Optimizing thinning regimes for Larix olgensis plantations: A dual-objective approach for carbon balance and wood production

Planted forests have emerged as crucial components in climate change mitigation, creating an urgent need for management regimes that optimize both timber economic returns and carbon sequestration potential. This study addresses a critical research gap by systematically evaluating how thinning regimes (frequency, intensity, timing and methods) jointly affect these dual objectives in Larix olgensis plantations. We developed an integrated stand-level management model incorporating carbon balance and timber production, optimized through a simulated annealing genetic algorithm (GASA). The Bayesian optimization method indicated the optimal parameter combinations of GASA were population size = 22, initial temperature = 10, cooling coefficient = 0.79, maximum iterations for external loop = 16, maximum iterations for internal loop = 45, and internal iteration count = 200, runtime = 55.64 ± 6.40 min. For stands with 3333 tree∙ha^-1 initial density and 16 m site index, the optimal composite management plan featured a 52-year rotation with five upper-layer thinning events, implemented at years 13, 18, 26, 32, and 39, with basal area-based thinning intensities of 12 %, 22 %, 25 %, 36 %, and 50 %, respectively. The net present value (NPV) of composite management is 302.09 thousand CNY∙ha^-1, which is more 77.08 thousand CNY∙ha^-1 than that of conventional management. While composite management reduced timber NPV by 2.52 % relative to conventional management, the benefits of carbon balance fully compensated for the NPV reduction in timber production, and the substitution effects under composite management completely compensated for the NPV losses caused by carbon emission penalties from wood products. The discount rate had the greatest effect on NPV; when the rate reached extreme values, the NPV difference between the two management strategies narrowed, and the likelihood of adopting composite management decreased. Composite management increased the carbon balance by 25.83 %, exceeding the 18.47 % increase in timber production compared with conventional management. Overall, carbon balance production plays a more important role in the composite management strategy, indicating that carbon sequestration serves as the dominant driver of this management system.