New look at world's forests shows many are expanding

For years, environmentalists have been raising the alarm about deforestation. But even as forests continue to shrink in some nations, others grow — and new research suggests the planet may now be nearing the transition to a greater sum of forests.

A new formula to measure forest cover, developed by researchers at The Rockefeller University and the University of Helsinki, in collaboration with scientists in China, Scotland and the U.S., suggests that an increasing number of countries and regions are transitioning from deforestation to afforestation, raising hopes for a turning point for the world as a whole. The novel approach, published this week in the online edition of Proceedings of the National Academy of Sciences, looks beyond simply how much of a nation’s area is covered by trees and considers the volume of timber, biomass and captured carbon within the area. It produces an encouraging picture of Earth’s forest situation and may change the way governments size up their woodland resources in the future.

“Instead of a skinhead Earth, we may enjoy a great restoration of forests in the 21st century,” says study co-author Jesse Ausubel, director of The Rockefeller University’s Program for the Human Environment.

The formula, known as “Forest Identity,” considers both area and the density of trees per hectare to determine the volume of a country’s “growing stock”: trees large enough to be considered timber. Applying the formula to data collected by the United Nations and released last year, the researchers found that, amid widespread concerns about deforestation, growing stock has expanded over the past 15 years in 22 of the world’s 50 countries with most forest cover. In countries where per capita gross domestic product exceeds $4,600 (roughly equal to the GDP of Chile), richer is greener. In about half the most forested countries, biomass and carbon also expanded. Earlier work showed that by the 1980s wooded areas in all major temperate and boreal forests were expanding.

Forest area and biomass are still being lost in such important countries as Brazil and Indonesia but an increasing number of nations show gains. The forests of Earth’s two most populated nations no longer increase atmospheric carbon concentration: China’s forests are expanding; India’s have reached equalibrium.

The researchers found that among the 50 nations studied, forest area in percentage terms shrank fastest from 1990 to 2005 in Nigeria and the Philippines, and expanded fastest in Vietnam, Spain and China. Growing stock fell fastest in Indonesia, Nigeria and the Philippines, and increased fastest in the Ukraine and Spain. In absolute terms, Indonesia and Brazil experienced the greatest losses of both forested square kilometers and cubic meters of growing stock; China and the USA achieved the greatest gains.

“For many years, the Earth has suffered an epidemic of deforestation. Now humans may help spread an epidemic of forest restoration,” says Ausubel.

When forest transition occurs at a global level depends largely on Brazil and Indonesia, where huge areas of tropical forests are rapidly being cut and cleared. Encouragingly, in many other tropical areas forests are regrowing. Studies in Central America show tree cover in El Salvador grew one-quarter from 1992 to 2001. Forests are also recovering fast in the Dominican Republic in harsh contrast to deforested Haiti, on the same Caribbean island.

“The main obstacles to forest transition are fast-growing poor populations who burn wood to cook, sell it for quick cash and clear forest for crops,” says study co-author Pekka E. Kauppi, of the University of Helsinki. “Harvesting biomass for fuel also forestalls the restoration of land to nature. Through paper recycling and a growing reliance on electronic communication, people help the transition by lessening demand for wood products.”

In addition to the measurement of forest area and growing stock, the researchers offer a formula to calculate atmospheric carbon being stored incrementally in the trees of a given area, knowledge critical for mitigating climate change. A rapid forest transition on a global scale would mean that atmospheric carbon dioxide might not rise as fast as many fear.

Proceedings of the National Academy of Sciences Online: November 13, 2006