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461 Journal of Paleolimnology 21: 461476, 1999. 1999Kluwer Academic Publishers. Printed in the Netherlands.
Environmental history of the Colombian savannas of theLlanos Orientales since the Last Glacial Maximum from
lake records El Pinal and Carimagua*
Introduction
The Late Quaternary environmental history of Neo-
tropical lowland ecosystems is still poorly known
despite their importance in the verification of global
climate models and a better understanding of global
biodiversity (Clapperton, 1993; Markgraf, 1993). The
major Neotropical lowland ecosystems are the two
main rain forest areas (Amazonia, and the Pacific rain
forest area of Choc) and several savanna areas. In
northern South America, the Llanos Orientales in
Colombia and the Orinoco Llanos in Venezuela
represent, after the cerrado in Brazil, the second
major Neotropical savanna ecosystem. Other large
savanna areas in northern South America (Figure 1)
are the Gran Sabana in Venezuela, the Rupununi-Rio
Branco savanna in Surinam, the Rio Jari savanna, and*This paper was presented at the 7th International Symposium
on Palaeolimnology (1997), held at Heiligkreuztal, Germany
Hermann Behling & Henry Hooghiemstra
University of Amsterdam, Hugo de Vries-Laboratory, Department of Palynology and Paleo/Actuo-ecology,
Kruislaan 318, 1098 SM Amsterdam (The Netherlands Centre for Geo-ecological Research, ICG), The
Netherlands (E-mail: [email protected])
Received 9 December 1997; accepted 6 June 1998
Key words: Colombia, Llanos Orientales, pollen analysis, savanna, gallery forest, vegetation and climate
history, Late Quaternary
Abstract
Late Quaternary environments have been studied by pollen analysis of lake sediments from the savannas of the
Colombian Llanos Orientales at 180 m elevation. The pollen record form Laguna El Pinal (408N, 7023W),
dated by 6 AMS radiocarbon dates, starts at 18,290 14C yr B.P. The record from Laguna Carimagua (404N,
7014W), also dated by 6 AMS dates, starts at 8270 14C yr B.P. Both records show a landscape dominated by
grassland savanna with only few woody savanna taxa, such as Curatella andByrsonima, frequent fires, and little
occurrence of forest and/or gallery forest along the rivers. The savanna ecosystem at the studied sites was relatively
stable during the last 18,000 yrs, but minor changes in floral composition, and in the proportion of savanna/forest,
have been recorded. Very little gallery forest and the non permanent lake conditions of Laguna El Pinal reflect
the driest period, interpreted to reflect low rainfall rates and long dry seasons during the Last Glacial Maximum
until 10,690 14C yr B.P. During the Late Glacial, Laguna El Pinal was a permanent shallow lake, and changed into
a lake with higher water levels during the Holocene, indicating wetter conditions. Expansion of regional gallery
forest also started at around 10,690 14C yr B.P. Little vegetational change observed in Laguna Carimagua at
5570 14C yr B.P., in combination with a simultaneous decrease of savanna observed in previously studied lakes,
suggest a change to regional wetter conditions. Thus, the Holocene before 5500 14C yr B.P. was somewhat drier
than the following period until about 3850 14C yr B.P. In both records, Late Holocene lake deposits are incomplete.
Shore vegetation of Laguna Carimagua always included a minor contribution of the palmsMauritia andMauritiella.
The marked increase of palms during the last c. 3800 yrs points to increased human impact on the vegetation
under the wettest Holocene climate regime.
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462
Figure 1. Map showing the major savanna areas of northern South America: (1) Llanos Orientales in Colombia and Orinoco Llanos in
Venezuela, (2) Gran Sabana, (3) Rupununi-Rio Branco savanna, (4) Rio Jari savanna and (5) coastal Guianan savanna. The inset map shows the
geographical location of the savanna sites mentioned in the text: Laguna El Pinal, Laguna Carimagua, Laguna Angel, Laguna Sardinas and
Laguna de Agua Sucia.
the belt of coastal Guianan savannas (Hueck & Seibert,
1972).
The first palynological data on the Holocene
vegetation history and climatic change of the Llanos
Orientales were published by Wijmstra & Van der
Hammen (1966). Other palynological data from
savanna ecosystems of northern South America are
available from the Gran Sabana in Venezuela (Rull,
1992), the Rupununi savanna in Surinam (Wijmstra
& Van der Hammen, 1966) and the belt of coastal
Guianan savannas in Surinam (Wijmstra, 1971),
Guyana (Van der Hammen, 1963) and French Guiana
(Tissot & Marius, 1992).
We collected lacustrine sediment cores for palyno-
logical studies to explore the regional history of
vegetation, climate, and human influence on the
tropical savanna ecosystem of the Llanos Orientales.
Starting from the city of Villavicencio, which is located
at the foothills of the Eastern Cordillera, we cored 13
lakes and swamps along a 500 km long transect from W
to E (Figure 1). The sites are located between the
latitudes of 330 and 430 N and the longitudes of 69
and 74 W, at elevations between 80 and 450 m in the
provinces of Meta and Vichada. In this paper we present
new pollen records of Laguna El Pinal and Laguna
Carimagua to compliment the information of the
previously studied Laguna Angel and Laguna Sardinas
(Behling & Hooghiemstra, 1998).
Study sites
Both lakes, Laguna El Pinal (408N, 7023W) and
Laguna Carimagua (404N, 7014 W) are about 20 km
distant from each other and lie at the same elevation of
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463
about 180 m in a relatively flat area in the central part
of the Llanos Orientales in the province of Meta
(Figure 1). The distance to Villavicencio, located atthe foothills of the Andes, is about 270 km.
Laguna El Pinal (Figure 2) is a shallow lake and had
a water depth of 70 cm during the coring operation, at
the end of February 1996 in the dry season. The lake
is c. 1200 m long and c. 300 m wide and looks like an
old meander. However, it is unlikely that it was a part
of a river, as the distance to the next river system of
the Rio Meta is several kilometers. Laguna Carimagua
(Figure 3) is also an isolated and shallow lake, c. 3 km
long and c. 1.5 km wide. The water depth was 80 cm
during the period of the coring, at the end of February.
The lake is located in a shallow depression in a flat area,
located above the large river system of the Rio Metain the north, and several much smaller river systems
at the south. Within several kilometers distance to the
lake, several small rivers, bordered by gallery forest,
originate.
The present-day vegetation of the studied region of
the two lakes is a grass savanna, which is being used
as pasture land. Extended areas of gallery forest grow
along the small river bodies. Laguna El Pinal is
surrounded by stands of the palmMauritia (local name
morichi) and by small areas of shrubby vegetation,
probably secondary. Laguna Carimagua, which is
located within the protected area of the agriculturalexperimental station Centro de Investigacion para la
Atillanura, Carimagua, also called Carimagua, is
surrounded mainly by stands ofMauritiella and some
Mauritia. Several small islands of pure Mauritiella
palms are found in the lake area (Figure 4). At the
northern edge, the lake is surrounded by grassland
(Figure 3), whereas the other parts of the lake arebordered by small patches of forest.
The vegetation of the Llanos Orientales is primarily
characterized by different herbaceous savannas with
shrubs and shrubby trees, and gallery forest along the
rivers. At some places between the rivers, patches of
forest occur in which the plant composition is
comparable to Amazonian forest. General data on the
flora and ecology of the savannas of the Llanos were
published by Cuatrecasas (1989), Gentry (1993),
Huber (1987), Hueck (1966), Hueck and Seibert
(1972), Pinto-Escobar (1993) and Vareschi (1980).
Blydenstein (1967) recognized 10 different plant
associations in the savannas of the Llanos Orientales.
According to Cuatrecasas (1989), characteristic taxa
for grass savannas are Poaceae, belonging to the genera
Andropogon , Eragrostis , Axonopus, Paspalum,
Aristida, Ctenium andPanicum. Characteristic shrubs
belong to the family Melastomataceae (Miconia,
Tibouchina), Papilionaceae (Clitoria), Ceasalpiniaceae
(Cassia), Lamiaceae (Hyptis), Sterculiaceae (Wal-
theria), Malvaceae (Sida,Pavonia) and other families.
Characteristic larger shrubs or trees, which can be also
very small in size (less than 50 cm high in areas with
frequent burning), are Curatella americana (Dill-
eniaceae), Byrsonima crassifolia (Malpighiaceae),Bowdichia virgilioides (Papilionaceae) and Pal-
icourea rigida (Rubiaceae). The composition and
distribution of different savanna plant communities
can be seen as the result of several environmental
Figure 2. View on Laguna El Pinal with stands ofMauritia palm around the lake.
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464
factors, including pedological, physical, biotic and
climatic factors (Cole, 1982, 1986; Medina & Silva, 1990).
Along rivers, lake shores and swampy areas, dense
stands of the palmMauritia are often found.Mauritia
swamp forest is called morichal. The less tall palm
Mauritiella grows at lake shores in shallow water and
surrounds several lakes in the Llanos Orientales.
The climate of the Llanos Orientales is strongly
seasonal. The marked annual dry period lasts about 4
5 months, from mid November to mid March. In the
northern part of the Llanos Orientales (province of
Arauca) the dry season is longer than in the southern
part (provinces of Meta and Vichada). In the Llanos
Orientales there is a precipitation gradient from
12002000 mm/yr in the northern region near the
Venezuelan border, to about 20002500 mm/yr in the
southern and southwestern parts of the savanna area.
The transition from savanna to the Amazon rain forest
occurs in the south, where annual precipitation is over
24002500 mm/yr. Mean annual temperature in the
study area is 2627 C with less than 3 C variation
between monthly means. The small annual temperature
oscillation contrasts to the 1015 C daily variation
(Blydenstein, 1967; Snow, 1976).
Figure 3. View on Laguna Carimagua, bordered by mainlyMauritiella palm vegetation, but at the northern border by open grass savanna.
Figure 4. Mauritiella-dominated vegetation on the islands of Laguna Carimagua.
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Methods
We used an echo sounder to determine the bathymetryof each lake. Sediment cores were collected in the lake
center where water was deepest. We used a modified
Livingstone piston corer from a wooden platform,
which was fixed on two inflatable rubber boats. The
studied core from Laguna El Pinal is 72 cm long and
from Laguna Carimagua is 95 cm long. Within 3 weeks
sediment cores were transported by air freight to
Amsterdam and stored at 4C in the laboratory prior
to analysis.
Accelerator Mass Spectrometry (AMS) radio-
carbon dates were obtained from 6 bulk samples of
1 cm core interval from core Laguna El Pinal, and 6
samples from core Laguna Carimagua were collectedand dated at the Van der Graaff Laboratory of the
University of Utrecht (Van der Borg et al., 1987).
For pollen analysis, samples of 1 cm3 were taken
in 2 cm intervals along the two cores. Prior to pro-
cessing, one tablet of exoticLycopodium spores was
added to each sample for calculation of pollen
concentration and pollen influx. All samples were
prepared using standard pretreatment techniques
including sodium pyrophosphate, acetolysis, and heavy
liquid separation by bromoform (Faegri & Iversen,
1989). Pollen residues were mounted in glycerin
gelatin and analyzed with a Zeiss microsope at 500 magnification. Identification of pollen grains and
spores was aided by pollen morphological descriptions
published by Behling (1993), Herrera & Urrego
(1996), Hooghiemstra (1984), Roubik & Moreno
(1991) and the reference collection of the Hugo de
Vries-Laboratory. About 300 pollen grains from non-
aquatic taxa were counted for the pollen sum.
The sample from Laguna El Pinal at 60 cm depth
contains too little pollen to obtain reliable statistics.
Pollen grains below 60 cm core depth were less well
preserved but a meaningful analysis was still possible.
Samples below 81 cm from Laguna Carimagua contain
either none, or a very low number of badly preserved
pollen grains; therefore this core interval was excluded
from analysis. Carbonized particles were not counted
on the pollen slides because during heavy liquid
separation many charcoal particles were eliminated
and, therefore, such results are not meaningful.
The pollen and spore data are presented in pollen
diagrams as percentages of the pollen sum. The pollen
sum excludes aquatic taxa, fern spores, moss spores,
fungal spores, and algae. Species of Cyperaceae grow
frequently in the savanna vegetation and were therefore
included in the pollen sum. We arrived at the following
ecological groups of fossil pollen: (1) shrubs and
trees from the forest and gallery forest along rivercurrents, (2) savanna shrubs and trees, (3) savanna
herbs, (4) aquatic taxa from lake shores, and (5) ferns.
Pollen diagrams were plotted with the software
TILIAGRAPH. For calculations we used TILIA and for
the cluster analysis of terrestrial pollen taxa we used
CONISS (Grimm, 1987).
Stratigraphy
The following lithological sequence was observed in
the cores:
Laguna El Pinal
050 cm black fine detritus mud, compact, very rare
plant remains, somewhat fine sandy
5060 cm gray-greenish fine sand, very compact
6064 cm gray-greenish clay with fine sand, very
compact
6472 cm light gray clay, compact, somewhat fine
sandy
Laguna Carimagua
018 cm dark brown-dark gray fine detritus mud,
medium compact, plant remains are very rare,somewhat fine sandy. At 18 cm depth: 1 cm thick
wood fragment
1830 cm dark brown-dark gray fine detritus mud,
somewhat clayey, medium compact, plant remains
are very rare, somewhat fine sandy
3060 cm dark brown-dark gray fine detritus mud,
somewhat clayey, medium compact, several grass
roots
6076 cm dark brown-dark gray clayey fine detritus
mud, compact, plant remains are very rare,
somewhat fine sandy
7681 cm dark brown-dark gray clay with fine
detritus mud, very compact, macroscopic plant
remains not visible, somewhat fine sandy
8195 cm white very fine silt, clayey, very compact.
Chronological control
The AMS radiocarbon dates of the two lake cores are
listed in Table 1. The 6 AMS dates from Laguna El
Pinal indicate glacial and Holocene lake deposits with
low sedimentation rates. The basis of the profile falls
during the Last Glacial Maximum (LGM), dated at
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466
18,290 90 14C yr B.P. The lowermost 20 cm of the
core represents 8000 yrs of the glacial period, suggesting
a very low sedimentation rate. Gaps, probably becauseof the dry environment (ephemeral lake, see discussion
of the results), are possible. The Late Glacial/Holocene
transition is well represented, but mid and late Holocene
deposits are apparently incomplete. Deposits of the
last 1000 yrs are not represented in the core. Similar
ages of AMS dates at 24 cm depth of 1065 14C yr B.P.,
and at 2 cm depth of 1261 14C yr B.P. suggest that the
topcore sediments are disturbed or absent. The
stratigraphy does not show a clear indication for gaps
in sedimentation.
The 6 AMS dates from Laguna Carimagua indicate
the deposit to cover the Holocene. The pollen record
begins at 80 cm depth, dated 8270 14C yr B.P. The AMSdate from the sample of the base of the core at 94 cm
depth is only 7830 14C yr old and might be contaminated
during core recovery, or by younger carbon from
decomposed rootlets. This date has been excluded for
the age calculations of the pollen zones. The
sedimentation rate in the uppermost part of the core is
very low and may suggest that sediment accumulation
is incomplete. The last c. 1400 yrs are not represented
in the core.
Laguna El Pinal
The pollen diagram of core El Pinal shows the most
abundant fossil pollen and spore taxa out of the 95
different types which have been identified (Figures 5a
& 5b). About 16 pollen types are still unknown. Pollen
concentration and pollen influx values are low in the
lower part of the core. Pollen concentration is higher
in the middle part of the core. Highest concentrationand influx values are found in the uppermost core
section. Charcoal particles are abundant in all pollen
samples, but are not quantitatively documented for
reasons mentioned earlier.
Based on cluster analysis, 3 pollen zones were
recognized in the pollen record of Laguna El Pinal:
zone ELP-I (7260 cm, c. 18,29010,690 14C yr B.P.,
6 samples), zone ELP-II (6049 cm, 10,6909340 14C yr
B.P., 5 samples), and zone ELP-III (490 cm, 9340105014C yr B.P., 25 samples).
The pollen record of Laguna El Pinal is char-
acterized throughout by savanna herb pollen types (95
80%), dominated by Poaceae, lower percentages ofCyperaceae, Asteraceae and several other herb taxa.
Highest values of Poaceae (8592%) are found in
zone ELP-I. The group of forest and gallery forest
shrubs and trees show a low representation between 5
and 17%. These shrub and tree percentages increase
from 5% in zone ELP-I to 1015% in zone ELP-II.
The group of forest and gallery forest shrubs and trees
consists mainly ofMauritia-type, Alchornea, Are-
caceae and Cecropia (highest percentages in zone
ELP-I), Melastomataceae, Myrtaceae and Celtis
(highest values in zone ELP-II), and some other taxa
with low representation. The representation of the groupof savanna shrubs and trees,Byrsonima, Curatella and
Didymopanax is very low, with values of < 12%.
Fern spores, except forIsoetes, are found in low
percentages.Isoetes spores are absent or rare in zone
Table 1. List of AMS radiocarbon dates of the samples of cores Laguna El Pinal and Laguna Carimagua, Llanos Orientales, Colombia
Lab. number Depth (cm) 14C yr B.P. 13C/12C r. Calendar age (cal B.P.)
Laguna El Pinal
UtC-5830 2 1065 36 27.1 979935
UtC-5831 24 1261 36 27.9 12601162
UtC-5832 48 9020 80 27.3 100359930
UtC-5833 52 10280 50 27.8 1224711963
UtC-5834 62 10790 60 25.6 1279712638
UtC-5481 72 18290 90 22.6 20093 19704
Laguna Carimagua
UtC-6075 0 1357 36 26.7 12951269
UtC-6076 11 4408 38 27.9 50405006, 49954872
UtC-6077 32 4999 40 28.2 58475834, 57495700,
56975663
UtC-6078 57 5522 41 27.6 63886376, 63146288
UtC-6079 80 8270 60 26.2 93739194, 91719152,
91289093, 90689049
UtC-4907 94 7830 60 26.7 86418637, 86048496
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ELP-I, abundant in zone ELP-II and less frequent in
zone ELP-III. Aquatic taxa are mainly represented by
Sagittaria, Eichhornia and in low percentagesUtricularia, Typha, Cabomba and Nymphoides.
Pollen grains of aquatics are rare or absent in zone
ELP-I, increase to 7% in zone ELP-II, and to 20% in
zone ELP-III. Cabomba, except for only one single
grain, is only found in zone ELP-III. Algal colonies of
Botryococcus are represented in all samples, but in the
lower part of the core percentages are higher. Fungal
spores show relatively low percentages.
Laguna Carimagua
The pollen diagram from Laguna Carimagua shows the
most abundant fossil pollen and spore taxa out of the98 identified types, including 14 unknown types
(Figures 6a & 6b). The downcore values of the pollen
concentration are relatively stable, but increase
slightly in the uppermost part of the core. Pollen influx
is highest in the middle part of the core. Charcoal
particles are abundant in all pollen samples, but are not
quantitatively documented for reasons mentioned
earlier.
Based on the cluster analysis and major changes
in the pollen assemblages, 3 pollen zones were rec-
ognized in Laguna Carimagua: zone CAR-Ia (8057 cm,
8270557014
C yr B.P., 12 samples), zone CAR-Ib(5711 cm, 55703850 14C yr B.P., 23 samples), and
zone CAR-II (110 cm, 38501360 14C yr B.P., 6
samples).
The pollen record of Laguna Carimagua is marked by
a high representation of pollen of savanna herbs (80
90%), primarily Poaceae and Cyperaceae. Percentages
decrease from 80% in zone CAR-Ib to 50% at the end
of zone CAR-II. The group of forest and gallery forest
shrubs and trees, primarily represented by pollen grains
of Mauritia-type, Mauritiella-type, Moraceae/
Urticaceae, Melastomataceae,Alchornea and Cecropia
show low percentages between 10 and 20%, but
increase up 50% in zone CAR-II. Related to this
ecological group there are a few differences between
subzones CAR-Ia and CAR-Ib: slightly higher per-
centages of the Mauritiella-type in zone CAR-Ia, and
slightly higher percentages of taxa such as Mimosa,
Acalypha and Macrolobium-type in zone CAR-Ib.
Comparing pollen zones CAR-I and CAR-II, it is obvious
that zone CAR-II is characterized by a high repre-
sentation ofMauritiella-type, higher percentages of
Mauritia-type,Alchornea, and Cecropia, and decreasing
percentages of Poaceae,Eichhornia andIsoetes.
Pollen grains of Byrsonima, Curatella, Didy-
mopanax, which belong to the group of savanna shrubs
and trees, are very low in the pollen record (< 12%).Aquatic taxa are mainly represented by Sagittaria and
Eichhornia, but also by a few pollen grains from
Ludwigia, Typha,Polygonum andNymphoides. Apart
from the significantly low percentages ofEichhornia
in zone CAR-II, aquatic taxa show little changes in the
downcore representation. The curve forBotryococcus,
as well as fungal spores, show clear fluctuations in the
pollen diagram. Percentages of the aquatic fernIsoetes
are highest in the lower part of the record and decrease
in zone CAR-Ib to be almost absent in zone CAR-II.
Reconstruction of paleoenvironmental change and
discussion of the results
From the LGM to the Late Glacial very little or no
pollen grains of aquatic taxa are present, and sub-
mersed aquatic Isoetes was absent in the Laguna El
Pinal. This suggests that the lake existed mainly during
the wet season, reflecting a dry environment with a
marked long dry season. Poorly preserved pollen
grains in the sediments representing this time period
might be caused by such an ephemeral lake. The marked
increase ofIsoetes spores and the presence of aquatic
taxa such as Sagittaria points to the formation of a
permanently shallow lake during the Late Glacialperiod from 10,690 14C yr B.P. onward. Precipitation
was probably higher and the dry season shorter than
during the previous period. It is interesting to mention
that in the province of Arauca, some 300 km further
north near the Venezuelan border, shallow lakes dry out
completely during the dry season and do not contain
any deposits yielding pollen. In Arauca annual pre-
cipitation (about 1200 mm) is lower and the dry
season (about 5 months) is longer than in region of the
lakes El Pinal and Carimagua.
The pollen record of El Pinal indicates the pre-
dominance of grassland savanna during the recorded
part of the last glacial and the Holocene. Although an
unknown fraction of the carbonized particles was lost
during sample preparation, the still high abundance of
these particles throughout the sediment core indicates
a high burning frequency. Savanna shrubs and trees were
apparently not frequent in the grasslands. Comparing
the proportions of the different ecological groups,
forested areas surrounding lakes or occurring along
small water courses were relatively rare. The pollen
record shows a Late Quaternary savanna ecosystem
with little change, but during the Late Glacial, around
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Figure5a.Percentagepollendiagramo
fcoreLagunaElPinal,LlanosOrientales,Col
ombia.
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470
Figure6a.Percentagepollendiagramof
coreLagunaCarimagua,LlanosOrientales,Colombia.
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471
Figure6b.Summarypollendiagramincludingpollenconcentrationandpolleninfluxr
ecords,andtheclusteranalysisdendrogramo
fLagunaCarimaguna.
Mauritia-typecurvecolored
blackinthesumo
fforestandgalleryfo
restshrubsandtrees.
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10,690 14C yr B.P., the area of forest and/or gallery
forest along the rivers increased probably about 50%,
reflecting a change to wetter climatic conditions. Incomparison to the extensive savanna grassland at that
time, areas of forest were still very small. At the Late
Glacial to Holocene transition, the pollen record from
El Pinal (zones ELP-II to ELP-III) shows a slight
change in forest composition: reduced presence of
Melastomataceae, Myrtaceae, and Celtis, and higher
presence ofMauritia-type and Alchornea. More
abundant Mauritia palm vegetation suggests wetter
conditions during the Holocene than during the Late
Glacial.Mauritia, as well asMauritiella, can be seen
as an indicator of higher moisture availability (Kahn
& De Granville, 1992; Henderson, 1995). The decline
ofIsoetes and the occurrence of the sea rose Cabomba(Cabombaceae; an aquatic with rhizomes, submersed
stem, and floating leaves; Maas & Westra, 1993) in the
lake also indicates higher lake levels during the
Holocene.
The Holocene part of the Laguna Carimagua record
is similar to the record of El Pinal, and both lakes show
a well documented and similar history of the regional
ecosystem. Except for the late Holocene period, there
are only minor changes in the vegetation of the savanna
ecosystem during the Holocene. The cluster analysis
dendrogram indicates a slight change around 5570 14C
yr B.P., at the transition from zone CAR-Ia to CAR-Ib.The lower abundance of the palm Mauritiella in zone
CAR-Ib may suggest slightly drier conditions, but the
slightly higher presence of several other taxa of the
forests and gallery forests may indicate wetter con-
ditions than in zone CAR-Ia. Hence we cannot arrive at
a conclusive interpretation for these changes.
A marked change occurred around 3850 14C yr B.P.
(interpolated age), primarily by the sudden high
abundance ofMauritiella, but also some other taxa
with an increased representation, such as Mauritia,
Alchornea and Cecropia. This change is related to
wetter conditions, i.e. an increase in precipitation and/
or a shorter dry season. The increase of the pioneer
and disturbance indicator Cecropia points to an
increase in human impact on the vegetation after 385014C yr B.P. (zone CAR-II). Interestingly enough, this
vegetational change is not recorded in Laguna El Pinal.
Pollen analysis of additional cores from this area are
in preparation and may provide a more substantiated
reconstruction of the beginning of human impact in
this part of the Llanos Orientales.
The present-day vegetation around the lake consists
of dense stands ofMauritia, but this is not reflected
in the pollen record. Some disturbance of the upper
core section was already inferred from the AMS dates,
and the absence of a clearMauritia peak in the pollenrecord may be another argument to suspect that the
record for the last thousand of years is incomplete. We
conclude that at least the last 1000 yrs are incomplete,
or missing, in both lake records. Perhaps the organic
rich sediments experienced a high level of decom-
position because of the shallow water.
Comparison with other pollen records of the
Llanos Orientales
The distance from our study lakes to Laguna Angel
(Behling and Hooghiemstra, 1998) is about 100 km
and about 200 km to Laguna Sardinas (Behling andHooghiemstra, 1998), and about 250 km to Laguna de
Agua Sucia (Wijmstra & Van der Hammen, 1966)
(Figure 1). The setting of Laguna Angel (428N,
7034W, 200 m a.s.l.) is comparable to the lakes in
this study: located between two larger rivers at some
45 km distance. Today, the forested area near Laguna
Angel and Laguna Sardinas is larger than in the region
of El Pinal and Carimagua. Laguna Sardinas (458N,
6928W, 80 m a.s.l.) is an isolated lake at the border
of a flood plain area and close to large areas with gallery
forest along a complex river system. Therefore, the
setting of Laguna Sardinas is different compared to thelakes Angel, El Pinal and Carimagua.
The record of Laguna Angel (5 pollen zones) starts
at 10,030 14C yr B.P., and that of Laguna Sardinas (6
pollen zones) at 11,570 14C yr B.P. The formation of
permanent lakes during the Late Glacial, as in Laguna
El Pinal, occurs at the same time and suggests wetter
climatic conditions than during the preceding full
glacial.
The palynological records from Lagunas Angel and
Sardinas (Figure 7) document, since the Late Glacial,
the predominance of grassland savanna with a small
contribution of savanna shrubs and trees, such as
Curatella,Byrsonima and Waltheria. The proportion
of grassland savanna, in comparison to forest and
gallery forests, is relatively constant after c. 11,00014C yr B.P. This relatively stable history of the savanna
ecosystem is supported by the newly studied sites,
but proportions of forest and/or gallery forest are
markedly lower in the region of El Pinal and Carimagua
than in region of Lagunas Angel and Sardinas. Further,
the floristic composition of the gallery forest in the
area of Lagunas Angel and Sardinas is subject to
considerable change throughout the records, which
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Figur
e7.SummarypollendiagramsofLagunaAngelandLagunaSardinas(afterBehlingandHo
oghiemstra,1998).
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474
contrasts to our newly studied sites. In the Laguna
Sardinas record, Alchornea significantly increases
during zone SAR-IIa (10,68010,07014
C yr B.P.).Alchornea also occurs more frequently in the gallery
forests during zone SAR-IIb (10,0709390 14C yr
B.P., the beginning of the Holocene), than in other
pollen zones. Further, the slightly higher presence of
theMauritia palm in the pollen zones SAR-I to SAR-
IIb may indicate wetter climatic conditions at the
transition from the Late Glacial to the Holocene. Such
vegetational changes are not found in the pollen record
of Laguna El Pinal, but other changes in El Pinal, e.g.
expansion of forest, also suggest wetter conditions
since c. 10,700 14C yr B.P. Sediments from Laguna
Sardinas, located at the edge of the floodplain area,
might be better suited to register signals of climatechange, expressed by changes and/or expansion of
gallery forests, than Laguna El Pinal, which is located
in an almost unforested grassland savanna with little
gallery forest.
A similar situation also prevails in the Holocene.
During the early and middle Holocene zones ANG-II
(97305260 14C yr B.P.) and SAR-III (93906390 14C
yr B.P.), savanna herbs are slightly more abundant than
during preceding periods. This period apparently re-
presents the maximum extension of grassland savanna
(Figure 6). There is no, or little, presence ofMauritia
during this period. This pollen evidence reflects thedriest period in the region of Lagunas Angel and
Sardinas, probably related to low rainfall rates and/or
an extended annual dry season. Such a vegetational
signal is not found in our newly studied sites.
The period represented by zones ANG-III (5260
3890 14C yr B.P.) and SAR-IV (63903680 14C yr B.P.),
shows a decrease of savanna herbs and an increase of
forest and gallery forest taxa. In the floodplains near
Laguna Sardinas, gallery forests expanded and the
surroundings of the lake became more forested. Wetter
climatic conditions, leading to a higher soil moisture
content, may have been an important factor to make this
vegetational change possible (Ross et al., 1992). This
climatic signal is not found in El Pinal, whereas in
Carimagua, only minor changes have been recorded
around 5570 14C yr B.P. without clear climatic impli-
cations. In view of the data of the other sites, it might
be plausible that the minor changes in the Carimagua
record indeed are related to a change to a wetter climate,
as evidenced by the records of Laguna Angel at 526014C yr B.P. and Sardinas at 6390 14C yr B.P.
The late Holocene period, represented by the zones
ANG-IV (3890 to c. 2000 14C yr B.P.) and SAR-V
(3680 14C yr B.P. to modern), is incomplete or missing
in both of these sites. The same situation holds for our
two new sites, probably because of the same reasons(high level of decomposition of the organic deposits).
The pollen records of Lagunas Angel and Sardinas show
that the most significant change occurred in the
uppermost pollen zone, primarily reflected by the
marked increase ofMauritiella in the area of Laguna
Angel and Mauritia in the area of Laguna Sardinas.
These changes have been interpreted as a result of an
increased human impact on the vegetation by an
intensified fire regime under wetter climatic con-
ditions (Behling and Hooghiemstra, 1998). A similar
environmental change is reflected in the record of
Laguna Carimagua around 3850 14C yr B.P., by an
strong increase of stands ofMauritella palms and theincreased presence ofMauritia. An increased presence
of palms is also reported from other sites in northern
South America (Rull, 1991, 1992; Behling and Costa,
1997).
The first pollen record from the Colombian savannas,
Laguna de Agua Sucia at 260 m elevation (Wijmstra &
Van der Hammen, 1966), lies at about 250 km distance
in the southeastern part of the Llanos Orientales
(Figure 1). This site lies in a region with higher
precipitation and a shorter dry season than is the case
in the region of the lakes Sardinas, Angel, El Pinal and
Carimagua. Laguna de Agua Sucia is also at shorterdistance to the Amazonian rain forest. The extrapolated
radiocarbon age at the base of this 5 m long core is
about 5100 14C yr B.P. Vegetational composition
(more shrubby savannas), and vegetational change
during the last 5000 yrs are somewhat different, but
inferred climatic changes are comparable to those of
the region of the central and central-eastern part of the
Llanos Orientales (Behling and Hooghiemstra, 1998).
Conclusions
The new pollen record of Laguna El Pinal extends the
environmental history of the savannas of the central
Llanos Orientales back to the LGM. Grassland savanna
vegetation, dominated by Poaceae, and with very little
occurrence of woody taxa such as Byrsonima and
Curatella, characterized the landscape in this area
since the LGM. The proportions of gallery forest along
river courses and/or forested areas in between river
systems have been always very small. During the Late
Quaternary, the floral composition of the savannas was
relatively stable in the studied areas.
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From the LGM until 10,690 14C yr B.P., Laguna El
Pinal was a shallow ephemeral lake, reflecting the
driest climatic conditions of the last 18,000 yrs: theannual precipitation must have been low and the annual
dry season long. Laguna El Pinal developed into a
permanent shallow lake during the Late Glacial, around
10,690 14C yr B.P. At other places in the Llanos
Orientales, permanent lakes also came into existence
during the same period (Laguna Angel around 10,03014C yr B.P., Laguna Sardinas around 11,570 14C yr B.P.),
indicating a change to wetter climatic conditions. The
increase of the forested area in the region of Laguna
El Pinal supports this interpretation. The vegetational
change in the area of Laguna Sardinas, i.e. an increased
presence ofMauritia andAlchornea, during the Late
Glacial, has not been observed in the area of El Pinal.This is probably because of the greater distance to
major river systems with gallery forests of the last
mentioned site.
Higher lake-levels in Laguna El Pinal, and the start
of the pollen record in Laguna Carimagua at 8270 14C
yr B.P., are indicative of wetter conditions during the
Holocene than during full glacial times. Minor changes
in the vegetation of the area of Laguna Carimagua at
5570 14C yr B.P. may be considered comparable with
an increase of the forested area in the record of
Laguna Angel at 5260 14C yr B.P., and in the record of
Laguna Sardinas at 639014
C yr B.P., and reflects mostpossibly a change to wetter climatic conditions. The
early Holocene was somewhat drier than the following
period until about 3850 14C yr B.P. The late Holocene
period, as far as recorded, is characterized by an
increase of the stands of the palm Mauritiella in the
surroundings of Laguna Carimagua. A marked increase
of palms in the regional vegetation was also observed
in the areas of Lagunas Angel and Sardinas, and in
other regions in tropical South America. This general
vegetational change is interpreted as reflecting in-
creased human impact on the vegetation under the
wettest Holocene climate regime.
Acknowledgments
The authors acknowledge Pedro Botero (IGAC) and
Carlos Botero for organizing the impressive coring
expedition and continuous valuable assistance in this
remote area of Colombia. Guido van Reenen (Am-
sterdam) assisted during part of the fieldwork. Elly
Beglinger and Annemarie Phillip (Amsterdam) are
thanked for preparing the pollen samples. Antoine
Cleef (Amsterdam) provided valuable information
during the evaluation of the data. Klaas van der Borg
(Utrecht) is acknowledged for the radiocarbon dates.The director of the Tropenbos-Colombia office, Juan
Saldarriaga, is thanked for the hospitality and con-
tinuous logistic support during field expeditions. The
Embassy of The Netherlands in Bogot is thanked for
assistance with sample transport. We thank John P.
Smol and two unknown reviewers for constructive and
valuable comments on the manuscript. We acknowledge
The Netherlands Foundation for Scientific Research
(NWO/GOA) for financial support (project number
750.195.10 to H. Hooghiemstra).
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