The use of multi-temporal Landsat normalized difference vegetation index (NDVI) data for assessing forest cover change of Lawarchara National Park

Lawachara National Park (LNP) is one of the most renowned protected areas in Bangladesh and a natural habitat of critically endangered Hoolock gibbon. The study's purpose was to assess the long-term change of forest cover using the Normalized Difference Vegetation Index (NDVI) technique and evaluate the impact of co-management. Landsat images acquired from the USGS glovis website were used to assess forest cover change using NDVI, a popular technique for identification and estimation of forest areas. NDVI value ranges from (− 1) to (+ 1); a negative value indicates non-vegetated areas including water bodies, road surfaces, settlements, etc., whereas a positive value near (+ 1) indicates the highest density vegetation. NDVI value (0) indicates bare land without vegetation. Based on NDVI values, the forest areas have been divided into four categories, namely: (1) very low or no vegetation area, (2) low-density vegetation area, (3) moderate-density vegetation area, and (4) dense vegetation area. A household survey was carried out among the people living in the adjacent villages to LNP. The study of assessing the forest cover change of LNP using remotely sensed data revealed that, after the initiation of co-management, the dense vegetation area increased by 8.62% in 2006 compared to 2001, but it decreased by 0.77% in 2014. In 2018, dense vegetation decreased by 3.86% relative to the dense vegetation area of 2014. If it is compared as a whole, it can be said that the forest cover has improved under co-management, and the household survey revealed that forest dependence has been reduced which might be considered as one of the reasons for forest cover improvement. However, more improvement can be achieved by focusing on the villages where forest dependence is still high. Betel leaf cultivation inside the forest area is creating a problem for wildlife and also hampering the natural composition of flora. Therefore, it is recommended to rehabilitate betel leaf cultivators outside the forest area with proper compensation. This will harness the full potentiality of the co-management practice, it needs complete monitoring and goodwill from every stakeholder, and hence it will bring good for the whole country.