Impact of co-management on tree diversity and carbon sequestration in protected areas: Experiences from Bangladesh

•The study captured the impacts of co-management on biodiversity conservation and carbon sequestration in forest protected areas of Bangladesh.•GIS assisted NDVI technique was used to increase precision in sampling process.•Phytosociological attributes were found better in control sites, whereas, biodiversity indices were almost similar in co-managed and control sites.•Carbon sequestration in forest biomass was slightly elevated in co-managed PAs compared to that in control sites.•Non-co-managed sites showed better biodiversity status than co-managed sites. Forest Protected Area (PA) co-management, which integrates local communities in the forest management structures, was started in Bangladesh in 2004 to effectively manage and conserve forest resources. This study has investigated if the initiative has met its objectives. Using NDVI maps, we applied a stratified random sampling framework to identify sample plots. Phytosociological and carbon-sequestration data were collected from two co-managed PAs (Lawachara National Park and Teknaf Wildlife Sanctuary) and adjacent reserve forests that are not under co-management regime. Results reveal that phytosociological attributes for both mature trees and naturally regenerated seedlings showed better results in co-managed sites than in non-co-managed sites. Plot mean species, genus, and family were 2.69, 2.64, 2.49, respectively, in the non-co-managed sites as opposed to 1.64, 1.60, and 1.46 in the co-managed plots. Simpson's Diversity Index was 0.11 and 0.15 in co-managed PAs and control sites, respectively. Given the standard normal distribution, the range of biomass carbon sequestration was (−300, 500) t/ha in the co-managed PAs as opposed to (−200, 400) t/ha in the control sites. Overall, sites without co-management showed better biodiversity status than the sites having co-management practices.