Tree diversity as affected by salinity in the Sundarban Mangrove Forests, Bangladesh

Abstract

A botanical expedition to the Sundarban Mangrove Forests (SMF) in March, 2010 was made to study the tree diversity and their abundance as affected by salinity gradient. In six quadrats of 25m × 25m each, distributed in all four Ranges, a total of eight tree species were recorded. A maximum number of five species occurred in relatively low saline sites. Tree zonation dynamics of the forests along salinity gradient revealed an increase in the number of Ceriops decandra (goran), a salt tolerant plant in the north-eastern parts of the SMF which was dominated by Heritiera fomes (sundri), a freshwater loving plant in 1960’s. Highest importance value index (IVI) was recorded for C. decandra, which was present in all sites, except Moroghodra, a freshwater zone in Nalianala (Khulna) Range. Comparison of the Landsat images of Nalianala and Chandpai Ranges during 1989, 2000 and 2010 revealed a decreased tendency of dominance of H. fomes in the two Ranges but increased tendency of Bruguiera sexangula (kankra), Excoecaria agallocha (gewa) and Sonneratia apetala (keora). Total tree cover in 2010 decreased by about 3% from that of 1989. The changes in the tree composition have been attributed to increased salinity. The changes in the physiography and tree composition of the two Ranges between 2000 - 1989 were considerable. Key words: Tree zonation; Salinity; Remote Sensing; GIS; Heritera fomes; Ceriops decandra DOI: http://dx.doi.org/10.3329/bjb.v40i2.9778 Bangladesh J. Bot. 40(2): 197-202 , 2011 (December)

Species diversity, change in forest cover and area of the Sundarbans, Bangladesh

“…The present study does not agree with the findings of Aziz and Paul (2015) and showed a great variation where the number of E. agallocha per ha showed a sharp increase. However, it is in agreement with the findings of Ahmed et al (2011) who have reported an increase of area coverage of this plant by 6.7%. The increase in the number might be due to the ban on collection of timber of this plant as it was done previously for the raw materials of Khulna News Paper Mills.…”

“…a further reduction by 48.65% in 1996 (Aziz and Paul 2015) who reported that (using "Table curve 2D" program) total number of plants would be reduced to 109 per ha in 2020 and number of H. fomes and E. agallocha will be 80 and 7. Ahmed et al (2011) have shown the reduction of H. fomes by 28.75% area coverage but an increase in E. agallocha by 6.7% i.e. 1016 ha between 1989 and 2010 in only two Ranges.…”

“…Hossain (2003) reported 44 undergrowth species of SMF. Ahmed et al (2011) recorded only 8 tree species growing in quadrats in their study. Although the mangrove forests of the world is conspicuous for the absence of reproducing under-story herbs and shrubs and for the absence of the vine life form (Janzen 1985), in the present study 3 shrubs and 5 herbs growing in the Sundarbans were recorded.…”

Stand structure and carbon storage in the oligohaline zone of the Sundarbans mangrove forest, Bangladesh

“…Very few previous studies have examined the stand structure, biomass, and carbon storage of Sundarbans Reserve Forest (SRF), Bangladesh with respect to its biodiversity and role as a carbon sink among the other forest ecosystems in the tropics (Iftekhar and Saenger 2008;Ahmed et al 2011;Rahman et al 2015), and no previous studies have examined the species wise contribution to the total carbon stocks of the mangrove communities in this area. In the present study, the structural characteristics of the mangroves within the oligohaline zone have been quantified with a view to assessing their role in total carbon stocks of the SRF, Bangladesh.…”

“…In Bangladesh the forest covers 6017 km 2 Chaffey et al (1985) divided the Sundarbans mangrove forest into three ecological zones: fresh water (oligohaline); moderately saline water (mesohaline); and salt water (polyhaline). Changes in salinity might be responsible for the spatial distribution of plant communities (Ahmed et al 2011).…”