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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: behling@bio.uva.nl)

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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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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Figure6a.Percentagepollendiagramof

coreLagunaCarimagua,LlanosOrientales,Colombia.

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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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