This approach takes into account tree density as well as overall tree cover to reveal a country's total forest resources, the team says.
In Japan, for instance, tree cover is shown to be virtually unchanged since World War II, but tree density has risen, producing an average annual 1.6 percent increase in forest biomass.
Lead author Pekka Kauppi of the University of Helsinki, Finland, admits that the study does not distinguish between planted, homogenous tree stands and biologically richer old-growth forests.
However, he says, much of the recorded increase involves both natural regeneration and the effects of reforestation programs, particularly in developing nations.
The study notes, for example, that tropical forest in El Salvador expanded more than 20 percent between 1992 and 2001.
Reforestation efforts in China have contributed to a 116-million-acre (47-million-hectare) increase in forest area since the 1970s, the study adds.
Increased human migration from rural to urban areas and higher agricultural yields may also have aided regeneration, the authors say.
Similar factors may have helped in India, where forest cover was found to have increased since 1990.
The team says forest trends in these and other developing countries may be mirroring those seen in the past in industrialized Western nations.
In the U.S., for instance, forests in Massachusetts, Pennsylvania, Ohio, and Illinois have expanded by half since the 19th century.
The authors say factors behind reforestation in North America and Europe range from increased conservation and farming productivity to a decline in newsprint demand following the rise of electronic media.
Whether the transition from deforestation to forest expansion becomes a truly global phenomenon will depend largely on Brazil and Indonesia, where huge areas of tropical forest are still being cleared, Kauppi says.
Indonesia has recorded a 6 percent annual loss in forest biomass between 1990 and 2005.
"But if China and India can do it, why not Brazil and Indonesia?" Kauppi said.
(Read related story: "Indigenous Lands Help Protect Amazon Forests, Study Finds" [February 28, 2006].)
Kauppi also points out that forests act as important carbon sinks, tying up carbon that would otherwise appear in the atmosphere as carbon dioxide, a major greenhouse gas.
He says global forest growth between 1990 and 2000 provided some 0.3 to 0.5 billion tons of extra carbon storage.
"For comparison, that's more than the carbon emissions of Germany," he said.
But conservation groups say the study's findings are overly optimistic.
Mark Aldrich of WWF International's Forests for Life Program says increased wood production from tree plantations may reduce pressures on natural forests.
But he adds that the authors' suggestion that the "end of deforestation is in view" is not supported by other evidence.
Aldrich says the same FAO report on which the new study is based found that 32 million acres (13 million hectares) of forest is lost annually.
"Whilst these losses are countered by an increase in forest growing stock in some countries, these forests do not have the same composition or provide the same variety of functions as natural forests," he said.
Aldrich adds that the European Environment Agency has reported that while the net area of forests in Europe is increasing, the level of biodiversity has shown a dramatic decline.
And where deforestation is fueled by agricultural expansion, such as in Brazil, Aldrich said, "there are few signs of this slowing given the huge and growing demand across the globe for products from palm oil and soy."
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