The Forest Engineering Department, Oregon State University, has evaluated several systems for thinning young timber stands on steep terrain. Stands averaged 35 to 40 years old and 25.4 to 35.6 cm (10-14 in.) dbh. Approximately 40 percent of the stems per hectare were removed in the thinning operations. This paper discusses research findings from 1972 to 1979 on felling and bucking as well as yarding. Felling and bucking production increased with thinning intensity. Tractor yarding production decreased with increasing slope percent. Total skyline logging cost ranged from 1.5 to 1.67 times that of tractor logging on slopes up to 40 percent. Prebunching logs to the skyline corridor increased yarding production for the machine on the landing. Using intermediate supports has extended yarding distances on convex slopes for short towers such as the Igland-Jones Trailer Alp.
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