The Tree Volume Equations System For Dahurian Larch In Different Region Of Daxinganling

Compatible volume models in different regions were developed using the error-in-variable equations system for dahurian larch (Larix gmelinii Rupr.) from the three different regions located in Daxinganling Region. [Method] Regional differences in the volume models were examined and tested using the nonlinear extra sum of squares method (F-test). Weighted regression was used to decrease heteroscedasticity of volume equations in three regions using variety forms of weight functions. The results indicated that volume models were significantly different among different regions (P<0.0001). Volume model in region 1 have large difference with region 3, volume model in region 2 have small differences with region 1 and region 3. Incorrectly applying volume model in different regions would result in larger prediction error. Weighted estimation will be better than the ordinary least squares estimation in terms of parameters stability and evaluation index. Based on MRE and TRE, the best weighting functions are 1/F(x),1/D49、1/D338 for regionl (-0.11、0.97), region 2 (0.04、0.08), and region 3 (1.04、0.93) respectively. Respectively, individual tree volume model is major component of forest inventory and growth and yield model. Volume models should consider the phenomena of heteroscedasticty, and the optimal weight functions of individual tree volume models don’t have a uniform format. To get the stability of parameters estimation, different weight functions should be analyzed in the process of the weighted regression. With the same method to establish two-and one-variable (diameter at breast height, and ground diameter) tree volume equations, height-dbh regression models, and ground diameter-dbh regression models. Using three height-dbh models and two ground diameter models to combined four tree volume table series model of consociation equations, making a comprehensive evaluation by six indicators, the results showed that the series volume model established by the first height-dbh model and ground diameter model which can achieve good results. The prediction errors of consociation equations are within ±3% in three different regions, the estimated accuracy of two-and one-variable (diameter at breast height, and ground diameter) tree volume equations, height-dbh regression models, and ground diameter-dbh regression models can reach 97%.