Close to the Flame

New research on Colorado forests challenges many of the old assumptions about the risks, severity and causes of the devastating wildfires of the past decade.

Work being done by scientists at Colorado State University and the University of Colorado Boulder could lead to important changes in how and when to prevent and fight severe fires in the future.

The effects of drought, warmer temperatures, pine beetle outbreaks, restoration and fire management practices all play a part in the current and future health of the state’s forests.

“All of the discussions have focused on the same old solutions: fire suppression, thin the forests, reduce some fuels,´ said Thomas Veblen, professor of geography at CU-Boulder and head of the biogeography lab. “But most people who work in this field say we can’t thin our way out of this. The big challenge is, how do we adapt to or mitigate the effects of global warming? We are just beginning to have realistic discussions about that.”

While it’s relatively safe to predict warmer temperatures these days, it’s harder to predict drought, according to Nolan Doesken, state climatologist with the Colorado Climate Center at Colorado State University’s department of atmospheric science.

“Over the last 20 years, predicting warmer than average temperatures has been a good bet because they have been warmer than average seven out of 10 years,” Doesken said. “We have seen a lot of warm springs and a lot of hot summers. We have had long periods of many consecutive days warmer than historically average. And that is a stressor to a natural ecosystem.”

But Doesken said there is no reliable method of predicting the amount of precipitation each year, or even the areas where it will occur. In 2011, for example, there was abundant water in northern Colorado, but extreme drought in the southern part of the state. But 2012 saw drought statewide and nearly all year long, similar to 2002, which had seen Colorado’s worst extreme drought in several decades.

Climate has been a contributing factor in wildfires such as those last summer, High Park near Fort Collins and Waldo Canyon in Colorado Springs, Doesken said. “But it’s certainly not the only factor. Are we warmer more often than we have been? Most likely. But did we also have drought in the past? Absolutely, probably every bit as bad as we’ve had the past few years.”

Fire behavior models that are used to predict the spread and severity of fires have used as a basis what the climate has been, not what it is likely to be in the future, Veblen said. “When we input, as an experiment, future parameters, we get incredibly high severity fires.”

Warmer, drier weather, particularly the 2001-02 drought, accelerated the pine beetle epidemic in the southern Rocky Mountains, which is estimated to have hit nearly 3,000 square miles of forests, according to a recent study by CU-Boulder doctoral student Teresa Chapman.

But her research showed that the outbreak is affected not only by warmer temperatures, but also by the fact that weather affects a tree’s ability to produce resin, the hydrocarbon that helps it ward off insects.

“Once the beetle populations are sufficiently high, there are so many millions of beetles attacking the tree that even if climate conditions return to normal precipitation, normal temperatures, there are just too many beetles for the weakened tree to defend itself,” Chapman said.

The study also revealed that the beetle outbreak originated in several locations and spread, rather than starting in one location, as some researchers had previously believed.

Fire management officials and others have assumed that all the trees killed by pine beetles must make forest fires worse and as a result have cleared and thinned the dead trees as a preventive measure.

But researchers such as Chapman and CU-Boulder’s Veblen are taking a second look at those assumptions.

A new study by Veblen will look at whether a beetle outbreak increases fire severity.

“That question has not been resolved yet,” Veblen said.

For example, a recent study conducted by Veblen and other researchers, using data from past fires in lodgepole pine forests in west-central Colorado, found that under extreme fire conditions there was no difference between stands infested by beetle kill and those that had not been affected.

Restoring forests in a way that enables them to withstand fires as well as prevent high-severity fires is the focus of new projects led by Tony Cheng. Cheng is director of the Colorado Forest Restoration Institute and an associate professor in the department of forest and rangeland stewardship, both at Colorado State University.

Studies show that historically, forests in Colorado have burned frequently, every five to 30 years, keeping down tree and plant growth. The result was low intensity surface fires that creep primarily along the ground.

But logging as well as management practices that dictated aggressive fire suppression have “altered that fire regime,” Cheng said.

The result is denser forests, particularly ponderosa pine forests, that generate super-intense fires when they burn.

Cheng’s project aims to remap and reconstruct what historic forest conditions might have looked like before the era of actively putting out fires. That might lead to reducing the number of trees and conducting prescribed burns that would return forests to historic conditions. The projects are on the Front Range and the Uncompahgre Plateau west of Montrose.

But as Cheng acknowledged, “Tree cutting in particular and prescribed fire burns are very socially controversial.”

So another aspect of the project is to get community members involved so they develop a better understanding of those historic forest conditions.

That’s not an easy proposition.

“There’s a value in living in Colorado forests,” Cheng said. “We have acculturated that; more trees are better. And that’s a problem because one part of restoration is actually having more frequent fires so that the forest functions normally. That’s a hard public safety issue to overcome.”

But current forest conditions, coupled with warmer and perhaps drier climates in the future, dictate that changes in fire management as well as land-use policies are necessary, the researchers agree.

“It’s not just about the fires today,” Cheng said. “It’s about the kinds of forests we are going to have for future generations.”

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