Investigation of Sundarbans ecosystem resiliency through multi temporal remote sensing data

Abstract

Mangrove ecosystems are distributed along the coast in the tropical and subtropical climate zone. They have a role as a defender from different calamities and critical breeding zone for shrimp and fish. In the recent past, Sundarbans protected us from two devastating cyclones called SIDR in 2007 and AILA in 2009 but faced significant damage of its own. It is vital to know how Sundarbans is recovering from such damage after the cyclonic disaster. There are several research articles and books on forest fire and forest resiliency. But there is a large gap to assess and monitor the recovery and resiliency of mangrove forests like Sundarbans which face different natural calamities and most susceptible to climate change. How a mangrove forest will recover after a natural disaster depends on the resiliency of the forest. The main purpose of this study to assess and monitor resiliency factors for a better understanding of the recovery and resiliency of Sundarbans. In this study, canopy density has been considered as forest health status and try to find out the relationships with other physical factors which may have some impact. To evaluate the forest canopy density, Higher-resolution Landsat satellite images of 30 × 30 m resolution has been used. In this study, 5 indices have been incorporated to assess the forest health status. A well-fitted index has been found out by accuracy assessment by comparing the outcome of different indices with the field observed dataset. An extensive field visit has also been conducted for this purpose. The result shows that NDVI (normalized difference vegetation index) provides a better result than others. I also investigated the damage and recovery of Sundarbans from major cyclonic events and found that the recovery rate varies in four ranges defined by the forest department of Bangladesh. As in different ranges, we have different species composition and dominancy and the recovery rate of different species is not the same. The negative trend in terms of canopy density has been seen mostly in Sundari dominated areas. This result indicates that while Sundarbans is resilient to the cyclonic event, long term degrading of canopy density could reduce this resiliency to a critical level. Anthropogenic disturbance is putting extra pressure on the resiliency of this mangrove forest. To assess the impact of different climatic parameters in Sundarbans, it has been tried to assess the relationship of different parameters like surface water salinity maximum temperature, minimum temperature, relative humidity, total rainfalls and concerning canopy density dynamics. It has been found that the surface salinity has an impact on canopy density but the relationship with other variables is negligible. The sensitivity of canopy density to surface salinity varies to different species, so it can be an effective way to ensure resiliency if we focus on species wise management plan rather than traditional methods. Involvement of local inhabitant in the management plan and familiarizing them about the forest resiliency and its importance can play a vital role to reduce anthropogenic disturbance on this world heritage.