USA — Some of the worst forest fires in Oregon’s recent history consumed far fewer trees and released far less carbon dioxide than previously estimated, a new study by Oregon State University researchers concludes.
After the B&B Complex fire in the Metolius River watershed in 2003, some researchers estimated that the fire released six times more carbon dioxide — a global warming gas — than all other energy and fossil fuel use that
year in Oregon.
But the OSU researchers observed forest growth in the Metolius basin in Oregon’s Cascade Range, concluding that far fewer trees were burned — 1 percent to 3 percent versus earlier estimates of 30 percent.
They estimated that the B&B fire and three other Metolius fires in 2002-03, covering 100,000 acres all told, produced only 2.5 percent of Oregon’s annual carbon emissions.
Timber harvest has much more effect on the amount of carbon in the atmosphere than fire, the researchers said. They called forest fires “a relatively minor player” in greenhouse gas reduction strategies compared to other
factors, such as human consumption of fossil fuels.
From 1992 to 2001, forest fires accounted for an average of 3 percent of the state’s emissions, the researchers estimated. In 2002, the worst fire year in recent history, fires accounted for 22 percent of emissions.
Researchers Garrett Meigs, a forestry research assistant and Beverly Law, a professor of forest ecosystems and society, observed generally abundant tree regeneration in the Metolius watershed. It looks like everything is
burning up in a forest fire, they said, but trees aren’t vaporized and many aren’t killed in low-severity fires.
Even when a very severe fire kills almost all of the trees in a patch, the scientists said, the trees are still standing and only drop to the forest floor, decay, and release their carbon content very slowly over several decades.
Grasses and shrubs quickly grow back after high-severity fires, offsetting some of the carbon release from the dead and decaying trees.
Some past analyses of carbon release have been based on studies of Canadian forests that are quite different than many U.S. forests, Meigs and Law said.
The research was published recently in the journal Ecosystems, and funded by the U.S. Department of Energy.