The driest of the North American prairies, the shortgrass lies within a rain shadow created by the Rocky Mountains. Clouds moving eastward across the mountains rise and cool, becoming less able to hold moisture, which is released as rain and snow. By the time the clouds reach the prairie, little moisture is left, creating the dry environment that fosters the shortgrass community. Adapted to a semi-arid climate, the “short grasses,” like buffalo grass and blue grama, are often no more than 6 to 12 inches high. But they are highly nutritious even when dry, offering valuable forage for wildlife and cattle. While much of the shortgrass proved unsuitable for agriculture—too far from water to irrigate and frequently too harsh even for dryland crops—the rich grasses could support cattle ranching. Using the land for grazing, rather than plowing it under for crops, has maintained perhaps 60 percent of the Eastern Plains as grassland, but its ecology has been changed.
Bison, which once roamed the Great Plains in the millions, “managed” grasslands through their grazing, trampling and wallowing. The land that bison herds once migrated across is now managed for cattle grazing, but cattle do not impact prairie ecology in the same way free-ranging bison did.
Significant reductions of black-tailed prairie dog populations have occurred since settlement of the West, as their habitat was converted into farmland and developed as cities and towns. In addition, prairie dogs are highly susceptible to sylvatic plague, a disease introduced in the early 1900s. Prairie dogs are controlled by many ranchers and farmers, in developed areas, because they compete with cattle for grass and their burrowing damages rangeland. Loss of prairie dogs affects a host of other wildlife species—predators such as ferruginous hawks that prey directly on the rodents and other species, like burrowing owls, that make use of prairie dog towns for nesting, shelter or other habitat needs.
Some species, including grizzly bears, wolves and black-footed ferrets, have been completely eliminated from the prairie—grizzlies and wolves were killed off through predator control efforts, and black-footed ferrets declined due to the reduction of prairie dog populations, their primary prey. Elk, mule deer and bighorn sheep, once common on the prairie or at its margins, are now mostly limited to the foothills and mountains. Ground-nesting birds such as prairie-chickens, plains sharp-tailed grouse and mountain plover have lost habitat as agriculture and ranching disrupted their grassland nesting grounds. Grassland songbirds, such as lark buntings, longspurs, horned larks and meadowlarks, lose habitat as grasslands are developed. Rapid suburban expansion along the Front Range has consumed hundreds of thousands of acres of prairie.
Thus, while the rolling grasslands of eastern Colorado appear unchanged, the decline of native wildlife signals clouds of change looming over the prairie.