Silvicultural Result of One-Grip Harvester Operation

Abstract A new method for measuring the silvicultural result of thinning is presented in the study. The measuring method was based on rectangular sample plots measured parallel to strip roads. An individual sample plot consisted of eight zones, each 30 m2 in area. Due to its considerable importance in Finland, the one-grip harvester operation was the harvesting system examined. The research material was collected from 15 stands amounting to a total area of 14.7 ha. The post-harvesting inventory provided good information on the removed and standing trees, their size and distribution. The number and distribution of standing and removed trees were according to Finnish thinning instructions, and thinning was typical low thinning, in which smaller trees and trees of low quality are removed. The average tree damage percentage, 4.6, is acceptable. However, the proportion of damage varied from 1.1% to 9.1% with different operators. The damage was highest during the summer. Small, superficial damage was typical. The average strip road width was 4.8 m, the distance between strip roads 19.8 m and the rut depth 0.6 cm. The economic consequences of the damage was estimated using a calculation model. The model estimates the losses caused by strip roads, tree and soil damage. The economic consequences of harvesting damage during the rotation period was 1158 FIM (1 U$ = 5.60 FIM). Strip roads make a significant contribution to the amount of costs. Due to the high variation in the harvesting quality, both the continuing supervision of the silvicultural thinning result and the training of machine operators are necessary. Thinning spruce stands during the sap period should be avoided due to the high risk of tree damage, and decay following damage. Generally, it is possible to obtain a good silvicultural thinning result with one-grip harvester operation.