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CHAPTER III AFFECTED ENVIRONMENT systems. Some of these areas have enough open water to provide waterfowl habitat. Others support trees and dense stands of cattails, rushes, or shrubs and are more valuable as cover and shelter for upland wildlife than for waterfowl. Agriculture-induced wetlands are not influenced significantly by river flows but could be affected by changes in water use. 2. SDecies of Special Concern--Vegetation Riparian vegetation is important because of its limited occurrence and high value to wildlife. A conspicuous and especially important element of the riparian ecosystem is the cottonwood tree. Cottonwood trees, especially when occurring in groves, provide important habitat for numerous species of wildlife, e.g., communal roost sites for wintering bald eagles and nesting habitat for great blue herons, raptors, and passerine birds. Many cavity nesting birds nest in cottonwoods. Cottonwoods also provide food for beavers, shade concealment, and thermal protection for mule deer and other mammals. ¦ Stands of cottonwoods have declined in recent years and the trend is still downward. It is generally believed that a major cause behind their decline is dam construction and operation which inhibited cottonwood regeneration by reducing historic high flows and sediment deposition. Preservation of remaining cottonwoods is important because of their high value to wildlife and the long time required for regeneration in the event they are lost. While herbaceous or shrubby vegetation can often recover in a few years, a cottonwood tree requires 50 years or longer to reach the size and maturity needed for some important habitat functions. 3. Species of Special Concern--Terrestrial Wildlife Cottonwood groves along rivers are used as communal roosts by bald eagles and as nesting and perching habitat by other raptors. Egrets, great blue herons, and night herons nest in cottonwoods. Waterfowl use the riparian zone as nesting and migration habitat. Greater sandhill cranes migrate along portions of the Green and Yampa Rivers and are accompanied by a few endangered whooping cranes from the Grays Lake population. Long, narrow belts of riparian habitat within the otherwise arid environment provide important travel lanes, as well as nesting habitat, for migratory passerine birds. The river otter once inhabited many streams and lakes of the Upper Basin. Though probably never abundant, the original otters are believed to have been completely extirpated from the State of Colorado many years ago. The river otter is now on the Colorado State list of threatened or endangered wildlife. The Colorado Division of Wildlife has a program for reintroducing otters from the Pacific Northwest and Wisconsin into the otter's historic range in the State. All but one of the stream segments listed as essential habitat for the otter are east of the Continental Divide and will not be affected by the recovery program. The one exception is the Gunnison River from Black Canyon of the Gunnison National Monument downstream to Colorado State Highway 92, and 5 miles upstream on all tributaries within this reach. III-19