Analysis of Causes of Top-Dying in Sundarbans Natural Forest Resources

Abstract

The Sundarbans is the largest, biologically richest, and most extensive mangrove forest in the world, which is also a world heritage saite. Heritierafomes (Sundri) tree is the most important ecologically dominant and economically valuable tree species in the Sundarbans. However, a serious disease (top dying) of H. fomes in Sundarbans is affecting millions of the trees. An inventory by Chaffey et al., (1985) revealed that there were about 45.2 million top dying trees in the Sundarbans of which 20 million had more than 50% of their crown affected by top dying. The loss of H. fomes will have a major impact on the Sundarbans mangrove ecosystem, as well as lead to economic losses.Despite various hypotheses as to the causes of this top dying, the underlying causes are still not well understood. The present work has explored some of the possible factors involved, focusing particularly on the relationship between the amount of top-dying in different places and the concentrations of a number of chemical elements present in the soil and water, in order to test the hypothesis that chemical pollution might be responsible. Other factors such as the pH, salinity and nutrient status were also assessed. Nine plots were selected for sampling of soil, water, and vegetation in order to categorize different areas in terms of their intensity of top-dying.63 soil samples and 9 water samples were tested, mainly by ICPMS, to investigate certain parameters of the soil and water, such as Sn, Exchangeable K, Soil pH, Pb, Zn, Ni, soil pH, CEC, soil nutrients, soil moisture content, and elemental concentrations of 32 other elements. Most of the elements studied had no significant correlation with the top dying of Heritierafomes.However, Sn, Exchangeable K, and soil pH were significantly related, and three elements, namely Pb, Zn, Sr, were also close to significance.Of the hypotheses previously put forward to explain top-dying, the present results do not support enhanced salinity as the cause. It is likely that several of the above-mentioned environmental factors interact with each other to induce top dying in Sundri.But, the present results have showed thatSn, Exchangeable K, Pb, Srand Zn could be directlylinked with top-dying of Heritierafomes (Sundri) in Sundarbans, probably particularly by weakening the vigour of the trees and allowing other factors such as pathological agents to attack the plants.