Construction of Compatible Growth Simultaneous Equations Model for Pinus tabuliformis Plantation

Taking the mountain plantation around Xining City as the research object, and using the forest resources update survey data in the past 2 years, a compatible growth simultaneous equation systems model of Pinus tabuliformis forest was constructed. The seemingly unrelated regression method was used to solve the model parameters. And the heteroscedastic correction was made to the model. Finally, testing the predicting effect and adaptability of the compatible growth simultaneous equation systems model. The results showed that the prediction accuracy of compatible growth simultaneous equation systems model for stand mean diameter, mean height and basal area were all above 93%, the MSE and TRE were within ± 2%, and the Chi-square test results were far less than the critical value. The prediction effect of compatible stand growth equation systems model was better than that of independent fitting model. At the young stage of P. tabuliformis, the diameter, tree height and basal area were positively correlated with stand density index and site class index. The diameter and tree height growth were more sensitive to the site class index, while the basal area growth was more sensitive to the stand density index. Based on the model prediction results, the rapid growth period of diameter of P. tabuliformis is 5–25 a, and the average annual growth is 0.33 cm. The rapid growth period of tree height is 5–30 a, and the average annual growth is 0.23 m. The basal area grows fastest before 15 a, with an annual growth rate of 0.13 m²/hm². The compatible growth simultaneous equation systems model of P. tabuliformis forest constructed in the study has high predicting effect, which can be used to predict the growth of diameter, tree height and basal area of P. tabuliformis stand in Xining City and similar ecological areas, providing reference for the prediction of stand growth and harvest and scientific and reasonable management.