Geography The Great Plains

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Science of the Expedition

In the 16th century Spanish explorers first saw the vast expanse of the grasslands, calling them a "sea of grass." The French colonists called them prairies, which means "large meadows." In many ways this term was certainly an understatement. In the historic period of the Indian occupation of the plains, before white intrusions, the prairies covered more land in what is now the United States than any other kind of vegetation - more area than the green deciduous forests of the east which spread from Maine to Georgia; more area than the deserts of the southwest; more area than the boreal forests of the north. Walt Whitman wrote of the prairie that it was "North America's characteristic landscape," and "while less stunning at first sight" than Yosemite, Niagara Falls and Yellowstone, "last[s] longer, fill[s] the aesthetic sense fuller, and precede[s] all the rest."

The grass sometimes stood taller than a man, and in many places a horseman had to stand on his horse's back to get his bearings. The tops of the undulating grasses waved in the breeze like the waves of the ocean, stretching like an unbroken expanse of water to the horizon. Lewis and Clark saw these lands, as did Pike and Long. The first white settlers of Indiana, Illinois and Missouri also saw them, then promptly plowed them up and planted crops. This pattern continued across the plains, until by 1900 there were barely any examples of prairie land left. Getting rid of the original plants and animals of the plains so quickly contributed greatly to soil erosion and created the dustbowl of the 1920s and 1930s.

The Great Plains are still there today, but are devoid of the prairie grasses which made them distinctive to their first European visitors and special to their first human occupants. In fact, the prairie ecosystem is probably the only ecosystem that we cannot see as it looked when Lewis and Clark saw it. The mountains are still there, the woodlands, the deserts, the rainforests, the ocean beaches, but the prairies are gone. You can see isolated areas of preserved prairie - for instance, at Tallgrass Prairie Preserve in Kansas, or the Allwine Prairie Preserve in Nebraska. But the vast seas of prairie are gone, probably forever.

The Great Plains cover about ¼ of the continent, extending from the Arctic tundra through the prairies to south Texas desert grassland. Ancient inland seas grew and waned across the continent's midsection, depositing layer upon layer of sediments. When the Rocky Mountains began to rise about 65 million years ago, they looked eastward toward flatlands covered with forests. As the Miocene Epoch began, the rainshadow of these mighty Rocky Mountains began to block weather patterns, clouds and moisture from the west, causing less precipitation. Desert plants moved in and grasses flourished in the cooler, drier climate. The Great Plains slowly became the climactic and biological barrier between east and west on the North American continent.

Grasshoppers, locusts and beetles feasted on the quick growing grasses. Mammals also adapted to the plains - those with grinding teeth, long legs, hoofed feet, and chambered stomachs. On the open plains, with no cover, animals had to run, burrow, or herd together for protection against predators. This became the home of the bison, pronghorn, prairie dog, jackrabbit, rattlesnake, wolf and coyote. The pronghorn is not a true antelope at all but a species unique to North America. Pronghorns are the only living animals with branched horns which shed sheathes over the horns annually. They can run at speeds up to 40 mph.

But unlike Africa's grasslands, where many species evolved together and continue to coexist, the grasslands of North America developed incredible populations of a single animal, the bison, with smaller numbers of elk and deer. Bison at one time existed in numbers up to 40 million, while pronghorns probably numbered 15 million. This region was teeming with wildlife during the prehistoric and Indian periods, one of the most biologically rich in the world, comparable to the Serengeti in Africa. Lewis and Clark and their men wrote in their journals about the unbelievable numbers of animals they encountered, at one point saying that they had to club the animals out of their way to proceed onward.

Sgt. John Ordway - May 9, 1805 - "The game is getting so plenty and tame in this country that some of the party clubbed them out of their way." Pvt. Joseph Whitehouse, May 9, 1805 - "The men informed us that the buffalo were so numerous and tame at a small distance from us that some of them went up near enough to strike them with clubs, but were so poor as not to be fit for use." William Clark, May 3, 1805 - "Great numbers of buffalo, elk, deer, antelope, beaver, porcupines, & waterfowls seen today, such as geese, ducks of different kinds, & a few swans." Sgt. Patrick Gass, May 27, 1805 - "The views from the hills are interesting and grand. Wide extended plains with their hills and vales, stretching away in lessening wavy ridges, until by their distance they fade from the sight. Large rivers and streams in their rapid course, winding in various meanders. Groves of cottonwood and willow along the waters intersecting the landscapes in different directions, dividing them into various forms, at length appearing like dark clouds and sinking in the horizon. These enlivened with the buffalo, elk, deer, and other animals which in vast numbers feed upon the plains or pursue their prey, are the prominent objects which compose the extensive prospects presented to the view and strike the attention of the beholder. . . There are Indian paths along the Missouri and some in other parts of the country. Those along that river do not generally follow its windings but cut off points of land and pursue a direct course. There are also roads and paths made by the buffalo and other animals; some of the buffalo roads are at least ten feet wide."

Through it all run the rivers, slow, lazy rivers winding through the flat plains, shallow and muddy. It is estimated that half of the original mass of the Rockies has been washed into the silt apron of the Great Plains by these rivers. The mightiest among them is, of course, the Missouri-Mississippi system. The Missouri River is 2,315 miles long and drains over 500,000 square miles, or 1/6 of the continental U.S. It flows from 14,000 feet high in the Rockies to 400 feet above sea level at St. Louis. The river flows through four sections - St. Louis to Yankton features high rainfall and humidity. Yankton to the Milk River features great sedimentary deposits, Milk River to Great Falls the river flows through semiarid plains, while from Great Falls to the headwaters the river passes through an alpine, Rocky Mountain region.

A description of the way the plains looked when Lewis and Clark first saw them might run like this:

Grasses a few inches high made up the "doormat" of the Rocky Mountains, that is, the strip of land running north and south just east of the mountains in todays' Colorado, Wyoming, Montana and Texas, the windswept, semi-arid and high plains of the West. Rainfall here is less than 20 inches a year, and grasses reach only 1½ feet tall. Common grasses were sagebrush and perennial shortgrass species like buffalograss (Buchloe dactyloidesi) and blue grama (Bouteloua gracilis).

Moving eastward, the plains sloped into the central lowlands where moister winds intruded. The sagebrush and shortgrass gave way to taller species like the little bluestem, switch grass and Indian grass. The central prairie was the midgrass prairie, the most extensive, with a maximum grass height of 4 feet. The boundaries of these prairie types were not well defined, and the central prairie actually extended eastward in some places all the way to Illinois. Here the moisture increased over the more arid area directly in the rainshadow of the Rockies. This was due to moist winds blowing up from the Gulf of Mexico, which met cool dry air from the north and formed weather fronts, along which rain fell. Common grasses were the western wheatgrass (Agropyron smithii) and little bluestem (Andropogon scoparius).

The last zone, furthest to the east, was that of the tall grasses. The tallgrass prairie, which edged into the Dakotas, Nebraska and Kansas and arced up to Alberta to the north. Here grasses could grow 8-12 feet tall. Common grasses were the big bluestem (Andropogon gerardii) and switch grass (Panicum virgatum). Rather than try to repel the animals that wished to forage on them, they simply offset the effects of grazing with more efficient root systems - they grew back more easily. Grasses near the Mississippi once soared to 12 feet tall, and there the eastern forests began to thrive and the Great Plains - and prairies - came to an end.

High evaporation and low rainfall makes it difficult for trees to grow on the Great Plains. Only along the river bottoms can most trees grow successfully in the natural way. The forests that lined the rivers in this dry country were affected over the millennia by prairie fires that roared into them from the surrounding grasslands. Soon the more vulnerable tree species were burned out, leaving the rivers edged with fire-resistant trees such as thick-barked oaks, willows and cottonwoods. The grasses were unaffected by these fires, since they rushed quickly over the surface of the land but did not touch the roots underground. Fire also destroys the dead plant material that accumulates among the grasses. If dead vegetation builds up, it smothers the growth of new grass in the spring; this is the single greatest natural factor in stopping the growth of tallgrass. Burning a prairie annually makes the growth of grass more abundant both below and above the ground. American Indians knew this and deliberately set the prairies on fire each year. The new green grasses sprouting up through the blackened earth attracted the bison, pronghorn and other grazing animals which the Indians needed to hunt for their survival.

Grasses are not the only plants on the prairie. One study of prairie plant life conducted near Lincoln, Nebraska located 237 different species of plants within one square mile of prairie. During the spring and summer the prairies are studded with the colors of wildflowers like prairie-smoke, Indian paintbrush, blazing star and long-headed coneflower.

The climate of the plains is harsh, with temperatures far below freezing in the winter and harsh, hot, direct sunlight in the summer. Tornadoes slash their way across the open land with winds sometimes in excess of 500 miles per hour.

Only remnants of the vast tallgrass prairie are still intact, scattered here and there in parks and refuges. Studies of such areas have shown that the original prairie was a remarkably productive and diverse ecosystem, with few equals in the world. Homesteaders in the tallgrass found the sod so dense that it broke their plows. In the plains further west they found shortgrass prairie and a more arid environment, with sod their only building material.

Grasses bind the soil together with their matted root systems. This is displayed in areas where the subsoil is little more than drifting sand dunes, such as north central Nebraska. There, grass-covered dunes occupy more than 19,000 square miles, nearly ¼ of the state. Some of the dunes rise to 200 feet tall. Sandhill grasses have spreading root systems near the surface, which not only assure maximum water-gathering ability but also bind the soil and reduce erosion. For example, the bush morning glory's roots may reach down 10 feet or more, with laterals fanning out 15 to 25 feet in all directions. Soapweed is another common plant of the sandhills region. It was this intertwined root system of unbelievable extent which kept the rich soils of the Great Plains intact. When the plows of the white farmers, the "sodbusters" broke through and destroyed this root system, the stage was set for disaster as loose soils could be blown away by the winds. This effect helped create the dustbowl of the 1920s and 30s. Only artificial, government subsidized irrigation, aided by river damming projects, has allowed the soil of the Great Plains to remain fertile and intact for the huge farming operations there. Without these activities the region would become a wasteland - because it no longer has its grasses with their extensive root systems and its animal tenders, the rodents and bison.

Prairie dogs, pocket gophers and other burrowing animals were shapers of the landscape, and kept the plains grassy for thousands of years. Digging far deeper than any plow, these rodents loosened soil already foraged and trampled by bison, mixed top layers with subsoil, aerated it, and gave water a way to percolate downward. As a result, the grasses regenerated. Lands the rodents once tended now fall gradually to thistle, scrub and mesquite. It is estimated that as many as 25 billion prairie dogs once inhabited the plains. One colony of 400 million observed in Texas in 1900 covered more than 25,000 square miles. Domestic cattle, confined to specific areas, overgrazed the grasses, which had no time to rejuvenate and dwindled. Ranchers believed the loss of the grasses was due to the prairie dogs, and began slaughtering them in unbelievable numbers. However, the prairie dogs were the true heroes of the successful formation of prairies.

Suggestions for further reading:

Daniel B. Botkin, Passage of Discovery New York: Perigree Books, 1999
Daniel B. Botkin, Our Natural History: The Lessons of Lewis and Clark
Patricia D. Duncan, Tallgrass Prairie: The Inland Sea Kansas City: The Lowell Press, 1979

Last updated: April 10, 2015

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