The tallgrass prairie is an ecosystem native to central North America. Natural and anthropogenic fire as well as grazing by large mammals (primarily bison) were historically agents of periodic disturbance, which regulates tree encroachment, recycles nutrients back to the soil, and catalyzes some seed dispersal and germination processes. Prior to widespread utilization of the steel plow, which enabled conversion to agricultural land use, tallgrass prairies expanded throughout the American Midwest and smaller portions of southern central Canada, from the transitional ecotones out of eastern North American forests, west to a climatic threshold based on precipitation and soils, to the southern reaches of the Flint Hills in Oklahoma, to a transition into forest in Manitoba. They were characteristically found in the central forest-grasslands transition, the central tall grasslands, the upper Midwest forest-savanna transition, and the northern tall grasslands ecoregions. They flourished in areas with rich loess soils and moderate rainfall of around 760 to 890 mm (30 to 35 in) per year. To the east were the fire-maintained eastern savannas. In the northeast, where fire was infrequent and periodic windthrow represented the main source of disturbance, beech-maple forests dominated. In contrast, shortgrass prairie was typical in the western Great Plains, where rainfall is less frequent and soils are less fertile. Due to expansive agricultural land use, very little tallgrass prairie remains.
History of origin and demise
Retreating glaciers deposited the parent material for soil in the form of till, i.e. unsorted sediment, about 10,000 years ago. Wind dropped loess and organic matter accumulated resulting in the deepest level of topsoil recorded anywhere. Animals like buffalo, elk, deer and rabbits added nitrogen to the soil through urine and feces. Prairie dogs, a ground-squirrel-like rodent considered a keystone species, dug tunnels that "aerated the soil and channeled water several feet below the surface." For 5000 to 8000 years, more than 240 million acres of prairie grasslands were a major feature of the landscape. Between 1800 and 1930 the vast majority were destroyed. Settlers transformed what they named "The Great American Desert," or "The Inland Sea," into farmland. Major reasons for the prairie's demise were the confined grazing pattern of European cattle versus bison, the near-extermination of prairie dogs, and the plowing and cultivation of the land, which breached tallgrass root systems and interrupted reproduction. Further, extensive tile drainage has changed the soil's water content and hydrodynamics, and ongoing soil erosion results in its increasing loss.
There are different estimates of how much original tallgrass prairie survives, ranging from less than 1 percent mostly in "scattered remnants found in pioneer cemeteries, restoration projects, along highways and railroad rights-of-way, and on steep bluffs high above rivers" to 4 percent.
Tallgrass prairie is capable of supporting significant biodiversity. Parts of the ecoregion among the "top ten ecoregions for reptiles, birds, butterflies, and tree species. [T]allgrass species are found in the understory layer." Oak (blackjack oak (Quercus marilandica) and post oak (Quercus stellata) ) and hickory tree species occur in some areas but generally in moderate densities. Bison (Bison bison) were a dominant species.
The tallgrass prairie biome depends on prairie fires, a form of wildfire, for its survival and renewal. Tree seedlings and intrusive alien species without fire tolerance are eliminated by periodic fires. Such fires may either be set by humans (for example, Native Americans used fires to drive bison and improve hunting, travel, and visibility) or started naturally by lightning. Researchers' attempts to re-establish small sections of tallgrass prairie in arboretum fashion were unsuccessful until they began to use controlled burns.
As its name suggests, the most obvious features of the tallgrass prairie are tall grasses, such as indiangrass (Sorghastrum nutans), big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), and switchgrass (Panicum virgatum), which average between 1.5 and 2 m (4.9 and 6.6 ft) tall, with occasional stalks as high as 2.5 to 3 m (8.2 to 9.8 ft). Prairies also include a large percentage of forbs, such as lead plant (Amorpha spp.), prairie rosinweed (Silphium terebinthinaceum), and coneflowers.
The tallgrass prairie survives in areas unsuited to ploughing: the rocky hill country of the Flint Hills, which run north to south through east-central Kansas; the eastern fringe of the Red River Valley (Tallgrass Aspen Parkland) in Manitoba and Minnesota; the Coteau des Prairies, which extends from South Dakota through Minnesota and into Iowa; and the far north portion of Oklahoma. In Oklahoma, the tallgrass prairie has been maintained by ranchers, who saw the hat-high grass as prime grazing area for cattle.
The 158 km2 (39,000-acre) Tallgrass Prairie Preserve in Osage County, Oklahoma, and the somewhat smaller 44.1 km2 (10,900-acre) Tallgrass Prairie National Preserve in Kansas, attempt to maintain this ecosystem in its natural form. They have reintroduced Plains Bison to the vast expanses of grass. Other U.S. preserves include Midewin National Tallgrass Prairie in Illinois, Broken Kettle Preserve and Neal Smith National Wildlife Refuge in Iowa, Konza Prairie in Kansas, and Prairie State Park in Missouri. In eastern North Dakota is Sheyenne National Grassland, the only National Grassland on the tallgrass prairie. There are also several small tallgrass prairie reservations in Cook County, Illinois, including the National Natural Landmark, Gensburg-Markham Prairie.
The original extent of tallgrass prairie in Canada was the 6,000 km2 (2,300 sq mi) plain in the Red River Valley, southwest of Winnipeg in Manitoba (see map). While most of Manitoba's tallgrass prairie has been destroyed through cultivation and urban expansion, relatively small areas persist. One of the largest blocks of remaining tallgrass prairie in Manitoba is protected by several conservation partners in a conservation area called the Tallgrass Aspen Parkland. The Manitoba Tall Grass Prairie Preserve, which occupies small portions of the rural municipalities of Stuartburn and Franklin, forms a part of the Tallgrass Aspen Parkland. This preserve contains about 4,000 ha (9,900 acres) of tallgrass prairie, aspen parkland and wetlands.
There is a small pocket (less than 5 km2 or 1,200 acres) 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 Reserve, and the Tallgrass Prairie Heritage Park. Aside from the Provincial Nature Reserve, all are operated by the City of Windsor's Parks and Recreation.
In Minnesota, Glacial Ridge National Wildlife Refuge was established in 2004. The core of the refuge is a preserved 5,000 acres (20 km2) tallgrass prairie remnant, and an additional 30,000 acres (121 km2) are either in the process of restoration or will be soon. According to The Nature Conservancy, so far 100 wetlands have been restored and 8,000 acres (32 km2) of land have been seeded with native plant species.
The Native Prairies Association of Texas was founded in 1986 to locate, restore and protect prairies in Texas. It currently protects about 2780 acres of Texas prairies.
- Buffalo Commons
- List of ecoregions in the United States (EPA)
- List of ecoregions in the United States (WWF)
- Range condition scoring
- Shortgrass prairie
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