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A SYSTEMS APPROACH TO UNDERSTANDING AND MANAGING RIPARIAN PLANT COMMUNITIES IN THE UINTA MOUNTAINS OF UTAH DENNIS J. HANSEN NATIVE PLANTS, INC. 360 WAKARA WAY SALT LAKE CITY, UTAH 84108 ABSTRACT This paper focuses on the interrelations of riparian plant com- munities, stream regimen, soils, and other factors along streams in the Uinta Mountains of Utah. Data measured at 71 sites included: vegetation, soil, stream, and solar irradiation. Vegetation units were separated using cluster analysis techniques into eight basic plant community types, named according to the predominant species in each type. The types (ranked from wet to dry according to plant water potentials) were: alder, willow, birch, conifer, cottonwood, aspen, hawthorn, and buffaloberry. One-way analyses of variance, multiple-pairwise comparisons and multiple-regression analyses were used to indicate significant differences in physical and biological parameters among clusters of plant communities. Community patterns were correlated with present and past alluvia- tion processes. Forward, stepwise discriminant analysis was used to select the ranked combinations of environmental variables which best discriminated between the riparian classification groupings developed by cluster analyses. Forward, stepwise multiple linear regression analyses were used to distinguish which combination of environmental variables was correlated to species' growth parameters. Successional trends are described and suggestions are made as to how these findings relate to manage- ment, or rehabilitation of riparian plant communities. INTRODUCTION Little is currently known about the riparian vegetation along streams draining the Uinta Mountains, or for that matter, Fiparian vegetation along most streams of the Rocky Mountains. Review of earl~er riparian studies in the Uinta's is presented by Hansen (1977). These studies take primarily descriptive or classificatory approaches to the riparian vegetation. There is little or no emphasis on those relations between vegetation and environ- mental factors that could help to explain why particular vegetation patterns exist in a given area. As demands for water increase, acquisition of water to fill these demands will be directed to diversion of runoff from high altitude watersheds. And, there will be a growing need to understand the relationship of vegetation to the various physical factors of the environ- ment. This will occur because of the need to more carefully assess manipu- lation of our environment, and also to more fully appreciate the biological complexity which has developed only over very long periods of time. 60