A Method for Estimating Tree Age Based on the Tree Trunk Diameter and the Average Radial Growth Rate in Recent Years

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.