Carbon sequestration potential of Sonneratia apetala plantation forests in the Chakaria Sundarbans: Effects of stand age and structure

Abstract

Coastal plantation ecosystems play a crucial role in combating global warming by serving as effective carbon sinks. Sonneratia apetala (Keora) is a fast-growing tree species that significantly influences local carbon sequestration rates, but still there is lack of knowledge about how this carbon sequestration rate changes with stand age and structure. So, we investigated how carbon stock changes across four different aged of S. apetala plantation forests (8, 16, 24, and 32 years) in the Chakaria Sundarbans. Twenty representative plots (20 m × 20 m) were selected from 4 different stand ages (8, 16, 24, and 32 years) using stratified random sampling design (SRSD) method. Soil organic carbon (SOC) content from 0 to 30 cm soil layers, aboveground biomass (AGB) and belowground biomass (BGB) were studied to calculate the total carbon stock (TCS). A positive correlation was observed between TCS and stand age. The TCS at the 8, 16, 24, and 32 years old plantation sites was 60.85, 109.73, 136.29, and 183.48 t ha⁻¹, respectively. The mean annual carbon accumulation rate (CAR) were 7.60, 6.86, 5.68, and 5.73 t ha⁻¹ year⁻¹ in these respective sites, indicated that the CAR significantly decreased with stand age. At the stand ages of 8, 16, and 24 years, soil organic carbon storage (SOCS) significantly outweighed total biomass carbon stock (TBCS), with percentages of 85.02 %, 60.68 %, and 55.65 % of TCS, respectively. However, at 32 years old stand, TBCS (54.77 %) exceeded SOCS (45.23 %). The TCS values were equivalent to 223.32, 402.71, 500.18, and 637.37 t ha⁻¹ CO₂ at 8, 16, 24, and 32 years old stands, respectively, revealed a significant potential for CO₂ sequestration. These findings can be used in the development of effective forest management strategies with restoring mangrove to maximize carbon storage potential in the southeastern coasts of Bangladesh, ultimately helping to reduce CO₂ gas emissions to combat adverse effect of climate change.