Major and trace elements in plants and soils in Horton Plains National Park, Sri Lanka: an approach to explain forest die back

Abstract

Forest die back has been observed from 1980s in the montane moist forest of Horton Plains in the Central Sri Lanka for which the aetiology appears to be uncertain. The concentration levels of Na, K, Ca, Mg, Fe, Mn, Cu, Ni, Zn and Pb in canopy leaves, bark and roots, which were collected from dying and healthy plants of three different endemic species, Calophyllum walkeri, Syzygium rotundifolium and Cinnamomum ovalifolium, from three different die back sites were studied. Soils underlying the plants were also analyzed for their extractable trace metals and total contents of major oxides. Analysis of dead and healthy plants does not show any remarkable differences in the concentrations of studied trace elements. The results show that there is a low status of pollution based on the concentrations of chemical elements of environmental concern. Extractable and total trace element analysis indicates a low content of Ca in soils due to high soil acidity that probably leads to Mg and Al toxicity to certain plants. Relatively high Al levels in the soil would affect the root system and hamper the uptake and transport of essential cations to the plant. It therefore seems that the forest declining appears to be a natural phenomenon, which occurs due to the imbalance of macro and micronutrients in the natural forest due to excessive weathering and the continuous leaching of essential elements.