Sierra Summit

Conversations and observations about California's mountains

January 19, 2009
Thin to Win - Forests, carbon, fire and climate change
A new study finds that thinning Sierra Nevada forests helps store more carbon over the long haul, making them more effective in the battle against global warming. 
The study, scheduled to appear in the journal Frontiers in Ecology and the Environment, a publication of the Ecological Society of America, can be found at:
All trees sequester carbon, of course. But across the Sierra - and much of the West - most trees also burn. Using computer models, the study's authors - Matthew Hurteau at the Northern Arizona University, Flagstaff and Malcolm North at UC Davis - found that after a century of growth, unburned stands stored the most carbon.  But when wildfire was taken into account, much of the carbon went up in smoke. If stand density was reduced before the forest burned, however, less carbon was lost. 

And the more big trees that remain, the better.

"If you want a make these stands more stable, so they can survive these fires, and not make large carbon releases, you need to direct them so they start putting a lot of growth into the large pine trees, which are very fire resistant," North told me not long ago. 

"People generally believe that with fire suppression, you get all this in-filling, all the stems are growing in there, that they would store more carbon - but we found that's not the case," North added. "There is actually less carbon in the stands because you've lost a lot of the big trees. So the small trees, you may have gazillions of them, but it doesn't make up for the fact that you had more large trees in the past."

So what do we do now with the Sierra climate warming and high-intensity, stand-destroying fire a growing threat?

"You need a combination of low-intensity thinning and prescribed burning," North said. "It's one of the great advantage we have in the Sierra: trees that are large and fairly old, if you release them, they actually start growing like a juvenile youngster again. They just start packing the carbon on.  And we have the potential, if we pay this short-term penalty, to make the forests in the Sierra a substantial sink for carbon - and off-set the fossil fuel release underway with human activity."

But the Hurteau and North study also suggested California carbon accounting practices actually contribute to the problem by counting timber harvest stock loss  as a carbon emission. "However, accounting for emissions from wildfire is not required," it says. "Current carbon accounting practices can be at odds with efforts to reduce fire intensity in many western U.S. forest types."






 





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About Sierra Summit

The Author
Tom Knudson lives in the Sierra Nevada and travels widely throughout the range. His hobbies include fly-fishing, backpacking and cross-country skiing. He is the recipient of numerous journalistic awards, including two Pulitzer Prizes, one for a 1992 Sacramento Bee series "Sierra in Peril," a watershed work about environmental threats to the mountain range. E-mail Tom at tknudson@sacbee.com.

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