To accurately estimate the pith position, a method was proposed for estimating the pith position by the crown width. The crown widths of 120 trees and radiuses of each disc extracted at the height of 1.3 m from these trees were measured in four directions. The crown and radius ratios of the length of each direction to the total length in that direction and the opposite direction were calculated. Using the crown ratio as an independent variable, as well as the radius ratio as a dependent variable, the linear, logarithmic, exponential, and polynomial models were built. The model with the highest R² was selected as the radius ratio model. The geometric center method and the crown width method were applied to estimate the pith position, and the estimation errors were calculated, respectively. The R² of the linear, logarithmic, exponential, and polynomial models were 0.405, 0.379, 0.403, 0.404, respectively, and the linear model was chosen as the radius ratio model. The prediction error based on the crown width was 7.6%, and that of the geometric center method was 10.1%. The findings indicate that the crown width method can improve the accuracy of estimating the pith position.

To improve the accuracy of tree age estimation by accounting for variations in radial growth, this study developed a diameter-age model that incorporates radial growth rate for seven typical tree species across subtropical to cold temperate regions. For each tree species, six trees were selected, including 2 dominant trees, 2 intermediate trees, and 2 suppressed trees. A total of 646 disks were collected at 1-meter intervals along the stems, starting at 0.3 m height. Disks diameters and tree-rings were measured, and the radial growth rate of each disk over the past two years was calculated. For each tree species, 2/3 of the data were randomly selected as the modeling dataset, while the remaining 1/3 served as the testing dataset. Based on scatter plots, select linear models, logarithmic models, and exponential models as candidate models. A logarithmic function best described the diameter-age relationship, while an exponential model best fit the radial growth rate -age relationship. A dual-factor nonlinear model combining both variables achieved the highest estimation accuracy (77.95%), significantly outperforming single-factor models based solely on diameter (52.72%) or growth rate (70.78%). These results demonstrate that integrating radial growth rate substantially enhances the precision of tree age estimation.