Construction of individual tree DBH growth models for natural Betula platyphylla forests in Daxing’an Mountains, Inner Mongolia of northern China

Objective In order to accurately predict growth and formulate adaptive management measures for natural Betula platyphylla forests in Daxing’an Mountains, Inner Mongolia of northern China, a mixed-effects individual-tree DBH growth model of Betula platyphylla, including climatic factors and tree size diversity factors, was developed.

Method The data were derived from the 8th and 9th national forest inventory in Daxing’an Mountains of Inner Mongolia, including 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 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 10-fold cross-validation method.

Result The logarithm of initial DBH, basal area of trees larger than the subject tree, standard deviation of DBHs, growth accumulation temperature and mean annual precipitation had significant effects on individual-tree DBH growth of Betula platyphylla. Compared with basic model, R_\rmadj^2 of final mixed-effects model increased by 0.120 6, and the root mean square error decreased by 0.097 1 cm², respectively. The prediction accuracy of the mixed-effects model improved significantly. The results of 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 of northern China.