Abstract:

【Objective】This study took the Larix gmelinii in the Greater Khingan Mountains as the research subject. Based on breast height form quotient, normal form quotient, and ground form quotient, individual tree volume models incorporating different form factors were constructed. These models were then compared and analyzed against traditional one-variable and two-variable volume models, as well as the two-variable volume model for L. gmelinii in Northeast China.【Method】Based on the measured data of L. gmelinii, a series of breast height form quotients, normal form quotients, and ground form quotients at different heights of the trunk were introduced into the traditional volume model. One-variable and two-variable tree volume models with different form quotients were constructed, respectively, and variance functions were introduced to eliminate the heteroscedasticity in the fitting process of each volume model. The mean absolute error (MAE), root mean square error (RMSE), relative root mean square error (RMSE%), determination coefficient (R²), and Akaike information criterion (AIC) were used as evaluation indexes to fit and analyze each model.【Result】(1) The two-variable and three-variable models constructed with the introduction of the breast height form quotient at 50% relative tree height fitted best, with the three-variable tree volume model reducing the RMSE by 44.4% compared to the two-variable tree volume equation. (2) The three-variable volume model constructed by introducing the normal form quotient,at 50% of the relative tree height performed the best, reducing the RMSE by 23.1% compared to the two-variable volume model that incorporated the ground form quotient. (3) For the ground form quotient, the three-variable volume model achieved the best fit when the variable was set at 60% of the relative tree height, while the binary volume model performed optimally when the variable was set at 50% of the relative tree height. The three-variable volume model incorporating the ground form quotient reduced the RMSE by 32.5% compared to the two-variable volume model. (4) Compared to the two-variable volume equation for Larix gmelinii used in Northeast China, the three-variable volume model incorporating the breast height form quotient reduced the RMSE, MAE, and RMSE% by 62.85%, 65.02%, and 67.14%, respectively. The three-variable volume model containing the breast height form quotient reduced the RMSE by 60.41% compared to the traditional two-variable tree volume equations.【Conclusion】The form quotient is an important index of stem form, and the introduction of breast height form quotient, normal form quotient, and ground form quotient into the traditional volume models can improve the accuracy of predicting tree volume. The three-variable tree volume model has the best prediction effect with the introduction of the breast height form quotient. Therefore, it is recommended to use this model to predict the tree stem volume of L. gmelinii in the region in the future.

Key words: Larix gmelinii, breast height form quotient, normal form quotient, ground form quotient, individual tree volume