A large and growing number of countries are reversing the longstanding trend toward destruction of their forests, a surprising new analysis has found.
"From the new data it seems possible that we could reverse a global trend that many people thought was irreversible," said Pekka Kauppi of the University of Helsinki in Finland, a lead author of the study, which appeared on Tuesday in the Proceedings of the National Academy of Sciences.
The report, by a team of researchers in Europe, the US and Asia, is a ray of hope at a time of ominous environmental warnings about global warming caused by man-made carbon emissions. Forests can act as pollution sinks, easing the emissions' effects to some degree.
The scientists say their study suggests that environmental damage can be reversed with a combination of policy and luck. Twenty years ago most scientists believed that deforestation was an inexorable result of industrialization and that the planet would soon be virtually denuded of trees.
"This is the first time we have documented that many countries have turned the corner, that gradually forests are coming back," said one of the authors, Jesse Ausubel of the Rockefeller University in New York, who added that he personally had expected to live in a "skinhead" earth by 2050.
But some experts reacted with caution to the results. The lack of good data on forests in many parts of the world meant that it was hard to be confident about the study's "positive indications of an important change," said Peter Holmgren, chief of forest resources development at the UN Food and Agriculture Organization in Rome.
He noted that much of the data for the new study was provided by governments themselves, which he says do not do a good job of measuring forests, or was done by aerial surveillance, which is notoriously unreliable.
"There are trends that these guys have observed that seem true, but it's difficult to state for certain," Holmgren said. "Is there a global paradigm change? We really don't know yet."
He called for countries to undertake systematic forest inventories.
The report on Tuesday acknowledges that in a few countries, notably Brazil and Indonesia, the destruction of forests remains a serious and worsening problem. Because of the continuing cutting in those countries, the global trend is still negative.
Yet the researchers, using new analytical techniques, calculated that in the last 15 years, in 22 of the 50 countries with the most forests, they had actually expanded and that many other countries were poised to make the transition from deforestation to reforestation in the coming decades.
The reversal is partly a result of social changes that occur as countries develop and become wealthier, the study said. For example, as rural dwellers move to the cities there are fewer people in the countryside to cut down trees for uses like heating and building.
But in nations like China, India and Turkey the shift also involved a strong measure of public policy, including tree planting campaigns, restrictions on clear-cutting and more efficient agricultural practices, which means that less land needs to be cleared for growing food.
"On a global level, deforestation will be reversed if we maintain this trend, which has involved a lot of different factors: a shift to highly productive agriculture in some places, as well as people like you and me reading newspapers on the Internet so that forest is not destroyed," Ausubel said.