Productivity and energy balance of forest plantation harvesting in Uganda

摘要

The study evaluated the productivity and energy balance of the harvesting and the extraction of wood in plantation of exotic tree species, i.e., Pinus patula (Schiede ex Schlectendahl et Chamisso) and Cupressus lusitanica (Mill.). The harvesting and extraction operations concerned clear-cut felling on two different types of terrain (gentle and steep terrain) and two levels of pruning. The results show that cutting is not affected by the terrain gradient whereas the pruning condition shows a significant effect on the delimbing operation. The productivity of cutting is evaluated at 28.1 m3·d-1 for unpruned trees and at 30.2 m3·d-1 for pruned trees. For the extraction phase, rolling was significantly affected by terrain conditions. On steep terrain, the gross productivity can be evaluated at 22.5 m3·d-1 for an extraction distance of 40 m, while for the same distance on gentle terrain the productivity decreases to 14.1 m3·d-1 . As a result, the steep terrain condition showed higher energy efficiency, suggesting that it is the more efficient system of extraction. The productivity model and the energy balance resulting from the study provide a better understanding of the variables affecting motor-manual cutting and rolling extraction in exotic plantations in Uganda.