关键词: 兴安落叶松, 抽样方法, 材积, 异方差, 预测精度

Abstract: [Objective] Study the influence of different sampling method on the prediction accuracy of the individual volume equation, and provide the basic data sampling technical basis for the compilation of different tree species volume tables and the establishment of the individual tree volume equation.[Method] Taking the Larix gmelinii volume equation as an example, four different sampling methods are designed for uniform, normal, right and left skewed distribution. According to different distributions, simple random sampling (SRS) of proc surveyselect module in SAS software is combined with conditional statements for sampling at different diameter class. Shapiro-Wilk method is used for normality test. Allometric models are fitted using GNLS in S-PLUS. Variance functions (including exponential function, power function and constant plus power function) were incorporated into generalized allometric models to reduce heteroscedasticity. Coefficient determination (R²), root mean square error (RMSE), mean absolute bias (MAB), and mean percentage of bias (MPB) were employed to evaluate the precision of different individual volume models.[Result] 1) Exponential function, power function and constant power function could reduce heteroscedasticity and power function with weighting factor V^ is the best. 2) Compared with the uniform model, these RMSE of the normal model, right model, and left model decreased by 31.6%, 23.1%, and 33.7% respectively. 3) Diameter class tests of different volume models showed that MAB and MPB of left model were less than those of the uniform model, normal model, and right models at 12-28 cm, 36-40 cm and 44-48 cm diameter classes, i.e. MAB and MPB of 6 groups out of 11 group diameter classes were the smallest; MAB and MPB of right model were less than those of the uniform model and normal model at 12-32 cm and 44-48 cm diameter classes, i.e. MAB and MPB of 6 groups out of 11 group diameter classes were the smallest; MAB and MPB of normal model were less than that of the uniform model at 12-32 cm and 40-44 cm diameter classes, i.e. MAB and MPB of 6 groups out of 11 group diameter classes were the smallest.[Conclusion] The prediction accuracy of the left model is higher than those of uniform model, normal model, and right model, the prediction accuracy of the right model is higher than those of uniform model and normal model, the prediction accuracy of the normal model is better than that of the uniform model. The order of the overall model prediction accuracy is:left model > right model > normal model > uniform model.

Key words: Larix gmelinii, sampling method, volume, heteroscedasticity, prediction accuracy