Modelling the biomechanical behaviour of growing trees at the forest stand scale. Part 1: 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.