Thinning improves timber yield and structure in Pinus Massoniana plantations: a 35-year experiment

• A 35-year study provides insights into seven thinning regimes’ long-term effects on plantations. • Optimal thinning treatments significantly enhance stand structure and economic returns. • Offers empirical guidance for tailored thinning intensity and timing for plantation. Thinning is a widely applied silvicultural practice in plantation forests, but its long-term effects on timber yield, quality, and stand development remain poorly documented, especially in subtropical conifer systems. A 35-year field experiment was conducted in Pinus massoniana plantations in southern China to evaluate how thinning regimes influence tree growth and timber structure over time. Seven treatments were applied, including early and delayed thinning at varying intensities, alongside an unthinned control. Growth and yield were assessed through repeated measurements of individual tree size, stand density, and timber volume across size classes. Results showed that thinning significantly improved individual tree diameter and volume compared to controls. Early-Intensive (i.e., early intensive thinning) and Early-Moderate & Late-Light (i.e., early moderate thinning followed by late light thinning) treatments consistently outperformed others, especially in promoting large-diameter timber, a high-value category in regional markets. A composite index integrating total stand volume, merchantable timber output, and large-diameter recovery confirmed these treatments as optimal. These findings provide long-term empirical evidence that appropriate thinning strategies can enhance both timber yield and quality in P. massoniana plantations. The results serve as a practical reference for forest managers seeking to improve stand structure and economic return, and underscore the importance of tailoring thinning intensity and timing to long-term silvicultural objectives.