落叶松人工林枝条直径和长度的非线性混合模型

基于95株落叶松解析木、843个枝条实测数据,构建了枝条直径和长度的传统非线性模型、含树木变量的非线性模型、非线性混合模型和含有误差结构的非线性混合模型,比较了各模型的拟合精度,分析了枝条直径和长度的变化规律。结果表明:含有误差结构的落叶松人工林枝条直径和长度非线性混合模型拟合精度最优,决定系数R2分别为0.783 7和0.865 7,均方根误差(RMSE)分别为0.377 7和0.286 6,且消除了异方差现象,独立样本检验结果也证实该模型是最优预测模型; 落叶松人工林枝条直径和长度与枝条所在位置和树木胸径、冠幅、高径比紧密相关,在树冠顶部分布的一级枝条直径和长度都较小,而在树冠底部分布的则较大,树冠下部枝条的直径和长度受树木形态因子的影响更明显。
The objective of this work was to establish the models for predicting branch diameters and lengths in the larch plantations. The traditional nonlinear model, including the trees variable nonlinear model, the nonlinear mixed models and the nonlinear mixed model containing the error structure of branch diameter and length were constructed based on the data of 843 standard branches collected from 95 sample trees, and the prediction accuracies were also evaluated, by the analyses of the changing rule of the branch diameters and lengths. The results indicated that the nonlinear mixed model with the error structure for the branch diameter and length prediction was the best, with R2 values of 0.783 7 and 0.865 7, and RMSE values of 0.377 7 and 0.286 6, respectively, and the phenomenon of heteroscedasticity was also elminated. The validation by using independent samples also verified that this model was optimal. The model showed that the branch diameter and length were closely related to branch location within the living crown and diameter at breast height, crown width, ratio of height to diameter. The diameter and length of branches were smaller in the top but was bigger in the bottom of crown. The diameter and length of branches in the bottom of crown were more obvious in different trees