Реферат: Desert Biome Essay Research Paper DESERT BIOMEAny
Desert Biome Essay, Research Paper
Any barren region that supports very little life may be called a desert. The cold expanses of Antarctica, extreme northern Asia, and Greenland are therefore true, but cold, deserts. Most commonly, however, the term desert is used for regions that are barren because they are arid, or dry. Arid deserts receive little precipitation and are characterized by specialized plants that tolerate drought conditions and salty soils, and by distinctive land features. Most desert areas get less than 5 inches (13 centimeters) of rain in a year. The rainfall is not only scanty but also uncertain. “Records at Iquique in northern Chile showed no rain for a period of four years. The fifth year brought 0.6 inches (1.5 centimeters), making a five-year average of 0.12 inches (0.3 centimeter). At another time 2.5 inches (6.4 centimeters) fell in a single shower. ” (Compton’s Encyclopedia)
Temperatures range widely in deserts. The greatest daily fluctuations occur in deserts near the equator. Temperatures above 100o F (38o C) occur regularly in summer. “Azizia, 25 miles (40 kilometers) southwest of Tripoli, in Libya, holds the record with 136.4o F (58o C), while Death Valley, Calif., comes close with 134o F (56.7o C). “(Genius book of world records 2000) Winters are cold in middle-latitude deserts, located far from the equator. “At Luktchin in central Asia the average temperature in July is 90o F (32o C), while the January average is 13o F (-10.6o C)–a range of 77 Fahrenheit degrees (42.6 Celsius degrees)”(Compton’s Encyclopedia). The temperature drops sharply in the desert night. Dry air, cloudless skies, and bare, dry earth furnish ideal conditions for the cooling of air after sunset. A 24-hour range of 25 to 45 Fahrenheit degrees (14 to 25 Celsius degrees) is common, and it may be as great as 60 to 70 Fahrenheit degrees (33 to 39 Celsius degrees).
In the deserts, ordinary wells can usually tap a supply of good water. Oasis settlements therefore are most often found where wadis are numerous. Ergs into which many wadis drain may have a water supply. Desert shrubs in the hollows between the dunes signal its presence. Desert soils are usually productive when given water. They are coarse textured and highly mineralized. Most widely cultivated are the water-transported soils of floodplains and alluvial fans. Plants of the desert depend on sources of water or the adaptations they have developed. Few parts of the desert are entirely barren. Where water seeps toward the surface, a great variety of plants spring up. After a rain low shrubs and grasses come to life. At blooming time, the plants are fragrant and bright with color. They grow quite far apart, instead of providing complete ground cover. Desert plants differ in the ways they adapt themselves to arid places. Those that depend on the rain sprout when it falls, bloom quickly, ripen their seed in a few days, then wither and die.
Other plants depend upon underground water and have long root systems. Various adaptations of the leaves prevent loss of moisture through transpiration. Cactus leaves, for example, are reduced to spines.
The most precious thing in the desert is water. Ordinary non-desert plants take up water from the soil by means of their deep roots and give off water through their leaves. This process is called transpiration. The cactus has no leaves or only very small ones that usually drop off as the plant matures. The cactus thus avoids a huge loss of water. Photosynthesis, the process by which plants make carbohydrates as fuel to meet their energy requirements, occurs on the green surface of the cactus stem. The stem is fleshy and thick and can store a large amount of water. Its tough skin keeps the water safely hoarded. Cactus roots spread out near the surface of the soil, enabling the plant to absorb water from a wide area during the infrequent, light rains that occur in the desert. With few exceptions, cacti bear tough, sharp spines. These spines help protect the plant from many desert-dwelling animals. The spines grow from small cushion-like tissues called areoles that are arranged in patterns on the surface of the plant. One of the most impressive cacti is the saguaro, the giant cactus of Arizona. Scientists place it in the genus Cereus. “Its stems and branches are like great spiny columns up to 2 feet (about 0.6 meter) thick. It often grows to a height of 50 feet (15 meters). It has long, tubular, showy flowers. The egg-shaped fruit is edible, with a crimson pulp.”(Compton’s Encyclopedia) Woodpeckers dig out their nests in the big stems. Elf owls often take over these nests when they are abandoned.
Desert life is a constant struggle for every form of life, plant and animal. Although this vast arid land is so harsh adaptation has played its part to supply these deserts with abundant source of life. Deserts are found on every continent but Antarctica. Here are the deserts found in North America.
North America Area (Sq. Miles)
Great Basin (southwestern United States) 190,000
Chihuahuan (northern Mexico) 175,000
Sonoran (southwestern U.S. and Baja California) 120,000
Colorado (California and northern Mexico) –
Yuma (Arizona and Sonora, Mexico) –
Mojave (southwestern United States) 25,000