Mangrove forest in Lubuk Kertang Village, West Brandan sub-district has been converted around 20 ha annually (1996–2016) into various non-forest land use. Rehabilitation can be a solution to restore the condition of the ecosystem so that it can resume its ecological and economic functions. This paper discusses the evaluation of mangrove rehabilitation carried out by planting 6000 propagules in December 2015 and 5000 seedlings in May 2016 with Rhizophora apiculata species in abandoned ponds. Monitoring was carried out every 6 months from 2016 to 2022. In the restored area, 11 true mangrove species and 3 associated mangrove species were found. The percentage of plants that survived after seven years was 69.42% for planting using propagules and 86.38% for planting with seedlings. The total biomass carbon stocks stored by 7-year-old plants using propagules was 51.18 Mg ha⁻¹, while the carbon stored by planting using seedlings was 56.79 Mg ha⁻¹. Soil carbon stocks at the planted site with propagules were 506.89 ± 250.74 MgC ha⁻¹, and at the planted site with seedlings were 461.85 ± 102.23 MgC ha⁻¹. The total ecosystem carbon stocks (including aboveground carbon) in the planted site using propagules were 558.07 MgC ha⁻¹, while planting using seedlings were 518.64 MgC ha⁻¹. The dataset and findings on the carbon storage evaluation of mangrove rehabilitation will be useful for blue carbon research community and policymakers in the context of the climate change mitigation strategy for Indonesia.

Mangrove forests play an important role in coastal areas from an ecological perspective, being able to store large amounts of carbon through sequestration and inhibiting climate change processes by absorbing CO₂ in the atmosphere. In recent years, there have been changes in the land cover of converted and degraded mangrove forests which have resulted in the release of carbon and an imbalance in soil structure, which in turn cause a flux of CO₂ into the atmosphere. This research was conducted at the Karang Gading and Langkat Timur Laut Wildlife Reserve (KGLTLWR) in North Sumatra, Indonesia. The study focused on six different land covers, namely natural forests, restoration, mixed agriculture, paddy fields, oil palm plantation, and ponds. This study aimed to measure the total carbon stock of mangrove forests that have been converted to other land covers and estimate the level of CO₂ flux in the area. A total of three transects and six plots for each land cover were used in this study; for tree biomass, a non-destructive method was used by recording every DBH > 5 cm, and for soil carbon, drilling was carried out, which was divided into five depths in each plot. CO₂ flux was measured using an Eosense Eosgp CO₂ sensor with the static closed chamber method. The highest carbon stock was found at 308.09 Mg ha⁻¹ in natural forest, while the lowest 3.22 Mg ha⁻¹ was found in mixed agriculture. The highest soil carbon was found at 423.59 MgC ha⁻¹ in natural forest, while the lowest 50.44 MgC ha⁻¹ was found in mixed agriculture dry land. The highest average CO₂ flux value of 1362.24 mgCO₂ m² h⁻¹ was found in mangrove restoration and the lowest in ponds was 123.03 mgCO₂ m² h⁻¹. Overall, the research results inform how much carbon stock is lost when converted to other land covers so that it can be used as a reference for policy makers to provide future management of mangrove forests and develop mitigation measurements to reduce carbon emissions.