Endangered Species Handbook

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Grasslands, Shrublands, Deserts

Drylands of the World: NORTH AMERICA: Page 1

     In the early 1800s when Lewis and Clark explored the West for President Thomas Jefferson, short and tallgrass prairies occurred in a wide north-south expanse from southern Canada to the Gulf of Mexico, covering at least 1.5 million square kilometers (945,000 square miles) (Knopf 1988). Tallgrass prairie, requiring a moist environment, with 50 to 100 centimeters of rain per year, grew in the eastern section, extending in a wide north-south band from southern Canada to southeast Texas and southwestern Louisiana, and from Illinois in the east to eastern Oklahoma and North Dakota in the west.  Tallgrass prairie once covered 577,500 square kilometers (365,825 square miles) (Knopf 1988).  Named for the grass species within this ecosystem that reach up to 12 feet in height, it grows in thick, luxuriant stands (Brown 1985).  Early settlers considered this habitat to be an impediment to farming and plowed millions of acres.   Soon after European colonization, the eastern grasslands were plowed into prime farmland. Today, tallgrass prairie is reduced to less than 1 percent of its original expanses.
 
     The tough, compacted shortgrass of the Great Plains further west required a heavy steel plow to break it apart, which was invented late in the 19th century, opening up additional millions of acres to cultivation (Ponting 1991). The United States government encouraged settlement by giving away plots of 160 acres of land to anyone who laid claim.  Settlers and professional hunters killed off the vast herds of American Bison, Black-tailed and White-tailed Deer, Elk, and Pronghorn Antelope, as described in Chapter One.  Much of what shortgrass prairie remains is federally owned.
 
     Settlers who plowed native grasslands did not appreciate the fragility of this environment, with its low rainfall and soil anchored by grasses. The topsoil was extremely deep, 5 inches or more, perhaps the world's richest soil.  It had built up over hundreds of thousands of years from grassland vegetation dying and enriching the soil, along with dung from untold numbers of bison and other ungulates.  Settlers deep-plowed this virgin prairie, reaping bumper crops for a few years. They enlarged their farm acreage by removing windbreak strips of vegetation and cutting tree groves.  The eradication of natural vegetation, especially trees, lowered the ambient humidity because of the massive amounts of water vapor they had emitted, reducing rainfall.  The lack of contour plowing encouraged erosion, as did the removal of the vegetation that held the soil in place. 
 
     This set the stage for major droughts which began in the early 1930s, and windstorms blew millions of tons of precious topsoil off the land.  The plains of Oklahoma were the first to experience massive dust storms, forcing thousands of farmers to abandon the region.  The phenomenon came to be known as the Dust Bowl.  Topsoil disappeared from plowed fields in Kansas, Colorado, western Texas, New Mexico, Nebraska and the Dakotas (Ponting 1991).  Winds swept away an estimated 350 million tons of topsoil in a single storm in May 1934, and blinding dust storms continued throughout the 1930s, darkening skies hundreds of miles away, as far east as New York City (Peck 1990).  By 1938, 10 million acres had lost 5 inches of topsoil, and another 13.5 million acres lost the top 2.5 inches (Ponting 1991).   An estimated 850 million tons of soil were being lost a year by the end of the 1930s, and the United States government began a program to restore the soil (Ponting 1991).  Throughout the prairies, approximately 18 million acres turned into shrub desert during the decade of the 1930s (Peck 1990).



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