Exploring the Effects of Thinning on Cunninghamia lanceolata Lamb. Carbon Allocation in Southwestern China Using a Process-Based Model

We investigated the effects of thinning intensity on the carbon allocation of Cunninghamia lanceolata Lamb. Hook by analyzing the stand growth and carbon content of a plantation under three thinning intensities (I: 70%; II: 50%; III: 30%) and with no thinning treatment. Using the carbon balance framework of the CROwn BASe (CROBAS) model and multi-source inventory data, we calibrated the parameters of the CROBAS-C. lanceolata (CROBAS-CL) model to simulate the carbon content in the plantation. We validated the CROBAS-CL model by comparing the predicted stand diameter at breast height (DBH) and stand height (H) with the measured values. Finally, the predicted stand carbon was compared with the soil carbon to assess the dynamics and allocation of ecosystem carbon content. Overall, our findings suggest that the predicted stand carbon of CROBAS-CL satisfies the statistical test requirements: the deviation of height and DBH predicted by the CROBAS-CL model from the measured height and DBH are less than 0.087 m and 0.165 cm, respectively. These results confirm that the model is useful for a dynamic prediction of stand carbon in C. lanceolata plantations. Based on the results of the proposed model, we determine that Thinning III (30% thinning intensity) is beneficial for the growth of C. lanceolata plantations and improving soil carbon sequestration. Additionally, the simulated carbon storage of an individual tree in the C. lanceolata plantation gradually increased with the tree age. Our study provides a strong reference for the efficient operation and management of C. lanceolata plantations in southwestern China.