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C lima te, Fire, a nd Veg eta tion betw een Abo ut 13,000 a nd9200 14C yr B .P . in the C hilea n La ke District

Patricio I. Moreno1

Institute for Quaternary Studies, Bryand Global Sciences Center, University of Maine, Orono, Maine 04469

Received July 13, 1999

A pollen record from Lago Condorito (41°45 S, 73°07 W) shows

hat North Patagonian Rain Forest taxa predominated between

bout 13,000 and 12,200 14C yr B.P. in the lowlands of southern

Chile, near the city of Puerto Montt. This was followed by the

xpansion and persistence of the conifer Podocarpus nubi gena

etween 12,200 and 9900 14C yr B.P. Trees favored by disturbance

xpanded between 11,200 and 9900 14C yr B.P., concurrent withharp and sustained increases of microscopic charcoal particles.

Taxa of low-elevation rain forests expanded and became more

iverse in pulses centered at 9900 and 9000 14C yr B.P., following

he disappearance of P. nubigena. These data suggest conditions

pproaching modern climate between about 13,000 and 12,200 14C

r B.P. The climate cooled between 12,200 and 9900 14C yr B.P.,

hen quickly warmed to interglacial conditions. Stand-replacing

res occurred near Lago Condorito between 11,200 and 9900 14C

r B.P., under cool-temperate, humid conditions. The proximity

nd reported antiquity of the Monte Verde archeological site raise

he possibility that these fires were set by human activi-

ies.© 2000 University of Washington.

Key W ords: climate; fire; vegetation disturbance; Chile.

INTRODUCTION

Although studies of fossil pollen and beetles from the south-

rn Chilean Lake District (40°–41°30ЈS) (Fig. 1) have clarified

ast environmental changes in the mid-latitudes of South

America (Heusser et al., 1995; Hoganson and Ashworth, 1992;

Markgraf, 1991; Villagran, 1980), a major question remains

nresolved: What was the precise timing and structure of

limate changes during the termination of the last ice age atouthern mid-latitudes? Conflicting results and divergent inter-

retations of paleoecological records have led to disagreements

bout the timing and structure of climate change between

5,000 and 10,000 14C yr B.P. Among other factors, these

ncertainties result from limited stratigraphic and chronologic

ontrol, low sampling resolution, differences in interpretation

f the fossil records, and spatial variability of paleoecological

hanges. Resolving these problems is crucial for determining

he intra- and interhemispheric extent of paleoclimate signals

during the last glaciation, a necessary step to unravel the

mechanisms that brought the last ice age to its end.

Major points of disagreement in paleoecological research in

the Chilean Lake District include the timing of the onset of

deglacial warming, the timing, frequency, and direction of

climate changes during the last termination, and the occurrence

and origin of late-glacial fires.Discrepancies about the timing, frequency, and direction of

climate changes during the last termination in the Lake District

and Isla Grande de Chiloe have led to proposals for a single-

step warming at 14,000 14C yr B.P. (Hoganson and Ashworth,

1992), a two-step model with a warming event at about 12,50014C yr B.P., followed by climate cooling starting at 11,000 14C

yr B.P. (Heusser, 1996, 1981), and a multi-step model with a

warming event at about 13,900 14C yr B.P. and as many as

three cooling events starting 11,000–13,000 14C yr B.P.

(Heusser, 1993; Heusser et al., 1995, 1996).

The presence or absence of a Younger Dryas-age cooling

event (11,000–10,000 14C yr B.P.) is one of the most contro-

versial issues related to paleoclimate in southern South Amer-

ica. Pollen evidence used to support the notion of a Younger

Dryas-age cooling from the Chilean Lake District and Isla

Grande de Chiloe (Heusser, 1993; Heusser et al., 1995, 1996)

lacks intersite coherence in terms of timing, duration, and

character of vegetation change. In addition, some fossil pollen

and beetle studies from this region (Hoganson and Ashworth,

1992; Markgraf, 1991; Villagran, 1991) do not indicate climate

cooling during Younger Dryas time. Recent pollen studies

suggest that late-glacial cooling occurred prior to Younger

Dryas time (Heusser et al., 1995, 1996). The co-occurrence of charcoal particles with Younger Dryas-age pollen assemblages

in a few sites has been explained as direct evidence of paleoin-

dian burning (Heusser, 1994) or decreased precipitation and

high climate variability extrapolated to both sides of the Andes

between 40 and 54°S latitude (Markgraf and Anderson, 1994).

Thus, it is necessary to assess the timing and character of

vegetation changes in relation to past changes in climate and

natural versus human-related disturbance regimes in order to

show whether or not a cooling of Younger Dryas age occurred

in southern South America.

The termination of the last ice age in the Chilean Lake

1 Present address: Departamento de Biologıa, Universidad de Chile, Casilla

53, Santiago, Chile.

Quaternary Research 54, 81–89 (2000)

oi:10.1006/qres.2000.2148, available online at http://www.idealibrary.com on

0033-5894/00 $35.00Copyright © 2000 by the University of Washington.

All rights of reproduction in any form reserved.

81



District featured abrupt vegetation and climate changes (Den-on et al., 1999; Moreno, 1997), sea-level fluctuations, volcanic

vents, the demise of the Pleistocene megafauna, and human

abitation (Dillehay, 1989, 1997). The extent to which these

onclimatic factors affected patterns and rates of vegetation

olonization and dispersal by means of disturbance and

nimal–plant interactions is unknown.

Little is known about the role of past fires as agents of

egetation change in South American temperate rain forests.

Recent studies have stressed the role of human disturbance and

nterannual climate variability in the incidence of forest fires

long the forest–steppe border in Patagonia (Kitzberger et al.,

997; Villalba and Veblen, 1997). Unlike the semiarid regionn the eastern flank of the Andes, the western side of the Andes

n the southern Chilean Lake District receives abundant storms

ecause of its location in the belt of westerly winds. Abundant

ear-round precipitation in this region supports broad-leaf rain

orests and suppresses natural fires. Modern forest fires do

ccur in connection with human disturbance, especially during

ry years, and with volcanic events such as pyroclastic flows.

n fact, most of the lowland rain forests of the Lake District

were cleared by the use of fire during European settlement in

he 19th century (Armesto et al., 1994). On the other hand,

yroclastic flow deposits in the Lake District often contain

scorched and charred wood (G. H. Denton, personal commu-

nication, 1998).

In this paper I report pollen and charcoal records with high

temporal resolution from Lago Condorito (41°45ЈS, 73°07ЈW)

in the Valle Longitudinal of the southern Chilean Lake District

(Fig. 1). Defining the stratigraphic distribution of charcoal and

vegetation changes at local and regional geographic scales is a

necessary step to discriminate the relative contributions of climate

change and fire disturbance as agents of vegetation change.

PHYSICAL AND VEGETATIONAL SETTING

The Valle Longitudinal of the Chilean Lake District is a

tectonic depression oriented along a north–south axis between

39°S and 41°30ЈS. It is bounded by the Cordillera de los Andes

to the east and the Cordillera de la Costa to the west. The

depression continues southward into the Seno Reloncavı sea-

way (Fig. 1). Many lakes dot formerly glaciated parts of the

Valle Longitudinal, and these lakes become progressively

larger from north to south, culminating with Lago Llanquihue.Lakes and mires in the Valle Longitudinal provide a wealth of

potential stratigraphic records for detailed studies of vegetation

and climate changes during the last ice age.

Precipitation occurs evenly throughout the year in the Seno

Reloncavı sector of the Lake District, with decreased frontal

activity during the summer months (Aceituno et al., 1993;

Miller, 1976). Abundant precipitation brought by the westerly

storms produces a temperate, maritime climate, similar to

climates of the Chilean channels farther south. The latitudinal

shifts of the westerly winds in the southeast Pacific region

result from the interaction between the subtropical Pacifichigh-pressure cell and the polar low-pressure belt. Seasonal

variations in the equator-to-pole temperature gradient force an

equatorward shift of the Pacific Anticyclone, which allows

penetration of westerly storm tracks to central Chile (31°S)

during the winter months (Aceituno et al., 1993; Miller, 1976).

During summer, the Pacific Anticyclone shifts southward, forc-

ing the westerlies to remain south of about 38°S on a semi-

permanent basis. This mechanism results in a gradient of

decreasing summer and total annual precipitation toward the

north, due to both a lower frequency of storm tracks and

intensification of the rain-shadow effect caused by the Cordil-

lera de la Costa, which increases in altitude to the north.Broad-leaf temperate rain forests were the predominant veg-

etation in the Lake District south of 38°S prior to European

settlement. Rain forests occupied the lowlands in the Valle

Longitudinal, the Cordillera de la Costa, and the Cordillera de

los Andes up to 1200 m elevation (Armesto et al., 1994) (Fig.

1). Strong climatic, topographic, and edaphic heterogeneities

lead to patterns of distribution of forest communities along

altitudinal and latitudinal gradients, forming the so-called

Valdivian, North Patagonian, and Subantarctic Rain Forest

communities (Schmithusen, 1956). Natural disturbance re-

gimes associated with volcanism and earthquake-triggered

FIG. 1. Map of the Chilean Lake District and Isla Grande de Chiloe,

howing the location of Lago Condorito (LC) and the Monte Verde (MV)

rcheological site.

PATRICIO I. MORENO2



andslides influence the distribution, composition, and struc-

ure of these forest communities. Climatic, tectonic, and an-

hropogenically related disturbance agents are particularly im-

ortant in this region (Veblen and Ashton, 1978).

The geographic distribution and floristic composition of plant

ommunities in the Chilean Lake District, along with the regional

atterns of pollen rain deposition, provide the modern analog for

nterpreting past pollen assemblages. The next few paragraphs

resent a brief description of the vegetation in the southern Lake

District and Isla Grande de Chiloe, based largely on Oberdorfer

1960), Schmithusen (1956), and Villagran (1980, 1993).

The species-rich Valdivian Rain Forest is the most diverse in

erms of floristic associations and canopy structure. The asso-

iation of Nothofagus dombeyi and Eucryphia cordifolia dom-

nates the foothills of the mountain ranges in the Lake District

rom 200 to 400 m elevation at about 41°S. Coastal regions

eature forests dominated by the evergreen trees N. nitida and

Aextoxicon punctatum. Abundant epiphytes and vines, partic-

larly ferns ( Asplenium dareoides, Polypodium feullei, and

more than a dozen species of Hymenophyllum), mosses, andhe angiosperms Hydrangea serratifolia and Pseudopanax la-

tevirens grow on the trunks of standing and fallen trees.

Bamboo species of the genus Chusquea (Poaceae) commonly

orm dense thickets in tree-fall gaps or cleared sites (Veblen

nd Ashton, 1978).

The North Patagonian Rain Forest replaces the Valdivian

Rain Forest communities at about 400 m elevation. In the

Cordillera de los Andes, Nothofagus dombeyi dominates all

ssociations of the North Patagonian Rain Forest, accompanied

y N. betuloides, Drimys winteri, Laureliopsis philippiana,

Weinmannia trichosperma, Lomatia ferruginea, Gevuina avel-ana, and several species of Myrtaceae ( Amomyrtus luma,

Myrceugenia chrysocarpa, among others). The conifers

Fitzroya cupressoides, Pilgerodendron uvifera, and Podocar-

us nubigena are characteristic of this forest community in the

mountain ranges above 600 m elevation. Volcanic disturbance

nd snow or rock avalanches often lead to the establishment of

monospecific stands of Weinmannia trichosperma, Nothofagus

dombeyi, and Fitzroya cupressoides at high elevations (Veblen

nd Ashton, 1978; Villagran, 1980).

The Subantarctic Rain Forest occurs near tree line at about

000–1200 m elevation in the Andes of the Lago Llanquihue

rea, with the deciduous Nothofagus pumilio and N. antarcticaccurring with Drimys andina and Maytenus disticha

Schmithusen, 1956). Wind shear and snow cover produce a

atchy krummholz pattern in the vegetation. Above the tree

ine, the high Andean vegetation consists of a mosaic of open

lant communities with grasses (Poa, Festuca, Stipa), compos-

te shrubs ( Baccharis, Perezia, Nassauvia), and herbs, all of

which thrive on unstable rocky substrates (Schmithusen, 1956;

Villagran, 1980).

Lago Condorito (41°45ЈS, 73°07ЈW) lies in the area of the

Valdivian Rain Forest, on a moraine belt parallel to the western

hore of the Seno Reloncavı seaway. The lake is elliptical in

shape, Ͻ1 ha in size, and has a single concave depression with

a maximum water depth of 2.7 m.

MATERIALS AND METHODS

Two overlapping sediment cores (PM10, PM11) were obtained

from the deepest part of Lago Condorito using a 5-cm-diameter

Wright square-rod piston corer. Both cores were stored at 4°C atthe University of Maine soon after they were collected.

X-radiographs, loss-on-ignition analysis (all measurements were

calculated based on the dry weight of a one-cubic-centimeter

sediment sample), and textural description of the sediments were

developed to document the stratigraphy of the cores. All analytical

data in this paper comes from core PM10 (Figs. 2–5).

Samples for pollen analysis were processed using 10%

KOH, sieving (120 m), 48% HF, and acetolysis. The pollen

slides were mounted in silicon oil and analyzed at ϫ400 and

ϫ1000 magnification. A minimum of 300 terrestrial pollen

grains for each level were counted whenever possible. Micro-

scopic charcoal particles (Ͻ120 m) found in the pollen slideswere assigned to two arbitrarily defined size classes of Ͻ25

and Ͼ25 m. Known amounts of Lycopodium spores were

added to known volumes of sediment to allow calculation of

pollen and charcoal concentrations. Based on the concentration

data and the interpolated age of each sample (see details

below), I calculated pollen and charcoal accumulation rates

(pollen grains or charcoal particles/cm2* yearϪ1).

RESULTS

Stratigraphy and Chronology

The two sediment cores obtained from Lago Condorito

contain a basal peat layer overlain by gyttja with varying

amounts of silt (Fig. 2). They also contain volcanic-ash layers,

the most prominent of which is a 15-cm-thick layer at 704 cm

depth (Fig. 2). Radiocarbon dates for the deposition of this ash

layer yielded a maximum age of 10,060 Ϯ 60 14C yr B.P.

(A-8060) and a minimum age of 9680 Ϯ 85 14C yr B.P.

(A-8070) (Table 1).

The basal deposits gave a radiocarbon age of 12,330 Ϯ 130

(A-6661), which is succeeded in stratigraphic sequence by

dates of 12,230 Ϯ 140 14C yr B.P. (Beta-60352) and 12,170 Ϯ90 14C yr B.P. (A-8066) (Table 1). These three radiocarbon

dates span 60 cm of sediment and overlap at the 2 level (Fig.

2), suggesting that the lowermost sample might be too young

and should be considered only as a minimum age for the onset

of organic deposition at the site. Thus, I excluded radiocarbon

sample A-6661 from the age model. I then calculated the

average age of samples A-8069 and A-8070, considering that

the 15-cm-thick volcanic ash layer was deposited instanta-

neously. An age model consisting of a third-order polynomial

(Fig. 2) was developed to assign interpolated ages to the pollen

levels, based on uncalibrated radiocarbon dates (Table 1).

FIRE AND VEGETATION DISTURBANCE IN SOUTHERN CHILE 83



Pollen and Charcoal Stratigraphies

In local pollen assemblage zone (LPAZ) CO-1 (13,000–

2,20014

C yr B.P.; CO ϭ Lago Condorito), the Myrtaceae-

Nothofagus dombeyi-type-Fitzroya/Pilgerodendron pollen as-

semblage is dominant. Other important taxa include Poaceae,

Pseudopanax, Hydrangea, Lomatia/Gevuina, and Escallonia

(Fig. 3). Taxa with trace percentages include Drimys, Podo-

carpus, and Laurelia. Pseudopanax and Hydrangea expanded

immediately after the percentage maximum of Myrtaceae at

FIG. 2. (top) Stratigraphic column of core PM10, showing radiocarbon ages, their depths, and the results of the loss-on-ignition analysis of core PM10.

Organic content is shown both as a percentage and as concentration. Dashed horizontal lines represent boundaries of local pollen assemblage zones from core

M10 (Figs. 3 and 4). (bottom) Age/depth curve of core PM10, showing the age model applied to the uncalibrated radiocarbon dates. Horizontal error bars

epresent Ϯone standard deviation; vertical error bars indicate the thickness of the sediment sample. The flatness of the age/depth curve at about 700 cm depth

epresents the instantaneous deposition of a volcanic ash horizon.

PATRICIO I. MORENO4



2,800 14C yr B.P. Arboreal pollen taxa dominate with a mean

f 91%. Abundant microscopic charcoal Ͻ25 m (Fig. 4)

ccurs during the early part of this zone, along with a promi-

ent peaks of Nothofagus dombeyi-type and Poaceae (five

tratigraphic levels) (Fig. 3).

LPAZ CO-2a (12,200 –11,100 14C yr B.P.) features the as-emblage Nothofagus dombeyi-type-Myrtaceae-Pseudopanax,

ccompanied by Podocarpus, Hydrangea, and Weinmannia

Fig. 4). Major declines are evident for Fitzroya/

Pilgerodendron, accompanied by conspicuous increases in the

nflux of Escallonia and Embothrium (Fig. 4). A short-lived

ncrease in charcoal occurs at 11,850 14C yr B.P. (Fig. 4). LPAZ

CO-2b (11,100–990014

C yr B.P.) is dominated by the assem-

lage Weinmannia-Nothofagus dombeyi-type-Tepualia, along

with Hydrangea, Podocarpus, Myrtaceae, and Pseudopanax

Fig. 3). Increases are evident for Griselinia and Poaceae; other

axa such as Lomatia/Gevuina and Embothrium reach their

respective minima in this zone (Figs. 3 and 4). Prominent

increases in charcoal started at 11,200 14C yr B.P. and persisted

until 9200 14C yr B.P. (Fig. 5).

LPAZ CO-3 (9900 –920014

C yr B.P.) shows the assemblage

Weinmannia-Tepualia-[ Nothofagus dombeyi-type-Pseudopanax],

accompanied by Hydrangea and Escallonia (Fig. 3). Con-spicuous features of this subzone are the disappearance

of Podocarpus and the expansion of Lomatia/Gevuina and

Embothrium (Figs. 3 and 4).

LPAZ CO-4a (9200 – 830014

C yr B.P.) is characterized by

the assemblage Eucryphia/Caldcluvia-Weinmannia-[Tepualia-

Poaceae], along with Pseudopanax, Nothofagus dombeyi-type,

Hydrangea, Myrtaceae, and trace amounts of Griselina, Escal-

lonia, and Embothrium (Fig. 3). LPAZ CO-4b (8300–720014

C yr

B.P.) features the assemblage Tepualia-Eucryphia/Caldcluvia-

Nothofagus dombeyi-type, resulting from the abrupt expansion of

Tepualia (Figs. 3 and 4) and decline of Weinmannia.

FIG. 3. Pollen and spore percentage diagram from core PM10. Notice the difference in scale between the different taxa. Dashed lines represent the

oundaries of local pollen assemblage zones.




DISCUSSION

Vegetation Changes

The Lago Condorito record shows the predominance of rain

orest taxa between about 13,000 and 12,200 14C yr B.P. with

Myrtaceae, Nothofagus dombeyi-type, Fitzroya/Pilgerodendron,

Pseudopanax, and Lomatia/Gevuina. The woody climbers

Hydrangea and Pseudopanax expanded abruptly after the peak

ercentage of Myrtaceae at 12,800 14C yr B.P. These datandicate the dominance of North Patagonian Rain Forest taxa,

ossibly a mosaic of swamp forest communities dominated by

myrtaceous species, and stands of cupressaceous conifers (pos-

ibly Fitzroya cupressoides) in waterlogged environments be-

ween about 13,000 and 12,200 14C yr B.P. The absence of

hermophilous species diagnostic of Valdivian rain forests sug-

ests temperate and humid conditions, somewhat cooler than

modern day climate in the lowlands of the southern Lake

District. Conspicuous peaks of Nothofagus dombeyi-type and

Poaceae occurred prior to 12,500 14C yr B.P., accompanied by

arge amounts of microscopic charcoal.

Changes in forest composition started with the rapid increase

of Nothofagus dombeyi-type and the conifer Podocarpus at

about 12,200 14C yr B.P. (Fig. 4), steady decline in Myrtaceae

and Fitzroya/Pilgerodendron, and consistently low values of

Lomatia/Gevuina. These changes indicate a shift to a forest

community that included shade-tolerant conifer species com-

monly found today at mid-elevations in the mountain ranges of

the study area. The accumulation rate diagram reveals a modest

expansion of the woody plants Escallonia, Embothrium, andEricaceae, indicating diversification of the shrub layer (Fig. 4).

The latter changes represent only a modest opening of the

forest canopy because the increase in shrubs and herbs is minor

in the percentage diagram (Figs. 3 and 4). The onset of the

vegetation changes at 12,200 14C yr B.P. follows a transition

from a basal peat layer to gyttja sediment in core PM10 (Fig.

2), and it coincides with low accumulation rate of microscopic

charcoal between 12,200 and 11,200 14C yr B.P. (Fig. 5).

Major vegetation changes started at 11,200 14C yr B.P. with

a rapid increase of Weinmannia, Tepualia, and Griselinia and

a persistent decline of all other trees (Podocarpus, Nothofagus

FIG. 4. Pollen accumulation rates of core PM10. Notice the difference in scale between the different taxa. Dashed lines represent the boundaries of local

ollen assemblage zones.

PATRICIO I. MORENO6



dombeyi-type, Lomatia/Gevuina, Escallonia, Myrtaceae),

woody climbers ( Hydrangea, Pseudopanax), and epiphytic

erns (Hymenophyllaceae, Polypodium). I interpret these

hanges between 11,200 and about 9800 14C yr B.P. as the

evelopment of a woodland dominated by Weinmannia, inter-

persed with thickets/shrublands of the hygrophilous Tepualia.

Weinmannia trichosperma is now found in several Valdivian

nd North Patagonian Rain Forest communities along a broad

atitudinal and altitudinal range in the temperate region of

outhern Chile. Weinmannia trichosperma is a shade-intolerant

mergent tree, described by Lusk (1996, 1999) as a long-lived

ioneer species tolerant of infertile, poorly drained soils. In

ddition, Tepualia thickets are known to expand following

isturbance in temperate forest communities (Ramırez, 1989).

n view of the autoecology of these species, the pollen assem-

lages between 11,200 and about 9900 14C yr B.P. indicate a

apid change from a closed-canopy rain forest community to a

woodland dominated by species favored by local disturbance.

This important vegetation change is accompanied by sharp

increases in the accumulation rate of microscopic charcoal

particles (see below).

Arboreal diversity increased in pulses centered at 9900 and

9100 14C yr B.P. with the expansion of thermophilous forest

taxa ( Lomatia/Gevuina, Pseudopanax, Escallonia, Griselina),

along with the Valdivian Eucryphia/Caldcluvia. The disap-

pearance of Podocarpus at 9900 14C yr B.P. was coeval with

major declines in the accumulation rate of Weinmannia and

Tepualia. These changes in the pollen stratigraphy indicate the

expansion and diversification of thermophilous rain forest trees

after 9900 14C yr B.P.

Fire History

The pollen record from Lago Condorito shows percentage and

accumulation-rate maxima of Poaceae coeval with a prominent

peak of particlesϽ25 m prior to 12,500 14C yr B.P. (Figs. 3–5).

I interpret this signal as representing small-scale vegetation dis-

TABLE 1Radiocarbon Ages from Core PM10

Core/thrust Depth (cm) Material Age (14C yr B.P.) ␦13C Laboratory no.

PM10T07 575–578 bulk 8570Ϯ 45 Ϫ29.3 NSRL-10721

PM10T07 613–615 bulk 9110Ϯ 45 Ϫ30.1 A-8587

PM10T09 685–688 bulk 9680Ϯ 85 Ϫ30.5 A-8070

PM10T09 724–726 bulk 10,060Ϯ 60 Ϫ28.4 A-8069

PM10T14 821–824 bulk 11,265Ϯ 65 Ϫ29.9 A-8068

PM10T15 848–852 bulk 11,435Ϯ 80 Ϫ29.5 A-8067

PM10T16 863–873 bulk 12,230Ϯ 140 Ϫ30 Beta-60352

PM10T16 873–886 bulk 12,170Ϯ 90 Ϫ32.1 A-8066

PM10T17 928–930 bulk 12,330Ϯ 130 Ϫ29 A-6661

FIG. 5. Accumulation rates of microscopic charcoal particles and selected taxa. Influx scales differ. Dashed lines represent the boundaries of local pollen

ssemblage zones.




urbance by fire in a landscape dominated by temperate rain forest

axa. Most probably the increase in Poaceae pollen represents the

xpansion of bamboo species of the genus Chusquea in small

orest gaps created by low-severity, local fire disturbance. This

art of the pollen record corresponds to a basal peat layer in the

tratigraphy of core PM10 (885–920 cm depth) (Fig. 2).

Charcoal accumulation rates declined and remained at low

evels between 12,500 and 11,200 14C yr B.P., with isolated

harcoal peaks at about 11,850 14C yr B.P. and 11,300 14C yr

B.P. (Fig. 4). This part of the pollen record shows a shift from

n assemblage dominated by the most thermophilous taxa of

North Patagonian Rain Forest communities to an assemblage

hat included the conifer Podocarpus, now characteristic of the

mid-to-high elevation belts in the mountain ranges of the

outhern Lake District and Isla Grande de Chiloe. The stratig-

aphy of core PM10 shows a transition from a basal peat to a

yttja sediment (Fig. 2) shortly before the vegetation change at

2,200 14C yr B.P. (885 cm depth). The changes in the litho-

tratigraphy are likely the result of increased precipitation,

igher effective moisture, or both.The accumulation rate of microscopic charcoal increased

etween 11,200 and 9900 14C yr B.P., coeval with the expan-

ion of species favored by disturbance (Weinmannia, Tepualia)

Fig. 5). During this vegetation change, most of the rain forest

axa that dominate the pollen record between 12,100 and

1,200 14C yr B.P. declined in abundance and remained at low

evels until 9900 14C yr B.P. (i.e. Podocarpus, Nothofagus

dombeyi-type, Pseudopanax, Myrtaceae, Lomatia/Gevuina,

Hydrangea). The disappearance of Podocarpus and the con-

urrent expansion of thermophilous rain forest taxa at 9900 14C

r B.P. occurred while charcoal remained abundant (Figs. 3–5).Several possibilities exist for the origin of these fire events.

Today, the occurrence of natural fires on the Pacific coast of South

America south of 40°S is greatly suppressed by the humid to

yperhumid temperate climates of southern Chile. Lightning

torms in the western slopes of the Andes are rare thanks to the

tmospheric stability imparted by the westerly winds.

Several active and extinct volcanoes occur in the Cordillera

e los Andes in the Lake District. Intensive volcanic activity in

he lowlands during the Quaternary produced lava and pyro-

lastic flows, ash falls, and lahars. Volcanism is thus one

gnition agent capable of overriding the climate conditions that

therwise greatly suppress natural fires in southern Chile.Pyroclastic flows are particularly important because their in-

endiary effect may extend many kilometers away from the

olcanic centers. The stratigraphy of core PM10 includes

rganic-rich gyttja deposited between 12,800 and 9900 14C yr

B.P., overlain by a volcanic ash layer with an interpolated age

f 9900 14C yr B.P. (Fig. 2). This ash is too young to explain

he initiation of local vegetation disturbance by fire in core

PM10 at 11,200 14C yr B.P.

Studies on the Monte Verde archeological site (41°30ЈS,

3°15ЈW) have suggested the presence of human settlers between

bout 12,500 and 12,00014

C yr B.P. in the southern Chilean Lake

District (Dillehay, 1989, 1997). Remains interpreted as partially

burned plant and animal artifacts in association with hearths from

the MV-II horizon have been cited as evidence for the presence of

early humans and their use of fire. Local human activities could

have been the ignition agent necessary for fire between 11,200 and

9900 14C yr B.P., given that the Monte Verde archeological site is

about 20 km from Lago Condorito (Fig. 1).

CONCLUSIONS

High-resolution pollen and charcoal records from Lago Con-

dorito show that North Patagonian Rain Forest taxa dominated

the Valle Longitudinal of the Southern Lake District between

about 13,000 and 12,200 14C yr B.P. Climate was slightly

cooler and wetter than it is today. Cold-resistant trees then

expanded and persisted in response to climate cooling between

12,200 and 9900 14C yr B.P. Forest diversification after 990014C yr B.P. included the expansion of thermophilous rain forest

species and the disappearance of Podocarpus. The character of the vegetation change at 9900 14C yr B.P. suggests a warming

that led to interglacial climate conditions.

Fire and vegetation disturbance are prominent features of the

Lago Condorito record between 13,000 and 10,000 14C yr B.P.

Stand-replacing fires led to the expansion of opportunistic

species favored by disturbance, replacing closed-canopy rain

forest vegetation. Most of the fires and vegetation disturbance

occurred too early to be related to a volcanic eruption about

9,000 14C yr B.P. The results shown in this paper indicate that

fire and vegetation disturbance between 11,200 and 9000 14C yr

B.P. occurred under cool-temperate and humid climate; these

conditions are known to suppress the initiation and persistence

of natural fires in southern Chile. Local vegetation disturbance

by fire during Younger Dryas time (11,200–9900 14C yr B.P.)

suggests the onset of climate instability leading to rainfall

variability at interannual or interdecadal time scales, a hypoth-

esis supported by additional high-resolution pollen and char-

coal stratigraphy from the study area (Moreno et al., 1999;

Moreno, in preparation).

The southernmost Chilean Lake District has frequent storms

from westerly storm tracks, is not affected by the rain-shadow

effect of the Cordillera de la Costa, and has a strong oceanic

influence from the Seno Reloncavı seaway. Thus, seasonalmoisture stress is not a satisfactory explanation for fire occur-

rence near the Lago Condorito site between about 13,000 and

9900 14C yr B.P. Lago Condorito is located close to the Monte

Verde archeological site, where the presence of hearths and

charred wood, bones, and artifacts has been cited as evidence

for use of fire by early humans (Dillehay, 1989, 1997).

Late glacial climate approached conditions slightly cooler

and wetter than modern-day climate between about 13,000 and

12,200 14C yr B.P. This was followed by a cooling event

between 12,200 and 9900 14C yr B.P. If humans were, indeed,

present in the southern Lake District at the end of the last ice

PATRICIO I. MORENO8



ge, they may have ignited fires that disturbed vegetation near

Lago Condorito between 11,200 and 9900 14C yr B.P.

ACKNOWLEDGMENTS

I thank G. L. Jacobson and G. H. Denton for supporting my doctoral studies

t the University of Maine; C. Villagran and J. J. Armesto for editorial

omments; B. Andersen, A. Hauser, C. Heusser, C. Latorre, T. Lowell, D.

Marchant, and C. Porter for help in the field; and T. Lowell for help in

ollecting the cores. The research was funded by the Office of Climate

Dynamics of the National Science Foundation (NSF), the National Oceanic

nd Atmospheric Administration, the National Geographic Society, and NSF’s

xperimental Program to Stimulate Competitive Research.

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