The high turnover between mangrove and non-mangrove is due
primarily to encroachment, erosion, aggradation, and mangrove
rehabilitation programs. The rate of erosion is highest at the
southern edges of Mayadwip, Bulcherry Island, and Bhangaduni
Island. For example, Bhangaduni Island lost one-fourth of its land
area (25.1%) and just less than one-fourth of its mangrove area to
erosion between the 1970s and 2000s. The majority of this loss in
this island occurred between 1989 and 2000s, which is evident
from the following illustrations (Fig. 5).
Due to aggradation, land continues to be made afresh in the
Sundarbans, offsetting a large part of the loss to erosion. This
process has increased the land and mangrove forest areas. Once the
new land is formed, such lands are typically colonized by a
sequence of plant communities, culminating in the establishment
of mangrove forests. Examples of aggradation can be seen in Fig. 5.
Between 1970s and 1990s, mangrove forest gained from
aggradation (2925 ha) nearly equals mangrove forest lost to erosion
(3157 ha). From the 1990se2000s, however, the rate of erosion
claimed seven times as much mangrove forest (4151 ha) as aggradation
created (592 ha). Erosion was concentrated along the banks
of major river channels and at the landewater interface with the
Bay of Bengal. Approximately half of the mangrove forested land
lost was at the extreme southern edge of the Sundarbans where
almost no compensating aggradation took place.
On the India side of the Sundarbans, the most dramatic area of
change is located approximately 14 km east of Kisoripur. In the
1970s image, 1085 ha of mangrove forest, interspersed with open
flooded areas, extended approximately 4 kminland from the Matla/
Bidya River. By 1990s, the classification shows that 13.27% of the
mangrove forest had been lost, and the boundary between