Carbon storage dynamics of subtropical forests estimated with multi-period forest inventories at a regional scale: the case of Jiangxi forests

Temperate and high-latitude forests are carbon sinks and play pivotal roles in offsetting greenhouse gas emissions of CO2. However, uncertainty still exists for subtropical forests, especially in monsoon-prevalent eastern Asia. Earlier studies have depended on remote sensing, ecosystem modeling, carbon fluxes, or single period forest surveys to estimate carbon sequestration capacities, and the results vary significantly. This study was designed to utilize multi-period forest survey data to explore spatial-dynamics of biomass storage in subtropical forests of China. Jiangxi province, a region with over 60% subtropical forest cover, was selected as the case study site and is located in central east China. Based on forest inventory data 1984-2013, and the stock-difference and biomass expansion factor methods, the carbon storage and density, of arboreal forests, economic forests, bamboo forests, woodlands and shrubberies were estimated. The results show that carbon storage increased from 159.1 Tg C in 1988 to 276.1 TgC in 2013, making up 3.1-3.8% of carbon stored throughout China. Among the four types of forests, the amount of carbon stored was as follows: arboreal forest > economic forest > bamboo forest > woodland and shrubbery. Arboreal forests accounted for 64.0-79.4% of the total. Forest carbon density increased from 21.2 Mg C ha(-1)in 1984 to 26.2 Mg C ha(-1)in 2013, equal to 61.2-70.2% of the average carbon density of China's forests in the same period. Forest carbon storage in Jiangxi will reach 355.5 Tg C and 535.8 Tg C in 2020 and 2030, respectively, and forest carbon density is predicted to be 31.9 Mg C ha(-1)and 46.4 Mg C ha(-1), respectively. As one of the few studies using multi-period data tracking biomass dynamics in Jiangxi province, the findings of this study may be used as a reference for other research. Using Jiangxi as a case study underlies the fact that subtropical forests in China have great carbon sequestration potential and have fundamental significance to offset global environmental change effects.