Prairie Grasses of North America
The temperate grasslands in North America are called prairies. At one time, prairies were the largest biomes in North America. Today only small patches of true grassland remain, and most of them are in state and national parks.
The loss of the great prairies was mainly caused by the movement of people from the settled lands of the United States after the Civil War (1861–1865) to open lands farther west. Many of the settlers were farmers, but some were hunters and traders. These early pioneers first affected the animal population in the prairie. Bison (commonly called American Buffalo in the United States) were killed for sport as well as for their hides and meat. Prairie dogs were poisoned because they were a nuisance to farmers and ranchers. Coyotes and wolves were hunted because they killed the rancher's animals.
In time the natural grass was killed as well. Cattle and sheep were brought in, and they overgrazed the land, meaning that they ate so much that the grass could not grow enough to produce food that kept the roots alive. Sheep often pull out the entire grass plant, roots and all. Farmers also helped destroy the grassland by replacing the natural grasses with crops such as wheat and corn.
When the prairie grassland was present, two basic factors kept grasses as the dominant plant. One was the occasional natural fires, caused by lightning. Any shrubs or trees that might have started growing in the area were burned. While the grass also burned, it was able to regrow from underground roots, unlike the shrubs and trees. Fires also cleared the ground of matted grasses that restricted new grass growth. The nutrients in the burned grass were added to the soil, making it fertile for new grass to grow in.
The second factor keeping other plants off the prairies were bison. The constant trampling of the ground by these heavy animals compacted (squeezed together) the soil so that water could not penetrate deeply enough to support the roots of trees or shrubs. Bison also rubbed against the trees on the edge of the grasslands. This helped the bison to shed their winter fur, but the rubbing also stripped the bark from some of the trees, causing the trees to die. Thus the boundaries of the grasslands were maintained.
To make a model of the height of grasses in the North American prairie.
- 1 sheet of 81⁄2-by-11-inch (21.25-by-27.5 cm) white copy paper
- green crayon
- transparent tape
- Use the ruler and pen to draw a line across the short side of the paper and indented 1⁄2 inch (1.25 cm) from the edge.
- Draw two more lines, 4 inches (10 cm) apart and parallel to the first line.
- Draw grass in the small section, as shown, and color it.
- In the center section, about 1 inch (2.5 cm) from the bottom, draw a 3-by-1⁄8-inch (7.5-by-0.3-cm) "cut out," as shown. Cut out this section.
- In the third section, 1 inch (2.5 cm) up from the bottom, draw a 2-by-6-inch (5-by-15-cm) "cut out," as shown. Cut out this section.
- Label the third section Prairie Grasses.
- Label the left side of the cutout areas in section three Average Yearly Rainfall and the right side Grass Height, as shown.
- Make a mark even with the top and on both sides of the cutout areas. Make two additional sets of marks, one 2.5 inches (6.25 cm) from the top mark and the other 5 inches (12.5 cm) from the top mark.
- Starting at the top mark on the left of the opening, label the average yearly rainfall: High, Med, Low.
- Starting at the top mark on the left, label the grass height: 48 in. (120 cm), 24–48 in. (60–120 cm), 6–24 in. (15–60 cm).
- Cut along the indicated line to separate the grass strip from the other sections.
- Score each fold line by laying the ruler along each of the fold lines, then trace the lines with the pen.
- Fold the paper along fold line 1, then along fold line 2, and secure the folded sections together with tape.
- Insert the top end of the grass strip in the grass strip slot so that the colored side of the strip is visible through the opening in the front of the model.
- Move the grass strip up and down to model the different heights of grass.