The relationship between soil geochemistry and die back of montane forests in Sri Lanka: a case study |
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| Authors: | P N Ranasinghe C B Dissanayake D V N Samarasinghe R Galappatti |
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| Institution: | (1) Geological Survey & Mines Bureau, No: 04, Galle Road, Dehiwala, Sri Lanka;(2) Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka;(3) Coconut Development Authority, Nawala Road, Narahenpita, Colombo, 15, Sri Lanka;(4) 72/2 Siri Niwasa Mawatha, Kalutara, Sri Lanka |
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| Abstract: | Tropical montane forests of Sri Lanka form a unique ecosystem with more than 50% of endemic plant species. It has been noted
that trees, belonging to different size and age classes of these forest, have been dying due to a yet unknown factor. This
phenomenon was first observed in the Horton Plains National Park, which is a high plateau, composed of tropical montane forests.
Later dying of forests were observed at several areas including Hakgala montane forest.
Physical parameters trace nutrients as well as toxic element concentrations in soils, were studied in order to identify the
possible geochemical factors behind the forest die back. Systematic soil sampling was carried out covering the entire Horton
Plains National Park and random samples were collected from Hakgala montane forest. Samples were analyzed for available Fe,
Mn, Zn, Cu, Ni, Cd, Al and Pb using standard colorimetric and atomic absorption spectrometric procedures. Physical parameters
such as pH, moisture content, and conductivity of the samples were also measured.
Among extractable micro-nutrients Cu and Zn, and Ni show no deficiency or excess levels. However, the recorded available high
concentrations of Fe, Mn and Al can be toxic to certain montane plant species. Acidic moist soil of the area may enhance the
toxic effects of these elements. Possible source of these elements should be the underground lithology of the area.
According to the results obtained, there is a relationship between forest die back and high Pb concentrations. The same phenomenon
was also observed in the Hakgala forest. The distribution pattern of Pb in the Horton Plains coincides well with the die back
distribution pattern. The observed Pb values at Horton Plains and Hakgala are almost similar to values observed at Pannipitiya
and Dombagaskanda locations, which are located close to main roads carrying heavy traffic. It is quite possible therefore,
that Pb toxicity may be a significant factor behind the forest die back even though other factors should not be completely
ruled out at this juncture. Strong monsoon winds, bringing Pb from the polluted southwestern part of the country, can be the
most possible source of soil Pb. Further studies however are indeed necessary to confirm the conclusion. |
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