Mangrove reforestation and afforestation programs have been initiated in many countries recently tocompensate for historical losses. At the same time, awareness of the high carbon (C) sink potential ofmangrove forests is growing, and C sequestration is beginning to be considered among forestation goals.To assess whether and at what rate C accumulates in the soil of young mangrove forests followingafforestation, we conducted a field study at an afforestation project in southeast China, includingrepeated measures taken over six years at two young forests (consisting of Kandelia obovata and Sonneratiaapetala, aged 0e6 years old), and also a chronosequence of forests aged 0 (mudflat), 6 (bothspecies), 20 (S. apetala), and 70 (K. obovata) years old. In the repeated measures, surface (0e10 cm) soil Cconcentration (%C of dry soil mass) increased significantly over six years, from 1.14% to 1.52% (K. obovata)and 1.23% to 1.68% (S. apetala). The rates of increase did not differ significantly between the two species,despite much greater biomass of S. apetala. In the chronosequence, soil C also increased with age acrosssites, but only the 70-year-old forest was statistically different, suggesting that localized environmentaldifferences may obscure age-related patterns in soil C. At all sites, soil C concentration for 1-m soil depth(0.62%e2.43%) was low compared to published global averages, yet the estimated soil C accumulationrate (155 g C m2 y1) was comparable to published averages for mature forests. We supported this fieldstudy with a literature review of similar studies containing soil C concentration data from youngmangrove forests: data compiled from 15 studies, comprising 31 sites, showed consistent, positivechanges in soil C concentration with forest age, even in the youngest (<5 years old) forests, supportingour field observation that soil C increases over time following mangrove afforestation.
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