Mangrove restoration built soil organic carbon stocks over six decades: a chronosequence study

Purpose: Mangrove restoration has been suggested to have a great potential for global change mitigation due to the large carbon sequestration capacity of mangroves. However, the temporal and spatial dynamics of soil organic carbon (SOC) storage following mangrove restoration remains less examined and reported. To fill the knowledge gap, this study examined the SOC stocks and soil physicochemical properties among bare mudflats and adjacent mangroves at different stand ages. Methods: We collected soil cores from bare mudflats and adjacent 7-, 10-, 15-, and 60-year-old mangroves on Ximen Island, Zhejiang Province, China. SOC, pH, salinity, particle size, and dry bulk density were determined. The analysis of variance was used to test for significant differences in above parameters among mangroves with different ages and mudflats. Pearson’s correlation was conducted to assess the relationship of SOC contents and other soil physicochemical properties. Results: Our results showed that SOC stock increased exponentially following restoration, reaching an asymptotic trend after 15-year mangrove restoration. The 60-year-old mangrove forests had significantly higher SOC stocks (94.31 ± 4.99 Mg OC ha⁻¹) compared to the unvegetated mudflat (76.25 ± 1.65 Mg SOC ha⁻¹) and the 7-year-old transplanted sites (79.04 ± 5.30 Mg OC ha⁻¹). Soil salinity, pH, and bulk density increased significantly within the whole depth, except decreasing trend of salinity in lower depth (> 25 cm). Soil texture was finer in mudflats and early stages of mangrove plantations than that in other sites. Conclusion: This study indicated that mangrove transplantation can substantially enhance SOC stocks within 15 years after afforestation. These results provide key data on the effectiveness of mangrove afforestation on carbon sequestration to inform blue carbon policies.