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predominant sediment source (Bilby et al. 1989). Sedimentation may also occur 

 around improperly constructed culverts, and to a lesser degree from the 

 logged-off land itself (Larse 1970). 



Stream Clearance 



Harvest of all streamside timber occurred until the early 1980s. While this 

 prac tice is now allowed only in exceptional situations, there are many streams 

 where the amount of large woody debris and the composition and structure of 

 riparian vegetation was degraded as a result of this activity, according to 

 Bilby and Ward (1991). They worked in the Chehalis Basin, and concluded that 



(1) Compared to old growth stream reaches, streams flowing through areas 

 clearcut within the previous five years tended to have: 



(a) smaller debris pieces (i.e., less stable fish cover); 



(b) fewer pools (i.e., less coho rearing area during the summer), and 



(c) less accumulated spawning gravel. 



(2) Compared to clearcut stream reaches, stream reaches passing through 

 second growth approximately 50 years old tended to have even less woody 

 debris than recently clearcut areas. Clearcutting had created riparian 

 stands composed largely of red alder, but this type of vegetation might 

 not supply sufficient large woody debris, especially to larger streams. 



Forestry Chemicals 



Forestry herbicides are used to kill hardwoods so that planted conifers can 

 grow without competition. Forest spraying has also been done for pest control 

 or to apply fertilizer. Forestry chemicals can enter steams either by runoff 

 or direct application over streams. In the Chehalis Basin, regulations cover 

 permissible chemicals, methods of application, and timing, but they remain a 

 common concern (CRC 1991). The direct effect of forest spraying on aquatic 

 life has not been documented in the Basin. 



Current Forest Practices 



Timber harvest continues to reduce abundance of the largest and most 

 persistent forms of wood, and thus impedes habitat recovery. For example, 

 salvage of red cedar after timber harvest is still a common practice in the 

 Pacific Northwest (Bilby and Ward 1991). Bilby (1984) studied the effect of 

 debris removal on Salmon Creek, a tributary in the Upper Chehalis sub-basin. 

 Removal of any type of large woody debris destabilizes the wood remaining in 

 the channel, thus allowing flushing of wood downstream, contributing to the 

 decrease in the amount of woody debris in natural fish rearing areas, and 

 destabilizing the stream channel (Bilby 1984). 



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