Desolate, forbidding? There was never a country that in its good moments was more beautiful. Even in drought, duststorm or blizzard it is the reverse of monotonous, once you have submitted to it.
Wallace Stegner, Wolf Willow
The first settlers traveling west across the prairie may not have noticed the gently rolling hills and purple-red vistas. Theirs was a difficult journey of incredible monotony over trackless grassland. Even today, the prairie landscape inspires little more than a casual glance out the car window. Perhaps, though, it is worth knowing that of the four major types of natural vegetation communities, the grasslands is the largest - 24% of the earth's vegetation. Grasslands or prairies once covered one third of the continent. Wind Cave National Park offers the opportunity to explore a remnant of this once vast ecosystem. The conditions that led to the present grassland are relatively recent. From the middle Miocene (about 15 million years ago) through the Holocene (about 8,000 years ago) the climate changed, causing a gradual shift in vegetation from semi-open woodlands to open grassland. As the amount of water evaporated exceeded the amount of water precipitated, these grasses, which are better adapted to arid climates, out-competed the trees and shrubs of the forest.
Mixed Grass Prairie
Wind Cave National Park is located where the grasslands meet the ponderosa pine forests of the uplifted Black Hills. Here, there is blending of the tall grass prairie species of the eastern Great Plains and the short grass species of the western Great Plains. These eastern and western prairies are differentiated by the types of forbs (herbaceous plants) and grasses found there. Each type reflects the amount of available moisture which decreases from east to west. The species composition is determined by the climate, fire frequency, and the degree and frequency of grazing. The mixed grass prairie is an ecotone that results where species composition is constantly shifting between the tall and short grass prairies.
The Prairie Plants
A plant community is the result of biotic factors (vegetation genetics, grazing), abiotic factors (climate, mineral soil, moisture) and their interactions. Since abiotic factors vary in even small areas, habitat gradients are produced. Because of this, many unique plant communities result such as big bluestem grass growing in depressions and needle-and-thread grass growing on eroded hillsides. There are approximately 140 million acres of mixed grass prairie in North America. Although grasses provide the most material (80 to 90% biomass), only 20% of the plant species are grasses. The rest are forbs which add to the diversity of forage, important for browsing animals like the pronghorn.
Grasses are able to maximize their growth and production even with constantly changing environments. They send more than half of their tissue or their roots, below the ground. This helps build and hold soil and creates a food store that the plants use during dominate periods such as winter or during droughts. Grasses have also adapted to pressure from grazing. Silica is assimilated by the plant into its cell walls. This makes the leaves coarse and less palatable. Also, the growing parts are at the base of the plant, so cropping off the top will not kill the plant. When the photosynthesizing tissue is removed by grazing, the rate of photosynthesis within the uneaten tissue is increased.
In response to wide temperature fluctuations, grasses have evolved to cool- and warm-season species. Cool-season grasses, such as needle-and-thread grass, grow well in the spring and fall when the temperatures are cooler and more water is available. Warm-season grasses, such as blue grama, await the summer months. They grow best in high temperatures.
Surviving the Winter
By winter the aerial portions of grasses have died and most of the plants' energy has been transferred to the root system. What remains is known as standing dead, the dry carpet of grass that crunches underfoot. This dead material is an important source of food for the grazing animals throughout the winter. It also provides fuel for periodic fires.
Fires burn the built up layers of dead material from previous years. It is fire that has helped shape the grassland community by killing competing trees and shrubs, effectively maintaining the balance between the forest and prairie. During a fire, most of the grass remains unharmed in the ground. After the fire, grasses benefit as more space, light and water become available for more growth.
The Future of the Prairie
The prairie is home to a variety of plants and animals. It is a place where deer, coyotes, pronghorn, prairie dogs, eagle, hawks and other wildlife flourish. The prairie is not only valued for its biodiversity, but for the wide-open space and magnificent beauty found there. With the westward advance and agricultural development of the grasslands it has become difficult to understand the prairie ecosystem. Continued management is needed to maintain and understand it. Wind Cave National Park and other protected areas offer us a glimpse of this vanishing community and an opportunity to understand it better.
The Prairie World. David Costello. Thomas Y. Crowell Company, New York, 1969.
Other Places to Visit
Badlands National Park, P.O. Box 6, Interior, SD 57750
Did You Know?
Winds caused by changes in barometric pressure are what give Wind Cave its name. These winds have been measured at the cave's walk-in entrance at over 70 mph. The winds at the natural entrance of the cave attracted the attention of Native Americans and early settlers.