Relationship Between Wood Productivity and Tree-Layer Carbon Sequestration Rate and Their Drivers in Pinus massoniana Plantations Under Forest Management

The coordinated enhancement of wood production and carbon sequestration in plantations is increasingly important for sustainable forest management and climate-change mitigation. However, quantitative evidence on how forest management can jointly improve these two functions remains limited. Based on 847 Pinus massoniana plantation plots (yielding 1184 consecutive-period observations) from China’s 7th–9th National Forest Inventories (covering 2004–2018), we quantified the degree of coordination between wood productivity and tree-layer carbon sequestration rate. Linear mixed-effects models, the piecewise structural equation model, and XGBoost-SHAP analyses were subsequently applied to identify the major drivers and threshold ranges of key stand factors. The results showed that mean carbon sequestration rate and wood productivity were 1.16 Mg/ha/yr and 4.17 m3/ha/yr, respectively. Among the examined management categories, plots with standing-volume harvest intensity < 0.15 (i.e., removing less than 15% of stand volume) showed the highest tree-layer carbon sequestration rate and wood productivity. Overall, wood productivity and tree-layer carbon sequestration rate showed broadly consistent responses across the examined management conditions, suggesting a generally high degree of coordination between the two functions. Stand structural attributes were the primary determinants of the degree of coordination, whereas management factors tended to strengthen this coordination both directly and indirectly through modifications of stand structure. Within the sampled range, a higher degree of coordination was associated with stand DBH values of 7.5–10.6 cm, stand density below 1071 trees/ha, stand age exceeding 29 years, and standing-volume harvest intensity approaching 0.12. These findings provide a quantitative basis for balancing timber production and tree-layer carbon sequestration, and offer practical implications for adaptive management of subtropical plantations under climate-mitigation and timber-supply objectives.