Bark beetle kill leads to more severe fires, right? Well, maybe

  • The 2011 Norton Point Fire in Shoshone National Forest, Wyoming, burned both beetle-damaged and healthy trees.

    Kari Greer and the USDA Forest Service
  • Beetle-killed trees in Colorado's Never Summer Mountains near Gould.

    Kari Greer and the USDA Forest Service
  • Tree mortality in 2011

    U.S. Forest Service, Forest Health Protection, Forest Health Technology Enterprise Team
 

The lodgepole pine and spruce-fir forests of the Intermountain West are reeling under a one-two punch: more frequent and severe wildfires, and an epidemic of tree-killing bark beetles.

Once-green forests are filled with red dying trees and patches of gray dead ones. From a distance, the effect is oddly beautiful. Up close, people often experience a visceral jolt, followed by a sense of alarm: Can't somebody do something?

Steve Currey has fielded his share of anxious phone calls. "A few years ago," he says, "we were under a lot of public pressure to stop the beetles from spreading further." Currey is director of bark beetle operations on the sprawling Medicine Bow-Routt National Forest in Wyoming and Colorado. The outbreak there started in northwestern Colorado in the mid-1990s and moved northeast to central Wyoming. "The beetles aren't killing every tree," Currey says, "but they are killing a majority of mature lodgepole pine, and we've lost half our limber pine, too." More than 116 million acres in the North American Rocky Mountains have been affected. "People are beginning to understand that this thing is too big to stop."

Wildfire and beetle epidemics both have long histories in Western forests. Their patterns have been shaped somewhat by human impacts, but outbreaks, which tend to be infrequent and severe, are driven by larger factors. Scientists believe a warming climate is the main factor behind the West's more frequent severe wildfires, and is also likely amplifying the current bark-beetle epidemic, the most widespread on record. Warmer winters allow beetles to spread into more northerly and high-elevation territory. Beetles reproduce more often during longer warm seasons, and more larvae survive winters.

It might seem that fire and bark beetles are locked in some malevolent feedback loop, with fires inviting beetles to devour weakened trees, and beetles creating fuel for future fires.

But "there were surprisingly little data backing up that conventional wisdom," says Monica Turner, a University of Wisconsin landscape ecologist and coauthor of a much-discussed 2011 study that examined links between beetle epidemics and wildfires in the Greater Yellowstone Ecosystem.

The study's findings -- that beetle attacks don't increase severe-fire risk, and may in fact reduce it as dying trees shed needles -- may sound counterintuitive. But they are in line with more than two decades of research indicating that, while bark beetle epidemics and fire are entwined in complicated ways, one does not necessarily amplify the other.

Yet this recent study -- which used a computer model that simulates fire behavior to predict severe-fire risk based on current conditions, unlike most of the previous research, which looked to historic beetle epidemics and fire patterns to unravel the relationship between the two -- has drawn sharp criticism, particularly from those who manage fires in beetle-killed forests. Turner and her colleagues say that large-scale removal of dead trees -- often proposed to reduce fire risk -- is "probably not needed" in lodgepole forests, which dominate the upper montane and lower subalpine zones of the Rockies. Critics counter that the study's methodology and narrow geographic scope don't justify its sweeping conclusion, and that it shouldn't be interpreted as a broad indictment of salvage logging. This collegial wrangle illuminates how messy -- yet essential -- it is to apply land-management science to management itself. And it raises the question: Should we do something with all that dead wood?

Frank Carroll
Frank Carroll Subscriber
May 15, 2012 02:47 PM
In fairness to every reader you must reveal that the unequivocal fire safety message sent to all fire teams on August 11, 2011, says that we may expect extreme fire behavior when fire danger is moderate in beetle-killed forests across the Rocky Mountains. This safety alert was based on observed conditions. This fact is related to low fuel moisture, solar heating of heavy ground fuels, and intesnse spotting as a result. Do not mistake this for another willy nilly scientific forestry debate. People will die.
Tim Baker
Tim Baker Subscriber
May 24, 2012 02:52 PM
There was a recent article in Forest Science (Hoffman et al., 2012, Numerical Simulation of Crown Fire Hazard Immediately after Bark Beetle-Caused Mortality in Lodgepole Pine Forests. Forest Science 58:178-188) that found results that contradict those reported above by Turner's group (Simard et al., 2011). Of course, part of the problem is in trying to use physics-based process models to figure out what's going on in the real world, but the discussion is interesting nonetheless.

I suspect that Hoffman et al. are closer on what happens in the period immediately after the infestation but the interesting problem is what happens if the fire doesn't occur for 3-5 years after the needles have fallen? As for salvage logging, I think it makes sense where it replaces harvesting live trees but certainly not everywhere simply because of the scale of the problem.