关键词: 杉木人工林, 林地期望价值, 最优轮伐期, 碳库动态耦合, 养分反馈

Abstract:

Objective: Cunninghamia lanceolata (Chinese fir) plantations in Fenyi City, Jiangxi Province were targeted. A land expectation value (LEV) model integrating the dynamic coupling between biomass and dead organic matter carbon pools was constructed to clarify the regulatory effect of the carbon pool coupling mechanism on the optimal rotation period and land expectation value of Chinese fir plantations, as well as the effects of key parameters, so as to provide quantitative support for the synergistic management of timber production and carbon sequestration in Chinese fir plantations. Method: Based on 40-year continuous positioning observation data from Chinese fir plantations in Fenyi City, Jiangxi Province, the classic Faustmann model was used as the framework to incorporate the dynamic coupling process of biomass and dead organic matter carbon pools, and set three scenarios: baseline (no carbon sequestration revenue, no nutrient-driven positive feedback, with biomass and dead organic matter carbon pools independent of each other), static carbon sequestration (with carbon sequestration revenue but no nutrient-driven positive feedback), and dynamic coupling (with carbon sequestration revenue and nutrient-driven positive feedback, with two carbon pools dynamically coupled). The dynamic characteristics of carbon pools and LEV under different scenarios were simulated. Furthermore, sensitivity analysis was conducted on three core parameters, carbon price (P_c), nutrient feedback coefficient (λ), and dead organic matter decomposition rate (α), to quantify the influence of key parameters on the optimal rotation period and LEV. Result: 1) The optimal rotation period for all three scenarios was 21 years, but the LEV in the dynamic coupling scenario was the highest (62 555 yuan·hm^?2), which was 169 yuan·hm^?2 higher than that in the baseline scenario and 21 yuan·hm^?2 higher than that in the static carbon sequestration scenario. The revenue increment came from two aspects: firstly, the direct carbon sequestration revenue brought by the increase in total carbon pool storage; secondly, the timber revenue increment driven by nutrient-driven positive feedback that promoted biomass growth and increased the proportion of large-diameter timber. 2) In the dynamic coupling scenario, the nutrient-driven positive feedback loop between the two carbon pools significantly improved the carbon pool accumulation efficiency. At age 21, the biomass carbon pool, dead organic matter carbon pool, and total carbon pool of Chinese fir plantations increased by 8.3%, 7.8%, and 8.2%, respectively, compared with the static scenario. Carbon pool accumulation showed obvious stage characteristics: nutrient cycling and synergistic accumulation between carbon pools were weak during the young forest stage, the difference expanded rapidly in the fast-growing stage, and the carbon pool in the dynamic scenario maintained steady growth in the near-mature stage, with long-term carbon sequestration capacity significantly superior to that in the static scenario. 3) Sensitivity analysis showed that within the range of realistic parameters, key parameters had no impact on the determination of the optimal rotation period, but their effects on LEV were clear: LEV increased significantly with the rise of λ, while the positive impact of P_c on LEV and the negative impact of α on LEV were both very small, with the magnitude of the impact was within 0.05%. Conclusion: Under the current timber-dominated management mode, the dynamic coupling effect between biomass and dead organic matter carbon pools does not change the widely adopted 21-year optimal rotation period of Chinese fir plantations. The dynamic coupling of the two carbon pools offset the discount loss of carbon sequestration through nutrient-driven positive feedback, realizing the coordinated improvement of carbon sequestration and timber revenue. Optimizing understory management of Chinese fir plantations and providing reasonable carbon price subsidies are effective approaches to activate the carbon pool coupling effect and thereby improve plantation management efficiency. This model exhibits strong adaptability to the ecological gradient differences in southern Chinese fir production areas and can provide quantitative technical support for the synergistic management of timber production and carbon sequestration in Chinese fir plantations.

Key words: Cunninghamia lanceolata plantations, land expectation value, optimal rotation period, dynamic coupling of carbon pools, nutrient feedback