Objective In order to accurately predict growth and formulate adaptive management measures for natural Betula platyphylla forests in Daxing’an Mountains, Inner Mongolia, a mixed-effects individual-tree diameter (DBH) growth model of Betula platyphylla including climatic factors and tree size diversity factors was developed.
Method The data were derived from the eighth and ninth national forest inventory in Daxing’an Mountains, Inner Mongolia, which included a total of 97 fixed sample plots and 4 785 sample tree observations of Betula platyphylla. Based on the selected data, the traditional growth model of individual-tree diameter (DBH) was constructed by stepwise regression method. Then, sample plot effects were added to construct individual-tree mixed-effects model of Betula platyphylla. Finally, we validated the basic model and the mixed-effects model by the 10-fold cross-validation method.
Result The results of the regression analysis showed that the logarithm of the initial DBH (lnDBH), basal area of trees larger than the subject tree (BAL), the standard deviation of the DBHs (SDDBH), growth accumulation temperature (DD5) and mean annual precipitation (MAP) had significant effects on the individual-tree DBH growth of Betula platyphylla. Compared with the basic model, the adjusted R square ( R_\rmadj^2 ) of final mixed-effects model improved by 0.120 6, and the root mean square error (RMSE) decreased by 0.097 1 cm2, respectively, which improved the prediction accuracy of the model significantly. The results of the 10-fold cross-validation indicated that the mixed-effects model also showed a better fitting result.
Conclusion The individual-tree DBH growth mixed-effects model of Betula platyphylla including climatic factors and tree size diversity factors can accurately predict the DBH growth of individual trees, which can provide support for scientific management of natural Betula platyphylla forests in Daxing’an Mountains, Inner Mongolia.
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