Variation in modulus of elasticity (E) along Acer platanoides L. (Aceraceae) branches

Arborists and managers of amenity trees could benefit from an improved understanding of how tree canopies withstand loading events such as wind, snow or ice. Knowledge of how material properties change along tree branches is important in understanding how a branch tips can bend in the wind yet resist displacement at the base which could lead to branch failure. Limited knowledge of modulus of elasticity (E or stiffness) in branch wood is available in the literature and is typically measured at only one location on a branch. This study investigated variation of E and density-specific E (E/ρ) at five locations along the axis of 20 branches from seven trees. E and E/ρ were found to be 70% lower at the branch tips than in the proximal locations. The variation in E was negatively correlated with the percentage of tissue area composed of vessels and positively correlated with mean fiber cell wall size, suggesting a balance between the two principle functions of hydraulics and mechanics. Reaction wood was observed in the form of gelatinous layers in fibers along the branch tops, but did not result in a difference in E between the top and bottoms at each branch location. It is proposed that differences in material properties are probably related to wood development type, as juvenile wood is considered to have lower stiffness than mature wood.