In an effort to offset greenhouse gas emissions and to mitigate climate change, research scientists report that soil in forests can capture and hold a large quantity of atmospheric carbon dioxide.

Reforesting lands that have lost their forest cover due to cultivation, clear-cutting or fire could sequester two petagrams – or two billion metric tons – of carbon in soils in a century, which is about 10 percent of total U.S. forest carbon sequestration, said Cornell doctoral candidate Kathryn Hofmeister, a co-author on University of Michigan-led research published in the Proceedings of the National Academies of Science (PNAS), Feb. 26.

The study examined the potential to expand the soil carbon sequestration in reforested areas.

“The ability of U.S. forestlands to offset our emissions of greenhouse gases, including carbon dioxide, is decreasing,” said Hofmeister, who conducts research in natural resources and hydrology. “This is partly due to a backlog in reforestation projects on public lands that has been increasing for several decades.

“Nationwide, since 2000, less than 10 percent of forests are replanted after disturbances that eliminate forest cover. Reforestation would increase the soil carbon sink and go a long way to mitigating climate change.”

Hofmeister conducted the study’s geographic information systems and mapping work, processing satellite imagery with on-the-ground measurements of topsoil carbon from databases, including U.S. Forest Service spatial data.

Reforesting U.S. topsoils could sequester 1.3 to 2.1 billion metric tons of carbon, accounting for nearly half of the soil carbon sequestration occurring in U.S. forests, according to lead author Luke Nave, of the University of Michigan. Stored carbon could increase dramatically if the reforested area – currently at 200,000 square miles – were to be expanded with further planting, he said.

Sequestering carbon should be a strong component in fighting climate change, according to Hofmeister. “And, unlike other biospheric sinks, such as trees themselves – which can burn up in fires – soil carbon is quite stable,” she said.

For the PNAS study, “Reforestation Can Sequester Two Petagrams of Carbon in U.S. Topsoils in a Century,” Hofmeister was supported by a National Science Foundation grant to Cornell. The U.S. Department of Agriculture-Forest Service and the National Science Foundation funded the research.