Pacific Northwest forest fires may play a minor role in climate change compared with fossil fuel use, according to a new analysis by Oregon State University researchers.

EUGENE — Pacific Northwest forest fires may play a minor role in climate change compared with fossil fuel use, according to a new analysis by Oregon State University researchers.

In a study conducted in the area of the B&B Complex fire that ravaged 92,000 highly visible acres along Highway 20 over Santiam Pass in 2003, scientists concluded that previous estimates suggesting the fire produced six times more carbon emissions than all other sources of greenhouse gas emissions in Oregon during that period were grossly off the mark.

Beverly Law, a professor of forest ecosystems and society at OSU, and her fellow researchers concluded that carbon emissions from four fires that burned in the Metolius River area in 2002 and 2003 produced just 2.5 percent of the state's annual carbon emissions in both those years.

The research, published in the December 2009 issue of the journal Ecosystems, also said that most of the carbon released during the wildfires came from burning on the forest floor rather than the trees themselves, and that quick regrowth of brush and grasses, which absorb more carbon than they release, helps mitigate the greenhouse-gas effects of fire.

Law and others have been studying the impacts of forests on greenhouse gases for well over a decade to understand the role of people and nature on climate change. Their conclusion: Even though a forest fire, with is towering plumes of smoke, may look like it is giving off vast amounts of greenhouse gases such as carbon dioxide, the people of Oregon give off far more of the gases as they drive and do other activities that burn fossil fuels.

After wildfires raced through the Metolius watershed in 2002-2003, the researchers looked at sections that had burned to learn whether on-the-ground measurements agreed with computer models and remote sensing data being used to calculate the carbon dioxide emissions from fire, Law said.

Previously, most such research had been done in arboreal forests of Canada and the temperate zones of the United States where trees, such as lodge pole pine, are much smaller than the timber that covers Oregon's Eastern Cascades, Law said.

Using the data from those forest fires to extrapolate the impacts of fire in the Pacific Northwest led to the overestimates of how much carbon the fires emit in Oregon, she said.

"We're not trying to slam the national estimates," Law said. Experts worked with the information they had available at the time. What she and her team found was that the severity of the fire and the type of forest that burns make a significant difference in the amount of carbon released.

Previous research looked mainly at the most severe fires that kill 80 percent to 100 percent of trees. But in Oregon, such fires represent just a fifth of all forest fires, in part because Oregon's trees are big, hard to burn and tend to survive fires.

Plus, even though severe fires do kill trees, they still only consume about 1 percent of the wood, Law said. Most of the dead tree is left standing, and it only slowly emits its carbon via decay when it falls to the forest floor and rots, she said.

In addition, because trees in the Cascades grow quickly, burned forests there regenerate rapidly and resume their carbon-collecting process. A burned forest in Eastern Oregon might take 20 to 30 years to resume its work as a "carbon sink," Law said, while a burned western Cascades forest might become a "carbon sink" again in five to 10 years in the western Cascades, Law said.

Timber harvest has much more impact on carbon dynamics than fire, Law and her colleagues found. Because of this, forest fires will be a relatively minor player in greenhouse gas mitigation strategies compared with other factors, such as human consumption of fossil fuels, they said.

Law hopes that scientists who model the effects of climate change will use the combustion factors captured in her on-the-ground research to improve their estimates about the impact of wildfires.

Burning fossil fuels plays a much more significant role in climate change than wildfire, she said.

Emissions from forest fires is "a drop in the bucket when we look at fossil fuel emissions," she said.

Even in 2002, the most extreme fire year in recent history, the researchers estimate that all fires across Oregon emitted only about 22 percent of industrial and fossil fuel emissions in the state, and that number is much lower for most years, about 3 percent on average for the 10 years from 1992 to 2001.