Climate-driven adaptive management improves productivity and carbon outcomes in larch plantations.

Planted forests play a critical role in timber production and climate change mitigation, yet their stand dynamics are increasingly influenced by changing climatic conditions. Conventional stand density management diagrams (SDMDs) are largely climate-insensitive, limiting their applicability under ongoing environmental change. To address this, we developed a climate-sensitive SDMD for larch (Larix spp.) plantations by incorporating the annual heat-moisture index (AHM) into the core size-density relationship using a power-law formulation. The results revealed a positive climatic sensitivity, with an estimated elasticity of 0.0906. Across the observed range of AHM (15-25), this corresponds to an increase of approximately 6% in quadratic mean diameter, highlighting a non-negligible climatic effect on stand development. Incorporating AHM altered the structure of SDMDs, leading to systematic shifts in diameter, volume, carbon stocks, and slenderness relationships along climatic gradients. Simulation results demonstrated that the intensity of first thinning decreased with increasing AHM (i.e., much warmer and drier conditions). Consequently, the climate-sensitive SDMD predicted differences of 34.5% in stand density, 26.7% in stand volume, and 24.3% in carbon stocks across the simulated AHM gradient, reflecting the indirect influence of climate on stand carbon through changes in tree size and stand density. This study provides a climate-sensitive decision framework for optimizing stand density management, linking climatic variability to forest productivity and carbon outcomes, and supporting adaptive management of larch plantations under changing environmental conditions.