Grasslands. Savannas are tropical grasslands that support scattered trees and shrubs. They often form a transitional biome

Transcription

1 Grasslands INTRODUCTION About 25% of Earth s land surface is covered by temperate grassland. These large expanses of flat or hilly country cover much of North America, as well as large areas of Europe, Asia, and South America. Most grasslands are found in the interiors of continents, where there is too little rainfall for a forest but too much rain for a desert. Rolling hills covered with grasses and very few trees are typical of North American grassland prairies. A few scattered trees are found on savannas, tropical grasslands of Africa. Temperate grasslands have subtle differences and different names throughout the world. Prairies and plains of North America are grasslands with tall grasses, while the steppes of Russia are grasslands with short grasses. Veldts are found in South Africa, the puszta in Hungary, and the pampas in Argentina and Uruguay. Savannas are tropical grasslands that support scattered trees and shrubs. They often form a transitional biome Page 1 of 6

2 between deserts and rain forests. Some temperate grasslands are also called savannas. The word savanna comes from the Spanish word zavanna, meaning treeless plain. Savannas cover almost half of Africa (mostly central Africa) and large areas of Australia and South America. ABIOTIC DATA The grassland climate is rather dry, averaging about 20 to 100 centimeters (8 40 inches) of precipitation a year. Summers are very hot and may reach 45 C (113 F). Winter temperatures often fall below freezing, which is 0 C (32 F). The soil of the savanna is poor in nutrients, compared to other types of grassland. Data from Missouri Botanical Garden The average rainfall for a grassland is about 75 centimeters (30 inches) per year. Savannas often have a season of heavy rainfall followed by a season of drought. Annual rainfall on most savannas ranges from 76 to 100 centimeters (30 40 inches). These moist grasslands support trees and tall grasses that may reach 3 meters (10 feet) tall. The heavy rain sometimes washes away the top layer of soil in the savanna. Valuable nutrients that support plant life are washed away with it. Other savanna environments receive as little as 25 centimeters (10 inches) of rain each year. Here grasses grow in short clumps, and trees are sparse. BIOTIC DATA Most savanna grasses grow in clumps and have deep roots. They turn brown and stop growing during the dry season. Trees shed their leaves to conserve moisture and energy. Page 2 of 6

3 Prairie dogs build extensive networks of tunnels underground. Pronghorn antelope are found grazing grasslands across western North America. The animals of the temperate grassland have developed ways to survive harsh conditions. The ground squirrel and kangaroo rat do not sweat. This helps them conserve water in the dry season. Bison grow thick coats that protect them during the harsh winters. Some grassland animals, such as gophers and prairie dogs, build underground burrows. They store food in their burrows and hibernate through the winter. American bison once roamed the plain in herds estimated as large as 50 million. By 1889 less than 1000 were bison left. They were important to the plains Indians for food, shelter, and clothing. Courtesy of R. Town, U.S. Fish and Wildlife Service The sharp-tailed grouse is a ground-dwelling bird of northern brushlands and prairies. During courtship, males gather in open areas, inflate reddish purple air sacs at the sides of the neck, and emit booming calls while strutting with tails raised and fanned and wings fluttering and quivering. Other animals that live or have lived in the temperate grasslands include wild horses, wolves, prairie dogs, jack rabbits, deer, mice, coyotes, foxes, skunks, badgers, blackbirds, grouse, meadowlarks, quail, sparrows, hawks, owls, snakes, grasshoppers, leafhoppers, and spiders. Page 3 of 6

4 Courtesy of John and Karen Hollingsworth, U.S. Fish and Wildlife Sservice There are several species of rhinoceros: black, white, Javan, Indian, and Sumatran. All are listed as endangered by the International Union for the Conservation of Nature and Natureal Resources. Once numerous in eastern and southern Africa, they are now found only in national parks and game reserves. Courtesy of Ken Stansell, U.S. Fish and Wildlife Service Giraffes are found in the African savanna south of the Sahara Desert. Giraffes feed almost exclusively on the leaves of acacia, mimosa, and wild apricot trees. They drink only rarely, taking in approximately 8 liters (2 gallons) of water in a week, and can go a long time with no water at all. The savanna of eastern Africa has more animals than any other grassland biome. A wide variety of animal life is adapted to the environmental conditions of this biome. For example, large herds of antelopes, zebras, and wildebeests migrate great distances to find grass and water. Predators, such as lions, hyenas, and cheetahs, follow and prey upon these herds. ISSUES Few natural grassland regions remain, because most have been turned into farms or grazing land. They suit these purposes because they are flat, are covered with grass, and have rich soil. In North America, the prairies were once inhabited by huge herds of bison and pronghorn antelope. These animals were hunted by wolves, bears, and other predators. Where prairies were turned into farmland, the large herds and the predators are now gone. Page 4 of 6

5 The rich soils make ideal farmland. Overuse of the land can deplete the soil of vital nutrients. Overgrazing, plowing, and excess salts left behind by irrigation waters have harmed some grasslands. Strong winds blow loose soil from the ground after plowing, especially during droughts. This caused the dust storms of the Great Plains of the United States, such as occurred during the Dust Bowl years in the 20th century. Page 5 of 6

6 Courtesy of John and Karen Hollingsworth, U.S. Fish and Wildlife Service A service botanist looks after an endangered western prairie fringed orchid in Nebraska. Fringed orchids are found in tallgrass prairies, most often in moist habitats or sedge meadows, and require direct sunlight for growth. They persist in areas disturbed by light grazing, burning, or mowing. As improved agricultural methods are found, more and more of the prairie is converted to farmland. This circle irrigation system conserves water and promotes crop rotation. This circle is approximately 0.4 kilometers (0.25 miles) in diameter. Many species of grasses, flowers, shrubs, and bushes form the base of the food web for birds, rodents, insects, and grazing animals. Plants and the animals that depend on them are lost when grassland prairie is converted to other land uses. Climate change is another issue for grasslands. Scientists continue to try to determine whether the climate is actually warming. Although these areas receive too little rainfall to sustain a forest, some of these areas had much denser foliage in the recent past. Studies suggest that even less water may be available in the future. This would affect the use of this land for grazing animals. If a drier climate causes some areas of the southeast or midwest to lose their ability to sustain a forest, those areas may come to resemble grasslands. A wetter climate, however, might enable forests to grow in areas that are now grasslands, while also allowing grasses to grow in areas that are deserts today. Page 6 of 6