The introduction of chain saws and tractors in the early 1950's marked the beginning of a change in tree harvesting techniques from the old manual methods to mechanized operations. It was followed by a rapid evolution both technically and systematically. Hence, the requirements for improved know- ledge of operational efficiency also increased. Changing relations between Man, machines and environment brought about new experiences and awareness of a physiological and ergonomic nature. Improved knowledge of both machine technology and planning of work on a small or large scale has grown increa-...