Dynamic growth models and estimation distinction of carbon stock for coniferous trees under different afforestation modes

Abstract

Many qualitative studies have found that mixed conifer–broadleaf forests provide higher ecological benefits than monoculture forests, and the demand for mixed forests is increasing. However, the carbon sequestration benefits of artificial mixed forests remain unclear. In particular, considering specific growth characteristics of plantation trees and capturing the dynamic changes in carbon sequestration over time are necessary. Using 456 tree disks for dendrochronological analyses, we established a dynamic growth model for the carbon stock of Pinus tabuliformis under three afforestation modes in the eastern Tibetan Plateau. Based on the fundamental growth model, nonlinear fixed-effect (NLFE) models with specific parameter combination constraints were established to improve model stability. Compared with other models, the NLFE model based on the Weibull equation, which uses the model parameters n and z as classification parameters, was the optimal model. This model was used to evaluate the potential contribution of afforestation modes to the growth of carbon stock in individual P. tabuliformis trees over 100 years and to predict the carbon sequestration benefits of mixed and pure forests. Conifer–broadleaf forests can bring lower initial returns but higher long-term returns than the other two afforestation modes, and such forests can store more carbon. In addition, this study provides a feasible method for establishing a carbon stock growth model with minimal sample damage as well as evaluation methods and basis for large-scale pure forest transformation and management strategies.