Abstract
AbstractThe tropical mangrove ecosystem harbors great potential for carbon offsetting schemes because of their exceptionally high carbon sequestration potential. These cannot only generate an income for local communities by financially compensating for the non‐exploitation of protected or replanted stands, but also simultaneously reduce emissions due to forest degradation and deforestation, thereby helping to counteract the global threat on these forests. As carbon is directly monetized through offsetting carbon emissions, accurate species‐specific estimation of carbon content in trees is essential and reduces the propagation of errors generated by accounting uncertainties. Accordingly, this study assessed variation in both carbon fraction and wood specific gravity among and within the 10 mangrove species occurring in Gazi Bay, Kenya. Significant interspecific differences were found with values ranging from 45.8% (Avicennia marina) to 49.8% (Ceriops tagal) for carbon fraction and from 0.58 (Sonneratia alba) to 0.93 (Pemphis acidula) for wood specific gravity. The influence of environmental factors (soil salinity, stand density, and elevation a.s.l. as a proxy for multiple interrelated conditions) was investigated, but only elevation a.s.l. appeared to have a species‐specific though moderate influence only on carbon fraction. Significant differences in carbon fraction and wood specific gravity were found between stem, aerial roots, and branches of Rhizophora mucronata. In contrast, no significant differences in carbon fraction were found among different stem tissues of A. marina, C. tagal and R. mucronata, the Bay's most abundant species. These results provide insight in carbon content variation, confirming the importance of considering species‐specific or even site‐specific values of carbon fraction and wood specific gravity, thereby rendering future carbon accounting more accurate.
Highlights
Mangrove forests are ecologically unique ecosystems that can be found in tropical and subtropical latitudes along the land–sea interface, bays, estuaries, lagoons, and backwaters (Mukherjee et al 2014)
We focused on explaining variation in both carbon fraction and wood specific gravity using general linear models on the environmental variables used for the initial hypothesis: elevation a.s.l. and salinity, with a strong preference for elevation a.s.l. because of its robustness compared to salinity (Discussion)
Significant sources of variation were found in carbon fraction and wood specific gravity, potentially having important influences on carbon accounting
Summary
Mangrove forests are ecologically unique ecosystems that can be found in tropical and subtropical latitudes along the land–sea interface, bays, estuaries, lagoons, and backwaters (Mukherjee et al 2014) They provide ecosystem services such as coastal protection, coastal fisheries, land-building, wood production, nutrient cycling, nursery and breeding protection to marine organisms, and opportunities for ecotourism (Lee et al 2014, Murdiyarso et al 2015). They bury carbon at a rate up to 50 times higher than tropical rainforests because they trap their own organic material, and litter from rivers and adjacent seagrass meadows (Bouillon 2011) Despite their role as important carbon sinks and the worldwide efforts to reduce carbon emissions, mangroves are threatened globally by deforestation resulting mainly from aquaculture and agriculture, and by deforestation’s indirect consequences which include drainage and high nutrient levels (Mukherjee et al 2014, Atwood et al 2017). This is especially alarming since mangrove forests present high attractivity for carbon offsetting schemes, making their protection a cost-efficient strategy for climate change mitigation (Siikam€aki et al 2012, Sitoe et al 2014, Murdiyarso et al 2015) while at the same time providing local communities with numerous additional ecosystem services (Locatelli et al 2004)
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