The Taper Equation of 3 Coniferous Tree Species Based on Nonlinear Mixed Effects Models

Taking the stem analysis data of 3 dominant species in 96 spruce-fir stands as an example, 2 commonly used taper equation are selected to construct taper equation of Pinus koraiensis, Abies fabri and Piceaasperata based on mixed effects models, the result will compare and verify the accuracy with that of the traditional method based on the verification data. The result shows the value of AIC, BIC, and −2logL are obviously decreased after considered the mixed effect model method, which indicates that the simulation effect of mixed model is higher than that of the traditional model. Three indexes of correlation coefficient, root mean square error, and determining average residual error, are used to compare the accuracy of taper equation, both the accuracy of simulation data and validation data all support above mentioned conclusion. The accuracy of the Max et al. segmented taper equation of 2 inflection points in simulation and verification is higher than that of Kozak et al. simple taper equation.