A MECHANICAL MODEL OF WIND-INDUCED NATURA L SWAYS OF TREES RELATED TOBRANCHING PATTERNS

Within the scope of a more general programme about the mechanics of wi nd-tree interactions, a model of the first bending-twisting modes of t ree sway has been developed. The model aims to relate the natural tree sways and its morphology via a preliminary architectural analysis. Me chanical simulations with the finite elements software Modulef take in to account branch strains. Initial results from a Maritime pine show 2 modes where strain is observed on the trunk. As there are no signific ant coupling effects between the trunk modes and the branch modes a si mpler model can be used based on the strain of a single trunk. Further results concern a Hevea, computed by the growth simulator AMAP from t he architectural modelling of the clone. The morphology of the studied tree is characterized by competitive main axes growing along the trun k (reiterations). In this case, the computed modes of vibration show c omplicated interactions between these branches and the trunk: only the first fundamental mode remains uncoupled. Different branches sway at the same time, thus resulting in significant effort at the joint. This explains the sensitivity of such a clone (with large branches) to win d forces.