Central and Southern mixed grasslands
Hays, Kansas, USA Photograph by The GLOBE Program
ContentsWWF Terrestrial Ecoregions Collection |
The Central and Southern mixed grasslands ecoregion extends over part of central Nebraska, central Kansas, western Oklahoma, and north-central Texas as far south as the Red River Valley in the USA. It separates the tallgrass prairie and the Central forests/grassland transition zone from the Western short grasslands. Essentially, this region is a broad ecotone that covers slightly more than 282,000 square kilometers. It is distinguished from the Northern mixed grasslands by warmer temperatures and a much longer growing season, and from the adjacent tallgrass and short grasslands by the intermediate stature of the grassland layer.
This ecoregion can be distinguished from the Central forests/grassland transition zone to the east by a relative scarcity of tree and shrub cover. The major ecological disturbance regimes are drought, the degree and intensity of grazing by domestic animals and wild ungulates, as well as fire disturbance. Contrary to the conventional conception of this region being comprised by rather level topography, there are some major elements, such as the Red Hills of southern Kansas and northern Oklahoma, which have severe undulation and peaks of up to 744 meters at Mount Nebo. A total of 404 different vertebrate species are found in the Central and Southern mixed grasslands.
Biological Distinctiveness
Black-tailed prairie dog (Cynomys ludovicianus) at Smithsonian National Zoological Park in Washington, D.C., USA. (Source: Joe Ravi via Wikimedia Commons) The mixed grass prairie contains the floristic elements of the tall and short grass prairies and, combined with a rich forb flora, contains the highest floral complexity of any North American grassland ecoregion. Typical grasses include Little Bluestem (Schizachyrium scoparium), Western Wheatgrass, (Elymus smithii), and Sideoats Grama Grass (Bouteloua curtipendula). These species mix with taller grasses in the wetter areas, but give way to shorter grasses in the drier areas (e.g., Bouteloua, Buchloe, Muhlenbergia, and Aristida). The effects of drought cycles and grazing intensity shift floristic composition to favor drought-tolerant species during dry periods and more shallow-rooted mesic loving plants during wetter periods.
The Central and Southern Mixed Grasslands is among the top ten ecoregions in the number of reptile species and is an important breeding area for endemic Great Plains bird species. It also contains very important stopover sites for migratory birds, particularly on wetland sites scattered throughout this ecoregion. The Platte River Valley in Nebraska is a prominent area for the Sandhill Crane (Grus canadensis); moreover, the Cheyenne Bottoms in Kansas is significant for populations of shorebirds during spring migration.
Flora and fauna of the ecoregion
There are 404 taxa of vertebrates occurring in the Central and Southern mixed grasslands.
Amphibians
Of the amphibians that occur in this ecoregion, notable representatives are: the Red-spotted Toad (Anaxyrus punctatus), who inhabits irregular rocky areas as well as grasslands; the American Bullfrog (Lithobates catesbeianus), the largest true frog in North America, and a species who overwinters at pond bottoms; the Rio Grande Frog (Lithobates berlandieri ), who reaches the northern end of its range in the southern part of this ecoregion; the Spotted Chorus Frog (Pseudacris clarkii), a fossorial anuran, whose larvae develop in ephemeral pools or permanent ponds; and Strecker's Chorus Frog (Pseudacris streckeri ), a burrowing frog often found in sand prairies .
Reptiles
A number of reptiles are native to the Central and Southern mixed grasslands, including the Black-tailed Rattlesnake (Crotalus molossus), a snake found in scree and other rocky areas, often stealing animal burrows; the Checkered Garter Snake (Thamnophis marcianus), found in dry grasslands proximate to surface waters; the Collared Lizard (Crotaphytus collaris), often found in rocky or bunchgrass locales; Red-lipped Plateau Lizard (Sceloporus undulatus), a fossorial reptile that may also hide in rock crevices; the
Conservation Status
Habitat Loss and Degradation
Overall, only approximately five percent of the remaining habitat is considered to be intact. During the Dustbowl of the 1930s, basal cover of grasses on even moderately grazed and overgrazed grasslands declined from 80 percent or more to less than ten percent in a span of three to five years, but has since partially regained its cover. Natural vegetation has been converted to cropland or pasture on about 90 percent of this ecoregion in Oklahoma and Texas. In Kansas and Nebraska, about 60 percent is in cropland and about 35 percent is grazed by domesticated livestock.
Remaining Blocks of Intact Habitat
Most of the remaining blocks of intact habitat are quite small. Some of the most prominent include:
- Wichita Mountains Wildlife Refuge, a 90 km2 site for re-establishment of American Bison, and an important area for conservation of the Black-capped Vireo (Vireo atricapilla), southeastern Oklahoma
- Platte River Valley, an important 45 km2 restoration site, a major stopover for migratory Sandhill Cranes in southern Nebraska
- Rainwater Basins, a 45 km2 area managed in part by USFWS (United States Fish and Wildlife Service), which includes a series of clay bottom wetlands that are highly fragmented - southern Nebraska
- Central Kansas wetlands, including Cheyenne Bottoms and Quivira National Wildlife Refuge in central Kansas
- Great Salt Plains in north central Oklahoma
- Red Hills of Oklahoma and Kansas
- Smokey Hills River Breaks of west-central Kansas (45 km2)
Degree of Fragmentation
Much of the ecoregion that occurs in Kansas and Oklahoma exhibts significant fhabitat fragmentation of grasslands associated with farming activities (i.e., unbroken sod). The remaining habitat in the balance of the ecoregion is also severely fragmented.
Degree of Protection
With the exception of a high level of protection in the Wichita Mountains and Salt Plains, remaining habitat in the ecoregion is essentially unprotected. Wichita Mountains Wildlife Refuge, in southwestern Oklahoma, has protected some wildlife habitat since 1901 and is the oldest managed wildlife facility in the USA. Measuring about 59,020 acres (238.8 km2), the Refuge holds a considerable diversity of species; in fact, 806 plant species, 240 species of birds, 36 fish, and 64 reptiles and amphibians are present within the Refuge.
Quivira National Wildlife Refuge saline pond. Source: Creative Commons The Cheyenne Bottoms has been a lake, dry lake or mudflat of variable extent historically. It presently consists of five distinct pools, patternated by dikes, canals, and pathways, that cover most of the extent of the preserve. The pools are typically less than 30 centimeters in depth. Mudflats, ponds and islands lie in the vicinity of the pools. Elevated topography consists primarily of grasslands and scattered trees. The Kansas State and Nature Conservancy lands are managed with the goal of a diverse marsh habitat formigrating and breeding waterfowl as well as shorebirds
The Quivira National Wildlife Refuge in central Kansas consists of approximately 13,000 acres of sand dunes covered with prairie grasses, along with notable saline marshes. The sand prairie has species from both the eastern tallgrass prairie and the western shortgrass prairie or steppe. Around 1500 acres within the Refuge is woodland dominated by Cottonwood, Black locust and Eastern Redcedar trees. A further 1200 acres of Refuge land is under cultivation with winter wheat and milo.
Types and Severity of Threats
The major threat is conversion to agriculture. Elevated wheat prices in the mid 1990s encouraged land conversion in western portions of the ecoregion. Center pivot irrigation has also caused conversion. Water flow into streams due to diversions is another problem. Fire apparently increases forage production in the eastern portion of this ecoregion, makes grasses more palatable, eliminates undesirable annuals, and suppresses the invasion of mesquite, juniper and cacti. Thus, fire suppression constitutes another threat. Overgrazing by domestic stock, particularly in riparian areas, is a localized serious threat.
Suite of Priority Activities to Enhance Biodiversity Conservation
- Management and preservation of wetlands, primarily by seeking to maintain water flows to wetland areas
- Improvement of grazing management to make it more compatible with biodiversity conservation, such as by encouraging rotation grazing and eliminating below market leases to ranchers
- Restoration and enlargement of the best representative areas for biodiversity
Conservation Partners
- Kansas Natural Heritage Inventory
- Natural Resources Conservation Service
- The Nature Conservancy of Nebraska
- U.S. Fish and Wildlife Service - wildlife refuges
- U.S. Forest Service - National Grasslands border this ecoregion
Relationship to Other Classification Schemes
The Central and Southern Mixed Grasslands corresponds to Omernik ecoregion 27 (Central Plains Grasslands) and most of Küchler units 62 (Bluestem-grama prairie) and 76 (Mesquite-buffalograss). It also corresponds to Bailey sections 332E (South Central Great Plains), 311A (Redbed Plains), and 315C (Rolling Plains).
References
- K.C. Benison and R.H. Goldstein. 2001. Evaporites and siliciclastics of the Permian Nippewalla Group of Kansas, USA: a case for non-marine deposition in saline lakes and saline pans. Sedimentology 48(1):165-188.;
- Cletis Eskew (November 1938). The Flowering Plants of the Wichita Mountains Wildlife Refuge. The American Midland Naturalist (American Midland Naturalist, Vol. 20, No. 3) 20 (3): 695–703
- Douglas S. Harvey. 2001.Creating a Sea of Galilee: The Rescue of Cheyenne Bottoms. Kansas History. Spring 2001
- J.M. Hoekstra, Molnar, J. L.; Jennings, M.; Revenga, C.; Spalding, M. D.; Boucher, T. M.; Robertson, J. C.; Heibel, T. J. et al. (2010). Molnar, J. L., ed. The Atlas of Global Conservation: Changes, Challenges, and Opportunities to Make a Difference. University of California Press. ISBN 978-0-520-26256-0
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