Résumé
Enhanced value of eucalypts from plantations for solid wood products remains limited by the appearance of end splits and warps when processing, and by the heterogeneity of their physical and mechanical properties. We studied variations of three properties : specific gravity, longitudinal modulus of elasticity and growth strains. The study focused on plantations from Congo, China, Spain and France. According to our results, a cross section presents two types of variations : 1) the first, whose origin is morphogenetic, is a progressive transition of wood structure from the young state to the adult one. This transition induces variations of properties of the radius or according to the age of trees, particularly specific gravity; 2) the second is linked to the presence of tension wood, which induces sharp circumferential variations. This second heterogeneity occurs occasionally without any real relationship with the developmental stage of the tree, especially growth strains. Comparing plots of the same species, but with different ages, allowed determination of the existence of an age threshold beyond which growth strains are lower. Tendencies observed from the bottom to the top of the bole : 1) in the outer part of the stem, specific gravity and longitudinal modulus of elasticity both decrease, 2) near the pith, both properties are increasing. This could mean that, at a given cambial age, the wood from the upper part of the stem would be less 'juvenile' than the wood from the bottom. Comparisons, on a clone, of the level of growth strains from various spacings did not show significant differences. On the contrary, the setting (fertility class) and the genotype would have a marked influence on the level of growth strains. (Résumé d'auteur)