Available online at www.sciencedirect.com

nology 149 (2008) 18–28www.elsevier.com/locate/revpalbo

Review of Palaeobotany and Paly

Vegetational and climatic history during the late Holocene in Lake Laja basin(central Chile) inferred from sedimentary pollen record

Laura Torres a,b,⁎, Oscar Parra c, Alberto Araneda b,c, Roberto Urrutia b,c,Fabiola Cruces a,b, Luis Chirinos d

a Departamento de Botánica, Universidad de Concepción, Barrio Universitario s/n, casilla 160-C, Concepción, Chileb GEP (Grupo de Estudios Paleolimnológicos), Unidad de Sistemas Acuáticos, Centro EULA-Chile, Universidad de Concepción, Chile

c Centro EULA-Chile, Universidad de Concepción, Barrio Universitario s/n, casilla 160-C, Chiled Departamento de Ingeniería, Pontificia Universidad Católica del Perú, Avenida Universitaria Cuadra 18 s/n, San Miguel, Lima 32-Apartado 1761, Perú

Received 23 November 2006; received in revised form 3 October 2007; accepted 12 October 2007Available online 22 October 2007

Abstract

This study reports a pollen analysis from Lake Laja, an Andean lake in central Chile, from 800 cal. yr BC to present. A 522-cm core was takenfrom the deepest part of the lake and pollen was analyzed according to conventional methods. The core was dated using 210Pb and 14C techniques.Lake Laja is located at 1360 masl, next to Antuco volcano and, due to the westerly circulation belt, the predominant climate in the area is humid-temperate and cool. Interannual climate variability is related to El Niño-Southern Oscillation. Currently, the vegetation cover is 53% native forest,27.8% shrub, 16% Andean steppe, and 3.2% annual and perennial prairies. The study results indicated that Nothofagus dombeyi-type, Nothofagusobliqua-type, Ephedra chilensis, and Poaceae were the most important taxa during the last 2800 yr BP. The climate was slightly less humidbetween 800 cal. BC and 660 AD than at present. Between 660 AD and 1561 AD, humid conditions increased with respect to the previous period.Later pollen records evidenced a drier period between 1561 and 1894 AD, corresponding to the last phase of the LIA in Europe. Finally, between1938–1968 AD, intense human impacts were evidenced by the appearance of Plantago and the increased frequency of Poaceae and Asteraceae.After 1968 AD, the pollen records show decreased anthropic disturbances, as well as increased humid conditions.© 2007 Elsevier B.V. All rights reserved.

Keywords: pollen; Late Holocene; climate changes; human impact; central Chile; Lake Laja

1. Introduction

Several pollen records show that moisture and temperaturesincreased from 4000 cal yr. BP in central Chile (Heusser, 1990;Villa–Martínez and Villagrán, 1997; Villagrán, 2001; Mal-donado and Villagrán, 2002; Villa-Martínez et al., 2003, 2004).However, most palynological studies do not have the appro-priate resolution for understanding climatic variations on short(i.e., decadal to century) timescales during the Late Holocene.Based on higher resolution studies during the Late Holocene,

⁎ Corresponding author. Departamento de Botánica, Universidad de Concep-ción, Barrio Universitario s/n, casilla 160-C, Concepción, Chile. Tel.: +56 412203301; fax: +56 41 2207076.

E-mail address: latorres@udec.cl (L. Torres).

0034-6667/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.revpalbo.2007.10.001

climatic events like the Little Ice Age (LIA) and MedievalWarm Period (MWP) are well reported in the NorthernHemisphere (see a review of Soon et al., 2003), but very littlehas been published about these events in South America (Soonet al., 2003; Habersettl et al., 2005). Thus, the question ofwhether the LIA and MWP were global events remainsunanswered (Mann, 2002). On the other hand, higher resolutionstudies of the last 400 years in Chile should contribute to ourunderstanding of the recent human impact on ecosystems. Fewstudies of either climatic anomalies or human impacts duringthe last 2000 cal. yr BP have been done for central Chile.

In Chile, paleo-palynological data is lacking that wouldreveal the characteristic vegetational and climatic changes of theLIA and MWP. However, other proxies have been used toprovide information about the climatic conditions during these

19L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

events. Villalba (1990,1994), and Lara and Villalba (1993)reported two periods of glacial advances (1270–1380 AD and1520–1670 AD). Likewise, Koch and Kilian (2005) reportedthat Glaciar Lengua and possibly all the glaciers of Gran CampoNevado reached their Holocene maximum during the LIA.Ortlieb et al. (2000) reported an episode of warmer sea surfacetemperatures eight centuries ago that coincided with the MWP.Lamy et al. (2001) found humid and less humid periods duringthe LIA and MWP, respectively. Bertrand et al. (2005) carriedout a high resolution study of the last 600 years, reporting a wetperiod from 1490 to 1700 AD and a dry period from 1700 to1900 AD, concluding that the LIAwas a global event. Recently,Araneda et al. (in press) used historical data to show a coolingperiod between the eighteenth and nineteenth centuries for SanRafael glacier.

In contrast to the above, some paleo-palynological studies inChile have analyzed the vegetational changes during a period ofintense human activity. Szeicz et al. (1998) did a study in thesouth of Chile (45°S, 72°W), concluding that the decreasedNothofagus forest during the twentieth century was the resultof human impacts. Later, Szeicz et al. (2003), working with apollen record from Lake Facil (44°S), suggested that the

Fig. 1. Study area showing the core sampling s

episodes of burning that occurred during the last 600 years werethe main factor in the dieback of Pilgerodendron uviferum(D. Don) Florin and the opening up of the forest canopy. Thisprobably also resulted from burning by native Chono peoples.For central Chile, Jenny et al. (2002) and Villa-Martínez et al.(2004) concluded that the vegetational changes in the LakeAculeo basin (lat. 34°S) over the last 250 years were related tohuman deforestation.

The aim of this research is to describe the vegetationalchanges during the last 2800 cal. yr BP through pollen analysesfrom Lake Laja, central Chile, in order to infer climaticvariations with special emphasis on the LIA and MWP andhuman impact over the last 400 years.

2. Materials and methods

2.1. Description of study area

Lake Laja (36° 54′S; 71° 05′W, Fig. 1) is situated at1360 masl in the Chilean Andes, with a maximum depth of135 m and a surface area of 87 km2. Because of the westerlycirculation belt, the climate is humid temperate to cool and less

ite and the bathymetric map of Lake Laja.

20 L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

humid in areas over 1800 masl. The average annual precipita-tion is 2172 mm, concentrated mostly between May and August(fall–winter), mostly in the form of snow. The driest months areJanuary, February, and March (summer). The lowest tempera-tures occur in June (on average, −0.3 °C) and the highest inJanuary (on average, 13.6 °C) (Conaf, 2004). Interannualclimate variability is related to El Niño-Southern Oscillation(ENSO) events, which are associated with abundant precipita-tion during the late spring (Aceituno, 1992; Montecinos andAceituno, 2003).

2.2. Geological and geomorphological characteristics

The valley where the Lake Laja basin is located was initiallycarved by lower Pleistocene glacial activity on a Tertiarybasement (Cura-Mallín and Trapa Trapa formations). Fourmajor Quaternary units were deposited unconformably overthis: the polygenic Quilleco alluvial cone, a Pleistocenevolcanic sequence, and the products of the Antuco Volcanoand the Antuco Volcano avalanche (Thiele et al., 1998).Volcanic activity has been continuous from the Pleistocene tothe present. This and glacial and fluvial actions are the mostimportant morphogenetic factors in the Lake Laja basin(Mardones, 2002).

Lake Laja is located next to Antuco Volcano. This volcano isa mixed and composite andesitic to basaltic andesitic strato-volcano of basalt, which started its activity ca. 130,000 yr BP(Thiele et al., 1998). Its first constructive phase (Antuco 1)ended at 9700±600 yr BP with the lateral gravitational collapseof the edifice; this event produced a major volcanic avalanchethat dammed the natural outlet of Lake Laja and its tributaries.Antuco Volcano is characterized by weak to medium strom-boliana activity and last erupted in 1911 (Niemeyer and Muñoz,1983; Thiele et al., 1998).

2.3. Current vegetation

The vegetation registry of the National EnvironmentalInformation Systems reported 55.8% vegetation coverage ofthe Lake Laja basin, distributed as follows: 53% native forest,27.8% shrub, 16% Andean steppe, and 3.2% annual andperennial prairies.

The current vegetation in the Lake Laja basin is composed ofAustrocedrus chilensis (D. Don) Pic. Ser. et Bizz, Lomatiahirsuta (Lam.) Diels ex Macbr, Maytenus boaria Mol., Schinuspolygamus (Cav.) Cabrera, Colletia ulicina Gill. et Hook., Ar-istotelia chilensis (Mol.) Stuntz, Orites myrtoidea (Poepp. andEndl.) Benth. and Hooker, and Ephedra chilensis K. Presl(Veblen and Schlegel, 1982; Hoffmann, 1982; Donoso, 1982).Nothofagus alpina (Poepp. and Endl.) Oerst., Nothofagusdombeyi (Mirb.) Oerst., Nothofagus antarctica (G. Forster)Oerst, Nothofagus obliqua (Mirb.) Oerst. var. obliqua andNothofagus pumilio (P. et E.) Krasser (Conaf, 1993). The mostabundant species in Parque Nacional Laguna del Laja areA. chilensis- O. myrtoidea. A. chilensis is associated withS. polygamus, C. ulicina, and Baccharis magellanica (Lam.)Pers. (Rondanelli et al., 2000). The tree line is formed by

N. pumilio stands of erect trees at ca. 1700–1750 m elevation,with some shrubby patches of N. Antarctica growing up to1800 m (Lara et al., 2001). The vegetation landscape at 1900 mcorresponds to high Andean steppe, with a communitydominated by the cushion plants Oreopolus glacialis, Acaenaspp., and Adesmia. Poaceae and annual herbs are also common(Badano et al., 2002).

2.4. Coring, dating and grain size

The 522-cm-long sediment core was taken from the deepestpart of the lake (Fig. 1) with an Uwitec platform. The coringtechnique involved overlapping the different consecutivessequences of the sediment record. Contiguous 1-cm sampleswere analyzed from the top 26 cm of the core for 210Pb andverified with 137Cs activity (Fig. 2). Ages were determined from210Pb activity by means of the CRS (constant rate supply)model. AMS 14C dates were obtained for three bulk sedimentsamples (Table 1). Radiocarbon determinations from bulksediment are problematic because of the variable sources ofcarbon available. Therefore, this type of carbonaceous sample isnot the most accurate. However, the three ages are coherent(Table 1) and, in conjunction with the 210Pb chronologies, weobtained reliable calibrated ages. Radiocarbon dates werecalibrated using the CALIB 5.0.2 program (McCormac et al.,2004). Based on the 210Pb and calibrated 14C ages, the age-depth model was developed to assign interpolated calendarages. The model corresponds to the second-order polynomial(Fig. 3).

Grain size measurements were performed on bulk sedimentusing a laser diffraction particle analyzer Malvern Martersizer2000 detecting a 0.02–2000 μm size range. Samples wereintroduced into a 100 ml demonized water tank free of additivedispersant, split with a 2000 rpm stirrer and crumbled withultrasonic waves. The grain size was classified according toWentworth (1922).

2.5. Pollen

Pollen samples were taken at 1-cm intervals along the top50 cm, at 2-cm intervals between 50 and 100 cm, and at 5–10-cm intervals between 100 and 522 cm. The criterion used for theinterval selection was the highest resolution during the last400 cal. yrs BP according to the top 100 cm of the age-depthmodel; the human impact is expected to be the most importantin this period. From each sample, 2.5 g of dry sediment weretreated with hydrofluoric acid and acetolysis (Erdtman, 1960)and mounted in Neo-Mount. Pollen preparations included theaddition of exotic Lycopodium spores to determine pollenconcentrations (pollen grains g−1). All samples were counted toa minimum of 500 pollen grains. Results are shown as per-centage total land pollen to land pollen types, and percentagetotal land pollen and fern spores for fern spores. The pollengrains were identified according to Marticorena (1968) andHeusser (1971).

The pollen assemblage zone boundaries were defined on thebasis of stratigraphically constrained incremental sums of

Fig. 2. 210Pb activity (a); Sedimentation rate (b); 210Pb dates (c); 137Cs activity (d). Full details in Quiroz et al., 2005.

21L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

square cluster analyses, CONISS (Grimm, 1987), and changesin the key taxa. Summary pollen diagrams were constructedusing the programs Tilia and Tilia-Graph (Grimm, 1991).

3. Results

3.1. Chronology and stratigraphy

Full details of 210Pb and 137Cs dating are provided by Quirozet al. (2005); however, part of the data is shown in Fig. 2. ThreeAMS radiocarbon dates (Table 1) and 210Pb provided the basisfor the age-depth model (Fig. 3). Radiocarbon dating indicatedthat the 522-cm-deep core extends back to 2800 cal. yrs BP. Thestratigraphy (Fig. 4) showed that the sedimentary column isconstituted by silt and sand. The mean grain size (Fig. 4) rangesbetween 2.5 Phi (158–160 cm) y 7.0 Phi (4–9 cm). The sand at

Table 1Radiocarbon ages from core Lake Laja

Lab. code Depth (cm) Age AMS 14C yr B.P. Calibrated age (AD/BC)

ETH-29664 320–321 1490±55 AD 527–653CLJ 320–321ETH-29783 402–405 1915±55 AD 1–230CLJ 402–405ETH-29784 519–522 3015±50 BC 1407–1125CLJ 519–522

The calibrated age are based on the 1σ confidence interval (95%).

31–33 cm corresponds to tephra and, according to the age-depthmodel, the interpolated age is 1911 AD, corresponding to thelast eruption of Antuco Volcano (Thiele et al., 1998). The 36–37, 50–51, and 55–59-cm intervals are tephra silts (5.85, 5.76and 6.51 Phi respectively, Fig. 4); based on the age-depthmodel, we obtained respective interpolated ages of 1890–1887 AD, 1838–1835 AD, and 1806–1820 AD for these

Fig. 3. Age-depth model for the Lake Laja record. ⁎ represents 210Pb dates and +calibrated 14C ages. The deviation values for the calibrated 14C ages areindicated in Table 1.

Fig. 4. Stratigraphy of the sedimentary column and grain size (Phi).

22 L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

intervals. Plant remains were found at 253–259 and 386–388 cm, whereas the sediments at 313–315 and 352–371 cmwere disturbed during the fieldwork, so that, in the latter case, itwas not possible to carry out pollen analyses.

3.2. Pollen

We identified six pollen assemblage zones (I, II, III, IV, Vand VI) (Figs. 5 and 6). Due to the loss of sediment, pollenanalyses were only carried out to 476 cm. The results areexpressed in relative abundance (Fig. 5) and pollen concentra-tions (pollen grains g−1, Fig. 6).

In Fig. 5, it is possible to observe very low AP and NAPvalues in zones I and II. Those sections probably correspond tosediments that arrived suddenly to the lake bottom hostsediment (landslides) originated by seismic or volcanic events,thereby explaining the low percentages of pollen in thosesamples.

Zone I: (476–309 cm; 800 cal. yr BC–660 AD) wasdominated by N. dombeyi-type (mean=35.3%) N. obliqua-type(mean=15.8%), and E. chilensis (mean=23%). The assem-blages were slightly dominated by arboreal pollen (mean=58.4%). In the upper part of the zone, Blechnum-type dis-appeared. Pollen concentrations were low with respect to theother zones. The total pollen concentration fluctuated between124,000 pollen grains g−1 in 800 cal. yr BC and 42,000 pollengrains g−1 in 237 AD. The most important concentrationscorrespond to N. dombeyi-type, N. oblique-type, E. chilensis,A. chilensis and Caryophyllaceae.

Zone II (309–121 cm; 660 AD–1561 AD) was dominated byN. dombeyi-type (mean=42.5%) and E. chilensis (mean=21%),which decreased with respect to the previous zone. N. obliquatype (mean=13.4%) and Poaceae (mean=5.5%) decreased incomparison with Zone I. Caryophyllaceae increased signifi-cantly in the middle of the zone. The lowest pollen concentra-tion was 22,800 pollen grains g−1 in 1058 AD and the highestwere 93,000 pollen grains g−1 in 1168 AD.

Zone III (121–69 cm; 1561–1766 AD) was characterized bythe dominance of N. dombeyi-type (mean=38.7%), E. chilensis(mean=23.8%), and N. obliqua-type (mean=13.3%). Theassemblage was dominated by arboreal pollen (mean=57.4%).This period was characterized by increased Poaceae, decreasedE. chilensis in the upper part of the zone, and the appearance ofBlechnum-type towards the upper zone boundary. The pollenconcentration showed a decreasing trend towards the upper partof the zone, whereas Umbelliferae increased. The total pollenconcentration reached a minimum (17,560 pollen grains g−1) in1736 AD and a maximum (137,402 pollen grains g−1) in1642 AD.

Zone IV (69–35 cm; 1766–1894 AD) was dominated byN. dombeyi-type (mean=32%), N. obliqua-type decreased to6% and A. chilensis increased (mean=10%). There was a sub-stantial rise in Poaceae (22.9%) and E. chilensis declinedslightly in this zone (mean=18.4%) with respect to the previouszone. Pollen concentrations decreased for all taxa in the middleof the zone and increased from 1876 AD, onwards. In 1774 AD,the total pollen concentration peaked (710.21 pollen grains g−1)and, in 1864, AD was at its lowest (7454 pollen grains g−1).

Fig. 5. Pollen percentage diagram. Note the different scales. AP: arboreal pollen; NAP: non arboreal pollen.

23L.Torres

etal.

/Review

ofPalaeobotany

andPalynology

149(2008)

18–28

Fig. 6. Pollen concentration (pollen grains g−1) diagram. Note the different scales. AP: arboreal pollen; NAP, non-arboreal pollen.

24L.Torres

etal.

/Review

ofPalaeobotany

andPalynology

149(2008)

18–28

25L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

Zone V (35–15 cm; 1894–1968 AD) was dominated slightlyby arboreal pollen (mean=50.8%). N. dombeyi-type decreased(mean=29.2%) and N. obliqua-type averaged 12%. The Poaceafamily increased to 25%, whereas E. chilensis decreased at11%. In this zone, there was an important increase in pollenconcentration, although prior to 1912 AD, the pollen concen-tration was very low. The highest total pollen concentrationvalue was 184,770 pollen grains g−1 (1949 AD) and the lowestwas 39,000 pollen grains g−1 (1923 AD).

Zone VI (15–0 cm, 1968–2001 AD) was dominated byarboreal pollen (mean=80%), specifically N. dombeyi-type(mean=37.8%),N. obliqua-type (mean=16.7%), andA. chilensis(mean=13.6%). Poacaea and E. chilensis declined drasticallywith regard to the previous zone (mean=5.9% and 2.9%,respectively). Total pollen concentration values decreased withrespect to the previous zone, too, reaching a maximum of 99,528pollen grains g−1 in 1984 and a minimum of 8347 pollengrains g−1 in 1999.

4. Discussion

The palynological record from Lake Laja shows significantchanges during the Late Holocene. The pollen record shows thatN. dombeyi-type, N. obliqua-type, E. chilensis, and Poaceaewere the most important taxa during the last 2800 cal. yrs BPand, during the first half of the twentieth century, an importanthuman influence was evidenced by the presence of Plantago

Fig. 7. Diagram showing the ratios between AP and E.chilensis and the relationship blower values (closer to zero) indicate dry conditions and the higher values (closer to 9wetter conditions.

and the increased Poaceae and Asteraceae (Figs. 5 and 6). Theresults suggest a fluctuation between drier and wetter periodsduring the last 2800 cal. yrs BP (Fig. 7).

Between 800 cal. yr BC and 660 AD (Zone I), N. dombeyi-type and N. obliqua-type dominated; however, E. chilensis, anarid-adapted species (Marticorena and Rodríguez, 1995; Ickert-Bond et al., 2003), reached important percentages in compar-ison with the present. This leads us to believe that the climaticconditions during this time were slightly less humid than atpresent. Two possible drier periods are evidenced by two peaksof E. chilensis, the first in 800 cal. yr BC and the second in660 AD. After this, the changes in the plant community from660 AD to 1561 AD (Zone II), characterized by the rise ofN. dombeyi-type as well as decreased pollen from Poaceae andE. chilensis, could be related to increased humid conditions.However, in this time period, three events with very low pollenpercentages and concentrations were evidenced in the record(Figs. 5 and 6). Considering the age-depth model, those eventsoccurred around 729 AD, 933 AD, and 1440 AD and wereprobably related to landslides from seismic or volcanic events.After 933 AD, when the MWP was evident in Europe, thepollen assemblages in Lake Laja allowed us to infer theprevalence of more humid conditions than nowadays. However,due to the low pollen resolution for that period, it was notpossible to assure the existence of such humid conditions.Nevertheless, the occurrence of a very diverse stratigraphy andthe fluctuations in grain size within this zone (Fig. 4) could be

etween N. dombeyi-type and E.chilensis as an indicator of humidity/aridity. Theand 6 in AP/E.chilensis and N. dombeyi type/E.chilensis, respectively) indicate

26 L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

related to a higher influence of runoff from the watershed,reinforcing the inference of higher precipitation for the period.Regrettably, few works have been carried out for this period incentral Chile that can be used for comparisons; decreasedrainfall during the MWP was shown for the south of Chile byLamy et al. (2001) and for South Eastern Patagonia byHabersettl et al. (2005).

Later, the relative abundance of Poaceae and E. chilensis (thelast in lower part of the zone) increased between 1561 and1766 AD (Zone III), as did the pollen concentrations ofChenopodiaceae and Asteraceae subf. Asteroidae, suggestingthe beginning of a drier period that intensified from 1766 to1894 AD (Zone IV) as shown by a decrease in N. dombeyi-typeand N. obliqua-type and important increases of Poaceae andA. chilensis (an arid-resistant species; Rodríguez et al., 1983).N. obliqua-type are associated with humid conditions (Rodrí-guez et al., 1983) and the tree growth of N. pumilio in the LakeLaja basin (species that forms part of N. dombeyi-type) shows apositive correlation with annual precipitation under a Medi-terranean-type climate in which water availability is a majorlimiting factor (Lara et al., 2001, 2005).

Increased Poaceae could be the result of human impacts andnot only due to lower precipitation (Bush, 2000). Prior to1550 AD (the arrival of Spanish conquerors in the region), theAntuco area was occupied by Pehuenches, a nomadic,harvester–hunter tribe, characterized by the absence of pre-hispanic agricultural activity (Torrejón, 2001). The results fromLake Laja agree with the aforementioned, because the pollenrecord shows a community dominated by arboreal pollen and alow percentage and concentration of Poaceae until 1720 AD(Figs. 5 and 6) evidenced minimal human impact.

After the arrival of the Spanish conquerors, the Pehuenchesacquired livestock and began farming, which increased thepressure on land use and vegetation and constituted the firstenvironmental disturbance produced by human activity in thearea (Torrejón, 2001). Thus, the increased Poaceae between1766 and 1894 AD (Zone IV) could be related to higheranthropic disturbances after 1766 AD. However, based onhistorical records, Torrejón (2001) concludes that the ecosys-tem's carrying capacity was not exceeded and that this ethnicgroup lived in equilibrium with the environment. On the otherhand, Poeppig (1826–1829) mentioned the scant Spanish andChilean occupation in the Antuco area due to its inhospitablenature from geomorphological and climatic points of view.Therefore, and according to previous authors, we think that theincrease in Poaceae between 1766 and 1894 AD is more relatedto lower precipitation levels than human impact.

This could be evidence of a drier period during the LIA incentral Chile. Ephedra chilensis is an arid-adapted species(Marticorena and Rodríguez, 1995; Ickert-Bond et al., 2003)and, in central Chile, N. Pumilio—a species that forms part ofN. dombeyi-type—indicates higher precipitation (Lara et al.,2001, 2005). Fig. 7 shows the ratios between AP and E. chilensis,along with the relationship between N. dombeyi-type andE. chilensis, used here as a proxy for humidity/aridity between800 cal. yr. BC and 1920 AD. After this date, this proxy becomesless valid since the most important changes in pollen should be

more related to human activity than climatic conditions (Torreset al., in preparation). Based on the above ratios, between 1561and 1894 AD (LIA in Europe), the climatic conditions in LakeLajawould have been drier than now, though a humid interruptionbetween 1720–1745 AD seems to have occurred.

In central Chile (32°–38°S), according to Jenny et al. (2002),the LIA began with a humid period (1300−1700 AD) and endedwith a drier period (1700−1850 AD). For Lake Puyehue (40°S),Bertrand et al. (2005) showed a humid period between 1490 and1700 AD and a drier period between 1700 and 1900 AD. Thedrier conditions during the LIA between 1700 and 1900 AD incentral-southern Chile agree well with the report from LakeLaja. Only Lamy et al. (2001) showed increased rainfall duringthe LIA around 41°S latitude.

An absence of pollen grains is evident between 30 and 33 cm(Zone V), dated at 1911 AD. This absence is related to the lasteruption of Antuco Volcano (Thiele et al., 1998). Between 1938and 1968 AD (Zone V), evident vegetational changes began thatwere related to human impacts. Non-arboreal pollen increased inthis period, specifically Poaceae.N. dombeyi-type andE. chilensisdecreased and Plantago appeared for the first time in the core(Figs. 5 and 6). Moreover, Poaceae pollen concentrationsincreased during this period (Fig. 6). Between 1938 and 1968,the anthropic intervention in the Lake Laja basin was strong andclosely related to hydropower, road building, tourism, andrecreational activities (Nardini and Montoya, 1993). We thinkthat the increased Poaceae from 1938 to 1968 resulted mainlyfrom an intensification of human activity. During these years,E. chilensis presented very low percentages and maybe it cannotsurvive in ecosystems with high anthropic disturbances.

The human impact in the Lake Laja basin began later than inother places in Chile. For example, Szeicz et al. (2003) reportedanthropic disturbances during the last 600 years in South Chileand Jenny et al. (2002) and Villa-Martínez et al. (2004)indicated human deforestation over the last 250 years in theLake Aculeo basin (lat. 34°S, central Chile).

Finally, from 1968 to 2001 AD (Zone VI), Poaceaepercentages and concentrations decreased drastically, whereasN. dombeyi-type and N. obliqua-type increased. This palyno-logical change evidenced a decrease in anthropic interventionrelated to the end of hydropower building (Nardini andMontoya, 1993) and the foundation of Parque Nacional Lagunadel Laja in 1957.

The fluctuation between drier and wetter periods during thelast 2800 cal. yrs BP in the Lake Laja basin could be related tothe frequency of ENSO events, which are, in the study area,associated with average rainfall anomalies in late spring(Montecinos and Aceituno, 2003). Other investigations incentral Chile have related the moisture changes with ENSO(Jenny et al., 2002; Villa-Martínez et al., 2003; Maldonado andVillagrán, 2006).

5. Conclusions

The palynological record from Lake Laja reveals a detailedanalysis of the vegetational and climatic history during the last2800 cal. yrs BP in central Chile. This is a paleo-palynological

27L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

study that concentrates mainly on climatic conditions during theLIA and MWP as well as the recent human impact in centralChile. The main conclusions from this study are as follows.

1. The results suggest a fluctuation between drier and wetterperiods during the last 2800 cal. yrs BP.

2. The climate was generally less humid than at presentbetween 800 cal. yr BC and 660 AD, as evidenced by therelation of N. dombeyi-type versus E. chilensis, but onehumid event between 148 AD and 94 AD is suggested.

3. Probably, the climate was wetter than at present during theMWP; however, higher resolution studies are needed for thistime.

4. The pollen record shows a drier period between 1657 and1894 AD as evidenced by increased Poaceae and E.chilensis. However, one humid period between 1720 ADand 1743 is suggested. This result suggests a drier periodduring most parts of the LIA.

5. Between 1938 and 1968 AD intense human impacts relatedto hydropower, road building, tourism, and recreationalactivities are evidenced by increased Poaceae and Asteraceaeand the appearance of Plantago.

6. Finally, from 1968 AD to the present, the palynologicalrecord reveals less anthropic intervention, as indicated by thedecrease of Poaceae and Asteraceae.

Acknowledgements

This research was supported by Fondecyt 1070508 andDIUC 204.310.039-1.0. The authors express their gratitude toCONICYT; Clodomiro Marticorena of the Botany Department,University of Concepción, for the help with pollen identifica-tion; Mauricio Aguayo and Alex Henríquez of EULA-Chile,University of Concepción, for the support in vegetablecartography; Fernando Torrejón of EULA-Chile, University ofConcepción, for critical comments; and finally, two anonymousreviewers for constructive comments.

References

Aceituno, P., 1992. Anomalías de precipitación en Chile central relacionadascon la oscilación del sur: mecanismos asociados. In: Ortlieb, L., Macharé, J.(Eds.), “Paleo ENSO records” Item. Symp. Extended abstracts. ORSTOM-CONCYTEC, Lima (1–5 pp.).

Araneda A., Torrejón F., Aguayo M., Torres L., Cruces F., Cisternas M., UrrutiaR., in press. Historical record of San Rafael glacier advances (NorthPatagonian Icefield): another clue for Little Ice Age timing in Souther Chile.The Holocene.

Badano, E., Molina-Montenegro, M., Quiroz, C., Cavieres, L., 2002. Efectos dela planta en cojín Oreopolus glacialis (Rubiaceae) sobre la riqueza ydiversidad de especies en una comunidad alto-andina de Chile central. Rev.Chil. Hist. Nat. 75, 757–765.

Bertrand, S., Boes, X., Castiaux, J., Charlet, F., Urrutia, R., Espinoza, C.,Lepoint, G., Charlier, B., Fagel, N., 2005. Temporal evolution of sedimentsupply in Lago Puyehue (Southern Chile) during the last 600 yr and itsclimatic significance. Quat. Res. 64, 163–175.

Bush, M., 2000. Deriving response matrices from central American modernpollen rain. Quat. Res. 54, 132–143.

Conaf, 1993. Plan de manejo Parque Nacional Laguna del Laja. CorporaciónNacional Forestal, Chile.

Conaf, 2004. Antecedentes sobre las áreas silvestres protegidas de la octavaregión del Biobio. Iván Benoit Contensse, Chile.

Donoso, C., 1982. Reseña ecológica de los bosques mediterráneos de Chile.Bosque 4, 117–146.

Erdtman, G., 1960. The acetolysis method. A revised description. Sven. Bot.Tidskr. 54, 561–564.

Grimm, E., 1987. CONISS: a Fortran 77 program for stratigraphicallyconstrained cluster analysis by the method of incremental sum of squares.Comput. Geosci. 13, 13–35.

Grimm, E., 1991. Tilia and Tilia Graph. Illinois State Museum, Springfield.Habersettl, T., Fey, M., Lücke, A., Maidana, N., Mayr, C., Ohlendorf, C.,

Schäbitz, F., Schleser, G., Wille, M., Zolitschka, B., 2005. Climaticallyinduced lake level changes during the last two millennia as reflected insediments of Laguna Potrok Aike, southern Patagonia (Santa Cruz,Argentina). J. Paleolimnol. 33, 283–302.

Heusser, C., 1971. Pollen and spores of Chile. Modern types of thePteridophytas, Gimnospermae and Angiospermae. University of Arizona.

Heusser, C., 1990. Ice age vegetation and climate of subtropical Chile.Palaeogeogr. Palaeoclimatol. Palaeoecol. 80, 107–127.

Hoffmann, A., 1982. Flora silvestre de Chile. In: Gay, Fundación Claudio (Ed.),Zona Araucana (Santiago de Chile).

Ickert-Bond, S., Skvarla, J., Chissoe, W., 2003. Pollen dimorphism in EphedraL. (Ephedraceae). Rev. Palaeobot. Palynol. 124, 325–334.

Jenny, B., Valero-Garcés, B., Villa-Martinez, R., Urrutia, R., Geyh, M., Veit, H.,2002. Early to mid-Holocene aridity in central Chile and the southernwesterlies: the Laguna Aculeo record (34° S). Quat. Res. 58, 160–170.

Koch, J., Kilian, R., 2005. “Little Ice Age” glacier fluctuations, Gran CampoNevado, southernmost Chile. Holocene 15, 20–28.

Lamy, F., Hebbeln, D., Rohl, U., Wefer, G., 2001. Holocene rainfall variabilityin southern Chile: a marine record of latitudinal shifts of the southernwesterlies. Earth Planet. Sci. Lett. 185, 369–382.

Lara, A., Villalba, R., 1993. A 3620-year temperature record from Fitzroyacupressoides tree rings in Southern South America. Science 260, 1104–1106.

Lara, A., Aravena, J., Villalba, R., Wolodarsky-Franke, A., Luckman, B.,Wilson, R., 2001. Dendroclimatology of high-elevation Nothofagus pumilioforests at their northern distribution limit in the central Andes of Chile. Can.J. For. Res. 31, 925–936.

Lara, A., Villalba, R., Wolodarsky-Franke, A., Aravena, J., Luckman, B., Cuq,E., 2005. Spatial and temporal variation in Nothofagus pumilio growth attree line along its latitudinal range (35° 40′ –55° S) in the Chilean Andes.J. Biogeogr. 32, 879–893.

Maldonado, A., Villagrán, C., 2002. Paleoenvironmental changes in thesemiarid coast of Chile (32° S) during the last 6200 cal years inferredfrom a swamp–forest pollen record. Quat. Res. 58, 130–138.

Maldonado, A., Villagrán, C., 2006. Climate variability over the last 9900 cal yrBP from a swamp forest pollen record along the semiarid coast of Chile.Quat. Res. 66, 246–258.

Mann, M., 2002. Little Ice Age. The Earth system: physical and chemicaldimensions of global environmental change. Encyclopedia of GlobalEnvironmental Change. Wiley & Sons, Ltd, Chichester.

Mardones, M., 2002. Evolución morfogenética de la hoya del río Laja y suincidencia en la geomorfología de la región del Bio Bio, Chile. Rev. Geogr.Chile, Terra Australis 47, 97–127.

Marticorena, C., 1968. Granos de polen de plantas chilenas. Gayana, Bot. 17.Marticorena, C., Rodríguez, R., 1995. Flora de Chile. vol 1. Pteridophyta-

Gimnospermae. Universidad de Concepción, Concepción (351 pp.).McCormac, F., Hogg, A., Blackwell, P., Buck, C., Higham, T., Reimer, P., 2004.

SHCal04 southern hemisphere calibration 0–11.0 cal Kyr BP. Radiocarbon46, 1087–1092.

Montecinos, A., Aceituno, P., 2003. Seasonality of the ENSO-related rainfallvariability in central Chile and associated circulation anomalies. J. Climate16, 281–296.

Nardini, A., Montoya, D., 1993. Planteamiento de un modelo decisional para lagestión integrada del sistema lago Laja-río Laja (con respecto al proyecto“Canal Laja-Diguillín”). Monografía científicas vol 3, Centro Eula-Chile.

Niemeyer H., Muñoz J., 1983. Hoja Laguna de la Laja, Región del BioBio.Servicio Nacional de Geología y Minería, Carta Geológica de Chile, N° 57.1:250.000.

28 L. Torres et al. / Review of Palaeobotany and Palynology 149 (2008) 18–28

Ortlieb, L., Escribano, R., Follegati, R., Zuñiga, O., Kong, I., Rodriguez, L.,Valdes, J., Guzman, N., Iratchet, P., 2000. Recording of ocean-climatechanges during the last 2000 years in a hipoxic marine environment offnorthern Chile (23° S). Rev. Chil. Hist. Nat. 73 (2), 221–242.

Poeppig, E., 1826–1829. Un testigo en la alborada de Chile. Traducción y notasde Carlos Keller. Empresa Editora Zig-Zag, Santiago de Chile.

Quiroz, R., Popp, P., Urrutia, R., Bauer, C., Araneda, A., Treutler, H., Barra, R.,2005. PAH fluxes in the Laja lake of south central-Chile Andes over the last50 years: evidence from a dated sediment core. Sci. Total Environ. 349,150–160.

Rodríguez, R., Matthei, O., Quezada, M., 1983. Flora Arbórea de Chile.Editorial de la Universidad de Concepción, Concepción, Chile.

Rondanelli, M., Rodriguez, J., Ugarte, E., Meier-Sarger, C., 2000. Estructura ycomposición de comunidades vegetales en que participa AustrocedrusChilensis (D. DON) Pic. Ser. et Bizz. En el parque Nacional Laguna Laja(37°22′ S; 71°26′ W), VIII región, Chile. Estudio preliminar. Rev. Geogr.Chile. Terra Australis 45, 31–48.

Soon, W., Baliunas, S., Idso, C., Idso, S., Legates, D., 2003. Reconstructingclimatic and environmental changes of the past 1000 years: a reappraisal.Energy Environ. 14 (2–3), 233–299.

Szeicz, J., Zeeb, B., Bennett, K., Smol, J., 1998. High-resolution paleoecolo-gical analysis of recent disturbance in a southern Chilean Nothofagus forest.J. Paleolimnol. 20, 235–252.

Szeicz, J., Haberle, S., Bennett, K., 2003. Dynamics of North Patagonianrainforests from fina-resolution pollen, charcoal and tree-ring analysis,Chonos Archipelago, Southern Chile. Aust. Ecol. 28, 413–422.

Thiele, R., Moreno, H., Elgueta, S., Lahsen, A., Rebolledo, S., Petit-Breuilh, M.,1998. Evolución geológico-geomorfológica cuaternaria del tramo superiordel valle del río Laja. Rev. Geol. Chile 25 (2), 229–253.

Torrejón, F., 2001. Variables geohistóricas en la evolución del sistemaeconómico Pehuenche durante el periodo colonial. Revista Universum 16,219–236.

Torres L., Parra O., Araneda A., Chirinos L., Cruces L., Urrutia R., inpreparation. Cambios vegetacionales en el siglo XX en una cuenca lacustrede Chile central: estudio del registro polínico sedimentario del lago Laja.

Veblen, T., Schlegel, F., 1982. Reseña ecológica de los bosques del sur de Chile.Bosque 4 (2), 73–115.

Villagrán, C., 2001. Un modelo de la historia de la vegetación de la Cordillera dela Costa de Chile central-sur: hipótesis glacial de Darwin. Rev. Chil. Hist.Nat. 74 (4), 793–803.

Villalba, R., 1990. Climatic fluctuations in Northern Patagonia during the last1000 years as inferred from tree-ring records. Quat. Res. 34, 346–360.

Villalba, R., 1994. Tree-ring and glacial evidence for the medieval warm epochand the little ice age in Southern South America. Clim. Change 26, 183–197.

Villa-Martínez, R., Villagrán, C., 1997. Historia de la vegetación de los bosquespantanosos de la costa de Chile Central durante el Holoceno medio y tardío.Rev. Chil. Hist. Nat. 70, 391–401.

Villa-Martínez, R., Villagrán, C., Bettina, J., 2003. The last 7500 cal yr B.P. ofwesterly rainfall in Central Chile inferred from a high-resolution pollenrecord from Laguna Aculeo (34°S). Quat. Res. 60, 284–293.

Villa-Martínez, R., Villagrán, C., Bettina, J., 2004. Pollen evidence for late-Holocene climatic variability at Laguna de Aculeo, Central Chile (lat. 34°S).Holocene 14 (3), 361–367.

Wentworth, C., 1922. A scale of grade and class terms for clastic sediments.J. Geol. 30, 377–392.