Growth stresses and physical-mechanical properties in reaction wood from various tropical species

Eleven trees from eleven different families amongst Angiosperms were selected after in-situ measurements of peripheral growth stresses. They showed high levels of dissymmetry for growth stress indicators (GSI) between the upper and lower side of the trunk. Eight test specimens: 50 mm longitudinal (L) x 20 mm radial (R) x 20 mm tangential (T), were taken from the vicinity of the eight growth stress measurements. Longitudinal MOE was measured in the green and dry states, as well as the R, T and L shrinkages. Occurrence of tension wood was observed on RT transverse faces of the shrinkage specimens. In nearly all cases the trend in the variation in MOE followed that of local growth stresses inside the tree with higher MOE for higher GSI. The similarity between variations of longitudinal shrinkage and GSI around the trunk was very high. Relationships between MOE, GSI, and R, T and L shrinkage were often highly significant. Anatomical observations at macroscopic or microscopic levels sometimes show clear distinction between wood associated to reaction stress and normal wood and sometimes not. Thus if tension wood is supposed to be at the origin of very high tensile growth stresses, anatomical or chemical features at the cell wall level should be investigated. Specific properties of tension wood fibres are discussed and their differences between species are examined. (Texte intégral