Of the 2.8 million km2 (1.1 million sq mi) of North American grasslands, about 22% of it is shortgrass prairie. The shortgrass prairie is located between the Rocky Mountains and the mixed-grass prairie. It stretches from central Alberta to central Texas, passing through southeast Wyoming and eastern Colorado to the panhandle of Nebraska and west Kansas through the high plains in Oklahoma, Texas, and northern New Mexico. It is not possible to delineate precise boundaries due to dynamic and shifting plant communities.
At 2.8 million km2 (1.1 million sq mi), grasslands are the largest vegetation formation in North America. About 22% of the grassland is shortgrass prairie. The shortgrass prairie is located between the Rocky Mountains and the mixed-grass prairie. It stretches from central Alberta to central Texas passing through southeast Wyoming and eastern Colorado to the panhandle of Nebraska and west Kansas through the high plains in Oklahoma, Texas, and northern New Mexico. It is not possible to delineate precise boundaries due to dynamic and shifting plant communities.
CLIMATE
The shortgrass prairie occurs in a semiarid climatic zone. It is the driest and warmest of the Great Plains grasslands, with cool winters and warm summers. Average precipitation is around 375 mm (15 in) ranging from 300 mm (12 in) in the north to 600 mm (24 in) in the south. Precipitation occurs in episodes so that a few precipitation events produce the majority of precipitation, with 2/3 of the precipitation occurring during the growing season. The mean temperature is 9°C (48°F) in the north and 16°C (61°F) in the south. Minimum temperatures are -15°C (5°F) in the north and 4°C (39°F) in the south and maximum temperatures are 18°C (64°F) in the north and 26°C (79°F) in the south. The growing season ranges from less than 150 days in the north to over 200 days in the south.
TOPOGRAPHY AND SOILS
The shortgrass region is flat and rolling with mesas and stream valleys. Rivers that cross the region include the Cimarron, Arkansas, Missouri, and Beaver. Most streams are ephemeral and dry up in the summer. They tend to have sandy/silty beds but may be rocky in some areas.
The soils of the shortgrass prairie are mainly Mollisols, but Entisols, Vertisols, Aridisols, Alfisols, and Inceptisols are also present. Overall, the soils are mostly coarse in texture, with the dominant texture being a fine sandy loam. The soils are the result of sedimentary deposits from the Rocky Mountains. Soil profile development is limited and more basic than forest soils. The coloring ranges from black in more mesic areas to brown in semiarid areas.
Current Plant Communities
Seventy percent of the shortgrass prairie still remains in natural vegetation. Large areas of this grassland have been converted to irrigated agriculture, and many abandoned crop fields from the 1930s have been left to revegetate naturally. Plowing this grassland caused permanent soil changes, such as a reduction in soil phosphorus. Some areas have been encroached by honey mesquite (Prosopis glandulosa var. glandulosa). This has formed shrubland or savannah-type vegetative structures with an understory of shortgrass species. Native prairie dogs have caused overgrazing resulting in range degradation. However this may, in part, be the result of anthropogenic changes (i.e., fragmentation and loss of predators) to prairie dog habitat.
Historic Plant Communities
The shortgrass prairie is a relatively young ecosystem, having formed between the middle Miocene and the early Holocene. It resulted in a gradual shift from semi-open forest with occasional grassy areas to open grasslands with few trees, due to factors such as increasing aridity, drought, and natural and anthropogenic fire. Due to the young age, the ecosystem lacks many endemic species. It is also the least productive of the central plains grasslands.
The region is dominated by shortgrasses such as buffalograss (Buchloe dactyloides) and blue grama (Bouteloua gracilis). These two grasses comprise 70-90% of the shortgrass prairie composition by weight. Only the most favorable, moister and eastern, sites contain tallgrasses such as sideoats grama (Bouteloua curtipendula) and little bluestem (Schizachyrium scoparium). Other grass species include hairy grama (Bouteloua hirsuta), western wheatgrass (Pascopyrum smithii), muhly grass (Muhlenbergia torreyi) and prairie threeawn (Aristida oligantha). Grasses “cured on the vine” have nutritional value when dormant.
Average aboveground net primary production is divided as follows: 65% graminoids, 13% succulents, 16% dwarf shrubs, and 6% forbs. Around 80% of the species in the shortgrass prairie exist only in riparian areas which constitute only around 5% of the Area.
Common shrubs and forbs include yucca (Yucca glauca), pricklypear cactus (Opuntia humifusa), prairie zinnia (Zinnia grandiflora), scarlet globemallow (Sphaeralcea coccinea), plains blackfoot (Melampodium leucanthum), slimflower scurfpea (Psoralea tenuiflora), skunkbrush (Rhus aromatic) and tree cholla (Opuntia immbricata).
ANIMALS
Large herbivores include pronghorn antelope (Antilocapra Americana), elk (Cervus canadensis) which is locally extirpated, white-tailed deer (Odocoileus virginianus) and American bison (Bos bison), also locally extirpated. Other mammals include the black-tailed prairie dog (Cynomys ludovicianus), swift fox (Vulpes velox), mountain lion (Puma concolor), black-footed ferret (Mustela nigripes) which is endangered, and the northern pocket gopher (Thomomys talpoides).
Birds include the burrowing owl (Athene cunicularia), mountain plover (Charadrius montanus), bald eagle (Haliaeetus leucocephalus), whooping crane (Grus Americana), lesser prairie chicken (Tympanuchus pallidicinctus), and northern bobwhite quail (Colinus virginianus). Important reptiles, amphibians, and insects include the Texas horned lizard (Phrynosoma cornutum), western diamondback rattlesnake (Crotalus atrox), massasauga (Sistrurus catenatus), plains leopard frog (Rana blairi), northern cricket frog (Acris crepitans), and harvester ants (Pogonomyrmex spp.).
Long-term Trends
The formation of Great Plains grasslands began 5 to 7 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, but these declined due to drier climate and colder temperatures. The shortgrass prairie that we know today developed following the retreat of the last Wisconsin glaciers approximately 10,000 years ago. Many areas were cultivated and then abandoned following the Dust Bowl to revegetate back to rangeland in the 1940s and 1950s. Many areas were plowed again in the 1980s.
Yearly and Seasonal Variation
In the shortgrass prairie, major vegetation changes occur due to drought and grazing pressure and fire is of secondary importance. The amount and seasonality of precipitation and temperature result in fluctuations in annual net production. Soils and plant types also influence production. Early summer climatic conditions favor C3 plants but 1 to 1 1/2 months later the climate favors C4 plants.
Disturbance Factors
Drought
Historical fire frequencies in level prairies were every 5-10 years and 15 to 30 years in prairies cut by breaks and streams. Historical fires burned across vast distances but are now limited by cultivated lands, roads, and fire suppression.
Fire
Historical fire frequencies in level prairies were every 5-10 years and 15 to 30 years in prairies cut by breaks and streams. Historical fires burned across vast distances but are now limited by cultivated lands, roads, and fire suppression.
Grazing
Historically, the shortgrass 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 to which the vegetation adapted in the process of natural selection. Prairie dogs affect the ecosystem through burrowing and grazing activities and consist of colonies that may cover tens to hundreds of hectares.
Other Disturbance Factors
Small-scale disturbances
Burrows cause small-scale disturbances. The mounds of soil produced from burrow construction can cover and kill whole or parts of plants. Recovery occurs after ceasing burrow construction.
Cattle fecal pats partially or totally kill plants and reduce plant cover due to the low plant stature in the shortgrass prairie. Recovery only occurs after pat decomposition which requires 2 years. Fecal pats can create resource gaps for intact seeds deposited with fecal matter.
Harvester ant nests clear vegetation from areas around their nests and collect foraged seeds underground. Abandoned nest sites are highly colonized by annual plant species. Furthermore, aboveground biomass is greater in the ring surrounding the nest most likely due to increased water availability
June beetle larvae (Phyllophaga fimbripes) feed on perennial plant roots, causing plant mortality. Patches killed range from 2 to 8 m in diameter and outbreaks occur periodically.
Storms
During the summer, atmospheric conditions are optimal for slow moving storms. The shortgrass prairie is prone to flash flooding, and the storms can produce hail and tornadoes. This area experiences an especially high frequency of large hailstones. Storms and their associated effects cause crop damage and endanger livestock and people.
Dust storms
Dust storms are natural and occur frequently during dry years. The Dust Bowl of the 1930s occurred across the Great Plains during a 22 year drought cycle. It contained the most severe dust storms on record and blame was placed on sod busters who plowed up the prairie. It resulted in many lands being placed under the Conservation Reserve Program.
Fire
The lack of fire in the shortgrass prairie results in some dramatic vegetation changes. Lack of fire facilitates woody plant encroachment and exotic invasions, causing detrimental alterations to native plant communities and habitat for wildlife.
Prescribed fire is a useful management tool for vegetation management. However, it comes with some management concerns such as the public’s fear of fire, the challenges of smoke management, and complex liability issues. Benefits of appropriately and wisely-used prescribed fires include enhanced biodiversity, suppressed woody encroachment, fire hazard reduction, improved forage for livestock, increased soil fertility, and improved wildlife habitat. Fire suppression activities cause fuel buildup and increase both the intensity and danger of wildfires.
Grazing
The shortgrass prairie is the third most important western range type for livestock production. As drought is a major disturbance, stocking rates during a drought period are of the utmost importance. If a range manager chooses not to destock the land, maintenance feeding with a complete diet may be required during drought conditions because the cattle are not able to utilize the remaining forage that is too short. Thus, the impact of grazing on the range during the drought is largely due to adverse impacts from trampling and dunging. Following the drought, recovery is affected by detrimental grazing which overuses recovering plant species. If range managers choose to destock, they must pay for dry lot feeding and transportation or sell their livestock.
Woody Plant Encroachment
Woody plants are promoted over grasses by changes in rainfall, lack of fire, and overgrazing. Because encroaching woody plants use available water, the grass cover becomes patchier and less likely to carry a fire, resulting in a self-reinforcing cycle of woody plant increases and grass cover reduction. Honey mesquite (Prosopis glandulosa) is one of the major encroaching woody species in the shortgrass prairie.
Invasive Species
Invasive species exploit disturbances caused by excessive grazing and trampling, insufficient grazing, and fire. They can reduce forage quality and quantity, decrease biodiversity, and alter ecosystem function. However, the shortgrass prairie is highly resistant to invasion, and cattle grazing is an effective means of controlling spread of some invasive plants. Common invasives include cheatgrass (Bromus tectorum), russian thistle (Salsola iberica), saltcedar (Tamarix spp.), fireweed (Kochia scoparia), old world bluestems (Bothriochloa spp.), crested wheatgrass (Agropyron cristatum), Japanese brome (Bromus japonicus), yellow sweetclover (Melilotus officinalis) and spotted knapweed (Centaurea stoebe).
Urbanization/Suburbanization
Due to a myriad of land management practices, the shortgrass prairie is extremely fragmented. For example, cultivation only uses 42% of the Great Plains area but fragments 100% of the area. Fragmentation reduces habitat quality and quantity, impedes the fire regime, and is severely detrimental to biodiversity. Population growth results in exurban development which causes habitat loss and increases the number of domestic predators, such as dogs and cats. It also facilitates the spread of exotic species.
Water Quality
Water in the shortgrass prairie region suffers from both quality and quantity issues. Pollution from agriculture, confined animal feeding operations (CAFOs), oil development, and other sources impair water quality. Reservoirs, channelization, impoundments, and withdrawal threaten flow regimes and riparian habitats. Grazing livestock also contribute to riparian area degradation. The falling water table and urbanization may reduce irrigation in favor of urban water demands.
The shortgrass prairie is well-suited for both beef cattle and sheep production, but sheep production is declining in the area. Beef cattle production is important but only 1% of the United States beef cattle population grazes in the shortgrass prairie.
Grazing Management Practices
Forage Sources and Seasonal Use
Supplementation with protein, minerals and energy is required from November until summer. Supplements include hay, energy and protein feedstuffs. Maintenance feeding may be necessary during drought years.
Fourwing saltbrush (Atriplex canescens) is beneficial when grazed in late fall or early spring because it is of good quality at this time and extends grazing season. Other complementary forages include Bozoisky wildrye and Hycrest wheatgrass.
Grazing Systems
Grazing is the dominant use of the shortgrass prairie’s natural vegetation. It is a sustainable practice at light to moderate stocking rates. In general, continuous grazing systems are superior to rotational grazing in terms of vegetative productivity and individual livestock performance. Cattle in continuous grazing systems usually do not require hay, but cattle may require protein supplement in winter. Rotational grazing is practiced on some ranches.
Poisonous Plants
Poisonous plants of the shortgrass prairie include broadleaf milkweed (Asclepias latifolia), locoweed (Astragalus spp.), larkspur (Delphinium spp.), bitterweed (Hymenoxys odorata), and sacahuista (Nolina texana).
Crop Production
Dryland farming may be successful during good years but is eventually unsuccessful due to extended droughts. There are many abandoned crop fields from the 1930s Dust Bowl that have been left to revegetate naturally. Irrigation can result in high levels of crop productivity. The major dryland crop is wheat, and the major irrigated crops are corn, soybeans, alfalfa, sugar beets, and cotton.
Commercial Hunting and Recreation
The following game species are commercially hunted: white-tailed deer, raccoon, squirrel, bobwhite quail, and mourning dove. Other recreation opportunities are fishing, hiking, bird watching, photography, and bicycling.
Restoration
Not enough is known to predict overall restoration project successes on long time scales in the shortgrass prairie. For any restoration project, it is recommended to emphasize a diverse mixture of native grasses and forbs, to understand the nature of the landscape, and to be aware of the inherent role of grazing on the prairie. Reseeded areas have a 30-50 year recovery period and require inputs to achieve necessary amounts of organic matter, carbon, and nitrogen. In these projects, it is important to consider spatial heterogeneity to determine which species to plant.
