The tallgrass prairie makes up the eastern portion of the North American Great Plains. It extends north and south from Manitoba to Texas in a fairly narrow band between the eastern deciduous forests to the east and the mixed grass prairie to the west. It passes through the eastern Dakotas, Nebraska, Kansas, and Oklahoma, forming a prairie peninsula that extends east into Minnesota and Iowa.
Historically, the tallgrass prairie occupied approximately 150 million acres (60 million hectares or 230,000sq mi). However, conversion to other land uses has made this grassland a globally endangered resource. Estimates of remaining tallgrass prairie range from 1% to 18% of its former distribution. The overall extent of all remnants is unknown because it is mostly scattered in relatively small tracts. The Flint Hills in Oklahoma and Kansas (3.8 million acres) is the only expansive and intact remnant of this grassland.
The tallgrass prairie experiences a continental subhumid, mesic, and temperate climate and possesses an east-west precipitation gradient and north-south temperature gradient. It is characterized by distinct dry and wet seasons, and temperature and precipitation extremes. The temperature extremes range from -35°C to 45°C with an average of 270 growing days. Average precipitation shifts from 50 cm in the northwest to 100 cm in the southeast but overall, the area is typified by low and irregular precipitation with periodic drought.
Topography and Soils
The tallgrass prairie has relatively level topography but relief is present in the form of scattered rolling hills, breaks, salt plains, low mountains, gypsum buttes, sandy flats and sand dunes; the north tends to be less flat than the south. The Flint/Osage Hills region in Oklahoma and Kansas possess rolling, sloping plains, low hills, and cuestas underlain with sandstone and limestone rock. A unique feature also dots across portions of the southern tallgrass prairie called mima mounds; they may also be termed “pimple mounds” or “prairie mounds”. They occur in the states of Oklahoma, Texas, Kansas, Arkansas, Missouri, and Louisiana on both flat and sloping topography.
Large rivers of the tallgrass prairie have seasonal high flows in late spring/early summer following spring runoff and much lower flows in late summer/early autumn. This flow fluctuation allows development of a mosaic of ephemeral habitats such as sandbars. The major rivers include the Red River, Missouri River, Arkansas River, and Mississippi River.
Prairie soils tend to be deep, fertile, dark, and mostly free of rocks for high crop productivity. Coloring ranges from black in more mesic areas to browner in semiarid areas. A yard square of tallgrass soil to a depth of 51 cm contains more than 110,000 arthropods and 5.4 million nematodes. Some areas have shallow and stony soils which protected them from plowing. These include the Flint/Osage Hills in Kansas and Oklahoma and the Prairie Coteau in northeast South Dakota.
Current Plant Communities
The tallgrass prairie has undergone great changes since the late 1800s. Most of the tallgrass prairie is cultivated and a large portion has been converted to tame pasture and rangeland for livestock.
Continuous grazing, fire suppression, and encroachment led to landscape changes such as increased woody plant cover, increases in exotic species, and decreases in the bounty of forbs. The Flint Hills remain an exception in one area: they did not have recent fire suppression or exclusion. Instead, the area underwent a change in fire frequency due to a change in primary function, from Native Americans’ habitat to cattle production.
Erosion and crop production caused soil fertility to decline. Plowing, erosion, and development have decreased the amount of prairie wetlands. Moreover, the modification of hydrology with reservoirs and/or navigation channels has changed flow rates and flood events to diminish ephemeral prairie wetland habitats such as sandbars. Streams suffer from increasing stream channel incision and some areas of the tallgrass prairie have been inundated by water due to reservoir projects on the Arkansas, Cimarron, Canadian and other rivers.
Remaining areas of the tallgrass prairie exist due to topography or soils unsuitable for farming. The Flint/Osage Hills were never plowed for crop production and are used as prime grazing land. The Nebraska sandhills and the prairie coteau in northeast South Dakota are some of the largest remaining tallgrass prairie tracts. The exact extent of remnants is unknown because the fragments are mostly scattered and relatively small. This results in management of small units to create a simpler landscape mosaic than was once present.
Historic Plant Communities
The tallgrass prairie contains over 500 species of plants, of which 95 % are perennials. The majority of the canopy is less than 1 m tall. As productive as the tallgrass prairie appears on the surface, approximately 85% of vegetative biomass and 60% of net primary productivity actually occurs belowground.
The plant community is dominated by the “four horsemen of the prairie”: big bluestem (Andropogon gerardii), switchgrass (Panicum virgatum), indiangrass (Sorghastrum nutans), and little bluestem (Shizachyrium scoparium). Little bluestem dominates uplands and big bluestem lowlands. Together, these two species comprise 80% by weight of tallgrass prairie composition. Other grasses include saltgrass (Distichlis spicata), eastern gamagrass (Tripsacum dactyloides), western wheatgrass (Agropyron smithii), and blue grama (Bouteloua gracilis).
While 80 to 90% of the biomass is grasses, forbs outnumber graminoids three to four times. The remaining 10-20% of biomass consists of forbs, but also woody species, succulents, lichens, and sedges as minor components. Common species of forbs and shrubs include annual sunflower (Helianthus annuus), leadplant (Amorpha canescens), scurfpea (Psoralea spp.), purple coneflower (Echinacea atrorubens), milk vetch (Astragalus spp.), fringed sagewort (Artemisia frigida), prickly pear (Opuntia spp.), and heath aster (Aster ericoides).
Woody species are a main component along waterways and other areas protected from fire. Common woody species in the tallgrass prairie include eastern redcedar (Juniperus virginiana), buckbrush (Symphoricarpos orbiculatus), bur oak (Quercus macrocarpa), smooth sumac (Rhus glabra), rough-leaf dogwood (Cornus drummondii), American elm (Ulmus Americana), common hackberry (Celtis occidentalis) and eastern redbud (Cercis canadensis). Wetland communities in the prairie go by many names, such as playas, prairie potholes, sloughs, bottoms, river flats, sandhill lakes, desert sinks, thermal seeps, rainwater basins, and gilgais.
The tallgrass prairie supports a wide variety of species containing around 150 species of birds, 30 reptiles and amphibians, and 31 mammals. Large herbivores include pronghorn antelope (Antilocapra Americana) which is locally extirpated, elk (Cervus canadensis ) which is locally extirpated, white-tailed deer (Odocoileus virginianus), and American bison (Bos bison). Other mammals include the prairie dog, Cynomys spp.; black-footed ferret (Mustela nigripes, endangered), white-tailed jackrabbit (Lepus townsendii), red fox (Vulpes vulpes), North American badger (Taxidea taxus), black bear (Ursus americanus), and mountain lion (Puma concolor).
Insects, reptile, amphibians, and fish include the monarch butterfly (Danaus plexiippus), American burying beetle (Nicrophorus americanus) (endangered), prairie mole cricket (Gryllotalpa major, endemic), bullsnake (Pituophis catenifer sayi), great plains toad (Bufo cagnatus), Texas horned lizard (Phrynosoma cornutum), alligator gar (Atractosteus spatula), and paddlefish (Polyodon spathula). Birds include the greater prairie chicken (Tympanuchus cupido), burrowing owl (Athene cunicularia), killdeer (Charadrius vociferous), red-tailed hawk (Buteo jamaicensis) and least tern (Sternula antillarum).
The formation of Great Plains grasslands began five to seven million years ago in the Miocene-Pliocene transition, with periods of forest/woodland/tundra/ice dominance depending upon climatic cycles and glacial/interglacial periods. The previous vegetation consisted of temperate and tropical forests that declined due to drier climate and colder temperatures. The Great Plains date back to the retreat of the last Wisconsin glaciers approximately 10,000 years ago. The current grassland biome formed 3000 to 4000 years ago. In the last 1500 years, the climate has been cooler and wetter, producing the current soils and vegetation. Many of these areas were revegetated back to rangeland in the 1940s and 50s following the Dust Bowl of the 1930s. Some were plowed again in the 1980s. Long-term negative effects on the prairie promote increased plant species, less palatable plant species, and invasive species.
Yearly and Seasonal Variation
Climate variability plays a major role in the tallgrass prairie in term of vegetation dynamics. Precipitation is especially responsible for ecotonal shifts. Periodic drought in the summer favors grass species and increases the mortality of woody saplings. Wetter periods promote forbs, woody species, and taller grasses. Overgrazing can reverse this by switching vegetation structure from tall perennial grasses to short perennial and annual grasses and forbs.
In addition, the fire regime varies among and within years due to climatic conditions and vegetation as well as to current and past fire policies. The trend of fire suppression has caused long-term changes on the vegetation structure. The lack of fire has allowed the encroachment of Eastern redcedar and non-natives.
Man-caused fire has shaped and allowed the tallgrass prairie to persist. Historically, fires burned across vast distances at frequencies of 3-10 years in level prairies and of 10-20 years in prairies cut by breaks and streams. European settlement and suppression of fire has accelerated plant succession from native prairie vegetation to shrublands/woodlands. Grassland fires are now limited by cultivated lands, roads, and fire fighters (see a wildfire in action).
Fire offers many benefits. It suppresses tree and shrub encroachment and restricts woody species to riparian and other protected areas, reduces competition from cool-season invaders, and improves the palatability and nutritional value of the grazable forage. Late spring burns benefit major tallgrasses; forbs might be impaired in amount of growth but overall forb diversity is not affected.
Historically, the tallgrass prairie was grazed by large herds of bison, antelope, deer, and elk along with colonies of prairie dogs. Except for prairie dogs, these species were migratory, continuously searching for green forage and responding to environmental variables such as precipitation, drought, and fire. This resulted in rotational grazing that allowed vegetation to recover in the absence of the herbivores; it also caused repetitive seasonal grazing pressures which the vegetation adapted to in the process of natural selection. Bison grazing increases plant species diversity.
Bison, deer, and prairie dogs still graze in some areas of the tallgrass prairie; however, livestock grazing is a primary use today. Palatable plants are selected first by grazers and are continually pressured. Different grazing strategies can alter the plant species composition and/or promote heterogeneity of the landscape. Improper grazing management techniques alter the plant communities and historical fire patterns; they can be disproportionately harmful to riparian areas. Short-term light grazing increases, and long-term heavy grazing decreases, plant productivity. Ideally (from an ecological view), proper grazing will create heterogeneity by transferring nutrients, reducing litter in grazed areas, and increasing the rate of nutrient cycling.
Periodic drought is a natural occurrence in the tallgrass prairie, and historically periodic drought and fire promoted grasslands. (Drought is common in Desert Shrublands also). Drought temporarily reduces vegetative productivity but can that quickly recover with onset of precipitation. However, grass survival is closely related to stocking rate; drought typically does not negatively affect tallgrass prairie, as long as grazing management is adjusted for the current climate. As one can see with the grazing example, other disturbances are more severe during drought. Furthermore, prolonged drought can cause shifts in species ranges, non-native invasion, and habitat degradation.
Mowing did not exist prior to European settlement, but now it is a common practice. It can benefit the prairie by controlling encroachment by woody species and removing litter but it also reduces heterogeneity. The effects of mowing vary depending upon the season; for example summer mowing promotes C3 species while spring mowing promotes C4 species. Long-term summer mowing lowers vegetative productivity whereas occasional spring mowing will increase productivity.
The tallgrass prairie experiences seasonal summer flooding following large thunderstorm events. Currently, these events have become exacerbated by land-use changes that increase flashiness of runoff.
The lack of fire in the tallgrass prairie results in some dramatic vegetation changes. It promotes woody encroachment and exotic invasions causing detrimental alterations to habitat for wildlife. Prescribed fire is a useful management tool for implementing a fire regime on a landscape (Figure E-1). It offers a lower cost option to wide variety of land management issues. However, it does come with some management concerns such as the public’s fear of fire, the challenge of smoke management, and complex liability issues. Benefits of appropriately and wisely used prescribed fires include enhanced biodiversity, suppressed woody encroachment, protection against catastrophic wildfires, improved forage for livestock, increased soil fertility, and improved wildlife habitat. Fire suppression has allowed encroachment of woody plants and buildup of fuel that increase the intensity and danger of wildfires. Drought increases wildfire prevalence throughout the tallgrass prairie.
Particularly worrisome invasive species of the tallgrass prairie include Japanese honeysuckle (Lonicera japonica); glossy privet (Ligustrum lucidum); Chinese privet (Ligustrum sinense); giant reed (Arundo donax); Chinese wisteria (Wisteria sinensis); lilac chaste tree (Vitex agnus-castus); Brazilian vervain (Verbena brasiliensis); guineagrass (Urochloa maxima); common periwinkle (Vinca minor); chinaberry tree (Melia azerdarach); Chinese tallow tree (Triadica sebifera); and Johnson grass (Sorghum halepense).
Endangered species, such as the black-footed ferret present their own problems. They are very expensive, and there is a lack of public acceptance in the Great Plains region of the Endangered Species Act and measures to ensure the survival of endangered species. This creates a high potential for conflict among stakeholders
Pollution from agriculture, confined feeding operations, oil development, and other sources impairs water quality. Reservoirs, channelization, impoundments, and withdrawal threaten flow regimes and riparian habitats. Riparian areas are degraded by grazing livestock. Accelerated rates of erosion result from a variety of current land management practices including cultivation and overgrazing.
The tallgrass prairie has been fragmented by cultivation and a myriad of land management practices. Although cultivation only uses 42% of the Great Plains as a whole, it fragments 100% of the landscape. Fragmentation reduces habitat quality and quantity, impedes the fire regime, is severely detrimental to biodiversity, and makes implementing the necessary disturbance regimes difficult or impossible.
Grazing Management Practices
Forage Sources and Seasonal Use
Seasonal forage sources come from winter cereals, native grass meadows and tame pastures planted to grasses like fescue and brome.
Cattle grazing is the dominant use of the remaining tallgrass prairie, but bison still graze in some areas. Stocker operations, seeking rapid weight gains, commonly occupy the gentler terrain and better pastures. Cow-calf operations typically are on rougher, less nutritious pastures.
The tallgrass prairie is grazed with many different strategies. Continuous grazing with a light to moderate stocking rate exhibits the best individual animal performance compared to specialized systems. It also provides ecological benefits by creating and a moderate level of habitat diversity and the necessary habitat structure and composition for wildlife species. Rotational grazing involves cross-fencing areas and moving cattle from pasture to pasture; this reduces the structural composition of the range. It is costly in terms of fencing but gives better results than season-long grazing. Intensive early stocking is a variation of season-long grazing that doubles the stocking rate and halves the grazing time. It gives best results with yearling cattle, commonly involves annual spring burn, is economical, and results in a homogeneous landscape.
Patch-burn grazing utilizes fire to manipulate livestock grazing areas and mimics historical grazing pattern. Benefits of patch-burn management include creation of a mosaic of sites with different burn histories, heterogeneity across the landscape, and increased soil nitrogen. It can be combined with other systems such as continuous grazing or intensive early stocking.
Toxic plants of the tallgrass prairie include poison hemlock (Conium maculatum); white snakeroot (Eupatorium rugosum); locoweed (Oxytropis lamertii); milkweed (Asclepias spp. ); water hemlock (Cicuta spp. ); and white larkspur (Delphinium carolinianum). Water hemlock is one of the most poisonous plants in North America.
Herbicides, seeding and fertilization have been used to increase grass production. Improved pastures have been developed using tall fescue and other improved pasture species.
Cultivation is widespread in the tallgrass prairie. Crops include food crops, such as peanuts, soybeans, corn, potatoes, sugar beets, and wheat. Cotton is grown for its fiber and annual cereals are grown for forage.
Fragmentation into small tracts makes restoring true ecological function to the tallgrass prairie. The four greatest threats to restoration attempts are invasive species, altered fire regimes coupled with woody encroachment, altered water flow, and development and/or fragmentation. Restoration efforts are impeded by economics and native seed availability. There still is not enough knowledge to predict responses on long time scales or overall restoration project success.
Homesteading and farming and ranching are part of the history of the Great Plains. Due to scarce wood resources, settlers employed the use of abundant limestone rock layers in the Flint Hills region for building. Although much of the area was successfully cultivated, it is only in rocky uplands where attempts to plowed failed. The oil and gas industry has been a major activity and source of pollution for over 80 years.
Oklahoma oil well (woodleywonderworks)