Résumé
The South American wood sector, especially the brazilian one, is characterised by a steady but sometime short-lived commercialisation of new timber species on the local market as well as for regional or international trading. Wood manufacturers must identify the most suited species according to their own processing constraints in relationship with the specific wood properties of the selected species. According to these operators, wood variations quite only correspond to differences between species. However, important variations of physical and mechanical properties are observed on sawn timber, leading to bitter technological problems during processing. The main characteristics commonly used to characterise any tropical species have been determined according to the CIRAD-Forêt's standard sampling procedure. The analysis of the variations of some of these properties (specific gravity, shrinkage, compression strength, bending strength, Young's modulus) brought out the respective effect of several factors : basically, type of botanical species, but also differences between trees (linked to any diameter and acre effect, even if very often, trees age is not known), and variations inside trees. Inter-species variations are frequently very high, but for some South American tropical timbers (i.e. Tauari, Wallaba, Curupixa), intraspecies variations can be higher. In particular, it is usually considered that intratree variations have not to be taken into account for timber from natural forest, and only concern plantations species. However, high variations inside trees have been observed for some species, such as Wallaba, explaining some technological problems occurring during processing. (Texte intégral)