49 



example, landslides occur at a magnitude and frequency characteristic of a specific 

 landscape and geologic setting. Landslides deliver new sediment and gravel to river 

 channels where it is sorted by flowing waters into spawning beds and used by the next 

 generation of salmon. Landslides are thus integral to the health of salmon populations 

 when they occur at natural frequencies. In turn, the salmon are genetically adapted to 

 such geologic conditions within their river of origin. However, an increase in landslide 

 frequency and magnitude within a watershed due to poor land-use management, such 

 as road building on steep unstable slopes, results in deleterious downstream impacts on 

 fish populations, on the riparian forest, and on the full array of organisms using the 

 riverine corridor. 



Hydrologic Patterns 



Hydrologic patterns of ecologically healthy watersheds in the Pacific Northwest are a 

 function of the timing and quantity of stream flow, characteristics of seasonal water 

 storage and source area, and the dynamics of surface-subsurface exchanges (Naiman 

 et al. 1992). Water flow in natural rivers is a complex pattern of fast and slow current 

 velocities, eddies, and backwater pools. The complexity of stream flow creates a rich 

 variety of habitats that harbor a large community of diverse plants and animals. In 

 addition, flooding plays a significant role in structuring the riparian forests throughout 

 much of the river system. For example, floods disturb existing vegetation (i.e. physically 

 remove or damage), and reconfigure landforms in active river channels. 



When the natural variation in stream discharge and water level is suppressed by water 

 diversions, dams, and channelization, many of the varied stream and riparian forest 

 habitats disappear along with much of the diverse flora and fauna that depend on their 

 existence. The flow of water from headwater streams to oceans creates strong physical 

 and ecological links between stream reaches that are othenwise separated geographically. 

 Ecologically healthy watersheds require these lateral, longitudinal, and vertical hydrologic 

 linkages between aquatic habitats. Because rivers and streams are a continuum of 

 physical and biotic processes the effects of manipulations at one site are never confined 

 to that one location. Thus, site-specific solutions are an ineffective approach to 

 watershed management. 



Riparian Forests 



Riparian forests are the heart of an ecologically healthy watershed (D6camps and Naiman 

 1989, Naiman and D^canips 1990). The riparian zone extends from the edge of the 

 average high water mark of the river or stream toward the uplands (Figure 1) (Naiman 

 et al. 1992). This zone includes terrestrial areas where vegetation and microclimate are 

 influenced by perennial or intermittent water associated with high water tables, and by the 

 ability of soils to hold water. Higher in elevation is the riparian "zone of influence," a 



