Desert
...ind shelter. Some of the animals go into underground burrows, where the air is a little cooler. Not all land classified as desert is equally arid. The driest parts may look very stony, but where there is more moisture there will be more plants, such as sage brush, seasonal grasses, and small shrubs. There may tree sized cacti, palo verde, and Joshua trees. These greener deserts may be home to quail, pygmy owls, and even desert foxes and hawks. A few tertiary consumers may be able to survive in these richer environments. An interesting desert "extra" is the oasis, a place where springs of water flow to the surface, providing an environment where palm trees and shrubs may grow. Though rare, oases gladden the hearts of travelers, and provide a refreshing micro-world with its own ecology. Desert: How deserts develop and change Most deserts lie between the latitudes of 15° and 35° on each side of the earth's equator. These latitudes are in zones of high atmospheric pressure—that is, areas in which cool air descends and becomes warm. These high pressure zones are created by the way the air moves over the earth. At the equator where temperatures are high, air becomes warm and rises. As the air rises, it cools and releases moisture over regions near the equator. In time, the air descends over areas that extend between 15° and 35° both north and south of the equator. As it descends, it becomes warm and dry. This warm air causes desert conditions. The Sahara and several other great deserts lie in this region. Regions separated from an ocean by mountains also tend to be dry. A moist wind blowing inland from an ocean loses its moisture as it rises over mountains and becomes cool. As the wind descends on the side of the mountains facing land, it becomes warm and dry. This warm air creates a rain shadow, or dry area. The North American deserts developed partly because of the rain-shadow effect. Cold ocean currents flowing next to a continent can cause deserts to form in areas along the coast. Deserts form because the cool winds that blow across the cold water and onto the land can carry little moisture. The Atacama Desert in South America is an example of such a desert. A change in climate can cause changes in the location and extent of deserts. During the last few thousand years, many deserts have formed as the world's climate has changed from cool and wet to warm and dry. Human activities have also caused desert regions to expand. This expansion occurs because of the continual loss of fertile land on the outskirts of deserts. This loss occurs chiefly from overgrazing—that is, from so much grazing by livestock that plant life is destroyed. Without the protective cover of plant life, wind and water increase soil erosion. This change of fertile land into a desert is called desertification. Other activities that cause desert expansion include mining, improper farming methods, and destruction of trees. Many kinds of cactus plants grow in the desert areas of the American Southwest. Like all desert plants, these cactuses can survive long dry periods and very hot temperatures. Here are the plants that appear on the illustration: 1. Jumping cholla 2. Mesquite 3. Jumping cholla 4. Barrel cactus 5. Saguaro 6. Bur sage 7. Organ-pipe cactus 8. Ocotillo 9. Paloverde 10. Prickly pear 11. Desert marigold 12. Brittlebush. Golden eagle Aquila chrysaetos 30 to 41 Cactus wren Campylorhynchus brunneicapillus 7 to 8 3/4 inches Gila woodpecker Melanerpes uropygialis 8 to 10 inches Elf owl Micrathene whitneyi 5 to 6 inches (13 to 15 centimeters) Gambel's quail Callipepla gambelii 10 to 11 1/2 inches (25 to 29 centimeters) Greater roadrunner Geococcyx californianus 20 to 24 inches (51 to 61 centimeters) Flowers of the desert This map shows where animals of the desert live. A desert climate supports only sparse vegetation and gives rise to tremendous sand dunes in the southwest African nation of Namibia. The air is hot during the day but cools rapidly at night. Animals and the web of life. Living things depend on one another. They are connected in what is sometimes called the web of life. Plants capture the energy from sunlight and use it to make roots, stems, leaves, flowers, and fruits. Animals eat the plants, or they eat other animals that feed on the plants. When animals die, their bodies decay and release materials that help fertilize the soil for plants. Animals and plants are also connected in other ways. When animals breathe, they take in oxygen from the air and give off carbon dioxide. Green plants take in carbon dioxide and give off oxygen in a food-making process called ...