EUGENE — When it comes to storing carbon, no national forest in the United States does more than the Eugene-based Willamette, according to a survey released by an environmental group.

In an analysis of data collected by the U.S. Forest Service, The Wilderness Society found that among the federally owned national forests, the top 10 for carbon storage are all in the Pacific Northwest, six of them in Oregon.

The Pacific Northwest climate offers plentiful rain and moderate temperatures that encourage tree growth, and the Willamette National Forest, at nearly 1.7 million acres, is a colossal forest. Only two of the other forests on the list are bigger.

So the Wilderness Society report is no big surprise to Mark Harmon, an Oregon State University professor of forest ecology, who has been studying carbon storage in forests for decades.

If anything, the results might underestimate the amount of carbon stored because the current science is better at estimating what's held in live trees, than what's in a forest's soils and dead wood, which also store carbon, he said.

A study published last summer in the Proceedings of the National Academy of Sciences concluded that Oregon's forests are among the best in the world at storing carbon, second only to forests in Australia.

The Willamette, once the nation's top timber producer before enforcement of federal laws severely limited logging, is home to many stands of big old trees, said Michael Anderson, a senior resource analyst with The Wilderness Society.

"We knew where old growth habitat was," Anderson said. "We had a sense that the Northwest had a lot bigger trees and denser vegetation than other parts of the country. And the Willamette National Forest in particular has always been seen as an especially productive forest."

All told, the United States' federal forests store 9.8 billion metric tons of carbon on about 19 million acres, Anderson said.

About 5.8 billion metric tons of carbon dioxide are released by fossil fuels burned in the United States annually, according to the Wilderness Society.

Organizations such as Anderson's view the carbon-storage capacity of these national forests as yet another reason to refrain from cutting them, right up there with the habitat they provide for wildlife, Anderson said.

A spokesman for the Willamette National Forest was not able to answer any questions about carbon storage on the Willamette or whether federal officials are considering carbon storage in their forest management strategies.

Anderson said the issue came up at the Copenhagen convention on climate change last year, with U.S. Secretary of Agriculture Tom Vilsack and leaders from several other nations making a commitment to reduce the rate of deforestation.

The Forest Service is in the process of developing new forest management regulations with a meeting in Portland planned for April, Anderson said.

"I know climate change is going to be one topic," he said.