Abstract
Mangroves are found throughout the tropics, providing critical ecosystem goods and services to coastal communities and supporting rich biodiversity. Despite their value, world-wide, mangroves are being rapidly degraded and deforested. Madagascar contains approximately 2% of the world’s mangroves, >20% of which has been deforested since 1990 from increased extraction for charcoal and timber and conversion to small to large-scale agriculture and aquaculture. Loss is particularly prominent in the northwestern Ambaro and Ambanja bays. Here, we focus on Ambaro and Ambanja bays, presenting dynamics calculated using United States Geological Survey (USGS) national-level mangrove maps and the first localized satellite imagery derived map of dominant land-cover types. The analysis of USGS data indicated a loss of 7659 ha (23.7%) and a gain of 995 ha (3.1%) from 1990–2010. Contemporary mapping results were 93.4% accurate overall (Kappa 0.9), with producer’s and user’s accuracies ≥85%. Classification results allowed partitioning mangroves in to ecologically meaningful, spectrally distinct strata, wherein field measurements facilitated estimating the first total carbon stocks for mangroves in Madagascar. Estimates suggest that higher stature closed-canopy mangroves have average total vegetation carbon values of 146.8 Mg/ha (±10.2) and soil organic carbon of 446.2 (±36.9), supporting a growing body of studies that mangroves are amongst the most carbon-dense tropical forests.
Highlights
Mangroves are found in inter-tidal areas in over 120 countries between 30° N and S latitude and provide a broad range of important ecosystem goods and services for surrounding coastal communities [1,2,3,4,5,6,7,8,9,10,11]
Mangroves have been found to be amongst the most carbon-dense forests in the tropics, with similar or greater above- and exceptionally larger below-ground stocks compared with the terrestrial systems reported in several studies [15,27,32,33,34,39]
Existing national-level maps include contemporary and historical areal extents for mangroves and provide the information required for quantifying the dynamics; these data lack the detail required for comprehensive ecosystem characterization and estimation of C stocks for distinct mangrove types
Summary
Mangroves are found in inter-tidal areas in over 120 countries between 30° N and S latitude and provide a broad range of important ecosystem goods (e.g., food; fuel; construction materials; medicine) and services (e.g., storm protection; erosive barriers; breeding, nesting, nursing and feeding grounds for marine, pelagic and terrestrial fauna; water filtration) for surrounding coastal communities [1,2,3,4,5,6,7,8,9,10,11]. The collective importance and value of mangrove ecosystems is receiving an increasing amount of attention [16,63,64,65,66,67] Owing to their value and rate of loss, up-to-date information representing the extent and status is critical for effective management and decision making [11]. Existing national-level maps include contemporary and historical areal extents for mangroves and provide the information required for quantifying the dynamics; these data lack the detail required for comprehensive ecosystem characterization and estimation of C stocks for distinct mangrove types. We use existing national-level maps to calculate the long-term dynamics and employ Landsat data to produce the first ever localized map (circa 2010) of mangrove ecosystems and surrounding terrestrial land-cover types for Ambanja and Ambaro bays. Using the localized map to partition the mangroves in to ecologically meaningful strata, we present the first estimates of total C stocks for Malagasy mangroves and compare them with published values for other terrestrial forest types
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