Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type. Temperate grassland regions include the Pampas of Argentina, southern Brazil and Uruguay as well as the steppes of Eurasia. Lands typically referred to as "prairie" tend to be in North America. The term encompasses the area referred to as the Interior Lowlands of Canada, the United States, and Mexico, which includes all of the Great Plains as well as the wetter, somewhat hillier land to the east.
In the U.S., the area is constituted by most or all of the states of North Dakota, South Dakota, Nebraska, Kansas, and Oklahoma, and sizable parts of the states of Montana, Wyoming, Colorado, New Mexico, Texas, Missouri, Iowa, Illinois, Indiana, Wisconsin, and western and southern Minnesota. The Central Valley of California is also a prairie. The Canadian Prairies occupy vast areas of Manitoba, Saskatchewan, and Alberta.
According to Theodore Roosevelt:
|"||We have taken into our language the word prairie, because when our backwoodsmen first reached the land [in the Midwest] and saw the great natural meadows of long grass--sights unknown to the gloomy forests wherein they had always dwelt--they knew not what to call them, and borrowed the term already in use among the French inhabitants.||"|
The formation of the North American Prairies started with the upwelling of the Rocky Mountains near Alberta. The mountains created a rain shadow that resulted in lower precipitation rates downwind, creating an environment which most tree species will not tolerate.
The parent material of most prairie soil was distributed during the last glacial advance that began about 110,000 years ago. The glaciers expanding southward scraped the landscape, picking up geologic material and leveling the terrain. As the glaciers retreated about 10,000 years ago, it deposited this material in the form of till. Wind based loess deposits also form an important parent material for prairie soils.
Tallgrass Prairie evolved over tens of thousands of years with the disturbances of grazing and fire. Native ungulates such as bison, elk, and white-tailed deer, roamed the expansive, diverse, plentiful grassland before European colonization of the Americas. For 10,000-20,000 years native people used fire annually as a tool to assist in hunting, transportation and safety. Evidence of ignition sources of fire in the tallgrass prairie are overwhelmingly human as opposed to lightning. Humans, and grazing animals, were active participants in the process of prairie formation and the establishment of the diversity of graminoid and forbs species. Fire has the effect on prairies of removing trees, clearing dead plant matter, and changing the availability of certain nutrients in the soil from the ash produced. Fire kills the vascular tissue of trees, but not prairie, as up to 75% (depending on the species) of the total plant biomass is below the soil surface and will re-grow from its deep (up to 6 feet) roots. Without disturbance, trees will encroach on a grassland, cast shade, which suppresses the understory. Prairie and widely spaced oak trees evolved to coexist in the oak savanna ecosystem.
In spite of long recurrent droughts and occasional torrential rains, the grasslands of the Great Plains were not subject to great soil erosion. The root systems of native prairie grasses firmly held the soil in place to prevent run-off of soil. When the plant died, the fungi, bacteria returned its nutrients to the soil.
These deep roots also helped native prairie plants reach water in even the driest conditions. The native grasses suffered much less damage from dry conditions than the farm crops currently grown.[dubious ]
Prairie in North America is usually split into three groups: wet, mesic, and dry. They are generally characterized by tallgrass prairie, mixed, or shortgrass prairie, depending on the quality of soil and rainfall.
In wet prairies the soil is usually very moist, including during most of the growing season, because of poor water drainage. The resulting stagnant water is conducive to the formation of bogs and fens. Wet prairies have excellent farming soil. The average precipitation amount is 10- 30 inches a year.
Mesic prairie has good drainage, but good soil during the growing season. This type of prairie is the most often converted for agricultural usage, consequently it is one of the more endangered types of prairie.
Dry prairie has somewhat wet to very dry soil during the growing season because of good drainage in the soil. Often, this prairie can be found on uplands or slopes. Dry soil usually doesn't get much vegetation due to lack of rain. This is the dominant biome in the Southern Canadian agricultural and climatic region known as Palliser's Triangle. Once thought to be completely unarable, the Triangle is now one of the most important agricultural regions in Canada thanks to advances in irrigation technology. In addition to its very high local importance to Canada, Palliser's Triangle is now also one of the most important sources of wheat in the world as a result of these improved methods of watering wheat fields (along with the rest of the Southern prairie provinces which also grow wheat, canola and many other grains). Despite these advances in farming technology, the area is still very prone to extended periods of drought which can be disastrous for the industry if it is significantly prolonged. An infamous example of this is the Dust Bowl of the 1930s, which also hit much of the United States great plains ecoregion - contributing greatly to the Great Depression.
Nomadic hunting has been the main human activity on the prairies for the majority of the archaeological record. This once included many now-extinct species of megafauna.
After the other extinction, the main hunted animal on the prairies was the plains bison. Using loud noises and waving large signals, Native peoples would drive bison in fenced pens called (buffalo pounds) to be killed with bows and arrows or spears, or drive them off a cliff (called a buffalo jump), to kill or injure the bison en masse. The introduction of the horse and the gun greatly expanded the killing power of the plains Natives. This was followed by the policy of indiscriminate killing by European Americans and Canadians and caused a dramatic drop in bison numbers from millions to a few hundred in a century's time, and almost caused their extinction.
The very dense soil plagued the first settlers who were using wooden plows, which were more suitable for loose forest soil. On the prairie the plows bounced around and the soil stuck to them. This problem was solved in 1837 by an Illinois blacksmith named John Deere who developed a steel moldboard plow that was stronger and cut the roots, making the fertile soils ready for farming.
The tallgrass prairie has been converted into one of the most intensive crop producing areas in North America. Less than one tenth of one percent (<0.09%) of the original landcover of the tallgrass prairie biome remains. States formerly with landcover in native tallgrass prairie such as Iowa, Illinois, Minnesota, Wisconsin, Nebraska, and Missouri have become valued for their highly productive soils and are included in the Corn Belt. As an example of this land use intensity, Illinois and Iowa for the United States, rank 49th and 50th out of 50 states in total uncultivated land remaining.
Drier shortgrass prairies were once used mostly for open-range ranching. But the development of the barbed wire in the 1870s and improved irrigation techniques, means that this region has mostly been converted to cropland and small fenced pasture as well.
Research, by David Tilman, ecologist at the University of Minnesota, suggests that "biofuels made from high-diversity mixtures of prairie plants can reduce global warming by removing carbon dioxide from the atmosphere. Even when grown on infertile soils, they can provide a substantial portion of global energy needs, and leave fertile land for food production." Unlike corn and soybeans which are both directly and indirectly major food crops, including livestock feed, prairie grasses are not used for human consumption. Prairie grasses can be grown in infertile soil, eliminating the cost of adding nutrients to the soil. Tilman and his colleagues estimate that prairie grass biofuels would yield 51 percent more energy per acre than ethanol from corn grown on fertile land. Some plants commonly used are lupine, big bluestem (turkey foot), blazing star, switchgrass, and prairie clover.
Because rich and thick topsoil made the land well suited for agricultural use, only 1% of tallgrass prairie remains in the U.S. today. Short grass prairie is more abundant.
Significant preserved areas of prairie include:
Virgin prairie refers to prairie land that has never been plowed. Small virgin prairies exist in the American Midwestern states and in Canada. Restored prairie refers to a prairie that has been reseeded after plowing or other disturbance.
A prairie garden is a garden primarily consisting of plants from a prairie.