A MECHANICAL MODEL OF WIND-INDUCED NATURAL SWAYS OF TREES RELATED TO BRANCHING PATTERNS

Within the scope of a more general programme about the mechanics of wind-tree interactions, a model of the first bending-twisting modes of tree sway has been developed. The model aims to relate the natural tree sways and its morphology via a preliminary architectural analysis. Mechanical simulations with the finite elements software Modulef take into account branch strains. Initial results from a Maritime pine show 2 modes where strain is observed on the trunk. As there are no significant coupling effects between the trunk modes and the branch modes a simpler model can be used based on the strain of a single trunk. Further results concern a Hevea, computed by the growth simulator AMAP from the architectural modelling of the clone. The morphology of the studied tree is characterized by competitive main axes growing along the trunk (reiterations). In this case, the computed modes of vibration show complicated 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 wind forces.