Planting Shrubs Along US Highways Would Sequester up to 7 Million Tons of Carbon

As you watch the miles roll by on family road trips this summer, look just behind the guard rails to see what some scientists believe is a significant untapped resource in the battle against climate change.

The land alongside the 4 million miles of U.S. public roadways, already being maintained by federal, state, and local governments, could be planted with vegetation that helps transfer carbon from the atmosphere into the soil, they say. Road banks and berms, in other words, could be managed as valuable "banks" for carbon sequestration.

"We're talking millions of acres," says biologist Rob Ament, of the Western Transportation Institute at Montana State University, who led a recent study to gauge carbon storage potential on just a fraction of that real estate – roadsides on federal lands.

Shrubs, grasses, and other plants already along roads in U.S. National Parks, wildlife refuges, and other public lands currently are capturing about 7 million metric tons of carbon each year, Ament said in a report on his findings at this month's North American Congress for Conservation Biology in Missoula. That's equivalent to the annual carbon emissions of 5 million cars—without any effort made to optimize the mix of plantings and soil management practices for carbon storage.

Add to that the strips of shrubbery and grass along U.S. highways outside federal lands. A previous study by the Federal Highway Administration concluded such roadside greenery stores enough carbon to counter the annual emissions of 2.6 million passenger cars.

Together, the roadside soils and vegetation on federal lands and along U.S. highways, comprising 10.5 percent of all public roads in the nation, are already capturing nearly 2 percent of total U.S. transportation carbon emissions, said Ament, whose team conducted the research for the Highway Administration's federal lands office.

"There is a significant amount of [carbon capture and sequestration] going on right now, passively," Ament said in an interview. "So the next step is to research active management techniques and take a good hard look at what's possible."

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