2022 年 1 期目录

  目的  准确预测林木的生存和枯损是森林生长收获模型系统中十分重要的组成部分。构建基于混合效应模型和生存分析方法相结合的林木生存模型,能够提高林木枯损模型的精度。   方法  以吉林省汪清林业局20块落叶松云冷杉林样地数据为例,基于生存分析方法中常用的6个时间参数分布回归模型（指数分布、Weibull分布、对数正态分布、对数Logistic分布、Gompertz分布及Gamma分布）,把林分因子和立地因子作为协变量加入到模型中去,构建林木生存模型。并在此基础上考虑样地的随机效应,并与传统模型的模拟效果进行比较。  结果  研究结果表明,随着单木初始胸径的增加,其枯损的风险降低,生存率提高;随着单木大于对象木断面积值的增加,其枯损的风险增加,生存率降低;随着林分密度的增加,林木枯损的概率增加,生存率降低;立地因子对林木的生存没有显著影响;6个参数分布回归模型中,Weibull分布的模拟精度最高。与固定效应模型相比,Weibull分布模型在考虑样地水平随机效应后,模型的模拟精度获得明显的提高,并且达到极显著程度。  结论  在森林经营中,要提高林木的生存率,需采取科学合理的经营方法和经营时间,避免使林分的密度过大。 

Compression deformation fixation and properties of Chinese fir pretreated with citric acid

ObjectiveIn order to improve the use value of fast-growing wood Chinese fir, this study investigate the effects of citric acid pretreatment and thermal compression treatment on the compression set of Chinese fir, so as to improve its shortcomings such as low density, poor dimensional stability and poor mechanical properties. MethodIn this study, Chinese fir pretreated with an aqueous solution of citric acid with varying mass fractions were evaluated at different hot-pressing temperature, then the set-recovery for water absorption and the set-recovery for moisture absorption of Chinese fir compressed wood were measured. Stress relaxation and Fourier infrared spectroscopy were used to investigate the deformation and fixation mechanism of Chinese fir compressed wood pretreated with citric acid, and physical and mechanical properties of Chinese fir compressed wood were characterized. ResultsThe set-recovery for water absorption of Chinese fir compressed wood decreased with the citric acid mass fractions and then increased slightly, while decreased with the hot-pressing temperature. The lowest set-recovery for water absorption and moisture absorption were 10.78% and 1.38%, respectively. This could be attributed to the fact that some components of wood were degraded by citric acid, inducing partial cleavage of connections among Chinese fir components, therefore the internal stress of Chinese fir compressed wood was released. In addition, citric acid may react with a small amount of hydroxyl of Chinese fir to form a cross-linked network. The polymer formed by the esterification of citric acid filled in the intercellular space of cell wall during the process of compression. At higher temperature, the polymer was soft and flexible, which promoted the release of the internal stress and the fixation of the Chinese fir compressed wood. The density of Chinese fir compressed wood increased with the compression ratios, and reached a maximum value of 0.717 g/cm3 when the compression ratio was 50%. Compared with the control, its density, bending strength, flexural elastic modulus and the hardness of compressed wood increased by 94.8%, 70.6%, 278.2% and 52.5%, respectively.ConclusionThe deformation of Chinese fir compressed wood was fixed effectively by citric acid pretreatment, and the physical and mechanical properties of Chinese fir compressed wood were improved significantly. The results of this study provide theoretical support and technical reference for adding high-value to application of fast-growing wood.