The tallgrass prairie is an ecosystem native to central North America, with fire as its primary perioic disturbance. In the past, tallgrass prairies covered a large portion of the American Midwest, just east of the Great Plains, and portions of the Canadian Prairies. They flourished in areas with rich loess soils and moderate rainfall of around 30 to 35 inches (760 to 890 mm) per year. To the east, where fire was infrequent and periodic blowdown represented the main source of disturbance, beech-maple forests dominated. Shortgrass prairie was typical in the western Great Plains, where rainfall is less frequent and soils are less fertile.