Coastal blue carbon ecosystems (mangroves, tidal marshes, and seagrasses) are known for storing carbon more efficiently than other terrestrial biomes. Amongst these ecosystems mangroves are the most carbon-efficient due to the relative high proportion of recalcitrant material in plant tissues. Although many studies have shown that much of the carbon is stored in the soils, a significant portion of carbon is stored in the aboveground biomass (AGB). Because AGB in mangroves is orders of magnitude higher than in any other blue carbon ecosystem, and because it can remain immobile for centuries, it is important to adequately quantify these stocks. Here, we provide a revised global mangrove AGB budget. Our approach was to use the coastal environmental setting framework to explain the global variation in mangrove AGB, in contrast to past works based either on latitude or climate. This approach recognizes geophysical variables (river discharge, tidal amplitude) to be, along with regional climate, responsible for global variation in coastal ecosystems attributes. To test this hypothesis, we compiled AGB data from 324 independent studies, representing 1710 sites, and covering 56 countries. Then, used multiple regression analyses to assess the effect of these environmental drivers on global mangrove AGB variability.
Results/Conclusions
Evapotranspiration, tidal amplitude and river discharge accounted for nearly 80% of the total variability in global mangrove AGB explained by our model (R2=0.17, df=224, P<0.000). Temperature and precipitation, and the interaction between these two variables explained the remaining variation in global mangrove AGB. Global mangrove AGB budget was estimated at 0.9 Pg, which is 3 to 5 times lower than past estimates. Our robust dataset also allowed for testing the performance of our model against observed data; on a per-area-basis there was no significant difference between observed (91 Mg ha-1) and modeled AGB (94 Mg ha-1). However, our per-area-basis estimate was 50% smaller than previous global estimates. Here we show that the use of the coastal environmental setting framework significantly improves global mangrove AGB estimates, providing empirical evidence for long established coastal ecology theory and contributing to strengthen the global carbon budget. In terms of application, our results reveal significant biases in current estimates both in terms of total and spatial variability of mangrove aboveground biomass. The results provided here will allow many countries to develop or review their national blue carbon inventories and potential CO2 emissions resulting mangrove conversion.