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Ecologists commonly separate Great Plains grasslands communities into types based on grass height: shortgrass prairie, mixed-grass prairie, and tallgrass prairie. Grass height correlates directly with precipitation and thus lessens with distance westward and with drought. Grass height correlates inversely with grazing intensity and thus shortgrasses expand eastward when grazing pressures are great and shrink westward when grazing pressures relax. Evidence about past distributions of shortgrasses, coupled with the prehistoric and historic abundances of large grazers and the black-tailed prairie dog (a shortgrass indicator), suggest a far-eastward occurrence of shortgrass prairie in the late Pleistocene (despite a relatively wet climate), a shrinkage westward by late prehistoric and early historic times, and a farther shift westward in response to the bison's demise in the 19th century. After cattle arrived in the late 1800s, shortgrass prairie expanded and contracted depending on the prevailing grazing philosophies, resulting grazing intensities, and periodic drought. Currently, taller grasses have prevailed for over a half century, and shortgrass prairie may be more restricted than it has been for millennia, because of a grazing philosophy that promotes moderate grazing. An emerging change in grazing philosophy may presage a gradual return of heavier grazing and another expansion eastward of the shortgrass prairie. Such an expansion, particularly if accompanied by grazing regimes patterned on early historic and prehistoric grazing, may enhance biodiversity, the stability of some soils, and under some circumstances, economic returns from ranching.