Effects of freezing on Young’s modulus for twigs of coniferous and deciduous trees and shrubs

Abstract

The mechanical behavior of frozen twigs may be important in understanding twig breakage during winter owing to wind or snow loading. While below 0 °C temperatures are known to increase the stiffness of wood, few studies have examined the effects of cold temperatures on the biomechanical properties of twigs of both coniferous and deciduous woody plants. In this study, we compared the effects of –11 to –14 °C temperatures on the Young’s modulus (E) of fine twigs of 14 species of woody plants. Twigs were 13%–304% stiffer when frozen than when thawed at room temperature (21 °C), with conifers showing the greatest percentage increase in stiffness. In general, more flexible twigs (when thawed) showed the greatest percentage increase in E when frozen. Greater stiffening of more flexible twigs may in part be the result of higher water contents but may also reflect differences in the relative importance of supercooling and extracellular freezing, with greater frozen stiffness associated with freezing. Our work suggests a direct link between cell physiology and whole organ biomechanics, and highlights reasons for differences in susceptibility to breakage due to wind or snow loading.