Visual assessment of wood quality in standing trees in Eperua falcata Aublet (Caesalpiniaceae) : growth stresses in buttresses in relation with their mechanical function

Chouquet Isabelle, Fournier Meriem, Thibaut Bernard. 1995. Visual assessment of wood quality in standing trees in Eperua falcata Aublet (Caesalpiniaceae) : growth stresses in buttresses in relation with their mechanical function. IAWA Journal, 16 (1) : 7. IUFRO World Congress. 20, Tampere, Finlande, 6 Août 1995/12 Août 1995.

Note générale : Résumé seul

Résumé : Eperua falcata (vernacular name 'Wapa') is an abundant species of the French Guianan forest. However, its wood is scarcely used because of high growth stresses. These growth stresses, as viewed by the wood technologist, are pre-stresses of green timber that are released during wood processing with unexpected splits and deformations. For the living tree, growth stresses are internal forces generated by wood differentiation that improve the mechanical strength and allow reorientations or stabilisations of unequilibrated (asymmetric) trees, when heterogeneous stresses, associated with tension wood, are generated. We studied the magnitude of growth stresses in relation with the tree morphology and especially its lean and asymmetry. For that, we measured residual strains at the stem periphery for at least 8 points of the circumference, at three heights (the bole base, 1.3 m and 3.3 m) of 10 trees (Yiyi forest, French Guiana). The measured strains are always tensile ones : wood in hardwoods is under longitudinal tension at the stem surface and this internal stress is higher than the bending (compressive or tensile) effects of gravity. The magnitude of residual strains is not related to the tree diameter (that is quite as expected) nor to the stem lean or the crown asymmetry. But high variations of growth stresses are related to the presence of buttresses that are more strongly prestressed in tension than the neighbouring wood, and therefore act mechanically as guy ropes. Moreover, these buttresses have no effects on wood located on higher parts of the stem, as the residual strains measured at 3.3 m are not related with other heights. Therefore, measurements of wood quality near the trunk base (for example, at the usual breast height) can give only poor information on the quality of the other parts of the stem. Furthermore, we found that when different imbalance factors as the slope and the crown asymmetry are considered, high values of residual strains are measured on buttresses (or sometimes on striations). This could be the expression of a reaction of the tree system of anchorage.

Mots-clés Agrovoc : Eperua falcata, aptitude à la conservation, propriété mécanique, propriété du bois

Mots-clés géographiques Agrovoc : Guyane française, France

Classification Agris : K50 - Technologie des produits forestiers

Auteurs et affiliations

• Chouquet Isabelle
• Fournier Meriem
• Thibaut Bernard

Source : Cirad - Agritrop (https://agritrop.cirad.fr/391136/)

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