The objective of this study was to discover the influence of edge trees, the trees along the side of the strip road, on the positioning of modern single-grip harvester during the first commercial thinning. The results indicate that there is one main working location in the strip road where the harvester is positioned in a distance of two consecutive edge trees. This main location is determined by an edge tree located about 1.2 m behind the boom base. There are also other working locations within a certain distance but in most cases the harvester was positioned same way to the main location, which enables the least restricted boom operations in the boom working sector. Positioning the harvester according to the edge trees does not explain the considerable productivity differences among experienced harvester operators, but the awareness and significance of the edge trees give trainees a valuable basis for outlining and planning work in early stages of training. The present findings are also beneficial from the cutting damage and harvester configuration points of view.