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Growth and value production of Douglas-fir under varying stand densities The investigation is focused on the effects of initial tree number and thinning on growth and value performance of Douglas-fir stands. Data base is a coordinated Douglas-fir spacing experiment in South Germany, started 40 years ago and comprising variants of tree numbers with 500, 1,000, 2,000 and 4,000 Douglas-firs per hectare. The treatment was performed according to a standardized experiment program. The results show that at low initial tree numbers, the diameter on breast height (DBH) of (pre)dominant trees at the beginning of the observations (with 12 m top height) is bigger than at higher initial plant numbers. Accordingly, the quotient of height (H) to DBH (as an indicator for tree's static stability) is lower. The further development of DBH and H/DBH quotient is decisively determined by stand treatment, which superimposes the effect of the initial tree number. The total volume growth shows a clear differentiation, too, the variants with initially high tree numbers appearing on top. In the monetary analysis, this ranking is reversed: despite a supposed inferior wood quality, the variants with lower initial tree numbers clearly outperform the ones with higher numbers in terms of value. From these results, the following silvicultural recommendations for Douglas-fir can be derived: the initial tree numbers should be in the range from 1,000 to 2,000 plants per hectare. On technically not accessible sites, even lower tree numbers may come into question. The strong influence of stand treatment on DBH and H/DBH development highlights the problem of postponed thinnings, for this causes growth and stability losses even under favorable starting conditions in terms of competition.

Ainsi, les relations entre les propriétés du bois et sa croissance en épaisseur, de même que le rôle joué par les conditions stationnelles sont encore peu connus. Dans un contexte où la demande en bois de qualité se fait toujours plus forte, l'hybride obtenu par le croisement entre le Noyer noir (Juglans nigra) ou le Noyer d'Arizona (Juglans major) et le Noyer commun (Juglans regia), plus connu sous le nom de Noyer hybride, est de plus en plus répandu en raison de ses performances en termes de croissance, et d'opportunités réduites de culture du Noyer noir et du Noyer commun. Cependant, très peu de pépinières en France comme en Allemagne cultivent jusqu'à présent les coûteux descendants hybrides (Juglans x intermedia) issus de ces croisements, ce qui explique leur faible disponibilité à l'heure actuelle. Cette situation explique la mise en place entre 2001 et 2005 d'un réseau de placettes expérimentales dans le Sud-Ouest de l'Allemagne par l'Institut de recherche forestière du Bade-Wurtemberg (Forstliche Versuchs-und Forschungs-anstalt Baden-Württemberg, FVA). Dans le cadre de cette expérience ont été cultivés des hybrides issus du croisement entre Noyer noir et Noyer commun les plus répandus dans le Bade-Wurtemberg jusqu'à présent. Ces hybrides sont disponibles à la vente sous les désignations commerciales NG23xRA et NG38xRA en tant qu'« hybrides intermédiaires » (J. nigra x regia) (photo 1, ci-contre). Les plants issus du croisement du Noyer noir d'Arizona et du Noyer commun, dits hybrides MJ209xRA (J. major x J. regia), sont aussi commercialisés sous le terme d'« hybrides Garavel ». Le FVA s'est procuré un total de 31 283 plants de ces trois hybrides en provenance de France pour la mise en place de l'expérimentation.

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.