关键词: 天然林, 转移矩阵生长模型, 均衡曲线, 碳储量

Abstract:

Objective: This study aims to develop a carbon-sink-oriented management system that is adapted to the ecological characteristics of natural forests in Zhejiang Province, and accurately quantify the key parameters and operational measures required to maximize carbon sequestration. The system is designed to provide a scientific basis for the management of natural forests and the improvement of carbon sink capacity in Zhejiang Province. Method: The entire natural forests across Zhejiang Province were used as the research object. Based on the data from the 9th (2019) National Forest Resource Inventory in Zhejiang Province and permanent-plot remeasurements conducted in 2023, a total of 1 307 permanent natural-forest plots unaffected by harvesting, fire, pests, or disease were selected to establish tree growth, mortality, and ingrowth models. Multidimensional covariates such as diameter at breast height (DBH), tree-species diversity, diameter-class diversity, and stand basal areacross-sectional area at breast height were incorporated to construct a transfer matrix growth model for natural forests in Zhejiang Province, achieving accurate simulation of stand dynamics. Based on the equilibrium theory for stand diameter distributions, 27 candidate equilibrium curves were generated as management targets by coupling three key parameters. Each curve represented a combination of post-harvest stand cross-sectional area at breast height (B), maximum retained-tree DBH (D), and adjacent diameter ratio (q). The tested values were 30, 35, and 40 m²·hm^–2 for B; 35, 40, and 45 cm for D; and 1.3, 1.5, and 1.7 for q. The transition matrix growth model was used to conduct dynamic simulation of 50-year growth and management with 10-year cutting cycles, and surplus trees removed during each intervention. The optimal carbon-sequestration scenario was selected using the equilibrium index (var), carbon stock (C), and annual carbon-stock increment (ic). Result: 1) The transition matrix growth model based on the 30% independent test setperformed well (RMSE=0.64 m²·hm^?2; MAE=0.62 m²·hm^?2). DBH, tree-species diversity, and other covariates significantly affected tree growth, mortality, and ingrowth. 2) Twenty out of the 27 candidate equilibrium curves attained equilibrium. The optimal curve was defined by B=40 m²·m^?2, D=45 cm, and q=1.3. 3) Under the guidance of the optimal curve, in simulating the growth of forest stands, a stable diameter-class structure dominated by oak species would be formed after 50 years, with carbon stock reaching 237.85 t·hm^?2, and significantly enhancing carbon-sequestration performance. Conclusion: This study develops a natural-forest carbon management framework integrating a transition matrix growth model with equilibrium curves. The optimal parameter combination is determined, which can jointly promote stand structural stability and carbon sequestration. This framework provides technical support for shifting natural-forest management in Zhejiang from passive protection to proactive carbon-sink enhancement.

Key words: natural forest, transition matrix growth model, equilibrium curve, carbon storage