Résumé
Mangroves are critical ecosystems given their key role in conserving biodiversity, protecting coastlines from erosion and supporting coastal resources. They may be impacted by oil and gas activities, either directly or indirectly. Restoring them is therefore of prime importance. In the Mahakam Delta, oil and gas exploration and production have been conducted for more than 40 years. This industry has operated in a quasi-pristine area barely affected by its activities until the mid 80’s. Toward the late 1980’s and until 2000, the delta was subject to massive and rapid development of shrimp farming and by 2001, 80% of the delta mangroves were destroyed and most of it replaced by ponds used for aquaculture. During the 2000’s, shrimps production in the delta decreased due to lack of nutrients in ponds, and a drop in shrimp prices due to the rise of imports worldwide. Numerous ponds were abandoned in the delta. This economic situation generated social instabilities that could threaten the oil and gas industry in the region. Therefore, in order to better protect mangroves and optimize restoration of damaged areas, Total E&P Indonesie has embarked on a mangrove restoration initiative in the Mahakam delta aimed at understanding the restoration processes through both natural recolonization and planting techniques. The general methodology implemented has been to i) describe the land occupation by acquiring satellite images, interpreting aerial photos, conducting field work, and establishing GIS maps, ii) inventory fauna and flora (mangroves, birds, fish and benthic invertebrates, mammals, reptiles and others), iii) conduct a monitoring of naturally re-colonized areas, replanted areas and original forest on selected areas. Results show that natural recolonization of a mangrove area can be very quick under certain conditions (subject to availability of seeds and easy access to the area to be recolonized). But in areas where seeds cannot easily migrate and access, or where seed supply is too difficult, replanting remains the best option. Social aspects have also to be taken into account: replanting promote the local commitment to sustainable environmental conservation. This paper will detail the methodology, present the scientific results and discuss the lesson learned.