Objective Masson pine (Pinus massoniana Lamb.) is an important plantation species in China. It not only provides essential economic benefits but also plays a crucial role in ecological services such as carbon sequestration, and adaption to climate change. Thinning is a vital technique in the management of plantations. However, the current practice of thinning in Masson pine plantations suffers from a qualitative rather than quantitative issue, which restricts the plantation management. This study aims to establish a density management diagram for Masson pine plantations to guide the precise thinning process.

Method Based on the permanent plot of pure Masson pine plantations in Hunan Province, the basic density management diagram was constructed obeying to the Reineke rule. Subsequently, carbon storage contours was further imposed on the basic stand density management diagram to produce the carbon storage management diagram. Finally, using the management diagram, the stand density of Masson pine plantations in Cili County in Hunan Province was evaluated.

Result In Cili County, Hunan Province, most of the stand density of Masson pine plantations were larger than the reasonable density range. This resulted in intense competition among trees for limited resources such as light, temperature, and moisture, and, in some stands, even severe natural mortality occurred. Thinning is urgently required to reduce stand density. A small number of stands were within the reasonable density range. These stands fully utilized natural resources with trees mutually promoting one another. Some stands had densities below the lower limit of the optimal range, resulting in inefficient utilization of forest land space and resource wastage. Understory planting is urgently needed.

Conclusion The stand density management diagram for Masson pine trees developed in this study can accurately guide forest management practices. Furthermore, it can provide an assessment of the rationality of stand density for forest management enterprise.