The tallgrass prairie of the United States and Canada is divided into three ecoregions: the Central, Northern, and Flint Hills tall grasslands. The Central Tall grasslands cover southern Minnesota, most of Iowa, a small section of eastern South Dakota, and extend as a narrow finger through eastern Nebraska and northeastern Kansas. The Central Tall Grasslands are the most mesic of the grasslands of the central plains (Risser et al. 1981). It can be distinguished from other grassland associations by the dominance of tallgrass species–a feature once relatively uniform across its range–and by the highest levels of rainfall (100 cm/yr). The Central Tall Grasslands also has the longest growing season of the ecoregions of the Great Plains. How abundant bison (Bison bison) were is uncertain, but elk (Cervus elaphus) were probably very important to this ecoregion.
The Central Tall Grasslands is separated from the Northern Tall Grasslands by a much higher diversity of species and by the presence of more northerly species in the Northern Tall Grasslands. The Central Tall Grasslands is demarcated from the Flint Hills Tall Grasslands to the south by soil type. The rocky, limestone soils of the Flint Hills made that ecoregion unsuitable for intensive agriculture. The soils of the Central Tall Grasslands presented no such problems to intensive farming and are now virtually converted to corn and soybean production. Historically, fire and drought and grazing by bison and other ungulates were the principle sources of habitat disturbance in this ecoregion.
The Central Tall Grasslands must have been one of the most visually appealing ecoregions of North America in its original state. Before being settled and converted, it was the largest tallgrass prairie on Earth. The large number of brightly flowering herbaceous plants added greatly to the plant diversity as well as to its physical beauty. The dominant grass species in this ecoregion are big bluestem (Andropogon gerardii), switchgrass (Panicum virgatum), and Indian grass (Sorghastrum nutans) (Küchler 1975). The richness of the herbaceous cover is obvious across this ecoregion: about 265 species constitute the bulk of the Tall-Grass Prairie in Iowa; 237 species were recorded in a square mile near Lincoln, Nebraska, and 225 species were recorded from the Missouri Valley (Weaver 1934?). Many of the plant species found here originated from several different regions; having been exposed to a wide range of climates over the long term, they exhibit relatively wide ecological ranges and thus are widespread throughout the Great Plains.
Because the Great Plains grasslands attained their current extent only in the post-glacial period, these associations are characterized by very low endemism in plants and animals. Low endemism is also characteristic of adjacent grassland ecoregions. Like other ecoregions of this section of North America, bison and elk once roamed these tallgrass prairies, where they were hunted by the prairie wolf (Canis lupus). These species are now gone.
Habitat Loss and Degradation
The Central Tall Grasslands is now the corn belt of the United States. Nearly all of this ecoregion has been converted to tilled crop land and the rest is used for haying and pasture.
Remaining Blocks of Intact Habitat
Essentially no sizeable blocks of intact habitat exist in this ecoregion. Remnants of the Central Tall Grasslands in southern Iowa and adjacent Missouri are restricted to 20 patches, all less than 0.08 km2 (20 acres) in size (USDA 1994). The Loess Hills in western Iowa (16 km2) and the Prairie Coteau in eastern South Dakota contain important remnants, although the former is rather linear in shape and grazed by livestock.
Degree of Fragmentation
Fragmentation is high among the few, widely scattered parcels of tallgrass prairie.
Degree of Protection
None of the remaining fragments have any formal protection, although restoration is underway at Walnut Creek National Wildlife Refuge in central Iowa.
Types and Severity of Threats
Because this ecoregion is virtually converted, future threats to the remaining tiny fragments are low.
Suite of Priority Activities to Enhance Biodiversity Conservation
•Working with appropriate agencies, efforts should be made to protect and restore the remaining fragments. This will be an uphill effort in most areas and perhaps futile in others because of the high value of the land for agricultural purposes.
•An example of an appropriate target for this approach would be the Prairie Coteau, which could be restored to an area as large as 162 km2.
•Dr. Clinton Owensby- world authority on the Tall Grass Prairie
•The Nature Conservancy, Iowa Field Office
U.S. Fish and Wildlife Service
Relationship to other classification schemes
Tall-grass prairie is derived from Sims (1988). It corresponds to Küchler (1985) unit no. 66 (Bluestem Prairie), and Omernik (1995) ecoregion 47 (Western Corn Belt plains). The tallgrass prairie defined above corresponds to Bailey (1994) as parts of sections 251B (North Central Glaciated plains Section), 251C (Central Dissected Till plains Section), and 222M (Minnesota and NE Iowa Morainal, Oak Savanna Section).
Prepared by: P. Simms, S. Chaplin, T. Cook, J. Shay, S. Smith, E. Dinerstein, K. Carney