Modélisation du comportement biomécanique de l'arbre dans son environnement forestier. Application au pin maritime

Le module AMAPméca permet de simuler le comportement biomécanique d'un arbre isolé dont l'architecture est entièrement décrite et utilise la Méthode des Eléments Finis en analyse linéaire. Le soucis díune meilleure prise en compte des grands déplacements, pouvant intervenir lors díun cycle de croissance, nous a conduit à développer les outils permettant de modéliser le comportement biomécanique de líarbre en analyse non linéaire. Il apparaît que ce type díanalyse ne se justifie que dans certains cas de chargements élevés. De plus, l'important coût de calcul quíelle occasionne síavère déjà pénalisant pour la simulation díun seul arbre. La prise en compte de líenvironnement forestier ouvre la voie à líétude des effets díun scénario sylvicole sur la forme future des arbres. A líéchelle spatiale du peuplement, on limite la description de líarbre à celle du tronc et du houppier. Deux modèles ont été implantés dans la plate-forme logicielle CAPSIS avec pour objectif díintégrer les aspects "forme" dans les modèles spatialisés de croissance des peuplements forestiers. Díune part, un modèle de régulation de la forme des troncs, soumis à des sollicitations internes et externes, a été développé. Il utilise les Matrices de Transfert des poutres dans líhypothèse des petits déplacements. Díautre part, un premier modèle de dissymétrie de la croissance des houppiers a été proposé. Il repose sur líutilisation des diagrammes de Voronoï pour traduire les effets de la compétition spatiale entre arbres voisins sur le développement des houppiers. Líutilisation conjointe de ces deux modèles ouvre la voie à líétude des relations existant entrelíexcentrement des houppiers et la mise en place progressive de la forme des tiges. Le problème de líévaluation des modèles díun point de vue numérique puis expérimental est abordé. Il ressort alors que cette phase reste suspendue à la connaissance parfaite de líhistorique des individus étudiés.The AMAPmeca module allows the biomechanical behaviour of a single tree, architecture of which is completely described, to be simulated. It is based on the Finite Element Method in linear analysis. A model of trees biomechanical behaviour has been developed in non linear analysis. It allows the large displacements which can occur during a cycle of growth to be taken into account. It seems that this type of analysis is only justified in certain cases of high loads. Furthermore, important cost of calculation that it causes already turns out punishing for the simulation of a single tree. The consideration of forested environment opens the way in study of the effects of the sylviculture on the future shape of trees. In spatial scale of the stand, we limit the description of a tree to the trunk and the crown. Two models were implanted in the software platform CAPSIS with the aim to integrate "shape" aspects into spatially explicit models of stand growth. A model of trunks shape regulation, subjected to internal and external loads, was developed. It uses the Transfer Matrix Method of beams in hypothesis of small displacements. A first model of asymmetry of the crown growth was proposed. It is based on use of Voronoï diagrams to translate the effects of the spatial competition between trees on the crown development. Joint use of these two models opens the way in study of the existing relations between crown eccentricity and progressive evolution of trunks shape. The problem of the models evaluation is approached in numerical and experimental point of view. It appears that this work remains suspended from the perfect knowledge of the studied individuals history

Modélisation du comportement biomécanique de l'arbre dans son environnement forestier (application au pin maritime)

BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Modelling the biochemical behaviour of growing trees at the forest stand scale. Part I: Development of an incremental transfer matrix method and application to simplified tree structures

Stem straightness defects are often associated with heterogeneities in wood structure in relation to tree tropisms. This paper presents a numerical model which is dedicated to simulate the biomechanical behaviour of growing trees. A simplified description of tree structure, separating trunk and crown, has been used in order to perform future calculations at the stand level. The model is based on the Transfer Matrix Method, which was adjusted under an incremental form to compute the evolution of trunk biomechanics during growth. Deflections due to self-weight distribution and straightening up reactions, which are associated with maturation strains of reaction wood cells, were considered. This model has been implemented in the CAPSIS software. Numerical results were compared to those obtained by the software AMAPpara, which is more applicable to the whole tree architecture level. Limits of the simplified description, which will be useful for studies at stand level, are discussed. (Résumé d'auteur