Food or forest? Allowing forests to regrow might help restore some of their massive carbon sequestration potential.
FLICKR/ALASKAN DUDE

As policymakers and scientists try to find the best way to pump emissions from coal-fired power plants into deep underground reservoirs, another carbon dioxide sink is already soaking up greenhouse gases and has the potential to soak up much more.

Temperate forests in eastern North America are storing only part of their historic carbon sequestration potential, according to ecologists at McGill University and the University of Wisconsin.

"There's quite a lot of potential for the future," said Jeanine Rhemtulla, a postdoctoral fellow at McGill and lead author of a study published in this week's Proceedings of the National Academy of Sciences.

As North American settlers moved west in the early 19th century, they cleared land for timber and agriculture, producing a third of the net carbon dioxide emissions since 1850, the researchers write. But as farms were abandoned and forests were allowed to regrow, the trees began sequestering more carbon, Rhemtulla said.

"Ecosystems provide all sorts of services, and this is a service that is often overlooked," Rhemtulla said. "It's an invisible thing that's happening with a great benefit that isn't always factored into decision-making."

Rhemtulla, David Mladenoff and Murray Clayton at the University of Wisconsin calculated the amount of carbon that Wisconsin forests stored prior to European settlement – before widespread logging and farming – and compared that with the amount of carbon stored today.

"The biological potential from 150 years ago suggests [these forests] can sequester more carbon," Mladenoff said.

The researchers estimate that sequestration potential in Wisconsin alone is 150 million metric tons – or one-third of the total carbon currently stored in the state's forests. They say Wisconsin could be indicative of the potential of other Eastern forests.

And the ecologists say their estimate is likely on the low end. They calculated historic and modern carbon storage potential in above-ground biomass only. Soils, dead trees and other woody debris scattered on the forest floor were not included in their calculations.

"We see a huge loss also below ground," Rhemtulla said. "Our back-of-the-envelope estimate is there's twice as much potential if we include the below-ground."