By Henry Fountain
New York, NY (April 29, 2008)- Trees have been fighting climate change for ages, using photosynthesis to remove carbon dioxide from the atmosphere and sequestering it for the long term in their tissues. Most forests are considered net sinks of carbon dioxide, meaning they store more carbon than they give up. But natural events can upset a forest’s carbon calculus. Big fires, for instance, spew plenty of CO2 into the atmosphere, and the dead trees that remain eventually decompose by microbial action, releasing more of the gas.
By killing trees by the thousands, widespread insect infestations can do the same thing. But rarely have insect blights been considered when determining a forest’s carbon balance.
Now Werner A. Kurz of Natural Resources Canada and colleagues have calculated the impact of an infestation of mountain pine beetles on pine forests in British Columbia. The effect, they report in Nature, is startling: the forests are now a large carbon source, and will remain so at least until 2020, long after the infestation peaks.
At more than 32 million acres and counting, the pine beetle blight is at least an order of magnitude larger than any previous recorded infestation by the insect. And global climate change, Dr. Kurz said, is partly responsible: winter temperatures no longer get low enough to kill off the beetle, and warmer summers allow greater reproductive success.
Dr. Kurz has been studying the carbon balance in Canada’s forests for years, and he developed a computer simulation that weighs many factors. The current work, he said, “is the first time I’m aware of that a study has been able to isolate the effect of the beetle.” The results show that in the worst years, the amount of carbon released in British Columbia forests will be roughly three-quarters of the average annual amount of carbon released, largely through fires, in all of Canada.
Dr. Kurz said the study showed how climate change, by making the infestation worse, creates positive feedback on future climate change by affecting forests that once removed a lot of carbon dioxide from the atmosphere.
“This particular piece of real estate is not going to do that,” he said. “To the contrary, it is actually adding to the burden.”
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