JOURNAL OF QUATERNARY SCIENCE (2009) 24(3) 248–258
Copyright ß 2008 John Wiley & Sons, Ltd.
Published online 27 November 2008 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/jqs.1233
Late Quaternary vegetation and fire history in the
northernmost Nothofagus forest region: Mallı́n
Vaca Lauquen, Neuquén Province, Argentina
VERA MARKGRAF,1,2* CATHY WHITLOCK,3 R. SCOTT ANDERSON2 and ADRIANA GARCÍA4
1
Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA
2
Center for Environmental Sciences and Education, and Quaternary Sciences Program, Northern Arizona University, Flagstaff,
Arizona, USA
3
Department of Earth Sciences, Montana State University, Bozeman, Montana, USA
4
School of Earth and Environmental Science, University of Wollongong, Wollongong, New South Wales, Australia
Markgraf, V., Whitlock, C., Anderson, R. S. and Garcı́a, A. 2009. Late Quaternary vegetation and fire history in the northernmost Nothofagus forest region: Mallı́n Vaca
Lauquen, Neuquén Province, Argentina. J. Quaternary Sci., Vol. 24 pp. 248–258. ISSN 0267-8179.
Received 28 December 2007; Revised 7 August 2008; Accepted 7 August 2008
ABSTRACT: The last 16 000 cal. a of vegetation, fire and limnological history are described from the
steppe-forest ecotone in the northernmost Nothofagus forest region east of the Andes (Mallı́n Vaca
Lauquen, Neuquén Province, Argentina, latitude 368 51.3360 S, longitude 718 02.5380 W). Between
16 000 and 14 800 cal. a BP, scrub steppe with substantial open ground expanded in formerly glaciated
valleys, whereas Nothofagus–Prumnopitys andina woodland covered mountain slopes. The site was a
relatively deep and unproductive small lake at this time. After 14 800 cal. a BP, both steppe and
woodland vegetation became denser, indicating increased moisture and temperatures, although not to
present levels. The lake was still relatively deep and dystrophic, but became more alkaline by
10 000 cal. a BP. Between 8900 and 5500 cal. a BP, conditions were markedly drier than before;
a Cyperaceae marsh developed and disturbance taxa increased. After 5500 cal. a BP, moisture
increased but varied greatly, as evidenced by fluctuating water levels and high fire activity from
5500 to 4400 cal. a BP and from 2300 to 1000 cal. a BP. Human activity, in terms of forest clearance
and livestock grazing, is documented in the uppermost levels. The evidence of high environmental
variability in the middle and late Holocene is consistent with the onset or strengthening of the El Niño–
Southern Oscillation, but differences in the timing of fire activity among sites on the west and east sides
of the Andes suggest that fuel conditions were important in determining the local occurrence of fire.
Copyright # 2008 John Wiley & Sons, Ltd.
KEYWORDS: Lateglacial; Holocene vegetation; fire and climate history; mid-latitude Argentine Andes.
Introduction
The Mallı́n Vaca Lauquen site is a 200 m diameter seasonally
inundated wet meadow, on the east side of the Andes of
Argentina at the steppe forest ecotone (latitude 368 51.3360 S,
longitude 718 02.5380 W, elevation 1567 m). The site was
previously the focus of a reconstruction of late Pleistocene/
Holocene vegetation and climate change (Markgraf, 1987).
With the more recent focus on the role of past fire activity in
shaping structure and distribution of temperate forests in
Patagonia and fire-producing climate conditions (Whitlock
et al., 2007), re-evaluation of this site, including new pollen,
charcoal and plant macrofossil analyses, seemed warranted.
Research on documentary evidence, fire-scarred tree rings
and sedimentary charcoal records has shown the importance of
* Correspondence to: V. Markgraf, 763 N. Pine Cliff Dr., Flagstaff, AZ 86001,
USA.
E-mail: [email protected]
past fires in Patagonia (Veblen et al., 1999; Huber and
Markgraf, 2003; Kitzberger and Veblen, 2003; Veblen et al.,
2003; Whitlock et al., 2006, 2007). These records document
latitudinal differences in the timing and duration of past fire
intervals, including those occurring in recent centuries
(Bianchi, 2000; Huber and Markgraf, 2003; Huber et al.,
2004; Whitlock et al., 2007). Fire activity has been attributed to
climate anomalies linked to the latitudinal position of the
Southern Westerlies and the strength and location of the
southeastern Pacific subtropical high-pressure system (Whitlock et al., 2007; Garreaud et al., 2008). In the mid-latitudinal
region of Patagonia (latitude 38–438 S), periods of weakened
and poleward-shifted Westerlies and a stronger than normal
subtropical high-pressure system produce drought conditions
and large areas burned as a result of higher than normal summer
temperatures and lower than normal summer precipitation
(Villalba, 1994; Kitzberger and Veblen, 2003; Whitlock et al.,
2007). At interannual and interdecadal scales, seasonal
moisture deficits and high fire occurrence are also related to
El Niño–Southern Oscillation (ENSO) and decadal climate
LATE QUATERNARY VEGETATION AND FIRE HISTORY
variability. North of latitude 388 S, including the study site,
winter and spring precipitation is somewhat enhanced during El
Niño events (Compagnucci and Vargas, 1998; Montecinos and
Aceituno, 2003), although it does not outweigh the moisture
deficit resulting from higher than normal summer and autumn
temperatures (Garreaud et al., 2008).
Our research objective was to reconstruct the environmental
history on the east side of the Andes at latitude 378 S at the
northern limit of mixed Nothofagus obliqua/N. pumilio forest
and the southern limit of the Monte desert scrub vegetation to
better understand the climate history of this transitional region.
We present pollen, charcoal and limnological data from Mallı́n
Vaca Lauquen in northern Patagonia. Two time periods are of
special interest: the Lateglacial and early Holocene interval
(16 000–8000 cal. a BP) when summer insolation was lower
than at present and ENSO variability was less pronounced (e.g.
Markgraf and Diaz, 2000; Moy et al., 2002), and the late
Holocene interval (last 3000 a) when ENSO variability was
strengthened.
Site description
Mallı́n Vaca Lauquen is located near the confluence of the
valleys of Lagunas Epulauquen and Vaca Lauquen about 60 km
249
north-west of the town of Andacollo, northwestern Neuquén
Province (Fig. 1). The lakes are dammed by recessional
moraines, the lowest of which lies at about 1500 m elevation.
The surrounding peaks are about 2500 m elevation. The
abundance of shrubs and introduced herbs in the local
vegetation attests to heavy livestock grazing. The present-day
vegetation consists of impoverished high-elevation bunchgrass
steppe (estepa graminosa; León et al., 1998) with Festuca
pallescens and shrubs in the families Asteraceae (Baccharis
ssp., Chiliotrichium rosmarinifolium, Chuquiraga ssp., Mutisia
ssp., Perezia ssp.) and Rhamnaceae (Colletia spinosissima), as
well as Berberis rosmarinifolia, Ephedra frustillata and
Eryngium paniculatum (Apiaceae). Native herbs include
Osmorhiza berteroi (Apiaceae), Calceolaria biflora (Scrophulariaceae), Quinchamalium chilense (Santalaceae) and Phacelia sp. (Hydrophyllaceae), among others. Introduced herbs
include Rumex acetosella and Plantago lanceolata. The
mountain slopes are covered by the northernmost extent of
southern beech (Nothofagus) forest, which is found up to
treeline at 1700 m elevation. Nothofagus obliqua dominates
lower elevation forests, while N. pumilio and N. antarctica
grow at higher elevations, forming a krummholz belt above the
treeline in the transition zone to the Andean tundra. N.
antarctica also grows on poor soils at all elevations. Few
Austrocedrus chilensis trees grow at lower elevations, and burnt
and dead trees of Nothofagus obliqua in the watershed offer
abundant evidence of fires in recent times.
Figure 1 Location of the Mallı́n Vaca Lauquen site, showing major topographic features and vegetation cover. Nothofagus forests are in green; the
steppe areas are in light brown, Andean tundra in grey
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
DOI: 10.1002/jqs
250
JOURNAL OF QUATERNARY SCIENCE
Given the absence of meteorological stations in this
mountainous region, mean annual precipitation and temperature were estimated at 700 mm and 48C, respectively, based on
data from the Climatologic Atlas of South America (J. A.
Hoffman, ed.), UNESCO, 1975. Precipitation occurs primarily
during autumm and winter months (April through July). A
review of the climate of Patagonia and its relation to major
vegetation zones lists mean annual precipitation at the steppe–
forest ecotone of about 600 mm and mean annual temperature
of 68C, based on 62 stations between latitudes 378 and 558 S
(Paruelo et al., 1998).
Methods
In 2002, three sediment cores, MVL-02A, MVL-02B, and MVL02C, were taken with a modified Livingstone corer from the
centre of the wetland. The most complete core, MLV-02C, was
342 cm long. In the laboratory, cores were split and the
sediments described. The core MVL-02A was analysed for
the upper 50 cm (this segment was not compacted compared to
the same segment from core MVL-02C), and core MVL-02C was
analysed between 50 and 342 cm depth. Magnetic susceptibility (MS; Sandgren and Snowball, 2001), was measured using
a Bartington MS meter with a hand-held MS2E sensor.
Measurements were taken every 0.5 cm along the entire length
of core.
For pollen analysis, 1 cm3 volumetric samples were taken at
2.5 or 5 cm intervals and prepared with standard techniques
(Faegri and Iversen, 1989). Pollen grains were identified at
400 and 1000 magnification, with counts ranging from 150
to 400 grains. Terrestrial pollen percentages were based on the
total sum of pollen grains from trees, shrubs and herbs and used
to calculate the percentages of terrestrial and aquatic
palynomorphs. Excluded from the terrestrial pollen sum were
Cyperaceae, fern allies (mostly undifferentiated Polypodiaceae
and a few Hymenophyllum and Pteris), aquatic taxa (Myriophyllum) and the algae Pediastrum boryanum var. longicorne
and Botryococcus. Escallonia and Caryophyllaceae were also
excluded from the pollen sum, given their erratic and probably
local occurrences in high numbers in some intervals. Escallonia
is a shrub that often grows at the margin of wetlands and
Caryophyllaceae (locally present taxa are within the genera
Stellaria and Arenaria pollen type) grow primarily on disturbed
sandy–gravelly soils. Lycopodium tracer spores were added to
each sample for calculation of pollen concentration
(grains cm3). Changes in pollen percentage and concentration
were used to interpret past vegetation changes supported also
by CONISS cluster analysis (Grimm, 1987). Pollen data were
plotted using TILIA programs (Grimm, 1992).
A total of 72 pollen, spore and algal types were identified.
Local tree taxa included Nothofagus dombeyi type (this pollen
type includes N. dombeyi, N. betuloides, N. pumilio and N.
antarctica; however, N. dombeyi and N. betuloides do not
occur north of latitude 378 450 S). In this record, this pollen type
probably reflects N. pumilio and N. antarctica. Other local tree
pollen taxa are Nothofagus obliqua type (N. obliqua, N.
procera) and Prumnopitys andina; rainforest taxa from the
lowlands west of the Andean crest included Hydrangea,
Myrtaceae and Weinmannia; and local steppe shrub taxa
consisted of Lomatia/Gevuina type, Rhamnaceae, Berberis,
Ribes and Verbena. Common steppe herbs were Acaena,
Chenopodiaceae, Wendtia, Plantago and Phacelia. Wetland
herbs (Ranunculaceae, Valeriana, Lamiaceae, Liliaceae, Gentiana) and introduced European taxa (Rumex, Plantago
lanceolata) were also present. Macrofossil remains were
Copyright ß 2008 John Wiley & Sons, Ltd.
identified (Table 1) and total number of oospores of
charophytes (Charales) plotted in the pollen diagram.
Microscopic charcoal particles (larger than 20 mm) were
counted on the pollen slides and converted to charcoal
concentration (particles cm3). These data were converted
charcoal accumulation rates (CHAR; particles cm2 a1) by
dividing concentration by the deposition time of each sample
(cm a1). In addition, samples of 1 cm3 volume were taken at
0.5 cm intervals for macroscopic charcoal and plant macrofossil analyses. These samples were washed through nested
metal screens of mesh sizes of 250 and 125 mm. The residues
were identified and counted under a stereo microscope.
Because both macroscopic charcoal size fractions showed
similar trends through time, charcoal counts were combined
and divided by sample volume to calculate charcoal
concentration (particles cm3). Charcoal concentrations were
resampled into contiguous 25 a bins (the median resolution of
the record) in order to sample over equally spaced time
intervals through the record. CHAR was determined by dividing
concentrations (particles cm3) by deposition time (a cm1)
using Char Analysis software (Higuera et al., 2008). The slowly
varying trend often referred to as background charcoal
(BCHAR) was determined with a 700 a lowess smoother,
robust to outliers. Throughout the paper, we distinguish
between microscopic CHAR from discontinuous pollen slides
and macroscopic CHAR from the high-resolution analysis of
contiguous samples. Charcoal and terrestrial plant remains
used for AMS radiocarbon dating were washed thoroughly with
distilled water.
Results
Sediment description and chronology
From the base at 342–220 cm depth, the sediment was
composed of laminated inorganic silty clay that above
250 cm depth became more organic. Between 220 cm depth
and the surface, the sediment consisted of compact peats with
darker and lighter horizons. The magnetic susceptibility record
(Fig. 3) indicates high magnetic susceptibility associated with
inorganic sediment below 250 cm depth and low magnetic
susceptibility above that depth in organic sediments. Peaks in
magnetic susceptibility corresponded to volcanic ash layers,
including three thick layers at 106.5–112 cm, 265.5–272.5 cm
and 315.5–320.5 cm depth.
Core depth was initially adjusted for minor sediment
compaction (of 2–4 cm/50 cm core segment) by multiplying
the compacted length by a correction factor (core length/
compacted length) to reconstruct the actual length of each core
segment. For the purpose of developing an age model, core
depth was further adjusted by excluding the three thick and
pumiceous volcanic ash layers (106.5–112 cm, 265.5–
272.5 cm and 315.5–320.5 cm original depth, Fig. 3), assumed
to represent rapid deposition. Hereafter, depth refers to
adjusted depth.
Eight AMS radiocarbon dates were obtained on sieved
charcoal and organic material (Table 2 and Fig. 4). Two of the
radiocarbon dates (AA-57612: 7790 65 14C a BP, 309–311 cm
original depth; and AA-65184: 3751 39 14C a BP, 145–
145.5 cm original depth) were out of sequence and not used
in the age model. Two other dates overlapped (AA-57613:
5162 14C a BP at 80.5 cm and AA-65183: 4505 14C a BP at
99 cm original depth), and probability calculations using BCal
(Buck et al., 1999) indicated that the older date was an outlier.
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
DOI: 10.1002/jqs
LATE QUATERNARY VEGETATION AND FIRE HISTORY
251
Table 1 List and counts of terrestrial and aquatic plant macrophytes and Cladocera remains identified (numbers cm3 volume)
Depth (cm)
Nitella opaca
Nitella hyalina
Characf. braunii
Hypericum sp.
Bryophyte spores
Utricularia sp.
Cladocera
Zones
2
4
6
6
10
8
0
5
0
0
0
0
1
6
4
0
5
6
0
0
0
0
0
7
5
20
20.5
28.5
29.5
12
22
40
18
18
13
34
13
0
0
0
0
0
0
0
0
15
0
15
18
0
0
0
0
0
2
6
0
4c
34.5
47
58.5
59.5
60
10
18
10
10
23
9
0
8
4
44
0
0
0
0
0
0
0
0
0
0
15
15
10
10
12
0
0
0
0
0
0
0
0
0
0
76.5
80.5
81.5
91.5
95
96
96.5
12
21
2
22
3
15
22
17
36
31
46
34
59
31
0
1
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
15
0
0
0
0
0
0
0
0
0
0
1
2
8
5
0
1
4a
115
0
13
0
9
0
0
0
3
214
216
235
239
239.5
28
42
31
43
84
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
321
16
0
0
18
0
3
0
1
Hence, only five dates were used to develop the age model after
conversion to calendar years before present (cal. a BP) using
CALIB 5.0 (Stuiver et al., 2005). The dates were calibrated using
Southern Hemisphere calibration to the date 4504 cal. a BP and
Northern Hemisphere calibration for the dates of 8171, 10 250
and 13 820 cal. a BP. The basal age of the core was extrapolated
to ca 16 000 cal. a BP.
A range of possible calibrated dates and probability
distributions were determined for every radiocarbon date
4b
using CALIB 5.0.1 (Stuiver et al., 2005). Monte Carlo sampling
was used to generate a cubic smoothing spline through all the
dates 2000 times, and the final age–depth model was based on
the median of all the runs (Higuera, 2008).
Based on this chronology, deposition times were about 30–
40 a cm1 between ca. 17 000 and 7000 cal. a BP, 10–
20 a cm1 between 7000 and 4000 cal. a BP, 10 a cm1
between 4000 and 2200 cal. a BP, 30–40 a cm1 between 2200
and 400 a cm1 and 10 a cm1 during the last 400 a.
Figure 2 Map showing sites of charcoal records (see Fig. 7)
Copyright ß 2008 John Wiley & Sons, Ltd.
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
DOI: 10.1002/jqs
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JOURNAL OF QUATERNARY SCIENCE
Table 2 List of radiocarbon dates, corresponding calibrated ages and information on materials dated
Lab code
Depth (cm)
14
C age
SD
d13C%
AA65182
AA57613
AA65183
AA65184
AA57611
AA65185
AA57612
AA65186
13
30.5–31
80.5–81.5
99–100
145–145.5
228.5–229
254.5–256
309–311
331–332
400
2740
5 162a
4 505
3 751a
8 171
10 250
7 790a
13 820
130
77
60
39
72
58
65
76
25
28.44
22
27.5
28.18
21.8
28.53
14.4
a
cal age BP
(median probability)
400
2 873
5 831
5 155
4 113
9 133
12 002
8 568
16 465
Upper
Lower
Material dated
2
5
5
4
9
12
8
16
2
5
4
3
8
11
8
16
European taxa
Sedge fragments
Sedge fragments/charcoal
Sedge fragments/charcoal
Sedge fragments
Organic fragments
Bulk sediment
Organic fragments
Bulk sediment
990
925
135
130
142
192
636
669
700
837
966
924
984
754
397
247
Dates not used in chronology.
Pollen and charcoal record
Throughout the record, the pollen assemblages are codominated by steppe and forest taxa, suggesting that, like at
present, steppe grew in the valleys and Nothofagus forest grew
on the mountain slopes. The pollen stratigraphy was divided
into five zones using a constrained cluster analysis (Grimm,
1987) of terrestrial and aquatic taxa (Fig. 5). Microscopic CHAR
provided a reconstruction of regional fire conditions, and
macroscopic CHAR was used to infer local fire conditions
(Fig. 6). The variable sedimentation rates suggest a changing
depositional environment and, for that reason, charcoal peaks
or particular fire episodes were not identified. Instead, total
macroscopic CHAR was used to infer general fire activity
during the time represented by different pollen zones.
Figure 3 Magnetic susceptibility of the Mallı́n Vaca Lauquen sediment core (original depth)
Copyright ß 2008 John Wiley & Sons, Ltd.
Zone 1 (320–288 cm depth; 17 000–14 900 cal. a BP)
featured 60–80% non-arboreal taxa, composed of Poaceae
(40%); steppe shrubs, including Asteraceae (10–15%), Ephedra
(2%), Rhamnaceae (5%) and Ericaceae (5–10%); and steppe
herbs (15–20%). Arboreal taxa Nothofagus dombeyi type and
Prumnopitys andina accounted for 10–20% each. N. obliqua
type and rainforest taxa were present in trace amounts.
Escallonia accounted for 5%. Pollen concentration was low.
with a mean of 400 grains cm3. Pediastrum boryanum var.
longicorne was abundant but fluctuated markedly (200–
1000%). At levels where Pediastrum boryanum var. longicorne
was less abundant, traces of Myriophyllum, rare Utricularia
seeds and oospores of charophytes were found. The charophyte
was identified as Nitella opaca (Table 1). Microscopic and
macroscopic CHAR values were negligible, suggesting that fires
were virtually absent.
The primary pollen constituents of this zone suggest
herbaceous grassland with open ground. A considerable
number of taxa were present that grow on sandy and rocky
substrates, such as alluvial fans and cobble shorelines (Ephedra,
Ericaceae (Pernettya), Plantago, Colobanthus (Caryophyllaceae)). These taxa are often found in Lateglacial basal samples,
reflecting colonisation of disturbed terrain (e.g. M. Pollux,
Markgraf et al., 2007) and thus the assemblage has no direct
analogue with modern steppe assemblages (Paez et al., 2001;
Markgraf et al., 2002). Despite the relatively high inorganic
content the deposition time was slow (30 a cm1).
Zone 2 (288–212.9 cm depth; 14 900–8600 cal. a BP) had
slightly higher values of Poaceae than before (up to 50%).
Nothofagus dombeyi type increased to 30%, whereas Prumnopitys andina decreased to 10%, and N. obliqua type
continued to be present in traces, reaching 2–5% at
some levels. Rainforest taxa (Hydrangea, Myrtaceae, etc.)
were more prominent during this interval. Pollen abundance of
steppe shrub taxa continued as before with a mean of 5%.
Pollen of open ground taxa (e.g. Plantago) decreased to
negligible amounts. Wetland herb types increased to 5%.
Pollen concentration continued to be low with 300–
400 grains cm3. Pediastrum boryanum var. longicorne
fluctuated around a mean of 200% and Nitella opaca appeared
in the upper part of this zone (ca. 10 800 cal. a BP) with
numbers between 20 and 50 cm3. At those levels, Pediastrum
boryanum var. longicorne was rare or absent. Microscopic and
macroscopic CHAR values were low in this zone but higher
than before, implying some fires in the region. The deposition
time was even slightly slower than in Zone 1 (40 a cm1). The
assemblage indicates a more diverse herbaceous steppe than
before, with less open and disturbed ground, comparable to the
palynologically defined ’mid-grass steppe’ of Paez et al. (2001)
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
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LATE QUATERNARY VEGETATION AND FIRE HISTORY
253
0
Age (cal yr BP)
2000
4000
6000
8000
10000
12000
14000
cubic spline interpolant, 95% CI
16000
350
300 250 200 150 100
50
depth below mud-water interface (cm)
00.02 0.0810 30 50
sed. rate resolution
(cm yr -1) (yr sample-1)
Figure 4 Age–depth model and sedimentation rates for the Mallı́n Vaca Lauquen record
or estepa graminosa (León et al., 1998). Reduced erosion,
inferred from the decreased magnetic susceptibility of the
sediments, could explain the markedly lower sedimentation
rates than in the previous zone. Nothofagus forest along the
mountain slopes, probably composed of both N. pumilio and
N. antarctica, became denser, limiting the habitat for
Prumnopitys andina.
Zone 3 (212.9–107.5 cm depth; 8600–5300 cal. a BP)
showed an increase of Nothofagus dombeyi type to 40%, on
account of a decrease of Poaceae (40–50%). Prumnopitys
andina decreased to trace amounts. Nothofagus obliqua type
appeared continuously, reaching values of 5% in the upper part
of the zone; steppe shrub pollen types continued with low
values; and rainforest pollen percentages decreased. Wetland
herb taxa slightly increased to 10% and Escallonia showed
several peaks of 15%. Pollen concentration continued low with
400 grains cm3, except for one high value at 110 cm depth.
High percentages of Cyperaceae (500–600%) indicate
initiation of wetland conditions, although some open water
must have existed intermittently to support the presence of
Myriophyllum, oospores of Nitella opaca and Botryococcus in
some levels. In the upper portion of this zone, Caryophyllaceae
pollen (Stellaria/Arenaria pollen type) appeared with values
between 100% and 500%, suggesting shoreline disturbance by
seasonal water-level fluctuations. Both macroscopic CHAR and
microscopic charcoal values increased in this zone. Macroscopic CHAR reached 0.80 particles cm2 a1, suggesting local
fires, and microscopic CHAR was moderate (100 particles cm2 a1),
Figure 5 Pollen record of Mallı́n Vaca Lauquen
Copyright ß 2008 John Wiley & Sons, Ltd.
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JOURNAL OF QUATERNARY SCIENCE
Figure 6 Charcoal record of Mallı́n Vaca Lauquen
consistent with more regional fire activity. Deposition time was
twice as fast (10–20 a cm1) as during zones 1 and 2, reflecting
the onset of peat growth.
Zone 4 (107.5–13 cm depth; 5300–400 cal. a BP) is
characterised by the onset of continuing presence of Nothofagus obliqua type together with high values of N. dombeyi
type. Rainforest and steppe shrub pollen types were sporadically present. Pollen of steppe herbs and wetland herbs were
less abundant overall compared with values in Zone 3. This
zone can be divided into three subzones based on changes in
the proportions of arboreal and non-arboreal taxa. The initial
subzone (4a: 107.5–60.2 cm depth; 5300–4200 cal. a BP) had
50% Poaceae, 30% Nothofagus dombeyi type, as well as
slightly higher percentages of Acaena and lower Asteraceae.
Pollen concentration continued low with 400 grains cm3,
although deposition time was high, as in Zone 3 (10–
20 a cm1). The middle subzone (4b: 60.2–30.8 cm depth;
4200–2200 cal. a BP) showed slightly lower values for Poaceae
(40% mean) and steppe taxa and slightly higher values for
Nothofagus dombeyi type (45%). Pollen concentration
doubled with values of 800 grains cm3, reaching a maximum
of 1200 grains cm3, while deposition time continues high (10
a cm1). The upper subzone (4c: 30.8–13 cm depth; 2200–
400 cal. a BP) featured an increase in Poaceae percentages to
50% and a decrease of Nothofagus dombeyi type to 40%.
Pollen concentration was slightly lower with 700 grains cm3
and deposition time was slower as well (30–40 a cm1).
Cyperaceae decreased to a mean of 200%, whereas aquatic
taxa increased. Among the aquatic taxa, Charophyte oospores
were persistently high, although highly variable, especially in
subzones 4a and 4c and one level in 4b. Charophytes were
dominated by Nitella hyalina (Table 1), a shallow-water species
that currently grows in 0.15–0.8 m water depth (Garcı́a, 1987;
Cáceres and Garcı́a, 1989); N. opaca, a species tolerating
deeper waters, was also present in low amounts. At one level in
Copyright ß 2008 John Wiley & Sons, Ltd.
subzone 4a, Chara braunii, a taxon commonly associated with
Nitella hyalina (Corillion, 1957), was found. Pediastrum
boryanum var. longicorne appeared intermittently with low
values in subzones 4a and 4c; Myriophyllum was essentially
absent except for occurrences in subzone 4a. Botryococcus had
rare occurrences. Subzones 4a and 4c indicate shallow,
fluctuating water levels; subzone 4b had high amounts of
bryophyte spores, indicating intermittently dry conditions.
During 4a, macroscopic and microscopic CHAR reached
their highest levels of the record (macroscopic CHAR was up to
12.0 particles cm2 a1 and microscopic CHAR reached 1516
particles cm2 a1). These high levels decreased dramatically
in subzone 4b, and after 3500 cal. a BP very few fires were
registered. In subzone 4c, CHAR levels were again elevated
(macroscopic CHAR was up to 14.50 particles cm2 a1 and
microscopic CHAR reached 6650 particles cm2 a1), indicating significant local and regional fire activity. The pollen and
charcoal data suggest that moisture variability must have been
higher overall, especially in the lower and upper subzones (4a
and 4c) than in the middle subzone to create conditions for
Nothofagus obliqua type to occur, and higher fire activity.
Overall conditions, however, were wetter than in Zone 3,
especially in subzones 4a and 4c.
Zone 5 (13–0 cm depth; 400–0 cal. a BP) showed a marked
decrease in Poaceae, coupled with an increase in Nothofagus
dombeyi type, steppe shrub taxa and mesic herbs. Introduced
European weed taxa appeared (Plantago lanceolata, Rumex
acetosella), indicative of grazing and logging. During the upper
part of this zone, Nothofagus dombeyi type also decreased,
documenting more intense forest clearance in more recent
times. Pollen concentration continued high with 800
grains cm3 and deposition time increased (10 a cm1),
suggesting higher erosional input. The charophytes, Nitella
hyalina and N. opaca, dominated during this interval, while
Pediastrum boryanum var. longicorne and Myriophyllum were
present intermittently, indicating seasonally fluctuating water
levels, as observed during fieldwork in 1981. CHAR values in
the last 1000 a are relatively low (macroscopic CHAR
was <0.90 particles cm2 a1 and microscopic CHAR was
<530 particles cm2 a1). These data suggest a limited role for
fire in the local watershed as well as regionally in recent
centuries.
Palaeoenvironmental and palaeoclimate
history
The general vegetation history inferred from this core is
comparable to the early study (Markgraf, 1987). However, the
additional detailed record of limnological changes and fire
history provide a more detailed palaeoenvironmental and
palaeoclimatic picture. The different proportions of aquatic
taxa in the two records are related to the fact that the present
record was taken in the deepest, wettest part of the basin, which
was dry in 2002 but inundated in 1981. The earlier core, taken
at a marginal location, showed high percentages of Botryococcus and low values of Pediastrum boryanum var. longicorne, indicating shallow and fluctuating water levels. The
present record has high amounts of Pediastrum boryanum var.
longicorne and only a few levels with Botryococcus, reflecting
its deeper water location.
During the last 17 000 cal. a, open-water conditions must
have existed in the shallow basin, allowing for the continuous
presence of aquatic taxa. Between 16 000 and 14 800 cal. a BP,
high amounts of aquatic taxa were present: Pediastrum
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
DOI: 10.1002/jqs
LATE QUATERNARY VEGETATION AND FIRE HISTORY
boryanum var. longicorne, an algae common in small, highelevation lakes (Komárek and Fott, 1983; Jankovská and
Komárek, 2000); the charophyte Nitella opaca, a cosmopolitan
species that thrives in water depths of 0.5–2.5 m, but also grows
in clear waters up to 40 m depth (Corillion, 1957); Utricularia, a
montane to subalpine, shallow-water plant; and shallow-water
diatoms growing in low-productivity environments (Fragilaria
construens, var. venter and Cyclotella stelligera in the basal
samples of the original core; Markgraf, 1987). These taxa
suggest clear, dystrophic and slightly acidic waters. Such lowproductivity environments were apparently common in the
Lateglacial period during the early stages of lake development
(Bradbury and Whiteside, 1980).
The initial terrestrial vegetation at Mallı́n Vaca Lauquen
between 17 000 and 14 900 cal. a BP was a shrub–steppe with
considerable open, sandy and gravely ground. This patchy
landscape suggests cool and dry conditions. An interesting
aspect of this interval is the occurrence of Prumnopitys andina
pollen, which is also documented at the Tagua Tagua site west
of the Andes at latitude 34.58 S (Heusser, 1990). Prumnopitys
does not occur at either site today, but scattered individuals
grow on the Chilean side of the Andes from latitude 35.58 S to
438 S at 600 and 1000 m elevation, in association with
Austrocedrus chilensis, Nothofagus obliqua, N. pumilio and
Lomatia hirsuta (Veblen et al., 1995). At latitude 388 S to the
south of Mallı́n Vaca Lauquen, Prumnopitys andina crosses the
Andes into Argentina as individual trees near upper treeline
(Donoso, 1974). This limited geographic and elevational
distribution is confined to areas of low temperatures and dry
summers (Veblen et al., 1995). Apparently, Prumnopitys andina
was more widespread than today on both sides of the Andes
during the initial period of deglaciation (Markgraf et al., 1992,
2002; Whitlock et al., 2001). Its presence at Mallı́n Vaca
Lauquen is consistent with about 68C cooler Pacific sea surface
temperatures (latitude 418 S, Lamy et al., 2004; latitude 348S,
Kim et al., 2002), a strengthened southeastern Pacific highpressure system, and weakened Southern Westerlies (Markgraf
et al., 1992; Lamy et al., 1999).
Between 14 900 and 8600 cal. a BP, the steppe environment
was more diverse than before and the high proportion of herb
pollen is characteristic of modern pollen assemblages from the
present-day grass steppe (Paez et al., 2001), where precipitation is about 500 mm (Paruelo et al., 1998). Forests on the
slopes around the site continued open with Prumnopitys andina
and Nothofagus pumilio/N. antarctica. Higher amounts of longdistance pollen from rainforest taxa are attributed to an
expansion of Valdivian rainforest in the Chilean lowlands
(Moreno, 1997, 2004). Initially the lake was still dystrophic but
increased abundance of the charophyte Nitella opaca by
10 000 cal. a BP suggests increased alkalinity. Conditions were
warmer and wetter than before, although the openness of the
forest at Mallı́n Vaca Lauquen suggests that precipitation was
less than at present. Fires were not a significant component of
the ecosystem, judging from low CHAR values.
Drier-than-present conditions have also been suggested from
marine and terrestrial records at latitude 348 S (Lamy et al.,
1999; Villa-Martı́nez et al., 2004). In contrast, records between
latitudes 40 and 458 S show rainforest expansion by 14 800 cal.
a BP, suggesting that moisture had reached present levels in that
region (e.g. Moreno, 1997, 2004; Villagrán, 2001; Markgraf
et al., 2002; Haberle and Bennett, 2004). Westerly winter
storms had apparently become established south of latitude
408 S at this time (Markgraf et al., 2002; Whitlock et al., 2006),
but the southeastern Pacific High continued to be stronger than
today. This combination resulted in a less pronounced
precipitation increase to the north of latitude 408 S than to
Copyright ß 2008 John Wiley & Sons, Ltd.
255
the south (Markgraf et al., 1992; Lamy et al., 1999; Romero
et al., 2006).
After 12 000 cal. a BP, however, aridity returned to mid
latitudes. This early Holocene (12 000–8000 cal. a BP) aridity
has been widely documented in marine and terrestrial records
between latitudes 54 and 338 S (Villagrán, 1991, 2001;
Markgraf et al., 1992, 2007; Lamy et al., 1999, 2001, 2004;
Huber et al., 2004; Moreno, 2004). In the rainforests west of the
Andes, drought- and disturbance-adapted rainforest elements
(especially Nothofagus obliqua and Weinmannia trichosperma) became dominant at that time (Villagrán, 1991,
2001; Moreno and León, 2003; Abarzúa and Moreno, 2008)
and high-latitude Nothofagus forests continued quite open
(Huber et al., 2004). The duration of this interval is longer and
more pronounced at high latitudes than at mid latitudes and
east of the Andes, as illustrated by a comparison of charcoal
records between latitudes 52 and 358 S (Fig. 7). Highest fire
activity at latitude 528 S occurred between 12 000 and
5500 cal. a BP and at 458 S between 11 000 and 7000 cal. a BP
(Rio Rubens: Huber et al., 2004; Mallin Pollux: Markgraf et al.,
2007). At latitude 42–358 S, west of the Andes, highest fire
activity occurred between 11 000 and 9000 cal. a BP and after
3000 cal. a BP (Lago Melli: Abarzúa and Moreno, 2008; Tagua
Tagua: Heusser, 1990; Purén-Lumaco: Abarzúa, pers. comm.).
East of the Andes at lat 418 S (Laguna el Trébol: Whitlock et al.,
2006), high activity is registered after 8000 cal. a BP with 1000
a long maxima centred at 6500, 4500, 3500 and 1000 cal. a BP.
Arid conditions during the early Holocene have been
attributed to substantially weaker Westerlies or latitudinally
shifted westerly storm tracks, related to a strengthened
southeastern Pacific High (Markgraf et al., 1992; Whitlock
et al., 2007). However, a poleward shift in the Westerlies does
not fully explain these east–west differences in fire activity. An
anomalous component of upper-level flow associated with the
west–east dipole may have resulted in opposite moisture
regimes west and east of the Andes, but this hypothesis bears
further study.
Mallı́n Vaca Lauquen did not show this early Holocene arid
and warm interval with high fire activity; instead conditions
continued cool and dry until 8600 cal. a BP. Only between
8600 and 5300 cal. a BP did conditions became markedly
warmer at Mallı́n Vaca Lauquen, based on the development of
Cyperaceae wetland in the shallow basin, only briefly
interrupted by periods with open water. Precipitation became
more variable, as evidenced by fluctuations in local shoreline
taxa (Escallonia, Arenaria/Stellaria pollen type) and between
steppe and forest taxa. The steppe assemblage compares with
present-day shrub steppe (estepa arbustivo-graminosa; León
et al., 1998, Paez et al., 2001), where precipitation is <400 mm
(Paruelo et al., 1998). Elevated levels of microscopic CHAR at
Mallı́n Vaca Lauquen, especially between 5000 and 4500 cal. a
BP, may have come from regional fires in the Chilean lowlands.
The Tagua Tagua site features high levels of charcoal at this
time (Heusser, 1990) (Fig. 7). Higher levels of charcoal and low
lake levels are also observed between ca 10 000 and 6000 cal. a
BP in a record from the Purén-Lumaco valley (latitude 388 300 S,
longitude 738 W), located on the southeastern slope of the
Coastal Chilean Range (Nahuelbuta Range, Abarzúa, pers.
comm.). The macroscopic charcoal record suggests some local
fires at Mallı́n Vaca Lauquen at about 7500 cal. a BP.
By 5300 cal. a BP, the present-day mixed Nothofagus
obliqua/N. pumilio forest had become established in the
region, indicating a shift to present-day winter rain/summer
drought conditions. High abundance of charophytes, Nitella
opaca and N. hyalina at Mallı́n Vaca Lauquen suggests more
permanent water than before. Nitella hyalina is a shallow-water
species growing at 0.15–0.8 m water depth (Garcı́a, 1987;
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
DOI: 10.1002/jqs
JOURNAL OF QUATERNARY SCIENCE
Ri
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this study
Figure 7 Charcoal records for sites in southern South America (for location of sites see Fig. 2)
Cáceres and Garcı́a, 1989), whereas N. opaca tolerates deeper
waters, generally around 2 m, but occasionally to 40 m depth
(Corrillion, 1957). The fluctuations between these two taxa
indicate variable conditions, with shallower water between
5300 and 4200 cal. a BP and after 2200 cal. a BP and slightly
deeper water between 4200 and 2200 cal. a BP. The
limnological changes seen at Mallı́n Vaca Lauquen are more
or less synchronous with fluctuations in the abundance of the
wetland taxon Typha at the Tagua Tagua site during the last
5000 cal. a (Heusser, 1990). Freshwater algae at Laguna de
Culeo during the last 2500 cal. a (Chilean lowlands at 348 S;
Jenny et al., 2002; Villa-Martı́nez et al., 2004) are also
interpreted to reflect increased moisture coupled with high
hydrologic variability.
Very high CHAR values between 5300 and 4200 cal. a BP
and to a lesser degree after 2200 cal. a BP indicate increased fire
activity locally and regionally, as a result of more fuel biomass
and more suitable fire climate. Reduction of Nothofagus
pumilio/N. antarctica forest cover and the expansion of
grassland and disturbance taxa are consistent with more fire
activity at this time. High charcoal abundance during this
interval is also seen in records from the Chilean lowlands at
Tagua Tagua (Heusser, 1990), the Purén-Lumaco valley
(Abarzúa, pers. comm.) and Lago Melli (Abarzúa and Moreno,
2008), beginning by 3000 cal. a BP.
Higher-than-present moisture coupled with increased multicentennial variability by 5000 cal. a BP has been inferred from
marine and terrestrial records (McGlone et al., 1992; Lamy
et al., 1999; Jenny et al., 2002; Villa-Martinéz et al., 2004). At
latitudes north of 408 S, it is likely that ENSO variability and
associated increased convective storm activity during El Niño
years increased fire activity in the last 5500 cal. a (Kitzberger
and Veblen, 2003) (e.g. Markgraf and Diaz, 2000; Moy et al.,
2002).
Multi-centennial records, such as those presented here,
cannot document ENSO’s inter-annual and inter-decadal
Copyright ß 2008 John Wiley & Sons, Ltd.
variability. However, the present-day correlation between El
Niño-related drought conditions (Montecinos and Aceituno,
2003) and historical fire years (Kitzberger and Veblen, 2003)
suggests that ENSO variability is a factor in mid-latitude fire
occurrence. Palaeoenvironmental records have indicated that
ENSO variability was strengthened during the mid and late
Holocene (McGlone et al., 1992; Moy et al., 2002), and strong
ENSO variations may account for high fire activity at 5000 cal. a
BP (primarily east of the Andes), 3000 cal. a BP and between
2000 and 1000 cal. a BP. One could speculate that high fire
activity in the late Holocene seen similarly in the mid latitudes
on both sides of the Andes reflects the influence of ENSO and
the build-up of fuels.
The last 400 cal. a show the influence of humans on the
vegetation and fire regimes of the Mallı́n Vaca Lauquen region.
A decrease in Poaceae and Nothofagus and an expansion of
European weeds (Rumex acetosella, Plantago lanceolata) are
noted in the pollen record and attributed to a decrease in
grassland from livestock grazing and a decrease of Nothofagus
due to forest clearance. The impact began in the 16th century
with the arrival of Spanish colonists. The markedly faster
deposition time after 400 a (30 a cm1) is probably not the
result of greater in-wash of clastic sediments into the basin
because magnetic susceptibility values are low. Instead, it may
be the result of greater water run-off leading to more persistent
moisture in the basin and wetland development. Low levels of
charcoal at this time, implying negligible or small-scale
burning, support the local wet site conditions.
Conclusion
High relief and steep climatic gradients in the southern Andes
produce diverse environments that are also reflected by a
J. Quaternary Sci., Vol. 24(3) 248–258 (2009)
DOI: 10.1002/jqs
LATE QUATERNARY VEGETATION AND FIRE HISTORY
diverse environmental history. Mallı́n Vaca Lauquen represents
the only high-elevation site so far studied with mixed
Nothofagus obliqua/N. pumilio forest located near the
transition to the Monte desert scrub vegetation. One unique
feature of the past history is the Lateglacial and early Holocene
(17 000–8600 cal. a BP) presence of Prumnopitys andina,
indicating cooler and drier summers than today. This might
perhaps explain the absence of fires in that area at this time. The
late appearance of Nothofagus obliqua after 5000 cal. a BP
represents another environmental change not seen in other
records. Together with more permanent water in the lake, the
presence of N. obliqua marks the establishment of the presentday winter rain/summer drought climate regime in the late
Holocene. Although Austrocedrus chilensis is locally present in
the forests in small numbers, it never played a major role in this
region’s past history, in contrast to records farther south and
east of the Andes.
Unlike most sites in southern Patagonia, which show high
fire activity in the early Holocene, Mallı́n Vaca Lauquen and
Laguna el Trébol at latitude 41.58 S record high charcoal levels
in the mid and late Holocene. At Mallı́n Vaca Lauquen, inferred
fire activity is highest between 5300 and 4200 cal. a BP and
after 2200 cal. a BP. The latitudinal differences in timing may
be related to fundamentally different climatic controls on fire
activity, in particular the stronger influence of ENSO variability
at mid latitudes. Additional records are needed in this region to
describe the geographic extent of this pattern and better
understand the underlying drivers of past fire activity.
Acknowledgements NSF grants to CW (ATM 0117160 and ATM
0714061) are acknowledged. We also thank Allison Bair, Caitlin
MacCracken and Jaime Toney for assistance with laboratory analyses,
and Victor Leshyk for help with the maps. Christy Briles helped with the
age model. Northern Arizona University, Laboratory of Paleoecology
Contribution 112.
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