Abstract
The Sundarbans - the world’s largest single block of tidal halophytic mangrove forest situated at the southwest of Bangladesh, plays a vital role in maintaining environmental sustainability of the country and the world in general. This study identified and quantified the extent and degree of damage caused to the floristic diversity of the Sundarbans by the tropical cyclone Sidr in 15 November 2007. It also quantified the extent and rate of the post-cyclone regeneration in the damaged flora. Unsupervised classification - ISODATA and the normalized difference vegetation index (NDVI) were carried out over a temporal series of 2007-2010 on four Landsat 7 Enhanced Thematic Mapper Plus (ETM +) images for the months of February. Land change analysis from the classification results show that three important floristic taxa - Heritiera fomes (Sundari), Excoecaria agallocha (Gewa) and Sonneratia apetala (Kewra) have been significantly affected by the cyclone. NDVI analysis indicates that 45% area of the Bangladesh’s part of the Sundarbans (approximately 2500 sq.km) was affected due to the cyclone action. Results further indicated that the average rate of post-cyclone floristic growth in 2009-2010 is four times higher than the average rate in 2008-2009. Thus the study identified a temporary loss of the diversity (in terms of relative abundance) in the affected three floristic taxa of the Sundarbans after that severe exogenous perturbation; which took three years to regenerate. Moreover, it showed the higher efficiency and promptness of remote sensing techniques in similar cases than the ground data based studies.
Highlights
The biodiversity and its conservation have been established as the primary indicators of environmental sustainability (Kates et al, 2001), whereas the assessment of biomass and floristic diversity in tropical forests has been identified as a priority by many international organizations (Stork et al, 1997)
This study aims at three objectives: (i) to identify the changes in the floristic pattern of the Sundarbans, in the preceding and following periods of the tropical cyclone Sidr; (ii) to identify specific floristic damage caused within the catchment extent of cyclone trajectory and their regeneration until year 2010; and (iii) to identify the relevance of the study results when comparing to previous ground data based studies about the Sidr effect on the Sundarbans (CEGIS, 2007; Hasegawa, 2010; Hossain & Begum, 2011; Paul & Dutt, 2010; Paul, 2009; Shamsuddoha & Chowdhury, 2007)
Since the trajectory of cyclone Sidr passed through the eastern part of the Sundarbans, cluster 2 is likely to be affected by the cyclone landfall
Summary
The biodiversity and its conservation have been established as the primary indicators of environmental sustainability (Kates et al, 2001), whereas the assessment of biomass and floristic diversity in tropical forests has been identified as a priority by many international organizations (Stork et al, 1997). It is an emerging issue that how the remote sensing technique can be best applied to identify patterns of floristic diversity on the Earth’s surface and to detect changes in them over time (Brink & Eva, 2009; Wood et al, 2002). Tropical cyclones have devastating impacts on the floristic diversity pattern of tropical mangrove forests; sometimes it takes a significant amount of time for the forest to regenerate which influences the environmental sustainability of the area (Elsner et al, 2008). They can cause temporary or permanent absence in the number and relative abundance of particular floristic taxa.
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