Managing Riparian Zones As Ecosystems
USDA Forest Service, PNW Research Station, Corvallis
Dept. Forest Science, Oregon State University
Dept. Fisheries and Wildlife, Oregon State University
The group of researchers and managers associated with the Andrews Experimental Forest on the Willamette National Forest (collectively referred to as the Cascade Center for Ecosystem Management) has been studying the ecology and management of stream and riparian systems for nearly two decades. We have recently published a review of scientific findings (Gregory et al. 1991) and guides for riparian zone management (Gregory and Ashkenas, 1990).
As an outgrowth of interdisciplinary work, we take an ecosystem approach to defining riparian zones, rather than using hydrologic or botanical definitions. Riparian zones are the zone of direct interaction between terrestrial and stream systems. Forest-stream interactions include: shading which regulates light available for aquatic primary production and for warming stream water; fine litter from terrestrial vegetation which is a food resource for aquatic organisms; coarse litter (e.g., fallen logs) that creates habitat structure and affects the ability of the aquatic system to retain dissolved and particulate organic matter; and biogeochemical cycling involving transfers among surface and groundwater systems and terrestrial vegetation. A variety of additional ecological linkages operate in riparian zones, such as the response of some wildlife species to the combined aquatic-terrestrial influences on habitat structure, composition, and microclimate found in riparian zones.
This functional definition and view of riparian zones provides a basis for making management decisions and stream networks within the context of full drainage basins. Although there are compelling reasons to plan at the basin scale, examples of how to do so are scarce. The conceptual framework developed from ecosystem and basin geomorphology perspectives provide a useful foundation.