树干平均密度的估计方法研究

Studies on the Estimate Method for Average Stem Density

估计密度的一般统计模型为：ｙ＝ｂｘ＋ｅ，其中ｙ为干重，ｘ为体积，ｂ为待估系数，即密度，ｅ为误差。式中ｂ值的估计，依据ｙ的方差与ｘ的关系的不同，有三种方法：（１）ｙ的方差与ｘ无关；（２）ｙ的方差正比于ｘ，即δ２ｙｘ＝ｘδ２；（３）ｙ的标准差正比于ｘ，即δｙｘ＝ｘδ。本文对这三种平均密度估计方法的结果进行了比较分析，并用哑变量方法对树干不同部位、不同龄组之间密度的差异性进行了检验。结果表明：方法（１）能较理想地描述树干材及树皮的体积和干重之间的关系，同时给出较小的误差估计；树干不同部位间密度总体上无显著差异，个别树种个别部位间有显著差异。不同龄组间密度无显著差异。据此，在利用材积密度法估计树干干重时，相同树种不同个体可以采用统一的平均密度值。

The model y=bx+e is used to estimate the density of stem,where y is dry weight, x is volume, b is density and e is error.According to the relationship between variance of y and x , there are three methods to estimate b: (1)variance of y is uncorrelated with x ;(2)the relationship between the variance of y and x is a positive correlation,or δ 2 yx =xδ 2 ;(3)the relationship between the standard deviation of y and x is a positive correlation, or δ yx =xδ. In this paper,the three methods were applied to estimate the average density of stem wood and bark,and the differences of the density in different positions of a tree and in different age class were analyzed with dummy variable method.The results showed:the effect of method (1) is better than the others.The differences of the density in different positions of a tree and in different age class are not significant.Same average density can be used to estimate stem dry weight of the same species of trees.