3.1.3. Sundarbans (Bangladesh and India)
From the 1970se2000s, mangrove forest in the Sundarbans
decreased by 1.2%. The rate of change, however, was not uniform
from the 1970se1990s and from 1990s to 2000s. From the 1970se
1990s, mangrove forest area increased by 1.4%, and from 1990s to
2000s, the area decreased by 2.5%. These changes are nonsignificant
in the context of errors associated with classification
and the dynamic nature of mangrove ecosystems. In other words,
these changes are well within the margin of error. For example,
because of the fluctuation of tide, certain areas in flooded areas,
barren lands, and water bodies could be misclassified from one
class to another. Small changes less than 3x3 pixels were not
detected from this study as this was the minimum mapping unit
used. This is expected to minimize the errors arising from missregistration
of satellite imagery.
While the measured net loss of mangrove forest was not
considerable, the change matrix (Table 5) shows that turnover was
much greater than net change. For example, 7% of the 1970s-era
mangrove forest had changed to non-mangrove, flooded, water
bodies, or barren lands by 2000. The largest category of mangrove
forest change was loss to flooded (4.6%). The change matrix also
revealed that during the same period approximately 37% of flooded
areas, 21% of barren lands, 8.3% of non-mangrove, and 2.2% of water
bodies were converted to mangroves. Similar patterns of change
were observed from the 1970se1990s and from 1990s to 2000s
(Table 5).
In all three classifications, 93e95% of mangrove forests, 93e96%
of water bodies, and 69e79% of non-mangrove areas did not
change. During the same period, the turnover for flooded areas and
barren lands was, however, quite high, only 30e35% of flooded and
15e50% of barren lands remain unchanged. The large change between
flooded and barren lands may possibly be due to variation in
tidal inundation at the time of satellite data acquisition. Major
change areas were concentrated either in the outer periphery or
near the shoreline (Fig. 4), caused by anthropogenic and natural
forces, respectively.