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." ..1'\"30 UJU<J :) DISCUSSION The riparian area, or zone, is a narrow strip paralleling the waters edge. That strip is usually only 3-6 feet wide. The riparian dependent vegetation gives way quickly to upland species wilhin the naow band. The riparian vegetation is characlerized by willows (exigua, bebbiana, and others), mountain alder, and birch (Befe). Narrowleaf cottonwood is scattered along the river, all hough reproduction is rarely evident. A bankfull in-stream water 1I0w has been defined as that which occurs wilh a periodicity of every eighteen months. That water level is indicated by mature and developing clumps of alder. Alder is the most well-defined and well-established species demarcating this line. Willow and birch may occur al the same elevation with respect to the water surface, but are more likely to be a foot or two above the alder. Forb and graminoid vegetation is sparse. Percent covers of these species did not exceed 10-15 percent in early September, no 5-10 percent in late October. Full cover of these lifeforms probably does not exceed 30 percent at the peak 01 growing season. Events exceeding bankfull are important because of their impact on recharging the water table, sedimenta- tion, deposition of organic material, seed dispersal, and perhaps triggering vegetative reproduction. CONCLUSIONS There is a direct relationship between riparian vegetation and the variability of in-stream flows. This is based on several observations. (a) Riparian vegetation occupies a narrow piece of terrain along the water courses. The species composi- tion is site specific, and ;s determined by the below-ground moisture regime. Changes in that moisture environment affect the existing community. Since reduced flows are the primary concern, that would result in a moving and probably declining community condition. (b) The edge, or ecotone between the riparian vegetation and the main water courses is abrupt. The absence of vegetation below thaf bankfulltevel can be attributed to fhe mechanical damage caused by seasonal peak flows. Any long-term sustained change in the bankfull level will result in riparian community changes. Changes in species composition and relative dominance will be the primary result, affecting a change in succession -- both the pathway and the rate. Sustained, reduced in-stream 1I0ws will require the riparian community to re-establish itsell at a lower elevation. (c) The ability of the vegetation to migrate with changing water levels is dependent on the reproduction mechanisms of each species. Some are seeders; more often they root sprout. If flow levels change significantly and quickly the likelihood that the riparian community can maintain itself is low, For example, a sustained increase in flows over a period of several years and for long durations will force the riparian community to .climb to higher ground." II the regeneration mechanisms permit the species to survive the raised water tables, and consequently the anerobic soil conditions, then the community will persist. However, if regeneration and survival does not occur rapidly enough, then the community will change, perhaps requiring decades to recover. Conversely, a sustained decrease in flows for a period of several years accompanied by Ihe reduction or eliminalion of seasonal flooding could have .the same result. That is, the regeneration mechanisms cannot keep pace with the changing below-ground environment. The regeneration mechanisms lor riparian species, especially narowleal cotonwood, alder, and willow is poorly understood, a best. Narrowleaf cotonwood reproduction is conspicuously absent in most cotonwood stands. There are Iwo notable exceptions. One is in the historically wide flood plains above 4