Pacific Northwest forests act as massive carbon banks

March 4, 2010 | 5:18 pm


The thick, wet forests of the Pacific Northwest are the carbon storage powerhouses of the U.S. -- in fact, they store more than 1-1/2 times as much carbon as the entire amount of carbon dioxide burned in fossil fuels throughout the country each year, a new study shows.

Two analysts for the Wilderness Society looked at data compiled by the U.S. Forest Service and identified 10 national forests, from the Tongass in southeast Alaska to the Siskiyou in southern Oregon, that together store about 9.8 billion metric tons of carbon on a total of 19 million acres.

By absorbing carbon dioxide, forests accumulate and store carbon in trees, roots and soil -- a valuable depository for greenhouse gases that, if released into the atmosphere, might contribute to climate change.

"To get a better idea of how much carbon this really is, we could compare it to the CO2 equivalent contained in the fossil fuels burned n the U.S. each year, about 5.8 billion metric tons," said Ann Ingerson, an economist for the Wilderness Society who co-authored the analysis with Mike Anderson, a senior resource analyst at the organization.

The federal Environmental Protection Agency estimates that about 11% of greenhouse emissions are offset each year in forests, urban trees and agricultural soils. States such as California increasingly are looking to preserve and expand their forests to counteract the effects of greenhouse gas emissions.

While forests act as carbon banks, logging, past studies have shown, often results in a large portion of a forest's stored carbon to be emitted back into the atmosphere, either through the burning of excess vegetation or the decay of what's left, Anderson said.

That was one of the points of the study: about 1 million of the 19 million acres of forests named as the heavyweight carbon banks have no formal protections in place against logging or other development.

The top 10 forests with the highest carbon density also include the Willamette, Umpqua, Siuslaw and Mt. Hood national forests in Oregon, and the Olympic, Gifford Pinchot and Mt. Baker-Snoqualmie in Washington.

And while tropical forests typically have the most robust carbon storage capacity on Earth -- usually 360 to 460 metric tons of CO2 equivalent per acre, compared to an average of 230 metric tons for forests in the Pacific Northwest -- some of the towering old growth stands of the Western Cascades appear to top the competition.

One study of the Wind River old growth forest in the Gifford Pinchot National Forest, cited in the Wilderness Society report, found carbon stocks of more than 900 metric tons per acre.

-- Kim Murphy

Map credit: The Wilderness Society