By Janet Raloff
The rocks and soil under a tropical forest have a surprising impact on the amount of climate-warming carbon that logging or clearing will release into the atmosphere — and even how likely the trees are to be cut at all, new research shows. Combined with another recent study highlighting the importance of rainforests as a source of new farmland, the study may help predict future forest losses.
Deforestation releases roughly a billion metric tons of carbon dioxide into the atmosphere each year, making it second only to fossil fuel burning in production of this greenhouse gas. In the current millennium, says Holly Gibbs of Stanford University’s Program on Food Security and Environment, global forest clearing has been totaling about 130,000 square kilometers a year. She says that translates into carbon dioxide emissions each year equivalent to the releases from 1.35 billion fossil-fueled cars.
“Rain forests were the primary source for new agricultural land” in the tropics during the 1980s and 1990s, accounting for more than 80 percent of new cropland and ranches, Gibbs and her colleagues report in a paper posted online August 31 in the Proceedings of the National Academy of Sciences. The tree cover lost over those two decades: more than 1 million square kilometers, or an area about the size of Alaska.
In a sense, that’s not surprising, says Gibbs. “Across the temperate world, we’ve already largely converted our available landscape to croplands and pasture. So almost all agricultural expansion since 1980 has been occurring in the tropics.”