Impact of increased salinity on the plant community of the Sundarbans Mangrove of Bangladesh

Abstract

The overreaching objective of the study was to assess the changes in eco-regional forest composition and the colonization of invasive plant species in the Sundarbans, the largest single block of tidal halophytic mangrove forest globally. The study also aimed to examine the relationship between different plant types and the salinity level. Additionally, the interconnection between the salinity and the ‘top dying’ disease of the pioneer and dominant species was also measured. Thirty sample plots were established at the mouths of an equal number of canals to collect the plant community’s primary data. In addition, secondary historical data were utilized to understand the natural dynamics of the forest eco-regions in this mangrove. The study revealed that the fresh swamp forests disappeared from their historical range. Over time, the Screw Pine (Pandanus tectorius) became extinct from the study area. Simultaneously, rice grass (Leersia hexandra) and wild rice (Potresia coarctata) stand on the brink of extinction. Sundari (Heritiera fomes), the pioneer and dominant species, suffers from the increased salinity, and its stocks are declining due to intensified “top dying” disease. In contrast, the salt lover species, notably white mangrove (Avicennia marina), enjoy the incremental hegemony. The abundance of the indicator species, Nypa Palm (Nipa fruticans), and Mangrove Date Palm (Phoenix pelludosa) show a declining trend because of increased salinity. A total number of 25 invasive plant species were enumerated in this study. Immediate mitigation actions are required to protect this alteration in the vegetation composition of this mangrove. Hence, the study proposed a conceptual model of a mitigation plan spotlighting the local pressures.