ABSTRACT
Forest, field, and urban patchworks of the Northeast give way west of the Appalachian Mountains to lowland agricultural fields and large, meandering rivers that drain the midcontinent. Westward beyond the Mississippi River, the green hazy flatness of this lowland gradually but noticeably becomes the beige and brown Great Plains, a semiarid land broken by telltale signs of irrigated agriculture. In the American Southwest beyond the southern Rocky Mountains, aridity claims the land almost fully and its character remains clear in rugged canyons and plateaus, mountains and dry basins. The humid and subhumid Central Lowland extends eastward from the 100th meridian across the Mississippi River to the Appalachian Mountains. Climate is a primary environmental system that has influenced the distribution and diversity of life on land. The Great Plains were largely settled in the late 1800s through the turn of the century aided by federal policies that enabled the transfer of public lands into private ownership.
