Sea of Grass

Sea of Grass

Chapter One

Prairie

In the bars and cafés around Cottonwood Falls, Kansas, regulars tell the story of a settler family that arrived in Chase County about 1860, their wagon loaded with the household goods and farm implements required to start a new life on the prairie. They encountered a member of the Kansa tribe, according to the story, and asked where they might find a good place to farm. He gave them a warning: Their steel plow would be useless here. Puzzled but undaunted, they claimed a homestead and hitched horse to plow, only to discover that he had been right. In this part of east-central Kansas, the hard limestone bedrock lies so close to the surface that a plow can’t carve a furrow without striking rock. Subsequent settlers got the message and chose to settle farther west. So by a quirk of geology, the Flint Hills region survived as a rare island of grass in a vast sea of corn and wheat. Today it covers some four million acres in eastern Kansas and northern Oklahoma and includes the Tallgrass Prairie National Preserve, the nation’s largest remaining patch of native tallgrass prairie. It may be the best place in the country to see the ancient landscape that shaped life here for centuries before Europeans arrived.

Standing on a rise at the center of the preserve you can see for miles and imagine the sea of grass early European explorers described centuries ago. The gently rounded hills roll like ocean swells—nothing but amber grass and prairie flowers to the edge of the sky. To the west, a lone bison grazes in a creek draw. To the northeast, a red-tailed hawk soars on the breeze, gracefully circling in its hunt for prey. The silence is immense until a breeze comes over a nearby rise, playing the grass like an instrument. This is what the prairie must have looked like two hundred years ago, when Lewis and Clark explored the West for President Thomas Jefferson. And five hundred years ago, when the Pawnee, Osage, Wichita, and Kansa people hunted buffalo and learned to turn the stone into weapons. Or even twelve thousand years ago, when this landscape emerged fresh to the sky after centuries under the combined forces of ice and geology.

Between sixty and eighty million years ago, the prairie had not yet made its appearance. A wide sea lay across the middle of what is now North America. As the planet warmed, the waters receded, leaving a moist plain covered by hardwood trees. Then, about 65 million years ago, a massive shift in the Earth’s tectonic plates caused a geological event known as the Laramide orogeny, which shoved the western half of the continent toward the eastern half, lifting a giant crust of rock that would become the Rocky Mountains and the Sierra Nevadas. By erecting a high barrier between the Pacific Ocean and the center of the continent, the mountains cast a “rain shadow’’ over the land to their east and gave the region its defining dry climate. When clouds roll into the West Coast from the Pacific they collide with the wall of mountains and dump most of their moisture on the western front in the form of rain or snow. As a result, the drier, eastern side of the Rockies receives just ten to fifteen inches of precipitation annually, one-half or one-third of what the rest of the continent typically receives. The central hardwood forests dwindled, eventually leaving a dry open plain.

This open expanse also left the wind free to blow, and blow it does—hard and incessantly. The winds dry up much of whatever moisture does fall from the sky and punishes any living thing that dares raise itself more than a few feet above the ground. The early climatologist Robert DeCourcy Ward described the dramatic effects of a warm westerly wind known as a chinook: “Evaporation and melting are so rapid that a foot of snow may disappear within a few hours, being sucked up from the ground without [leaving] even a trickle of water . . .”

And because this wide plain lies hundreds of miles from either coast, it lacks the moderating influence of the Pacific and Atlantic oceans. The result is wild temperature extremes, from 30 or 40 degrees below zero in the winter to 110 degrees or more in July and August.

Still, millions more years passed before the prairie grassland made its appearance. Some twenty thousand years ago, much of North America was covered by the Laurentide ice sheet, a towering glacier that stretched from the Arctic Ocean as far south as Iowa and as far east as New England. As it crawled south across the continent, it scraped the land flat, scooping up rocks and boulders and grinding them to fine gravel. When it receded, starting about eighteen thousand years ago, it deposited this gravel as a layer of fine glacial till, leaving behind a vast, mineral-rich plain stretching from the Rocky Mountains to the Mississippi River and parts of Illinois and Indiana. Over the ensuing centuries, rivers flowing down from the Rockies carried an additional fine sediment of eroded rock and spread it in alluvial layers across the plain. Westerly winds dropped an even finer coating of rock dust, adding another endowment of minerals. Then millions of mammals and plants lived and died there, bequeathing their own rich organic material to the ground. The resulting layer of earth was deep, porous, full of tiny microbes, and packed with carbon—the perfect medium to produce one of the greatest ecosystems on the planet.

Even so, the unforgiving climate made this place hostile to virtually every form of plant life but one: the hugely adaptable family Poaceae—grass. Poaceae’s twelve hundred species are found all over the globe, from Patagonia to Uzbekistan, and account for all the world’s leading food grains—corn, rice, wheat, barley, and oats. On North America’s great plain more than one hundred species took root, perfectly adapted to a place that was dry and windy. The roots of prairie plants such as switchgrass, big bluestem, and blazing star reach as much as twelve feet underground, where they tap deep stores of moisture to survive dry spells. The same roots create long vertical channels where rainfall can penetrate far into the soil, hide from the sun, and replenish the grass. When winter’s frigid temperatures approach, these grasses pull energy from their leaves and stems into their roots, then store it there to produce new growth when spring arrives. These root webs also create a sort of underground forest populated by mites, tiny worms, beetles, ants, bacteria, and fungi—all of them feeding off soil nutrients and nourishing them in return. These immense root networks give prairie sod a density unrivaled in other places. The conservationist and writer John Madson has noted: “One may dig a trowel into a lowland forest floor and come up with soil that is not wholly occupied with plant parts, but in the tallgrass prairie every cubic inch of soil surface is a mass of rootlets.’’ A cubic yard of big bluestem sod, he wrote, can contain nearly thirteen miles of tiny roots and root hairs. And when the roots die, they deposit additional organic matter to enrich the soil.

Aboveground, too, grasses are exquisitely adapted to a dry climate. Their profusion of narrow blades can capture huge amounts of sunlight—one acre of grass can contain ten acres of leaf surface—while leaving little area for moisture to evaporate. In addition, these blades typically are coated with tiny hairs or ridges that protect moisture from the wind. Like other plants, they have stomata—miniature valves that inhale carbon dioxide and exhale water vapor—but unlike most other plants, many species of grass can shut their stomata in the heat of day to retain water, then open them in the cool of the night.

Grasses also flourished because they can turn the region’s scourges to their advantage. Wildfires that are common on the prairie—some caused by lightning, some set by people—kill off bigger, woodier competitors such as sumac and red cedar and burn away the layer of dead grass known as thatch that can smother young grass shoots. Grasses survive fire because 80 percent of their biomass lies belowground in the form of roots and horizontal underground stems known as rhizomes, which protect their stores of water and carbohydrates until the flames pass. In much the same way, prairie grasses adapted to survive the grazing animals that have populated the region for centuries. Most plants have nodes where new growth sprouts; in most grasses that node lies close to the ground, even belowground, safe from the teeth of elk, antelope, and bison.

By the time Europeans arrived in the sixteenth century, grasslands covered one-fifth of North America, an expanse exceeded only by the boreal forest.