Carbon Budget as a Tool for Assessing Mangrove Forests Degradation in the Western, Coastal Wetlands Complex (Ramsar Site 1017) of Southern Benin, West Africa

Abstract

Mangroves are among the carbon-richest forests in the tropics, containing an average of 1,023 t carbon per ha. Mangrove deforestation generates global emissions of 0.02–0.12 Pg carbon per year, while storing up to 20 Pg C annually (Donato et al. 2011), roughly equivalent to 2.5 times annual global carbon dioxide (CO2) emissions despite accounting for only around 0.7 % (around 140,000 km2) of global tropical forests (Giri et al. 2010). Apart from high carbon storage potentials, mangroves provide other valuable ecosystem services like protection from storms, floods, and erosion; provision of timber and non-timber forest products (Daïnou et al. 2008); processing of waste and nutrient pollution; aquaculture and agriculture support; and habitat for aquatic and terrestrial species. In Benin, the total mangrove cover is about 66 km2 within its 120 km littoral zone consisting largely of a sandy coast without developed estuaries and deltas. The mangroves of Benin tend to be limited to the edge of the extensive network of brackish coastal lagoons in the south of the country. Despite replanting efforts, these mangroves are in an advanced state of degradation (UNEP 2007). Because of their large ecosystem, carbon stocks, their vulnerabilities to land use, and the numerous other ecosystem services they provide, mangroves are increasingly considered as prime ecosystems participating in climate change mitigation strategies through reforestation and restoration (Alongi 2002; Donato 2012). To participate in global climate change-related processes, such as reduced emissions from deforestation and degradation (REDD+), and Clean Development Mechanism (CDM), it is necessary to determine carbon stocks and emissions baselines. Many carbon stock assessments in mangrove ecosystems have been carried out recently around the world (Donato et al. 2011; Kauffman and Donato 2012; Adame et al. 2013) mainly assessing mangroves from more or less temporal sample plots in mostly undisturbed states. Until recently in Central Africa (Ajonina et al. 2013), lack of permanent mangrove sample plots made it difficult to gauge mangrove ecosystem recovery dynamics from increasing degradation pressures for its vital ecosystem services that sustain coastal rural economies, especially in the west–central African region. The present study was carried out to assess carbon stocks in mangrove ecosystems subjected to various level of degradation as part of a larger initiative to set up a CDM tree planting project to restore degraded mangrove areas of southern Benin.