiny Bug Are Killing North America's Great Forests. Andrew Nikiforuk. Greystone Books, 2011. 240 pp.

First version October 16, 2011
Revised: November 11, 2011 (added B. Bentz et al.); February 10, 2012 (added R2 survey results and MPB working group); March 25, 2012 (added 'Empire of the Beetle' and link to David Suzuki article); April 18 2012 (added Mitton and Ferrenberg article).

This compilation with annotations and selected quotations Copyright © 2011, 2012 St uart Wier     Reproduction, reuse, or redistribution prohibited without prior written consent of the author.

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