Height-diameter Models of Chinese Fir (Cunninghamia lanceolata) Based on Nonlinear Mixed Effects Models in Southeast China

摘要

Tree height and diameter at breast height are two important forest factors. The best model from 23 height-diameter equations was selected as the basic model to fit the height-diameter relationships of Chinese fir with one level (sites or plots effects) and nested two levels (nested effects of sites and plots) Nonlinear Mixed Effects (NLME) models. The best model was chosen by smaller Bias, RMSE and larger _Radj2. Then the best random-effects combinations for the NLME models were determined by AIC, BIC and -2LL. The results showed that the basic model with three random effects parameters &Phi &Phi &Phi₁ &Phi₂ and &Phi₃ was considered the best mixed model. The nested two levels NLME model considering heteroscedasticity structure (power function) possessed with higher predictable accuracy and significantly improved model performance (LRT = 469.43, p<0.0001). The NLME model would be allowed for estimating accuracy the height-diameter relationships of Chinese fir and provided better height predictions than the models using only fixed-effects parameters.