Tree biomechanics.

Abstract This review of tree biomechanics covers recent research publications that offer new insights into how trees respond to mechanical loads and resist failure, especially in winds. Biomechanical studies using dynamic rather than static structural methods are showing that the form of the tree influences dynamic response in winds and differences in tree morphology can produce extreme behaviours such as very little or nearly critical dissipation of stem oscillations. Biomechanical studies on trees that measure the forces, stresses and strains are reviewed including a new method of optical strain measurement where small dots (speckle) sprayed on tree surfaces show the strain distribution of trunks and branches under load. The role of stress and strain in tree growth is currently an important research question and the review includes papers that are indicating that strain may be the factor, more than stress, in triggering adaptive growth response. The importance of the form of trees influencing their wind loading is leading to investigations of the importance of branches, especially in winds where they act like coupled oscillators attached to an oscillating trunk to modify sway behaviour. Branch unions are being studied and new concepts on their attachment are also reviewed. Collectively, these developments are leading to a better understanding of tree biomechanics and the complex dynamic response of trees in wind.