Ecosystem carbon accumulation of Sonneratia apetala mangroves along an afforestation chronology in Bangladesh

Coastal plantation ecosystems play a vital role in the protection of coastal regions, biodiversity conservation, and the provision of valuable ecosystem services. These ecosystems have been recognized for their capacity to sequester carbon, making them instrumental in mitigating global warming. In this study, we assessed ecosystem carbon (EC) density levels in Sonneratia apetala planted coastal ecosystems in the Char Kukri-Mukri and Montaz mangrove reserves in the south-central Bangladesh. Using 48 representative plots from four stand ages (8–32 years), carbon density changes in trees and soil (0–15 and 15–30 cm) were evaluated. Results showed significant differences in vegetation carbon (VC) density, soil organic carbon (SOC) concentration, SOC density, and EC density among different stand ages, soil depths and mangroves. The increased EC density in Char Kukri Mukri (12.21 t ha⁻¹ yr⁻¹) and in Char Montaj (12.62 t ha⁻¹ yr⁻¹) with advancing stand ages (year-8 to year-32) provides empirical evidence of the effectiveness of afforestation in enhancing EC density in S. apetala planted mangroves. Regardless of stand age, the higher SOC density found in the upper soil layer (51 t ha⁻¹ in year-32 stand) compared to the lower layer (38 t ha⁻¹ in year-32 stand) in both mangroves highlights that the majority of soil carbon is concentrated in the top 15 cm of the forest floor. Within the 0–30 cm soil layer, SOC density demonstrated an increasing trend, with rates of 1.30 t ha⁻¹ yr⁻¹ in Char Montaj, and 1.33 t ha⁻¹ yr⁻¹ in Char Kukri Mukri mangroves between year-8 and year-32 stands. This study provides valuable insights for policymakers, land managers, and conservation practitioners, emphasizing the significance of coastal plantation ecosystems in carbon sequestration and the need for informed management strategies to optimize their climate mitigation potential.