Forest carbon emission mitigation schemes seek to protect tropical forest, combat effects of climate change, and offer potential cash and development opportunities. Reducing emissions from deforestation and degradation (REDD+) projects based on a foundation of accurate carbon stock assessment provide such an opportunity for Papua New Guinea. The objective of this study was to quantify the carbon stock of the central forests of Manus Island, Papua New Guinea, and identify factors that underpin any observed variation within it. We employed the Winrock Standard Operating Procedures for Terrestrial Carbon Measurement for plots and associated measurements. In 75 variable-radius nested plots (total area ≤14.4ha), we assessed above-ground and total carbon stock of stems ≥5cm diameter at breast height via general linear models in a model-selection framework. The top models described variation in average carbon stock at 95% lower and upper confidence interval in above-ground biomass solely in terms of forest type: primary hill forest 165.0MgCha-1 (148.3-183.7, n≤48), primary plain forest 100.9MgCha-1 (78.0-130.6, n≤10) and secondary hill forests 99.7MgCha-1 (80.9-122.9, n≤17). To a lesser extent, above-ground carbon stock increased with slope and varied idiosyncratically by the nearest village. Our estimates are comparable with published studies for Papua New Guinea and the wider tropical region. These data should strengthen pre-existing knowledge and inform policies on carbon accounting for REDD+ projects in the region.
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