STARKVILLE, Miss.—Over the past hundred years, the George family’s farm has been sharecropped, grazed by cattle and planted with cotton. By the late 1980s, Clayton George was growing soybeans and struggling to make ends meet.

A new federal program offered farmers money to reforest depleted land. Pine trees appealed to Mr. George. He bought loblolly seedlings and pulled his pickup into a parking lot where hands-for-hire congregated.

“We...