Effects of Thinning Type on the Harvester Productivity and on the Residual Stand

Harvester productivity, extraction rate, selection criteria for harvesting a tree, and logging damage after different thinning types were studied in northern Sweden. Thinning operations were mechanized and carried out according to normal Swedish practice. The treatments were supervised thinning from below, supervised thinning from above, and unsupervised thinning from above. Time consumption per tree and harvester productivity in thinning from below were significantly different from thinning from above. Extraction rate was higher than the desired level in one plot for unsupervised thinning from above. One plot had a thinning ratio high enough to fit the definition for thinning from above, due to trees harvested independently of thinning type. Mean diameter for damaged and suppressed trees harvested was not different between treatments. No differences in the frequency for size and type of logging damage was found between treatments. For thinning from below, damage was located higher up on the stem than for thinning from above. This study concludes that differences in thinning ratio may be reduced when carried out in commercial forestry, due to the harvest of damaged, suppressed, and, to some extent, strip road trees. Harvester productivity increases with increased thinning ratio. To attain the desired stand densities and to keep damage level down, a skilled and motivated harvester operator is needed.