Interview with David Montgomery, a geomorphologist - a scientist who studies the forces that shape the landscape. His two books, one on soil and the other on salmon are, he says, "parallel stories of decline linked by the fact that one of the main forces shaping the landscape is you and me." Montgomery is the author of Dirt: The Erosion of Civilizations, in which he argues that conventional agriculture, characterized by mechanization such as plows and tillers, has resulted in mining soil to produce food. Plowing leaves soil bare, he explains, and exposes it to the elements leaving it vulnerable to erosion. Conventional tillage also reduces soil organic matter - the microorganisms and nutrients that make soil productive and fertile. Montgomery warns that soil erosion is now outpacing soil production and this can have dire consequences since it's "an essential resource renewable only at a glacial pace." He's also the author of King of Fish: The Thousand-Year Run of Salmon, a study of the forces that have all but eliminated this magnificent fish from its original habitat in Europe, Britain, and eastern North America.