AbstractsEngineering

Amounts of natural debris in small headwater streams under old growth stands of Douglas-fir vary from 6 1/2 tons per 100 ft. of stream to 26 tons per 100 ft. of stream, depending on terrain and timber characteristics and sequence in the natural accumulation-flushing cycle. Approximately 10% of the weight of total debris is in the size class smaller than 10 cm in diameter. After falling, there was an increase of debris depending on stream protection measures, falling methods and environmental factors. After yarding, the amount of total debris was reduced on the average to almost 50% from what it was originally. At the same time, the amount of branch-type debris increased although the amount of finer debris (<1 cm) decreased. A wide buffer-strip provided an almost complete physical barrier against debris movements, while a very small buffer-strip provided much less stream protection in terms of logging residue. Cable-assist falling methods minimized breakage and provided for cleaner yarding as compared to conventional timber falling.