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.

Mangrove forest in the Mekong Delta plays important roles in protecting coasts from soil erosion and strong waves, supplying seafood, and accumulating carbon. Despite these benefits, mangroves have been and continue to be severely damaged by the impacts of natural and socioeconomic activities. In recent years, large areas of mangrove forest have been restored through planting and other various management actions. In this study, we analyzed high-resolution WorldView-2 images to quantify changes in the mangrove forest in seven coastal provinces (Tien Giang, Ben Tre, Tra Vinh, Soc Trang, Bac Lieu, Ca Mau, and Kien Giang) of the Mekong Delta from 2015 to 2020. Our study is one of the first to analyze mangrove forest change at the commune scale, the smallest official administrative unit in Vietnam, to determine the area of restored mangroves. The potentials and challenges in future mangrove restoration were also assessed by analyzing satellite imagery and field survey data. In the study area, mangrove forest area increased by 11,184 ha (approximately 2,237 ha per year) from 79,593 ha in 2015 to 90,777 ha in 2020. A total area of 16,138 ha (approximately 20.3%) was lost due to mangrove conversion to other land uses, aquaculture activities and coastal erosion, etc., while 27,322 ha (approximately 34.1%) was restored or newly planted during state- and NGO-funded mangrove restoration projects and programs. These results confirmed that mangrove restoration projects and programs have played a significant role in maintaining and increasing mangrove forest cover in Mekong Delta. The results can also assist managers and decision makers in mangrove restoration evaluation, and suggest analyzing WorldView-2 images to monitor mangrove restoration over time in Vietnam.

Mangrove forest plays a very important role for both ecosystem services and biodiversity conservation. In Vietnam, mangrove is mainly distributed in the Mekong delta. Recently, mangrove areas in this region decreased rapidly in both quality and quantity. The forest became bare, divided and scattered into many small patches, which was a major driver of ecosystem degradation. Without a quantitative method for effectively assessing mangrove health in the regional scale, the sustainably conserving mangrove is the challenge for the local governments. Remote sensing data has been widely used for monitoring mangrove distributions, while the characterization of spatial metrics is important to understand the underlying processes of mangrove change. The objectives of this study were to develop an approach to monitor mangrove health in Mui Ca Mau, Ca Mau province of Vietnam by utilizing satellite image textures to assess the mangrove patterns. The research result showed that mangrove areas increased double by 2015, but the forest had become more fragmented. We can be seen those changes in land use mainly come from land conversion from forest to shrimp farms, settlements areas and public constructions. The conserving existing mangrove forest in Mui Ca Mau should consider the relations between mangrove health and influencing factors indicated in the manuscript.

Background and Objectives: In northern Vietnam, nearly 37,100 hectares of mangroves were lost from 1964–1997 due to unsustainable harvest and deforestation for the creation of shrimp aquaculture ponds. To offset these losses, efforts in the late 1990s have resulted in thousands of hectares of mangroves being restored, but few studies to date have examined how effective these efforts are at creating restored mangrove forests that function similarly to the intact mangroves they are intended to replace. Materials and Methods: We quantified and compared soil carbon (C) stocks among restored (mono and mixed species) and intact mangrove forests in the provinces of Quang Ninh, Thai Binh, Nam Dinh and Thanh Hoa in northern Vietnam. A total of 96 soil cores up to a depth of 200 cm were collected every 25 m (25, 50, 75, 100, 125, and 150 m) along 16 linear transects that were 150 m long and perpendicular to the mangrove upland interface (six cores along each transect) at Quang Ninh (four transects), Thai Binh (five), Nam Dinh (four) and Thanh Hoa (three). Five-cm-long soil samples were then collected from the 0–15 cm, 15–30 cm, 30–50 cm, 50–100 cm, and >100 cm depth intervals of each soil core. Results: The study confirmed that the soil C stock of 20–25-year-old restored mangrove forest (217.74 ± 16.82 Mg/ha) was not significantly different from that of intact mangrove forest (300.68 ± 51.61 Mg/ha) (p > 0.05). Soil C stocks of Quang Ninh (323.89 ± 28.43 Mg/ha) were not significantly different from Nam Dinh (249.81 ± 19.09 Mg/ha), but both of those were significantly larger than Thai Binh (201.42 ± 27.65 Mg/ha) and Thanh Hoa (178.98 ± 30.82 Mg/ha) (p < 0.05). Soil C stock differences among provinces could be due to their different geomorphological characteristics and mangrove age. Soil C stocks did not differ among mangroves that were restored with mixed mangrove species (289.75 ± 33.28 Mg/ha), Sonneratia caseolaris (L.) Engl. (255.67 ± 13.11 Mg/ha) or Aegiceras corniculatum (L.) Blanco (278.15 ± 43.86 Mg/ha), but soil C stocks of those mangroves were significantly greater than that of Kandelia obovata Sheue, Liu & Yong (174.04 ± 20.38 Mg/ha) (p < 0.05). Conclusion: There were significant differences in the soil C stocks of mangrove forests among species and provinces in northern Vietnam. The soil C stock of 20–25-year-old restored mangrove forest was not significantly different from that of intact mangrove forest.