The report shows a 15-year increase in forests, which give off oxygen and absorb carbon dioxide scientists believe causes global climate change.

"This great reversal in land use could stop the styling of a Skinhead Earth and begin a great restoration of the landscape by 2050, expanding the global forest by 10 percent -- about 300 million hectares, the area of India," said Jesse Ausubel, an environment expert at Rockefeller University in New York.

Carbon dioxide released from cars and power plants collects in the upper atmosphere and prevents heat from escaping Earth, much as glass keeps heat inside a greenhouse.

"Forest area and biomass are still being lost in such important countries as Brazil and Indonesia, but an increasing number of nations show gains," said the report in the US journal Proceedings of the National Academy of Sciences, chartered by Congress to advise the United States on science policy.

"The forests of Earth's two most populated nations no longer increase atmospheric carbon concentration: China's forests are expanding; India's have reached equilibrium -- changes due in large part to urban migration, agricultural yield increases and reforestation policies," said the report released by the academy.

Among the 50 countries studied, forests shrank fastest in percentage terms in Nigeria and the Philippines, and expanded fastest in Viet Nam, Spain and China, during the 15 years covered in the study, 1990 to 2005.

Forested areas fell fastest in Indonesia and Brazil, while gains were highest in China and the United States.

The study was written by six experts in forestry, environmental technology, ecology, geography, resource economics and agronomy in China, Finland, Scotland and the United States.

The study said that the scientists, "following independent lines of thinking, came to agree that forest transition on a major scale is underway and have now collectively demonstrated it."

"Without depopulation or impoverishment, increasing numbers of countries are experiencing transitions in forest area and density," adds Pekka Kauppi of the University of Helsinki.

"While complacency would be misplaced, our insights provide grounds for optimism about the prospects for returning forests," he said.

The study also said that tree planting for materials such as paper is an improvement over cutting old-growth forests.

The authors predicted that the share of industrial wood production in forest plantations will grow from an estimated one-third today to half by 2025 and to three-quarters by 2050.

"Plantations and the trade to make them effective reduce the impact of industrial pressures on the expanse of natural forests, which may be rich in soil carbon and biodiversity," added Roger Sedjo, an economist at Resources for the Future, a Washington think tank.

The study used data from the UN Food and Agriculture Organization, which measured area covered by forests, the volume and tonnes of biomass.

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