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Afforestation is replacing deforestation in an increasing number of countries, highlighting the positive impact that government policies — including those in China and India — are having on forest expansion, say scientists.

However, the research published in the Proceedings of the National Academy of Sciences yesterday (November 13) shows that in many developing countries forests are shrinking, but this situation could be reversed.

The scientists developed a new method to calculate carbon stored in forest areas, information that is critical to the study of climate change. The technique is a reliable way of translating forest area, volume and biomass across countries.

One of the study's authors, Jingyun Fang of Peking University in Beijing, China, says the new approach will affect how carbon credits are calculated, adding that it will "encourage governments to consider the value of reforestation".

Instead of simply measuring the areas covered by trees, the researchers calculated the volume of a country's 'growing stock' — trees large enough to be considered timber — as well as the amount of biomass and atmospheric carbon stored in forests.

They used data from a UN report, and found that between 1990 and 2005, forest stocks rose in 22 of the world's 50 most forested countries.

Forest area shrank fastest in Nigeria and the Philippines, and expanded fastest in China, Spain and Vietnam.

In China, reforestation and afforestation efforts, spurred by government policy, allowed forest areas to increase from 96 to 143 million hectares.

These changes are also due to urban migration and agricultural yield, and they have led the team to predict that more nations will achieve forest transition, where reforestation overtakes deforestation, in the next three years.

But the scientists also warn of the negative effect of bad land management.

"The main obstacles to forest transition are fast-growing poor populations who burn wood to cook, sell it for quick cash, and clear forest for crops," said lead researcher Pekka Kauppi of the University of Helsinki, Finland.

Forest transition at a global level will depend largely on Brazil and Indonesia, where huge areas of tropical forest are being cut and cleared.

"I think we need more effort to protect and restore primary forests, especially tropical rain forests," Fang told SciDev.Net.

"As our report has indicated, forest area and biomass are still being lost in two critical tropical countries, Brazil and Indonesia," he added.

The authors also suggest that the expanding forests can compensate for industrial emissions by capturing and storing carbon. The research may have an impact on discussions at the United Nationals Framework Convention on Climate Change held in Nairobi, Kenya until November 17.

Link to full paper in Proceedings of the National Academy of Sciences

Reference: Proceedings of the National Academy of Sciences doi: 10.1073/pnas.0608343103 (2006)