A combined pollen and phytolith record for fourteen thousand years of vegetation change in northeastern Thailand

ELSEVIER Review of Palaeobotany and Palynology 103 (1998) 83–93

A combined pollen and phytolith record for fourteen thousand years ofvegetation change in northeastern Thailand

L. Kealhofer a,Ł, D. Penny b

a Department of Anthropology, The College of William and Mary, P.O. Box 8795, Williamsburg, VA 23187-8795, USAb Department of Geography and Environmental Science, Monash University, Clayton 3168 Vic., Australia

Received 17 October 1996; revised version received 19 May 1997

Abstract

Pollen and phytolith analyses of a 6.18 m core (3KUM) extracted from Lake Kumphawapi, northeastern Thailandprovide the oldest continuous sequence of vegetation change for continental Southeast Asia. The combined microbotanicaldata suggest human=environment interaction from at least the Early Holocene to the present. An amelioration of aridLate Pleistocene environments in this region is indicated by the development of herbaceous swamp and swamp forestcommunities at the core site. Early Holocene vegetation changes reflect the rapid expansion and diversification ofmixed-deciduous forests, which may also have been disturbed by anthropogenic burning. The Late Holocene reductionin dry-land forest and the subsequent establishment of secondary-growth forests, suggests a further change to burningregimes. Changes in both human subsistence strategies as well as climate occurred during this period, including thecritical transition to rice agriculture. These changing subsistence patterns are reflected in the Kumphawapi record byevidence of shifting burning regimes, including indirect evidence of agricultural activities in the Middle Holocene. Thetiming and nature of agricultural development indicated by the archaeological data for northeastern Thailand needs to bere-evaluated in order to account for the burning regimes and vegetation changes evident in the 3KUM microfossil record. 1998 Elsevier Science B.V. All rights reserved.

Keywords: pollen; phytoliths; palaeovegetation; Thailand

1. Introduction

Current archaeological data for northeastern Thai-land do not date beyond the 4th millennium B.C.,limiting our understanding of Late Pleistoceneand Early Holocene human=environment interaction.Palaeoenvironmental data within Thailand, and low-land continental Southeast Asia in general, are alsosparse (Maloney, 1992). Pollen research in Thailandhas, until recently, focused on vegetation response to

Ł Corresponding author. E-mail: [email protected]

Holocene sea-level changes (Pramojanee and Hast-ings, 1983; Stargardt, 1983; Hastings, 1983; Mal-oney, 1990; Sangsuwan et al., 1987), while phytolithstudies have focused on Holocene sequences in cen-tral Thailand (Kealhofer and Piperno, 1994; Keal-hofer, 1998). Late Quaternary palynological recordsfrom the interior of Thailand are virtually unknown(but see Hastings and Liengsakul, 1984; Bishop etal., 1992). The only site in Thailand with bothpollen and phytolith data is Khok Phanom Di, onthe southern central plain (Maloney, 1990; Maloneyand Rovner, 1990; Kealhofer and Piperno, 1994).

0034-6667/98/$19.00 c 1998 Elsevier Science B.V. All rights reserved.PII: S 0 0 3 4 - 6 6 6 7 ( 9 8 ) 0 0 0 2 9 - 3

84 L. Kealhofer, D. Penny / Review of Palaeobotany and Palynology 103 (1998) 83–93

Recently, preliminary pollen (Penny et al., 1996)and phytolith data (Kealhofer, 1996), have becomeavailable from Nong Han (‘Lake’) Kumphawapi innortheastern Thailand.

This paper synthesises Kealhofer’s (1996) phy-tolith sequence with new palynological data fromthe same core, thereby providing the first compre-hensive and continuous record of palaeovegetationchange from the Late Pleistocene for this region.This synthesis contributes significantly to the debateon Pleistocene–Holocene transitions and the envi-ronmental and climatic contexts of human settlementand subsistence change.

2. Site description and methodology

Nong Han Kumphawapi (17º080N, 103º010E) is alarge, shallow lake (<4 m water depth), in the SakonNakhon basin of the Khorat Plateau, northeasternThailand (Fig. 1). The depression occupied by thelake formed either as a result of the dissolution ofunderlying salt sequences in the Upper CretaceousMaha Sarkham Formation (Rau and Supajanya,1985), or by the abandonment of a palaeochannelof the Mekong River, whose current channel is some90 km to the north (Moore, 1988; Parry, 1990).

The lake presently supports an extensive floatingherbaceous swamp, dominated by grasses (Poaceaeincluding Phragmites sp.) and sedges (Cyper-aceae). Other common taxa include Eichhorniacrassipes, Ipomoea aquatica, Ludwigia adscendens,L. octovalis, Nelumbo nucifera, Nymphaea lotus,Nymphoides indicum, Persicaria attenuata, Saccha-rum spp., Typha angustifolia, Salvinia cuculata, andseveral fern taxa which occur as an epiphytic ele-ment on the floating or partially rooted herbaceoussubstrata.

A 6.18 m sediment core (3KUM) was recoveredfrom the southern portion of the lake (see Fig. 1) inDecember 1993 with a modified Livingstone corer(Kealhofer, 1996). Sediment sub-samples were takenfrom the core for pollen and phytolith analyses, andseven samples were submitted for radiocarbon dating(Table 1; see also Kealhofer, 1996; White, 1998).

Samples for pollen analysis were treated initiallywith Na4P2O7 to deflocculate clays. Samples werethen agitated through 120 and 5 µm mesh sieves. The

Table 1Calibrated ages were calculated using OxCal v.2.18 (see White,1998). The median age of the calibration range is given betweenbrackets

Sample Lab. Age š error Calibrated 2σ B.C.depth (#) (yr B.P.) (95.4% confidence)(cm)

85 BETA 93027 5540š 70 4520 (4380) 4240136 BETA 93028 6080š 60 5140 (4690) 4830152 BETA 93209 6270š 100 5430 (5190) 4950255 BETA 93030 8610š 100 7920 (7700) 7480355 BETA 93031 8570š 110 7950 (7715) 7300540 BETA 72096 9170š 130 8550 (8250) 7950580 BETA 72097 12220š 70 12750 (12400) 12050

organic fraction of the remaining material was thenfloated off using heavy liquid (Na6[H2W12O40]H2O;s.g. 2.0). Samples were then acetolysed and de-hydrated. Sediment samples for phytolith analysiswere processed according to the method detailedin Piperno (1988) (see Kealhofer, 1996). Sampleswere sieved through 250 and 60 µm mesh, and de-flocculated in Na(CO3)2. Fine clay particles wereremoved by gravimetry, and each sample dividedinto two additional fractions also by gravimetry, andthen wet ashed in Schulze solution. The phytolithswere then floated on a heavy liquid (ZnBr in HCl;s.g. 2.35).

3. Results

3.1. Stratigraphy and chronology

As with other sedimentary profiles taken fromLake Kumphawapi (Penny et al., 1996), the 3KUMsequence contains three distinct sedimentary units.The lower unit consists of olive-grey fine sands (6.18to 5.70 m) overlain by extremely uniform olive-brown organic clay loams (5.70 to 1.40 m). Theseorganic clays are in turn overlain by dark-brownorganic-rich lacustrine muds (1.40 to 0 m), witha distinct facies boundary between the upper twounits. Radiocarbon dates taken from this sequence(Table 1) indicate that the basal sand unit is of LatePleistocene age. The similarity in the radiocarbondates taken from the organic clay loam unit indicate aperiod of extremely rapid deposition commencing in

L. Kealhofer, D. Penny / Review of Palaeobotany and Palynology 103 (1998) 83–93 85

Fig. 1. Site location, Nong Han Kumphawapi.

the Early Holocene (7–8 ka), and ending in the Mid-dle Holocene (5–6 ka). This would in part explainthe homogeneity of these sediments, and suggestsa period of high energy sediment transport in thecatchment. The absence of any material coarser thanfine clays in this unit would indicate sorting, possiblyas a result of filtering through floodplain swamp veg-etation. The deposition of organic rich muds, with anapparently lower sedimentation rate, began approxi-

mately 6000 years before present (4600 cal. yr B.C.),and continues to the present.

3.2. Microfossil sequence

The results of pollen analysis are given in Fig. 2,and phytolith data are presented in Fig. 3. Pollen andphytolith assemblages will be described according tothe general sequence established in Kealhofer (1996).


Fig.

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taxa

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.


Fig.

3.Se

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3KU

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3.3. Late Pleistocene (6.18–5.3 m) >14,000–<8250yr B.C.

Pollen is not present in the olive-grey Pleistocenesands below 5.5 m, suggesting oxidisation. Phy-toliths, however, are abundant in these sediments.The phytolith assemblage for this period is domi-nated by Panicoid and Bambusoid grass forms. Ar-boreal types are very poorly represented, both interms of strength of representation and diversity offorms, with Arecaceae being the most common ar-boreal phytolith. Several shifts occur in arboreal andgrass taxa, suggesting fluctuations in both rainfalland temperature, which may relate to contemporaryfluctuations identified in south central China (e.g.,An et al., 1993; Sun and Chen, 1991).

Correspondence analysis of phytolith samplesfrom the 3KUM sequence (Kealhofer, 1996) indi-cates that the Pleistocene assemblages are distinctfrom later assemblages. They contain a specificgroup of unknown grasses (possibly Arundinoid),a non-Sativae series rice, and the Chloridoid grassgenus Dactyloctenium. Kealhofer (1996) suggeststhat this assemblage describes a distinct temperatureand humidity regime, without a modern analogue,and argues that the paucity of arboreal types as wellas the presence of Chloridoid grasses mark an aridperiod.

The pollen evidence available for the end of thisperiod (from 5.5 to 5.3 m) supports this interpre-tation. The dominant arboreal pollen types repre-sented in these sediments are Celtis and Pinus, whilePoaceae is the dominant non-arboreal family. Thepaucity of arboreal pollen types means that thereis no clear signal as to the nature of dry landcommunities, or at least no evidence of the plantcommunity associations evident in the region today.While this can, in part, be explained by the absencefrom the pollen record of the currently dominantDipterocarpaceae (due to entomophilous pollinationstrategies; see Ashton, 1982; Bera, 1990), the Pleis-tocene pollen assemblages suggest a xeric, speciespoor, and strongly seasonal vegetation.

Despite this apparently arid environment, thepresence of surface water is indicated by Panicoideaeand Oryzoid grasses and Cyperaceae in the phytolithrecord, and by Cyperaceae and Ludwigia pollen.This may mark the initial occurrence of standing

water in the Kumphawapi basin, reflecting a pro-gressive climatic amelioration after the last glacialmaximum.

An intriguing aspect of this Late Pleistocene=Early Holocene flora is the presence of Barringtonia,Carallia brachiata, Eugenia=Melaleuca type, andLagerstroemia. These taxa are often found in variousassociations in lowland Southeast Asia as a swampforest element (De Haan, 1931; Endert, 1932; VanSteenis, 1934), but the associations suggested by the3KUM pollen record bear no floristic relationship tomodern freshwater swamp forest in Thailand (Smiti-nand, 1989). The relatively strong representation ofBarringtonia pollen in the microfossil sequence sug-gests a local source, as this genus is pollinated bynocturnal animals (Tomlinson, 1986), and is there-fore notoriously under-represented in pollen spectra.There are currently 11 species of Barringtonia inThailand (Chantaranothai, 1995), of which seven oc-cur in coastal or evergreen forest communities in thesouth of Thailand. Four species have a broader dis-tribution and are associated with swamp or riparianenvironments (B. acutangula, B. augusta, B. race-mosa and B. rimata). Similarly, Carallia brachiata,the only species of freshwater mangrove (or morecorrectly, ‘mangal associate’ — Tomlinson, 1986)recorded in the northeast of Thailand (Smitinand,1980), is described as occurring in the littoral offreshwater swamps (Hou, 1958).

While Barringtonia, Carallia and Eugenia=Melaleuca type are undoubtedly part of a swampmargin or riparian community, Lagerstroemia ismore problematic. Eight species of Lagerstroemiaoccur in northeastern Thailand (Smitinand, 1980;White, 1995), exhibiting a range of environmen-tal preferences. Given this habitat variation withinthe genus and difficulties in the identification ofLagerstroemia pollen to species level, the ecology ofthis taxon in the 3KUM record is uncertain. How-ever, recent ethnobotanical research conducted in theKumphawapi region revealed a community type col-loquially known as ‘din thaam’, characterised byBarringtonia acutangula and Lagerstroemia flori-bunda (White, 1995). This community type is prin-cipally a riparian or floodplain element along thestreams feeding into Nong Han Kumphawapi, ratherthan a swamp margin or swamp forest commu-nity, and is strongly reliant upon a specific seasonal


flooding regime. It is possible, then, that these taxademonstrate the presence of seasonally inundatedfloodplains or stream margins in the Kumphawapicatchment from the Late Pleistocene.

The presence of Uncaria=Wendlandia-type pollenin these Late Pleistocene assemblages is also enig-matic. As has been noted elsewhere (Penny et al.,1996), genera of the Naucleaeceae (Rubiacae) arecommon throughout the Kumphawapi pollen record.Without this taxonomic specificity, ecological or en-vironmental interpretations of these taxa are difficult.Penny et al. (1996) have argued that the presence ofthese taxa indicate a disturbed marginal or riparianswamp, based on vegetation descriptions from PapuaNew Guinea (Garrett-Jones, 1979).

3.4. Early Holocene (5.3–2.2 m) ca. 8000–7000 yrB.C.

Fluctuations in the representation of phytolithtaxa in the Early Holocene suggest a period ofinstability. Panicoid grass phytoliths decrease in bothabundance and diversity from this time, while anincrease in Bambusoid grasses, concomitant withtemporary declines in both arboreal and Panicoidphytoliths at 4.9 m suggest disturbance throughburning (Kealhofer, 1996). This instability may beof anthropogenic origin, as no evidence of com-parable vegetation=climatic fluctuations are foundin adjacent regions (e.g., Flenley, 1984; Heaney,1991; Feng et al., 1993). After these initial oscilla-tions, the phytolith assemblages reveal a more stableregime, with an increase in the diversity of Bam-busoid grasses, a decline in Panicoid grasses, andindicators of a more forested environment (non-tax-onomically specific forms, such as various spheretypes and sclereids, that are produced only by trees).

The Early Holocene pollen flora also suggesta diversification of arboreal taxa, with increasesin Pinus, Quercus, Combretaceae=Melastomataceaetype, Elaeocarpus, Mallotus, Macaranga, and othertaxa. The extremely strong representation of grassesduring this period, in the absence of pollen evidencefor a herbaceous swamp on site, suggest a rela-tively open dry-land vegetation, incorporating openwoodlands to dry=mixed deciduous forest. A mas-sive spike in sedimentary charcoal occurs between3.5 and 2.5 m (approximately 9 ka B.P.). This is

synchronous with the highest occurrence of burnedphytoliths. Most of these were Bambusoid grasses,suggesting the burning of mixed or dry deciduousforests (Kealhofer, 1996). Interestingly, the pollendata reveal no significant response to this increasein burning. Pinus, still the dominant arboreal pollentype, suffered a decline in representation associ-ated with this early increase in burning, but othertaxa did not respond similarly. This supports Keal-hofer’s (1996) suggestion that this Early to MiddleHolocene burning was, while of apparently increasedfrequency, of low intensity (see Stott, 1986).

3.5. Middle Holocene (2.2–1.2 m) ca. 7000–3000 yrB.C.

Pollen data for this period show significantchanges in the local flora, with dramatic increasesin sedges and fern spores. As has been noted above,these taxa are strongly represented in the modernherbaceous swamp at this site. We suggest thatchanges in the representation of these taxa in theMiddle Holocene represent the early expansion ofthis community type. The increase in fern spores isparticularly interesting, given their restriction to thefloating herbaceous mats in the modern flora. Thesechanges in the pollen record may record the liftingof the herbaceous root mat in response to an increasein water level, suggestive of a broader hydrologicalchange in the basin. Coincident with the develop-ment of herbaceous swamp is the disappearance ofBarringtonia, and the increase in the representationof Carallia brachiata pollen, which may also beto-ken a change in the hydrological regime, such as astronger wet season, or a decline in seasonality. Inlight of the emergence of herbaceous swamp at thistime, these pollen data potentially mark a period ofhigher available moisture. The phytolith data supportthis interpretation, with increases in Cyperaceae andOryza phytoliths.

Interestingly, at this time both the nature of sed-iments deposited at the core site and the rate ofsediment deposition markedly changed. Radiocar-bon samples taken from above (BETA 93028) andbelow (BETA 93029) this horizon date this sedi-mentological change to between 6080 and 6270 yrB.P. (uncal.). Sediments deposited after this hori-zon are highly organic dark lake muds, with the


organics largely derived from the newly developedherbaceous swamp. This phenomena has also beenrecorded in other sediment profiles taken furthernorth in the Kumphawapi basin, dating to between4950 (Wk-2366) and 5650 (NZA-5766) yr B.P. (un-cal.) (Penny et al., 1996). The difference in timingbetween the center and north end of the lake indi-cates a time-transgressive sedimentological changerelated to the migration of lake margins northwardacross the basin. We suggest that the developmentof herbaceous swamp is associated with this expan-sion.

3.6. Late Holocene (1.2–0 m) 3000 yr B.C.–Present

Unfortunately, phytoliths do not occur in the up-per metre of the microfossil sequence. The pollendata for this period reveal the further development ofthe local herbaceous swamp communities. Caralliabrachiata undergoes a sustained decline at this time,and Eugenia=Melaleuca-type and Lagerstroemia areless strongly represented and more unstable. A sub-stantial increase in Naucleaceae type pollen, thoughtto be Cephalanthus (not shown in Fig. 2), is charac-teristic of this period.

A second increase in sedimentary carbonised par-ticles occurs in the upper metre of the record.Many of the familiar dry land taxa, such asCeltis, Combretaceae=Melastomataceae, Diptero-carpus, Lithocarpus=Castanopsis, Macaranga, Mal-lotus, Trema and so on, are significantly reduced ordisappear from the record. The notable exception isPinus, which attains its strongest representation. Incontrast to the Early Holocene increase in burningdescribed above, Late Holocene burning appears tohave had a dramatic effect upon dry land arborealcommunities. We suggest this may represent new andintensified anthropogenic activities. Several taxa in-crease in the upper 50 cm of the 3KUM record,such as Celtis, Combretaceae=Melastomataceae,Macaranga, Mallotus and Trema, suggesting the es-tablishment of re-growth or secondary forest.

4. The issue of burning

Phytoliths, unlike pollen, preserve direct evidenceof fire. Burned phytoliths contain black occluded

carbon (Piperno, 1988), and are occasionally slightlydistorted in shape. Brown staining of phytoliths isalso common in soil samples, but this staining maybe related to the presence of iron, or other miner-als, in addition to carbon (Kepax, 1975; Wilding etal., 1977). Because phytoliths directly reveal burn-ing, it is possible to identify which specific taxa areburned. This can provide clues as to seasonality ofburn (which plant parts are burned), intensity of burn(which taxa in a community are burned), and indi-rectly, the role of anthropogenic agents. The patternof phytolith burning for this sequence is discussedelsewhere (Kealhofer, 1996), however, several pointscontribute to this discussion.

Burned phytoliths are at a maximum in the LatePleistocene=Early Holocene, suggesting that peoplewere involved in burning, since this was a timewhen seasonality was at a minimum and precip-itation at a maximum (Heaney, 1991; Liu et al.,1992). Cultural burning is ethnographically, and eth-nohistorically, documented as a means to increasegrazing for species hunted, to encourage the growthof specific economically useful species, to clear theundergrowth for travel, security, and aesthetic pur-poses (e.g., Mellars, 1976; Stott, 1986; Head, 1994).In the Kumphawapi record, Bambusoid phytolithsare the most commonly burned, with burned arborealphytoliths rare, indicating that low intensity litterburns were commonly set in the region (Stott, 1986).This does not fit with a slash and burn subsistenceregime, where a more diverse set of burned specieswould be expected.

The frequency and=or intensity of burning de-clines during the Middle Holocene, coincident witha change in type of plants being burnt, with riceand weed phytoliths more commonly burned, andburned Bambusoid phytoliths less commonly repre-sented. This might mean that burning shifted outof the forest and into the rice or agricultural fields.Burning stubble in the fields is common practiceacross Thailand, and many other countries, today(Tanabe, 1994). Unfortunately, the lack of preservedphytoliths in the upper metre of sediment makes itimpossible to address burning in the same way forthe Late Holocene. The carbon peaks and vegetationchanges in the pollen samples, however, as notedabove, reveal new patterns of anthropogenic burningin the Late Holocene.


5. Discussion and conclusion

The pollen and phytolith evidence presented herereveal a complex series of palaeovegetation changesfrom the Late Pleistocene to the present. In general,the pollen and phytolith data sets give a remarkablycomplementary picture of environmental change, de-spite the disparate range of taxa identifiable by eachtechnique and the different taphonomy of each mi-crofossil assemblage.

In terms of palaeoclimate reconstruction, both thepollen and phytolith data indicate a dry, unstableand relatively species poor Late Pleistocene=EarlyHolocene. These data agree with other palaeoenvi-ronmental records revealing an arid and distinctlyseasonal Late Pleistocene climate due to a steepernorth–south temperature gradient creating strongerwinter monsoons (Verstappen, 1975, 1980; Fontugneand Duplessy, 1986; Kutzbach and Street-Perrot,1985; Van Campo, 1986). The fluctuations seen inthe Late Pleistocene vegetation, if representative ofsharp shifts in seasonality, may be evidence for or-bital forcing events suggested for adjacent regionsca. 10–13 ka (Aharon, 1984; Kanari et al., 1984).

The Early Holocene diversification of dry landforests indicated by the pollen and phytolith data pre-sented here would suggest an easing of this tempera-ture gradient and higher available moisture. Sun andChen (1991) report a similar Early Holocene amelio-ration in Chinese palynological records, with the es-tablishment of deciduous forest linked to an increasein temperature. Similarly, Bishop and Godley (1994)provide palaeochannel discharge estimates for theYom River, north-central Thailand, which indicatethe greatest bankfull discharge occurred during theEarly to Middle Holocene. While the arboreal com-ponent clearly increased during the Early Holocene,the very rapid and extensive deposition of sedimentduring this period suggests that extensive areas wereeither thinly vegetated or bare. This is distinctly dif-ferent from temperate regions, where erosion andaggradation declined substantially during the EarlyHolocene as vegetation stabilised the landscape.

The Middle Holocene hydrological changesposited on the basis of the development of herba-ceous swamp and the decline in ‘din thaam’ typevegetation are more difficult to interpret in simpleclimatic terms. Clearly, the development of floating

herbaceous swamp must be related to an increase inwater levels at the core site, but the fact that thisevent is time-transgressive between cores suggestsa gradual filling of the lake basin from the south,rather than a distinct climatic change in the strengthor intensity of the summer monsoon. The possibilityof the tectonic damming of the southern outflow ofthe lake by the development of the Ban Don Kaeo‘salt mound’ (Rau and Supajanya, 1985), or a lagin the response time of the system to an Early–Middle Holocene climatic amelioration must also beconsidered.

The evidence from Kumphawapi provides notonly a record of specific regional successions, butalso of human environmental relationships that de-veloped over the last 14,000 yr. Patterns of burningand vegetation change during the Early Holocenedo not seem to reflect natural events, certainly notany known in adjacent regions. Clearing the under-storey of the forest through burning may have serveda variety of purposes, not only subsistence related.Changing strategies of burning by the late 5th=early4th millennium B.C. potentially reflect the intensifi-cation of agricultural activities. With the increasingimportance of wet rice agriculture, broadcast burningwould have decreased. How Late Holocene burningpatterns related to later shifts in agricultural or otherstrategies will require further investigations.

Acknowledgements

This research is part of a multi-disciplinary studyby the Thailand Palaeoenvironmental Project (TPP— Dr. Joyce White, Dr. Lisa Kealhofer, Dr. BernardMaloney, Dr. Mauro Cremaschi), and Monash Uni-versity. This research is funded by the Australian Re-search Council, Monash University Maritime Conti-nent Project, National Geographic, the SmithsonianTropical Research Institute and the Friends of BanChiang. We wish to thank J. White, J. Grindrod,P. Bishop, D. Piperno, S. van der Kaars, P. Grave,P. Kershaw, F. Neiman, NRC Thailand, the Ban Chi-ang villagers, Stuart Fleming, Director of MASCAUniversity of Pennsylvannia, Glen Russell, Instituteof Archaeology, UCLA, and Marley Brown, Direc-tor of the Department of Archaeological Research,Colonial Williamsburg.


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Documents

A combined pollen and phytolith record for fourteen thousand years of vegetation change in northeastern Thailand