Verlag der Österreichischen Akademie der Wissenschaften

Abstract:
Mangrove ecosystems are rapidly disappearing worldwide at a rate of 1-2 % annually due to a combination of climate change and increased anthropogenic pressure and if the current trend continues unabated, mangrove forests may vanish completely within the next 100 years (DUKE et al. 2007). In an extensive review of the status of the world’s mangroves between 1980 and 2005, the FAO (2007) calculated a decrease in mangrove forest area of approximately 20 %. The nation of Senegal, in cooperation with Oceanium (a local NGO) and the Livelihoods Fund (a carbon investment fund), has been supporting the replanting of mangrove forests around vulnerable coastlines in the Sine Saloum and Casamance estuaries within the framework of a Clean Development Mechanism (CDM). The difficulty that the Livelihood Fund faces is the continual monitoring of these plantations, allowing investors to track the value of their investment as the forest grows. Presently, solely ground based sampling schemes are used to collect the necessary information which is both expensive and limited by accessibility. A remote sensing based approach, using satellite imagery, can potentially provide wall-to-wall coverage of the plantation areas and increase the level of efficiency in which the project is evaluated by optimizing the amount of field data needed for an accurate assessment of the plantations. To-date, the monitoring of young mangrove reforestation efforts has not been performed with remote sensing based techniques (FIELD 1999). The main objective of the current study is to consider the potential for using TerraSAR-X for the routine monitoring of young mangrove plantations, between 1 and 5 years old, and to determine if tree density (number of tree per hectare) can be accurately derived from the data. In addition, the acquisition mode of TerraSAR-X was examined to determine the optimum data parameters. The study investigated 3 groups of plantations, established between 2008 and 2012, in the Casamance estuary near the communities of Thiobon, Cap Skiring and Ziguinchor in south western Senegal, located between 12° 15’ and 13° 06’ North and 16° 15’ and 16° 48’ West.