Land-water interactions: the riparian zone

The interface between aquatic and terrestrial environments in coniferous structure, composition, and function of the riparian zone had received little consideration in ecosystem level research, because this zone forms the interface between scientific disciplines as well as ecosystem components. In some climate-vegetation zones particular aspects of riparian zones have received much study. nparinpiant communities in arid lands have been studied extensive!y, primarily in terms o TdfeTbiiatJohnson and Jones 1977 Thomas et al 1979) Research on riparian 'egetation along major rivers has dealt mainly with forest composition and dynamics (for example, Lindsey et al. 1961; Sigafoos 1964; Bell 1974; Johnson et al. 1976). Riparian vegetation research has been largely neglected in forested mountain land, where it tends to have smaller areal extent and economic value than upslope vegetation. yre!pian zone is an integral part of the forest/stream ecosystem complex. This chapter synthesizes general concepts about the riparian zone in northwest coniferous forests and the results of coniferous forest biome research on: (1) structure and composition of riparian vegetation and its variation in time and space; and (2) functional aspects of the riparian zone in terms of physical, biological, and chemical terrestrial/aquatic interactions. We emphasize conditions observed in mountain streams and small rivers. The riparian zone may be defined in a variety of ways, based on factors such as vegetation type, groundwater and surface water hydrology, topography, and ecosystem function. These factors have so many complex interactions that defining the riparian zone in one sense integrates elements of the other factors. We prefer to define the riparian zone functionally as that zone of direct interaction between terrestrial and aquatic environments. Vegetation, hydrology, and topography all determine the type, magnitude, and direction of functional relationships. The direction of riparian interactions refers to the notion that the terrestrial system may affect the aquatic or vice versa. In arid land