Aboveground biomass and carbon stock estimation using UAV photogrammetry in Indonesian mangroves and other competing land uses

Mangrove ecosystem is one of coastal wetlands that have experienced significant anthropogenic driven degradation and conversion, which have resulted in substantial carbon releases to the atmosphere and the oceans. However, carbon stock assessments and monitoring for mangroves are mostly confined to in situ methodologies, which has limited further understanding of wider-scale spatial variations and additional driving factors of carbon loss. Here,we report a novel application using unmanned aerial vehicles (UAVs) to estimate and compare aboveground biomass (AGB) carbon stocks of mangrove forests with two alternate replacement commercial land uses (oil palm and coconut plantations) in Lubuk Kertang and Pulau Sembilan, North Sumatra, Indonesia. We generated high-accuracy digital surface models (DSMs) and digital terrain models (DTMs), as well as elevation data from a global navigation satellite system (GNSS). Through analysis, we highlight how mangrove forest conversion to oil palm and coconut plantations significantly decreases the aboveground biomass carbon (AGB) and carbon stocks (AGC) of selected mangrove ecosystems in Indonesia. In this study, spatially mapped biomass carbon measurements were found to be more accurate when cross-validated with in situ measurements. AGC stocks were found to be over 10- to 12-fold that of converted oil palm and coconut plantations across selected study sites. The generated biomass carbon stock product provides new knowledge of carbon stock distribution in Indonesia across mangrove forests and two alternative commercial land use types within similar topographical landscapes. This combined methodological approach may be a useful tool to assist with blue carbon inventories as well as for selecting specific mangrove conservation and restoration areas across larger spatial scales.