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By Maggie Fox, Health and Science Editor
WASHINGTON, April 23 (Reuters) - Mountain pine beetles that are destroying forests along much of the Rocky Mountain range are doing so much damage that they may affect climate change, Canadian researchers reported on Wednesday.
The damage is nearly equivalent to the polluting effects of forest fires, they report in the journal Nature.
"In the worst year, the impacts resulting from the beetle outbreak in British Columbia were equivalent to 75 percent of the average annual direct forest fire emissions from all of Canada during 1959-1999," Werner Kurz of the Canadian Forest Service in Victoria, British Columbia and colleagues wrote.
Usually, a forest is a carbon "sink," soaking up carbon dioxide that would otherwise affect the atmosphere and help hold in heat.
The beetle, Dendroctonus ponderosae, changed that. Dead trees release carbon as they rot, and of course fail to use carbon dioxide as they would if alive.
"This impact converted the forest from a small net carbon sink to a large net carbon source both during and immediately after the outbreak," the researchers wrote.
"The predicted emissions are larger than the total average sink of all of Canada's managed forest over the last decade."
The beetles lay eggs under the bark of mature lodge-pole pine and jack-pine trees, eventually killing them. Once beetles infest a tree, it cannot be saved.
They have ravaged 50,000 square miles (130,000 square kilometers) of forest in western Canada alone. Hundreds of thousands of square miles (km) have also been damaged in the United States.
"Insect outbreaks such as this represent an important mechanism by which climate change may undermine the ability of northern forests to take up and store atmospheric carbon, and such impacts should be accounted for in large-scale modeling analyses," the researchers wrote.
Ironically, climate warming has allowed the Dendroctonus ponderosae pine beetle to venture further north.
Woodpeckers and insects such as clerid beetles that feed on the pine beetles can control them, and early fall freezes can kill the larvae.
It takes five days of temperatures of at least -30 degrees F (-34 C) to kill the beetles, according to Colorado State University researchers.
They used computer models to estimate that the beetles could undo energy-saving efforts made by Canada to reduce its carbon emissions as agreed under the United Nations Kyoto protocol, which took effect in 2005.
"Here we estimate that the cumulative impact of the beetle outbreak in the affected region during 2000 to 2020 will be 270 megatonnes (of) carbon on average over 374,000 square km (144,000 sq mile) of forest," they wrote.
"According to the new calculations, by 2020 the beetle outbreak alone will have released 270 megatonnes of carbon dioxide into the atmosphere."
Canada's government has set a net target of reducing emissions by 20 percent below 2006 levels by 2020.
Human activity in Canada released the equivalent of 747 megatonnes of carbon dioxide into the atmosphere in 2005, compared with 596 megatonnes in 1990, according to Statistics Canada.
(Editing by Will Dunham and Sandra Maler)