Correlation model between stump diameter and volume of Larix olgensis plantation based on TLS

To explore the extraction accuracy of ground-based laser radar (TLS) for each relative high diameter of Larix olgensis, and the relationship between stump diameter and wood volume of Larix olgensis under different stand conditions in southern Heilongjiang Province, verify the effect of different modeling methods in the prediction of wood volume, and provide a scientific basis for predicting single wood volume when only stumpwere left.

Eight samples of Larix olgensis plantation plots were used as the research objects, and stump diameter (d_st) and diameter at breast height (DBH) extracted by TLS were substituted into One variable volume formula to obtain volume (V). The basic model of stump diameter and volume was constructed by nonlinear least square method, and the generalized model was constructed by adding trees per hectare (N) and tree AGE (AGE). Then, the sample plot was added as a random effect to construct a mixed effect model, and the prediction effects of different models were compared. Finally, the model was tested by the method of diameter order comparison.

The extraction accuracy of TLS at stump diameter is 93.42%, which is 5.56% lower than that of DBH (96.37%). There is a high correlation between the analytical wood volume (V_解) of 40 trees and the calculated wood volume (V) of One variable volume formula (R²=0.986 2), and the average relative error (RE) is 9.83%. Among the basic models, the Berkhart model has the smallest stump mean square error (RMSE=0.194 9) and the best fitting effect (R²=0.845 2, R_a²=0.844 8). In the correlation analysis, V is positively correlated with d_st and AGE, and negatively correlated with N. Among them, the influence of AGE on V is slightly larger than that of N. The R_a² of the generalized model is 7.98% higher than that of the basic model, and the RMSE is reduced from 0.195 5 to 0.194 9. In the mixed effects model, random effects performed best in b₁ and b₂ positions, R_a² increased by about 1.66% compared with the generalized model, and RMSE decreased from 0.195 5 to 0.194 2. When 11 cm ≤ d_st < 43 cm, the Mean absolute error (MAE) of the Berkhart model, the generalized model and the mixed effects model increased with the increase of the stump diameter (d_st) in the diameter order test. And the growth rate of MAE is from large to small: basic model > generalized model > mixed effect model.

Stump diameter (d_st) and DBH extracted by TLS can be used as modeling data. The mean value of RE with V is within the qualified range (±10%), and V can be used as modeling data. The goodness of fit of the basic model from large to small is: Berkhart model > Krenn model > Meyer model > Gehrardt model. The addition of N and AGE in the generalized model significantly improved the prediction accuracy of the model. The mixed effects model performed better than the generalized model in terms of evaluation metrics R_a² and RMSE.