Climate In the middle of
North America is a huge area of land which was once covered
with grasses and colorful wild flowers. The French called
the rolling plains of grass "prairie", from the word for a
meadow grazed by cattle. The prairies are a type of
grassland dominated by herbaceous plants and grasses. Very
few trees grow on the prairies and are usually widely
scattered. The prairies form a
triangular area from Alberta, Saskatchewan, and Manitoba
down through the Great Plains to southern Texas and Mexico,
and approximately 1,000 miles from western Indiana westward
to the Rocky Mountains. They cover about 1.4 million square
miles. As you move from
east to west, the rainfall in the prairies decreases.
Climates are more moist close to the mountains and to the
east and north; they are driest in the central portions.
This creates different types of prairies, with the tallgrass
prairie, known as the true prairie, in the wetter parts.
Grasses such as big
bluestem,
and Indian
grass, and
many species of flowers grow here. The plants can sometimes
grow to be 10 feet tall. Mixed-grass prairies are found in
the central Great Plains, and shortgrass prairie towards the
rain shadow of the Rocky Mountains. The rain shadow causes
Pacific ocean moisture to rise and cool, dropping as rain or
snow on the western side of the mountains instead of on the
prairies. Precipitation in the
prairies can reach from about 12.6 inches in the shortgrass
prairie to 21.7 inches in the tallgrass prairies. The prairies were
maintained in their natural state by climate, grazing and
fire. Rainfall varies from year to year in the prairies.
There is usually a long dry period during the summer months.
Every 30 years or so there is a long drought period which
lasts for several years. The most famous drought was in the
1930s, when the prairies were called the "Dust
Bowl". The climate of the
prairies is influenced by its mid-continental location, and
the sheltering effect of the Rocky Mountains. Being located
far from the moderating effects of oceans causes a wide
range of temperatures, with hot summers and cold winters.
Strong winds blow across the endless plains during both
summer and winter. Every one to five
years fire would spread across any given area of land. These
fires moved rapidly across the land and did not penetrate
into the soil very far. They killed most saplings, and
removed the thatch of dead grasses, allowing early flowering
spring species to grow. Prairie plants have
adapted to fires by growing underground storage structures,
and having their growth points slightly below ground
surface. The soil under a prairie is a dense mat of tangled
roots, rhizomes, bulbs, and rootstock. The plants die back
every winter, but are kept alive from year to year by the
underground root system. Roots of prairie plants can by
longer than the plant is tall. The roots of big bluestem may
be 7 feet long, and switchgrass roots can be 11 feet long.
Two-thirds of most prairie plant are below the ground. Some
roots die each year and decompose, adding lots of organic
matter to the soil. That's why the soil of prairies is so
fertile. Before settlers
moved west, the prairies were covered with herds of grazing
animals, such as buffalo, elk, deer, and rabbits. These
animals increased the growth in prairies by adding nitrogen
to the soil through urine and feces, and creating open areas
for plants that like to have the soil dug up.
Prairie
dogs dug
huge underground tunnel systems which aerated the soil and
allowed water to reach several feet below the surface.
Today very little of
the original prairies survive, only one to two percent. Much
of the land has been turned into agricultural uses, urban
areas are moving in, and fires are being suppressed. The
genetic and biological diversity of the plants are
disappearing. The herds of thousands of buffalo were all but
wiped out. There is a strong movement to educate people
about prairies. Many states are rehabilitating what is left
of their prairies and reintroducing the native wildlife and
plants. Please visit our
image
gallery of
the prairies.
bibliography: "Prairie Portrait",
http://www.ag.usask.ca/exhibits/walkway/plains/portrait.html,
(June 2001). "Prairie Climate",
http://www.ag.usask.ca/exhibits/walkway/plains/climate.html,
(June 2001). "Prairie",
http://www.IowaPrairieNetwork.org/what_is_prairie.htm,
(June 2001). "Tallgrass Prairies
of Illinois", http://www.inhs.uiuc.edu/~kenr/prairiebiodiversity.html,
(June 2001). "Prairie Grass
Cultural Guide by Prairie Frontier and photos" ,
http://www.prairiefrontier.com/pages/prairegrs.htm,
(June 2001). "The Grassland
Biome", http://www.richmond.edu/~ed344/webunits/biomes/grass.html,
(June 2001). "Grassclimate",
http://www.richmond.edu/~ed344/webunits/biomes/gclimate.html,
(June 2001). "Tallgrass Prairies
of Illinois", http://www.inhs.uiuc.edu/~kenr/prairieintroduction.html,
(June 2001).
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