Study on Variation of Wood Bending Properties among Trees of Taxodium Ascendens Plantation

Abstract In wood structural design, the modulus of elasticity (MOE) and modulus of rupture (MOR) are two key indexes of wood mechanical properties. In this study, Taxodium ascendens . Brongn plantation grown in terrestrial site were selected for the research material to study variation patterns of wood flexural elastic modulus and wood bending strength within-tree and among-trees. The results showed that the flexural modulus of elasticity and flexural strength for Taxodium ascendens increased first in radial direction from pith to bark, then to flatten out. Their longitudinal variation pattern showed increasing pattern first from the base of the trunk upward and then tended to flatten out too. Their average values were 5004 MPa in flexural modulus of elasticity and 65.3 MPa in flexural strength (bending strength or modulus of rupture) respectively. The mean values of flexural modulus of elasticity and flexural strength of Taxodium ascendens varied in the ranges of 4643 MPa to 5523 MPa and 57.0 MPa to 70.4 MPa, respectively. The mean values of flexural modulus and flexural strength were smallest at the base and the highest at breast height, when the age of the specimens within trees was more than 20 years old. The flexural modulus of elasticity and flexural strength of Taxodium ascendens varied significantly among trees. There was a highly significant positive correlation between MOE and MOR. According to the China grading standards of wood physical and mechanical properties, (Wood mechanical grade I is below 7.4 GPa in MOE and grade II is below 54.1 MPa∼88.0 MPa in MOR), the wood bending strength of Taxodium Ascendens is small and weak. Its wood is not suitable for structural material with high strength.