Between 40 and 64 million years ago, the Rocky Mountains and Black Hills rose to block the flow of Pacific moisture into the interior of North America. Newly evolved, grasses flourished in the changing climate and replaced the retreating forests. Their abrasive, high silica content discouraged early soft toothed browsers that preferred more tropical leafy vegetation. From the Rockies to the Appalachians and from Alberta into Texas, grasslands extended unbroken over a third of the continent and once supported some of the greatest herds of herbivores the world has ever known. The vast expanse was only occasionally interrupted by scattered slough and wetlands or ribbons of deciduous woodlands along the major streams and rivers. The space was open and the views endless.
Superbly adapted to more arid environments, the narrow, waxy-coated leaves of grasses conserve moisture and are arranged more or less vertically along the stem for maximum photosynthetic efficiency. Extensive fibrous root systems, often reaching depths twice the height of the above-ground plant, establish contact with deep sources of moisture. Roots also represent stored energy to produce new plant tissue. Since the growing center of a grass is at the base of the leaf where it joins the stem, growth can continue if the leaf is cut. If the top of a shoot is bitten off or burned, protected young shoots hidden inside a series of wraparound tubes may emerge. During the growing season about half of the plant is found below ground. Energy transfer to root storage in the winter increases to over 80%.
Badlands National Park is located at the western edge of the mixed grass prairie. The mixed grass prairie of the central United States is actually a transition zone between the more arid shortgrass prairie to the west and the more moist tallgrass prairie to the east, but because of its size is considered worthy of separate distinction. Warm or cool-season plants, grasses make efficient use of seasonal trends. Cool-season grasses grow early in the season as well as in the late summer and fall attaining greater heights than the warm-season species that come alive during the hot summer months. They are distributed along a continuum from east to west, decreasing in height with a general decrease in available moisture.
Most of the 56 different types of grasses found in the Badlands are native, having developed over millions of years. Taller western wheatgrass, green needlegrass, and needle-and-thread grass dominate low moist spots while shortgrass communities of blue grama and buffalo grass cover drier, rocky outcrops. A number of exotic grasses were introduced as settlers immigrated to this country.
Although grasslands may vary considerably from one location to the next, they are all dominated by grasses and nearly devoid of trees. To those who traveled the early pioneer trails, they were thought to be alien, inhospitable, and incapable of supporting crops. Many today still perceive our grasslands as empty and desolate as we travel from one coast to the other, as quickly as possible, over one of our nation's richest and most productive ecosystems.
Grasslands support more than just grasses. Within them one may discover many kinds of wildflowers, desert plants, and occasional trees that provide food and habitat for a unique assembly of birds, mammals, reptiles, amphibians, and insects. Researchers counted 134 different vertebrate species associated with a community of prairie dogs and also discovered an invisible prairie consisting of countless microscopic soil organisms equal to the total weight of all the vegetation.
Although nomadic hunters and gatherers had occupied the region successfully since the end of the last ice age, Major Stephen H. Long reported during an 1820 expedition that, The scarcity of wood and water, almost uniformly prevalent will provide an insuperable obstacle in the way of settling the country. His description of the Great American Desert stuck in the popular imagination as many died crossing some of the most fertile land on the continent in an attempt to reach the forested landscapes of Oregon. Extreme seasonal temperatures, extended periods of drought, incessant winds, cycles of prairie fire, and grasshoppers so big they could dig the potatoes right out of the ground, were environmental hardships that postponed settlement of the Great Plains for many years.
Precious topsoil is the product of a complete grassland ecosystem involving all the plants and animals over many millennia. Because of their agricultural value, grasslands have been converted to food production. Corn and soybeans have replaced the tall grasses and the mixed grass regions are now the wheat belt. Where irrigation systems are not practical, livestock grazing has transformed the shortgrass prairie. As a result, natural grasslands have all but disappeared. Visitors can still experience this important ecosystem in Badlands National Park where the largest and finest remnant of mixed grass prairie is preserved.