Half a century of dynamic coastal change affecting mangrove shorelines of French Guiana. A case study based on remote sensing data analyses and field surveys

The mobile mud banks, several kilometres wide and about 30 km long, which form the sedimentary environment of the coast of the Guianas are a consequence of the huge particulate discharge of the Amazon. These mud banks shift towards the northwest, influenced by the combined action of accretion and erosion, a process also affected by periodic variability. Because of this movement, the coastline is unstable and continuously changing. Such changes determine the structure and composition of mangrove forests, the only type of vegetation adapted to this dynamic environment. The objectives of this study were to identify coastal changes that took place over the last 50 years, and to relate them to natural processes of turnover and replenishment of mangrove forests. These objectives have been achieved through a combination of remote sensing techniques (aerial photographs and SPOT satellite images) and field surveys in the area of the Sinnamary Estuary, French Guiana. Ground data were collected in representative mangrove forest stands, chosen as a function of their growth stages and their structural features, from pioneer and young stages to adult, mixed and declining formations. The coastline changes and the mangrove dynamics over the 1951-1999 period are analyzed through production of synthetic digital maps, showing an alternation of net accretion (1951-1966) and erosion periods (1966-1991), followed by the present accretion phase. Based on this structural, functional and historic, information, a global scenario of mangrove forest dynamics is proposed, including a model of forest development, forest gap processes and sedimentological dynamics. The results of this research are discussed within the context of regional (coastal Amazonian area) and global climate. (C) 2004 Elsevier B.V. All rights reserved.