Old-growth retains carbon, study finds

A group of forest scientists from the United States and Europe reports that a growing body of evidence settles an old question over whether old-growth forests store more carbon dioxide from the atmosphere than they release.

Based on a review of research from more than 500 forest sites around the world, the answer, being published today in an online edition of the journal Nature, is that most forests between 15 and 800 years old do, and the total amounts to about 1 billion metric tons a year, or about 10 percent of the net carbon uptake worldwide.

Co-author Beverly Law, a professor of global change forest science at Oregon State University, said the findings argue for including credit for preserving old-growth forests in the Kyoto Protocol and cap-and-trade schemes for controlling greenhouse gas emissions blamed for global warming.

"If you have an old-forest on the ground, it's probably better to leave it there than to cut it," she said. "For the countries that did sign on to Kyoto, it is suggesting that perhaps they need to consider unmanaged primary forests in their carbon accounting."

The United States did not sign the Kyoto agreement.

"The absolute amount of carbon stored in these forests is significant," Law said from her office in Corvallis. "Once you disturb them by logging or fire, there is carbon loss. When that occurs, there is material left on site that decomposes. And some is lost in the manufacturing process."

At U.N. talks last month in Ghana aimed at a new global warming treaty, delegates agreed that countries should be compensated for slowing or halting deforestation, and that countries where forests have largely been depleted should be rewarded for conserving and expanding their forest cover.

About 30 percent of the world's forests have not been significantly logged, and about half of that is in the boreal and temporal forests of the Northern Hemisphere, Law said. The review estimated that 1.3 billion metric tons, plus or minus 500 million metric tons, of carbon are absorbed by these forests annually.

The conventional wisdom for the last 40 years, based on one study of a young plantation forest, has been that old-growth forests were carbon neutral, giving up as much from decomposition and gases released from the trees as they drew out of the atmosphere during photosynthesis, Law said.

Law is science chair of the AmeriFlux network of about 100 forest research sites around the country that measure carbon absorption, including one outside Sisters, Ore.

Those sites and a similar network known as CarboEurope have been finding since the 1990s that once most forests get more than 15 years old they absorb more carbon dioxide than they release, and continue doing so for centuries, she said. It just took several years to compile the research.

Ram Oren, a professor of forest ecology at Duke University also involved in the AmeriFlux network, said the evidence has been mounting for years showing forests are net carbon sinks, but this is the first time he has seen a total calculated.

"This represents the acknowledgment of something that the scientific community has already been sharing for awhile, that the old paradigm is incorrect," Oren said from his office in Durham, N.C. "Now lets see the impact of it," on greenhouse gas policy.