Changes of ecosystem carbon stock following the plantation of exotic mangrove Sonneratia apetala in Qi'ao Island, China.

Carbon storage is one of the main objectives for mangrove afforestation. Planting of the exotic species Sonneratia apetala can rapidly increase the mangrove area and biomass. Here, we studied the change in vegetation and the soil carbon stocks along the chronosequence of S. apetala plantations in Qi'ao Island, China. Five sites, including rehabilitated S. apetala of different ages (1, 4, 9, and 15 years) and 40-year-old mature native Kandelia obovata forests were investigated. Vegetation biomass and the soil carbon content from 0 to 100 cm were analyzed. The ecosystem carbon density (vegetation and soil) was then calculated. A positive and linear relationship was observed between the vegetation carbon stocks and age of S. apetala. The 15-year-old S. apetala already had a similar biomass to 40-year-old K. obovata. However, its soil and ecosystem carbon densities remained lower than those of K. obovata. Different from K. obovata, the majority of the biomass of S. apetala was reserved within the stem. Mature K. obovata had a larger proportion of soil carbon stock to ecosystem carbon stock. S. apetala can accumulate biomass rapidly, but it had a lower ecosystem carbon stock than the native mature K. obovata.