夏季与秋季钩梢对5年生毛竹竹材物理力学性质的影响

Influence of Obtruncation in Summer and Autumn on Physical and Mechanical Properties of 5 Years Old Culms of Phyllostachys pubescens

毛竹林钩梢是预防雪灾的重要抚育措施,一般在秋季进行。而随着劳动力成本日趋高涨,劳动强度相对较低的夏季钩梢则成为了一种新的技术选择。为了弄清夏季钩梢对竹材物理力学性质的影响,试验分别选取夏季钩梢、秋季钩梢和未钩梢毛竹(Phyllostachys pubescens)林的5年生立竹试材,比较分析钩梢尤其是夏季钩梢对竹材物理力学性质的影响。结果表明:夏季或秋季钩梢对竹材的3种密度指标(基本密度、气干密度和绝干密度)、体积干缩率、顺纹抗压强度、顺纹抗剪强度和弦向抗弯弹性模量均没有显著影响。钩梢毛竹竹材的纵向干缩率显著低于未钩梢毛竹,顺纹抗拉强度显著高于未钩梢毛竹,而同时弦向抗弯强度也高于未钩梢毛竹,差异接近显著水平(P=0.050 1);夏季钩梢竹材的径向干缩率高于秋季钩梢和未钩梢毛竹,差异也接近显著水平(P=0.050 8)。逐项分析结果表明钩梢显著降低了基部竹材的纵向干缩率,夏季钩梢对增加竹材径向干缩率的作用主要表现在基部和中部。竹材力学性质的逐项分析结果表明不同钩梢处理同一部位间没有显著差异,但其部位效应更加显著。以上结果说明夏季钩梢与秋季钩梢均不会降低毛竹竹材的物理使用价值。

Obtruncation management in autumn is widely used in northern Zhejiang Province to protect Moso bamboo plantation from snow disaster. As the labor costs rise steadily, relatively lower labor intensive management,i.e. ,obtrucation in summer, may be a better choice. But there exists a question on whether this practice would adversely affect the physical and mechanical properties of bamboo culms.This study investigated the influence of obtruncation on 5-year-old culms of Phyllostachys pubescens by determining the parameters of the physical and mechanical properties of three parts （ bottom, middle and top） of three kinds of culms （ those obtruncated in summer and autumn, and the control）.The results showed that there was no significant difference in basic density, air-dry density, over dry density, compressive strength parallel to grain, shear strength parallel to grain, tangential bending strength and elastic modulus of bending strength between the treatments and the control. There were significant differences in longitudinal shrinkage, volume shrinkage and tensile strength parallel to grain between the culms obtruncated in summer and autumn, and the control, and significant differences in radial shrinkage between the culms obtruncated in summer and obtruncated in autumn, and great differences existed in different parts of the three kinds of culms.The results indicated that the management of obtruncation in summer had no significant adverse influence on the physical and mechanical properties of culms,which means that obtruncation management can be extended to protect bamboo plantation from snow disaster.