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boundary Smr-l/Smr-2. Consequently, the accumulation of the sediments
analysed has begun in Subatlantic time.
LPAZ Smr-2 (55-0 cm)
In this zone an increase in the presence of
Pinus diploxylon-type
up to
45-50
%
is registered, together with a rise in the pollen frequency of
Pinus
рейсе
reaching 30 % in the uppermost sample. Lower percentages are recorded
for
Abies, Fagus,
and for pollen from almost all deciduous trees (
Carpinus,
Acer, Corylus, Quercus, Alnus).
Pollen of
Picea
keeps nearly the same values
(less than 10
%)
as in the previous zone. Quite common are pollen grains of
Juniperus.
A reduction in the presence of herb pollen is also observed. Partly,
this reduction in
NAP
representation could be linked with the aeration of the
soft undecomposed
Sphagnum
peat, characteristic for the uppermost 30 cm,
thus creating unfavourable conditions for the preservation of the pollen grains.
The presence of
Poaceae
pollen declines to 5-10 %. The same tendency is
recorded for
Taraxacum-type, Ranunculus
-type,
Dianthus-type, Scleranthus,
etc. Spores of Polypodiaceae are not so common in contrast to the abundance
of spores of
Selaginella selaginoides.
Zone Smr-2 reveals the vegetation changes at high altitudes during the last
centuries. The increase in total
AP
is mainly contributed by
Pinus mugo, Pinus
sylvestris
and
Pinus рейсе.
An enlargement of the areas in the subalpine zone
occupied by dwarf-pine
(P. mugo)
and junipers (
Junperus
) is observed. Quite
probably, this enlargement resulted after the abandonment of the practise to
burn the dwarf-pine and part of the coniferous forests at high altitudes in order
to increase the high-mountain pasture land. Similarly, a wider spread of
Pinus
рейсе
in the upper part of the coniferous belt on the north-facing steep slopes
in the surroundings of the lake, shaping the upper tree-line, has taken place.
Abies alba
has retreated to the lower part of the coniferous belt, giving away
to
Picea abies
in many places.
Recent pollen and plant macrofossil data from the sediments of Lake
Ostrezko-2 (Tonkov, Marinova, in press) and from Lake Panichishte (В о z i 1о v a
et al., 2002) revealed that the final late expansion of
Picea
in the Rila
Mountains has coincided with the duration of the Little Ice Age in medieval
time (1550-1850 yrs. AD) when temperatures dropped and humidity increased
( Gr oov e , 1988).
The proposed reconstruction of the vegetation for zone Smr-2 is supported
by the analysis of the modern surface moss pollen samples that are dominated
by
Pinus diploxylon-type, Pinus рейсе,
and partly
Picea.
Acknowledgements.
This investigation was corned out with the financial support through
Project N 101/2004 by the Research Fund at Sofia University „St. Kliment Ohridski“. The author
is thankful to the reviewer Prof. Dr. E. Bozilova for the critical comments and suggestions on the
manuscript.
13
Электронная Научная СельскоХозяйственная Библиотека