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Encyclopedia of Global Resources part 34

Encyclopedia of Global Resources part 34 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the U.S. Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 300 Deserts Global Resources In the United States cool deserts sagebrush grass and salt-desert shrub types occur in old lake beds. Ancient Lake Bonneville in northern Utah and Lake Lahontan in Nevada once occupied much larger areas and dominated the landscape. These deserts are also influenced by the Sierra Nevada and Cascade Mountain ranges which cast a rain shadow effect on their eastern valleys. Intermittent drainages wadis or arroyos often cut across desert landscapes they contain running water only during or immediately after a rainfall event. These drainages support unique vegetation and ser ve as important habitats for birds and other animals. Another major feature of deserts is that nutrients are often limiting. Soil nitrogen and organic matter are especially low in these ecosystems. Free-living and symbiotic nitrogen-fixing bacteria are scarce in deserts. Research indicates that lichens and algae forming crusts on desert soils may be the major source of soil nitrogen for plant growth. Desert Adaptations Rainfall events occur infrequently in deserts. Both plants and animals must have adaptations to take advantage of these episodic periods of available water to sur vive in these harsh environments. Thus one sees flushes of desert flowers during spring and summer months especially in years when rainfall is abundant. These same flowers may not be seen again for several years. Desert plants exhibit several adaptations that allow them to exist successfully under these stressful conditions. Some plants such as mesquite have deep root systems that allow access to deep sources of water. They do not have to rely on rainfall during the growing season. Some plants have dense shallow root systems that allow them to tap soil water in the soil surface from light showers. Some plants have both types of root systems. Cactus and other succulents have the ability to store water in their tissues for use during periods of low rainfall. Some plants such as the creosote bush .