Examining the effects of economic zone construction on mangrove forest using before-after-control-impact (BACI).

Mangrove forests along land-sea interface are threatened, although they provide diverse ecosystem services. Mangrove transplantation has been conducted in Bangladesh since 1966 to protect coastal areas, although an economic zone project started in 2016 has affected the forest. To evaluate the impact of the project on the mangrove, changes in normalized difference vegetation index (NDVI) were monitored before (2011) and after (2021) the economic zone construction by IKONOS (0.8 m in resolution) and TripleSat (0.8 m) imageries. Before-after-control-impact (BACI) assessment was applied to investigate the effects on the ecosystems with forests surveyed in 18 plots of which disturbance intensities were scored by hierarchical disturbance rank. NDVI decreased in 17.4% of the study area, primarily due to road construction and forest degradation near the economic zone. In all affected plots, NDVI was lower in the after-period than in the before-period. Inland areas showed a positive relationship with NDVI in the after-period compared to seaside. The impact extended up to approximately 20 km beyond the zone, indicating that the effects of construction were extensive. Periods and disturbance intensities were negatively correlated with NDVI changes. In this study, BACI assessment was applied to remote sensing for the first time and identified that low NDVI occurred in the intermediate area, confirming the negative impact of road construction on mangrove for long distance from the project. Considering that human activity leads to mangrove deterioration in both proximal and remote areas, a BACI-based assessment should be adopted when evaluating impacts on mangroves even at remote sensing.