Boffins report that forests worldwide are becoming bigger carbon sinks in a so-called "Great Reversal" after centuries of deforestation and decline.
"With so much bad news available on World Environment Day [5 June] we are pleased to report that, of 68 nations studied, forest area is expanding in 45 and density is also increasing in 45," said Pekka Kauppi of the University of Helsinki. "Changing area and density combined had a positive impact on the carbon stock in 51 countries."
Previous studies on the world's forests have tended to focus solely on forest area, often measured by satellite, but according to the US and European researchers compiling the report this misses out on the fact that in many cases more tree mass is appearing as forests get denser, with taller trees and more of them.
"To speak of carbon, we must look beyond measurements of area and apply forestry methods traditionally used to measure timber volumes,” says forestry expert Paul Waggoner.
"Forests are like cities: they can grow both by spreading and by becoming denser," says Iddo Wernick, another study author.
For example, according to US Forest Service figures, US timberland grew by only 1 per cent over the period 1953 to 2007. But this figure doesn't reflect the true story: the volume of growing stock increased by 51 per cent, and overall national forest density was well up.
Around the world, according to the scientists, "most regions and almost all temperate nations have stopped losing forest ... Europe, like the US, demonstrated substantial density gains, adding carbon well in excess of the estimated carbon absorbed by the larger forested area ... Even in the South American nations studied, more density helped maintain regional carbon levels in the face of deforestation."
Another study author, Jesse Ausubel, says that in fact a "Great Reversal" in the world's forests is under way, as density increases – coupled with small area increases in many nations – now outweigh area losses in such locations as South America. After hundreds of years of decline, the amount of growing wood is now climbing, sucking carbon out of the atmosphere as it does so.
The study authors suggest that not only is the future of the world's forests not as dire as had been thought, but forestry management could seriously cut down on atmospheric carbon.
"In 2004 emissions and removals of carbon dioxide from land use, land-use change and forestry comprised about one-fifth of total emissions. Tempering that fifth by slowing or reversing the loss of carbon in forests would be a worthwhile mitigation. The great role of density means that not only conservation of forest area but also managing denser, healthier forests can mitigate carbon emission," says Aapo Rautiainen of Helsinki uni, lead author of the study.
The new forestry study is published here in the journal PLoS One. ®