Effects of Close-to-Nature Conversion on Pinus massoniana Plantations at Different Stand Developmental Stages

Close-to-nature (CTN) forestry integrates multiple forest functions and emphasizes forest ecosystem conservation. Within this framework, forests are typically maintained as uneven-aged mixed stands with multiple vertical layers and are managed following the defined stand developmental stages, that is, the various phases of forest succession. This study aimed to evaluate the long-term effects of CTN management on the stand structure and growth of Pinus massoniana using data from 28 plots managed with the CTN approach and 58 plots of traditional monocultures in southern China. A comparison was performed between three vertical layers across five developmental stages of the CTN stands and the monoculture stands. The results showed that the tree species diversity improved in the CTN stands, with a decrease in the importance value of P. massoniana. The conversion did not change the diameter growth averaged over all species, but it did promote the radial growth of P. massoniana in the canopy layer. The stand growth, in terms of the basal area and the volume of the canopy trees, declined in the CTN stands during the final two stages, as harvesting took place, and the volume growth of P. massoniana also decreased in the CTN stands. However, the conversion seemed to improve the stand productivity of the subcanopy and regeneration layers, where higher relative dominance values of all species were observed, especially during the later stages. Overall, the CTN conversion tended to benefit the stand structure and improve the single tree growth of P. massoniana rather than the total stand growth.