GEOLOGICA CARPATHICA, OCTOBER 2005, 56, 5, 447—453
Late Holocene vegetation changes in the Northern Pirin
Mountains (southwestern Bulgaria). Palynological data from
Lake Suho Breznishko and Lake Okadensko
and IVANKA STEFANOVA
Sofia University, Biological Faculty, Department of Botany, 8 Dragan Tzankov, 1164 Sofia, Bulgaria; firstname.lastname@example.org
Limnological Research Center, University of Minnesota, 310 Pillsbury Drive SE, MN 55455 Minneapolis, USA; email@example.com
(Manuscript received July 8, 2004; accepted in revised form March 17, 2005)
Abstract: The pollen stratigraphies of Lake Suho Breznishko (1963 m a.s.l.) and Lake Okadensko (2475 m a.s.l.) in
the Northern Pirin Mountains of southwestern Bulgaria record the vegetation history since about 6000 years ago. An
initial open Betula forest contained minor Pinus peuce, documented by macrofossils, as well as Abies. Conifers that
had dominated at higher elevations elsewhere then expanded downslope, and after 4300 yr BP Pinus peuce was joined
by Pinus diploxylon-type (including P. sylvestris, P. mugo, and P. heldreichii) and Picea. Maxima of microscopic and
macroscopic charcoal, along with increases of Juniperus, Pteridium, non-arboreal pollen (including anthropogenic
indicators), and algal remains, suggest significant human impact on the vegetation after about 4000 yr BP.
Key words: Holocene, Bulgaria, Pirin Mountains, paleoecology, pollen analysis, microscopic charcoal particles.
The numerous glacial lakes and the geographical position
of the Pirin Mountains in southwestern Bulgaria within the
transitional zone between continental and submediterra-
nean climates provide excellent opportunities for paleoeco-
logical investigations and reconstruction of Late Glacial
and Holocene vegetation changes, which have been influ-
enced by many factors, including climatic fluctuations, im-
migration processes, and human impact (Bozilova 1977;
Stefanova & Bozilova 1992, 1995; Stefanova & Oeggl
1993; Panovska et al. 1995; Stefanova 1997, 1999; Bozilo-
va et al. 2002; Tonkov et al. 2002; Atanassova & Stefanova
2003; Stefanova & Ammann 2003; Tonkov 2003). Howev-
er, information is limited concerning human activity as well
forest fires, which are one of the most important natural and
anthropogenic factors in the distribution of natural vegeta-
tion. Today the forests in this area show little human impact,
and no records exist concerning fire frequency. To examine
these issues, this study includes the analysis of microscopic
and macroscopic charcoal particles parallel to pollen analy-
sis in cores from two lakes in the Northern Pirin Mountains.
Because the two lakes are at different elevations and are on
different types of bedrock, comparison of the pollen profiles
could allow evaluation of the effects of these two factors on
the forest composition.
Regional climate and vegetation
The Pirin Mountains (Fig. 1) are composed largely of
Precambrian crystalline rocks (Boyagjev 1959), cut by
numerous glacial cirques now occupied by small lakes.
The northern part of the mountains is the most monolithic,
and the highest part extends up to 2914 m a.s.l.
The climate of the mountains below an altitude of
1000 m a.s.l. is transitional continental/submediterranean,
and above this altitude it is a typical montane climate. The
annual precipitation above 2000 m a.s.l. is 1100—1200 mm,
with a maximum in November—December and a mini-
mum in August (Ivanov et al. 1964).
The nature of the vegetation in the Pirin Mountains is
determined by the elevation and by the distance from the
Mediterranean area. According to Veltshev (1997), several
vegetation belts are represented:
– The lowest belt, up to 500 m a.s.l., is locally repre-
sented only in southern part of the mountains and con-
sists of communities with the Mediterranean elements
Quercus coccifera, Juniperus excelsa, Phyllirea latifo-
– The belt of xerothermic oak forest (about 500—700 m
a.s.l.) is formed by Quercus cerris, Q. pubescens, Q.
frainetto, and Carpinus orientalis.
– In the mesophilous and xeromesophilous Quercus-
Carpinus belt (up to 800—900 m a.s.l. or locally 1000 m
a.s.l.) communities of Quercus dalechampii and Carpi-
nus betulus are typical, but Pinus nigra, Ostrya carpini-
folia, and Corylus avellana also occur.
– The belt of Fagus forest (from 900—1000 to
1500—1600 m a.s.l.) has Fagus sylvatica as dominant, but
it is represented in the Northern Pirin Mountains only by
fragments. Communities of Abies alba, Pinus nigra, P.
peuce, and Picea abies occur locally.
– In the coniferous belt (between 1500—1600 m and
2000—2200 m a.s.l.) communities of Pinus sylvestris and
Picea abies are most abundant. The Balkan endemic spe-
448 ATANASSOVA and STEFANOVA
cies Pinus peuce and the relict subendemic species Pinus
heldreichii are also present.
– The vegetation in the subalpine belt (about 2000—2500 m
a.s.l.) is dominated by Pinus mugo, Juniperus sibirica,
and Vaccinium myrtillus.
– The alpine belt (above 2500 m a.s.l.) communities
of Sesleria comosa, Festuca airoides, Agrostis rupestris,
and Carex curvula are common on silicate terrane and
Sesleria coerulans, S. corabensis, and Carex kitaibeli-
ana on marble terrane.
Sites of investigations
The two sites of investigation are located in different
parts of the Northern Pirin Mountains. Lake Okadensko at
2475 m a.s.l. is situated in the Okadenski cirque in north-
western part of the mountains, where marble occurs in the
bedrock. The lake today is less than a meter deep. Pinus
Fig. 1. Location of the investigated sites in Northern Pirin Mts.
1 – Lake Suho Breznishko (1963 m a.s.l.). 2 – Lake Okadensko
(2475 m a.s.l.).
mugo and Juniperus sibirica grow in its surroundings. The
upper forest limit in the area is formed by Pinus hel-
dreichii, which prefers calcareous substrates. Lake Suho
Breznishko at 1963 m a.s.l. lies in the granitic area in the
northeastern part of the mountains. As the smallest of the
three cirque lakes in the Breznishki cirque, it is 125 m
long and 75 m wide and is largely dried out. Subalpine
communities of Pinus mugo and Juniperus sibirica are
common in the surroundings, as well as scattered Pinus
peuce and Picea abies, which form the upper forest limit.
Material and methods
Coring, chemical treatment, and calculations
The sediment cores were taken with a Dachnowsky corer.
Samples at 2—3 or 5 cm intervals were treated with HF and
acetolysis (Faegri & Iversen 1989). The lowest 10 cm (silt
ko contained no pollen grains, but the rest of the core is rich
in organic matter and wood fragments, in contrast to the
sediments of Lake Okadensko, which consist of gyttja. The
pollen sum of AP (arboreal pollen) + NAP (non-arboreal pol-
len) excludes Cyperaceae and fen and aquatic plants and
also spores of Pteridopsida, and their percentages are calcu-
lated on the basis of the pollen sum. At least 1000 AP grains
were counted for each level. For calculations and drawing
of the pollen diagrams the programmes TILIA and TILIA
GRAPH were used (Grimm 1992). Microscopic charcoal
particles were counted on the pollen slides without addi-
tional preparation (Clark 1982). Microscopic charcoal was
identified as black, opaque, angular fragments. The results
are expressed as concentration in 1 cc of the sediments (us-
ing Lycopodium tablets – Stockmarr 1971). Many authors
recommend the size-class method (Waddington 1969),
which involves measuring the area of each charcoal parti-
cle, but Tinner & Hu (2003) point out that it is unnecessary
to measure charcoal areas in standard pollen slides. Samples
at 5 cm intervals were studied for macroscopic charcoal par-
ticles under a binocular microscope (up to 40
tion), and single seeds of Pinus mugo, P. peuce, and fruits of
Carex were found at different levels in the sediments of lake
Suho Breznishko. The macroscopic charcoal particles are
presented in the charcoal diagram as absolute numbers.
Green algae Pediastrum and Botryococcus also occur in the
pollen slides. Their frequency is presented as a percentage
of the pollen sum. Pediastrum and Botryococcus are usu-
ally classified as indicators of eutrophic to mesotrophic
conditions (Komarek & Jankovska 2001).
Results and discussion
Lithology of Lake Suho Breznishko sediments
0—10 cm Polytrichum sp. mosses;
10—23 cm light brown gyttja;
23—65 cm dark brown gyttja;
65—105 cm black gyttja;
HOLOCENE VEGETATION IN THE PIRIN MTS (SW BULGARIA) 449
105115 cm dark grey-brown gyttja;
115120 cm grey gyttja with an admixture of sand;
120130 cm light yellowish silt with small stones of
Lithology of Lake Okadensko sediments
05 cm organic material;
585 cm grey gyttja;
85100 cm grey gyttja with an admixture of sand.
Radiocarbon dating was performed at the AMS Lab of
the University of Arizona. Radiocarbon dates (uncali-
brated) are listed in Table 1 and shown on the pollen dia-
grams. For Lake Okadensko one sample of gyttja was
dated by AMS because macrofossils were not found.
To facilitate description and understanding of the veg-
etation succession, the percentage pollen diagrams
(Figs. 2 and 3) are divided into pollen assemblage zones
Table 1: Radiocarbon dating was performed at AMS Lab of Uni-
versity of Arizona.
Table 2: Description of the pollen zones.
(PBr-1 to PBr-4 in Lake Suho Breznishko and POk-1 to
POk-3 in Lake Okadensko). The zone boundaries were
determined by CONISS (Grimm 1992). Short descriptions
of the pollen zones are presented in Table 2.
Lake Suho Breznishko
PAZ PBr-1 (120104 cm) represents forest development
before 5740 yr BP, when open communities of Betula pen-
dula (2635 %) surrounded the lake, which is the lowest
cirque lake in the region. Also at the mire Praso (1900 m)
and at Lake Popovo 6 (2190 m) Betula was dominant be-
tween 7200 and 6500 yr BP (Stefanova & Oeggl 1993;
Stefanova & Bozilova 1995). At Suho Breznishko Abies
(57 %), Pinus haploxylon-type (P. peuce 35 %) and Pi-
nus diploxylon-type (P. sylvestris, P. mugo 20 %) are well
represented. They had already expanded at higher eleva-
tions by 6500 yr BP, as around Lake Dalgoto at 2310 m
(Stefanova & Ammann 2003) and Lake Ribno Banderishko
at 2190 m (Tonkov et al. 2002), although at the latter site P.
peuce is rare. Pollen of Quercus (35 %), Tilia (39 %), Ul-
mus, and Corylus, believed to have blown up from lower
elevations (Stefanova & Ammann 2003), are well repre-
sented, because the relatively high values of NAP (35 %) sug-
gest an open landscape with low local pollen production.
In PAZ PBr-2 (10473 cm) the increase of Abies (710 %),
Pinus peuce (617 %), and Pinus diploxylon-type (up to
50 %) occurred after 5740 yr BP, indicating the lowering
of the conifer belt in the mountains, partly replacing Betu-
la, which shows fluctuating values (1025 %). At Lake Suho
Breznishko the presence of P. peuce is confirmed by the finding
Lab. No Depth (cm)
Lake Suho Breznishko 1963 m a.s.l.
Lake Okadensko 2475 m a.s.l.
LPAZ Depth (cm)
LPAZ Depth (cm)
Picea (25 %) and Fagus (up to 3 %) are characteristic.
High values for Pinus diploxylon-type (4557 %).
Increase in anthropogenic indicators like Scleranthus,
Pinus diploxylon-type is the dominant with
5060 %, Pinus peuce, Abies, and Picea
decrease. Secale and Triticum oc c ur as
indicators of human activity increse.
Pinus peuce (up to 23 %), Abies (12 %), and Pinus
diploxylon-type (up to 60 %) have their maximal values.
First increase in Picea and Fagus.
Upper border is marked by decrease in Pinus peuce and
Picea has an absolute maximum of 12 %.
Pinus peuce (520 %) and Pinus diploxy-
lon-type (1060 %) fluctuate.
Decrease in Picea at the upper border.
Increase of Abies (710 %), Pinus peuce (617 %), and
Pinus diploxylon-type (2550 %). Betula (1025 %) is
Sharp decrease in Betula characterizes the upper border.
Among the arboreal taxa (AP up to 85 %)
dominant are Abies (up to 20 %), Pinus
peuce (1015 %), and Pinus diploxylon-
type (up to 50 %).
Upper border is marked by decrease of
Abies and increase of Picea.
Betula has maximal values with 2035 %. Pinus
diploxylon-type is 1030 % and Pinus peuce, Abies,
Quercus, Tilia, and Corylus are 39 %. Among the herb
taxa (NAP up to 35 %) Poaceae, Taraxacum-type,
Achillea-type, Rumex and Apiaceae are important.
Upper border is marked by decrease of Betula and
increase of Pinus peuce, Abies, and Pinus diploxylon-
450 ATANASSOVA and STEFANOVA
of two seeds at 85 cm (estimated date 5200 yr BP). Microscopic
charcoal has a maximum at 75 cm, where macroscopic charcoal
was also found, one piece being 0.5 cm long.
In PAZ PBr-3 (73—43 cm) pollen maxima of Pinus peuce
(19—23 % and Abies 11—12 %) were supplemented by Pinus
stomata as well as two seeds of P. mugo (at 45 and 55 cm) and
two seeds of P. peuce (at 55 cm).
PAZ PBr-4 (43—0 cm, 4300 yr BP to present) shows high
percentages of Pinus diploxylon-type (45—57 %). Finding of
one seed of P. mugo at 35 cm reflects a further expansion of
P. mugo. P. peuce and Abies were reduced, as is the case at
Dalgoto (Stefanova & Ammann 2003). Picea increased, as it
Fig. 2. Simplified percentage pollen diagram of Lake Suho Breznishko.
Fig. 3. Simplified percentage pollen diagram of Lake Okadensko.
became a dominant tree in the upper part of the coniferous
belt, along with P. peuce (Stefanova 1999; Stefanova & Am-
mann 2003). Fagus also expanded at Lake Suho Breznishko
at this time.
Palynological results at Lake Kremensko 5 (Atanassova &
Stefanova 2003) indicate possible Late Glacial refugia of Pi-
cea in the Pirin Mountains, but expansion is rather late in
comparison with the Carpathian Mountains (Ralska-
Jasiewiczowa 1980), where it became important in the mid-
Holocene, and the Gutaiului Mountains in NW Romania
(Bjorkman et al. 2003), where it occurred already by
10,750 cal yr BP.
HOLOCENE VEGETATION IN THE PIRIN MTS (SW BULGARIA) 451
Microscopic charcoal particles show maxima at 32 cm
and 23 cm and, macroscopic charcoal was also found at
20 cm and at 25 cm (Fig. 4).
Increase of Botryococcus in PAZ PBr-3 and PBr-4 could
indicate increased eutrophication of the lake.
The pollen diagram for Lake Okadensko shows that the
vegetation changes around the lake for the last about 4300
years are similar to those around Suho Breznishko. PAZ
POk-1 shows the last stage of high distribution of Abies to-
gether with Pinus peuce and P. diploxylon-type (including
P. sylvestris, P. mugo, and P. heldreichii). The beginning of
PAZ POk-2 marks the increase of Picea in the region shortly
before 2140 BP. Increasing percentages of Pinus diploxy-
lon-type are connected with expansion of P. mugo around
the lake and the dominance of P. heldreichii and P. sylves-
tris in the coniferous belt. The higher elevation of Lake
Okadensko explains the lower concentration of microscopic
charcoal particles in the sediments (Fig. 5). Macroscopic
charcoal particles were found at 80 and at 55 cm.
Archaeological sites in the area of the Northern Pirin
Mountains are scarce, but the Early Neolithic settlement
of Dobriniste in the foothills indicates that this area was
occupied rather early – about 5600—5500 BC (Nikolov
1996). The valley of the Struma River was also a very
favourable place for Neolithic people (Grebska-Kulowa
1998). No data exist concerning the prehistoric devel-
opment of animal husbandry in the Pirin Mountains,
but it is known that in historical times some semi-no-
madic tribes drove their flocks from high parts of the
mountains (Rila, Pirin, Rhodopes) to the Aegean Sea in
autumn and back to the high mountains in summer.
In the pollen diagram for Lake Suho Breznishko the first
sharp increase of microscopic and macroscopic charcoal
particles occurs at 75 cm (upper boundary of PAZ PBr-2)
(Fig. 4). A slow increase of Juniperus occurs in the PAZ
PBr-3. This could be interpreted as the result of a local fire
as the first forest clearance in the region. Significant presence
of anthropogenic pollen indicators in this PAZ are absent.
Increase in NAP values and significant change in the taxo-
nomic composition of the NAP pollen types in PAZ PBr-4
show features of increasing anthropogenic impact after
4353 BP. Increase in percentages of Chenopodiaceae, Scler-
anthus, Plantago lanceolata, Cirsium-type,
aviculare, and the appearance of Pteridium suggest grazing
in close vicinity of the lake. Increase of microscopic and mac-
roscopic charcoal at 20—32 cm depth in the sediments indicates
possible fire in the surroundings. We suggest that fire was used
for forest clearance to open areas for grazing and husbandry.
At the same time after 4353 BP pollen grains of Secale
and Cerealia-type occur in the sediments, indicating human
activity in the lower part of the mountains.
Maximal occurrence of microscopic charcoal particles
with single macroscopic charcoal pieces in Lake Okadensko
Fig. 4. Charcoal diagram of Lake Suho Breznishko.
Fig. 5. Charcoal diagram of Lake Okadensko.
452 ATANASSOVA and STEFANOVA
(after 2140 BP) is synchronous with the increase of NAP,
finds of Secale and Triticum type, and increases of Cichori-
aceae, Scleranthus, and Chenopodiaceae. We suggest that
forest clearance by fire in the vicinity of Okadensko Lake
was also possible at that time. Probably the combination of
climatic changes over the last 4000 years and also the human
activity in the high mountains forced the spread of Juniperus
and Pinus mugo into the upper forest limit.
These are the first data on the use of fire for forest clearance
in the Pirin Mountains, but additional investigations are nec-
essary for more detailed conclusions.
The pollen records of Lake Suho Breznishko and Lake
Okadensko provide new information on the Holocene vege-
tation changes caused by climatic fluctuations but also by
forest fire in the Northern Pirin Mountains. The paleoecologi-
cal reconstruction starts from approximately 6000 years BP
with the expansion of Betula forests, forming the upper tree-
line together with Pinus sylvestris, P. peuce, and P. mugo. Af-
ter 5700 years BP coniferous vegetation expanded, replacing
Betula forests. At both sites the prominence of Abies shifted
to that of Picea, although at the lower site the change oc-
curred about 2000 years earlier, and the Abies phase was ac-
companied by Alnus, Betula, Quercus, Tilia, and Corylus
and the Picea phase by Fagus, whereas at the higher site
these temperate taxa are poorly represented. Expansion of Pi-
cea was probably forced by global climatic changes (van
Geel et al. 1998) as well as by human activity. Forest distur-
bance has been shown to favour spruce regeneration in the bo-
real forest of northern Sweden (Bradshaw & Zackrisson 1990).
The present study illustrates the importance of the analysis
of macrofossils and of micro- and macro- charcoal particles
parallel to the pollen analysis of mountain-lake sediments.
Stomata analysis confirms the presence of important taxa in
the surroundings of the investigated sites. Large charcoal par-
ticles indicate local fire, which could be an important factor
for forest changes. The general conclusion of the present
study is that fire was used for forest clearance to open areas
for grazing and husbandry in the high Pirin Mountains after
5700 yr BP. Probably not only climatic changes in about the
last 4000 years but also the human activity in the high moun-
tains forced the spread of Juniperus and Pinus mugo at the
upper forest limit and the expansion of Picea.
We thank Plamen Stefanov, Ivaylo Ste-
fanov, and Mihail Bonkin for taking the cores, Elena Marino-
va for the maps, and H.E. Wright for discussion and
improvement of the English text.
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