Techniques and Systems for Boom- Corridor Thinning in Young Dense Forests

Young dense stands could be thinned and the cut trees could be sold for bioenergy purposes, thus generating an income at an early stage of rotations. However, to make the utilization of young stands competitive, the costs of harvesting must be reduced while the value of the remaining stands is maintained at high levels. A possibility could be to develop a strip road and boom-corridor system for thinning young stands with high biomass, as an alternative to conventional pre-commercial thinning. The objectives of the studies underlying this thesis were to evaluate the effects of using new methods and techniques intended to promote efficient felling, bunching and compression of trees in boom-corridor thinning systems. As shown by simulations, combining boom-corridor thinning methods with conventional accumulating felling heads (AFHs), improved AFHs for multiple felling (AFH-2m2) and new techniques for continuous felling boom-corridor-wise (AFH-corr) would provide higher productivity in the order AFH-corr > AFH-2m2 > AFH (the AFH-corr system gave about two-fold higher productivity compared to the AFH system) (I). In field studies, boom-corridor thinning using a conventional AFH gave a significant, 16%, increase in productivity compared to a standard thinning from below treatment (II). The potential utility of a prototype felling head designed for continuous felling in boom-corridors in the field was also studied (III). The results show that felling speeds of about 1.3 m×s-1 can be achieved if cranes that allow higher movement speeds are used. Further, the performance of a prototype compression processing device was investigated in field studies, and the results show that the density of fresh Scots pine bunches could be increased by up to 160%, while reducing their ash contents (and hence nutrient losses) by 50% (IV). It was also found that load compression techniques can raise payloads (IV). In conclusion, if new techniques especially designed for boom-corridor thinning are developed and used in appropriate harvesting systems the productivity, cost-efficiency and profitability of the operation can be greatly increased.