The purpose of the present paper was to investigate the accumulation of growth stresses in a cross section of a tree in active reorientation process and its biomechanical performances i.e. up-righting efficiency and stem flexibility. Effect of two factors was analysed in details: occurrence of juvenile wood and viscoelasticity of wood tissues. In a phase of active re-orientation, wood tissues close to the pith are submitted to significant levels of compressive stresses. Production of juvenile wood in earlier stage of a tree life seems to increase the stem flexibility during active reorientation for both softwoods as well as hardwoods. Concerning the viscoelasticity of wood tissues, only minor effect has been observed in softwoods while an important positive impact has been pointed out in hardwoods. Set of simulations with increasing level of maturation strains in reaction tissues indicate possible trade-off between the stem flexibility and the up-righting efficiency.