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Late Holocene vegetation changes in the Northern Pirin

Mountains (southwestern Bulgaria). Palynological data from

Lake Suho Breznishko and Lake Okadensko






Sofia University, Biological Faculty, Department of Botany, 8 Dragan Tzankov, 1164 Sofia, Bulgaria;


Limnological Research Center, University of Minnesota, 310 Pillsbury Drive SE, MN 55455 Minneapolis, USA;

(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.

Study area

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-
lia, etc.

– 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-

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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

× magnifica-

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;

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HOLOCENE VEGETATION IN THE PIRIN MTS  (SW BULGARIA)                                            449

105–115  cm  dark  grey-brown  gyttja;

115–120 cm  grey  gyttja  with  an  admixture  of  sand;

120–130 cm  light  yellowish  silt  with  small  stones  of


Lithology  of  Lake  Okadensko  sediments

0–5 cm  organic  material;

5–85 cm  grey  gyttja;

85–100 cm  grey  gyttja  with  an  admixture  of  sand.

Radiocarbon  dating

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.

Pollen  stratigraphy

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  (120–104 cm)  represents  forest  development

before  5740 yr  BP,  when  open  communities  of  Betula  pen-

dula  (26–35 %)  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

(5–7 %),  Pinus  haploxylon-type  (P.  peuce  3–5 %)  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  (3–5 %),  Tilia  (3–9 %),  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 (104–73 cm) the increase of  Abies (7–10 %),

Pinus  peuce  (6–17 %),  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  (10–25 %).  At  Lake  Suho

Breznishko the presence of P.  peuce is confirmed by the finding

Sample ID 

Lab. No  Depth (cm) 


C Dates 

uncal. BP 





Suho Br-1 

Suho Br-2 











4353± 50 

5742± 44 


roots charcoal 



Lake Suho Breznishko 1963 m a.s.l. 

Lake Okadensko 2475 m a.s.l. 

LPAZ  Depth (cm) 


LPAZ  Depth (cm) 




Picea (2–5 %) and Fagus (up to 3 %) are characteristic. 

High  values  for  Pinus  diploxylon-type  (45–57  %). 

Increase  in  anthropogenic  indicators  like  Scleranthus, 








Pinus diploxylon-type is the dominant with 

50–60  %,  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 (5–20 %) and Pinus diploxy-

lon-type (10–60 %) fluctuate. 

Decrease in Picea at the upper border. 



Increase of Abies (7–10 %), Pinus peuce (6–17 %), and 

Pinus  diploxylon-type  (25–50  %).  Betula  (10–25  %)  is 

still significant. 

Sharp decrease in Betula characterizes the upper border. 



Among  the  arboreal  taxa  (AP  up  to 85  %) 

dominant  are  Abies  (up  to  20  %),  Pinus 

peuce  (10–15  %),  and  Pinus  diploxylon-

type (up to 50 %). 

Upper  border  is  marked  by  decrease  of 

Abies and increase of Picea. 

PBr-1  104–120 

Betula  has  maximal  values  with  20–35  %.  Pinus 

diploxylon-type  is  10–30  %  and  Pinus  peuce,  Abies, 

Quercus, Tilia, and Corylus are 3–9 %. 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-






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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.

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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.

Lake Okadensko

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.

Human impact

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.

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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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