Tiny, winged bark beetles have been the ecological bad guys of the West for more than a decade, and rightfully so. They've killed off millions of acres' worth of trees in Colorado. Now all those dead trees are feeding the flames across tens of thousands of acres in the southern part of the state.
The West Fork Complex fire raging through southwest Colorado has already burned through more than 75,000 acres, including wide stretches of tinder-dry trees hit by beetle damage. With 600 people evacuated from homes, and nearly 900 firefighters on the scene, it is considered to be the worst fire to hit the Rio Grande National Forest.
Fire crews don't expect to make much progress on containing the inferno — actually three lightning-sparked blazes that have joined together — until they get some rain and cooler temperatures. That's a grim outlook, made grimmer by the droughts and summer heat that scientists have linked to global climate change.
Are the beetles to blame for wilder wildfires? Not long ago, experts would have said yes. But more recent research suggests that the connection between Colorado's beetle infestation and the vulnerability to wildfires is more complex than that.
"The culprit here is the unusual weather conditions, which might become the new norm with climate change," said Jesse Logan, a retired U.S. Forest Service researcher who has spent decades studying the mountain pine beetle's effect on Western forests.
Drought conditions have persisted for months across southern Colorado and other Western regions, and the Forest Service says Colorado hasn't been experiencing winter temperatures cold enough to trigger significant insect mortality. Drought and warmer winters contribute to the pine beetles' advance, while drought and the hotter summer weather contribute to wildfires. The result? Conditions that favor the beetles as well as the blazes.
Logan has seen this before — in 1988, when wildfires swept over more than a million acres in and around Yellowstone National Park. "Independent of what the beetle had done in certain areas of Yellowstone, the whole thing went up in flames," he told NBC News. "You can point your finger in various directions. It might be the mountain pine beetles, or it might be lack of response to a lightning strike. But really what was driving that was unusually dry weather conditions, and that's what's happening in Colorado."
Both the wildfires and the beetle outbreak can be considered effects of climate change — a subject that will be the focus of a major speech by President Barack Obama on Tuesday. And like many of climate change's effects, how they interact is more complicated than it seems.
Meet the beetles
The mountain pine beetle is native to the forests of western North America, from New Mexico all the way up into Canada. They're winged, black or brown bugs that range in length from a mere eighth of an inch to a third of an inch (3 to 8 millimeters). Their favorite targets are mature lodgepole pines, which they attack by tunneling just under the bark. That's where they chew up the tree's juicy inner bark and lay their eggs. The infestation eventually kills the tree, and then the next generation moves on to the next tree.
The Forest Service says the area affected by pine beetles has grown to 3.4 million acres in Colorado since 1996, plus 3.7 million acres in Wyoming and South Dakota. The pace of the U.S. infestation is slowing, but that's only because mature pine trees have been depleted in the core areas of the outbreak.
The impact of all that forest damage on fire risk is a subject of scientific debate. One recent study, published in the journal PLOS ONE, reported that the fire risk appeared to be elevated in infested forests. A different study, published in Ecological Monographs, said the risk was reduced. This week's West Fork Fire in Colorado was stoked by trees killed off by spruce beetles, a species related to the mountain pine beetle. However, a study in the journal Ecoscience said spruce beetle infestation should reduce vulnerability to extreme fires.
The only consensus is that it depends on the situation. "There could be cases where a bad beetle outbreak could have a big effect, or there could be cases where it would have little effect or almost no effect," said Chad Hoffman, a professor of fire science at Colorado State University.
If a beetle-killed tree stands long enough to lose its highly flammable pine needles, it becomes less prone to catch fire. And when the dead tree falls to the forest floor, that increases the gap between surviving trees, making it more difficult for a blaze to jump from the crown of one tree to the next. However, that gap could let gusts of winds blow through more easily, whipping up a forest fire once it does get started.
What is to be done?
Scientists are working out strategies to deal with the beetle outbreak as well as wildfire risks, but it's a tricky issue. Some argue that the Forest Service's policy of suppressing fires contributed to the spread of the pine beetles, by leaving so many mature lodgepole pines intact.
"It's a scary thing when we start looking at our intervention in the ecosystem, because we can push things out of whack without much effort," said Allan Carroll, a forest ecologist at the University of British Columbia.
If anything, the beetle outbreak is more serious in Canada than it is south of the border. "We anticipate losing pretty much two-thirds of the mature pines" in British Columbia's forests, Carroll said. And it could get worse: The beetles have spread across the Rockies to Alberta, the next province over. If the climate conditions are right, there's a chance that the bugs could advance eastward all the way across Canada, and down to the U.S. Great Lakes region as well.
The strategies for fighting off the beetles range from removing the dying trees to spraying pesticides to burning or harvesting the mature lodgepole pines that the beetles love so much — even before they're infested. That last strategy is the one the Canadians are using east of the Rockies.
How about eradicating the beetles? That may sound like a final solution, but even if it were possible, forest scientists would advise against it. Carroll pointed out that the bugs are part of a natural circle, in which mature pines fall prey to the bugs and eventually burn in fires like the ones sweeping through Colorado this summer. Such fires consume the remaining trees in a stand, but they also release the seeds from lodgepole pine cones — beginning a new circle of life.
"There's a school of thought that says without the mountain pine beetles, we wouldn't have lodgepole pines," Carroll said.
More about pine beetles and wildfires:
- Twin plagues: Beetles and fires devour forests
- Forest-eating beetles contribute to climate change
- Wildfire coverage from NBC News
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.