Saving carbon by burning forests

The landscape is still mostly desolate 15 years after fire ripped through the Mount Falcon Park in Jefferson County, Colorado. A new study suggests controlled burns, by keeping fire intensity low, can help reduce emissions generated by wildfires. All photos courtesy Tim Jones/flickr

17 March 2010

New study suggests prescribed burns can reduce carbon dioxide emissions generated by forest fires.

Daily Climate staff report

BOULDER, Colo. – By now most everyone knows that forests sequester carbon and that forest fires pump enormous amounts of that stored carbon skyward.

But researchers are coming to a somewhat contrary conclusion: Carefully controlled burns can help reduce forest carbon emissions.

The most recent study, from the National Center of Atmospheric Research and Northern Arizona University, looked at dry forests of the western United States and discovered that prescribed burns can reduce carbon fire emissions by nearly a quarter throughout the West – and by as much as 60 percent in some forests.

"It appears that prescribed burns can be an important piece of a climate change strategy," said NCAR scientist and lead author Christine Wiedinmyer in a statement. "If we reintroduce fires into our ecosystems, we may be able to protect larger trees and significantly reduce the amount of carbon released into the atmosphere by major wildfires."

The study was published in the journal Environmental Science and Technology.

Wildfires often destroy large trees that store significant amounts of carbon. Prescribed fires are designed to burn underbrush and small trees, which store less carbon. By clearing out the underbrush, these controlled burns reduce the chances of subsequent high-severity wildfires, thereby protecting large trees and keeping more carbon locked up in the forest.

"When fire comes more frequently, it's less severe and causes lower tree mortality," said Matthew Hurteau of Northern Arizona University and the study's co-author. "Fire protects trees by clearing out the fuel that builds up in the forest."

Forests have emerged as important factors in climate change. Trees store, or sequester, significant amounts of carbon, thereby helping offset the large amounts of carbon dioxide emitted by factories, motor vehicles, and other sources. When trees burn down or die, much of that carbon is returned to the atmosphere. It can take decades for forest regrowth to sequester the amount of carbon emitted in a single fire.

In the western United States, land managers for more than a century have focused on suppressing fires, which has led to comparatively dense forests that store large amounts of carbon.

But these forests have become overgrown and vulnerable to large fires. Changes in climate, including hotter and drier weather in summer, are expected to spur increasingly large fires in the future.

This could complicate U.S. efforts to comply with agreements on reducing carbon emissions. Such agreements rely, in part, on forest carbon accounting that calls for trees to store carbon for long periods of time. Large carbon releases from wildland fires over the next several decades could influence global climate as well as agreements to reduce emissions.

There are some caveats, the authors warn: This is simply the first step in evaluating the potential of using prescribed burns to reduce wildfire emissions and to increase the long-term stability of forest carbon. Different variables such as fire intervals and combustion efficiencies could compromise savings. And large fires – such as the Yellowstone fires of 1988 – could dramatically increase total wildfire emissions, reducing any savings from prescribed burns.

"While it can be costly to set controlled fires, there is also a cost in leaving forests vulnerable to larger fires," Wiedinmyer said. "More research can help forest managers make better decisions about our forests and climate change."

Reach Daily Climate editor Douglas Fischer at dfischer [ at ] dailyclimate.org 

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