HIGHMORE, S.D. -- Bruce Roseland runs cattle here in the heart of the South Dakota grasslands, in the same place where his great-grandfather ranched more than a hundred years ago. But today, when he looks out his kitchen window, the prairie that once reached from horizon to horizon is gone.

Instead, he sees neat rows of corn marching up to the edge of the blue sky, growing where not too long ago it never grew at all.

"Did we ask the Indians' permission to come out here and destroy their way of life?" said Roseland, who will be the last of the men in his family with the gnarled hands of a rancher. "Well, that's what's happening to us. Except it's technology."

The 10,000-year-old native prairie that once stretched from Saskatchewan to the Gulf of Mexico has become one of the most threatened ecosystems on Earth -- more so even than the world's tropical rain forests, ecologists say. In Minnesota and elsewhere, only about 1 percent of the original prairie now lies untouched, and every year across the Great Plains millions more acres of grasslands are turned into corn, soybeans and other crops.

This hastening transformation is being propelled by a perfect alignment of forces -- rising global demand for food and energy, advances in farm technology and, some say, federal policies that take the risk out of farming marginal lands.

Together, those forces are giving a boost to an otherwise lackluster economy, especially in the rural Midwest.

But conservationists say the country is facing the loss of a national heritage and an irreplaceable ecological resource.

These biologically rich grasslands and wetlands cleanse the water of great river basins, reduce the pace of global warming and support a web of life that includes thousands of unique plants, birds and other animals. In Minnesota, that concern has prompted a coalition of state and conservation leaders to launch an ambitious, $3.5 billion project to restore some of the rare grasslands the state has lost over the last century.

"If we went out there and cut down redwoods in California, we would have people up in arms," said Dave Trauba, who manages a protected state prairie in central Minnesota. "But we lose prairie every day."

Since 2008, the rate of land conversion nationally has exploded.

In just four years, some 37,000 square miles of grasslands, wetlands and shrublands have been converted to row crops, according to the Environmental Working Group (EWG) and the Defenders of Wildlife, which analyzed federal satellite images to document the change.

Minnesota and the Dakotas alone lost an area the size of Connecticut.

Of the Minnesota land that was once tallgrass prairie, only one-fourth is in grasses of any kind today, according to satellite data. And only about 300 square miles, scattered in remnants across the state, remains in its virgin state.

The change, said Scott Faber of the EWG, "is unlike anything we've seen in a generation."

The same transformation is speeding across much of the globe. Temperate grasslands have become one of the most threatened biomes on Earth, disappearing eight times faster than they are being protected, according to a pioneering study published in Ecology Letters, a respected environmental science journal.

The Corn Belt moves west

It's dry in central South Dakota this year, much as it is across North America. But this was always a semi-arid place, a region where people habitually talk about rainfall in fractions of a hundred -- like the "three-hundredths" of an inch that fell on parts of Jim Faulstich's ranch one day in late July.

The rain brought a faint blush of green and a sparkle of wildflowers to his tan pastures and perked up his fat cattle. But the nearby crops were struggling.

As he drove down the straight roads that form a giant checkerboard on the flat land, Faulstich pointed out fields of burnt corn and stunted soybeans rising from the dead grasses.

In recent years, new varieties of genetically modified corn and soybeans have allowed farmers to push the Corn Belt westward, planting row crops on land once better suited to grazing cattle. Today, that tough prairie sod doesn't have to be plowed, just planted. The new corn and soybean seeds are immune to Roundup; farmers can kill the native grasses with the herbicide, then plant right over them.

It's just one of the new technologies that have helped farmers conquer the dense thatches of grass that thwarted the original pioneers. But the climate in central South Dakota is harsh: Roundup killed the grass, but drought is killing the crops.

The natural events -- heavy spring rains and bone-dry summers -- that are a part of life in the Dakotas might have made farmers more cautious, despite the new seed varieties. But today federally subsidized crop insurance often means they get a payoff even when nature doesn't cooperate.

According to one federal study, the 16 South Dakota counties that experienced the greatest loss of grasslands are also the counties most susceptible to drought and crop loss. Farmers in those counties also had twice the insurance payments as the rest of the state.

"The greatest losses of habitat are in those parts of the country where the government is providing the greatest amount of crop insurance," Faber said.

Over the past 15 years, farmers in Minnesota collected some $3 billion in crop insurance payments, according to Faber's organization. Farmers in the Dakotas received considerably more.

A lifelong farmer and rancher who can name all the wildflowers that bloom in his pastures, Faulstich is appalled by what he sees happening around his pastures. But he understands it all too well.

Livestock operators just can't compete against the combined forces of crop insurance and high commodity prices. Around Highmore, they estimate they can make $50 to $100 an acre by grazing cattle; corn is fetching $300 or more per acre this year, regardless of how good the yields are.

"It's hard to argue with it from an economic perspective," Faulstich said.

To the defenders of federal farm programs, however, crop insurance is a vital safety net for farmers and the nation's food system; they say it plays only a minor role in farmers' decisions.

Record commodity prices, new types of seed and agricultural technology are far more influential, said Thomas Zacharias, executive director of National Crop Insurance Services in Kansas City.

"Yes, crop insurance is one of several factors," he said. "But the primary factors are product price, and you do have the progression of new crop technology."

A changing landscape

Those forces already have altered the landscape in Minnesota, where most native prairie disappeared decades ago. Now they are transforming the land around Highmore.

Not too long ago, most of South Dakota was sea of grass that changed colors with the seasons, dotted with the "prairie potholes" that give the region its name -- ponds and wetlands filled with ducks and white egrets. Today, only 60 percent of the state is in grass, according to data from EWG, and in North Dakota it's about half.

Faulstich sees the resulting changes every season. Local roads, he said, sometimes flood. Heavy spring rains, once sequestered by wetlands and deep-rooted prairie plants, instead pour off the cropped fields. Eventually the water, often carrying fertilizer, herbicides and pesticides, makes its way to the Missouri River, then to the Mississippi and eventually to the Gulf of Mexico's "dead zone'' -- an area near the mouth of the great river, now nearly 6,000 square miles in size, which is so polluted that it can no longer sustain most aquatic life.

More corn and soybeans means fewer birds. In the dry summer months, some of the richest soil in the world sometimes blows away on the wind.

These days Faulstich is telling his story in Washington, D.C. This year or next, Congress is expected to take up a new farm bill that could determine the fate of his way of life and, perhaps, the Midwestern prairie.

"If we need more corn and it's a level playing field, that's the way it is," he said. "But if there are incentives to make this happen - that's a disaster in the making."

'We love ethanol'

Brian Hefty, who is reaping the benefits of the new agriculture, sees things differently. He dismisses the arguments for preserving more prairie with a critical question:

"How much do you need?" he asked.

Hefty and his brother, Darren, are third-generation South Dakota farmers. They own 2,500 acres of corn and soybeans near Sioux Falls, and they run a chain of 34 stores that provide farmers in eight states with seeds, chemicals and equipment to drain their fields. Around the company's main office north of Sioux Falls, corn is now as common as it is in Minnesota. A handwritten sign in the window of the gas station down the road reads "We Love Ethanol."

The Hefty Brothers are widely known among Midwestern farmers as the blond and jovial hosts of "Ag Ph.D.,'' a folksy cable TV show where they teach all the latest farming techniques and technology. Their annual farm fests draw hundreds to workshops on topics like patterned tile drainage and navigating wetland protection rules.

In making the case for modern agriculture, Hefty shows a serious side that his TV fans don't always see. He also illuminates the deep philosophical divide between agriculture and conservation. Productive land, he said, is an improvement over land in its natural state.

"Don't tell us what we have to do with our land," he said in an interview. "We are trying to make it better."

True, he acknowledged, South Dakota is "pretty dry" compared to the rest of the Corn Belt. Still, farmers should grow corn here because the new technology and the quality of the soil allow them to grow some of the best corn on Earth.

"There aren't many places better than this," he said.

The latest advances in agriculture are also good for the environment, he said. Roundup Ready corn reduces soil erosion because farmers can plant with less plowing, he said. "Now I can plant seed without massive tillage."

And the new seeds, by generating higher yields per acre, mean less land has to be used to fulfill demand, he said. As a result, Hefty said, the United States has the cleanest water and one of the most productive food systems in the world.

"In a good share of the world, they don't care about the environment," he said. "They want to eat."

The cost

Today, that sort of gruff pragmatism trumps the simple grace of the Dakota prairie, says William Moseley, a Macalester College professor who studies food security and global land use. Compared to the mountains of the west and the northern forests, "it's not a charismatic landscape," he said. "A lot of people aren't motivated to save it."

Nonetheless, he and his peers argue, its environmental value is profound.

First and foremost, say ecologists, is water quality. The deep-rooted native plants and the wetlands act as sponges in the great watersheds that drain into the Missouri, the Minnesota and the Platte rivers. They slow flooding and cleanse water. In the right places, on hills or as buffers between cropped fields and streams, they also act a natural filter for fertilizers, pesticides and herbicides that would otherwise drain into creeks, streams and eventually the mighty Mississippi.

The grassy thickets and pothole ponds also provide a home for hundreds of species of wildlife. Ecologists often refer to the remnant native prairies as "an ark" for the many plants, insects and animals that are native to the Upper Midwest.

The northern plains that include Minnesota, the Dakotas and Canada are called "the duck factory," because nearly half the nation's wetland and grassland birds are born there, and many of those species are in decline. Many other animals are already gone, especially the large creatures like elk, bison and prairie wolves. Now, the smaller ones are at risk as well.

And once native prairie is plowed, it's gone, ecologists say. It takes decades of careful planting and management to restore the complex web of life that includes microbes and tiny insects invisible to the human eye.

"When preserving wildlife, there are thresholds," said Joe Fargione, a prairie specialist with the Nature Conservancy. "You can keep species if you lose half or 70 percent" of an ecosystem. But if you go beyond that, you start to see losses of species. Compared to rain forest habitat, we may be closer to those critical thresholds."

Perhaps least appreciated, however, is the role grasslands play in storing carbon, which, when released into the atmosphere as carbon dioxide, is a major contributor to global warming.

Their vast underground root systems, which can reach depths of eight or nine feet, hold an astonishing one-third of the world's carbon stocks. That's almost as much as the amount stored by forests, according to the World Resources Institute, an environmental think tank. On average, every time an acre of grassland is plowed, it releases 60 tons of carbon dioxide into the atmosphere -- about the amount emitted annually by 30 passenger cars.

Preserving grasslands as a hedge against climate change makes sense, even after considering the environmental benefits of ethanol, said Jason Hill, a University of Minnesota professor who studies grasses and biofuels.

It will take a century before the carbon saved by burning corn ethanol equals the amount unleashed by plowing up the grassland used to produce it in the first place, he said.

Trading grassland for ethanol, Hill argues, "is going in the wrong direction."

A ribbon of prairie

A century after Minnesota lost most of its native prairie, the state and 10 of its leading conservation groups now want to bring some of it back. Last month, they announced a plan to spend $3.5 billion in the next quarter-century to buy or protect 2.2 million acres of grasslands along the state's western edge.

On a map, the area looks like the long-branched root of a Big Bluestem, only this one stretches from Canada to Iowa. It would include what's left of the state's native prairies, connected by ribbons of less bio-diverse grasslands and working pastures. Cattle and other livestock, they hope, can replace the buffalo that once played a vital role in keeping the prairie healthy.

But Dru Tosel shows what the conservationists are up against. He farms about 880 acres around Appleton, Minn., near the Lac qui Parle Wildlife Management area, one of the largest pieces of native prairie left in the state.

Much of the area has remained untouched by modern agriculture because it was viewed as unworkable. Ten thousand years ago, the glacier that molded the Midwestern landscape left behind millions of boulders, some the size of a Volkswagen Bug. But these days, that doesn't stop farmers like Tosel. Last year he bought a parcel of land from an estate, including 55 acres adjacent to the wildlife area that had never been plowed.

On a bright day in August, the former professional wrestler, wearing a Vikings-purple shirt, stood proudly in a monochromatic field of soybeans that reached up to his knees and out to the edge of the road.

"Everything you see in beans was native prairie," he said.

Tosel and his two sons and a son-in-law spent the last year pulling out cottonwood trees and boulders -- they filled 225 semitruck loads of rock that he sold for landscaping in the Twin Cities.

Their sweat equity, he said, has doubled the value of that land.

Nowadays, a lot of farmers own the excavation equipment needed to do that kind of work, Tosel said. And the young men in his family are ambitious. "They want to jump on it with both feet."

Protected areas like the 2,000-acre Lac qui Parle prairie are of no value to his community, Tosel said.

"How much land do they need?" he asked, referring to the few bird watchers and hunters who make use of it.

Appleton was a once-thriving rural town with a flour mill and families on every quarter section. But today many of the farmhouses are abandoned, the main street businesses are struggling, and the recent closing of a privately owned prison took another 350 jobs.

The state's prairie plan will just make it harder for young farmers like his sons to buy land to get started, Tosel said.

"I have to create opportunities for them," he said. "They are going to live here."

It's a familiar story to Pete Bauman, who works on prairie conservation with landowners in Minnesota and the Dakotas for the Nature Conservancy.

"America was founded on one grand idea -- private land ownership," he said. "That you can do what you want with your property."

That can, however, include leaving it in grass. Herb Hamann, an 83-year-old rancher in Clear Lake, S.D., just over the border from Minnesota, took a one-time payment in exchange for a promise to leave his 5,000 acres in grass even after he dies.

"That's the way I want it," he said. "If I ever get to the right place, I want to look down and say that land can't ever be broke."

The state's prairie plan, which the Nature Conservancy helped craft, is designed to leverage that kind of private interests by buying easements from landowners and allowing livestock grazing.

"If we are going to be more proactive about preserving the prairie, we have to do more about addressing opposition in local communities," said Tom Landwehr, Minnesota's commissioner of natural resources.

But time may be running out.

Last month, as Tosel stood at the juncture of his new soybean field, a cornfield and a prairie, he pulled out his phone to check the day's commodity prices. Corn closed at $7.46 a bushel, soybeans at $16.46.

This year he plans to break another 23 acres of native prairie.

Josephine Marcotty • 612-673-7394