The carbon sequestration capacity of the forest ecosystem normally increases overage due to the carbon dynamic in below canopy and soil. The carbon dynamic is reflective of the forest characteristics and their interactions with climate, topographic, and soil conditions. In this study, we measured the carbon content and carbon density of canopy, shrub, understory vegetation, litter, and soil, and assessed carbon dynamics in three forest ecosystems (Cunninghamia lanceolate, Pinus massoniana, and Evergreen broad-leaved forests) with a combination of data from Fujian Provincial forest resource inventory. This study showed that the carbon content of the canopy layers increased over time, and the carbon content of the topsoil (0-30 cm) in the young forests was significantly higher than that in other age groups in Cunninghamia lanceolata forest and Pinus massoniana forest. Due to the carbon differences in the soil layer, the carbon stocks of the C. lanceolata forest and the P. massoniana forest declined from 1996 to 2007, but the carbon stocks of Evergreen broad-leaved forest increased. Besides, using the traditional carbon content coefficient (0.5) might underestimate the carbon sequestration potential of these forest ecosystems, especially for the mature forests. The coniferous forests displayed a short-term reduction in the carbon stocks of ecosystems between 10 and 20 years after afforestation, and the decline cannot be ignored in the carbon budget.
Keywords: Carbon content; Carbon sequestration; Forest ecosystem types; Subtropical forest.