![]() Therefore, we hypothesize that trajectories of carbon accumulation in mangroves may be significantly different between reforestation and afforestation actions, given the differences in the suitability of preexisting versus novel settings for mangrove biomass development. When restored in aquacultural ponds with high antecedent productivity, mangroves exhibited higher biomass carbon sequestration rates compared with those on less productive sites even though aquaculture previously dominated 6. In addition, varying hydrogeomorphic settings and nutrient availabilities might also influence the carbon stocks of mangrove forests through growth adjustments 20, 21. For instance, in regions that suffered historical hypersalination-driven death after road levee construction, restored mangroves could store greater amounts of organic matter and nutrients in sediments than currently conserved mangrove area 19. Whether mangroves previously grew on a site might also reflect the local geomorphic and biophysical property constraints, which would further influence mangrove succession and carbon flux dynamics. Prior land use certainly influences restoration trajectories in terrestrial forests 17, 18. While climate factors were found to influence mangrove growth on the continental scale, regional and local factors such as ecogeomorphic settings and environmental conditions are also important 16. mixed-species stocking planting density related to carbon and sedimentation) 12, 13, 14, 15, with few assessments focusing on the role that establishment location, past land tenure, or silvicultural action may have. Mangrove restoration pathways that maximize carbon sequestration potential have been explored, but these have mostly postulated questions related to tree species selection 11, 12, or how attaining restoration might occur most efficiently (e.g., natural process vs. Quantification of possible differences in ecosystem benefits such as carbon sequestration between mangrove reforestation and afforestation is thus crucial for formulating policies and plans that specify mangrove restoration protocols to enhance blue carbon potential and help with mitigating global climate change. Afforestation sites (e.g., mudflats) may have lower land costs, but the survival rate of seedlings is often low because of inappropriate hydrodynamic conditions. Reforestation may avoid conflicts of converting other vulnerable ecosystems to mangroves but still face tenurial problems, especially for the abandoned maricultural ponds. Generally, the trade-offs in choosing between reforestation and afforestation relate to the recovery efficiency and the sociopolitical complexities of land tenure 9, 10. Reforestation refers to expediently restoring mangroves in areas that suffered from fairly recent degradation or deforestation by anthropogenic and natural factors 5, 6, while afforestation refers to establishing mangroves in areas where mangroves did not previously exist 7, 8. ![]() These restoration projects were carried out according to local policy and environmental settings 3, whilst they could be generally classified into two categories by silvicultural design: reforestation or afforestation 4. ![]() Since the 1970s, mangrove restoration projects have been initiated in regions such as Southeast Asia, East Asia, and South America 2, 3. Along with avoiding conflicts of habitat conversion, mangrove reforestation should be given priority when designing nature-based solutions for mitigating global climate change.Ĭonsidering the significant potential for carbon sequestration and greenhouse gas offsets, blue carbon ecosystems, such as mangrove forests, saltmarshes, seagrass beds, and upper estuarine tidal wetlands, have gained global prominence for climate mitigation as a nature-based solution 1. Reforestation of all physically feasible areas in the deforested mangrove regions of the world could promote the uptake of 671.5–688.8 Tg CO 2-eq globally over a 40-year period, 60% more than afforesting the same global area on tidal flats (more marginal sites). Greater carbon accumulation was mainly attributed to favorable intertidal positioning, higher nitrogen availability, and lower salinity at most reforestation sites. Here, we integrated results from direct field measurements of over 370 restoration sites around the world to show that mangrove reforestation (reestablishing mangroves where they previously colonized) had a greater carbon storage potential per hectare than afforestation (establishing mangroves where not previously mangrove). However, blue carbon benefit has not been compared between these two silvicultural pathways at the global scale. Significant efforts have been invested to restore mangrove forests worldwide through reforestation and afforestation. ![]()
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