Tallgrass Prairie Ecosystem
What is it?
In the early years of westward expansion, the vast expanses of tallgrass prairie awed eastern settlers, who were equally amazed that people who appeared to be walking through the prairie in the distance were actually on horseback. They soon discovered that Native Americans had long adapted their cultures to these vast areas, among other things by relying on the vast herds of bison that roamed the prairies and plains.
Tallgrass prairie is first and foremost a grassland, dominated by a suite of tall grasses that can attain height of over 6 ft on good productive soils. Big bluestem, Indian grass, Switch grass, little bluestem, and prairie dropseed comprise the matrix. On thinner, drier soils, little bluestem, side-oats grama, Junegrasses dominated, some reminiscent of the mixedgrass prairie to the west. In the swales, Prairie cordgrass and Canada bluejoint dominated.
But this matrix of grasses also contained a wide array of forb, some like the silphiums, raising their sunflower-like heads above the grasses, others, like blazing stars or mountain mint, mixing in, and still others, like Starflowers and Lupines, emerging in the spring or after prairie burns, before the grasses overtopped them. Tallgrass prairie also is home to a diverse group of animal species, in particular insects and grassland birds. Many threatened or endangered species can be found in the remaining parcels of tallgrass prairie. Prairie chickens and many species of butterflies such as the Dakota skipper attract special attention of conservationists.
Tallgrass prairie begins in the east, in Ohio, Michigan, Indiana and Ontario as somewhat isolated patches, restricted to dry soils, or droughty southwest slopes, where an occasional fire might prevent tree closure. But brushy scrub oaks can be found throughout the grass layer, quickly resprouting and ready to re-emerge and overtop the grasses. Moving west into Minnesota, Wisconsin, Illinois, and Missouri, the prairie expanses open up and form large square miles of open grassland, with scattered oak savannas and woodlands in the draws or next to fire breaks. Here, in the core of the prairie peninsula, the relative balance of prairie to woodland has constantly shifted over thousands of years as climate and fire regimes favored one or the other. From this area in the central United States, tallgrass prairie reaches westward into the eastern Dakotas, Nebraska, and Kansas and southward to Texas. The Flint Hills in Kansas and Oklahoma include some of the largest tracts of intact tallgrass prairie still remaining. In these eastern plains states, where drought and fire combine to exclude all but the hardest oaks, especially bur oak, the tallgrass prairie reaches its most expansive condition, dominating the skyline, and the trees and shrubs recede to the narrow draws and stream bottoms.
Prairie grasses sink their roots deep, providing a firm anchor to the soil and access to soil moisture deep underground. The natural decomposition of these prairie plants, in particular their root systems, along with replacing fires added layers of organic matter to the soils and helped create the rich, black soils in some of the best farming land in places like Iowa, Illinois, Minnesota, and Nebraska.
Fire is a natural component of the tallgrass prairie and is fundamental in its formation and continuation. These fires can help replace essential minerals and nutrients to the soil. It reduces plant litter and restricts tree growth, enabling prairie grasses to continue to establish and flourish. Typically, natural prairie fires are started by lightning approximately every 1-5 years, most commonly in mid- to late-summer. Historically, Native Americans used fire in the tallgrass prairies to attract grazing animals and provide natural fire breaks around settlements. Prairie fires could be destructive during European settlement. Droughts in combination with land clearing and insufficient knowledge of natural prairie ecosystems led to some devastating fires that caused loss of lives, livestock, homes, and sometimes entire towns. During the drought of 1871 (the same year as the great Chicago fire), fires started near Breckenridge, MN spread along a 100 mile front to the “Big Woods” area of central Minnesota. In recent history, restoration efforts have included prescribed burning to help promote tall grass prairie. These prescribed burns also can be used to help protect towns and homes around these sites from future prairie fires.
Grazing also was a natural component of tallgrass prairie ecosystems. Prior to European settlement, grazing the tallgrass prairie was primary by large herbivores such as bison, elk, and deer. Since European settlement, areas of tallgrass prairie have been converted to pasture for cattle. Cattle grazing can mimic previous grazing and has been used as a part of tallgrass management to help conserve and restore tall grass prairie areas. However, overgrazing can be very detrimental to these ecosystems. As grazing pressure increases, it can lead to invasion by annual species such as smooth brome, soil erosion, and a severe decrease in species diversity.