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Nation's forests help offset greenhouse gas emissions

October 15, 2010 |  7:36 pm

Trees

U.S. forests sequester enough carbon every year to offset roughly 11% of the country's industrial greenhouse gas emissions, according to a new federal report.

The inventory ranks California among the top states in forest carbon storage, not far behind its woodsy neighbors to the North, Oregon and Washington.

Shifting land-use patterns -- particularly the 20th century abandonment of farms in the East and the subsequent regrowth of woodlands -- have helped turn U.S. forests as a whole into a carbon sink, meaning they absorb more carbon dioxide from the atmosphere than they release through natural processes.

From a global warming perspective, that is a welcome trend and one that creates the potential for forest owners to sell credits on emerging carbon markets. But it also raises questions of how -- and whether -- forests can be managed to maintain that role.

The majority of the nation's 797 million acres of forestland is in private ownership, much if it in the East, where development is chewing into the woods.  "There is a real concern that the continued loss of open space and development into forest lands in the East, in particular, is going to reduce the amount of carbon we have in our forests,” said U.S. Agriculture Deputy Under Secretary Ann Bartuska.

On Western public lands, wildfire and tree mortality from bark beetle epidemics could put a dent in forest carbon storage.

Before settlement, woodlands were probably in carbon equilibrium, releasing about as much carbon as they took up, said David Cleaves, U.S. Forest Service climate change advisor.When the settlers cleared vast expanses of forest and burned trees as fuel, a long-term rise in forest emissions was set in motion, peaking in the early 1900s.

That started to reverse as the woods reclaimed fields and a federal policy of suppressing wildfire allowed dense, young stands to grow, increasing not only the amount of woodland, but the volume of carbon stored per acre.

Now the nation's forests bank an estimated 41.4 billion metric tons of carbon -- roughly the equivalent of 20 years of U.S. fossil fuel emissions, Cleaves said. Every year, the Forest Service says new growth absorbs carbon dioxide in quantities that are the equivalent of taking 135 million cars off the road.

--Bettina Boxall

Photo: Headwaters Forest in Humboldt County. Credit: Associated Press

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