Mangrove Forest Cover Changes in Indian Sundarban (1986–2012) Using Remote Sensing and GIS

Abstract

The Indian Sundarban, a world heritage site, consists of an area of about 6312.768 km2 (2012) out of which 2122.421 km2 is covered by mangrove forests. The total forest cover of the Indian Sundarban, as assessed by Remote Sensing studies for the year 1986, was about 2246.839 km2, which gradually declined to 2201.41 km2 in 1996, to 2168.914 km2 in 2001 and to 2122.421 km2 in 2012. Strangely, there has been a loss of 124 km2 of mangrove forest cover in spite of the significant addition of forest by plantation in the northern part and the emergent ‘char lands’ within the tidal creeks. But the erosion and submergence of the southern sea-facing mangrove islands is even more significant as a result of the strong coastal erosion and sea level rise. The present study identifies six major classes of forest cover by supervised and unsupervised classification of the mangrove forest area, which are Dense Forest, Degraded Forest, Saline Blanks, Water Body, Sand (beaches/dunes), and Mud flats. The principle sequence of forest cover change observed was the transformation of Dense Forest area to Degraded forest and then to Saline blanks, with an occasional reversal of change in isolated cases under specific conditions. Saline blank formation is most dominant in Herobhanga, Ajmalmari East, West and North West, Dulibhasani East and Dulibhasani with significant increase with time. Among the total land use change during the last 26 years, about 47 % of it have been the change of Dense Forest to Degraded Forest, Saline Blanks or Creeks, notwithstanding minor amount of regeneration in some cases. The saline blanks occupy about 12 % of the total changed area at the expense of Dense Forest, Degraded Forest, Creeks/Waterbody which may be due to increasing tidal inundation, an increase of temperature and a reduction of annual rainfall in the area probably in response to climate change.