Forests in the Interior West could soon flip from carbon sink to carbon source, forest experts say. The region's forests once absorbed and stored more carbon from the atmosphere than they released. But huge conflagrations -- like the 138,000-acre Hayman Fire in Colorado in 2002 and the Yellowstone fires of 1988, which scorched 1.2 million acres -- combined with a series of severe bark beetle infestations and disease outbreaks, have left large swaths of dead, decomposing trees in almost every major Western forest.
Those dead trees are releasing massive amounts of carbon dioxide, turning the region into a net emitter of carbon rather than a CO2 sponge. The reversal, which has already occurred in Colorado and is anticipated in several other states, is the result of misguided forest management practices and a changing climate, forest experts say.
Rising temperatures, resulting in shrinking snowpacks and drier conditions, have left the region's forests more susceptible to disturbances, such as wildfires, bark beetles and disease. "In the Interior West, we've had a lot of these disturbances," said Dave Cleaves, the Forest Service's climate change adviser, who served as director of the agency's Rocky Mountain Research Station from 2005 to 2007.
But temperature alone is enough to cause mortality in some forests, scientists have found. According to a study published last year in the journal Science, the death rate for Western old-growth forests -- which are generally more resilient and more stable than younger forests -- has doubled in the past few decades as temperatures have risen. More trees are dying, while regeneration rates remain unchanged, the study found (Land Letter, Jan. 29, 2009).
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http://www.nytimes.com/gwire/2010/11/11/11greenwire-interior-west-forests-on-verge-of-becoming-net-78105.html
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