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2 provided by the river. Riparian areas generally have higher productivity than nearby upland areas in terms of plant and animal biomass and tend to support more species. Riparian areas also are important in the ecological functioning of rivers and streams and regulate nutrient input to the aquatic system (Gregory et al. 1991; Gilliam 1994; Vought et al. 1994). The elevation of riparian zones above rivers and the species composition within these zones are largely functions of river flow, especially minimum and maximum flows and seasonal variations in these values (Stromberg 1993; Auble et al. 1994). Disturbance, especially as related to flood events, also plays a major role in determining species composition in riparian zones (Bendix 1994). For these reasons, the riparian vegetation of regulated rivers, where all of these parameters are often modified, is usually different than the riparian vegetation of unregulated rivers (Carothers and Brown 1991; Nilsson et al. 1991). The study reported herein was undertaken to evaluate the effects on riparian vegetation of several potential hydropower operational scenarios at Flaming Gorge Dam, Utah. The Green River below the dam supports a well-defined riparian zone that has increased and changed in response to hydropower operations and other dam operations that began following completion of the dam in 1963. Changes in hydropower operations could result in further changes in the size of the riparian zone as well as the species composition within that zone. The hydropower operational scenarios evaluated in this report include (1) year-round high fluctuation, (2) seasonally adjusted high fluctuation, (3) seasonally adjusted moderate fluctuation, and (4) seasonally adjusted steady flow (Figure 1*). All scenarios would feature minimum releases of 800 cfs and maximum releases of 4,700 cfs (maximum power plant capacity), but the amount of daily fluctuation would be very different among scenarios. For the three seasonally adjusted scenarios, the magnitude of fluctuations would vary from month to month and would be restricted to meet target flows at Jensen, Utah (approximately 90 mi downstream of the dam). These target flows were established by the U.S. Fish and Wildlife Service in its Biological Opinion regarding operation of the dam, which was issued in 1992 (USFWS 1992). Details on these operational scenarios are provided by Yin et al. (1995). The principal differences among the operational scenarios are summarized as follows: • Year-Round High Fluctuation: Under the year-round high fluctu- ation scenario, there would be no limit on maximum daily fluctuations, and releases would vary from 800 to 4,700 cfs each day. Ramp-rate restrictions would be 3,900 cfs/h (minimum flow to maximum power plant capacity). This operational scenario is representative of current maximum power plant operations using monthly release volumes historically set by the Bureau of Reclamation and was evaluated for comparative purposes. This operational scenario would not comply with the USFWS Biological Opinion. Consideration of this operational *For readability, all figures and tables are placed in sequence following Section 5 of this report.