Irrigation units prepare to deliver water to farmland in southwest Kansas near Dodge City, Kansas in 2012. (Reuters/Kevin Murphy)

This story has been updated.

The Great Plains lost more grassland to agriculture in 2014 than the Brazilian Amazon lost to deforestation, says a recent report from the World Wildlife Fund. And it argues that the continued expansion of cropland in the region may be threatening birds, pollinators and even drinking water, while releasing millions of tons of carbon dioxide into the atmosphere each year.

The Great Plains region is a vast expanse of land, mostly covered in grassland and prairie, stretching from northern Texas all the way up through Montana and the Dakotas into Canada. For more than a century, the area has been known chiefly for cattle ranching — but in more recent years, millions of acres have also been converted into farmland for crops like wheat, alfalfa, corn and soybeans.

While deforestation and the expansion of agriculture in places like the Amazon Basin are well-known issues around the world, the decline of grassland and prairie ecosystems may be much less publicized, even in North America which is home to one of the “last great extents of temperate grassland on the planet,” according to Martha Kauffman, managing director of the WWF’s Northern Great Plains program.

“To see the losses occurring here is something generally under the radar, something most Americans aren’t aware of,” she said.

The new report, based on data from the U.S. and Canadian governments, suggests that more than 53 million acres of land in the Great Plains have been converted to cropland since 2009. From 2014 to 2015 alone, approximately 3.7 million acres were lost. Currently, just over half the Great Plains — about 366 million acres in total — remain intact, the report claims.

“Those areas can really provide vital services to our nation’s people and wildlife,” said Tyler Lark, a Ph.D candidate at the University of Wisconsin-Madison’s Center for Sustainability and the Global Environment, who was not involved with the new report.  Conversion “has big impacts on water and climate and other ecosystem services.” Lark has previously published research on the expansion of cropland in the United States.

 The two greatest concerns about grassland conversion in the Great Plains involve reduced water quality and increased greenhouse gas emissions, said Kaufmann.

“When that grassland is plowed up, when the root systems and structures are removed, the water-holding capacity of that landscape goes down significantly,” she said. When that happens, excess water runs off and can introduce extra sediment into the streams and rivers where it ends up, she said.

Land-use changes and conversion to farmland is also a known contributor to greenhouse gas emissions, releasing carbon dioxide that was previously stored in the soil and grass. Referencing a report from the U.S. Geological Survey on carbon storage in the Great Plains, the WWF report charges this is another consequence of converting the Great Plains to croplands.

However, the USGS report also notes that, overall, the Great Plains region is considered a carbon sink, meaning it stores more carbon than it emits. That’s not to say the conversion of grasslands isn’t still worrisome from a climate perspective. If emissions from the Great Plains continue to increase, that means that the region may begin to store carbon at lower and lower rates each year. The USGS report predicts the Great Plains will remain an overall carbon sink at least through the year 2050, but if these trends continue decades down the line, the region could eventually reach a tipping point and become a carbon source.

The WWF report also expresses concern about the impact of conversion on natural habitat for pollinators and grassland bird species. In fact, a recent study indicated that corn and soybean cropland has been increasing in some areas of the Great Plains where beekeepers house their honeybee colonies — a potential problem for the keepers, who generally prefer to avoid those types of crops when selecting suitable locations for their apiaries. But it’s unclear whether the expansion of cropland has actually had an impact on the pollination services provided by bees in the area.

Lark said some states have introduced what’s known as a “sodsaver” provision, which essentially reduces the economic and financial incentives for farmers to plow land that hasn’t previously been used for growing crops. The idea is to encourage the preservation of uncultivated land. Since the provision only stands in a few states, though, Lark added that a nationwide sodsaver provision could help slow the loss of natural landscapes in the Great Plains.

 According to Nelson, one additional strategy for preserving the grasslands could be to improve the sustainability of livestock ranching — which typically doesn’t lead to plowing or converting the land — so that ranchers can more readily compete for land. But there’s a balance to be struck there, as well. The raising of livestock, and particularly cattle, is well-known for its high levels of greenhouse gas emissions, include methane, which has a shorter lifespan in the atmosphere than carbon dioxide but is a significantly more potent greenhouse gas.

“[That’s] one of the things we’re looking at, trying to figure out what the trade-off is,” Nelson said.