Abstract
Forester thins out trees in order to increase the commercial value of the timber, therefore it is important to minimize the damage of forest stand by cable skidding operations. The purpose of this study is to make clear the relationships between the damages on forest stand and the profile indexes of terrain in the case of the thinning operations by a running skyline system using a small skidder mounted a yarder with tower. The more the horizontal intersection angle between the skyline and the maximum gradient line at the yarding trail or the more the volume of lateral skidded logs, the more pieces of trees were damaged by the skidding operations. And the less the vertical clearance between the ground and the skyline, the harder soil compaction occurred at the yarding trail by logs. It was not obvious that the area of scraped forest floor consist-ing of the litter, intermediate and humus layer related to the profile indexes of terrain using a linear regression method. On the discussion of the individual cases, it seemed reasonable to suppose that the area of scraped forest floor increased at the setting where the vertical clearance between the skyline and the ground was not enough for high skidding or the horizontal intersection angle between the skyline and the maximum gradient line was large. In conclusion, it follows from these results that the profile classification observed by the field survey is effective to design the location of cable cranes with considering to ensure the less damage of forest stands.
