The tallgrass prairie is an ecosystem native to central North America with fire as its primary periodic 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 more infrequent and soils are less fertile.

The ecosystem

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As the name suggests, the most obvious features of the tallgrass prairie are tall grasses such as big bluestem and indiangrass, which average between 5 and 6 feet (1.5 and 2 m) tall, with occasional stalks as high as 8 or 9 feet (2.5 or 3 m). Prairies also include a large percentage of forbs, such as leadplant, prairie dock, and coneflowers.

The tallgrass prairie biome depends upon prairie fires, a form of wildfire, for its survival and renewal. Tree seedlings and intrusive alien species that do not have the fire-tolerance of deep perennial root-systems are eliminated by periodic fires. Such fires may either be set by humans (for example, Native Americans used fires to drive buffalo and improve hunting, travel, and visibility) or started naturally by lightning. Attempts to re-establish small sections of tallgrass prairie in arboretum fashion were unsuccessful until controlled burns were instituted.

Technically, prairies have less than 5-10% tree cover. A grass-dominated plant community with 10-49% tree cover is a savanna.

Due to accumulation of loess and organic matter, parts of the North American tallgrass prairie had the deepest topsoil ever recorded. After the steel plow was invented by John Deere, this fertile soil became one of America's most important resources. Over 99% of the original tallgrass prairie is now farmland.

Pockets of tallgrass prairie survival

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The primary exception to this rule was in areas unsuited to plowing: the rocky hill country of the Flint Hills, which run north to south through east-central Kansas and the far north portion of Oklahoma. It is there that the tallgrass prairie was maintained by ranchers, who saw the hat-high grass as prime grazing area for cattle. A 39,000 acre (158 km²) Tallgrass Prairie Preserve in Osage County, Oklahoma, and a smaller Tallgrass Prairie National Preserve in Kansas, attempt to maintain this ecosystem in its natural form, and have reintroduced bison to the vast expanses of waving grass. The main range of Tallgrass Prairie in Canada is the 6,000 square kilometre plain in the Red River Valley, southwest of Winnipeg in Manitoba (see map). However only 100 square kilometres of this are publically protected.

There is a small pocket (less than 5 square km) of Tallgrass Prairie in the southwest corner of Windsor, Ontario, protected by Ojibway Park, and Spring Garden ANSI (Area of Natural Scientific Interest), along with the inter-connected parks: Black Oak Heritage Park, Ojibway Prairie Provincial Nature Reserveand the Tallgrass Prairie Heritage Park, all operated by the City of Windsor's Parks and Recreation, aside from the Provincial Nature Reserve.

Tallgrass prairie restoration

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The Midewin National Tallgrass Prairie, founded in 2004 near Elwood, Illinois, was as of 2006 the largest tallgrass prairie restoration area in the United States.

Prairies