Exactly when the first of those hunting people arrived on the scene is a mystery. Until recently, most archaeologists asserted that humans (members of a genus that was born in East Africa some 2 million years ago) entered North America from Asia, by crossing the Bering land bridge and traveling down an ice-free corridor into the plains. This migration was believed to have happened within the last 11,000 to 12,000 years. Recently, however, archaeologists have uncovered evidence that people were living in Chile at least 1,000 years earlier than this, a discovery that has made the old timelines suspect. But whether the first people arrived 60,000 or 30,000 or 15,000 years ago, over the Bering land bridge or (as some suggest) by boat, as a massed arrival or in staggered groups, we know that by about 11,000 years ago, they were established across the north-central and southern plains. Equipped with elegantly chipped fragments of stone and bone, these hunters killed and butchered not only bison but also camels, horses, mastodons, and—their specialty—mammoths. At sites from Alberta to Texas, the proof of their presence—blackened hearths, discarded tools, and cracked marrow bones—lies buried where they left it so long ago. In some places, the skeletons of several large mammals lie strewn about the camps, testimony to the success of these recent immigrants.
Three-flowered avens, seen in bud at left, is also known as prairie smoke or old man’s beard in tribute to its feathery seedheads, seen here.
But inevitably, on a planet where change is the only constant, their success was fleeting. By 13,000 years ago, the fabulous array of large mammals that the newcomers had encountered on the plains was already disappearing. As many as fifty species—including giant beavers, ground sloths, lions, cheetahs, dire wolves, saber-toothed cats, horses, camels, mammoths, and mastodons—all became extinct within a few thousand years. Did an exploding population of well-fed humans hunt the animals into oblivion, as some archaeologists suggest? Or was climate change the culprit? The evidence suggests that, between about 13,000 and 10,000 years ago, average global temperatures first dropped abruptly and then rebounded. On the North American plains, these climatic changes ultimately translated into a dramatic shift in vegetation patterns. Pushed by warmer, drier conditions, the spruce forests gave way to pines, then in places to open, mixed woodlands, and ultimately to grass. In the blink of an eye (relatively speaking), a carpet of grasses spread out across the plains, blued by sage and beardtongue and enlivened by patches of golden beans, blazing stars, and prairie smoke, or three-flowered avens. The prairies of historic times had finally been created.
Until quite recently (geologically speaking), North America was home to many different kinds of pronghorns— some diminutive, some with multiple horns. The modern species is the only one to survive the extinction crisis at the end of the Ice Age.
Although the species is old as the hills, researchers are only now beginning to map their preferred calving grounds and seasonal migrations.
This new grassland was big and bold, but it was also much less varied than the mixed landscape of tundra, grass, and forest that it had displaced. And perhaps this in itself is enough to explain the disappearance of the Ice Age megamammals, which required a rich and varied supply of foods that grasslands alone could not provide. Yet if the new habitats were insufficient to 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.
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> 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.
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THE GEOGRAPHY
OF GRASS
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.
Although grasses are the most important plants on the prairies in terms of sheer volume, wild flowers (or forbs) also make a vital contribution. With a species list that numbers into the thousands, forbs add diversity to the wall-to-wall carpet of grass, thereby enriching the entire ecosystem. The more plant species are present, the more animals are able to find what they need, whether it be nest sites, daytime shelters, or feeding opportunities. This grasshopper nymph, for example, is taking advantage of the nutritious petals of a prairie sunflower.
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 an
d 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.
Sometimes called turkey foot or beardgrass, big bluestem can be recognized by its distinctive three-pronged heads. The fuzzy hairs on the heads are inconspicuous, scentless flowers.
Prairie grasses also have another ingenious way of evading the demands of the sun. Like many other grassland creatures (prairie dogs, ground squirrels, cottontails, badgers, and so on), they take refuge underground. What we think of as “grass”—the aboveground leaves and stems—actually constitutes less than half of the organism. Between 60 and 80 percent of the plant, by weight, typically grows below ground. The roots extend down from the base of the stems like a tangled head of hair, as main roots divide into minor roots and then into root hairs. A 10-foot (3-meter) stand of big bluestem is anchored under ground by a mass of coarse, fibrous roots that reaches as much as a good 12 feet (or 3.6 meters) into the earth. Blue grama, for its part, seldom lifts its seed heads very far above the ground, but its network of fine, branching roots can sometimes probe the soil for water almost 6 feet (2 meters) down!
These extensive systems of roots push thirstily through the soil, intent on sucking up every available drop of water. But if the soil is very dry, as it is during periods of drought, the roots can’t draw in enough moisture to keep pace with losses from the stomata. Grasses respond by transferring their most valuable resources (including sugars and proteins) from their leaves into their roots and, especially, into their rhizomes—those aggressive, underground stems that are familiar to anyone who has ever battled with quack grass in the garden. Dead to the world above ground—withered and crisp—the plants live frugally below the surface, drawing on their cached supplies and biding their time until the weather improves. When the rains eventually return, as inevitably they do, the grasses explode into action, sending out fresh rhizomes, which in turn put out fresh leaves and roots, to produce a burgeoning network of tender growth. The amazingly resilient blue grama can revive from dormancy, green up, and grow on as little as .2 inches, or 5 millimeters, of rainfall.
Prairie grasses are not all equally capable of coping with drought. In general, tall grasses, including big bluestem and other shoulder-high species such as switchgrass and Indian grass, require the most moisture, while short grasses like blue grama, galleta, and the stubby little buffalo grass are the most resistant to drought. Midheight species, including needle-and-thread grass, rough fescue, and western wheatgrass (a.k.a. bluejoint, for its bluish leaf nodes), tend to fall somewhere in between. But all prairie grasses can contend with drought more successfully than can most deciduous trees—which is why the prairies are prairies instead of forests. The grasslands are an expression of the drought-prone prairie climate and a living response to the geography of the midcontinent.
The ability to survive episodes of drought is a basic requirement for life on the Great Plains.
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> PLANTS FIGHT BACK
Prairie plants have come up with many ingenious strategies for coping with water shortage. A few, like the pincushion cactus, are genuinely drought resistant. In other words, they can store water in their own tissues (in their enlarged stems) and draw on it as needed. Others, including many grasses and wildflowers, attempt to evade drought by going dormant and retreating underground, where they linger on in the form of seeds, rhizomes, or tubers. But if some plants favor patient waiting, others put their faith in speed. Instead of trying to sit out the drought, they attempt to avoid it entirely.
Take, for example, the prairie crocus, or pasque flower. An inexhaustible source of pleasure for people on the northern plains, crocuses appear on the trailing edge of winter as tight clusters of furry, pointed buds that push up through the dead grass like so many inquisitive snouts sniffing for spring air. Without pausing to grow leaves, the plants burst directly into bloom, producing ground-hugging whorls of silky, lavender sepals. By the time most other wildflowers put in an appearance several weeks afterward, crocuses are already sporting headdresses of shiny, plumed seeds. Before the growing season has even properly begun, their reproductive task has been completed.
By getting off the mark so early, crocuses are able to draw on a relatively certain supply of water from snowmelt. And although they are exposed to the bluster of winter’s last blast, they are protected from the wind by a coat of hairs that holds in heat and moisture. They also take shelter by crouching close to the ground, well bedded in grass, creeping juniper, and other plants. Thus protected, crocuses speed through their reproductive cycle and avoid the stress of coping with drought in the hot, dry days of July and August.
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Weather Matters
To the homesteaders who came to the Great Plains from Europe or eastern North America in the late 1800s and early 1900s, converting the prairies to croplands must have looked like a dream. Except for the trees that crept in along the rivers, the land lay open to the plow, offering little apparent resistance to the farmers’ ambitions. But the settlers’ early optimism was soon blighted by widespread droughts, as the dry summer of 1889 was followed by the dry years of 1890, 1894, 1910, and 1917, and then by the bleak decade of the 1930s. Life on the prairies was not as easy as it had seemed. For what no one at first quite realized was that grasslands are semiarid zones—better watered than deserts but less humid than forests. The farmlands that the settlers had known in Europe and the East had typically been wrested from the forest and, even after the trees were gone, still received enough rainfall to support a natural vegetative cover of broad-leaved woodlands. But the weather on the prairies naturally favored not trees but grass, and that simple fact made all the difference.
left: Pincushion cactus
right: Prairie crocus, or pasque flower
Like most of the world’s great grasslands, the Great Plains of North America lie squarely in the middle of a large contine
ntal land mass. As a result, the region is isolated from the influence of all four oceans—north, south, east, and west— and, as it happens, from any other significant body of water. Without the moderating influence of water (slow to heat and slow to cool), the plains are subject to violent oscillations of temperature. In the northern prairies, in particular, the temperature can span 140˚F in the course of a year, from a brittle –40˚F in midwinter and to a stifling 100˚F in summer. (That’s a range of 80˚C, from a low of around –40˚C to a high of over +40˚C.) The effect of these wild seasonal deviations is equivalent to moving up and down the continent every twelve months. Saskatoon, for example, has an average January temperature of 0˚F (–17˚C), well below that of Anchorage, Alaska. But in July, Saskatoon’s average heats up to 66˚f (19˚C), almost on a par with that of Los Angeles. And though the southern plains are spared the worst extremes of winter, they still get taken for quite a ride. The average January temperature in Amarillo, Texas, for example, is a mere 35˚f, or 2˚c, cooler than Vancouver far to the north; but in July, the north Texas plains can be among the hottest places on the continent. (If prairie people are obsessed by the weather, it may simply be because we have a lot of weather to obsess about!)
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