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Managing the nation’s landscapes with carbon in mind — from prairies to farms to urban and northern forests — could cut greenhouse gas emissions as much as 21 percent annually, or about equal to the discharge of all cars and trucks on the road today.

And Minnesota is among the states that could do the most: It ranks 8th overall, with the potential to reduce its net carbon emissions by up to a third, according to a study published Wednesday in the journal Science Advances.

The strategy won’t solve climate change on its own, said the lead author, Joe Fargione, an ecologist with The Nature Conservancy in Minneapolis. But the study, which measured 21 specific practices, illustrates that such “natural climate solutions” have enormous potential.

“It reduces the risk of catastrophic climate change, which is going to be hard to do from the energy sector alone,” he said.

Moreover, they are all changes that can be adopted by individual landowners, homeowners and farmers, or by local and state governments, while providing the added benefits of cleaner water and air and healthier soils, said Bonnie Keeler, a University of Minnesota ­professor who studies the social value of nature.

“This is not a radical shift in behavior,” Keeler said. “It’s good land management.”

But the shift would come at a steep price for some, at least in the short run. For example, a significant portion of the benefit in Minnesota would come from planting cover crops, which protect bare soil from erosion, consume excess nitrogen and pull carbon from the air. But that’s something farmers would have to choose to do. And while use of cover crops such as rye is on the rise, especially to reduce runoff and fertilizer contamination of water, it’s a steep climb, said Paul Porter, a U agronomy professor.

Farmers “are not going to do this on vast acreages,” at least in the near term, he said. For that to change, he said, “it has to be economical” for farmers, and right now it’s not.

The study examined what contributions natural climate solutions could make in achieving the U.S. carbon reduction goals established by the Paris climate accord — emissions that are 26 to 28 percent below 2005 levels by the year 2025.

The authors, 36 researchers from 22 conservation and academic institutions, then estimated the amount of carbon that would be sequestered by 21 different land management practices without reducing the production of food and fiber. The practices included replanting forests, better management of nitrogen and manure, planting cover crops, extending the life of trees before harvesting them for timber, and restoring low-quality croplands to wetlands and prairies.

At most, under one scenario, the country could reduce carbon by 21 percent of the net emissions it produced in 2016. The vast majority would come from reforesting land, for example, that has been lost to urban sprawl, primarily in the northeast and south central regions of the country. That would exclude productive farmland.

“We want to conserve good farmland,” Fargione said.

Extending harvest cycles on privately held timber lands would also provide a significant benefit.

Tree stewards

In Minnesota, adopting 11 of the practices could reduce 33.75 percent of the 80 million net tons of carbon the state produces each year. An estimated 50 million tons is already held in the land, primarily in the soils, grasses and forests that make up its primary ecosystems.

“The single biggest thing we need to do is not convert forest to non-forest use,” said John Rajala, who manages a family­-owned timber and milling company in Deer River, Minn. “Second is to promote long-lived species on as many sites as possible.”

Rajala Cos. has been managing its 20,000 acres of timber land with those goals in mind for years. It plants long-lived, harvestable species such as white pine, but also those that will prevail in the warmer and wetter decades to come.

Rajala’s company makes durable construction materials and cabinets that can last for decades, rather than short-lived consumer products that contribute to climate change as soon as they get tossed — “so we stop this cycle of throwaway consumerism,” he said.

“The products we make are almost as important as the way we manage the forest,” Rajala said.

Managing public forest lands, however, can be more complicated. Craig Schmid, deputy director of forestry for the Minnesota Department of Natural Resources, said managers do consider what species to plant to ensure a viable future for its 5.6 million acres of forests. And the DNR has recently formed a climate change advisory group. But it does not manage timber harvests for longevity and carbon sequestration, he said. Rather, harvests are driven in part by the needs of Minnesota’s forest industry, which depends on younger trees.

Some conservation groups have been critical of the DNR’s recent forest management plan, saying it did not do enough to consider the implications of climate change.

“It was a huge missed opportunity,” said Don Arnosti, executive director of the Izaak Walton League in Minnesota.

Many of the cost barriers could be addressed with a global carbon market, Fargione said, one that would provide farmers and timber companies with financial credits for practices that sequester it.

“If you were paying for them in the price of carbon, [the measures] would be cost-effective,” he said.

Josephine Marcotty • 612-673-7394