Carbon rise found in old forest soil

Jeff Barnard, Ap Environmental Writer

Published December 1, 2006 at midnight

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GRANTS PASS, Ore. - Researchers have found that soils in an old- growth forest in southern China are storing carbon at a rapid rate.

If common to the soils of other old-growth forests, the finding could add combating global warming to the reasons for preserving them from logging, some scientists say.

The finding from soils in China goes against the generally accepted idea that old-growth forests are in balance, giving up as much carbon through decomposition as they take in from falling leaves and dying roots.

Why the soils act as a carbon sink remains unknown, but the study in the journal Science gives a new way to think about how carbon works in old-growth forests, said Xuli Tang, a scientist with the South China Botanical Garden in Guangzhou, China, and co-author of the study.

"No country in the world has been trying to (preserve) old-growth forest from carbon sink perspective because of the existence of the traditional paradigm," although China is doing some large-scale forest restoration projects that could serve as significant carbon sinks, he said by e-mail.

Many scientists believe that an increase in carbon dioxide and other greenhouse gases from burning oil and coal is causing rising temperatures around the globe that are changing the climate, melting polar ice caps, raising sea levels and contributing to a growing number of plant and animal species going extinct.

One strategy for combating global warming is finding ways to store carbon so it is not released into the atmosphere.

By virtue of their age, old-growth forest soils are generally believed to be in balance, with the amount of carbon added to the soil from falling leaves, branches and dying roots offset by an equal amount of carbon released by the microbes that eat the leaves, branches and roots.

The research was conducted in the Dinghushan Biosphere Reserve in the southern China province of Guangdong, which is covered with a 400-year-old subtropical evergreen broadleaf forest.

Taking a total of 230 samples over 24 years from the top eight inches of soil, the researchers found organic carbon levels went from about 1.4 percent in 1979 to 2.35 percent in 2003, an increase of 68 percent.

John Aber, professor of environmental studies at the University of New Hampshire, who did not take part in the study, said he was skeptical of the results, because they go against the prevailing research and are based on a relatively small number of samples.

However, given the high rate of change found in the study, the increased carbon may be coming from some recent change in the environment, such as industrial pollution, he said.

That could happen two different ways, he said. Increased nitrogen in the air could fertilize the forest, leading to more leaves falling to the ground and increasing carbon in the soil. An increase in toxins falling to the forest floor or increased acidity would slow down decomposition, leaving more carbon in the soil.

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