Mangrove restoration elevates local carbon storage but changes centennial-scale carbon burial dynamics

Mangrove forests are some of the most effective carbon sinks on Earth, but they are globally threatened. Understanding the effects of active restoration efforts on mangrove blue carbon dynamics has therefore become a conservation priority. Here, we reconstructed mangrove carbon storage over the past 200 years in northern Vietnam, comparing old-growth forest, areas of artificial restoration and areas of natural spontaneous regeneration. The amount of carbon in the old-growth forest sediments has been higher than the restored or regenerated areas since the 1960s, highlighting the blue carbon benefit of established habitat. Stable isotope signatures indicate this stored carbon has been consistently dominated by marine plants and algae for at least the past 120 years. However, since the 1960s in the restored mangrove area, there has been a shift in the carbon source towards a dominance of mangrove-derived organic matter. This suggests that restoration activities may change the carbon cycling of mangrove forests, creating a ‘closed’ system of autochthonous carbon fixation and storage, and reduced interaction with marine-derived carbon. Mangrove restoration therefore holds potential for promoting blue carbon storage, but this may coincide with a loss in external linkages – which may have cascading impacts on wider ecosystem functioning. Careful consideration of blue carbon actions must therefore be taken to yield optimal conservation benefit.