Concentrated in 16 western states, rangelands comprise 770 million acres (311.6 million ha) and over one-third of the land base in the United States. Rangelands are vegetated predominately by shrubs, and they include grasslands, tundra, marsh, meadow, savanna, desert, and alpine communities. They are fragile ecosystems that depend on a complex interaction of plant and animal species with limited resources, and many range areas have been severely damaged by overgrazing. Currently over 300 million acres (121 million ha) within the United States alone are classified as being in need of conservation treatment and management. Effective range-management techniques include soil conservation, preservation of wildlife habitat, and protection of watersheds.