Monday, September 04, 2006

Grassland soils save the world from CO2

"A grassland ecosystem can, despite appearances, contain more carbon than a forest ecosystem," writes Fred Pearce in Managing Wholes ( Research by Greg Retallack, a soil scientist at the University of Oregon in Eugene, suggests that soils under grassland played a key role in balancing CO2 in the biosphere. "The emergence of the first grasses was the breakthrough. Grass doesn't hold much CO2 itself, but it can create mollisols, soils that are very rich in organic matter and hence carbon," writes Pearce. He quotes the scientist Retallack: "Typically they are 10 per cent organic matter down to a depth of a metre, whereas forest soils are only that rich down to about 10 centimetres". In the past 40 million years, tall grasslands spread across the globe, invading forest zones. These ecosystems, according to Retallack, took control of the planetary thermostat, lowering CO2 levels. New grazing animals evolved to live on and coexist with the grasses. "The co-evolution of grasses and grazer created a carbon-hungry ecosystem of a kind never before seen," says Retallack. "I think mollisols are saving our skins right now. Without them the world would be a lot hotter."

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