Effects of Freezing Preservation and Loading Rate on Root Mechanical Properties of Four Hyrcanian Forest Tree Species

Abstract

Root biomechanical properties, including tensile strength, tensile force, and Young’s modulus, are fundamental parameters governing vegetation-induced soil reinforcement. However, the effects of sample preservation and loading rate on these properties remain insufficiently understood, limiting the reliability and comparability of root biomechanical data. This study investigated the influence of loading rate and freezing preservation on the mechanical properties of roots from four dominant Hyrcanian forest tree species. Fresh roots were tested at two loading rates, and an additional experiment evaluated the effect of one month of frozen storage before tensile testing. Freezing significantly increased tensile force, tensile strength, and Young’s modulus, while also improving the consistency of diameter–property relationships. These increases most likely resulted from structural and moisture-related changes induced by freezing rather than reflecting the natural mechanical behavior of roots, indicating that frozen samples may overestimate root reinforcement capacity. In contrast, loading-rate effects were generally limited and species-dependent. Root diameter increased tensile force but was generally associated with lower tensile strength and Young’s modulus. These findings highlight the importance of standardized testing protocols to improve the reliability of root biomechanical data and the accuracy of soil bioengineering applications.