Ergebnisse eines Grünästungsversuchs mit Bergahorn, Buche, Eiche und Esche

Results of a green pruning experiment with maple, beech, oak, and ash Object of the investigation is a pruning experiment in maple, beech, oak and ash stands in southwest Germany, which started in 2004. Aim of the experiment was to quantify the effects of green pruning on wood decay, discoloration, epicormic shoot formation, radial increment, and occlusion time. At top heights of 8–14 m, trials for each species were placed in stands where the natural pruning had not yet reached the achieved knot-free bole length. In each trial, ten trees were pruned in spring and summer respectively, by cutting 40% of the crown in average and branches up to 80 mm diameter. Additionally, ten unpruned trees were selected on each trial and, as the pruned trees, released from competitors. In 2011 and 2012 respectively, the trees were felled and measured, and wood samples with branches were taken and analysed. Results show that green pruning did not cause any wood decay. Compared to the control trees, increased discoloration was observed in the stems of the pruned trees. However, this was limited to the knotty center of the trunk and did not diffuse to the knotless part. Pruning intensified the formation of epicormic branches, but, except for oak, these branches diminished to the level of the control trees already during the time of observation. Radial increment shows a short-term decrease due to the green pruning, but with an extent below the effect of the dry year in 2003. With branch diameters of 3–4 cm, the pruned trees needed three to five years until the branching wounds were occluded, whereas about nine years were necessary for trees with natural pruning.