Anticipating the variance of predicted stand volume and timber assortments with respect to stand characteristics and field measurements
Anticipating the variance of predicted stand volume and timber assortments with respect to stand characteristics and field measurements
复制标题
预测林分体积和木材种类相对于林分特征和现场测量的差异
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
M. Maltamo
中科院分区：
文献类型：
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作者：
A. Kangas;M. Maltamo
几种模型和/或几种变量组合可用于预测林分直径分布。通常，在所有条件下都使用固定模型和固定变量组合。然而，校准程序使得从许多可能性中选择测量组合成为可能，尽管所使用的模型是固定的。在这项研究中，利用额外的林分特征来校准预测直径分布的有效性进行了检验。试验了9种测量策略对林分积、锯材积和纸浆材积的预测效果。在每种策略下，这些变量的观测误差被建模为基面积、基面积中值直径和茎数的函数。模型的估计分三步进行。首先，对观测误差拟合普通最小二乘（OLS）模型；然后，利用OLS残差估计方差函数。最后，以估计的方差函数为权重，采用加权似不相关回归（SUR）分析对观测误差进行建模。利用估算模型可以预测不同变量组合下各林分预测体积特性的精度和准确度，从而选择不同林分的最佳测量组合。
Several models and/or several variable combinations could be used to predict the diameter distribution of a stand. Typically, a fi xed model and a fi xed variable combination is used in all conditions. The calibration procedure, however, makes it possible to choose the measurement combination from among many possibilities, although the model used is fi xed. In this study, the usefulness of utilizing additional stand characteristics for calibrating the predicted diameter distribution is examined. Nine measurement strategies were tested in predicting the total stand volume, sawlog volume and pulpwood volume. The observed errors of these variables under each strategy were modeled as a function of basal area, basal area median diameter and number of stems. The models were estimated in three steps. First, an Ordinary Least Squares (OLS) model was fi tted to the observed errors. Then, a variance function was estimated using the OLS residuals. Finally, a weighted Seemingly Unrelated Regression (SUR) analysis was used to model the observed errors, using the estimated variance functions as weights. The estimated models can be used to anticipate the precision and accuracy of predicted volume characteristics for each stand with different variable combinations and, consequently, to choose the best measurement combination in different stands.