Mangroves’ ability to store carbon (C) has long been recognized, but little is known about whether planted mangroves can store C as efficiently as naturally established (i.e., intact) stands and in which time frame. Through Bayesian logistic models compiled from 40 years of data and built from 684 planted mangrove stands worldwide, we found that biomass C stock culminated at 71 to 73% to that of intact stands ~20 years after planting. Furthermore, prioritizing mixed-species planting including Rhizophora spp. would maximize C accumulation within the biomass compared to monospecific planting. Despite a 25% increase in the first 5 years following planting, no notable change was observed in the soil C stocks thereafter, which remains at a constant value of 75% to that of intact soil C stock, suggesting that planting effectively prevents further C losses due to land use change. These results have strong implications for mangrove restoration planning and serve as a baseline for future C buildup assessments.

Local communities play a key role in ecosystem restoration due to their invaluable traditional ecological knowledge. While community-led mangrove restoration has been practiced in Madagascar for decades, the factors influencing the success of the restoration remains understudied. Despite the extensive local knowledge, the complexity of factors influencing restoration success requires outside technical expertise. This study aimed to investigate the drivers of mangrove restoration success in southwest Madagascar. The survival rate of mangroves planted from 2015 to 2022, including Rhizophora mucronata, Bruguiera gymnorrhiza, and Ceriops tagal was assessed using the sampling methods for tree planting inventory with circular plots. R version 4.2.2 was used for descriptive statistics analysis. The correlation between the survival rate and plantation density, species composition, and number of participants was assessed using a Principal Component Analysis. As a result, the mean survival rate of the 440,990 planted mangroves, with a density of 4628 ± 317 trees/ha⁻¹ was 82.5 ± 1.8%. Our study showed that plantation density and species composition are not correlated with survival rate. However, the survival rate is inversely correlated with the number of participants. The findings of this paper showed that both traditional ecological knowledge and scientific observations are vital to informing mangrove reforestation.

The database compiles data (in Arias-Ortiz et al., under review in Ecosystems) on biogeochemical characteristics (density, organic carbon and total nitrogen, stable carbon and nitrogen isotopes and sediment grain size) of mangrove forest soils in Tsimipaika Bay, Madagascar. Pb-210 concentrations of the first 40 cm are included. The dataset compiles data for a total of 10 cores (5 cores from an intact forest and 5 from a deforested area) along with surface water dissolved organic carbon (DOC) concentrations measured at 8 stations. Enquiries about the dataset may be sent to Ariane Arias-Ortiz: aariasortiz@berkeley.edu

Mangrove, recognised as an important blue carbon sink, play a key role in climate change mitigation. Although the amount of blue carbon stored in mangroves has been well-documented yet the layout and size of sampling plots for blue carbon stock assessment vary considerably among studies across at local, regional and global scales. Therefore, in this study, we assessed the vegetation carbon stock using circular and square plot layouts having different size. A total of nine plots, each with 45 nested subplots per plot design were established across three classes of mangrove forests: closed canopy, open canopy and degraded. The diameter at breast height of trees within the plots was measured. The vegetation biomass was estimated using allometric equations. The mass of carbon was calculated by converting biomass to carbon using the conversion factors. Our results showed no significant difference in overall vegetation carbon stock between circular (67.96 ± 10.62 Mg C ha-1) and square plots (51.88 ± 8.27 Mg C ha-1). Similarly, vegetation carbon stock from open canopy and degraded mangroves did not differ significantly between circular and square plots. However, vegetation carbon stock in circular plots (159.81 ± 9.54 Mg C ha-1) versus square plots (119.96 ± 10.89 Mg C ha-1) were significantly different within closed canopy mangrove forests. Overall, vegetation carbon stocks did not differ significantly between plot layouts when all forest classes were combined. These results indicate that plot shape has limited overall influence on vegetation carbon stock estimates except in closed canopy mangroves, where circular plots yielded approximately 33% higher carbon stocks than square plots due to larger area. This supports the case for harmonising plot design when pooling or comparing data across mangrove national forest inventories, REDD+ projects and other monitoring, reporting and verification systems, both in Madagascar and elsewhere.

Mangroves canopy structure, shaped by natural disturbances and human activities such as wood extraction and charcoal production, together with environmental drivers, strongly influences carbon (C) storage patterns. Although they are key blue carbon ecosystems (BCE), yet site-level data on total ecosystem carbon stocks (TECS) and influence of drivers remain limited in Madagascar. Thus, this study quantified aboveground carbon (AGC), belowground carbon (BGC), and soil organic carbon (SOC) across 66 plots in the southern Morondava mangroves along a canopy-cover (CC) gradient ranging from dense to open canopy stands. We applied Random Forest (RF), Generalized Additive Models, and Linear Mixed-effects Models to identify key drivers and predict spatial patterns of C stocks. Average AGC ( 1SE) declined strongly with canopy degradation, ranging from 42.6 ± 19.2 Mg C ha⁻¹ in dense canopy stands to 11.9 ± 18.9 Mg C ha⁻¹ in open canopy stands, while BGC varied less across classes. The SOC dominated TECS (84.7%; 283.48 Mg C ha⁻¹ ± 128.2 Mg C ha⁻¹) across all the canopy cover classes, highlighting the dominant role of soil in BCE storage. Some degraded stands showed relatively high SOC, suggesting legacy C accumulation and sediment-driven stabilization processes. Spatial predictions fitted by the most performed model (RF) revealed highest C stocks in dense mangrove stands and lowest in degraded areas. Vegetation structure, hydrology, topography, and site-specific conditions were the main determinants of C distribution. These results highlight the decoupling between biomass and soil C responses to degradation. The study provides actionable insights for BCE management in Madagascar, emphasizing the conservation of intact mangrove stands while recognizing the persistence of substantial SOC stocks in degraded ecosystems as well enhance carbon sequestration via restoration activities.