Carbon storage in evergreen broad-leaf forests in mid-subtropical region of China at four succession stages

To better understand the effect of forest succession on carbon sequestration, we investigated carbon stock and allocation of evergreen broadleaf forest, a major zonal forest in subtropical China. We sought to quantify the carbon sequestration potential. We sampled four forest types, shrub (S _R), pine (Pinus massoniana) forest (P _F), pine and broadleaf mixed forest (M _F) and evergreen broadleaf forest (B _F). A regression equation was constructed using tree height and diameter at breast height (DBH) and elements of total tree biomass. The equation was subsequently utilized to estimate tree carbon storage. The carbon storage of understory, litter, and soil was also estimated. Carbon storage in biomass increased significantly from the early succession stage S _R (6.21 t·ha^?1) to the late stage B _F (134.87 t·ha^?1). The biomass carbon stock of forest layers generally increased with succession except for the understory. The soil organic carbon storage for the total profile increased with forest succession, from 51.16 to 90.49 t·ha^?1, but the contribution of SOC to the carbon stock of the forest ecosystem declined from 89.18% to 40.15%. The carbon stock at ecosystem scale increased significantly with succession from S _R (57.37 t·ha^?1), to P _F (154.20 t·ha^?1), to M _F (170.96 t·ha^?1) and to B _F (225.36 t·ha^?1), with carbon stock of B _F 3.93 times that of S _R. The forests in our study have great potential for increasing carbon sequestration, and large areas of secondary or degraded evergreen broadleaf forests in the subtropical zone of China could be a great carbon sink in future.