Soil and Aboveground Carbon Stocks in a Planted Tropical Mangrove Forest (Can Gio, Vietnam)
Résumé
Can Gio mangrove is the largest mangrove forest in Vietnam, covering approximately 35,000 hectares. This forest was partially destroyed during the war, and restored between the late 1970s and the early 1990s. Currently, the Can Gio mangrove forest regenerates naturally, and presents a specific species zonation along the intertidal elevation gradient with Rhizophora apiculata trees dominating the inner forest, and Avicennia alba trees colonizing riverbanks at lower elevation. Mangroves are considered as having a key role in climate change mitigation, because of their capacity to store large quantities of carbon. Along with climate and tree species, the position in the intertidal zone affects mangrove carbon storage capacity. The objectives of this study were to determine the aboveground biomass, the quality and the quantity of the organic matter (OM) stored beneath each mangrove zone, as well as the soil physicochemical characteristics, that may influence soil OM. C stocks in the aboveground biomass increased landward, from 24.3 ± 5.1 Mg C/ha in the fringe A. alba zone to 118.8 ± 9.5 Mg C/ha in the R. apiculata zone. The specific zonation resulted in soil physicochemical gradients, with higher carbon content, lower pH, and lower redox values, from the mudflat to the inner forest. In addition, δ 13 C values and C/N ratio suggested a higher contribution of mangrove-derived OM in the inner forest compared to the fringe forest. Soil carbon stocks in the R. apiculata forest, down to one meter, represented almost three times the stock in the aboveground biomass. However, when considering only the upper soil, down to 40 cm depth, which was related to forest plantation as evidenced by δ 13 C values and C/N ratios, stocks in the soil and in the aboveground biomass were similar, and the carbon burial rate was lower than 1 Mg C/ha/yr.
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