利用度量误差模型方法建立相容性立木生物量方程系统

本文以马尾松(Pinus massoniana)地上生物量数据为例,通过利用度量误差模型方法,研究建立了地上生物量与干、皮、枝、叶4个分量的相容性方程系统。首先,从各个分量所占比例变化特点分析入手,采用比值函数分级联合控制和比例函数总量直接控制2种方案构建了以地上总生物量为基础的相容性方程系统,其中对地上总生物量模型的估计,又采取了独立估计和联合估计2种处理方法。结果表明,分级联合控制方案和总量直接控制方案效果基本相当,而独立估计方法和联合估计方法也几乎没有差异。然后,还对一元、二元和三元模型的拟合效果进行了对比分析,结果显示随着解释变量的增加,估计值的标准误差和平均预估误差会有所下降,但对模型效果的改善幅度并不大。最后,对各个分量占地上总生物量的比例随直径的变化特点进行了分析,结果表明干材生物量所占比例随林木直径的增大而提高,干皮和树叶生物量所占比例则随林木直径的增大而下降,而树枝生物量所占比例相对比较稳定。本文所建立的相容性生物量方程系统,地上总生物量的预估精度达到95%以上,树叶生物量的预估精度最低,但也达到了85%以上。

Using Measurement Error Modeling Method to Establish Compatible Single-Tree Biomass Equations System

A system of equations for total biomass and the components must be compatible or additive, that is, the predicted values from the component biomass equations should add up to the predicted value from the total biomass equation. Based on the above-ground biomass data of Masson pine (Pinus massoniana) of southern China, the compatible systems of single-tree biomass equations for total above-ground biomass and the four components (stem wood, stem bark, branch, and foliage) were established using the error-in-variable modeling method in this paper. Firstly, starting from the analysis of properties of the component proportions to total biomass, two alternative approaches, controlling jointly from level to level by ratio functions and controlling directly under total biomass by proportion functions, were presented to design the compatible system of biomass equations based on the above-ground biomass which could be estimated independently apart from the system or estimated simultaneously in the system. It was showed that the approach controlling jointly by ratio functions was same effective as the one controlling directly by proportion functions, and the method that total above-ground biomass being estimated independently had almost the same prediction precision as that being estimated simultaneously. Secondly, the goodness-of-fit between biomass models with one variable and two or three variables were compared, and the results showed that the standard error of estimate (SEE) and mean prediction error (MPE) would decreased with increasing explainable variables, but the contribution to prediction precision was not high. Finally, the properties of the proportions of four components to total above-ground biomass were analyzed, and the results showed that the proportion of stem wood would increased with growing diameter, the proportions of stem bark and foliage would decreased with growing diameter, and the proportion of branches might be relatively stable. From the compatible system of biomass equations established in this paper, the prediction precision of total above-ground biomass estimate was higher than 95%, and the precision of foliage biomass estimate was the lowest but higher than 85%.