白桦和水曲柳树干温度日变化的空间变异及其影响因子

植物温度是森林生态系统能量平衡和植被呼吸估算的重要参数.采用T型热电偶监测树皮和木材特性各异的2个阔叶树种(白桦和水曲柳)不同深度、高度和方位的树干温度(T_s),探索T_s日变化的空间变异及其影响因素.结果表明: T_s月平均日变化格局与空气温度呈相似的正弦曲线,但T_s变化滞后于空气温度,时滞从树皮表面处的0 h增加到6 cm深度处的4 h.随测定深度的增加和高度的降低,T_s日变化的峰值和日较差均逐渐减小.T_s周向差异不大,休眠季节白天南向、西向T_s日峰值略高.两树种树皮和木材的热学特性(比热容和导热系数)的差异,会通过影响树干表面与外界的热交换和树干内部热扩散而造成T_s径向变化的种间差异.白桦树皮较高的反射率削弱了太阳辐射对T_s的影响.多元逐步回归分析表明,环境因子可以很好地估测T_s日动态(R²>0.85),影响程度依次为空气温度>水汽压>净辐射>风速.估算生物量热储和树干表面CO₂通量时应考虑T_s径向、纵向和种间差异.

Compatible biomass models of natural spruce (Picea asperata).

By using nonlinear measurement error method, the compatible tree volume and above-ground biomass equations were established based on the volume and biomass data of 150 sampling trees of natural spruce (Picea asperata). Two approaches, controlling directly under total aboveground biomass and controlling jointly from level to level, were used to design the compatible system for the total aboveground biomass and the biomass of four components (stem, bark, branch and foliage), and the total-ground biomass could be estimated independently or estimated simultaneously in the system. The results showed that the R² of the one-variable and bivariate compatible tree volume and aboveground biomass equations were all above 0.85, and the maximum value reached 0.99. The prediction effect of the volume equations could be improved significantly when tree height was included as predictor, while it was not significant in biomass estimation. For the compatible biomass systems, the one-variable model based on controlling jointly from level to level was better than the model using controlling directly under total above-ground biomass, but the bivariate models of the two methods were similar. Comparing the imitative effects of the one-variable and bivariate compatible biomass models, the results showed that the increase of explainable variables could significantly improve the fitness of branch and foliage biomass, but had little effect on other components. Besides, there was almost no difference between the two methods of estimation based on the comparison.