Some Properties of Astronium graveolens Wood Along the Stem

ABSTRACT We investigated the axial variation of specific gravity, shear parallel to the grain and anatomical features of Astronium graveolens wood and related these properties to the anatomy along the stem. We felled five 20-year-old trees and cut discs from four different stem heights, including stem base, 1 meter, 2 meters and 3 meters, for a total of 20 discs, and studied wood samples near the bark and at the base of trunk. Axial variations found appear to provide a balance between mechanical strength of the wood at stem base by the higher density and higher shear by the increase in ray frequency that contributes to locking the vertical cells and growth rings, thus preventing the stem from easily breaking when bent. For hydraulic conductivity, vessels with smaller diameter and frequency at the stem base help prevent the occurrence of embolisms that would reduce water flow along the main stem.

摘要 我们研究了Astronium graveolens木材的比重（specific gravity）、顺纹剪切强度（shear parallel to the grain）及解剖特征（anatomical features）沿轴向的变化，并将这些特性与树干不同高度处的解剖结构相关联。我们采伐了5株20年生的林木，从树干基部、1米处、2米处及3米处共4个不同高度位置截取圆盘试样，总计获得20个圆盘，并对树皮附近及树干基部的木材样本开展分析测试。本次研究发现的轴向变化规律，似乎实现了木材力学性能的优化平衡：树干基部较高的比重提升了木材整体力学强度，而木射线频率（ray frequency）的增加则强化了顺纹剪切强度，这有助于固定纵向细胞与生长轮（growth rings），进而避免树干受弯时轻易发生断裂。针对导水率（hydraulic conductivity）而言，树干基部管径更小、分布频率更低的导管（vessels），可有效防止栓塞（embolisms）的发生——此类栓塞会降低主干内的水分输送效率。