Geography - The Great Plains
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
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