基于树种组成的大兴安岭天然林主要树种树高⁃胸径曲线研究

Modelling height⁃diameter curves of main species for natural forests based on species composition in Greater Khingan Mountains,northeast China

【目的】分析混交林中不同树种组成情况对单木树高⁃胸径关系的影响,构建大兴安岭地区兴安落叶松和白桦的树高曲线模型,为森林质量精准提升提供理论依据。【方法】以大兴安岭中部地区112块兴安落叶松(Larix gmelinii)⁃白桦(Betula platypiylla)混交林的样地调查数据为基础,采用多元逐步回归建立包含单木、林分和树种组成信息的兴安落叶松和白桦树高⁃胸径预测基础模型,并采用层次分割方法量化不同变量对单木树高⁃胸径关系的影响程度。最后,采用混合模型方法解决样地调查数据中存在的嵌套效应和异方差问题。【结果】大兴安岭地区兴安落叶松⁃白桦混交林中主要树种(兴安落叶松和白桦)单木树高⁃胸径关系除受自身胸径大小影响,还受林分特征(优势木树高、林分平均胸径和林分平均树高)和树种组成(兴安落叶松、白桦蓄积比例)信息的共同影响,其对各树种树高⁃胸径变异的解释能力依次为单木胸径(82%)>林分因子(16%)>树种组成(2%);各树种树高⁃胸径混合模型均以包含3个随机参数、方差协方差结构pdSymm和异方差校正函数varPower的组合最优,兴安落叶松和白桦单木树高⁃胸径混合模型的调整决定系数(R^(2)_(adj))分别较基础模型提升约2.50%和3.44%,达到了0.7895和0.7447。【结论】在具体的森林经营实践中,可通过采伐或补植的方式来调整林分的树种组成情况以达到促进林木树高生长的作用。

【Objective】An in⁃depth understanding of how species composition influences the relationship between individual tree height(HT)and diameter at breast height(DBH)in mixed forests is important for effective implementation of forest quality improvements.【Method】The functions relating the HT and DBH of individual larch(Larix gmelinii)and birch(Betula platyphylla)were estimated using multiple stepwise regression with tree,stand,and species information extracted from 112 larch⁃birch mixed forests in the central part of Greater Khingan Mountains.The effects of the different variables on the relationship between HT and DBH were quantified using hierarchical partitioning.Finally,mixed⁃effects modelling techniques were employed to characterize nesting effects and solve heteroscedasticity problems within the sample survey data.【Result】The correlations between HT and DBH of the main tree species in Greater Khingan Mountains were affected simultaneously by the DBHs of the individual trees,stand characteristics(i.e.,HT of dominant tree,as well as mean DBH and HT of the stand),and species composition(i.e.,the volume percentage of larch and birch).The individual contributions on the HT⁃DBH relations from the various variables were as follows:DBH of individual tree(82%)>stand characteristics(16%)>species composition(2%).Furthermore,the mixed⁃effect models of HT⁃DBH were each optimally combined with three random parameters,as well as variance covariances with pdSymm structure and heteroscedasticity correction with varPower functions,in which the values of R_(adj)both increased by about 2.50%and 3.44%(0.7895 of larch and 0.7447 of birch)when compared with that of the basic model.【Conclusion】From the perspective of forest management practices,individual tree HT growth can be promoted by adjusting the species composition of forests through suitable cutting or replanting.