Résumé
The effect of viscoelasticity and juvenile wood on biomechanical performances of a tree in reorientation process was investigated numerically by calculating the up-righting efficiency and flexibility of a titled stem. During a reorientation process, the central part of a tree stem is submitted to high levels of prestresses so that its flexibility drops dramatically. Two factors influence biomechanical performances of a tree in reorientation process: the production of juvenile wood in earlier stages of its life and the viscoelastic properties of wood tissues. Juvenile wood increases the flexibility of the stem for both softwoods and hardwoods. In the case of softwoods, viscoelasticity has only a minor influence on the stem flexibility. By contrast, it has an important positive impact on the flexibility of hardwoods and thus allows to speed up their reorientation process. The trade-off between stem flexibility and the efficiency of its reorientation may imply a biological limit on the magnitude of growth strains