Browsing by Author "Raatevaara, Antti"

Pruning of Scots pine is a traditional silvicultural method where branches are removed, usually up to 4–6 meters of height. Objective is to obtain better log and finally sawn timber quality. Pine branches fall off naturally as well but artificial pruning hastens the process of forming branchless sapwood. However, pruning of Scots pine has proven to be poorly profitable and is often described as silvicultural technique for active forest owners who do not set remarkable economical goals for their actions. Economic efficiency of pruning is weakened by the lack of quality-based pricing of timber whereupon forest owners or timber merchants do not get sufficient payment for their efforts. Highly developed x-ray log scanners at sawmills are capable of measuring log-internal quality at appropriate resolution. Measured information of log quality is utilized for log sorting at sawmills but it could also be used as the basis of pricing the timber. The aim of this thesis is to examine how pruning shows in log-internal quality which is measured by x-ray log scanner and what kind of differences arise between pruned and reference logs. The material for the thesis included 557 pruned and 111 reference logs which were harvested from a pine stand located in Ruovesi. The time elapsed from pruning was 33 years. The differences between pruned and reference logs were evaluated by quality attributes which were knottiness index, log top-end knottiness index, average knot cluster length, relative volume of largest knot and knot cluster, annual ring width and sapwood density. Finally, the quality differences between pruned and reference logs were inspected with predictions of sawn timber quality which were derived through knottiness index values. The internal quality of pruned proved to be better in every quality defining attribute. Statistical significance (p-value<0.001) between attribute means was found in average knot cluster length and in relative volume of knot as well as knot cluster. The predicted sawn timber quality distribution among the pruned A-graded logs, had 20% increase in U/S-quality and 2% decrease in VI-quality. The results of this thesis confirm the earlier findings that pruning of Scots pine is unsuitable at mesic pine stands and the selection of stands for pruning should be considered carefully. In case of the experimental stand, the sealing-off of pruned branches and the formation of knotless sapwood was still in progress while trees were harvested. In further studies, the effect of pruning on internal quality of timber should be considered with wider sample which consists of stands from divergent site types.