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Acer platanoides L. individuals were dissected to determine if branch allometry changed as branches increased in length. Branches were found to transition from a log-log curvilinear relationship to a linear relationship when above 3,000 mm in length. The log-log linear relationship was best modeled with the elastic similarity model. The total number of subordinate lateral branches was found to increase rapidly after the primary branch length surpassed 3,000 mm, suggesting that branches are transitioning to a structural role as size increases. The shift in allometry appears to correspond to a shift from increasing slenderness ratio (length/radius) with increasing branch length to decreasing ratio, and is likely due to a transition from flexible sun branches to stiffer structural branches.

Tree biomechanics studies using dynamic methods of analysis are reviewed. The emphasis in this review is on the biomechanics of open-grown trees typically found in urban areas, rather than trees in forests or plantations. The distinction is not based on species but on their form, because open-grown trees usually grow with considerable branch mass and the dynamic response in winds may be different to other tree forms. Methods of dynamic analysis applied to trees are reviewed. Simple tree models have been developed to understand tree dynamic responses, but these largely ignore the dynamics of branches. More complex models and finite element analyses are developing a multimodal approach to represent the dynamics of branches on trees. Results indicate that material properties play only a limited role in tree dynamics and it is the form and morphology of the tree and branches that can influence the dynamics of trees.

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.