Mechanized Energy Wood Harvesting from Early Thinnings
AbstractThe felling and bunching of small diameter trees in Finland is still largely carried out manually using a chain saw and clearing saw. The felling of small diameter trees has been developed and mechanized. In addition to the high felling costs of small trees, the move towards mechanized harvesting is also caused by a shortage of professional lumberjacks, the possibility of all-year-round mechanized energy wood harvesting, and an increasing demand for energy wood. The research investigated the productivity, costs and silvicultural result of the guillotine blade equipped, multi-tree-processing Naarva-Grip 1600-40, for small diameter energy wood harvesting. Work-studies were carried out in six young stands at the first thinning stage. In mechanized energy wood harvesting with the Naarva-Grip 1600-40, an average of 73% of the trees felled were multi-tree-processed. The multi-tree-processed proportion increased to 96% in dense Scots pine (Pinus sylvestris L.) sites with small trees. One bunch consisted of approximately 3.2 trees. The average density and volume of removal had the greatest effect on the productivity of the felling-bunching work. Felling-bunching was carried out on the sites at a rate of 106-422 trees per effective hour (E0, excluding delay times). Productivity on the different sites varied from 3.0 to 7.2 m3/E0, giving an average of 4.7 m3/E0 (weighted by felling volume) with an average tree size on the site of 32 dm3. When the size of the felled trees was under 20 dm3, the felling-bunching costs were over 20 US$/m3. When the average tree size on the site increased to 50-70 dm3, the felling-bunching costs approached the 10 US$/m3 level. During the research, the Naarva-Grip 1600-40 proved to be competitive compared to the other multi-tree-processing, energy wood felling heads on the market. In order to keep the felling-bunching costs at a reasonable level, mechanized harvesting should be targeted at sites where the average size of the trees removed is over 30 dm3, and the energy wood volume at felling over 30 m3/ha.