— Mixed, dense forest in Vesijako, Finland, with exceptionally high forest biomass (Image: Erkki Oksanen, Finnish Forest Research Institute)
Growing stock change between 1990 and 2005; green indicates countries that gained growing stock, red countries lost growing stock, brown experienced no change. There was insufficient data for nations in yellow (Graphic: University of Helsinki)
Contrary to common belief, forests in many nations are expanding not shrinking, say researchers. They say that while the majority of the world's most forested countries are still losing trees, the number that are gaining forests is rising.
However, much of the new forest is cultivated, not natural, leading some experts to caution that planted forests do not support the same level of biodiversity.
The new work assessed the 50 most-forested countries around the world from 1990 to 2005. It reveals that forest area increased in 18 of the 50 nations, while total biomass increased in 22 countries.
There is a trend towards an improvement in forests both in terms of the area they cover and in terms of their condition, says Roger Sedjo of Resources for the Future, an independent institute in Washington DC, US.
Sedjo and colleagues say improved yields in the agriculture mean less land is needed to feed populations, allowing some to be returned to forest.
Richer is greener
The researchers used data from the United Nation's Food and Agriculture Organization to draw up each countrys "forest identity" - the area of land covered by forest, volume of timber, biomass and amount of carbon captured within the countrys forests. Most previous studies of national forests have considered only the area covered.
They defined as "growing stock" the number of trees large enough to be used commercially as timber. Their study showed that among the relatively rich countries surveyed, all had an increasing growing stock. These nations all had a GDP above $4600 per capita, roughly equivalent to that of Chile.
The authors point out that some countries poorer than this appear better able to manage their forests than others, indicating that good forest management is not purely dependent on wealth.
Rather, they suggest that the relatively rich countries studied do not rely so heavily on their forests and also have a degree of political and social order that allows them to better manage their natural resources.
Mark Aldrich of WWFs forest landscape restoration programme says the research is interesting and sound. But he says that although it does show that a considerable amount of agricultural land is being returned to forest, it risks hiding that large extents of natural forest are still being cut down in many countries.
The research by Sedjo and his colleagues show that the two nations that have suffered the greatest losses in area of forest and volume of growing stock are Brazil and Indonesia.
Aldrich points out that natural forests play roles that cultivated forests cannot replace, both in terms of housing a huge amount of biodiversity and in the ways in which they support local human populations.
He also says the problems with the datasets provided by the Food and Agriculture Organization could have flawed the study. The FAO gathers its data from national governments, which do not use standardised definitions to describe their forests.
Journal reference: Proceedings of the National Academy of Sciences (vol 103, p 17574)