The tallgrass prairie exists today only in those areas which are not tillable or have soils not conducive to farming. The original prairie spanned 100 million hectares, but today is represented in large part by the Flint Hills of Kansas and the Osage Hills of Oklahoma.

Location. Originally tallgrass prairie occupied a north-south strip ranging in width from 240 to 960 kilometers, extending through the central part of the United States from the Gulf of Mexico to Canada, mainly west of the Mississippi River. The 99th meridian was its approximate western boundary. The central portion of the True Prairie extended eastward across Illinois.

Altitude. Sea level to 915 meters, but 80% of the area lies below 610 meters. It is a comparatively flat land without prominent topographic features.

Climate. Precipitation averages from 65 to more than 90 centimeters, enough for surface water to penetrate to ground water. That permits the growth of the deep-rooted mid and tall perennial grasses of the typical True Prairie. The area is bounded on the east by 100-cm isohyet and on the west by the 75-cm isohyet. The growing season varies from 120 days in the north to 300 in the south.

Soils. True Prairie soils are mollisols with organic matter and fertility exceptionally high. Many of these soils developed on loess deposits and have soil textures which vary from silt loam to silty clay in the surface horizons. Sandy soils which support tallgrass vegetation, such as the Nebraska Sandhills, are primarily Entisols with little horizonation and have low organic matter and fertility.

Vegetation. The area is dominated primarily by tall grasses and a mixture of forbs. Big bluestem (Andropogon gerardii), indiangrass (Sorghastrum nutans), and switchgrass (Panicum virgatum) are the primary tallgrass species. In areas of adverse moisture stress certain midgrasses are a part of the stand, i.e., little bluestem (Andropogon scoparius), western wheatgrass (Agropyron smithii), and sideoats grama (Bouteloua curtipendula). Much of the area has been invaded by a variety of woody species - roughleaf dogwood (Cornus asperifolia), buckbrush (Symphoricarpos orbiculatus), smooth sumac (Rhus glabra), eastern redcedar (Juniperus virginiana), osageorange (Maclura pomifera) and others. Fire absence has been the primary cause of woody plant invasion. Contrary to popular belief, overgrazing has tended to reduce woody plant invasion. Principal weedy forbs are ironweed (Vernonia baldwini), woolly verbena (Verbena stricta), and curlycup gumweed (Grindelia squarrosa). Areas that have been plowed and allowed to return to grass by natural succession have almost pure stands of prairie threeawn (Aristida oligantha) and in later stages of succession a mixture of prairie threeawn and tall dropseed (Sporobolus asper). Along the western edge of the True Prairie, there is a transition zone where needlegrass (Stipa spartea) and western wheatgrass (Agropyron smithii) are mixed in considerable abundance with the bluestem and with the mid and short grasses.

Vegetation on sandy areas is dominated by tallgrass species also. Sand bluestem (Andropogon hallii), prairie sandreed (Calamovilfa longifolia), and needleandthread (Stipa comata) are the principal grass species there. The native grasslands in the sandhills areas of western Kansas and, to a certain extent, in eastern Colorado and west-central Oklahoma, which were once mid- and tallgrass prairie, have largely been destroyed and their cover now consists mainly of shrubs (sagebrush, etc.) and of weeds and annual grasses. On those sandy regions, the average annual precipitation may be as little as 38 to 50 cm, but as a result of the permeable nature of the soil there is much less runoff, deeper penetration of water, and better water relations in terms of wilting point which affect availability of soil moisture. The deeper moisture penetration permits growth of deeper-rooted grasses. Tall and mid grasses once dominated such areas.

Management. The tallgrass prairie area was used from the mid-1880's to the early-1900's as a transient steer grazing area. Steers from the southwestern United States were trailed to the Flint Hills and Osage Hills (later shipped by railroads) for summer grazing prior to being sold as grass-fat beef (Allred, 1950). Later, yearlings were summered there prior to feedlot feeding in the Midwest. In recent years, cow-calf operations have replaced many of the transient steer operations. At present about half of the area is used for cow-calf, and half for steer grazing. Many cattle are grazed year-round on bluestem pastures with protein supplement supplied during winter months. Energy is supplied for pregnant cows during later winter, usually as sorghum grain. Stocking rates vary with pasture condition and individual variability. The summer grazing period runs from around May 1 to October 1 (earlier starting date in the southern bluestem areas). Cow-calf operations require around 3.3 - 4.1 ha per cow-calf unit year-round. Controlled spring burning to the Flint Hills and Osage Hills is an integral part of management for increased livestock performance and maintenance of a high quality stand of range plants. When woody species amounts become excessive, herbicides are commonly used as an initial control with prescribed burning as the following treatment.