Il est probable que les changements climatiques futurs diminuent la croissance forestière en région tempérée. Cette vulnérabilité des espèces face aux contraintes du climat peut être étudiée via les cernes des arbres. Ces derniers sont en effet des archives du carbone utilisé par les arbres pour leur croissance, en lien avec les caractéristiques spécifiques de gestion du carbone et de réponse au climat. L'objectif principal de cette thèse est de déterminer, à partir des cernes, les réponses fonctionnelles de trois essences forestières tempérées (Fagus sylvatica, Quercus petraea et Pinus sylvestris) aux variations climatiques. Pour cela, nous avons réalisé une approche expérimentale en étudiant deux proxys (ou indices climatiques) : la croissance et la composition isotopique en 13C (δ13C) des cernes, à deux échelles temporelles : interannuelle et saisonnière. A l'échelle interannuelle, sur la période 1960-2007, une étude dendrochronologique a été réalisée sur les trois essences et a été complétée par l'analyse du δ13C des cernes (en relation avec le climat). A l'échelle saisonnière, nous avons déterminé précisément, sur une année (2009), les dynamiques de croissance du cerne et les variations de δ13C intra-cerne. Nos résultats mettent en évidence une sensibilité de la croissance et du δ13C des cernes des trois essences aux sécheresses estivales. Grâce à la complémentarité des proxys et des échelles temporelles, nous avons également trouvé des réponses climatiques contrastées entre espèces. La croissance du Hêtre est la plus réactive au climat d'une année à l'autre. Cette croissance ainsi que le δ13C des cernes sont fortement sensibles aux températures de juillet, en plus des précipitations printanières et estivales. Cette réponse immédiate au climat peut être expliquée par une forte dépendance de la croissance au fonctionnement foliaire et une faible utilisation des réserves carbonées pour assurer le début de la croissance. Le Chêne présente lui des arrières-effets climatiques sur sa croissance, via une forte sensibilité aux sécheresses de l'automne précédent, contrairement aux deux autres espèces. Ce résultat est à mettre en relation avec l'utilisation importante de réserves carbonées par rapport aux assimilats pour la croissance du bois initial, cette dernière étant très rapide, comme nous l'avons observé grâce à l'analyse saisonnière de la croissance. Concernant le Pin, la croissance, parce qu'elle dure plus longtemps que celle des décidues, est influencée par les températures et les précipitations de juin jusqu'à août. Le δ13C des cernes de pins est celui qui enregistre le plus la réponse au VPD, aussi bien à l'échelle saisonnière qu'interannuelle, probablement du fait d'une forte sensibilité de la conductance stomatique à ce paramètre. Les informations fournies par les cernes permettent d'appréhender la survie des espèces face aux changements climatiques futurs et peuvent être utilisées pour comprendre le dépérissement lié à ces changements.

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Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

This thesis introduces the use of molecular methods for the conservation of several species of endangered saproxylic beetles in Europe. It focuses on the questions related to the DNA preservation and microsatellites development, as well as the evolutionary history and conservation of threatened species. Using the combination of mitochondrial and nuclear markers, the genetic diversity and reintroduction history of Cerambyx cerdo was assessed and the phylogeography of Rosalia alpina from the whole range of its distribution was studied. This information is valuable for designing more efficient conservation strategies.

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The full-field optical techniques such as e.g. a digital image correlation are capable to fully reflect the natural wood heterogeneity. Therefore, this thesis aspires to contribute to the experimental mechanics of wood and wood-based composites by the implementation of the full-field optical technique based on the digital image correlation to the standard mechanical tests. A supplementation of the conventional displacement sensors should help to obtain more precise mechanical characteristics and to do more sophisticated analyses of the deformation behaviour of wood and wood-based composites. The experimental part of the thesis is divided into the five independent case studies listed as the original papers. The measurements were carried out on the most wide-spread wood species in central Europe such as European beech (Fagus sylvatica, L.) and Norway spruce (Picea abies, L. Karst). Beside the solid wood, the new wood-based sandwich structure, which consists of a core made from birch plywood and the particleboard facings, was investigated too. The loading of the samples was carried out using of the standard mechanical tests such as tension, compression, three-point bending and torsion test. In the first study, the full-field deformation data were used to indentify reasons for the non-standard deformation behaviour of spruce and beech wood during compression parallel to grain. Reason for this was recognized in the abrubt compression of damage zones located near the compression plates, which induced the expansion of the middle zone located between them. The second study aimed to find out neutral axis position in native and thermally modified beech wood during the conventional three-point bending test. The relative neutral axis position was obtained from mutual position of the neutral axis and centroidal axis, which was determined based on the appropriate image processing methods. It was found that the neutral axis and centroidal sample axis are almost coincident. Objective of the third study was to determine both longitudinal shear moduli of beech wood with help of the full-field shear strains, obtained from a single torsion test, together with use of the appropriate analytical solutions for the calculation of the stress distribution within the radial and tangential direction on the longitudinal-radial and longitudinal-tangential sample surfaces. Both longitudinal shear moduli increasingly mutually differed as the load increases. Within the fourth study, verification of the elastic material model used in finite-element analyses was carried out with help of full-field deformations induced around notches within dog-bone shaped sample during the uniaxial tension. Great correlation was found between numerically predicted and experimentally measured strain data sets for both longitudinal-radial and longitudinal-tangential shear planes. The fifth study dealed with the characterization of elastic deformation behaviour of newly developed wood-based composite with a sandwich structure. Based on the full-field strain analysis the local strain concentrations were identified. They took place within the core during flatwise compression, and within the facings, when the edgewise compression test was done. A variety of presented results confirmed widespread applicability of optical methods in the mechanics of materials. Therefore, the utilization of full-field optical method based on digital image correlation in experimental mechanics of wood and wood-based composites can be highly recommended.

European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst) are the most abundant deciduous and coniferous tree species in the Czech Republic. Both beech and spruce are due to their sensitivity to drought threatened by ongoing climate change that can cause deterioration of their vitality in current habitats. Drought periods are already becoming longer and stronger and previously rare spring droughts become more frequent. The dissertation thesis is based on experiments with Norway spruce and European beech seedling exposed to different levels of drought (well-watered, moderate drought and severe drought). After three to six weeks of drought, the seedlings were well-watered for another two weeks and their response of physiology, anatomy and morphology was evaluated. Experiments were conducted with seedlings at early stage of leaf development and with fully developer leaves to compare response to spring and summer drought. Overall drought response was stronger in spring. Both spring and summer drought reduced gas exchange parameters (in both beech and spruce seedlings up to 100 %), hydraulic conductivity and less strongly also fluorometric parameters. Efficiency of water use in stressed seedlings decreased in spring, while it increased in summer. Shoot and leaves biomass was more reduced by drought than root biomass. Tree-ring width decreased about two times more in beech seedlings than in spruce seedlings. Vessel and tracheids in stem and shoots reduced their number and size, on the contrary, vessel size increased in beech petioles. After rewatering the reduced parameters increased, however, hydraulic conductivity, anatomy and morphology did not reach values of well-watered seedlings. While most of physiological parameters restored in moderately stressed seedlings, in severely stressed seedlings mainly gas exchange parameters remained lower.