icu

yleK4QE,ts, Rore

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se of sa2000a; McEwan et al., 2001; Heckenberger et

wealth of complex archaeological sites in Amazonia in recent years, (Lombardo, 2010; Lombardo and Prmers, 2010; Lombardo et al.,

Quaternary Research 80 (2013) 207217

Contents lists available at ScienceDirect

Quaternary

.e lcountering the long-held view (e.g. Meggers, 1954) that Amazoniawas a largely untouched wilderness prior to European colonization(Denevan, 1992, 2011). The Llanos de Moxos, a vast seasonally oodedforestsavanna mosaic of lowland Bolivia, is one such region rich inarchaeological features, which is recognized as one of the most heavilyimpacted regions of Amazonia in pre-Columbian times (Denevan, 2001;Mayle et al., 2007; Erickson, 2008; Mann, 2008; Heckenberger andNeves, 2009; Schaan, 2012). The numerous earthworks identied inthe Llanos de Moxos are regionally distinct, and feature raised elds(Erickson, 1995; Walker, 2004, 2008; Lombardo et al., 2011a), habita-tion mounds (Erickson, 2000b; Erickson and Bale, 2006; Prmers,

in press), archaeological excavations of mounds and ring-ditches(Dougherty and Calandra, 1984; Walker, 2004; Erickson and Bale,2006; Walker, 2008; Prmers, 2009), and botanical surveys of modernvegetation associated with articial earth mounds (Erickson and Bale,2006; Erickson, 2010) have attempted to determine the extent of pasthuman agency in shaping the landscape and vegetation of the region.These studies, however, do not offer a temporal dimension to the ques-tion of past human impact and legacy on the current vegetation mosaic.In this study, we used palaeoecological methods to examine past vegeta-tion change, agriculture, and land use associated with the monumentalmound culture in the southeastern Llanos de Moxos. The temporal per-2009; Lombardo and Prmers, 2010; Lomring-ditches (Walker, 2008; Prmers, 2009;and causeways (Erickson and Bale, 2006;2010; Lombardo et al., in press), and shweirs (the effort invested in cataloguing and ident

Corresponding author.E-mail address: b.whitney@ed.ac.uk (B.S. Whitney).

0033-5894/$ see front matter 2013 University of Whttp://dx.doi.org/10.1016/j.yqres.2013.06.005al., 2008; Prssinen et al.,ealed an ever-increasing

still under debate.GIS analysis of the spatial distribution of earthwork features2009; Lombardo, 2010; Schaan, 2012) have revArchaeologyBoliviaAmazonPollenPhytolithsMaizeSavannaAnthropogenic resCharcoal

Introduction

New archaeological work and the umounds. The charcoal decline pre-dates the arrival of Europeans by at least 100 yr, and challenges the notionthat the mounds culture declined because of European colonization. We show that the surrounding savanna soilswere sufciently fertile to support crops, and the presence of maize throughout the record shows that the areawas continuously cultivated despite land-use change at the end of the earthmounds culture.We suggest that burn-ingwas largely conned to the savannas, rather than forests, and that pre-Columbian deforestationwas localized tothe vicinity of individual habitation mounds, whereas the inter-mound areas remained largely forested.

2013 University of Washington. Published by Elsevier Inc. All rights reserved.

tellite imagery (Erickson,

archaeological features in the Llanos de Moxos, the extent to whichits patchwork landscape is largely natural (Langstroth, 2011) or insteaddomesticated by pre-Columbian human agency (Erickson, 2006), isPre-Columbianlab

rge lake (14 km ), Laguna San Jos (1456.97S, 6429.70W).We found evidence of high levels of anthropogenicurning from AD 400 to AD 1280, corroborating dated occupation layers in two nearby excavated habitationKeywords:mosaic of the Llanos de Moxo

2Pre-Columbian landscape impact and agrof the Llanos de Moxos, lowland Bolivia

Bronwen S. Whitney a,, Ruth Dickau b, Francis E. Maa School of Geosciences, The University of Edinburgh, Drummond St., Edinburgh EH8 9XP, Ub Department of Archaeology, Laver Bldg., North Park Rd., University of Exeter, Exeter EX4c Department of Geography and Environmental Science, University of Reading, Whiteknighd Museo de Historia Natural Noel Kempff Mercado, Universidad Autnomia Gabriel Ren M

a b s t r a c ta r t i c l e i n f o

Article history:Received 26 April 2013Available online 13 July 2013

We present a multiproxy stuMonumental Mounds Regionhabitationmounds associated

j ourna l homepage: wwwbardo et al., in press),Erickson, 2010), canalsLombardo and Prmers,Erickson, 2000a). Despiteifying the abundance of

ashington. Published by Elsevier Inlture in the Monumental Mound region

a,c, J. Daniel Soto d, Jos Iriarte b

UKeading RG6 6AB, UKno, Av. Irala 565, Casilla 2489, Santa Cruz, Bolivia

f land use by a pre-Columbian earth mounds culture in the Bolivian Amazon. TheMR) is an archaeological sub-region characterized by hundreds of pre-Columbianth a complex network of canals and causeways, and situated in the forestsavannallen, phytolith, and charcoal analyses were performed on a sediment core from a

Research

sev ie r .com/ locate /yqresspective offered through this palaeoecological investigation providesinsight into pre-Columbian impact and examines the legacy ofpast human activity within the modern landscape.

Study area and archaeological context

The Llanos de Moxos is an extensive hydrological savanna and for-est mosaic (130,000 km2) (Fig. 1A) that experiences seasonal

c. All rights reserved.

ooding with the passage of the South American summer monsoon.Annual precipitation ranges from 2000 mm (north) to 1200 mm(south). Around the city of Trinidad, capital of the Department of Beni,annual precipitation averages around 1800 mm (Pouilly and Beck,2004). The majority (6080%) of annual rainfall occurs between De-cember and March in the austral summer (Pouilly and Beck, 2004),with a dry season lasting approximately ve months fromMay to Sep-tember. The low relief of the basin, combined with thick hard-packedQuaternary clays (Clapperton, 1993) gives rise to seasonally inundatedsavannas that dominate much of the landscape (Hanagarth, 1993).Tropical forest occupies areas of higher relief, specically forest islandsand abandoned river leves, that rise above the level of inundation(Langstroth, 1996, 2011). The Llanos deMoxos is characterized by distinc-tive geo-ecological regions, and this landscape heterogeneity is shown tohave inuenced different land-use patterns by pre-Columbian people(Lombardo et al., 2011b).

This study focuses on the Monumental Mound Region (MMR, afterLombardo et al., in press), which is situated ca. 50 km east of Trinidad(Fig. 1A), where over 100 large habitation mounds, locally called lomas,have been identied (Lombardo andPrmers, 2010).More than 40 radio-carbondates from the excavations of two lomas, Salvatierra andMendoza,constrain the MMR occupation period to between AD 500 and AD 1400(Lombardo and Prmers, 2010). Many of these sites are situated onabandoned river leves, where pre-Columbian people not only used,but modied and built upon, naturally-occurring higher elevationterrain for habitation, as evidenced by dense domestic refuse and con-struction layers. Of the various earthworks found in the MMR, habitationmounds required the most labour for construction and are thought tohave featured prominently in political and ritual life (Lombardo andPrmers, 2010).

canals, causeways, andwater reservoirs. For example, at Loma Salvatierra,the pyramidal mounds, which reach to a height of 7 m, are arranged in aU-shaped format enclosing a plaza area on top of the main habitationmound. These large complexes also contain hundreds of burials belong-ing to all occupation periods, including smaller burial mounds possiblybuilt for high-ranking individuals, as shown by a male burial unearthedin Salvatierra which was accompanied by prestigious grave goods in-cluding a metal plate, ear pieces, bracelets and a jaguar teeth collar(Prmers, 2009). In addition to these large-scale habitation mounds,smaller forest islands feature prominently in the area, the majority ofwhich are hypothesized to have been once occupied (Langstroth, 1996)or articially constructed (Erickson, 2006; Lombardo and Prmers,2010). GIS-based site-distribution analysis of the MMR suggests thatthe high number and density of habitation mounds and forest islands,together with their linking canals and causeways, formed a complexinfrastructure that, to date, comprises the only region in the Llanos deMoxos in which a hierarchical, regionally organized, pre-Columbiansociety is clearly documented (Lombardo and Prmers, 2010; Lombardoet al., in press).

In contrast to the raised-elds region of the northwestern Llanos deMoxos, there are no clear landscape features in the mounds region thatcould represent ancient raised-eld remains (Lombardo and Prmers,2010). An examination of soil properties in distinct geoecologicalregions of the Llanos de Moxos has revealed that, although the MMR isseasonally ooded, its soils exhibit higher fertility compared to thenorthwest of the Llanos de Moxos where the raised elds are located(Lombardo et al., in press). The relatively base-rich Andean-derivedsoils of the mound region are hypothesized to be sufciently fertile tohave supported crops (Langstroth, 2011; Lombardo et al., in press). Fur-thermore, Lombardo et al. (2012, in press) suggest that the numerous

Llans, a

208 B.S. Whitney et al. / Quaternary Research 80 (2013) 207217Habitation mounds are typically constructed of an elevated plat-form, 35 mhigh, but can reach up to 21 m in height and cover areas aslarge as 20 ha (Erickson, 2006; Lombardo and Prmers, 2010). Theyform part of a more complex, well-planned architectural design that in-cludes several associated structures, such as pyramidal mounds, plazas,

Figure 1. (A) Ecosystem map of northern Bolivia showing the location and extent of thework vegetation, as well as the location of canals, causeways, mounds, and forest island

(1) and Mendoza (2), habitation mounds from which dated excavations constrain the earthidentied canals and ditches (totalling 957 km) represent drainageand irrigation channels built to control water levels among cropsgrown on savannas, but this has not been veried with eld excavationdata. Macrobotanical investigations of mound sediments, and starchgrain and phytolith analyses of ceramic plant-processing tools and

os de Moxos; (B) Detailed map showing the location of Laguna San Jos amid the patch-fter Lombardo and Prmers (2010). Also shown are the locations of Lomas Salvatierra

mounds culture occupation period from AD 500 to AD 1400 (Prmers, 2009).

an anchored coring platform. The core was cut into 0.5-cm consecutiveincrements, which were then stored in air tight plastic vials. Rapid veg-etation surveys were conducted on the northeastern lake shore to aidthe interpretation and identication of pollen and phytolith data. Com-monly encountered plant species were identied by DS and recordedin Table 1. Voucher specimens were also collected and housed at theHerbario del Oriente Boliviano (USZ) of the Noel Kempff MercadoNatural History Museum in Santa Cruz, Bolivia.

Chronology

The core chronology is based on three AMS 14C dates, all of whichwere obtained from non-calcareous bulk sediment. Due to the ab-sence of terrestrial plant macrofossils and insufcient concentrationsof large (N250 m) charcoal particles in the core sediments, bulk sed-iments were chosen for radiocarbon dating. The horizons chosen fordating were based on key changes in the charcoal curve (presentedbelow). The three radiocarbon dates (Table 2) were calibrated usingthe IntCal09 calibration curve in OxCal version 4.1 (Bronk Ramsey,2009) and date ranges are reported with 95% condence intervals.The age model was created through linear interpolation betweencalibrated 14C dates and an assumed modern age for the core top(sedimentwater interface) (Fig. 2). Age estimations were roundedto the nearest 10 yr.

Multiproxy analyses

Pollen analysiswas performed at 1-cm resolution, and samplesmea-suring 1 cm3 were prepared following the standard chemical-digestionprotocol (Fgri and Iversen, 1989; Bennett andWillis, 2002), includinga sieving stage to concentrate large cultigen pollen types, such asZ. mays (Whitney et al., 2012). Standard terrestrial pollen counts

209B.S. Whitney et al. / Quaternary Research 80 (2013) 207217containers excavated from Lomas Salvatierra and Mendoza, revealedthat the earth mounds culture relied on a diversity of plants, includingmaize (Zea mays), manioc (Manihot esculenta), yam (Dioscorea spp.),squash (Cucurbita spp.), peanut (Arachis hypogaea), cotton (Gossypiumsp.), and palm fruits (Arecaceae) (Bruno, 2010; Dickau et al., 2012).However, the agricultural strategy of pre-Columbian people in thisseasonally ooded landscape remains unresolved (Lombardo andPrmers, 2010).

The abundance of higher elevation terrain once occupied bypre-Columbian people, on which forest is currently growing, hasled to speculation that the current spatial extent of forest covermay be articially high due to the human-made alterations in reliefin the Llanos de Moxosmosaic landscape (Erickson, 2006). Currently,approximately 25% of the patchwork landscape in the MMR region issituated on higher, terra rme (non-ooded) ground that supportsforest (Lombardo et al., in press). If the majority of mounds, forestislands, canals and ditches were created for habitation and drained-eldagriculture, pre-Columbian people may have profoundly and irreversiblychanged the relative abundance of seasonally ooded versus terra rmeterrain. Following the decline of the pre-Columbian mounds culture,possibly related to European colonization (Denevan, 2001; Erickson,2010), it has been argued that forest recovery on abandoned moundsand islands may have resulted in articially high levels of arboreal coverin the MMR (Erickson, 2006).

Aims

This multiproxy palaeoecological study, combining fossil pollen,phytolith and charcoal analyses, reconstructs vegetation and land-usehistory from prior to themound occupation period until present to elu-cidate the extent of vegetation changes associatedwith landscape alter-ation for habitation and agriculture. The aims of this study are threefold:(i) to determine the agricultural strategy of the monumental moundsculture; (ii) to determine the extent to which the pre-Columbianmounds people cleared naturally occurring forest during the moundsoccupation period; and (iii) to ascertain whether they augmented themodern level of forest cover in the MMR through the past creation,and subsequent abandonment, of habitation mounds and drainedsavannas.

Methods

Study site

Laguna San Jos (referred to henceforth as LSJ, 1456.97S,6429.70W) is located close to the excavated andwell-dated habita-tion mounds of Salvatierra and Mendoza (Fig. 1B) (Prmers, 2009).Archaeological investigations revealed an intense domestic occupationof these platform habitation mounds, as indicated by the large numberof pottery shards and animal bones recovered in distinct refuse layers(Prmers, 2009; Jaimes Bentancourt, 2012). Radiocarbon dating of ex-cavated layers in the mounds shows that the main occupation periodoccurred from AD 500 to AD 1400 (Prmers, 2009; Dickau et al., 2012).

LSJ is a large, at-bottomed lake (14 km2) with a maximum depthof ca. 1.0 m in the dry season, with no inowing rivers or streams. It issituated among open seasonally inundated savannas (Fig. 1B), with afringing strip of forest b20 m inwidth, around its shore. Lomas Salvatierraand Mendoza are located approximately 5 km and 6 km, respectively,from the nearest lake shore. LSJ is also situated among a number of canals,ditches and reservoirs (Lombardo and Prmers, 2010), and the nearestcanal is located b100 m from the lake (Fig. 1B).

Sediment collection and eld surveys

A 30-cm sediment core was extracted ca. 500 m from the northeast

shore of LSJ (Fig. 1B) in July 2010 using a Perspex tube and piston fromTable 1List of species recorded at LSJ and the vegetation types in which they were located. Alsolisted is the collection number (DS) of voucher specimens for the herbarium of theNoel Kempff Mercado Natural History Museum in Santa Cruz, Bolivia.

Collectionnumber

Species Family Vegetation type

1404 Inga ingoides (Rich.) Willd. Fabaceae Gallery forest1405 Rynchosia sp. Fabaceae Gallery forest1406 Ludwigia grandiora (Michx.)

Greuter & BurdetOnagraceae Open forest

1407 Cecropia cf. concolor Willd. Urticaceae Gallery forest1408 Selenicereus cf. grandiorus (L.)

Britton & RoseCactaceae Gallery forest

1409 Hymenachne donacifolia(Raddi) Chase

Poaceae Gallery forest

1410 Ficus eximia Schott Moraceae Gallery forest1411 Hydrocotyle cf. ranunculoides L. f. Araliaceae Open forest1412 Urera caracasana (Jacq.)

Gaudich. ex Griseb.Urticaceae Gallery forest

1413 Panicum sp. Poaceae Open forest1414 Digitaria ciliaris (Retz.) Koeler Poaceae Open forest1415 Aeschynomene foliolosa Rudd Fabaceae Open forest1416 Pavonia corymbosa (Sw.) Willd. Malvaceae Gallery forest1417 Erythrina fusca Lour. Fabaceae Gallery forest1418 Ludwigia helminthorrhiza

(Mart.) H. HaraOnagraceae Open forest

Eclipta sp. Asteraceae Gallery forestMomordica charantia L. Cucurbitaceae Gallery forestHura crepitans L. Euphorbiaceae Gallery forestCanna glauca L. Cannaceae Open forestPolygonum sp. Polygonaceae Open forestMarsilea sp. Marsileaceae Open forestSterculia apetala (Jacq.) H. Karst. Sterculiaceae Gallery forestThalia geniculata L. Marantaceae Open forest

totalled 300 grains, and large pollen grains (N53 m), concentratedthrough the ne-sieving methodology, were scanned for Z. mays andother crop taxa producing large pollen, such as M. esculenta (manioc)and Ipomoea batatas (sweet potato). Pollen identication was madewith reference to tropical pollen oras (Roubik and Moreno, 1991;Colinvaux et al., 1999), a digital pollen catalogue (Bush and Weng,2007), and a Neotropical pollen reference collection consisting ofN1000 specimens,whichpredominantly originate from lowlandBolivia,housed at the School of Geosciences, The University of Edinburgh. Z.mays pollen grains were identied using the criteria outlined in Holst

Results

Modern vegetation

Results of the rapid vegetation survey are presented in Table 1.Much of the survey was conducted in the thin strip of gallery forestthat surrounds LSJ, where the majority of the 23 recorded specieswere found. Gallery forest trees next to the lake are of low stature, mea-suring ca. 1012 m, and dominant trees species include Inga ingoidesand Hura crepitans. The grass, Hymenachne donacifolia, is also abundant

210 B.S. Whitney et al. / Quaternary Research 80 (2013) 207217et al. (2007), including an examination of the distribution of intertectilecolumellae using phase contrast at 1000 magnication. Equivalentvolumes of residue were scanned for large grains, as determined bycounting to approximately the same number of exotic Lycopodiumspores in each sample (Stockmarr, 1971;Whitney et al., 2012). Calcula-tion of 95% condence intervals was achieved using a modication ofMaher's lognormal distributions in Psimpoll (http://chrono.qub.ac.uk/psimpoll/psimpoll.html, accessed 24/04/2013).

Phytoliths were analyzed at 2- to 3-cm resolution to complement thepollen analysis. Preparation of samples for phytolith analysis followed theprotocol outlined in Piperno (2006). Samples measuring approximately5 cm3were pre-treated to remove clays throughdeocculation, agitation,and gravity sedimentation. Samples were divided into silt (A/B-fraction,b50 m) and sand (C-fraction, N50 m) fractions. A 3-ml subsample ofeach fraction was digested for carbonates (36% HCl) and organics (70%HNO3), and phytoliths were concentrated by heavy liquid otationusing ZnBr2 prepared to a density of 2.3 g/cm3. Approximately 10 mg(not standardized) of extracted phytolith residue was mounted fromeach sample. If processed samples yielded less than 10 mg, all of the res-idue was mounted and scanned. Entellan mounting medium was usedto permit three-dimensional viewing of phytoliths. For the A-fraction,phytoliths were examined and described at 500magnication. A mini-mum of 200 phytoliths was counted, and the rest of themicroscope slidewas scanned to identify any other diagnostic types. For theC-fraction, the entire slide was scanned at 200 magnication andall diagnostic phytoliths counted. Phytoliths were identied usinga comparative collection of over 750 tropical and subtropical spe-cies from South America, housed at the University of ExeterArchaeobotany Laboratory. The collection includes taxa from low-land Bolivia, which were obtained from the Herbario del OrienteBoliviano of the Noel Kempff Mercado Natural History Museumin Santa Cruz, Bolivia. Reference works were also consulted for theidentication of phytoliths (e.g., Piperno, 2006; Iriarte and Paz,2009; Dickau et al., 2013; Watling and Iriarte, 2013).

Macroscopic charcoal was analyzed at 1-cm resolution to determinepast levels of anthropogenic burning. Samples measuring 1 cm3 wererst treated with 5% (w:v) sodium pyrophosphate to disaggregate theclayey sediments and then rinsed through 250- and 125-m sieves, asis standard methodology (Whitlock and Larsen, 2001). The two sepa-rate size fractions (N250 m, 250125 m) were retained and countedfor charcoal fragments using a stereomicroscope. Charcoal concentra-tions were plotted with both pollen (Fig. 3) and phytolith (Fig. 4) strat-igraphic plots so that levels of anthropogenic burning and vegetationchange can be directly compared. All stratigraphic plots were createdin C2 (Juggins, 2003).

Table 2Details of AMS radiocarbon dating results and calibration using the IntCal09 curve.

Publicationcode

Sample identier Conventional 14C age(yr BP 1)

SUERC-43149 San Jose 1213 743 38SUERC-34151 San Jose 2222.5 1061 37SUERC-43150 San Jose 24.525 1739 35in this gallery forest. The fringingmarshy habitat along the lake shore isdominated by Thalia geniculata, and Ludwigia grandiora is frequentlypresent. LSJ, and the gallery forest that surrounds it, are located withinopen seasonally inundated savannas interspersed with forest islandsand patches of degraded forests (Fig. 1B).

Stratigraphy and chronology

The 30-cmcore is composed of uniformly brown-grey claywith verylow organic content (b2% by loss-on-ignition) that grades gradually tobrown-grey clay mixed with sand near the base of the core (Fig. 3).The absence of any abrupt lithological changes suggests that sedimenta-tion was continuous throughout the 30-cm core, representing approxi-mately the past 3000 yr. The sedimentation rates at LSJ are comparableto those of other lowland Bolivian lakes of similar size, whether they arebased upon bulk-sediment dates (Mayle et al., 2000; Burbridge et al.,2004) or terrestrial plant macrofossils (Whitney et al., 2011). Thereare no reversals in the dating. The agedepth relationship for thebottom 6 cm of core, however, was determined by extrapolation fromthe lowest date, thus these oldest age estimates should be viewedwith caution.

Pollen

Pollen preservation was very poor in the lowermost 5 cm of thecore, so these samples were not analyzed for pollen (Fig. 3). Pollen as-semblages in all samples are dominated by herb taxa. Poaceae (2546%)and Cyperaceae (1428%) are most abundant throughout the core,but Mimosa (06%), Gomphrena (04%), Chenopodiaceae/Amaranthus(02%), and Asteraceae (27%), of which Ambrosia (01%) was countedseparately, are all consistently present throughout. Common tree pollentypes that occur throughout the core include Cecropia (920%),Moraceae/Urticaceae (813%), Anadenanthera (04%), Celtis (04%),Gallesia (26%), and Acalypha (03%). Palm (Arecaceae) pollen ispresent throughout (13%), but often poorly preserved and in lowabundance. Calculated 95% condence intervals (not shown) demon-strate that there are no signicant changes in the percent abundanceof key pollen types throughout the record, with the exception of thesurface sample (01 cm),which contains signicantly lower abundanceof Cecropia (10%), and the lowest analyzed sample (25 cm), which con-tains higher Poaceae values compared to the rest of the analyzed assem-blages. The poor preservation of pollen grains in this lowermost sample,compared with the rest of the core, may explain the relatively highabundance of robust Poaceae pollen grains in this sample.

Carbon content(% by wt.)

13CVPDB 0.1 Calibrated date AD(2)

0.6 19.9 1297 820.43 18.4 960 650.3 17.8 311 89

Figure 2. Agedepth model for the 30-cm sediment core from Laguna San Jos. The model is built using three AMS 14C dates calibrated using IntCal09 (Bronk Ramsey, 2009); the 2error is presented for the calibrated dates.

211B.S. Whitney et al. / Quaternary Research 80 (2013) 207217Z. mays pollen is present in the majority of samples (Fig. 3), butabsent in the uppermost two samples, and is least abundant in theoldest samples (1925 cm). Maize pollen was found in the lowestsample analyzed for pollen, dating to ca. AD 180. Concentrations ofFigure 3. Relative percent abundance of key pollen types, including raw count data for Zeadiagram is zoned according to charcoal data (presented on the right) to highlight the occupmaize pollen are very low throughout, thus we reported only thenumber of grains found in each sample (Fig. 3), which approxi-mately equates to maize pollen concentration per 0.25 cm3 ofsediment.mays grains that were retrieved using the methodology of Whitney et al. (2012). Theation period in the Monumental Mounds Region.

Figure 4. Relative percent abundance of phytolith data. Rare types (b2%) are marked with (+). As shown in Figure 3, the data are zoned according to changes in the charcoal concentrations to highlight the occupation period in the Mon-umental Mounds Region (presented on the right of the diagram).

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213B.S. Whitney et al. / Quaternary Research 80 (2013) 207217Phytoliths

Phytolith assemblages are better preserved at the base of the corecompared to pollen. Therefore, one phytolith sample was analyzed at29 cm (860 BC) where no pollen was preserved. Similar to the pollenassemblages, phytolith assemblages are dominated by herb taxa.However, the phytolith assemblages show more variability throughthe core (Fig. 4), particularly with uctuations in the abundance ofPoaceae and Asteraceae. Asteraceae dominates the phytolith assem-blages toward the base of the core (2765%), between 29 cm (860BC) and 21 cm (AD 990), after which it declines to 512%, beforepeaking again at 11 cm (AD 1380) (31%). Poaceae phytoliths areless abundant at the base of the record (1329%), with a very lowvalue of 4% at 26 cm (80 BC). Poaceae phytoliths are highly abundant(3249%), however, in the uppermost four samples dating fromaround AD 1500 until present. The most common phytoliths of thePoaceae family originate from Panicoid grasses, which are typical ofvarious terra rme and wetland habitats in tropical regions. Panicoidphytoliths are highest in the uppermost three horizons analyzed at6 cm, 3 cm, and 1 cm, dating from around AD 1670 until present.Other abundant Poaceae phytoliths include Bambusoideae (17%)and Oryzoideae (09%), the latter of which shows a small peak at9 cm (AD 1500). Additional herb phytoliths that occur commonlythroughout the core include Marantaceae (618%), common to thefringing wetland vegetation of the lake, and Heliconia (611%), ob-served throughout the wet savanna of the region.

Phytoliths of arboreal taxa show lowest abundance in the bottomsection of the core (1124%), from 29 to 21 cm, dating from approxi-mately 860 BC to AD 1000 (Fig. 4). As is common practice, the phytolithassemblages were not spiked with an exotic marker to determine abso-lute concentrations (Stockmarr, 1971), as is typical of pollen analysis.Thus, it cannot be determined whether the low values for tree taxa atthe base of the core are caused by inated Asteraceae values within aclosed sum. The arboreal phytoliths are characterized by abundantglobular granulates, which peak at 16 cm (AD 1170), correspondingto the middle of the mound occupation period. Arecaceae globularechinate phytoliths are also common among assemblages (1028%),with the exception of the lowest sample analyzed at 29 cm (860 BC)where they do not exceed 5%. The number of burned phytoliths in eachanalyzed horizon was not systematically recorded, although charredphytoliths were found to be more abundant between 21 and 11 cmdepth (ca. AD 1000 to 1380).

Charcoal

Charcoal concentrations in both size fractions show a similar trend;concentrations are lowest at the base of the core (Figs. 3 and 4), be-tween 30 and 26 cm (1120 BC to 80 BC), and increase after 25 cm(AD 180), the horizon at which the oldest maize pollen grain wasrecorded. Charcoal values peak around 21 cm (AD 1000). After AD1000, charcoal concentrations decline steadily until ca. AD 1280 afterwhich they remain low until present.

Discussion

Interpretation of pollen and phytolith signals

A comparison of modern phytolith and pollen assemblages fromsoils and articial traps, respectively, fromvegetationplots in a diversityof tropical lowland ecosystems (Gosling et al., 2005, 2009; Burn et al.,2010; Jones et al., 2011; Dickau et al., 2013) has shown that phytolithsand pollen are complementary proxies for the reconstruction of tropicalvegetation. In particular, the taxonomic resolution of grass and herbphytoliths is sufciently high to distinguish wetland and terra rmesavanna ecosystems (Dickau et al., 2013), which cannot be achieved

through pollen analysis (Jones et al., 2011). Furthermore, pollenassemblages in articial trapswithin savannas have been shown to cap-ture the pollen of wind-blown arboreal taxa, such as Moraceae, fromneighbouring forest (Jones et al., 2011), but in contrast, arborealphytoliths are shown to reect a local signal in soils sampled from thesame savanna plots (Dickau et al., 2013). In general, however, arborealtaxa are identiable to a higher taxonomic resolution palynologicallythan is achievable through phytolith analysis. In the savannaforestmosaic of the Llanos de Moxos, therefore, the complementary combina-tion of pollen and phytolith analyses is an excellent approach (Mayleand Iriarte, in press) for the examination of pre-Columbian land use.

Pollen and phytolith analyses are complementary, not only in termsof bridging taxonomic gaps inherent to each proxy, but also in terms oftheir differing spatial scales of source vegetation. Phytolith assemblagesgenerally reect in situ decay of plant matter from vegetation growinglocally (Piperno, 1988, 2006; Iriarte et al., 2010). Although alluvial andcolluvial processes might provide a mechanism for transportation andredeposition of phytoliths (Fredlund and Tieszen, 1994; Dickau et al.,2013), phytoliths do not undergo the same degree of transportationas does wind-blown pollen, for example. Thus the catchment area ofphytolith assemblages derived from lake sediments is likely to representthe vegetation adjacent to the shoreline, particularly in large, at-bottomed lakes, such as LSJ, where there is no mechanism that con-centrates deposition of plant remains towards the centre of the lake.This is borne out by the surface-sediment phytolith assemblage,which is consistent with the inventory of local vegetation around thelake (Table 1).

By contrast, decades of pollen catchment modelling research intemperate latitudes (Jacobson and Bradshaw, 1981; Sugita, 1994,2007) have shown that: i) pollen assemblages from lakes withlarge surface areas, similar to LSJ, represent averaged regional vegeta-tion (N50 km 50 km) (Sugita et al., 1999), and ii) large lakes are in-sensitive to detecting patch-size vegetation change in the surroundinglandscape (Sugita, 1994; Sugita et al., 1999). The applicability of thesepollen catchment studies for our study area might, understandably, bequestioned, given the much higher proportion of wind-pollinated treetaxa in temperate forests compared with those of the tropics. However,we are condent of the regional representativeness of the pollen signalfrom LSJ because the key arboreal pollen types in themodern (core-top)assemblage are wind-pollinated and well-dispersed, such as Moraceaeand Cecropia (Gosling et al., 2005, 2009; Burn et al., 2010; Jones et al.,2011). Furthermore, the most common arboreal taxa in the mod-ern pollen assemblage are rare or absent in the shore-line forest(e.g. Moraceae, Anadenanthera,Gallesia) (Table 1), but common constit-uents of the terra rme forests across the mounds region (Langstroth,1996; Erickson and Bale, 2006). Thus, the phytolith signal in LSJ mostlikely represents the local shoreline and savanna vegetation immediate-ly surrounding the lake (b1 km), whereas the pollen record reects theaggregate proportions of forest versus savanna vegetation of the MMR.

The pollen data indicate that in the ca. 4500-km2 region in whichmounds and forest islands were mapped (Lombardo and Prmers,2010), the proportion of forested terrain, which currently covers 25%of the landscape, was largely unaltered over the past 2000 yr. Giventhe large size of LSJ (14 km2), uctuations in forest cover on the scaleof individual mounds (b20 ha) or clusters of mounds could have oc-curred without having been detected in the pollen record (Sugita etal., 1999), especially given that the cumulative area of mapped moundsand forest islands is b800 ha (Lombardo and Prmers, 2010) or b1% ofthe total forested landscape. However, if a high proportion of the forestcover was cleared during the mound occupation period, a clear declinein arboreal pollenwould be expected alongside the peak in charcoal, es-pecially with respect to wind-dispersed Moraceae pollen, which is themost abundant pollen type in modern assemblages of lowland Boliviantropical forests (Gosling et al., 2005, 2009; Burn et al., 2010). Instead,our 2000-yr pollen record shows no signicant change in the abun-dance of this pollen type. Any change in the levels of forest cover, there-

fore, must have occurred in relatively small patch sizes, perhaps

214 B.S. Whitney et al. / Quaternary Research 80 (2013) 207217restricted to individual habitation mounds, with forest in the inter-mound areas kept largely intact. Fuel for anthropogenic res mighthave originated from these smaller forest clearances, but given that theregional-scale relative abundances of forest and savanna did not changesignicantly, it is more likely that the charcoal peak originated fromextensive burning of savannas, either to clear natural savanna for initialcultivation or to clear and maintain agricultural elds after harvest.

By contrast, the phytolith data, which likely represent shorelinevegetation and savannas proximal to the lake, show signicant uctu-ations throughout the record. In particular, Asteraceae dominates thelowest assemblages (860 BC to AD 1000) and Poaceae values rise atthe top of the core (post AD 1500). Asteraceae is often associatedwith disturbed or open vegetation (Piperno, 2006). However, in anexamination of soil phytolith assemblages in a diversity of ecosystemtypes, Dickau et al. (2013) demonstrated that Asteraceae phytolithsoriginate from a number of sources, such as semi-deciduous andevergreen forests, and terra rme (cerrado) and wetland savannas.Therefore, it is difcult to interpret the high Asteraceae values thatoccur at the base of the core. Given that the diagnostic Asteraceaephytoliths are broad and at platelets, their high abundance in thelower core section may reect the ease by which they are transportedon re draughts, compared to other phytolith morphotypes, becausethe peak in Asteraceae broadly coincides with higher levels of burning.The ecological signicance of the high abundance of Asteraceaephytoliths, however, is largely speculative. Variations in Poaceaephytoliths show there was a greater expanse of grass adjacent tothe lake in themost recent samples (post AD 1670).Within the Poaceaesum, however, the levels of terra rme taxa (Bambusoideae, Chusquea)versus the wetland grass subfamily (Oryzoideae) show little variationthrough the core, which implies that the area of seasonally inundatedsavannas near the lake was not signicantly altered over the past3000 yr. Phytoliths indicative of shoreline taxa and seasonally oodedsavanna, such as Heliconia spp. and Thalia spp. (Marantaceae), a com-mon component of the shoreline vegetation (Table 1), show little vari-ation throughout the record, which suggests that the fringing wetlandsof LSJ were not heavily impacted by past human activity.

Pre-Columbian occupation and agriculture

The charcoal data show that the greatest change throughout the~3000-yr record occurred from AD 400 to AD 1280. Charcoal parti-cles N100 m are generally considered to represent a local burningsignal (Whitlock and Larsen, 2001), but given that LSJ has a verylarge surface area, which is known to increase charcoal catchmentsize (Power et al., 2010), we conservatively interpret that only theN250-m size fraction represents local burning. The similar pattern ofchange shown in both charcoal size fractions, however, implies thathigher levels of local and extra-local burning, compared to present, oc-curred in the same time period. The origin of these past res was likelyanthropogenic because multiple studies demonstrate that climate dur-ing the late Holocene in the Bolivian Amazon became progressivelywetter over the past 2000 yr (Mayle et al., 2000; Burbridge et al.,2004; May et al., 2008). Therefore, the pattern of increased re fromAD 400 to AD 1280 does not follow the expected trend if climate wasthe key control on burning at this time, pointing to an anthropogeniccause for the changes in re regime at our site. Furthermore, this periodof increased burning is coeval with the dates of human occupation de-termined through archaeological excavations (AD 500 to AD 1400) atthe neighbouring Mendoza and Salvatierra mounds (Prmers, 2009).We therefore argue that the charcoal peak reects the height of anthro-pogenic burning in the mound region.

The decline of the mound culture occupation is well-constrained bya bulk sediment date of AD 1297 82 from the end of the charcoalpeak (12.513 cm) (Table 2). Although this represents a mid-rangeage estimate for the decline in charcoal at LSJ, the 95% condence

range of the date spans AD 1220 to AD 1380, which coincides with theterminal occupation dates determined by Prmers (2009). Our datedcharcoal curve bolsters the archaeological evidence that themound cul-ture declined in the pre-contact period, challenging thewidely-held as-sumption (Denevan, 2001; Erickson and Bale, 2006; Erickson, 2010)that the earth-moving pre-Columbian cultures of the Llanos de Moxosdisappeared as a result of European colonization and the introductionof Old World diseases, such as smallpox, after AD 1492.

Despite the reduced charcoal values relating to the decline in themound culture, however, the continuous presence of maize throughoutalmost the entire core indicates that people continuously lived and cul-tivated crops in the mound region from at least AD 180 until present.This agrees with the rst European accounts of the southeastern Llanosde Moxos in AD 1617, in which they noted the impressive area of eldsunder cultivation and the vast quantity of maize produced (Denevan,1966). Thus, although we show that the pre-Columbian mound culturemanaged the landscape more intensively through re in the perioddating from AD 400 to AD 1280, the presence of maize pollen clearlyindicates that the region was continuously occupied through both thepre- and post-Columbian periods. We can reject the possibility thatthese pollen grains originated from wild teosinte, the pollen of which issimilar in morphology and size to that of maize (Holst et al., 2007), be-cause teosinte is native only toMesoamerica and does not occur naturallyin southwestern Amazonia (Doebley, 1990; Fukunaga et al., 2005).

Maize pollen grains are large (55110 mdiameter) and poorly dis-persed from their source plants, which means they are grossly under-represented in lake sediments (Jarosz et al., 2003; Lane et al., 2010).At LSJ, the recovery of maize pollen should be further hampered be-cause the core site is located 500 m offshore and the lake is both shal-low and at-bottomed, which prevents sediment focusing towardsthe middle of the lake. Maize pollen, however, was found in most hori-zons. The recovery of this poorly dispersed pollen type from this sitesuggests that the crops were grown in savannas adjacent to the lake,and possibly along the lake shore. Our data support the interpretationof Lombardo et al. (in press), who suggest that the relatively fertilesoils east of Trinidad, created in the mid-Holocene through the migra-tion of the Rio Grande and with it, the deposition of base-rich Andeansediments (Plotzki et al., 2011), were capable of supporting agriculture.The relatively higher soil fertility east of Trinidad, compared with otherareas in the Llanos de Moxos, has been offered as an explanation for theabsence of raised elds in themound region (Lombardo et al., 2011b, inpress), which is supported by our palynological evidence for maizeagriculture close to LSJ.

Although Dickau et al. (2012) showed that the pre-Columbian earthmounds culture relied on a diversity of crops for food, onlymaize pollenwas recovered from our record. The sieving methodology employed forthis study (Whitney et al., 2012) has proven effective for the isolation ofCucurbita spp. (squash),M. esculenta (manioc), and I. batatas (sweet po-tato) at other archaeological sites in the tropical Americas (Iriarte et al.,2012; Rushton et al., 2013). However, pollen of these other staple cropsis noticeably absent from the record at LSJ, which could be due to one oftwopossibilities; either crops other thanmaizewere grown too far fromthe lake shore to be detected in the record, or maize dominated the dietof the pre- and post-Columbian societies in the mound region. Giventhat Dickau et al. (2012) reported greater abundance of starch grainsand phytoliths from maize, compared with other crops, in ceramicsfrom neighbouring excavated mounds (Mendoza and Salvatierra), it islikely that maize was the staple crop in this region.

Pre-Columbian landscape impact in the Monumental Mounds Region

With the exception of higher abundance of Asteraceae phytolithsat the base of the core, which, as discussed, might signify any numberof taphonomic or local vegetation changes, the pollen and phytolithrecord at LSJ displays no signicant changes associated with thepeak period of mound occupation, as indicated by the peak in char-

coal and higher concentrations of Z. mays pollen. Despite the elevated

215B.S. Whitney et al. / Quaternary Research 80 (2013) 207217levels of anthropogenic burning centred at AD 1000, there is no dis-cernible decline in arboreal taxa in pollen assemblages associatedwith the charcoal peak (Figs. 3 and 4). The large surface area of LSJ(14 km2), however, means that the LSJ pollen signal predominantlyrepresents the regional-scale vegetation (N50 km 50 km) in whichthemounds are situated (Sugita et al., 1999), and the fossil pollen signalwill not detect localized patch-scale changes comparable in area to indi-vidual mounds or mound complexes (Sugita, 1994, 2007). Thus, thestatic arboreal pollen curves demonstrate that any forest clearancesmust have occurred at patch-size scaleswhichwere cumulatively insuf-cient in area to markedly reduce the regional-scale extent of forestcover. If there had been large-scale deforestation associated with thispre-Columbian mound culture, then one would instead expect to nda clear expansion in arboreal pollen due to forest recovery after theend of the mound culture at AD 1280. This pattern, however, is notobserved in our pollen data.

Lombardo et al. (in press) argue that the pre-Columbian moundculture altered the hydrology in the savannas through the creationof drainage ditches and canals to irrigate elds. Although our pollenrecord indicates that maize crops were grown in the vicinity of LSJ,near which canals and reservoirs can also be identied, the phytolithassemblages do not show any clear changes in the relative abundanceof wetland versus terra rme herb taxa coincident with the charcoalpeak and occupation as identied through archaeological excavations(Prmers, 2009). Our phytolith data therefore imply that, althoughthese canal and ditch features are common on the landscape, thepre-Columbian landscape engineering did not greatly alter the rela-tive abundance of wetland versus terra rme habitat in the creationand maintenance of agricultural elds in close proximity to the lakeshore. Instead, one of the greatest changes in the phytolith record oc-curs towards the top of the core (post AD 1670) where the abundanceof Panicoid grasses is much higher compared to the pre-Columbianperiod. The latter may reect changes associated with European colo-nization and the maintenance of forest clearings near the lake afterthe introduction of cattle in AD 1682 (Langstroth, 2011). These phy-tolith assemblages suggest that post-contact local clearances adjacentto the lake might have been greater than the level of impact thatoccurred during the pre-Columbian period.

The number and diversity of earthwork structures in the Llanos deMoxos, which augmented the extent of terra rme habitat in this naturallymosaic environment, has ledmany to conclude that the Llanos deMoxos isa largely anthropogenic landscape (Erickson, 2006, 2010; Lombardo andPrmers, 2010). In the MMR east of Trinidad, hundreds of habitationmounds and occupied forest islands have been identied, alongside nu-merous canals, ditches and reservoirs (Lombardo and Prmers, 2010),and vegetation surveys of abundant economically-important plantspecies growing on and around habitation mounds (Erickson and Bale,2006), have all supported the hypothesis that the conguration of thelandscape and its associated vegetation was heavily manipulated bypre-Columbian people. Given the vast number of these anthropogenicearthworks across the landscape, one might reasonably speculate thatmuch of the forestwas also cleared during the period of earthmounds oc-cupation (Erickson, 2006). An unexpected nding from our pollen datafrom LSJ, however, is that the majority of forest across the MMR wasleft standing by the earth mounds culture. We also show that the extentof forest habitat was not altered signicantly through savanna drainageor the creation of articial relief, as this too would have been reectedin our pollen record. Anthropogenic impact on savannas was greater, aspre-Columbian people intensely burned and managed the savanna land-scape, and the cultivation of crops likely occurred in existing savannaareas, without necessitating the clearance of additional land. Lowre activity after AD 1280, inferred from our charcoal data, sup-ports the assertion of Erickson and Bale (2006) that the modernlandscape reects the product of less intense human managementin recent times and a reduction in the annual burning of the

savanna.Instead of altering the regional abundance of forest habitat, we inferthat the pre-Columbian earth mounds culture built many of their earth-works by augmenting the existing topography on abandoned river le-ves (Lombardo and Prmers, 2010). Their modication of the existinglandscape did not cumulatively create enough new terra rme habitatoutside areas of naturally higher relief to demonstrably alter levels of ar-boreal taxa in the pollen record. We infer that the pre-Columbian earthmounds culture inuenced vegetation on local scales, equivalent to indi-vidual articial mounds or mound complexes, but did not deforest theinter-mound area, which comprises the vast majority of the regional for-ested landscape. Although our data show that forest was not extensivelycleared in the period occupied by the mounds culture, the regional-scalepollen record from LSJ is insensitive to detecting the extent to whichpeople altered the species composition of forest growing on and aroundindividual habitation mounds, such as the selective management to en-courage the growth of economically-useful species (Erickson and Bale,2006). Further analysis of small lakes (b1 ha), which reect localizedvegetation signals, will be required to understand the temporal changesin composition of forest on and around the habitationmounds and forestislands.

Conclusions

Peak levels of anthropogenic burning, inferred from charcoal data,demonstrate that theheight of themonumentalmounds culture occurredfrom AD 400 to AD 1280 in the Llanos de Moxos. The end of the moundoccupation and associated land-use change is well-constrained by radio-carbon dating which precedes European arrival in the New World by atleast 100 yr. The pre-contact date of the charcoal decline contradicts thenotion that earth-mound cultures of the Llanos de Moxos declined asa result of European colonization and associated introduction of OldWorld diseases (Denevan, 2001; Erickson and Bale, 2006; Erickson,2010). We demonstrate that maize was a staple crop, as supported byprevious archaeobotanical analyses of excavated mounds that showedmaize was abundantly processed. Our results support the hypothesisthat specialized earth structures, such as raised elds, were not requiredto growmaize on the relatively fertile soils of the savannas in themoundsregion. Despite the reduction in anthropogenic burning after AD 1280,associated with land-use change and the decline of the earth moundsculture, the region was continuously cultivated with maize throughmuch of the colonial period.

Aerial photographs and satellite imagery have demonstrated thatsome of the greatest evidence of landscape alteration in the Amazon todate (Denevan, 2001; Mayle et al., 2007; Erickson, 2008) comes fromthe vast forestsavannamosaic landscape of the Llanos deMoxos. Despitethis strong evidence of humanmodication of theMonumental MoundsRegion, contrary to expectation, we found no evidence from our pollendata for regional-scale deforestation in pre-Columbian times. Any defor-estation associatedwithmound occupationmust have occurred at scalestoo small to be detectable by the regional-scale pollen signal of our studysite, Laguna San Jos (LSJ). Furthermore, the landscape engineering thatcreated additional terra rme habitat also occurred at scales too small tobe detectable by the pollen record from LSJ. Instead, the inuence oflandscape engineering on vegetation likely occurred at the scale of indi-vidual articialmounds ormound complexes. However, because thepol-len signal from our lake site reects regional scale forest composition,our record is insensitive to anthropogenic forest management at andaround individual habitation mounds. Consequently, we cannot ruleout the possibly that this pre-Columbian culture domesticated theirforests by actively selecting for economically-useful species over otherless useful species (Erickson and Bale, 2006).

Acknowledgments

Research for this manuscript was supported by a Leverhulme

Trust research project grant (F/00158/Ch) awarded to FEM and JI.

216 B.S. Whitney et al. / Quaternary Research 80 (2013) 207217Radiocarbon dates were granted by the NERC radiocarbon facility toFEM (allocation numbers 1527.1010 and 1623.0312). Fieldwork lo-gistical support was provided by the Noel Kempff Mercado NaturalHistory Museum, Santa Cruz, Bolivia, and Programa de Conservacinde la Paraba Barba Azul, Trinidad, Beni Department, Bolivia. Wethank Oscar Saavedra for his guidance and eld assistance in themounds region, and also Jane Bunting, University of Hull, for her valu-able advice on the representativeness of pollen records from largelakes. We also thank two anonymous reviewers whose commentsimproved this manuscript.

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217B.S. Whitney et al. / Quaternary Research 80 (2013) 207217

Pre-Columbian landscape impact and agriculture in the Monumental Mound region of the Llanos de Moxos, lowland BoliviaIntroductionStudy area and archaeological context

AimsMethodsStudy siteSediment collection and field surveysChronologyMultiproxy analyses

ResultsModern vegetationStratigraphy and chronologyPollenPhytolithsCharcoal

DiscussionInterpretation of pollen and phytolith signalsPre-Columbian occupation and agriculturePre-Columbian landscape impact in the Monumental Mounds Region

ConclusionsAcknowledgmentsReferences