51 



transition area between the riparian zone and the upland forest where vegetation still 

 influences the stream under some conditions (Gregory et ai. 1991). The riparian forest 

 is shaped by channel geomorphology, frequency, magnitude, and timing of flooding, the 

 spatial position of the channel in the watershed, and the disturbance regimes (Naiman 

 et al. 1 992). The maintenance of riparian forests in their historic abundance and condition 

 is essential to the long term vitality of a watershed. 



Riparian forests provide a number of ecological services to the stream. These include: 



1) Control of stream temperature resulting in part from the density of the tree 

 canopy in forested streams. Stream temperature is critical in spawning and rearing 

 habitat, and plays a role in the level of aquatic productivity. 



2) The addition of large amounts of leaves, cones, wood, and dissolved nutrients 

 to streams (Gregory et al. 1991). These materials are sources of nourishment for 

 the aquatic organisms living in the streams. 



3) Contribution of large woody debris in healthy forested streams large woody 

 debris is the principle factor structuring aquatic habitats (Naiman et al. 1992). 

 Without this woody structure stream biodiversity and carrying capacity for fish are 

 greatly diminished. Large wood also shapes the stream channel structure and its 

 ecological processes. 



4) The foundation for wildlife habitat including thermal and resting cover, corridors 

 for migration and substrate for substantial biological activity by microorganisms, 

 invertebrates, and other aquatic organisms (Naiman 1990, Gregory et al. 1991, 

 Naiman et al. 1992). 



The biotic complexity provided by a functional riparian forest is essential to the ecological 

 health of rivers and streams. 



Habitat Characteristics 



In ecologically healthy watersheds, there are strong interactions between river and stream 

 channel geomorphology, hydrology, spatial position of the channel, and the riparian forest 

 that provides habitat for terrestrial and aquatic organisms (Naiman et al. 1992). The 

 result of these interactions is habitat complexity and variety. Gradients in current velocity 

 and temperature, patches of rock and gravel of different sizes, piles of branches and 

 leaves, small dams formed by dead trees and a multitude of other distinct patches 

 created by the complex interplay between water movement, geologic events and riparian 

 vegetation ail provide the diversity of habitats required by a rich commmuity of organisms 

 for shelter, food, and reproduction. 



