Selective thinning and initial planting density management promote biomass and carbon storage in a chronosequence of evergreen conifer plantations in Southeast China

Abstract Climate change and human activities have continuously decreased productivity, carbon storage and soil fertility of global plantations under continuous planting. However, this situation can be largely reversed through appropriate planting density and thinning management. We evaluated the effects of initial planting density and selective thinning management on biomass accumulation and carbon stocks in different plantation compartments, on soil carbon stocks in different stand stages of a chronosequence of evergreen (Cunninghamia lanceolata) plantations in typical hilly and mountainous areas of Jiangxi Province, Southeast China. The result showed that biomass components and carbon storage of tree, understory and the whole ecosystem in C. lanceolata plantations were significantly higher with than without selective thinning treatment, in the low (1150 trees ha−1) than in the high (2460 trees ha−1) initial density in our study. Aboveground vegetation biomass and carbon storage in C. lanceolata plantations increased with stand stages. However, carbon storage of 0-10 cm and 20-40 cm soil depth decreased with stand stages, which indicated certain degraded characteristics of soil carbon in the C. lanceolata plantations. Interestingly, low initial density increased the biomass and carbon storage of trees, shrubs, herbs and 0-20 cm soil depth greater in the pre-mature and mature stands compared to high initial density. Furthermore, these positive effects of low density increased with selective thinning. According to regressions and Detrended Correspondence Analysis (DCA), increment in carbon of trees and 0-10 cm soil with the stand age were significantly higher in the low initial density and with selective thinning than in other three treatments. Therefore, selected thinning and relatively appropriate density might have a significantly positive role in carbon storage of the ecosystem in different stand ages, especially showing a increasing trend of soil carbon. Our results provide the important evidence for selective thinning management of C. lanceolata plantations with regeneration, which plays an important role in improving the carbon storage of degraded C. lanceolata plantations.