A case study of prebunching and swinging : a thinning system for young forests

Commercial thinning young growth forests is an increasingly\ud important silvicultural technique for improving second growth\ud management of Douglas-fir stands. Research aimed at advancing the\ud efficiency of skyline logging operations in small wood timber stands\ud is essential in order to make thinning these young stands economical.\ud The purpose of this study was to evaluate one case of prebunching\ud small logs to a skyline corridor with a portable winch and swinging\ud the logs to a haul road with a conventional mobile yarder. Prebunching\ud involves lateral yarding of logs from both sides of a skyline corridor\ud and decking the logs along the corridor.\ud The multiinoinent time study method was used for obtaining data\ud that was analyzed with multiple linear regression procedures. Predicted\ud hourly and daily production rates were determined from the\ud regression equations. The yarding system involving prebunching was\ud compared to a similar system without prebunching on a cost basis.\ud This study showed that prebunching logs to a skyline corridor\ud reduced the conventional mobile yarder's yarding time 65 percent and\ud more than doubled log and volume production per day. The results\ud favored the prebunching and swinging yarding technique. Several\ud suggestions, that require additional research, were made for\ud modification in the system that may improve the overall operation