There are no encompassing statistics about how much land is being cleared, but farmers and environmentalists around the region agree that the available figures and anecdotal evidence suggest a significant increase in the amount of dormant land going back into production. There is debate over whether this should be a source of concern.

Craig Cox, the head of the Midwest office of the Environmental Working Group, which has released a report warning about farmland erosion, stressed that the more aggressive farming tactics, like removing trees that act as windbreaks or buffer areas that surround streams, put both land and water at risk.

“It’s really disturbing,” Mr. Cox said. “Farmers are pushing as hard as possible to get every last bushel out of every last acre.”

In Iowa, the nation’s biggest producer of corn and soybeans, farmers insist that they are simply getting more value from their land. Darrell Coddington, a farmer who runs an excavation business, has spent much of the past year clearing additional land in the hilly and wooded southern part of the state, including places that used to be left alone and derided as a “cocklebur farm,” referring to the thorny weed.

While working one overgrown parcel for a neighbor, Mr. Coddington discovered a rusting horse-drawn plow buried beneath a foot of earth, a find that suggested the land had not been farmed in a century. And while expanding his own cropland he decided to tear down the empty family homestead, an action that he described as sad but economically justified.

“Hey,” he said, “it was farm ground before they built it.”

The force pushing more land into production is the rise in crop prices: in the past five years corn prices tripled and those for soybeans doubled because of swelling worldwide demand, including demand for ethanol production. At the same time yields have spiked because of genetically engineered crops and improvements in farming technology, which are also allowing farmers to grow in previously inhospitable areas.