Tree Damage in Single-Grip Harvester Thinning Operations

Abstract Tree damage in a one-grip harvester operation was assessed by observing the number of contacts with standing trees and damage resulting from these contacts. The processing phase for a single tree was called a cycle. On average, 19.3% (14.5–25.4%) of cycles involved contacts with standing trees. One third of the contact trees were removed during harvesting. Of the struck trees left standing, 28.2 % were damaged. The probability of contact damage was 1.5 times higher in the summer than in other seasons. Mean damage percentage in the study stands was 3.4 ( range 0.0–8.6%). Contacts with standing trees were explained by machine operator, stem volume of processed tree and the number of trees on the working area. The probability of damage resulting from contact was explained by harvesting season and size of processed tree. A model was developed to predict tree damage. The model consisted of a contact model and a damage model formulated using logistic regression. The tree damage model and the productivity models can be used, for example, in comparing different thinning regimes in model stands. The operator had considerable influence on both the harvesting quality and productivity, and there was a large variation between machine operators. High productivity and a good silvicultural result were highly correlated.