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Quaternary Science Reviews 27 (2008) 2546–2567

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Quaternary Science Reviews

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The late Quaternary decline and extinction of palms on oceanic Pacific islands

M. Prebble a,*, J.L. Dowe b

a Department of Archaeology and Natural History, Research School of Pacific and Asian Studies, College of Asia and the Pacific, The Australian National University, Canberra,ACT 0200, Australiab Australian Centre for Tropical Freshwater Research, James Cook University, Townsville, Queensland 4811, Australia

a r t i c l e i n f o

Article history:Received 16 August 2008Received in revised form22 September 2008Accepted 23 September 2008

* Corresponding author. Tel.: þ61 2 61254342.E-mail address: matthew.prebble@anu.edu.au (M.

0277-3791/$ – see front matter � 2008 Elsevier Ltd.doi:10.1016/j.quascirev.2008.09.015

a b s t r a c t

Late Quaternary palaeoecological records of palm decline, extirpation and extinction are explored fromthe oceanic islands of the Pacific Ocean. Despite the severe reduction of faunal diversity coincidental withhuman colonisation of these previously uninhabited oceanic islands, relatively few plant extinctions havebeen recorded. At low taxonomic levels, recent faunal extinctions on oceanic islands are concentrated inlarger bodied representatives of certain genera and families. Fossil and historic records of plantextinction show a similar trend with high representation of the palm family, Arecaceae. Late Holocenedecline of palm pollen types is demonstrated from most islands where there are palaeoecological recordsincluding the Cook Islands, Fiji, French Polynesia, the Hawaiian Islands, the Juan Fernandez Islands andRapanui. A strong correspondence between human impact and palm decline is measured from paly-nological proxies including increased concentrations of charcoal particles and pollen from cultivatedplants and invasive weeds. Late Holocene extinctions or extirpations are recorded across all five of theArecaceae subfamilies of the oceanic Pacific islands. These are most common for the genus Pritchardiabut also many sedis fossil palm types were recorded representing groups lacking diagnostic morpho-logical characters.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

A rift in Quaternary science exists over whether the faunalextinctions that have occurred on previously uninhabited ecosys-tems across the world were climatically driven or anthropogenic(Burney and Flannery, 2005, 2006; Wroe and Field, 2006; Koch andBarnovsky, 2006; Brook et al., 2007). Palaeoecological data fromoceanic islands have provided fuel for this debate in effectivelydemonstrating a close association between the timing of faunalextinctions, particularly of avifauna and land snails, and humancolonisation (James, 1995; Steadman, 2006). By contrast, the effecton island floras is not well understood. Palaeoecological data frommany oceanic islands and adjacent continental landmasses of thePacific have shown impacts on indigenous vegetation followinghuman colonisation (Flenley et al., 1991; Parkes, 1997; McGlone andWilmshurst, 1999; Stevenson et al., 2001; Athens et al., 2002;Haberle, 2003; Fall, 2005; Mann et al., 2008; Wilmshurst et al.,2008; Prebble and Wilmshurst, in press), but thus far few recordshave provided evidence of floral extinctions.

Prebble).

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The palaeoecological record of Rapanui (Easter Island, Chile)provides the most convincing case of the almost complete decima-tion of an island flora that followed human colonisation (Hunt andLipo, 2006; Hunt, 2007; Mann et al., 2008). Initial human impactbegan less than 1000 yr cal BP and was as devastating to the flora as itwas to the fauna. Late Holocene pollen records from Rapanui reveal11 plant extinctions identified to at least the family level (Flenleyet al.,1991; see Table 1). Subsequent analyses of archaeological woodcharcoal, radiocarbon dated to after 600 yr cal BP, has revealeda further seven plant extinctions, some of which may be endemicspecies (Orliac and Orliac, 1998; see Table 1). Other extinctions arerepresented by microfossils that await further systematic analysis orthe discovery of additional diagnostic macrofossil material. The mostnotable extinction amongst these taxa is Paschalococos disperta. Thispalmwas initially recognised in the fossil pollen record to family level(Heyerdahl and Ferdon, 1961) and later by subfossil endocarpmaterial by Dransfield et al. (1984) that showed alliance to, but werenevertheless significantly different in size and shape from, Jubaeachilensis from mainland Chile (Zizka, 1991).

Hunt (2007) has summarised the evidence for human-inducedpalm extinction on Rapanui. Bork and Mieth (2003) and others (e.g.Mann et al., 2008) have found evidence such as palm root casts,presence of charcoal particles, sedimentary changes and archaeo-logical features indicating that a dense palm forest grew on parts of

Table 1List of indigenous angiosperm trees (except palms) that represent island-based plant family extinctions or extirpations from oceanic islands in the Pacific during the LateQuaternary. Extinction: represents the global extinction of a species. Extirpation: represents a local extinction, with extant representatives surviving on other islandsExtinction or extirpation status is tentative for all taxa and all of these events probably occurred after initial human colonisation of the islands.

Plant family Species or generic affinity/extinction orextirpation

Islands Time of extinction(yr cal BP)

Reference

Araliaceae cf. Meryta (possibly endemic)/extinction Rimatara (FrenchPolynesia)

<900 M. Prebble, unpublished pollen data

Combretaceae Terminalia cf. glabrata/extirpation Rimatara <900 M. Prebble and N. Porch, unpublished macrobotanical andpollen data

Combretaceae Terminalia glabrata/extirpation Mangaia (Cook Islands) <10 G. McCormack, unpublished dataCunoniaceae cf. Weinmannia (possibly endemic)/

extinctionMangaia (Cook Islands) <2500 Ellison, 1994

Elaeocarpaceae cf. Aristotelia/extirpation Kermadec Group (NewZealand)

<250 M. Prebble and J. Wilmshurst, unpublished pollen data

Elaeocarpaceae Aristotelia/extirpation Three Kings (New Zealand) <50 C. West, unpublished survey dataElaeocarpaceae cf. Elaeocarpus floridanusa/extirpation Rapanui (Chile) <600 Orliac and Orliac, 1998Euphorbiaceae cf. Macaranga spp./extinction Rapanui <2000 Flenley et al., 1991Flacourtiaceae cf. Xylosma suaveolens/extirpation Rapanui <600 Orliac and Orliac, 1998Malvaceae cf. Hibiscus (possibly endemic)/extinction Laysan (USA) <100 Athens et al., 2007Myoporaceae Myoporum rimatarensis/extinction Rimatara <80 Meyer et al., 2004Myrsinaceae cf. Myrsine/extinction Rapanui <600 Orliac and Orliac, 1998Myrtaceae cf. Metrosideros/extirpation Rapanui <2000 Flenley et al., 1991Pittosporaceae cf. Pittosporum/extinction Rapanui <600 Orliac and Orliac, 1998Santalaceae Santalum ellipticum/extirpation Laysan <50 Athens et al., 2007Santalaceae Santalum fernandezianum/extinction Juan Fernandez (Chile) <200 Wester, 1991Sapotaceae cf. Pouteria grayana/extirpation Rimatara <900 M. Prebble, unpublished dataRhamnaceae cf. Alphitonia zizyphoides Rapanui <600 Orliac and Orliac, 1998Rubiaceae cf. Coprosma, Psydrax, Psychotria/

extinctionsRapanui <2000 Flenley et al., 1991; Orliac and Orliac, 1998

Rutaceae cf. Melicope/extinction Rimatara <900 M. Prebble, unpublished pollen dataUlmaceae cf. Trema/extirpation Rapanui <2000 Flenley et al., 1991Urticaceae cf. Premna/extirpation Rapanui <700 Orliac and Orliac, 1998

a Orliac and Orliac (1998) previously designated Elaeocarpus tonganus, but the Rapanui species is more likely to be aligned with E. floridanus (Florence, 2004).

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2547

the island. On Poike Peninsula, soil profiles overlying abundantcharred palm bases or stems do not exceed 700 yr cal BP. Meith andBork (2003) suggested that anthropogenic fires destroyed the palmforest within 200 years of human settlement, after which a humicsoil horizon characteristic of grassland vegetation developed. Manypalm endocarps have been located in archaeological and non-archaeological deposits showing gnaw marks indicative of thePacific rat (Rattus exulans). Such evidence has lent support to theidea that rats may have compounded the decline of palms, alsoaffected by human activity, by restricting regeneration throughseed predation (Hunt, 2007).

Even with the abundant evidence for the role of human impact,the timing and cause of palm extinction on Rapanui has beenvigorously debated (Flenley and Bahn, 2002; Rainbird, 2002; Dia-mond, 2005; Flenley and Bahn, 2007; Hunt, 2007). This debatecomes in spite of the robust palaeoecological evidence for human-induced vegetation change on numerous other oceanic Pacificislands. At most sites the palynological evidence includes the rapidinflux of charcoal particles, pulses of soil erosion, and increases inthe abundance of grasses and certain fern taxa coinciding with thedecline of trees (Athens and Ward, 1993; Kirch and Ellison, 1994;Kirch, 1996; McGlone and Wilmshurst, 1999; Dodson and Intoh,1999; Athens et al., 2002; Fall, 2005; Kennett et al., 2006; Prebbleand Wilmshurst, in press).

In this paper, we apply a palaeoecological approach to theextinction and human impact debate by addressing the decline,extirpation or extinction of palms from the oceanic Pacific islands.We use sedimentary swamp archives, as they often providecontinuous records of ecological conditions and biological repre-sentation that exist both before and after human colonisation. Weuse the oceanic Pacific islands as they appear to be ecologicallysensitive to human impacts and were colonised in the lateHolocene, a period captured in organic rich sedimentary archives

on many islands. Finally, we assess fossil records of palm declineand extinction by integrating modern phytogeographic data ofpalms.

2. Background

2.1. Island biogeography and oceanic Pacific islands

Oceanic islands have been integral for understanding the evolu-tionary history of biotas and for theories of biogeographic patterning(MacArthur and Wilson, 1967; Paulay, 1994; Whittaker, 1998; Whit-taker et al., 2000; Vitousek, 2002). The composition of species on anoceanic island may directly reflect the processes of immigration suchthat taxa on more remote oceanic islands comprise a nested subset ofthose on the nearest landmass. New species can arise on islandsfollowing colonisation and subsequent evolutionary differentiation.These hypotheses have been tested for a range of different oceanicisland plants and other organisms using molecular phylogeneticapproaches to assess relatedness among island endemic lineages, aswell as associations between species on different archipelagos withcontinental congeners (Givinish et al., 1995).

Biogeographic research is weighted towards understanding therole of speciation at the expense of understanding extinctionprocesses (Johnson et al., 2000; Emerson, 2002). Part of theproblem is the paucity of fossil records essential for defining thepast distribution and timing of species extinctions. This issue aside,extinction processes should be more apparent on oceanic islandsgiven the premise that large areas hold more species than smallareas and larger populations persist longer than small populations(Bond, 1995). In this sense, islands have been predisposed to higherrates of extinction than on continental landmasses, an hypothesissupported by abundant fossil evidence for extinct avifauna (James,1995; Steadman, 2006) and land snails (Solem, 1990; Lee et al.,

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–25672548

2007). This rich fossil evidence has made oceanic islands usefulmicrocosms of what has become a global debate on late Quaternaryextinction centred on two hypotheses, climate-driven or human-caused extinction.

The oceanic Pacific islands have been critical to island bioge-ography research given that they were never connected to anycontinental landmass and have only been forming since the Eocene(Dickinson, 2001). The extensive stretches of ocean in the Pacificrepresent formidable dispersal barriers and filters for oceanicisland biota that must rely solely on dispersal from distant sourcepopulations. Some Pacific islands are formed from remnantGondwanan landmasses including New Caledonia, New Zealand,and parts of the Solomon Islands and the Fiji Archipelago. In thecontext of this research, the larger islands of Fiji are not regarded asoceanic islands per se, as they have been subaerial since the Eocene.However, these islands are still examined as their biotas arepredominantly oceanic in function. True oceanic islands, such asthe Lau group, are also associated with the Fiji archipelago.

2.2. Climate/geodynamic related or human-caused extinctions onthe oceanic Pacific islands

An abundance of proxy palaeoclimatic records from deep-seadrilling, coral archives and other sources has shown thatpronounced climate change events characterise the late Quaternaryof oceanic islands, as they do for continental landmasses (Corregeet al., 2000; Woodroffe et al., 2003; Conroy et al., 2008). Majorcatastrophic late Quaternary geological events have been recordedfor many oceanic Pacific islands including earthquakes andtsunamis (Moore and Moore, 1984; Burney et al., 2001), continuinghotspot volcanism (e.g. Galapagos Archipelago; see Munro andRoland, 1996), or resurgent volcanic eruptions along platesubduction zones (e.g. Kermadec Group; see Worthington et al.,1999). Late Quaternary sea-level fluctuations have resulted inmassive contractions of oceanic islands particularly on low-lyingatolls (e.g. Tuamotu Archipelago, French Polynesia) in which entirearchipelagos were submerged. Some sub-Antarctic oceanic islandssupported Pleistocene ice sheets that expanded during glacialmaxima reducing habitat for terrestrial biota (McGlone, 2002).

The late Quaternary has shown an apparently unprecedentedglobal pattern of temporally stepwise megafaunal collapse, begin-ning with the Australian continent 40 000–60 000 years ago,spreading to the New World at the end of the Pleistocene w12 000years ago, then on to the numerous oceanic Pacific islands in thelate Holocene (Martin and Steadman, 1999; Burney and Flannery,2005). This pattern is without major exception for biotas thatincluded animals not only with large body size but also lowreproductive rates (Johnson, 2002; Koch and Barnovsky, 2006).Oceanic islands lack megafauna but show a bias towards extinctionof the largest vertebrates, but smaller extinct vertebrates are alsofound within the same fossil records (Steadman, 2006). In mostcases extinctions are recorded in the fossil record within a fewcenturies of initial human colonisation.

The human-caused continental extinction of a diverse assem-blage of late Pleistocene and Holocene fauna, particularly of large-bodied animals, continues to be debated. On oceanic islands,however, few animals (fossil or extant) approach the arbitrary 44–250 kg size-range quoted by some authors as defining megafauna(Choquenot and Bowman, 1998; Stuart, 1999). Guthrie (2004) hasargued that postglacial sea-level rise made the oceanic islands ofthe Aleutian group too small to ever sustain mammoth populationsdespite the bridges formed between the islands and the adjacentmainland during the Pleistocene. With the exception of the extantgiant tortoises (Geochelone elephantopus) of the Galapagos Islands,which currently face extinction, the largest terrestrial animalsknown from the oceanic Pacific islands are the relatively

lightweight (<8 kg), flightless ground dwelling megapodesincluding the extinct Megapodius sp. from Tonga. Large pigeons anddoves are known from the fossil record, including an extinct Duculasp. from Tonga and Macropygia spp. from the Society and Mar-quesas Islands (Steadman, 2006).

2.3. Defining the causes of plant extinctions on oceanic islands

Extinctions have occurred as a function of many evolutionaryand ecological processes, but separating out these factors isa complex task. Molecular-based phylogenetic analyses haveprovided substantial evidence for rates of speciation on islands,however, in the absence of fossil or historical evidence there areenormous difficulties in identifying extinction rates given the limitsplaced on sampling extinct or ‘ghost’ lineages (Thorpe and Mal-hotra, 1998; Bromham and Woolfit, 2004). In cases where mono-phyletic lineages have been demonstrated, a trait common to islandfloras, the known geological age and spatial distribution of youngoceanic islands is often directional and this can be used to cross-check the direction of species dispersals and radiations. Thedistances or gaps separating intrageneric or intraspecific phyloge-nies can in some cases be explained by extinction events withina chronological framework independently controlled by radio-metric ages for island subaerial formation, e.g. Cyanea and Argyr-oxiphium on the Hawaiian Islands (Givinish et al., 1995; Baldwinand Sanderson, 1998, respectively), and Robinsonia on the JuanFernandez Islands (Sang et al., 1995). For more reliable evolutionarymodelling of extinction processes greater resolution and integra-tion of fossil data is required.

Outside of human intervention, plausible ecological mecha-nisms for plant extinctions on oceanic islands include competingspecies interactions, abrupt climatic events, climate change, andchanging island insularity associated with geological activity andfluctuating sea-levels. Palaeoecological data, particularly fromrecent epochs, have in part established the chronological contextfor these processes by recording ecological trends both before andafter human colonisation. Fine-scale vegetation changes can bemeasured from fossil proxies (e.g. microfossil and macrobotanicalanalyses) and then used to infer conditions under which certainplant taxa have declined. Similarly, palaeoclimatic patterns can beinferred from a number of fossil, chemical and sedimentary proxiesfrom the same archives. However, demonstrating the timing ofplant extinction is difficult given that fossil evidence can onlyprovide a chronological estimation.

Defining the cause of extinction requires long fossil records thatbegin before a population started to decline and extend until itsextinction or functional extinction (James and Price, 2008). Thus, inorder to demonstrate human driven extinctions, fossil records arerequired that exceed the age of initial human colonisation. Incontexts like Australia this is complicated by the lack of fossilrecords that even encompass the 40 000–60 000 years of humancolonisation. By contrast, there is an abundance of fossil recordsfrom oceanic Pacific islands that exceed the late Holocene humancolonisation, thus allowing an assessment of the chronology ofplant extinction.

Palaeoecological records from oceanic islands have also playeda key role in the debate on the extent of human impact on previ-ously unoccupied ecosystems (Burney, 1997; Athens et al., 2002;Prebble and Wilmshurst, in press). On a number of oceanic islandsthe same sedimentary archives that have been used for mappingfine-scale vegetation change have also provided indications ofinitial human colonisation and in some cases the introduction ofagricultural practices have been detected through the identificationof pollen from introduced cultigens and invasive weeds (Athens,1997; Parkes, 1997; Denham et al., 1999; Kennett et al., 2006;Prebble and Wilmshurst, in press). Fossil evidence for human-

Table 2Supra-generic groups of the Arecaceae with representative genera from the Pacific,east of New Guinea. (classification and nomenclature adapted from Asmussen et al.,2006; Pintaud and Baker, 2008).

(subtribe [-inae], tribe [-eae] or subfamily [-oideae])

CALAMOIDEAEMetroxylinae

Metroxylona

Calaminae

Calamusa, Retispatha, Daemonorops, Ceratolobus, PogonotiumNypoideae

NypaaCORYPHOIDEAELivistoninae

Livistonab, Licuala Pritchardiopsis, Johannesteijsmannia, PholidocarpusCaryoteae

Caryota, Arengab, Wallichia

CEROXYLOIDEAECeroxyleae

Juaniaa,c, Oraniopsis, Ceroxylon, Ravenea

ARECOIDEAEPelagodoxeae

Pelagodoxab, SommieriaArchontophoenicinae

Actinokentia, Chambeyronia, Kentiopsis, Actinorhytis, Archontophoenix,Arecinae

Arecab,d, Pinangaa(only some species), NengaBasseliniinae

Cyphosperma, Lepidorhacchis, Physokentia, Basselinia, Burretiokentia,CyphophoenixCarpoxylinae

Carpoxylon, Neoveitchia, Satakentia,Clinospermatinae

Clinosperma, CyphokentiaLinospadicinae

Howeac, Calyptrocalyx, Linospadix, LaccospadixPtychospermatinae

Balaka, Drymophloeus, Solfia, Veitchia, Adonidia, Brassiophoenix, Carpen-taria, Normanbya, Ponapea, Ptychococcus, Ptychosperma, Wodyetia,Rhopalostylidinae

Hedyscepeb, Rhopalostylisc

Non-aligned ARECOIDEAE genera

ClinostigmaCocosa,d (known to be indigenous on some islands)

CyrtostachysHeterospatheHydriasteleRhopaloblaste

Non-aligned CORYPHOIDEAE generaPritchardiaa,c

Taxa listed in bold have been identified or tentatively identified from fossil recordsfrom oceanic islands in the Pacific. Genera in italics are not represented on theoceanic Pacific islands, underlined genera are restricted to New Caledonia.

a Possess diagnostic pollen types.b Possess pollen types with morphologies that overlap with many tribes and

subtribes.c Possess pollen types with diagnostic value only in that they represent a single

palm type within the family or a subfamily located on only one island.d Genus or representatives of genus was introduced to oceanic Pacific islands soon

after initial human colonisation.

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2549

caused plant extinctions has been identified from discrete sedi-mentary deposits found in limestone caves or archaeologicaldeposits, for example, the palm endocarps from Rapanui (Drans-field et al., 1984). Such deposits are generally allochthonous, asplant materials have been introduced by mechanisms other than

natural plant dispersal routes. These sites can provide valuableinformation on the possible cause of extinction including directexploitation by humans or by their commensal herbivores (e.g.rodents), but provide limited information on other human activitiesinvolved in the extinction process such as fire or land clearance.

The advantage of many palaeoecological records for mappingextinction events, particularly palynological records from sedi-mentary swamp contexts, is that they are mostly hypo-autochthonous whereby the original context and spatialrelationship of plants, extinct or extant, are preserved. This is espe-cially the case in tropical environments where most plants producepropagules including pollen and seeds that are locally dispersed byanimals (mainly invertebrates) and are not dispersed large distancesby wind (Bush and Rivera, 1998). The local representation of plantfossil assemblages in sedimentary deposits combined with otherindicators of disturbance (e.g. charcoal particles), anthropogenic orotherwise, provides greater definition of the ecological processesinvolved in plant extinction. From the same palynological records,the timing and localised extent of human impact can be measuredagainst a sufficiently long baseline before human colonisation todemonstrate the prevailing ecological trends (i.e. the response ofvegetation or individual plant taxa to climate change).

2.4. Plant extinctions on oceanic Pacific islands

The extinction bias towards large-bodied animals on oceanicislands has been well documented (Steadman, 2006) as it has oncontinents, but what of large-bodied plants (trees) with lowreproductive rates? Trees form a large proportion of island biomassand biodiversity, but compared to faunal extinctions relatively fewfloral ones have been recorded. For example, only 3 out of >2000vascular plants have become extinct on New Zealand, but none ofthese are trees (Sax et al., 2002). Is this trend different for oceanicislands?

Miocene fossil records from the sub-Antarctic oceanic islandspoint to numerous pre-Quaternary tree extinctions followingOligocene–Miocene cooling, including fossil palms (Couper, 1960).Miocene–Pliocene plant fossil data are currently available fromonly a limited number of lignite and other fossil bearing depositsfrom tropical oceanic Pacific islands including Palau (FederatedStates of Micronesia), the Marshall Islands and Rapa (French Poly-nesia). Pliocene or older lignites have been identified from otheroceanic islands (e.g. Cemetery Bay, Norfolk Island, Macphail andNeale, 1996), but have yet to be examined for plant fossil bearingpotential. The most fossil rich record comes from Eniwetok Atoll(Leopold, 1969) in the Marshall Islands (Federated States ofMicronesia). Drilling revealed w1200 m of carbonate sedimentscomposed of coral and lagoon sediments overlying a volcanic base.One Miocene pollen unit was identified yielding 17 extant angio-sperm genera. With the exception of the common tropical strandtrees Pandanus (Pandanaceae), Pisonia (Nyctaginaceae), Argusiasyn. Tournefortia and Cordia (Boraginaceae), all genera includingpalms represented by a Livistona type palm pollen (Leopold, 1969,plate 305) were probably extirpated during Quaternary sea-levelmaxima or in earlier periods. Six of the extant genera identified onEniwetok are common in the tropical Pacific and still inhabit theSouthern Marshall Islands; including Sonneratia (Sonneratiaceae),Rhizophora and Bruguiera (Rhizophoraceae), Lumnitzera (Com-bretaceae), Morinda and Randia (Rubiaceae) and a further five arefound in Western and Central Micronesia, but not in EasternMicronesia, Ceriops (Rhizophoraceae), Terminalia (Combretaceae),Avicennia (Verbenaceae). Extant Livistona species occur on theadjacent archipelagos of Ogasawara (Japan), the Philippines and theSolomon Islands.

Fossil evidence of Pleistocene plant extinctions from oceanicislands is lacking. Fossil deposits of Widdringtonioxylon antarcticum

Norfolk Raoul

Tawhiti Rahi

RapanuiRapa

TubuaiRimatara

TahitiMo’orea

Tinian

LordHowe

FIJI

PAPUANEW GUINEA

AUSTRALIA

HAWAIIANISLANDS

160°160°140°E 140°

ECUADOR

COLOMBIA

MEXICO

UNITED STATES of AMERICA

PERU

SAMOA

PHILIPPINES

TAIWAN

JAPANCHINA

TONGA

180°120° 120° 100°W 80°

20°

0°

20°

40°

NEW CALEDONIA

NEWZEALAND

VANUATU

SOLOMONISLANDS

CHILE

ARECOIDEAEArecoideae extirpation/extinctionRhopalostylidinae extirpationRhopalostylis decline

Paschalococos disperta extinctionDecline/extinction of unknown palm

pollen

Howea decline

Fig. 1. Geographic distribution of the Arecoideae subfamily of the Arecaceae. Tribes, subtribes and genera within these subfamilies having Pacific oceanic islands representatives arelisted in Table 2. This figure does not incorporate the distribution of Cocos nucifera, also in the Arecoideae, as this remains unclear due to its domestication and translocation byhumans to many tropical islands. Oceanic islands with Holocene palaeoecological records showing a decline or extirpation of this subfamily are also indicated.

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–25672550

from Kerguelen, a sub-Antarctic island in the Indian Ocean, repre-sents the only Pleistocene record of a tree extinction from anoceanic island (Phillipe et al., 1998). A 2 m section of wood found ina glacial moraine suggests that this species survived throughout

PA PU A NE W GUINE A

A USTRALI A

HI

SAMOA

PHILIPPINES

TAIWA N

JAPAN CHIN A

TONG A

NEW CALEDONI A

NEW ZEALAND

Mangai a

A

Au

Minami Dait o

COOK IS

Laysan

A

Pritchardia Pritchardia extiCORYPHOIDEAE Liviston adeclin

140°E 120° 160°160° 180°

Fig. 2. Geographic distribution of the Coryphoideae subfamily of the Arecaceae. This subfam(see Table 2). Oceanic islands with Holocene palaeoecological records showing a decline ornaturalised Pritchardia.

glacial expansion and other major climatic changes. The extirpationand extinction of terrestrial biota on Pleistocene atolls and islandsmust have occurred many times following complete inundationduring the postglacial marine transgressions. Estimates of

AWAIIA N SLAND S

Society Is

ECUADO R

COLOMBI A

MEXICO

UNITED STATES of AMERICA

PERU

Galapagos Is

20°

0°

20 °

40°

Rimatar a Tubuai

tiu

st ral A rc hi p el a g o

CHIL E

LAND S Tuam ot u A rc h ip e l ag o

F IJI VANUATU

SOLOMON ISLANDS

A rpation

e Naturalised Pritchardi a

140° 120° 100°W 80°

ily is only represented on Pacific oceanic islands by the genera Livistona and Pritchardiaextirpation of these genera are also indicated. Inset A shows the current distribution of

FIJI

PAPUANEW GUINEA

AUSTRALIA

HAWAIIANISLANDS

160°160°140°E 140°

ECUADOR

COLOMBIA

MEXICO

UNITED STATES of AMERICA

PERU

SAMOA

PHILIPPINES

TAIWAN

JAPANCHINA

TONGA

Juan Fernandez Is

180°120° 120° 100°W 80°

20°

0°

40°

NEW CALEDONIA

NEWZEALAND

VANUATU

SOLOMONISLANDS

CHILE

CEROXYLOIDEAE

CALAMOIDEAEMetroxylon declineMetroxylon extirpation

CEROXYLOIDEAE decline

NYPOIDEAE20°

Fig. 3. Geographic distribution of the Calmoideae, Nypoideae and Ceroxyloideae subfamilies of the Arecaceae. Tribes, subtribes and genera within these subfamilies havingPacific oceanic islands representatives are listed in Table 2. Oceanic islands with Holocene palaeoecological records showing a decline or extirpation of these subfamilies are alsoindicated.

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2551

interglacial and interstadial sea-levels are known for the latePleistocene Pacific from a series of dated uplifted-coral terraces inthe Huon Peninsula, Papua New Guinea (Chappell et al., 1996). Theclosest series of uplifted terraces in the oceanic Pacific islands thatprovide any indication of Pleistocene sea-level come from the FijianArchipelago (Nunn and Omura, 1999) and bathymetric mappingindicates substantial inundation of these islands during the latestmarine transgression (Gibbons and Clunie, 1986). A mid-Holocene(4000–6000 yr cal BP) sea-level rise of up to w2 m in the centralPacific (Dickinson, 2001) is known to have inundated atolls of theTuamotu Archipelago (French Polynesia; Pirazolli and Montaggioni,1986). However, fossil evidence for plant extinctions on atolls hasnot become available due to the lack of depositional settings thatretain terrestrial organic matter following marine inundation. Onecharacteristic of oceanic island floras as opposed to other organ-isms is that they are extremely vagile and can rapidly colonise new

Table 3A comparison of palm diversity based on the numbers of genera and species globallyand for the Pacific islands inclusive of oceanic and continental fragments.

Globalgenerac

Globalspeciesc

Ratiod Pacificgenerac

Pacificspeciesc

Ratiod

Calamoideae 21 620 39.5 2 9 4.5Nypoideaea 1 1 1 1 1 1Coryphoideae 46 455 10 5 35 7Ceroxyloideaeb 8 42 5 1 1 1Arecoideae 108 1250 11.6 32 121 3.8

a The Nypoideae is monogeneric and monotypic.b The Ceroxyloideae has only a single genus and species in the oceanic Pacific

islands.c Numbers of genera and species may vary according to taxonomic acceptance

and classification systems.d Ratio is the average number of species in genera within each subfamily, and may

be interpreted as a broad measure of speciation levels.

landforms and rapidly re-colonise frequently disturbed environ-ments (Carlquist, 1996). Plant endemism is very low on atolls, thusthe gradual inundation by rising sea-levels would at most extirpateplants indigenous to tropical coasts.

Radiometric dating of volcanic deposits on Raoul, in the Ker-madec Group (New Zealand) has revealed that the island wasperiodically buried by large volumes of ejecta throughout the latePleistocene and Holocene (Worthington et al., 1999). The DenhamBay caldera erupted w2200 yr cal BP and the ejecta volume wascomparable in magnitude to the 1883 Krakatau eruption. Thiseruption must have resulted in total biological sterilisation of theisland, even of buried plant propagules. Large trees on Raoul (Sykes,1977) have colonised and in most cases re-colonised the islandsince this eruption including: Pseudopanax arboreus (Araliaceae),Rhopalostylis baueri (Arecaceae), Corynocarpus laevigatus (Cor-ynocarpaceae), Aristotelia cf. serrata (Elaeocarpaceae), Homalanthuspolyandrus (Euphorbiaceae), Pisonia umbellifera (Nyctaginaceae),Pittosporum crassifolium (Pittosporaceae), Melicope ternata (Ruta-ceae), Melicytus ramiflorus (Violaceae) and the endemic speciesMyrsine kermadecensis (Myrsinaceae) and Metrosideros kermade-censis (Myrtaceae). The seed source for most of these trees mayhave come from neighbouring islands in the Kermadec Group (115–160 km from Raoul), mainland New Zealand (950–1000 km fromRaoul) or in the case of R. baueri probably from Norfolk (Australia)w1370 km to the west.

By far the most robust evidence for plant extinction or extirpationon oceanic Pacific islands comes from Rapanui where both archae-obotanical and palaeoecological records support extinction events(Flenley et al.,1991; Orliac and Orliac, 1998; Hunt, 2007; Mann et al.,2008). These records demonstrate an association between thetiming of floral demise and human colonisation. At low taxonomiclevels, as exhibited in the faunal extinction record (Steadman, 2006),plant extinctions on Rapanui are concentrated in certain families

Table 4Palaeoecological records of Pritchardia decline and/or extinction from oceanic island sites in the Pacific (arranged according to latitude). A summarised palynological record ofMaunutu, listed in bold is presented in Fig. 5.

Site Island Decline orextirpation

Age for palm decline orextirpation (yr cal BP)/reference

Age of initial human colonisation(yr cal BP)/reference

Reference

Laysan Laysan, Hawaiian Islands,U.S.A.

extirpation <5000 and after 1822 AD 1822 AD/Rauzon, 2001 Athens et al., 2007

M�ah�a’ulep�uMakauwahia

Kaua’i, Hawaiian Islands Decline and/orextirpation;

<1200 1200/Burney et al., 2001 Burney et al., 2001

‘Uko’a O’ahu, Hawaiian Islands Extirpation ¼ 1200/Tuggleand Spriggs, 2000

Athens et al., 1992

Maunawili O’ahu, Hawaiian Islands Extirpation ¼ ¼ Athens and Ward, 1997Kawai Nui O’ahu, Hawaiian Islands Extirpation ¼ ¼ Hammatt et al., 1990Fort Shafter

FlatsO’ahu, Hawaiian Islands Extirpation ¼ ¼ Athens et al., 1992

Kapunahalab O’ahu, Hawaiian Islands Extirpation ¼ ¼ Athens and Ward, 1996Hamakua O’ahu, Hawaiian Islands Extirpation ¼ ¼ Athens and Ward, 1993Liliha O’ahu, Hawaiian Islands Extirpation ¼ ¼ Athens and Ward, 1995Kalaeloa (Ordy

Pond)O’ahu, Hawaiian Islands Extirpation ¼ ¼ Athens et al., 2002

�Ohi’apilo Moloka’i, HawaiianIslands

Decline ¼ 1000/Weisler et al.,2006

Denham et al., 1999

Temae Mo’orea, Society Islands,French Polynesia

Extirpation <1500 1200/Anderson andSinoto, 2002

Parkes, 1997

Te Roto Atiu, Cook Islands Extirpation <1500 1100/Kirch and Khan,2007

Parkes, 1997

Veitatei Mangaia, Cook Islands Extirpation <2500 ¼ Ellison, 1994Tamarua West Mangaia, Cook Islands Extirpation ¼ ¼ Ellison, 1994Maunutu

(Fig. 5)Rimatara, Austral Islands,French Polynesia

Extirpation <900 900/Prebble andWilmshurst, in press

Prebble and Wilmshurst, in press;Prebble and Porch, unpublished data

Mihiurac Tubuai, Austral Islands,French Polynesia

Extirpation <900? 900? Prebble and Porch, unpublished data;

a Fossil pollen and fruit identified.b Fossil pollen and palm root concretions identified.c Only fossil fruit identified; pollen yet to be examined ¼ As above.

Table 5Palynological records with signatures of human impact showing the decline and/or extinction of diagnostic palm pollen (excluding Pritchardia) from oceanic islands of thePacific. Summarised palynological records of the sites listed in bold are presented in this paper.

Taxa Site(s) Island Approximate age rangeencompassed in record(yr cal BP)

Approximate age forinitial palm decline(yr cal BP)

Decline orextinction

Reference

cf. Hedyscepe canterburyana(Rhopalostylidinae type)

KingstonCommon

Norfolk, Australia 5500 <1000a extirpationor extinction

Macphail et al., 2001

Howea spp. Old SettlementBeach Swamp

Lord Howe, Australia 250 <200 decline Dodson, 1982

Livistona cf. chinensis Minami Dait�olagoon

Minami Dait�o, Japan 7500 <1500 decline Kuroda, 1996

Metroxylon cf. amaricarum Yela Kosrae, FederatedStates of Micronesia

3500 <2000a extirpation Ward, 1988; Athens et al., 1996

Metroxylon cf. amaricarum Okat Kosrae, FederatedStates of Micronesia

3800 <2000a extirpation Athens et al., 1996

Metroxylon cf. amaricarum IARII Laguas Guam, MarianaIslands

9300 <3000a decline Athens and Ward, 2004

Metroxylon cf. vitiensis Vunimoli Viti Levu, Fiji 6000 <3000a decline Southern, 1986Metroxylon cf. vitiensis Bonotoa Viti Levu, Fiji 4300 <3000a decline Southern, 1986Metroxylon cf. vitiensis Sari Vanua Levu, Fiji 6000 <2500a decline G. Hope and J. Stevenson,

pers. comm..Paschalococos disperta Most lake

calderasRapanui, Chile 35 000 <2000a extinction e.g. Dransfield et al., 1984; Flenley

et al., 1991; Mann et al., 2008cf. Pinanga sp. (Arecoideae

type)Sari Viti Levu, Fiji 6000 <5000b extirpation

or extinctionG. Hope and J. Stevenson, pers.comm..

Rhopalostylis cf. baueri KingstonCommon

Norfolk, Australia 5500 <1000a decline Macphail et al., 2001

Rhopalostylis cf. baueri Denham Bay(Fig. 8)

Raoul, KermadecGroup, New Zealand

300 2200c/w300a decline Prebble and Wilmshurst,unpublished data

Rhopalostylis cf. sapida Tawhiti-rahi Poor Knight Islands,New Zealand

700 <300–200a,d extirpation J. Wilmshurst, pers. comm..

a Ages for palm decline, extinction or extirpation fall within the period of initial human colonisation of each island (see Anderson, 2002 for a summary of archaeological datafor initial colonisation of the Pacific Islands).

b Ages for cf. Pinanga (Arecoideae type) extirpation or extinction on Viti Levu precede initial human colonisation of the Fijian Archipelago.c Rhopalostylis was most likely extirpated from Raoul after the 2200 yr cal BP Denham Bay volcanic eruption, after which palms must have re-colonised the island prior to

300 yr cal BP.d Rhopalostylis seedlings have recently been found on Tawhiti Rahi regenerating from pigeon dispersed seed (West, 1999).

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–25672552

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2553

and genera. The extirpation of representatives of entire plant fami-lies on Rapanui is very high when considering that very few recordsof this nature exist on other oceanic Pacific islands. Aside fromRapanui and excluding palms, the extinction or extirpation of plantfamilies on oceanic islands (Table 1) has only been recorded on theremote islands of Rimatara (French Polynesia), Laysan (HawaiianIslands) and the Juan Fernandez Islands (Chile). Plant familyextinctions can be attributed to the Malesian floral attenuation fromthe west continental islands to the east oceanic islands which hasreduced large families and genera often to single representatives asis demonstrated by the tree flora of Raoul. Such a pattern could beenhanced by selective human exploitation of trees for fuel, timber orforest clearance by fire. The extinction of Santalaceae, for example,can be explained by the historical exploitation of sandalwood(Santalum spp.) for perfume wood (Wester, 1991). Whereas theextinction of Rubiaceae trees on Rapanui seems more surprisinggiven the high rate of diversification on islands that has resulted innumerous Hawaiian Island endemics adapted to different ecologicalconditions (e.g. Psychotria, Nepokroeff et al., 2003).

Preferential selection by invasive alien herbivores and seedpredators of trees with edible fruits or seeds must also have influ-enced these extinction patterns as has been proposed for theHawaiian Islands and Rapanui (Athens et al., 2002; Hunt, 2007). Forthe Hawaiian Islands, the suggestion of rat-induced plant extinctionthrough seed and flower predation was made on the basis ofdeclines in a number of species detailed in palynological records,but without any supporting evidence from additional proxies.

3. Methods

3.1. Phytogeographic records

The Arecaceae has five recognised evolutionary lineages that aredesignated as subfamilies in the most recent phylogenetic classi-fication (Asmussen et al., 2006; Dransfield et al., 2008). Eachsubfamily has developed independently from a purported Creta-ceous origin for the family, with distinct morphologies,

Table 6Extant or extinct fossil palm pollen types found in palaeoecological deposits from the oceaet al. (2007). Micrographs of a number these fossil pollen types are presented in Fig. 4.

Genus Aperture Exine Numbers of extant oceanic isla

Cocos asymmetricmonosulcate, rarelytrichoto-monosulcate

intectate,thick (w7 mm)

1 (C. nucifera)

Hedyscepe asymmetricmonosulcate

finely scabrate 1 (H. canterburyana)

Howea asymmetricmonosulcate

finely scabrate 2 (H. belmoreana, H. forsteriana

Juania symmetricmonosulcate

rugulate, finelyrugulate-striate

1 (J. australis)

Metroxylon(notM. sagu)

disulcate reticulate 5 (M. amicarum, M. paulcoxii, MM. vitiense, M. warburgii)

Nypa zonosulcate spinose-tectate,spines with swollenbases

1 (N. fruticans)

Paschalococosa symmetricmonosulcate

finely rugulaterugulate

0 (P. disperta)

cf. Pinanga variable verrucate orgemmate

1 (P. insignis); probable extinctFiji. P. insignis Philippines to Ca

Pritchardia asymmetricmonosulcate,occasionallytrichotomosulcate

granular, areolate,fossulate orminutely reticulate

28 (23 from the Hawaiian IslanPacific Islands: P. thurstoni; P. pP. vuylstekeana P. pericularum,

Rhopalostylis asymmetricmonosulcate

finely reticulate toclavate

2 (R. baueri, R. sapida)

a Endocarps, wood charcoal and phytoliths have also been described (e.g. Dransfield etOrliac, in press).

reproductive habits, dispersal patterns, and ecological and envi-ronmental parameters (Dransfield et al., 2008). Palms are primarilyconfined to equatorial and tropical regions with increasing speciesdiversity in areas of high humidity, high rainfall and fertile soils(Svenning et al., 2008). However, palms were once geographicallymore widespread than at the present, and fossils have been foundin most regions of the world (Harley 2006). All the five subfamilies(Calamoideae, Nypoideae, Coryphoideae, Ceroxyloideae and Are-coideae) have representatives in the oceanic Pacific islands (seeTable 2). Based on recent accounts of the Pacific palm floras (Doweand Cabalion, 1996; Doyle and Fuller, 1998; Hodel and Pintaud,1998; Dowe, 2002; Dowe and Chapin, 2006; Hodel, 2007; Trenelet al., 2007; Pintaud and Baker, 2008), we established the distri-bution ranges for the systematic groupings of the palm subfamilies(Figs. 1–3) providing a biogeographic outline for interpretingpalaeoecological records of palm decline, extinction or extirpation(Table 3).

3.2. Palaeoecological records

We review the palaeoecological studies carried out on a varietyof late Quaternary sedimentary deposits from the oceanic Pacificislands with palm fossils represented and contribute summaries ofpreviously unpublished results. Most records are published or areavailable from the Indo-Pacific Pollen Database held at TheAustralian National University (Hope et al., 1999). Most records areof Holocene age and are derived from a variety of swamp depositswith rich organic sediments. As the fossil record of Pritchardia hasbeen examined by a number of authors (Athens et al., 2002;Hunt, 2007) we briefly summarise the available Holocene recordsfor this genus (Table 4). We also examine palynological recordsfrom oceanic Pacific islands that reveal palm pollen types whichshow either palm decline (Table 5) or no apparent decline(Table 6).

In an attempt to explain palm decline or lack of palm decline inresponse to human impact on oceanic Pacific islands, we presentfive swamp records preserving palm pollen, which reveal aspects of

nic islands of the Pacific. Morphological descriptions follow the terminology of Punt

nd species Oceanic island distribution Systematic reference

Tropical Pacific Thanikaimoni, 1970;Jagudilla-Bulalacao,1997

Lord Howe (Australia) Norfolk(Australia)

) Lord Howe (Australia) Harley and Baker, 2001

Juan Fernandez Islands (Chile) Harley, 1999, 2006,Dransfield et al., 2008

. salomonense, Republic of Palau/Federated Statesof Micronesia. Fiji, Samoa, oceanicSolomon Islands, Vanuatu

Harley, 1999, 2006,Dransfield et al., 2008

Oceanic Solomon Islands andMariana Islands

Harley, 1999, 2006,Dransfield et al., 2008

Extinct Dransfield et al., 1984

ion on Vanua Levu,roline Islands

Republic of Palau/FederatedStates of Micronesia

Ferguson et al., 1983;Harley, 2006

ds; 5 from otheracifica,

P. mitiaroana)

Hawaiian Islands; oceanic Fiji;Tonga, French Polynesia,Cook Islands

Selling, 1948;Dransfield and Ehrhart, 1995;Harley, 1999, 2006

Norfolk (Australia), Kermadecs,Poor Knights (New Zealand)

Cranwell, 1953

al., 1984; Cummings, 1998; Orliac, 2003; Horrocks and Wozniak, 2008; Delhon and

Table 7Palaeoecological records of the decline and/or extinction of palms (identified from monosulcate palm pollen) from the Pacific. Also includes the continental islands of Fiji.

Island Site Decline,extinction orextirpation

Age for initialpalm decline(yr cal BP)

Extant indigenous palm genera withmonosulcate pollen

Affinity for monosulcate palm pollentypes based on phytogeographicrelationships

Reference

Tinian, NorthernMarianas, U.S.A.

Hagoi Decline orextirpation

<4000 Cocos? Arecoideae (not Cocos), Athens and Ward,1998

Tahiti, Society Islands,French Polynesia

Vaihiria extirpation <1000 Cocos? Arecoideae, (not Cocos), Coryphoideae Parkes et al., 1992

Mo’orea, SocietyIslands, FrenchPolynesia

Temae extirpation <4500 Cocos? Arecoideae (not Cocos), Coryphoideae Parkes, 1997

Rapa, AustralArchipelago, FrenchPolynesia

Tukou(Fig. 5)

extinction orextirpation

<500 None Arecoideae (not Cocos) This paper

Rimatara, AustralArchipelago, FrenchPolynesia

Maunutu(Fig. 6)

extinction orextirpation

<500 Cocos? Arecoideae (not Cocos) Prebble andWilmshurst, inpress

Viti Levu, Fiji Voli Voli decline orextirpation

<5500 Balaka, Calamus, Cocos, Cyphosperma,Hydriastele, Neoveitchia, Physokentia,Veitchia

Arecoideae (not Cocos) Hope et al., 1999,G. Hope pers.comm.

Viti Levu, Fiji Bonotoa decline <3500 ¼ Arecoideae, Coryphoideae Southern, 1986;Hope et al., 1999

Viti Levu, Fiji Vunimoli decline orextirpation

<3500 ¼ Arecoideae, Coryphoideae Southern, 1986

Viti Levu, Fiji Tagamaucia decline orextirpation

<7000 ¼ Arecoideae, Coryphoideae Southern, 1986;Hope et al., 1999

Norfolk, Australia KingstonCommon

extirpation orextinction

<800 Rhopalostylis Arecoideae (not Cocos) Macphail et al.,2001

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–25672554

palm decline, extirpation or extinction that occurred prior toEuropean arrival. In most of the palynological studies presented,indirect signals of human arrival include increased concentrationsof charcoal particles and associated vegetation changes. The chro-nologies of initial human colonisation established for the oceanicislands examined rely on archaeological data in combination withpalynological changes indicating human impact. We presentrecords with both pre-human colonisation and human impactcontexts and show how a range of proxies provide a reliable meansof highlighting background ecological change and the downstreamecological consequences of human colonisation including palmdecline and extinction.

In the palynological records presented, sediment cores weregenerally sampled at regular intervals and processed for paly-nomorphs using standard procedures as described by Mooreet al. (1991). We have chosen to present records where allsamples have been spiked in the initial processing step withexotic Lycopodium spores to allow palynomorph and charcoalparticle concentrations to be calculated. The concentrations ofArecaceae type pollen, and key indicator taxa (e.g. exotic anddisturbance taxa) were obtained by counting pollen and sporesas a ratio of the added exotic Lycopodium spores (Stockmarr,1971). In most cases the concentrations of microscopic charcoalfragments were obtained by counting as a ratio of the addedexotic Lycopodium spores (per cm3). Other methods includecounting charcoal fragments as a proportion of the total particle

Table 8Islands with palaeoecological records used in the present study indicating their isolation

Location Nearest continentallandmass/distance (km)

Nearest large oceanic isladistance (km)

Rapa, Austral Archipelago,French Polynesia

New Zealand/3600 Raivavae/520

Rimatara, Austral Archipelago,French Polynesia

New Zealand/3200 Rurutu/150

Viti Levu, Fiji New Caledonia/1150 Vanua Levu/60Vanua Levu, Fiji New Caledonia/1150 Viti Levu/60Robinson Crusoe, Juan

Fernandez Islands, ChileSouth America/520 Alexander Selkirk/180

Raoul, Kermadec Group, NewZealand

New Zealand/950 Macauley, Kermadec GroNew Zealand/120

sum or counting the aerial coverage of fragments on a preparedmicroscope slide.

For each of the studies presented, radiocarbon dates were cali-brated using the program CALIB Version 5.0 (Stuiver et al., 2005)and are presented in Table 5. The main sedimentary characteristicsof each record are described in Table 6. The percentages of the mainvegetation types (trees and shrubs, herbs, ferns and fern allies) andthe concentrations of Arecaceae pollen types, key indicator taxa,charcoal particles and total palynomorphs were placed intostratigraphic diagrams for comparison using the program C2 DataAnalysis Version 1.4 (Juggins, 2005). The stratigraphy of each recordpresented is divided into three zones (pre-human, initial humanimpact and recent human impact where applicable), defined onthe basis of the main vegetation signals, charcoal particle concen-trations, and the presence of exotic taxa introduced first at initialhuman colonisation, and later by Europeans.

3.3. Historical data

We also review the palaeoecological studies carried out on veryrecent sediments which document the decline of palms afterEuropean colonisation of a number of islands. We focus on twoislands (Raoul, Kermadec Group, New Zealand) and RobinsonCrusoe (Juan Fernandez Islands, Chile) which show sharp responsesto human impact. These records have been retrieved from the Indo-Pacific Pollen Database and previously unpublished datasets.

and timing of initial colonisation. Also includes the continental islands of Fiji.

nd/ Island area(km2)

Maximum elevation abovesea-level (m)

Age of initial human colonisation(yr cal BP)/reference

38 650 750/Kennett et al., 2006

8 80 850/Prebble and Wilmshurst, inpress

10 400 1300 3000/Nunn, 20075600 1000 3000/Nunn, 2007

93 920 After 1574 AD/Woodward, 1969

up, 30 520 600/Anderson, 2001

Fig. 4. Micrographs A and B: Arecoideae type pollen from Core 6 160 cm, TukouSwamp, Rapa, French Polynesia. C and D: Arecoideae type pollen from Core 1 Transect2 185 cm, Maunutu Swamp, Rimatara, French Polynesia. E and F: cf. Meryta (Araliaceae)type pollen from Core 1 T2 205 cm, Maunutu Swamp, Rimatara, French Polynesia. Gand H: cf. Pinanga (Arecoideae) type pollen from Core 1 410 cm, Sari Swamp, VanuaLevu, Fiji. I and J: Rhopalostylis type pollen from Core X06/8 35 cm, Denham Bay, Raoul,Kermadec Group, New Zealand. K: D-section core showing holding fossil Pritchardiafruit from Mihiura Swamp, Tubuai, French Polynesia. L: Fossil Pritchardia fruits MihiuraSwamp Core 2 (350 cm), Tubuai, French Polynesia.

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2555

Presentation of these records follows that described above.Evidence for palm decline on the oceanic Pacific islands sinceEuropean colonisation of islands is also obtained from historicalbotanical survey data. These surveys not only record the decline ofpalms but often identify the ecological mechanism for decline,usually resulting from a range of human impacts.

3.4. Taxonomic and phytogeographic affinity of the fossilpollen types

The morphology of the fossil palm pollen is described followingthe classification of Harley (1999, 2006) and Dransfield et al. (2008)who have summarised the distribution of palm pollen characters,emphasising the diagnostic value of aperture and exine structurefor distinguishing genera and in some cases species. Morphologicaldescriptions follow the terminology of Punt et al. (2007). Basedon the morphological descriptions of each diagnostic fossil type(Table 7) or unknown palm types (Table 8), taxonomic and phyto-geographic affinities for fossil types from each palynological recordare proposed.

4. Results and discussion

4.1. Oceanic Pacific island palm phytogeography

Palms on oceanic Pacific islands follow the general trends ofhabitat preferences as do those in nearby areas such as Malesia andSoutheast Asia, being found mostly in mesic terrestrial environ-ments in complex rainforest associations. Table 3 providesa comparison of global diversity of palms, with those occurring onthe oceanic Pacific islands. Overall, there is less diversity withregard to genera and the numbers of species in genera than forpalms globally. The most diverse and widespread subfamily is theArecoideae which has representatives in most archipelagic groupsfrom the Solomon Islands, south to New Zealand, and east to FrenchPolynesia (Fig. 1). A confounding factor is that the relatively lowratio of species to genera (i.e. levels of anticipated speciation) in theArecoideae in the oceanic Pacific islands is related to the presenceof monotypic or small genera in the area.

The second most diverse subfamily is the Coryphoideae (Fig. 2),which has widespread distribution from the Solomon Islandsthrough Vanuatu, New Caledonia, Fiji to French Polynesia andHawaii, but not to the islands to the south of New Caledonia, nor tothe east of French Polynesia. Apart from the monotypic Pritch-ardiopsis on New Caledonia, the Coryphoideae in the westernoceanic Pacific islands is represented by a few outlier species in thespecies rich genera of Licuala and Livistona, genera that have theirgreatest diversity to the west in Malesia and Australia. Conversely,the genus Pritchardia, with 26 species, is an example of a genus withhigh levels of speciation and island endemism. Pritchardia is mostdiverse on the Hawaiian Islands with 24 species, most of which areendemic to single islands in that archipelago and known by smallpopulations. Otherwise, the genus has three widespread outlierspecies occurring in Fiji and Tonga (P. thurstonii), the Cook Islandsand French Polynesia (P. mitiaroana), and known only fromunequivocally wild populations (P. pritchardia) but otherwisewidespread as an adventive and cultivated plant in the oceanicPacific islands (Hodel, 2007).

The third most diverse subfamily is the Calamoideae (Fig. 3)which is represented by two genera, of which Calamus is mostdiverse in Malesia and southeast Asia (with about 360 species) andextends to Fiji in the Pacific (with a single widespread species). Thesecond genus, Metroxylon (7 spp.), has its greatest diversity in thewestern oceanic Pacific islands from Solomon Islands east to Samoaand north to Micronesia (with 6 spp. endemic to the oceanicislands), and with one species shared with Malesia to the west. The

Table 9Palaeoecological sites used in the present study and radiocarbon data with calendar ages of previously uncalibrated records. Radiocarbon ages were calibrated with Calib(Stuiver et al., 2005) using the SHCAL04 Southern Hemisphere (McCormac et al., 2004) calibration dataset.

Figure Location Site; reference Lab code Depth (cm) 14C age BP 1s Method Calibrated age range 2s BP

Fig. 5 Rapa, Austral Archipelago, French Polynesia Tukou C6; Prebble, unpublished OZH282 120–122 840 70 AMS 569–904UCIG6015 210–212 2190 140 AMS 1738–2465UCIG6014 210–212 2465 30 AMS 2346–2697

Fig. 6 Rimatara, Austral Archipelago, French Polynesia Maunutu C1T2; Prebble andWilmshurst, in press

WK17008 75–77 500 35 AMS 470–544WK17009 105–107 918 32 AMS 722–905WK22538 125–127 930 35 AMS 728–907WK22539 275–277 1941 35 AMS 1717–1920

Fig. 7 Robinson Crusoe, Juan Fernandez Islands, Chile La Pina JFRC-PI; Haberle,unpublished data

OZF279 44–45 555 30 AMS 505–553OZF280 90–95 1410 40 AMS 1179–1343

Fig. 8 Raoul, Kermadec Group, New Zealand Denham Bay X06/8; Wilmshurstand Prebble, unpublished data

WK21624 33 101 30 AMS 0–253WK21625 37 146 30 AMS 0–269

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oceanic Pacific distribution of the monogeneric and monotypicNypoideae and the Ceroxyloideae (Fig. 3) is anomalous as they areonly represented by Nypa fruticans (restricted to the Marianas andKosrae, Federated States of Micronesia), and Juania australis(restricted to Robinson Crusoe of the Juan Fernandez Islands, Chile),respectively.

The predominant phylogenetic relationships of oceanic Pacificislands palms are with taxa in New Guinea and Malesia, and toa lesser extent Australia, North America and South America. Rela-tionships with Australian palms lie primarily in the landmasses ofGondwanan origin, such as New Caledonia and New Zealand, andthere is otherwise a biogeographic disjunction between Australia/New Caledonia/New Zealand, and the oceanic Pacific islandsarchipelagos to the north and east. There is also a disjunctionbetween French Polynesia, which is the eastern limit of Malesian-centred diversity attenuation and the oceanic Pacific islands that lieclose to South America: namely J. australis on Robinson Crusoe, JuanFernandez Islands, Chile, which has its closest affinity with taxafrom South America.

4.2. Pre-Quaternary fossil records of oceanic Pacific island palms

The fossil record of palms is rich and widespread and has beensummarised by Harley (2006). Palm floras originated in wet-trop-ical regions as early as the mid-Cretaceous. This tropical affinity hasmeant that fossil records of palms have been used as an importantindicator of changing past climatic conditions, particularly for theOligocene–Miocene cooling (Morley, 2000). These records alsoshow that the palm flora of the African continent and Indian sub-continent was considerably more diverse than at present (Harleyand Morley, 1995; Pan et al., 2006; Harley, 2006).

The earliest palm fossils in Australia have been dated to the earlyPalaeocene, and with other significant records from the earlyEocene and late Oligocene (Greenwood and Conran, 2000),although putative palm pollen types have been found almostcontinuously across all stratigraphic ages. Most Australian palmfossils have not been assigned to extant taxa. Those that have beenassigned identities include macrofossils and fossil pollen of Nypa

Table 10Palaeoecological records from the islands used in the present study. Presented is a summ

Figure Site Elevation abovesea-level (m)

Type of deposit Depth osurface

Fig. 5 Tukou C6 0–3 Estuarine backswampformed behind an alluvial delta

0–240

Fig. 6 MaunutuC1T2

2–4 Moat-swamp behindraised limestone shelf

0–750 (

Fig. 7 La PinaJFRC-PI

650 Forest hollow 0–150

Fig. 8 Denham BayX06/8;

3–5 Backswamp formed behindvolcanic beach sands

45

(as Nipa and Spinizonocolpites) found in Eocene deposits froma number of locations in Australia (Pole and Macphail, 1996).A specimen from Pliocene deposits in New Zealand has beenassigned to the genus Cocos (C. zeylandica) because of the distinc-tive and characteristic three pores in the endocarp (Berry, 1926;Couper, 1952). Other fossil pollen types including Arecipites (alsoArecipites cf. Rhopalostylis sapida), Palmidites and Dicolpopollis(Metroxylon affinity) appear in Australia and New Zealand after theUpper Eocene (Raine et al., 2008). These records indicate that manypalms probably arrived in New Zealand after the break-up ofGondwana and were available for dispersal before the emergenceof the main oceanic archipelagos in the Pacific.

Fossil records of palms from oceanic islands of the Indian Oceanexist for the drowned Tertiary islands of Ninetyeast Ridge includingArecipites and Spinizonocolpites (Kemp and Harris, 1975), and for thesub-Antarctic island, Kerguelen described as Monosulcipollenitesminimus Levet-Carette (Harley, 2006). However, considering thatthe first oceanic islands in the Pacific, outside of Gondwana,emerged in the Eocene, fossil records fail to indicate the timing orposition of the initial appearance of palms on the oceanic islands.Fossil palm pollen has been recorded from Miocene (Entewok;Leopold, 1969) and Pliocene (Rapa; Cranwell, 1964) deposits. Giventhat most oceanic islands are in the West Pacific and are of lateMiocene to Pliocene (10–1.8 ma) age, from the configuration ofislands it can be assumed that the direction of plant dispersalshould follow a west to east direction (Carlquist, 1996). Very fewMiocene deposits have been described from oceanic Pacific islands.The drill cores from Eniwetok Atoll (Leopold, 1969), describedabove, reveal Livistona type palm pollen.

One of the few Pliocene deposits of value for fossil palmresearch is a shallow lignite seam located at Arahu at the north-east head of Ha’urei Harbour on Rapa at around 200 m in eleva-tion. This represents one of only two lignite deposits in the oceanicisland Pacific, the other located at Babeldaob in Palau (FederatedStates of Micronesia). The Arahu deposit, like at Babeldaob, formedprior to the erosional dissection of a former lake caldera that nowforms the harbour on the southeast side of the island. Cranwell(1964) examined some of the Arahu lignite collected in 1934 for its

ary of the main sedimentary characteristics of each record.

f record below(cm)

Pre-human sediments Initial human impactsediments

Pandanus leaf and wood peat overlyingestuarine sands and silts

Organic silts and clays

250 presented) Pandanus and Acrostichum leaf peat Organic silts

Juania leaf peat Organic clays

Organic clays and silts with fineorganic lenses

Organic silts and clays

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M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2557

palynological potential identifying some ‘palmoid’ grains, indica-tive of an island-based extinction of the Arecaceae, given thecurrent lack of any indigenous palms on Rapa. Prebble (in press)undertook further examination of the Arahu lignite seam, butfailed to locate any Arecaceae type pollen. Taccaceae pollen wasidentified which has a distinct sulcus with even margins, verysimilar to many palm pollen grains, including Pritchardia (Selling,1948). Also identified were high proportions of sedges (Cyper-aceae), Zingiberaceae, Myrtaceae, Piperaceae, Sapindaceae, andRubiaceae of a type comparable to the endemic Coprosma rapensis.Cranwell (1964) also identified a few grains of the gymnospermgenus Dacrydium (not of the New Zealand species D. cupressinum),which she considered to be a contaminant. This could also havebeen derived from a wind blown dispersal during the late Miocenefollowing the pacific expansion of Dacrydium into areas such asNew Zealand (Pole, 2001) and potentially the islands of Fiji (M.Macphail, pers. comm.).

4.3. Late Pleistocene fossil records of oceanic Pacific island palms

Late Pleistocene fossil palm representation on the oceanicPacific islands is limited by the number of available terrestrialorganic sedimentary deposits. The main Pleistocene depositsrecording palms are from the Hawaiian Islands and Rapanui wherelarge lake calderas preserve organic sediments. From the HawaiianIslands, fossil palm (cf. Pritchardia) stems found near sea-level atAliapa’a Kai salt lake on O’ahu date from 100 000 yr BP (Lyon, 1930)indicate that palms were abundant on the islands during thePleistocene (Carlquist, 1980; Cuddihy and Stone, 1990; Athens,1997). From the palynological record of Ka’au Crater, O’ahu, (460 mabove sea-level), Hotchkiss and Juvik (1999) show that Pritchardiapalms were locally abundant around 35 000 yr cal BP but declinedduring the Last Glacial Maximum (LGM). Pritchardia respondedquickly to rising precipitation levels and temperature after the LGMwith the highest palm pollen representation recorded throughoutthe Lateglacial. Palm pollen decreased in the early Holocene asother wet forest taxa including Metrosideros (Myrtaceae) increasedin abundance.

A number of Pleistocene palynological records from the calderalakes of Rapanui show large proportions of palm pollen repre-senting the extinct P. disperta (Dransfield et al., 1984; Flenley et al.,1991). From Rano Aroi and Rano Raraku, Flenley et al. (1991)suggest that palm pollen by nature of their affinity to subtropicaland tropical climates indicate warmer conditions. Palm pollen isdominant in sediments radiocarbon dated to 32 000–35 000 yr cal BP but declined during the LGM where in somesections pollen is poorly preserved. The late Pleistocene sequencesfrom Aroi and Rano Raraku vary but palm pollen generallyincreases by the end of the Lateglacial.

Macrofossil evidence of Rhopalostylis is recorded from theHutchison formation on Raoul in the Kermadec Group, New Zea-land (Eagle, 2001) dating to less than 100 ka based on Uranium/Thorium ages of lavas underlying the deposit (Worthington et al.,1999). A series of large scale volcanic deposits including andesiteand pyroclastic flows have been recorded on Raoul, the oldestdating to 1.4 ma and the most recent at 2200 yr cal BP (Wor-thington et al., 1999). Most of these eruptions must have resulted intotal biological sterilisation of the island including Rhopalostyliswhich may have re-colonised the island several times in thePleistocene and Holocene.

4.4. Holocene fossil records of oceanic Pacific island palms

Declines and/or extirpations of nine taxa recognisable fromdistinctive fossil palm types have been recorded from upward of40 sedimentary deposits located on 19 different oceanic islands

Depth (cm)

Anal

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(Tables 4 and 5). Of these records 18 deposits from nine islandsshow a decline or extirpation of the genus Pritchardia (Table 4).Palm extirpations are recorded on 11 islands, although some ofthese records may represent species extinctions. Rapanui is theonly island with fossil deposits recording a palm speciesextinction, of the genus Paschalococos, which was described asa distinct taxon based on the differences of subfossil endocarpsto similar species (Dransfield et al., 1984; Zizka, 1991). Descrip-tions of the designated pollen types are given in Table 6 withmicrographs of the main types presented in Fig. 4. A further 10pollen records from seven islands reveal the decline, extirpationor extinction of palms, which can only be designated as Areca-ceae pollen and at best described to subfamily (Table 7).Considerably more systematic observations of both micro- andmacrofossils are required in order to confirm any generic orspecies affinities.

Using Holocene palaeoecological records from five differentoceanic Pacific islands (Table 8) we present a range of palynologicaldata which are intended to represent palm extirpation or declineon human impacted sites utilising a range of reliable proxies forinitial human impact. The radiocarbon chronologies and generalcharacteristics of each sedimentary archive are described in Tables9 and 10, respectively. We attempt to show how palms haveresponded to ecological changes prior to human impact, primarilysea-level change. We firstly examine sites on small and remoteoceanic islands including Rapa and Rimatara in the Austral Archi-pelago (French Polynesia), which currently have no survivingindigenous palms.

4.4.1. Tukou Core 6, Rapa, Austral Archipelago, French PolynesiaTukou marsh (Fig. 5) lies on the south side of the broadest river

delta and associated estuarine mud flats of Ha’urei Harbour. Suchmarshes are typical of coastal embayments where organic sedi-ments have accumulated over inorganic silts and clays since sea-level stabilisation within the last 4000 yr cal BP. The marsh iscomprised of mostly exotic weed vegetation. Abandoned Colocasiaesculenta (Araceae) agricultural terrace features surround themarsh and lie 50 cm or more above the marsh surface. Tukou Core 6is positioned in the centre of the marsh records more than2500 yr cal BP of vegetation change. The pre-human zone between2500–800 yr cal BP is characterised at the base by the presence ofArecoideae pollen, Cyperaceae pollen and high proportions of fernspores indicative of an alluvial or estuarine coastline. By around1000–1500 yr cal BP a Pandanus (Pandanaceae) swamp forest hasdeveloped at the site. After around 800 yr cal BP, in the initialhuman impact zone, Pandanus pollen concentrations declinesteeply in response to increasing Poaceae and Cyperaceae pollen,charcoal particle concentrations and the initial appearance ofColocasia pollen after 800 yr cal BP. Arecoideae type pollen is notrepresented in this zone suggesting that either palm populationswere always very low or initial human impact was severe, causingrapid palm decline.

No indigenous palms survive on Rapa and there are nohistorical records of palms apart from the probable recentintroduction of C. nucifera (Arecoideae). The few coconut treesthat survive on Rapa do not set mature fruit presumably inresponse to the subtropical climate. In his ethnography of Rapa,Stokes (m.s.) recorded from informants in 1920 a local traditionreferring to Haari rohutu, a palm goddess represented by an idolfigure wrapped in palm fiber. Unfortunately, no traditions refer toa palm tree or its demise. The close association between theeventual absence of most coastal lowland forest taxa in the recenthuman impact zone and the first appearance of European weedssuggests coastal swamp forest including palm had long sincedisappeared by initial European colonisation in 1814 AD (Ellis,1831).

Table 11Examples of palaeoecological records from oceanic islands in the Pacific with signatures of human impact showing no apparent decline and/or extinction of palm pollen(monosulcate palm pollen excluding Cocos nucifera).

Island Sites Approximate age forinitial humancolonisation (yr cal BP)

Approximate age rangeencompassed in record(yr cal BP)

Extant indigenous palm generawith monosulcate pollen

Affinity for palmpollen types excludingC. nucifera

Reference

Yap, Federatedstates ofMicronesia

Fool 3500 3500 Clinostigma, Cocos?, Hydriastele,Ponopi

Arecoideae Dodson and Intoh,1999

Totoya, Fiji Dravawal, Jigojigo,Keteira, Lawakile,Udu, Yaro

3500 2200 Balaka, Cocos?, Veitchia Arecoideae, Coryphoideae Clark and Cole,1997; Clarke et al.,1999

Viti Levu, Fiji Voli Voli FV VOL 1 3500 6000 Balaka, Calamus, Cocos,Cyphosperma, Hydriastele,Neoveitchia, Physokentia, Veitchia

Arecoideae, Coryphoideae Hope et al., 1999;G. Hope pers.comm.

Viti Levu, Fiji Nadrala 3500 2200 ¼ Arecoideae, Coryphoideae Hope et al., 1999,G. Hope pers.comm..

Viti Levu, Fiji Nadrau 3500 2300 ¼ Arecoideae, Coryphoideae Southern, 1986;Hope et al., 1999

Vava’u, Tonga Avai’o’vuna 3000 4500 Cocos?, Pritchardia, Veitchia Arecoideae, Coryphoideae Fall, 2005Vava’u, Tonga Ngofe 3000 6000 Cocos?, Pritchardia, Veitchia Arecoideae, Coryphoideae P. Fall, pers. comm.

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2559

4.4.2. Maunutu, Rimatara, Austral Archipelago, French PolynesiaAccording to Dickinson (2001), Rimatara is one of six makatea

type islands of the Cook–Austral groups of islands that consist of anannular limestone plateau that surrounds a degraded volcanicbedrock core. A unique characteristic of makatea islands is theextensive sediment-filled and waterlogged depressions that extendout like a moat, between the inner rim of the annular limestone andthe base of the inland volcanic core. Most of these ‘moat deposits’are covered with swamp vegetation. Maunutu swamp on Rimataraprovides one example of a palaeoecological record from a moat-swamp similar to those examined on Mangaia (Ellison, 1994) andAtiu (Parkes, 1997), both makatea islands in the Cook Islands.Further descriptions of this record can be found in Prebble andWilmshurst (in press) (Fig. 6).

The 7.5 m C1T2 record (2.3 m shown in Fig. 6) shows morethan 3000 yr cal BP of palm decline and probable extirpation. Thepre-human zone, between 900–2000 yr cal BP, is dominated byPandanus pollen and Acrostichum (Pteridaceae) fern spores. Thehigh concentrations of Pandanus pollen indicate a swamp forestwith a fern understorey. The initial appearance of Colocasiapollen from the introduced horticultural crop, the decline ofPandanus pollen and high concentrations of charcoal particles inC1T2 after 800 yr cal BP indicate that the Pandanus swamp forestwas burnt-off in the processes of establishing Colocasia cultiva-tions along the most inland areas of Maunutu swamp. Additionaldisturbance indicators including Poaceae pollen and Dicranopteris(Gleicheniaceae) spores provide additional support for initialhuman impact on Rimatara. More recent human impacts areindicated by the presence of Commelina diffusa (Commelinaceae)a weed introduced after 1822 AD (Ellis, 1831), which now

Table 12Critically endangered oceanic Pacific island palms from the IUCN list 2007.

Taxa Island Numb

Carpoxylon macrospermum Aneityum, Tanna and Futuna, Vanuatu ?Pelagodoxa henryana Unknown UnresPritchardia affinis Hawai’i, Hawaiian Islands 60P. aylmer-robinsonii Nihoa, Hawaiian Islands 2P. hardyi Kaui’i, Hawaiian Islands 30P. kaalae O’ahu, Hawaiian Islands 150P. limahuliensis Kaui’i, Hawaiian Islands 100P. munroi Molokai, Hawaiian Islands 1 or 2P. napaliensis Kaui’i, Hawaiian Islands 90P. schattaueri Hawai’i, Hawaiian Islands 12P. viscosa Kaui’i, Hawaiian Islands 4

dominates the swamp vegetation along with other introducedweeds.

Like on Rapa, no indigenous palms survive on Rimatara andthere are no historical or ethnographic records of palms apartfrom the probable introduction of C. nucifera. Only one Arecoideaepollen type (Fig. 4 plates A and B), similar to that described fromRapa, is found in the pre-human sediments. Pollen from an extinctor extirpated cf. Meryta spp. (Araliaceae) was identified, repre-senting a family extinction on Rimatara. Very few low-pollenproducing taxa are identified in samples where extremely highconcentrations of Pandanus pollen and Acrostichum spores domi-nate the record. Three Arecaceae pollen types including a Pritch-ardia type, Arecoideae type (Fig. 4 plates C and D) and onedegraded palm type (similar to the Arecoideae type) within theinitial human impact zone and are recorded in high concentra-tions at around 750 yr cal BP. The later two types are not recordedin the recent human impact zone. The close association betweenthe decline of Pritchardia type palm pollen and the first appear-ance of European weeds suggests palm extinction took place soonafter European contact in 1822 AD. A number of plant species havedeclined since this time, probably as a result of direct browsing byEuropean stock animals (e.g. goats), including a Myoporum(Myoporaceae) recorded historically but not in the most recentbotanical surveys (Meyer et al., 2004; see Table 1.). C. nuciferapollen is only recorded in the recent human impact zone and isprobably a recent human introduction given the lack of diagnosticcoconut pollen from any pre-human sediments. We discount thehuman introduction of Pritchardia and other palms to the island,particularly given the pre-human record of Arecoideae typepollen.

ers in wild Main threats

habitat lossolved, may be no wild populations

habitat loss, invasive alien speciesnatural disastersinvasive alien speciesinvasive alien species, natural disastersinvasive alien species

? invasive alien speciesinvasive alien speciesinvasive alien speciesinvasive alien species, natural disasters

Table 13A selection of palm taxa (or close relatives) from oceanic Pacific islands showing recent population declines.

Species Island(s) Maximum height (m) Main cause of decline Reference

Rhopalostylis baueri Norfolk, Australia; Raoul, New Zealand >10 Feral animal browsing and habitatclearance

Green, 1994; Sykes, 1977

Juania australis Juan Fernandez Islands, Chile 15 Feral animal browsing and habitatclearance

Henderson et al., 1995; Sanders et al.,1982

Pritchardia spp. Hawaiian Islands 25 Feral animal browsing and habitatclearance

Chapin et al., 2004

Metroxylon vitiense Oceanic island Fiji 16 Agricultural development McClatchey et al., 2006Livistona chinensis Minami Daito, Japan >10 Urban and agricultural development Dowe, 2001

M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–25672560

4.5. Holocene records of Pritchardia decline and/or extirpation

In addition to the palm pollen sequence from Maunutu onRimatara, several records of Pritchardia decline have been ana-lysed from the Hawaiian Islands (see Athens, 1997; Athens et al.,2002; Burney et al., 2001; Hunt, 2007 for a summary), threerecords from the Cook Islands and one further macrofossil (fruit)record from Tubuai, also in the Austral Archipelago (Table 4). Asingle undated profile from Mihiura swamp on Tubuai revealedPritchardia type fruits (Fig. 4 plates K and L) at depths rangingfrom 3.2 to 3.8 m, probably from a pre-human sedimentarycontext. The widespread decline of Pritchardia species on theHawaiian Islands has also been documented in archaeobotanicalsequences and further evidence from both fruit and trunkmacrofossils indicates that Pritchardia was one of the mostabundant trees prior to human settlement on Kauai (Burneyet al., 2001) as it probably was on other Hawaiian islands (Athenset al., 2002). Palynological records from most islands in theHawaiian Archipelago have recorded declines of Pritchardia pollenfrom pre-human sediments in which palm pollen often comprisesup to half of the pollen within the palynological assemblages(Table 4; Fig. 2).

4.6. Holocene palynological records with no apparent declines inArecaceae palm pollen

A few palynological sites from oceanic Pacific islands (Table 11)show that despite strong signatures of human impact includingincreases in disturbance indicators such as Poaceae pollen andcharcoal particles, there is no apparent decline in Arecaceae pollen.Many palms may maintain population structure despite distur-bance events by a range of ecological and biological mechanisms.The primary reason for survival on larger and less remote islandsincluding Tonga will be the size of palm populations and theirwidespread distribution but also their level of dependence onextant animal seed dispersers and pollinators. Adaptation toa wide-range of soils’ substrates and hydrological regimes, havingnon-specialised seed dispersal or being resilient to fire may beother important factors in predicting palm survival (Vormisto et al.,2004).

Some palms may respond positively to human colonisationincluding C. nucifera. Although not discussed in this paper, macro-fossil remains of C. nucifera nuts, exceeding the age of initial humancolonisation, have been described from Aneityum in Vanuatu(Spriggs, 1984). Also several pollen records show that C. nuciferawas present on some islands prior to human arrival (e.g. Laysan,Hawaiian Islands; Athens et al., 2007). However, the pollen recordof C. nucifera is unequivocal, in that most pollen types are poorlydescribed. It has been proposed that C. nucifera were initiallydomesticated in Southeast Asia and then introduced by humans tomany islands with indigenous populations of wild type indigenoustrees, but also to other islands without indigenous coconut (Harries,1978; Harries et al., 2004).

4.7. Recent declines of oceanic Pacific island palms

Accumulated historical and palaeoecological evidence indicatesthat on most oceanic island archipelagos palms were more wide-spread. Historical botanical survey data provide the greatestnumber of plant extinction records by virtue of the large amount ofdata. From the most recent IUCN Red List (IUCN, 2007), the majorityof recorded plant extinctions to 2007 are from the oceanic Pacificislands, Madagascar and the Mascarene Islands (Maunder et al.,2002), especially the Hawaiian Islands and French Polynesia fromwhich botanical surveys have accumulated large datasets over thelast 100 years. When examining palms (Table 12), the IUCNconsiders four genera (12 species) from the oceanic Pacific islandsto be critically endangered. However, the significance of theseendangered species is difficult to assess. The historical distributionof palms recorded is complicated by human impacts which mostlypreceded any empirical botanical or ecological studies.

The initial impact of early Europeans on oceanic Pacific islandswas not often recorded before any systematic botanical observa-tions. Sandalwood, for example, was exploited from many oceanicPacific islands during the 19th century for the perfume trade thatresulted in ecological degradation of island vegetation (Shineberg,1967; Wester, 1991). The impact of the introduction of exoticanimals including rats, pigs and goats and invasive plants uponinitial European colonisation has had massive consequences forisland floras. Declines are best known for representatives of theHawaiian Island Pritchardia (e.g. Chapin et al., 2004), but a numberof studies now show that representatives of other genera haveshowed population declines predominantly in response to exoticinvasive species (Table 13).

Palaeoecological records provide one means of assessing histor-ical impacts on vegetation in the absence of botanical observations,allowing the scale of forest decline to be assessed as well as detectingincidents of fire and the invasion of exotic plants (Haberle, 2003;Prebble and Wilmshurst, in press). The following two palae-oecological records from two different oceanic Pacific islands high-light how palms have declined following European colonisation.

4.7.1. La Pina, Robinson Crusoe (Masafuera), Juan FernandezIslands, Chile

Bosque La Pina (Fig. 7) lies at around 600 m on the southeastslopes of Robinson Crusoe, an oceanic island situated w600 kmfrom the coast of mainland Chile in Juan Fernandez Islands (Fig. 3).A 1.45 m peat core shows around 1500 yr cal BP of peat accumu-lation overlying relatively inorganic basal clays. From around 1500–1200 yr cal BP, J. australis palm pollen is recorded in very highconcentrations (up to 10 000 000 grains per cm3) indicating highlylocalised pollen deposition. The consistent rise in fern spores(including Blechnum and Histiopteris incisa) and charcoal particlesat around 25–30 cm indicate initial human impact on the island,taking place sometime after 1574 AD. At this time concentrations ofJuania pollen drop to the low levels recorded in the organic sectionsof the core and suggest rapid palm forest clearance followingincreased burning.

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505-533 yr cal BP

1179-1343 yr cal BP

After 1574 AD

Analyst S. Haberle

Zones

Fig. 7. Palynomorph concentration and summary proportional data for Core 1 from Bosque La Pina Swamp, Robinson Crusoe, Chile. Results are plotted against depth and radiocarbon ages. Selected taxa are presented including Juania typepollen. Percentages are derived from the total palynomorph sum and the diagram is zoned on the basis of pre- and posthuman impact vegetation changes.

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Analyst M. Prebble

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ean

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Fig. 8. Palynomorph concentration and summary proportional data for Core X06/8 from Denham Bay Swamp, Kermadec Group, New Zealand. Results are plotted against depth and radiocarbon ages. Selected taxa are presented includingRhopalostylis type pollen. Percentages are derived from the total palynomorph sum and the diagram is zoned on the basis of pre- and posthuman impact vegetation changes.

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Historical records of human activity on the island (Woodward,1969) reveal that goats were introduced upon initial Europeandiscovery in 1574. Weeds such as Rumex acetosella were introducedalong with more stock animals in 1740. This was followed in the1890s by the introduction of Eucalyptus and Pinus timber trees. Thesubsequent invasion of these exotic species followed repeatedburning of indigenous forest resulted in the rapid decline of palms.

4.7.2. Denham Bay, Raoul, Kermadec Group, New ZealandThe Denham Bay (Fig. 8) core is situated approximately 200 m

from the shoreline of the main bay on the west side of Raoul, anoceanic island situated w970 km off the coast of mainland NewZealand. The swamp is built up behind beach sands and is currentlycovered with sedges and grasses and surrounded by expandingMetrosideros forest. Organic clays and silts with fine organic lensesoverly basal clays with lower concentrations of pollen and spores.Based on two recent radiocarbon ages, taken at the core base, thisshort 42 cm record only captures up to 250 yr cal BP of vegetationchange on the island. As Raoul was initially colonised by Polyne-sians around 700 yr cal BP and probably abandoned soon after themain faunal resources had been exhausted (Anderson, 2001), thiscore does not provide any indication of initial human colonisationof the island.

Rhopalostylis palm pollen (Fig. 4 plates I and J) is abundant in thebasal zone of the core along with Pseudopanax (Araliaceae) andHomalanthus (Euphorbiaceae) pollen and may represent pre-European impact vegetation. Spikes in charcoal particles andPoaceae pollen appear above this zone (pastoral grass zone) inassociation with the rapid displacement of forest taxa. This zone isfollowed by a prolonged period of fern dominance (fern zone).These changes may represent initial European settlement of theisland beginning in 1814 at Denham Bay following the establish-ment of a whaling station on the island. Goats and pigs wereintroduced on the island sometime before 1836 in the process ofexpanding the whaling station (Straubel, 1954). Sheep werebrought on to the island in 1883–84 after the cessation of thewhaling industry and large tracts of low elevation forest werecleared for pasture. In the upper part of the core Rhopalostylis andMetrosideros re-enter the record in greater abundance. Theexpansion of these taxa followed the end of farming practices in themid-1900s and the eradication of feral goats and pigs in the 1970s(Sykes and West, 1996).

Rhopalostylis has survived throughout recent historical impactson the vegetation of Raoul re-colonising areas previously cleared foragriculture. The Denham Bay palynological record shows that priorto the expansion of European settlement on Raoul, Rhopalostyliswas probably more abundant and may have dominated the coast-line of the island. This palm re-colonised the island after the2200 yr cal BP Denham Bay eruption that resulted in decimation ofthe islands biota. Seeds were probably sourced from Norfolk (Aus-tralia) and dispersed by birds, most likely parrots and pigeons. Nobird dispersal of palm fruits from distant islands has been recordedon Raoul, although R. sapida seedlings have been found on TawhitiRahi in the Poor Knights islands (Fig. 1) dispersed by birds morethan 20 km from mainland New Zealand (West, 1999).

4.7.3. Palms unknown in wild as indicators of island extirpationThere are a number of palm species in the oceanic Pacific

islands that are thought to have otherwise originated in theregion but have never been recorded or collected in anunequivocal wild state. Among these is Pelagodoxa henryana(Arecoideae) which was first described from Nuku Hiva, Mar-quesas, French Polynesia from a grove apparently associated withcleared land near a village. Brown (1931) noted the occurrence ofPelagodoxa from Raivavae, Austral Archipelago, French Polynesiaand assumed that this palm was transported to the island from

Nuku Hiva. This species is also known from adventive populationsin Vanuatu and the Solomon Islands (Dowe and Chapin, 2006).The closest relatives of P. henryana occur in New Guinea (Staufferet al., 2004).

Other species of unknown provenance include Pritchardiapacifica, which is most likely to have originated in Fiji, but no wildpopulations presently occur there (Hodel, 2007). This species isvery widely cultivated in the oceanic Pacific islands, and is adven-tive and naturalised on many islands (Dowe and Cabalion, 1996). Afurther two Pritchardia species, P. pericularum and P. vuystekeanawere described from cultivated plants in Herrenhausen Gardens,Germany, though their provenance was recorded as the TuamotuArchipelago. However, no species matching the descriptions ofeither of these have been recorded or collected there, and the onlyCoryphoid palm species that occurs there, P. mitiaroana on Maka-tea, bears little resemblance to either taxa (Hodel, 2007). It isprobable that the wild populations of the four abovementionedspecies have been extirpated.

5. Conclusions

We have examined the available fossil records and more recenthistoric evidence showing declines, extirpation or extinction ofpalms from the oceanic Pacific islands. Palaeoecological records ofthe genus Pritchardia provide the best evidence for human-medi-ated extirpation with three island records situated outside itsmodern distribution. In many of the palaeocological recordsexamined extinctions or extirpations are identified by monosulcatepollen indicative of the palm family but not diagnostic of higherorders beyond subfamily. In these records extirpation or extinctionis determined by the modern absence of extant palms with thispollen type. Further systematic microscopy is being conducted todetermine the generic affinity of these fossil types, now possible formany genera of the Arecaceae using electron microscopy (Drans-field et al., 2008).

A number of palaeoecological records show the prevailingecological trends both before and after human colonisation. Pleis-tocene records, from Rapanui and O’ahu (Hawaiian Islands) showthat palms responded quickly to rising precipitation levels andtemperature after the LGM, but declined in the Holocene as otherwet forest taxa became more abundant (Flenley et al., 1991;Hotchkiss and Juvik, 1999). There is no evidence to suggest thatpalms approached extinction following abrupt regional climatechange events recorded from a range of climate proxies elsewhere inthe Pacific. Prior to human impact, changing island insularity asso-ciated with geological activity and fluctuating sea-levels are themost likely causes of abrupt palm decline or extirpation. Theprobable extirpation of Pinanga from the coastal lowlands of VanuaLevu, Fiji by around 5000 yr cal BP may have resulted from risingsea-level.

Several late Holocene palaeoecological records from a numberof islands reveal strong evidence for human-mediated palm declineand extinction. In most records a close correspondence existsbetween evidence for rapid forest clearance indicated by increasedcharcoal particles and declines in pollen of forest taxa, includingpalms. Some records also reveal the rapid invasion of introducedweed species, further indication of human-mediated habitatmodification. Palm extinctions or extirpations on Rapanui, Rapa,Rimatara and the Hawaiian Islands were a result of human impact.On these islands, already limited in natural resources, palmsprobably occupied prime soils preferred for C. esculenta cultivationby the Polynesian population. The selective impact on large trees,including palms, occupying large tracts of productive land wasinevitable and essential for sustained island colonisation. On largerand less remote islands extinctions or extirpations are rare despitethe abundant evidence for substantial vegetation change following

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initial human colonisation. The decline of the lowland and coastalpalm genus, Metroxylon, on the large islands of Fiji, may representthe combined effects of changing coastlines following mid–lateHolocene sea-level fluctuations that left coastal palm populationsmore vulnerable to initial human impact at around 3500 yr cal BP.

Historical records of human activity on the oceanic Pacificislands reveal that feral animals and invasive weeds introducedsince European colonisation have had a profound impact on palmpopulations. Long-term botanical survey data and ecologicalstudies have revealed for many oceanic island palms that everyaspect of the ecology and biology of palms has been affected byinvasive species. Such effects include, seed predation, disruption ofpollination and seed dispersal and direct damage from herbivores.These studies have also shown that the invasion of exotic specieshas continued following repeated burning of indigenous forestresulting in the rapid decline of palms. The historically documentedecological disruption caused by invasive alien species and the directhuman modification of indigenous forest habitats leaves few otherplausible mechanisms that could explain extinction events, bothnow and in the past.

From this review of evidence for palm declines on oceanicPacific islands we conclude the following:

1. The diversity of palm lineages in the oceanic Pacific islandsdrops with the increasing remoteness of islands.

2. Fossil pollen records of palm declines, extirpations andextinctions are biased towards more remote oceanic islands.

3. Little unequivocal fossil evidence is available to suggest thatlate Quaternary plant extinctions, namely of palms, occurredon oceanic islands prior to human colonisation. However,extinctions can be inferred on the basis of changing islandinsularity associated with geological activity and fluctuatingsea-levels (i.e. marine inundation of islands).

4. Palm species now absent on oceanic Pacific islands werewidespread and locally abundant. In addition, palms may havebeen predisposed to extinction given their size (<10 m inheight) and slow reproductive rates.

5. Palms often dominate environments with high humidity, highrainfall and fertile soils, but on remote oceanic islands theseareas were preferred for crop cultivation at initial humancolonisation suggesting that palms were predisposed tohuman-mediated extinction.

6. Long-term ecological data of islands only recently colonised byhumans suggests that the loss of seed dispersers and pollina-tors following human colonisation has also contributed to palmdecline and extinction.

Acknowledgements

We thank a number of people for freely sharing their datasets:G. Hope, D. O’Dea, J. Stevenson, S. Haberle, J. Wilmshurst andM. Macphail. We thank A. Bright from ANU Cartography for earlierrenditions of the maps. M. Macphail offered considerable assis-tance in interpreting the Tertiary fossil record. We are also gratefulto G. Hope for developing the free-access Indo-Pacific pollendatabase based at the Australian National University (www.palaeoworks.anu.edu.au). We would also like to thank the ARCEnvironmental Futures Network (R. Hill) for funding a workshop(October 2006, ANU, Canberra) linking biologists and palae-oecologists in resolving issues of plant extinction on oceanicislands. This study was financially supported by the University ofAuckland (Nga Pae o te Maramatanga Fellowship to M. Prebble)and an ARC Discovery Grant (DP0878694) to M. Prebble andN. Porch.

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