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Primary successional trends suggest that species with seeds dispersed by wind and water (e.g., willows, cottonwood, alder, and to a lesser extent birch) colonize bare mineral substrates at about the same time. Once these plants are established, environmental conditions such as flooding, drought, grazing or other pressures favor one species over others. When individual plants reach about one meter in height, they attract birds that disperse seeds and berries. This enables many understory shrubs and forbs to become established. Once larger shrubs and trees become established they may persist for some time (for several decades as determined by dendro- chonology of selected tree species) even though the stream may change course. Drier conditions may thin the canopy and favor establishment of understory species that are more subject to fires. Fires alter community composition. It appears that under drier conditions the establishment of cottonwoods, alders, birch, and willow is restricted due to competition from aggressive herbs and grasses and from. lack of adequate soil moisture. Management implications of these findings are that plant establish- ment is a critical factor in riparian plant community patterns. Sites with dry soil surfaces but relatively high water tables (5 to 10 feet) can often support a variety of species such as cottonwood, hawthorn, buffalo- berry, and conifers if these plants can be protected from competition long enough to develop a supporting root system. Other species such as alder, birch and willow are more dependent on the influence of water, either by flood action or inundation, to maintain themselves relatively free from competition. Management strategies to maintain these communities must incorporate artificial or natural manipulation of the stream channel. This is especially true along the drier lower reaches of the stream. If natural reproduction of the mesic species of shrubs and trees is desired, then those managing water diversion projects should recognize the role of the flooding regime and the need for fine texture materials. The use of control or diversion structures that encourage the formation of point bars, or the use of beaver for diversion of the stream channel into smaller flooding channels, will be neceessary to main- tain or enhance riparian vegetation, particularly the alder, willows, and cottonwoods. These species are important in providing stream bank stability, COver for fish and habitat for wildlife. In the past we have mapped these riparian communities but seldom recognized why certain patterns have occurred. The future of riparian systems belongs to those who have the foresight to recognize the dynamic state of flux, the inter- relations of the components of these riparian systems, and who act respon- sibly in their management. LITERATURE CITED Hansen, D. J. 1977. Interrelationships of valley vegetation, stream regimen, soils, and solar irradiation along the Rock Creek in the Uinta Mountains of Utah. Ph.D. Dissertation, University of Michigan, 179 pp., Ann Arbor, Michigan. 65