Old Forest Stores Much More Carbon
4 December 2006
In a study published in Science this week, scientists show that an old forest in southern China is soaking up carbon from the atmosphere considerably faster than expected.
The reasons for this are not known but the 24-year study could mean that much greater value is placed on the preservation of ancient forest, as it could be so useful in combating climate change. This could lead to financial incentives for people to preserve existing forest as part of carbon offsetting.
24 Years of Study
The research was conducted in the Dinghushan Biosphere Reserve in the southern China province of Guangdong, which is covered with 400-year-old subtropical evergreen broadleaf forest.
The group of scientists measured carbon in the soil collected 230 samples over 24 years from 1979 and 2003. They found that organic carbon concentrations in the top 20 centimetres of the soil increased in that period from about 1.4% to 2.35%, an increase of 68%.
During the study, researchers also observed a decrease in the amount of leaves and branches falling to the forest floor, a decrease in soil moisture, and an increase in soil acidity.
Status of Old Forest May Change
Classified as forests at least 100 years old, old-growth forests are widespread in tropical and subtropical developing countries. Until now, they were not thought to absorb and store significant amounts of greenhouse gases from the atmosphere.
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. At the moment, protecting forests from deforestation is not included in the global carbon trade, a mechanism enabling industrialised countries to pay developing nations for reducing the latter's carbon dioxide emissions. This could be set to change, making preservation of old forest more attractive.
Developing countries with abundant old-growth forest cover could ask rich countries for compensation through the global carbon trade, said team leader Guoyi Zhou from the Guangdong Province-based Dinghushan Forest Station, Chinese Academy of Sciences.
High Carbon Uptake Can't Yet be Explained
Why the soils act as a carbon sink remains unknown, but the study 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. The authors say their findings point to the need for further research on the complex responses of old-growth forest to global environmental change.
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 might be coming from some recent change in the environment, such as industrial pollution, he said.
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