Dolores River Core Science Report

Home Browse Search

Dolores River Dialogue Riparian Vegetation Analysis David Merritt, June 3, 2005 The purpose of the following discussion is to give the reader a general familiarity with some basic principles in riparian plant ecology, to relate these principles to the riparian vegetation of the Dolores River, and to provide recommendations for modifying streamflow and fluvial processes to achieve specific management goals. The first section, River processes, riparian vegetation and flow components, provides concepts that relate the life-history of riparian plants to attributes of the hydrologic regime (flow components). The second section, Riparian vegetation of the Dolores River, highlights the few studies that have taken place along the Dolores River that have described the riparian plant communities and changes in them over the past couple of decades. The third section, An approach to inventorying the riparian vegetation of the Dolores River, discusses some considerations for developing an inventory and monitoring system for the Dolores River so that current condition, trends through time, and responses of riparian plants to management activities can be quantified. The last section, Changes in flow regime on the Dolores River, flow components, and vegetation, discusses the biologically relevant changes in flow regime that have occurred since the operation of McPhee dam began in 1984 and provides some discussion of the changes in riparian plant community composition and population structure that are likely to have occurred along the Dolores River as a result of changes in physical processes. Flow recommendations are provided. River processes, riparian vegetation and flow components Riparian vegetation is responsible for many of the human-valued ecological services provided by rivers. Plants growing along rivers provide habitat structure, shelter and roosting areas for insects and animals, and inputs of carbon (leaves and wood) and nutrients that support aquatic communities (insects, amphibians, and fish). Plants also contribute to water quality through filtering and uptake of nutrients, chemicals, and metals, and filtering of sediment through stabilizing stream banks and channel features. Plant communities growing along rivers are disproportionately species rich compared to upland plant communities (Naiman et al. 1993). Maintaiiung or restoring the processes that support native plant communities and disfavor exotic species is becoming increasingly important in river management worldwide. The availability of water along rivers is one factor that contributes to the lush, productive and diverse vegetation that characterizes river valleys in the western US relative to surrounding uplands. The most extensive deciduous forests in arid regions of the West occur along rivers. The formation and maintenance of riparian (streamside) forests and native-dominated woodlands require specific processes that facilitate their establishment and development: occasional overbank flooding, the redistribution of sediment on bars and across the floodplain, and hydrograph attributes that favor seedling recruitment. In the absence of such processes, Western riparian communities shift from those dominated by disturbance adapted species such as cottonwood, willow, and annuals to later successional species such as pereniuals and woody species (eg., box elder, rabbitbrush, wild privet, big sage, western juiuper). A variety of other factors influence composition and structure of the vegetation that grows in riparian areas. An understanding of the factors that lead to the range of possible vegetation types along a particular reach of river can be helpful in evaluating relative trade offs -- the cost of 42