Field observations of this study indicated that forest
dieback was significantly higher in slope areas of the
Hakgala SNR facing strong winds. Also it was
noticed that strong monsoonal winds impact the
forest canopy by causing the shedding of a
considerable amount of plant leaves. This study
proves the presence of high extractable Mn, Fe, Al
and Pb levels in upper montane forests of Hakgala
SNR. It is noteworthy to record higher extractable Pb
and Al values on slopes, where the dieback is more
intense than on flat areas. Except for some individual
species, no common significant correlation could be
observed between intensity of unhealthiness and any
of the studied elements. The study found toxic levels
of Al and Pb in plant leaves of certain species.
Both leaf Fe and Mn contents do not show any
significant relationship with unhealthiness. Also there
is no possible mechanism to explain the enhancement
of toxic effect of Mn and Fe derived from underlying
rocks which triggers the forest dieback during the last
three to four decades. Further, plants do not show
symptoms related to Mn and Fe toxicity. Although no
direct common relationship between leaf Al level and
health of the studied plants could be established,
stresses imposed on plants by high Al contents in
trees and soils cannot be neglected. The high Al
contents in the leaves of dying plants belonging to the
most dieback susceptible species is a clue for
possible Al toxicity. Increased soil acidity (pH 4.4 to
5.7) can trigger the dissolution of toxic Al
underlying rocks and soils to make them readily
available for uptake by plants. Also the impact of the
recorded toxic concentrations of Pb in plants cannot
be ruled out even though there is no direct common
relationship between plant Pb levels and dieback
intensity, which could be expected due to
modification of Pb absorption in plants after the
commencement of dying back process. However, an
increase in Pb levels in Calophyllum walkeri,
Cinnamomun ovalifolium and Syzigium
rotundifolium which are highly susceptible for
dieback is noteworthy. Such an increase could not be
observed in plants belonging to low dieback
susceptible species. Increased Pb levels in soils on
slope areas, differences between total and extractable
soil Pb levels, amounts of washable Pb levels on
plant leaves before and after the banning of Pb
containing gasoline usage and Pb levels in plants
from different parts of the country suggest air
pollution as the main Pb source in montane forests.
Strong monsoonal winds as well as transboundary
effects could be responsible for bringing Pb from the
industrialized western province of the country. Also
there is a possibility of Pb transport from
industrialized South Indian cities. Pot studies are
suggested as the next step for dieback research to
understand the toxic threshold levels of different
plant species for Al and Pb. Further studies have to
be carried out to identify the atmospheric pollutant
The Faculty of Natural Science Research Grant
(2006) of the Open University of Sri Lanka provided
financial assistance for the field work and chemical
analyses. Thanks also go to the Wildlife Department
of Sri Lanka for granting permission for sampling at
the Hakgala Strict Nature Reserve. Chemical
analyses were done at the Geological Survey &
Mines Bureau in Sri Lanka. We wish to thank Ms.
Elizabeth Fein of Kent State University for her kind
support in editing the manuscript.
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