An all-out effort to reforest land across the United States could plant trees on another 133 million acres to help soak up carbon dioxide and limit global climate change.

That was the finding of a report released Tuesday by The Nature Conservancy that found up to 68 billion trees could be planted on those acres to capture 333 million tons of carbon dioxide per year, the equivalent to removing 72 million cars from the road.

The report found Minnesota could add another 3.6 million acres of trees to its landscape with 3.1 million more acres possible in Wisconsin. Even farm states like Iowa, with 1.9 million acres of potential new forest, and North Dakota at 68,000 acres, could contribute to the effort to keep carbon locked up so it doesn’t go into the atmosphere where it creates the greenhouse effect by trapping heat near the Earth.

Trees utilize carbon dioxide to grow and can store it in wood, roots, leaves and nearby soil. Carbon dioxide from human-caused sources — such as vehicle engines and coal-fired powerplants — is widely considered the leading cause of global climate change that is raising temperatures, spurring changes in precipitation and storm patterns and melting ice worldwide, raising ocean levels and causing flooding.

Nationally, the study found planting trees on former livestock pasture lands — most of which were previously forested — could add 65.5 million acres of trees, the largest category, while planting trees in now-open urban areas could add another nearly 19 million acres.

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In Minnesota, the study found that farm pastures — many of them no longer used for livestock grazing — could contribute more than 2 million acres for new forest, while open, mostly treeless urban areas could add another 638,000 acres. Planting trees along flood plains could add more than 500,000 acres of trees in Minnesota, with another 473,000 acres added by planting trees as streamside buffer zones that also would improve water quality.

“Planting trees to restore forests where it makes good economic and ecological sense is a powerful natural solution to global warming,” said Meredith Cornett, the Duluth-based director of conservation science for The Nature Conservancy in Minnesota, in a statement. “But prior to this analysis, there was no quick and easy way to figure out where exactly we might put all those new trees.”

A pine tree seedling is planted.  A new study by The Nature Conservancy found that 68 billion new trees could be planted across the country to slow climate change. But, currently, only 1.3 billion trees are planted each year in the U.S. (Photo courtesy of The Nature Conservancy)
A pine tree seedling is planted. A new study by The Nature Conservancy found that 68 billion new trees could be planted across the country to slow climate change. But, currently, only 1.3 billion trees are planted each year in the U.S. (Photo courtesy of The Nature Conservancy)

Cornett said the study is a guide of potential areas to look at and doesn't presume that trees should be planted on all open areas, such as active croplands or even native prairie or restored grasslands which, when left undisturbed, also capture and hold carbon dioxide.

In Wisconsin, the study also found former pasture land as the largest opportunity for tree planting at 1.7 million acres followed by marginal farmland, of which 468,000 acres could be converted to trees.

The study found that an additional 158,000 acres of land in St. Louis County could be planted with the potential to absorb 209,000 tons of carbon dioxide annually while Douglas County, Wisconsin, could add another nearly 50,000 acres of trees to soak up 70,000 tons of carbon dioxide.

So far the potential outpaces the supply of tree seedlings. While there's space for 68 billion new trees nationwide, only about 1.3 billion are planted each year.

The Minnesota Department of Natural Resources wants to increase the number of seedlings it produces each year to more than 10 million. But to reforest 1 million acres, less than one-third of the state's potential, Minnesota would need about 1 billion seedlings.

Efforts are underway to find ways to produce more seedlings. The University of Minnesota Duluth and Northeast Regional Sustainable Development Partnership are working with local farmers to establish a growers network that could help address the seedling shortfall. With start-up funding from the Institute on the Environment’s Impact Goal program, the Forest Assisted Migration Project, was initiated to help build a regional market for climate-adapted seedlings that will thrive under already warming conditions.

Foresters, land managers and others can find The Nature Conservancy mapping tool at reforestationhub.org.