Short-term prediction of the evolution of mangrove surface areas: The example of the mud banks of Kourou and Sinnamary, French Guiana.

International audienceThe aim of this study is to predict the short-term evolution of the surface areas of mangroves colonizing the mud banks of French Guiana from the comparative analysis of a series of satellite images. Two banks have been thus monitored: those of Kourou and Sinnamary. Sediment concentration values, grain sizes and topographic data were obtained for the Kourou bank, enabling the definition of the threshold elevation for mangrove colonization and analysis of colonization patterns over the mud bank. Digital elevation models were constructed from SPOT and Landsat7 images and shoreline detection carried out for the two study sites by extracting the mud-water interface at different tidal levels. The images were also used to examine the evolution of the mangrove areas and their expansion rates. The threshold of potential colonization has been estimated from field measurements carried out on the Kourou bank at about 2.45 m. The results confirm this threshold and highlight its relevance for predicting large-scale colonization by A. germinans. By confronting the geographic limits of the threshold defined from the digital elevation models and mangrove surface area, it comes out that within 3 years over 90% of the intertidal mud bank with an elevation higher than that of the threshold is covered by a dense cover of mangroves. It is thus possible to predict the short-term evolution of mangrove surface areas but the rates of colonization of the mud bank vary considerably as a function of available intertidal area. The results highlight divergent rates of mangrove area expansion between the two banks although certain similar points were remarked. This entails difficulties in predicting both the long-term mangrove expansion areas and rates. Uncertainty is exacerbated by the numerous climatic, geomorphic, oceanic and biological factors that need to be considered when analyzing the colonization process