Introduction Riparian zones exist because: (1) water is available to plants during their entire growing season, (2) this water promotes dominance of plant species that need a water table near their root zone during their entire growing season, and (3) if the water table near the root zone of water-loving plants is removed they are replaced by plant species capable of occupying more xeric land areas which have no permanent water table during an entire growing season. Because water supply in the semiarid western United States is often limited in quantity and distribution, condition and aerial extent of riparian zones can be the focus of emotional discussion between a multitude of users and managers of wildland drainage basins. This paper will, therefore, provide a general perspective of water storage potential in non-man manipulated western drainage basins before settlement. This effort will set the stage for reflecting on how man has influenced streamside zones and manipulated water thus creating or reducing land mass capable of supporting riparian plant species to present time. This paper, however, only represents this author's first attempt to review historical literature and provide himself with a logical basis to help evaluate current research needs and direction. At best, the content should offer food for thought after also reading, "Hydrologic Impacts in Riparian Zones" of this same proceedings.
Six historical periods are identified for the convenience of presenting this paper. These are: (1) before western immigration, 1804-1840, (2) during western immigration, 1840-1870, (3) during settlement, 1870-1930, (4) after creation of reservoir storage, 1930-1960, (5) while emphasizing multiple use management, 1960-1975, and (6) while emphasizing the need to distinguish riparian zones from other vegetation types for changing land and water management policies, 1975-1986.
Change in riparian zones will be attributed to: (1) natural and introduced large grazing animals, (2) alteration of flow caused by diversion of water for irrigation and reservoir storage, (3) multiple use of watersheds, and (4) present exploration for oil and gas.
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