The mechanics and morphology of branch and coppice stems in three temperate tree species

Abstract

Key message: Sycamore and ash trees were found to be greater E in their coppices, but horse chestnut was stiffer in its branches, this could be related to node frequency. Abstract: In this study, mechanical and anatomical properties of branch and coppice shoots of sycamore, horse chestnut and common ash were investigated along the length of their shoots and to relate these differences to their morphology and wood density. A series of 3-point bending tests were made along the lengths of the branches and coppices shoots at different diameters to determine the mechanical properties. The morphology was also characterized. Our results showed clearly that sycamore and horse chestnut trees were found to have greater flexural stiffness (EI) in their branches than the coppices, but coppices were stiffer (higher E) than branches in ash. Sycamore also surprisingly showed greater flexibility (higher E) in its coppices than the branches. The differences between branch and coppice shoots were explained by the morphology. Since the clearest morphological differences between the branches and coppices were in leaf node frequency, and linear regression analysis showed that the mechanical properties were negatively affected by higher leaf node frequency. Sycamore and ash had more leaf nodes in their branches than coppice shoots and consequently the mean E was lower in the branches; conversely horse chestnut had more leaf nodes in its coppice shoots which consequently had a lower mean E. The leaf nodes could also provide greater flexibility in the parallel plane since there is gap in nodal region and the arrangement of fibres are quite different here. The morphological differences could explain lower mechanical properties around the nodal region. The results also showed that mechanical properties were higher at the base and lower at the tips of branch and coppice shoots. These results cast light on the use of coppicing in particular tree species.