sustain mammoths, they appeared perfectly suited to the bison, which soon emerged as the dominant grazing animal on the open range.
As the great herds drummed across the prairie, they of course had no conception of how their homeland had been shaped. The evidence of that drama lay unnoticed beneath their hooves—long-buried evidence of onrushing seas, rising mountains, silt-burdened rivers, and towering cliffs of ice. But the bison were untroubled by the traumas of the past, as they flowed across the horizon toward the present.
> THE CREATION OF BEAR BUTTE, MONTANA
This a northern Cheyenne story, as told by Jessie Beaverheart American Horse of Lame Deer, Montana. Once there was a very beautiful young woman, whose father was determined to choose the right husband for her. Many men came to ask for her, but her father turned them all away. Finally, a tall, handsome young man, with two fine bay horses, appeared. “I am Cheyenne,” he proclaimed. “I have been a Cheyenne as long as there have been Cheyennes.” Although the father found him mysterious, he presented the young man to his daughter, who happily agreed to marry him.
After a while, the new husband told his wife, “There is one thing you must never do. Never turn your back on me.” He refused to explain this rule except to say that something terrible would happen if she ever broke it.
A year passed and the couple had a son. When the child was just a few months old, his father started teaching him how to ride. The mother protested—the baby was too young—and when her husband refused to listen, she snatched the infant and ran. “I told you never to turn your back on me!” the man howled, and he took off after them. When the woman looked back, she discovered that she was being pursued not by a man but by a grizzly bear.
Desperate, she ran to the top of a little mound and called out to Maheo, Above Person, for help. Right away, the hill began to lift up into the air, carrying the woman and child to safety. By the time the bear reached the hill, it was too steep and slippery for him to climb. Today, you can still see the marks left by his claws as he tried to scramble up the butte and, if the light is right, you can even make out the moccasin tracks of the woman and little boy. It is one of the places in the old Cheyenne country where women can look for power.
{ three }
I am the grass. Let me work.
CARL SANDBURG, “GRASS,” 1918
NATIVE GRASSES ARE the heart and soul of the prairie, the living link between the physical resources of the Great Plains— sunshine, rain, and soil—and almost every other aspect of the ecosystem. At first glance, grasses may look simple or even primitive. In fact, they are highly evolved organisms, especially adapted to cope with extreme climatic uncertainties, including frequent drought. From probable origins in the African region of the supercontinent Pangaea some 60 million years ago, grasses have migrated to every continent except Antarctica and have diversified into about 10,000 species throughout the world. Of these, some 140-odd species, in 41 genera, naturally occur in the Great Plains grasslands. That’s twelve dozen distinctly different native grasses! Some of them, like the magnificent big bluestem, or turkey foot (so called for its large, three-lobed seed head), grow up to 10 feet (3 meters) tall. Others, like the stick-in-your-socks specialist needle-and-thread grass, seldom exceed 3 feet (1 meter) in height. At the low end of the scale are species like the diminutive blue grama, which grows close to the ground and rarely raises its elegant, eyebrow-shaped seed heads more than a few hand widths above the soil.
Yet despite these obvious differences, the prairie grasses all share one crucial ability. They are tuned in to the climate, able to dial their metabolisms down when conditions are unfavorable for growth and speed them up when the weather improves. Far from being passive stalks blowing idly in the wind, prairie grasses are lean, mean growing machines, designed to make the most of limited and unreliable resources.
Managing Moisture
One key to the prairie grasses’ success is their ability to conserve water. Like most plants, grasses take in water through their roots and lose it as water vapor through tiny mouth-shaped valves, or stomata, in their leaves. The larger the surface of the leaf and the more stomata it bears, the greater the risk that the plant will lose too much moisture through evaporation and collapse. Grasses are protected from this trauma by having a reduced number of stomata and by the design of their leaves, which take the form of narrow blades. What’s more, the surfaces of these reduced leaves are often modified—corrugated with ridges or covered in hairs—so that the wind can’t sweep across the surface and draw out moisture. The roughened surface holds a thin layer of humid air next to the leaf and thus helps to reduce the “evaporative demand,” or drying power, of the atmosphere. Some grasses, including western wheatgrass, June grass, and blue grama, roll up the edges of their leaves during times of drought to help keep their tissues from drying out.
Why aren’t the stomata kept tightly closed to seal moisture inside the leaf? The reason is that the stomata also supply plants with fresh air. Leaves are miracle workers, able to take carbon dioxide from the air and water from the soil, zap them with solar energy, and transform them into food. This process— photosynthesis—not only produces the sugars and other organic molecules that plants need to maintain themselves and to grow but also feeds microbes, worms, insects, fish, birds, and mammals. If plants sealed their stomata, this life-sustaining process would come gasping to a halt for lack of carbon dioxide. But if the stomata are thrown wide open, the plants risk death due to the loss of moisture through their gaping valves.
Prairie grasses resolve this dilemma by strategic scheduling. In the fierce blaze of the midday sun, the stomata close so that water vapor is held in and carbon dioxide is kept out. In this state, the leaf can capture solar energy and store it in energy-rich molecules (a process that requires sunlight but not carbon dioxide). Then, in the cool of the evening, when the evaporative demand drops off, the stomata snap open, letting water vapor trickle out but also permitting carbon dioxide to flood into the leaf. By mobilizing the energy that was stockpiled earlier in the day, the leaf uses this carbon dioxide to manufacture the sugars and other molecules that it needs for growth (a process that can be accomplished in total darkness). The result is that prairie grasses are partially nocturnal; they do most of their growing at night or in the early hours of the morning.
Prairie grasses also have another ingenious way of evading the demands of the sun. Like many other grassland creatures (prairie
