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Anticipated changes in climate and research findings on the drought sensitivity of beech have triggered controversial discussions about the future of European beech. We investigated the growth response of beech on the tree-and stand-level in mature stands to three different thinning intensities (no thinning, strong thinning, very strong thinning) on a northeast-and southwest-facing slope in Southwest Germany. Linear mixed-effects models were formulated to describe effects on growth parameters on the tree-and stand-level (diameter, height, basal area, volume). At the stand-level, the stand basal area increment and stand volume increment were lower on the thinned plots. At the tree-level, the basal area increment significantly increased with increasing thinning intensity. The growth of individual trees was also influenced by initial tree size, the size-related rank of the tree within a stand, and by the aspect of the site. Our data indicate that growth of European beech is impaired on the southwest-facing slope with a warmer and drier climate and that a very strong thinning regime applied at advanced age can accelerate growth of European beech trees even on the warmer and drier site. Our findings, therefore, imply that in a warmer climate intensive thinning may also represent an important adaptive forest management measure in European beech stands. OPEN ACCESSForests 2015, 6 3257

Background: Wood density is considered to be the most important predictor of wood quality but despite its importance, diffuse-porous tree species have been the subject of only a limited number of studies. The importance of European beech forests for Central Europe calls for profound research to examine the potential impact of a warmer climate on the quality of beech timber. Methods:In this study we analysed the influence of tree-ring width and tree-ring age on the wood density of beech, and whether the wood density response to these two parameters is modified by aspect. A linear mixed-effects model for wood density was constructed for mean density data measured with high frequency densitometry on stem discs from 72 beech trees sampled from two different aspects (northeast -NE and southwest -SW) of a valley in southwestern Germany.Results: Part of the variability of mean annual wood density was explained by cambial age: an increase in cambial age resulted in an increase in mean wood density. Tree-ring width and aspect had only a small influence on wood density. Wood density on the SW aspect was lower than on the NE with a difference of approximately 0.006 g/cm 3 . The between-tree variability was very high.Conclusions: The significant interaction between cambial age and aspect reflects the importance of site conditions at older tree ages: with increasing cambial age the difference between aspects becomes stronger. Our results give a better understanding of the importance of site conditions on the wood quality of beech.

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The importance of European beech (Fagus sylvatica L.) for the Central European forest and wood sector demands profound research to examine the adaptive capacity of beech forests to changing environmental conditions. Quantitative wood anatomy is a valuable tool for studying the relation between structural and functional traits of trees, but due to the laborious methodology not many studies have thus far been performed on the conductive tissue of broadleaf tree species with diffuse-porous wood structure. The aim of our research was to test the effects of aspect and thinning on vessel anatomical features of European beech (vessel density, vessel size, total vessel area, vessel groups and hydraulic conductivity). Our analysis of increment cores of trees sampled from a long-term experimental research area on the Swabian Alb showed that (i) the variations in different vessel traits were mainly controlled by tree-ring width. Additionally, we could observe that (ii) thinning contributed to a safer water transport by decreasing vessel size and that (iii) the aspect modified these responses. Our results provide new insights into the plastic response of European beech wood anatomy to warmer climatic conditions and demonstrated that thinning of the forest stands modified the water-conducting system to become more resistant against hydraulic failure.