Analysing the long-term effects of artificial pruning of wild cherry by computer tomography

摘要

The wild cherry (Prunus avium L.) is a species that does not exhibit fast natural pruning. Artificial pruning is consequently a prerequisite for the production of valuable timber, which is at the same time often accompanied by unwanted decay that decreases wood quality. This study aims to reveal the factors affecting the speed of branch stub occlusion, and the relationship between stub occlusion and the subsequent formation of decay within stem wood. For this study, 11- and 23-year-old wild cherry trees with documented pruning history were sampled at two experimental sites in Bavaria with varying site class, spacing and thinning variants. The wood structure of the specimens was analysed by computer tomography (CT scanning), which allows for the examination of occlusion of pruned knots as well as the presence of decay. No significant differences between the branch diameters determined by CT scanning and manual measurement were found, proving the reliability of measurements from CT scans. Decay reduced the wood density by 40–60% compared to sound wood. Even small fluctuations in wood density caused by decay that were not visually recognisable could be detected in the CT images. The results suggest that the speed of stub occlusion is significantly positively affected by the diameter growth of the tree stem. The average wound occlusion was 1.3 mm per 1 mm stem diameter growth with a significant difference between sites. A relation between stub occlusion duration and the presence of decay was also found. Serious decay was detected after 3 years on the better, and after 4 years on the less favourable site. Based on these results, reliable pruning recommendations could be derived with regards to maximum branch diameter for pruning depending on a tree’s specific diameter growth, without risking severe stem decay.