Determination of vegetation degradation using NDVI analysis in the Sundarbans from 1975 to 2025

The world’s largest mangrove forest is situated in the southwestern part of Bangladesh, which is known as the Sundarbans. The Sundarbans was recognized as a world heritage in 1997. The Sundarbans plays a crucial role in biodiversity conservation, coastal protection, and carbon sequestration. Despite its ecological importance, day by day the famous forest is faced with biotic and abiotic interferences such as salinity intrusion, elevated mean sea level, and human-induced disturbances, etc. The aim of the study was to determine vegetation variations from 1975 to 2025 using Landsat-derived Normalized Difference Vegetation Index (NDVI) data and imagery from Landsat 2, 5, 8, and 9, etc. The total vegetation areas were classified into no vegetation, thin vegetation, and dense vegetation groups. Afforestation and deforestation trends were also detected from 1975 to 2025. The findings of the present study revealed that dense vegetation was dropped by over 34%, while non-vegetation areas expanded by 6% during five decades. The maximum deforestation occurred between 2015 and 2025 in the southern and southeastern zones of the Sundarbans, and the afforestation rate was also higher between 2005 and 2015. This study identified spatial hotspots of ecological change and underscores the limitations of NDVI only approaches while proposing a replicable remote sensing framework for mangrove monitoring. The results of the study will be helpful to offer critical insights for conservation planning and sustainable management of the Sundarbans and other vulnerable coastal ecosystems all over the world.