ORIGINAL PAPER Analysing the long-term effects of artiﬁcial pruning of wild cherry by computer tomography Thomas Seifert • Martin Nickel • Hans Pretzsch Received: 7 May 2009 / Revised: 10 May 2010 / Accepted: 28 May 2010 / Published online: 22 June 2010 Ó Springer-Verlag 2010 Abstract 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 valu- able 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 experi- mental 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 reli- ability 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 differ- ence 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. Keywords Prunus avium  CT scanning  Wound occlusion  Stub occlusion  Decay  Guidelines for pruning  Non-destructive testing of wood Introduction In conifer species artiﬁcial pruning is a long-established technique for the enhancement of wood quality (Mayer- Wegelin 1937; O’Hara 2007). Despite early works on artiﬁcial pruning of hardwoods (Moss 1937; Roth 1948; Zimmerle 1943), pruning of hardwoods has never reached the same level of importance as the pruning of conifers. During the past decades artiﬁcial pruning of hardwood species has internationally received increasing attention (Bredenkamp et al. 1980; Montagu et al. 2003; Kerr and Morgan 2006; Hein and Spiecker 2007). Decay has been especially identiﬁed as a problem when hardwood species were pruned (Green et al. 1981; Glass and McKenzie 1989; Barry et al. 2005). This statement is also particularly valid for wild cherry (Prunus avium L.), a deciduous tree species native to Europe, Northern Africa and Western Asia. Wild cherry is a tree species that naturally grows in mixed stands and is grown in commercial forests for biodiversity and aesthetic reasons. Its Communicated by R. Matyssek. T. Seifert (&) Department of Forest and Wood Science, Stellenbosch University, Private Bag X1 7602, Matieland, South Africa e-mail: seifert@sun.ac.za M. Nickel  H. Pretzsch Chair of Forest Growth and Yield Science, Technische Universita ¨t Mu ¨nchen, Am Hochanger 13, 85354 Freising, Germany 123 Trees (2010) 24:797–808 DOI 10.1007/s00468-010-0450-9