Dieback in Tropical Montane Forests of Sri Lanka: Anthropogenic or natural phenomenon?

Abstract

Forest health of Tropical Upper Montane Rain Forests of Sri Lanka which are considered as “Biodiversity Hotspots” merit global attention. They are now rapidly diminishing due to a hitherto little understood phenomenon called forest dieback. This study examines the contribution of possible soil nutrient and toxic element factors for the health of Hakgala Tropical Upper Montane Forest. During the first stage, N, K, Ca, Mg, Zn, Cu , Fe, Mn and Al levels were studied in plots situated in the forest at locations of different dieback stages. Al, Mn, Fe and Pb concentrations in 30 individuals of 08 most susceptible plant species at different dieback stages and of soils of the immediate vicinity were determined during the second stage. Collected plant leaves were analyzed for total element levels and soils for extractable element levels. Geographical locations and the rate at which forests are being affected since last three decades suggest that forest dieback in Sri Lanka is not caused by a natural phenomenon. Results of the first stage of the study reveal that N, K, Ca, Mg, Zn, Cu were not in excess nor at deficiency levels. The second stage revealed the presence of high DTPA extractable Pb, Mn, Fe and KCl extractable Al in soils. The most important observation was the presence of higher than normal accumulations of Pb and Al in plant leaves. The plants belonging to some dieback-susceptible species showed an increasing trend of both Al and Pb levels in their leaves.