Individual-tree diameter growth model for Korean pine plantations based on optimized interpolation of meteorological variables

Abstract

To explore the influence of meteorological variables on the growth of Korean pine (Pinus koraiensis Sieb. et Zucc.) plantations and provide a scientific reference for the production and management of Korean pine, three approaches to interpolate meteorological variables during the growing season (i.e., May–September) were compared in Heilongjiang Province, China. Optimized meteorological variable interpolation results were then combined with stand and individual tree variables, based on data from 56 sample plots and 2886 sample trees from Korean pine plantations in two regions of the province to develop an individual-tree diameter growth model (Model I) and an individual-tree diameter growth model with meteorological variables (Model II) using a stepwise regression method. Moreover, an individual-tree diameter growth model with regional effects (Model III) was developed using dummy variables in the regression, and the significance of introducing these dummy variables was verified with an F-test statistical analysis. The models were validated using an independent data set, and the predictive performance of the three models was assessed via the adjusted coefficient of determination ( $${R}_{a}^{2}$$ ) and root mean square error (RMSE). The results suggest that the growth increment in tree diameter of Korean pine plantations was significantly correlated with the natural logarithm of initial diameter (ln D), stand basal area (BAS), logarithmic deformation of the stand density index (ln SDI), ratio of basal area of trees larger than the subject tree to their initial diameter at breast height (DBH) (BAL/D), and the maximum growing-season precipitation (Pgmax). The individual-tree diameter growth models of Korean pine plantations developed in this study will provide a good basis for estimating and predicting growth increments of Korean pine forests over larger areas.