As forests die, questionable anxieties thrive
Beetles, fire-suppression have little effect on wildfire, experts say
By Clint Talbott
The forest around Grand Lake, Colo., is neither pretty nor, for the most part, green. Whole mountainsides are draped with dead trees bearing orange needles and bare branches. The pine beetles have attacked, and people have responded with chainsaws, insecticides and anxiety about fire.
Conventional wisdom suggests that decades of U.S. Forest Service policy of extinguishing all fires on public lands—also called “fire suppression”—have left forests more prone to beetle attacks, and that these dead trees are more likely than live trees to erupt in wildfires.
But the latest and best scientific research does not buttress conventional wisdom. The research suggests that the pine-beetle outbreaks coincide with warmer, drier years. It finds no compelling evidence that once the dead needles have fallen from the trees (i.e. when the “red phase” disappears a few years after attack) dead stands of pine are more likely than live stands to burn. Scientists also find no evidence that this outbreak is unprecedented over time spans of several centuries, or that human fire-suppression has made western U.S. forests unusually prone to fire.
Further, a team of scientists suggests that some policies and treatment options—thinning forests far from human homes, for instance—is ineffective.
Thomas Veblen, a professor of distinction in geography at the University of Colorado, acknowledges the barrier of intuitive wisdom. “The knee jerk response from the public, politicians and many forest managers was that dead trees would result in a great increase in fire hazard,” he says.
But in several controlled experiments, other researchers have found that dead trees—even those bristling with dry, brittle needles—are not more likely to ignite.
Tania Schoennagel, a research scientist in the geography department and a member of Veblen’s lab, notes an experiment in which a stand of trees was “girdled,” or chainsawed around the perimeter to cut off the trees’ circulation (and ultimately simulate pine-beetle kill).
That dead stand of trees and a still-living stand were ignited, and both groups burned the same, Schoennagel noted. High-severity, infrequent fires are normal for boreal and high-elevation forests, she adds. “What we saw in Yellowstone in 1988 was completely business as usual for lodgepole pines, although terrifying for humans.”
Such conclusions contradict conventional wisdom, which has driven major public policies and expenditures.
“The large stands of beetle-kill trees seen today in Colorado pose a threat of severe wildfire, placing numerous communities at risk,” Mark Rey, former undersecretary of agriculture, said in 2006.
At the time, Rey was endorsing an expansion of the Healthy Forests Initiative and the Healthy Forests Restoration Act, which were predicated on the belief that fire-suppression efforts of the last century have created unhealthy, unnaturally dense forests that were thus prone to wildfire.
As he announced the Healthy Forests Initiative in 2002, former President George W. Bush said the nation had shirked its obligation to preserve “good forests” for future generations: “We need to thin. We need to make our forests healthy by using some common sense,” the president said.
“We need to understand, if you let kindling build up and there’s a lightning strike, you’re going to get yourself a big fire.” In the context of forest policy, the president used the phrase “common sense” six times that day.
Veblen, Schoennagel and leading experts from Colorado State University and the University of Idaho have responded to such intuitive knowledge with a rigorous assessment of research on forest-insect outbreaks and wildfire.
The resulting report, “Recent Forest Insect Outbreaks and Fire Risk in Colorado Forests,” is available at http://welcome.warnercnr.colostate.edu/images/docs/cfri/cfri_insect.pdf.
That report addressed common questions about forest health, fire suppression, wildfire risk and beetles. Following are some questions and answers from the report and from Veblen and Schoennagel, who discussed their research recently:
• Are the dense forests in Colorado the unnatural consequence of fire-suppression and lack of timber harvesting?
It depends, but for the most part, no. At higher elevations, high tree density “is a natural condition” of lodgepole-pine and spruce-fir forests. These forests burn infrequently but intensely, and there is no evidence that the wildfires have gotten worse as a result of human forest management.
At lower elevations, ponderosa-pine forests have, in some cases, become more dense. These generally lower-density forests normally experience more frequent but lower-intensity fires that tend to remove smaller trees and shrubs but leave larger trees alive.
Veblen, Schoennagel and the synthesis team note that dense stands of ponderosa pine have always existed in some places. However, the proportion of dense ponderosa-pine forests increased in the 20th century “in part because of fire suppression, but also because of climatic conditions conducive to tree growth and natural recovery of forests that were burned or logged in the late 19th century,” the report states.
• Do outbreaks of mountain pine beetles and other forest insects increase the risk of severe wildfires?
No. The assumed link between insect outbreaks and forest fires is not well supported, “and may in fact be incorrect or so small an effect as to be inconsequential for many or most of the forests in Colorado,” the report states.
When dense forests burn, they usually succumb to “crown fires,” which devour the limbs and needles of standing trees with such rapidity and ferocity that they can be nearly impossible to control. Crown fires are not finicky; they consume fuel, dead or alive.
“Tree-killing insects do not really increase the amount of fuels in a forest stand; what they do is shift some of the live fuels into the dead-fuel category,” the synthesis report states. “Both live and dead fuels can carry fire under very dry weather conditions.”
• Do large swaths of insect infestation and dead trees mean that a forest is “unhealthy”?
No. The term “forest health” is ambiguous, the authors note. “From a purely ecological standpoint, dead and dying trees do not necessarily represent poor ‘forest health.’ They may instead reflect a natural process of forest renewal,” the report states.
Dead trees can provide wildlife habitat, and as they decompose, they can help regenerate soil.
• Does a large insect outbreak constitute an “emergency”?
No. People like green forests. But from an ecological perspective, “insect outbreaks are part of the natural rhythm of change in forest ecosystems and are followed by a gradual redevelopment of the forest through natural ecological processes.”
• Should humans deploy insecticides? Should they log or burn beetle-killed forests?
It depends. Insecticides can help save trees around a person’s home or on other small scales. But they can’t stop beetle outbreaks on the scale of forests, the authors say.
Logging or burning sections of forests is “unlikely” to prevent insect outbreaks. First, “It will never be feasible to intensively manage all of the forests of Colorado,” they contend. Second, insect outbreaks are largely driven by climate—drought and warm temperatures.
Research shows that the area of land burned by wildfire between 1987 and 2003 was six times greater than that which had burned in the previous 16 years. That research shows that the same time period was characterized by increased spring and summer temperatures, longer fire seasons and earlier snowmelt.
“The new paradigm is accepting the effects of global warming,” Veblen observes, adding that the Healthy Forests Initiative and its companion policies “basically ignored warming.”
As with insecticides, it makes sense to remove dead trees and other fuels near homes and offices. The synthesis report notes research showing that the heat released even from intense crown fires will not ignite wooden walls at distances of 40 meters or more.
Veblen suggests a prescription. “We have to look at mitigation,” he observes. “Any fuels treatment needs to be implemented near homes” or perhaps in some cases near reservoirs. He suggests in the wildland-urban interface, where people will live in or near wildlands, homes undergo Firewise treatment, which reduces the fuel near human structures. (See www.firewise.org.)
“It doesn’t make a lot of sense to go into backcountry areas and thin trees. … That’s just a never-ending process.” The U.S. Forest Service oversees 193 million acres of public land. Between 2001 and 2008, the federal agencies treated about 29 million acres.
Schoennagel concurs. Thinning projects are expensive, and the wood they produce is not profitable, she says. “I always look out over this sea of forests. I think, ‘How could (thinning) have a fundamental impact?’”
In fact, she has led a study of 44,000 fire-mitigation treatments; it found that only 11 percent of the area treated was within 2.5 kilometers of the wildland-urban interface. That study was recently published in the Proceedings of the National Academy of Sciences. (See sidebar.)
Veblen says that adaptation, not just mitigation, should be part of the policy debate.
Adaptation—which might be viewed as “accepting that which you cannot change”—should drive policies that restrict residential developments in fire-prone areas, Veblen adds.
Underscoring that point, Veblen notes that fire history studies show that about 80 percent of the ponderosa-pine zone in Boulder County is naturally predisposed to burn in high severity fires similar to the 2002 Hayman Fire, which burned 138,000 acres—60,000 of them on one day. “For Boulder County, the Hayman-type event is not unprecedented,” Veblen adds.
Given the observed trends of hotter, drier years and their correlation with extreme fires, Veblen says, there’s no reason to believe those trends will reverse. “More fires like the Hayman event are likely to occur in the future.”