Comparison on Correlation Models for Ground Diameter and DBH of Pinus massoniana

In December 2019, 4 sample plots were established in near-maturing Pinus massoniana forest in Dong’an county, Hunan province for determination of ground diameter and DBH. 11 mathematical models in SPSS curve regression analysis were fitting to make compare. The result demonstrated that 4 models had higher R2, like conic, cubic curve, power function. Nonlinear regression analysis of SPSS on these models showed that the power function curve equation by Gauss-Newton method was the optimal fitting model, y = 0.599 484x1.078 469, with adjustment of the correlation coefficient (R??2= 0.960808) the largest. Fitness test of the model indicated that the total relative difference was -1.34%, between -5% to 5%, with absolute mean percentage error of 7.6%.