Quaternary Science Reviews 27 (2008) 2546–2567 Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev 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, Australia b Australian Centre for Tropical Freshwater Research, James Cook University, Townsville, Queensland 4811, Australia a r t i c l e i n f o a b s t r a c t Article history: Received 16 August 2008 Received in revised form 22 September 2008 Accepted 23 September 2008 Late Quaternary palaeoecological records of palm decline, extirpation and extinction are explored from the oceanic islands of the Pacific Ocean. Despite the severe reduction of faunal diversity coincidental with human colonisation of these previously uninhabited oceanic islands, relatively few plant extinctions have been recorded. At low taxonomic levels, recent faunal extinctions on oceanic islands are concentrated in larger bodied representatives of certain genera and families. Fossil and historic records of plant extinction show a similar trend with high representation of the palm family, Arecaceae. Late Holocene decline of palm pollen types is demonstrated from most islands where there are palaeoecological records including the Cook Islands, Fiji, French Polynesia, the Hawaiian Islands, the Juan Fernandez Islands and Rapanui. A strong correspondence between human impact and palm decline is measured from palynological proxies including increased concentrations of charcoal particles and pollen from cultivated plants and invasive weeds. Late Holocene extinctions or extirpations are recorded across all five of the Arecaceae subfamilies of the oceanic Pacific islands. These are most common for the genus Pritchardia but also many sedis fossil palm types were recorded representing groups lacking diagnostic morphological characters. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction A rift in Quaternary science exists over whether the faunal extinctions that have occurred on previously uninhabited ecosystems across the world were climatically driven or anthropogenic (Burney and Flannery, 2005, 2006; Wroe and Field, 2006; Koch and Barnovsky, 2006; Brook et al., 2007). Palaeoecological data from oceanic islands have provided fuel for this debate in effectively demonstrating a close association between the timing of faunal extinctions, particularly of avifauna and land snails, and human colonisation (James, 1995; Steadman, 2006). By contrast, the effect on island floras is not well understood. Palaeoecological data from many oceanic islands and adjacent continental landmasses of the Pacific have shown impacts on indigenous vegetation following human colonisation (Flenley et al., 1991; Parkes, 1997; McGlone and Wilmshurst, 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 records have provided evidence of floral extinctions. * Corresponding author. Tel.: þ61 2 61254342. E-mail address: matthew.prebble@anu.edu.au (M. Prebble). 0277-3791/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2008.09.015 The palaeoecological record of Rapanui (Easter Island, Chile) provides the most convincing case of the almost complete decimation of an island flora that followed human colonisation (Hunt and Lipo, 2006; Hunt, 2007; Mann et al., 2008). Initial human impact began less than 1000 yr cal BP and was as devastating to the flora as it was to the fauna. Late Holocene pollen records from Rapanui reveal 11 plant extinctions identified to at least the family level (Flenley et al., 1991; see Table 1). Subsequent analyses of archaeological wood charcoal, radiocarbon dated to after 600 yr cal BP, has revealed a further seven plant extinctions, some of which may be endemic species (Orliac and Orliac, 1998; see Table 1). Other extinctions are represented by microfossils that await further systematic analysis or the discovery of additional diagnostic macrofossil material. The most notable extinction amongst these taxa is Paschalococos disperta. This palm was initially recognised in the fossil pollen record to family level (Heyerdahl and Ferdon, 1961) and later by subfossil endocarp material by Dransfield et al. (1984) that showed alliance to, but were nevertheless significantly different in size and shape from, Jubaea chilensis from mainland Chile (Zizka, 1991). Hunt (2007) has summarised the evidence for human-induced palm 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 archaeological features indicating that a dense palm forest grew on parts of M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2547 Table 1 List of indigenous angiosperm trees (except palms) that represent island-based plant family extinctions or extirpations from oceanic islands in the Pacific during the Late Quaternary. Extinction: represents the global extinction of a species. Extirpation: represents a local extinction, with extant representatives surviving on other islands Extinction 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 or extirpation Islands Araliaceae cf. Meryta (possibly endemic)/extinction Rimatara (French Polynesia) Rimatara Combretaceae Terminalia cf. glabrata/extirpation Combretaceae Terminalia glabrata/extirpation Cunoniaceae cf. Weinmannia (possibly endemic)/ extinction Elaeocarpaceae cf. Aristotelia/extirpation Elaeocarpaceae Elaeocarpaceae Euphorbiaceae Flacourtiaceae Malvaceae Myoporaceae Myrsinaceae Myrtaceae Pittosporaceae Santalaceae Santalaceae Sapotaceae Rhamnaceae Rubiaceae Rutaceae Ulmaceae Urticaceae a Aristotelia/extirpation cf. Elaeocarpus floridanusa/extirpation cf. Macaranga spp./extinction cf. Xylosma suaveolens/extirpation cf. Hibiscus (possibly endemic)/extinction Myoporum rimatarensis/extinction cf. Myrsine/extinction cf. Metrosideros/extirpation cf. Pittosporum/extinction Santalum ellipticum/extirpation Santalum fernandezianum/extinction cf. Pouteria grayana/extirpation cf. Alphitonia zizyphoides cf. Coprosma, Psydrax, Psychotria/ extinctions cf. Melicope/extinction cf. Trema/extirpation cf. Premna/extirpation Mangaia (Cook Islands) Mangaia (Cook Islands) Time of extinction (yr cal BP) Reference <900 M. Prebble, unpublished pollen data <900 M. Prebble and N. Porch, unpublished macrobotanical and pollen data G. McCormack, unpublished data Ellison, 1994 <10 <2500 Kermadec Group (New <250 Zealand) Three Kings (New Zealand) <50 Rapanui (Chile) <600 Rapanui <2000 Rapanui <600 Laysan (USA) <100 Rimatara <80 Rapanui <600 Rapanui <2000 Rapanui <600 Laysan <50 Juan Fernandez (Chile) <200 Rimatara <900 Rapanui <600 Rapanui <2000 C. West, unpublished survey data Orliac and Orliac, 1998 Flenley et al., 1991 Orliac and Orliac, 1998 Athens et al., 2007 Meyer et al., 2004 Orliac and Orliac, 1998 Flenley et al., 1991 Orliac and Orliac, 1998 Athens et al., 2007 Wester, 1991 M. Prebble, unpublished data Orliac and Orliac, 1998 Flenley et al., 1991; Orliac and Orliac, 1998 Rimatara Rapanui Rapanui M. Prebble, unpublished pollen data Flenley et al., 1991 Orliac and Orliac, 1998 <900 <2000 <700 M. Prebble and J. Wilmshurst, unpublished pollen data Orliac and Orliac (1998) previously designated Elaeocarpus tonganus, but the Rapanui species is more likely to be aligned with E. floridanus (Florence, 2004). the island. On Poike Peninsula, soil profiles overlying abundant charred palm bases or stems do not exceed 700 yr cal BP. Meith and Bork (2003) suggested that anthropogenic fires destroyed the palm forest within 200 years of human settlement, after which a humic soil horizon characteristic of grassland vegetation developed. Many palm endocarps have been located in archaeological and nonarchaeological deposits showing gnaw marks indicative of the Pacific rat (Rattus exulans). Such evidence has lent support to the idea that rats may have compounded the decline of palms, also affected by human activity, by restricting regeneration through seed predation (Hunt, 2007). Even with the abundant evidence for the role of human impact, the timing and cause of palm extinction on Rapanui has been vigorously debated (Flenley and Bahn, 2002; Rainbird, 2002; Diamond, 2005; Flenley and Bahn, 2007; Hunt, 2007). This debate comes in spite of the robust palaeoecological evidence for humaninduced vegetation change on numerous other oceanic Pacific islands. At most sites the palynological evidence includes the rapid influx of charcoal particles, pulses of soil erosion, and increases in the abundance of grasses and certain fern taxa coinciding with the decline 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; Prebble and Wilmshurst, in press). In this paper, we apply a palaeoecological approach to the extinction 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 provide continuous records of ecological conditions and biological representation that exist both before and after human colonisation. We use the oceanic Pacific islands as they appear to be ecologically sensitive to human impacts and were colonised in the late Holocene, a period captured in organic rich sedimentary archives on many islands. Finally, we assess fossil records of palm decline and extinction by integrating modern phytogeographic data of palms. 2. Background 2.1. Island biogeography and oceanic Pacific islands Oceanic islands have been integral for understanding the evolutionary history of biotas and for theories of biogeographic patterning (MacArthur and Wilson, 1967; Paulay, 1994; Whittaker, 1998; Whittaker et al., 2000; Vitousek, 2002). The composition of species on an oceanic island may directly reflect the processes of immigration such that taxa on more remote oceanic islands comprise a nested subset of those on the nearest landmass. New species can arise on islands following colonisation and subsequent evolutionary differentiation. These hypotheses have been tested for a range of different oceanic island plants and other organisms using molecular phylogenetic approaches to assess relatedness among island endemic lineages, as well as associations between species on different archipelagos with continental congeners (Givinish et al., 1995). Biogeographic research is weighted towards understanding the role of speciation at the expense of understanding extinction processes (Johnson et al., 2000; Emerson, 2002). Part of the problem is the paucity of fossil records essential for defining the past distribution and timing of species extinctions. This issue aside, extinction processes should be more apparent on oceanic islands given the premise that large areas hold more species than small areas and larger populations persist longer than small populations (Bond, 1995). In this sense, islands have been predisposed to higher rates of extinction than on continental landmasses, an hypothesis supported by abundant fossil evidence for extinct avifauna (James, 1995; Steadman, 2006) and land snails (Solem, 1990; Lee et al., 2548 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2007). This rich fossil evidence has made oceanic islands useful microcosms of what has become a global debate on late Quaternary extinction centred on two hypotheses, climate-driven or humancaused extinction. The oceanic Pacific islands have been critical to island biogeography research given that they were never connected to any continental landmass and have only been forming since the Eocene (Dickinson, 2001). The extensive stretches of ocean in the Pacific represent formidable dispersal barriers and filters for oceanic island biota that must rely solely on dispersal from distant source populations. Some Pacific islands are formed from remnant Gondwanan landmasses including New Caledonia, New Zealand, and parts of the Solomon Islands and the Fiji Archipelago. In the context of this research, the larger islands of Fiji are not regarded as oceanic islands per se, as they have been subaerial since the Eocene. However, these islands are still examined as their biotas are predominantly oceanic in function. True oceanic islands, such as the Lau group, are also associated with the Fiji archipelago. 2.2. Climate/geodynamic related or human-caused extinctions on the oceanic Pacific islands An abundance of proxy palaeoclimatic records from deep-sea drilling, coral archives and other sources has shown that pronounced climate change events characterise the late Quaternary of oceanic islands, as they do for continental landmasses (Corrège et al., 2000; Woodroffe et al., 2003; Conroy et al., 2008). Major catastrophic late Quaternary geological events have been recorded for many oceanic Pacific islands including earthquakes and tsunamis (Moore and Moore, 1984; Burney et al., 2001), continuing hotspot volcanism (e.g. Galápagos Archipelago; see Munro and Roland, 1996), or resurgent volcanic eruptions along plate subduction zones (e.g. Kermadec Group; see Worthington et al., 1999). Late Quaternary sea-level fluctuations have resulted in massive contractions of oceanic islands particularly on low-lying atolls (e.g. Tuamotu Archipelago, French Polynesia) in which entire archipelagos were submerged. Some sub-Antarctic oceanic islands supported Pleistocene ice sheets that expanded during glacial maxima reducing habitat for terrestrial biota (McGlone, 2002). The late Quaternary has shown an apparently unprecedented global pattern of temporally stepwise megafaunal collapse, beginning with the Australian continent 40 000–60 000 years ago, spreading to the New World at the end of the Pleistocene w12 000 years ago, then on to the numerous oceanic Pacific islands in the late Holocene (Martin and Steadman, 1999; Burney and Flannery, 2005). This pattern is without major exception for biotas that included animals not only with large body size but also low reproductive rates (Johnson, 2002; Koch and Barnovsky, 2006). Oceanic islands lack megafauna but show a bias towards extinction of the largest vertebrates, but smaller extinct vertebrates are also found within the same fossil records (Steadman, 2006). In most cases extinctions are recorded in the fossil record within a few centuries of initial human colonisation. The human-caused continental extinction of a diverse assemblage of late Pleistocene and Holocene fauna, particularly of largebodied 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) has argued that postglacial sea-level rise made the oceanic islands of the Aleutian group too small to ever sustain mammoth populations despite the bridges formed between the islands and the adjacent mainland during the Pleistocene. With the exception of the extant giant tortoises (Geochelone elephantopus) of the Galápagos Islands, which currently face extinction, the largest terrestrial animals known from the oceanic Pacific islands are the relatively lightweight (<8 kg), flightless ground dwelling megapodes including the extinct Megapodius sp. from Tonga. Large pigeons and doves are known from the fossil record, including an extinct Ducula sp. from Tonga and Macropygia spp. from the Society and Marquesas Islands (Steadman, 2006). 2.3. Defining the causes of plant extinctions on oceanic islands Extinctions have occurred as a function of many evolutionary and ecological processes, but separating out these factors is a complex task. Molecular-based phylogenetic analyses have provided substantial evidence for rates of speciation on islands, however, in the absence of fossil or historical evidence there are enormous difficulties in identifying extinction rates given the limits placed on sampling extinct or ‘ghost’ lineages (Thorpe and Malhotra, 1998; Bromham and Woolfit, 2004). In cases where monophyletic lineages have been demonstrated, a trait common to island floras, the known geological age and spatial distribution of young oceanic islands is often directional and this can be used to crosscheck the direction of species dispersals and radiations. The distances or gaps separating intrageneric or intraspecific phylogenies can in some cases be explained by extinction events within a chronological framework independently controlled by radiometric ages for island subaerial formation, e.g. Cyanea and Argyroxiphium on the Hawaiian Islands (Givinish et al., 1995; Baldwin and Sanderson, 1998, respectively), and Robinsonia on the Juan Fernandez Islands (Sang et al., 1995). For more reliable evolutionary modelling of extinction processes greater resolution and integration of fossil data is required. Outside of human intervention, plausible ecological mechanisms for plant extinctions on oceanic islands include competing species interactions, abrupt climatic events, climate change, and changing island insularity associated with geological activity and fluctuating sea-levels. Palaeoecological data, particularly from recent epochs, have in part established the chronological context for these processes by recording ecological trends both before and after human colonisation. Fine-scale vegetation changes can be measured from fossil proxies (e.g. microfossil and macrobotanical analyses) and then used to infer conditions under which certain plant taxa have declined. Similarly, palaeoclimatic patterns can be inferred from a number of fossil, chemical and sedimentary proxies from the same archives. However, demonstrating the timing of plant extinction is difficult given that fossil evidence can only provide a chronological estimation. Defining the cause of extinction requires long fossil records that begin before a population started to decline and extend until its extinction or functional extinction (James and Price, 2008). Thus, in order to demonstrate human driven extinctions, fossil records are required that exceed the age of initial human colonisation. In contexts like Australia this is complicated by the lack of fossil records that even encompass the 40 000–60 000 years of human colonisation. By contrast, there is an abundance of fossil records from oceanic Pacific islands that exceed the late Holocene human colonisation, thus allowing an assessment of the chronology of plant extinction. Palaeoecological records from oceanic islands have also played a key role in the debate on the extent of human impact on previously unoccupied ecosystems (Burney, 1997; Athens et al., 2002; Prebble and Wilmshurst, in press). On a number of oceanic islands the same sedimentary archives that have been used for mapping fine-scale vegetation change have also provided indications of initial human colonisation and in some cases the introduction of agricultural practices have been detected through the identification of 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- M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Table 2 Supra-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]) CALAMOIDEAE Metroxylinae Metroxylona Calaminae Calamusa, Retispatha, Daemonorops, Ceratolobus, Pogonotium Nypoideae NypaaCORYPHOIDEAE Livistoninae Livistonab, Licuala Pritchardiopsis, Johannesteijsmannia, Pholidocarpus Caryoteae Caryota, Arengab, Wallichia CEROXYLOIDEAE Ceroxyleae Juaniaa,c, Oraniopsis, Ceroxylon, Ravenea ARECOIDEAE Pelagodoxeae Pelagodoxab, Sommieria Archontophoenicinae Actinokentia, Chambeyronia, Kentiopsis, Actinorhytis, Archontophoenix, Arecinae Arecab,d, Pinangaa(only some species), Nenga Basseliniinae Cyphosperma, Lepidorhacchis, Physokentia, Basselinia, Burretiokentia, Cyphophoenix Carpoxylinae Carpoxylon, Neoveitchia, Satakentia, Clinospermatinae Clinosperma, Cyphokentia Linospadicinae Howeac, Calyptrocalyx, Linospadix, Laccospadix Ptychospermatinae Balaka, Drymophloeus, Solfia, Veitchia, Adonidia, Brassiophoenix, Carpentaria, Normanbya, Ponapea, Ptychococcus, Ptychosperma, Wodyetia, Rhopalostylidinae Hedyscepeb, Rhopalostylisc Non-aligned ARECOIDEAE genera Clinostigma Cocosa,d (known to be indigenous on some Cyrtostachys Heterospathe Hydriastele Rhopaloblaste Non-aligned CORYPHOIDEAE genera Pritchardiaa,c islands) Taxa listed in bold have been identified or tentatively identified from fossil records from oceanic islands in the Pacific. Genera in italics are not represented on the oceanic Pacific islands, underlined genera are restricted to New Caledonia. a Possess diagnostic pollen types. 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. b caused plant extinctions has been identified from discrete sedimentary deposits found in limestone caves or archaeological deposits, for example, the palm endocarps from Rapanui (Dransfield et al., 1984). Such deposits are generally allochthonous, as plant materials have been introduced by mechanisms other than 2549 natural plant dispersal routes. These sites can provide valuable information on the possible cause of extinction including direct exploitation by humans or by their commensal herbivores (e.g. rodents), but provide limited information on other human activities involved in the extinction process such as fire or land clearance. The advantage of many palaeoecological records for mapping extinction events, particularly palynological records from sedimentary swamp contexts, is that they are mostly hypoautochthonous whereby the original context and spatial relationship of plants, extinct or extant, are preserved. This is especially the case in tropical environments where most plants produce propagules including pollen and seeds that are locally dispersed by animals (mainly invertebrates) and are not dispersed large distances by wind (Bush and Rivera, 1998). The local representation of plant fossil assemblages in sedimentary deposits combined with other indicators of disturbance (e.g. charcoal particles), anthropogenic or otherwise, provides greater definition of the ecological processes involved in plant extinction. From the same palynological records, the timing and localised extent of human impact can be measured against a sufficiently long baseline before human colonisation to demonstrate the prevailing ecological trends (i.e. the response of vegetation or individual plant taxa to climate change). 2.4. Plant extinctions on oceanic Pacific islands The extinction bias towards large-bodied animals on oceanic islands has been well documented (Steadman, 2006) as it has on continents, but what of large-bodied plants (trees) with low reproductive rates? Trees form a large proportion of island biomass and biodiversity, but compared to faunal extinctions relatively few floral ones have been recorded. For example, only 3 out of >2000 vascular plants have become extinct on New Zealand, but none of these are trees (Sax et al., 2002). Is this trend different for oceanic islands? Miocene fossil records from the sub-Antarctic oceanic islands point to numerous pre-Quaternary tree extinctions following Oligocene–Miocene cooling, including fossil palms (Couper, 1960). Miocene–Pliocene plant fossil data are currently available from only a limited number of lignite and other fossil bearing deposits from tropical oceanic Pacific islands including Palau (Federated States of Micronesia), the Marshall Islands and Rapa (French Polynesia). Pliocene or older lignites have been identified from other oceanic islands (e.g. Cemetery Bay, Norfolk Island, Macphail and Neale, 1996), but have yet to be examined for plant fossil bearing potential. The most fossil rich record comes from Eniwetok Atoll (Leopold, 1969) in the Marshall Islands (Federated States of Micronesia). Drilling revealed w1200 m of carbonate sediments composed of coral and lagoon sediments overlying a volcanic base. One Miocene pollen unit was identified yielding 17 extant angiosperm genera. With the exception of the common tropical strand trees Pandanus (Pandanaceae), Pisonia (Nyctaginaceae), Argusia syn. Tournefortia and Cordia (Boraginaceae), all genera including palms represented by a Livistona type palm pollen (Leopold, 1969, plate 305) were probably extirpated during Quaternary sea-level maxima or in earlier periods. Six of the extant genera identified on Eniwetok are common in the tropical Pacific and still inhabit the Southern Marshall Islands; including Sonneratia (Sonneratiaceae), Rhizophora and Bruguiera (Rhizophoraceae), Lumnitzera (Combretaceae), Morinda and Randia (Rubiaceae) and a further five are found in Western and Central Micronesia, but not in Eastern Micronesia, Ceriops (Rhizophoraceae), Terminalia (Combretaceae), Avicennia (Verbenaceae). Extant Livistona species occur on the adjacent archipelagos of Ogasawara (Japan), the Philippines and the Solomon Islands. Fossil evidence of Pleistocene plant extinctions from oceanic islands is lacking. Fossil deposits of Widdringtonioxylon antarcticum 2550 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 CHINA UNITED STATES of AMERICA JAPAN ARECOIDEAE Arecoideae extirpation/extinction Rhopalostylidinae extirpation Rhopalostylis decline TAIWAN MEXICO Howea decline Paschalococos disperta extinction Decline/extinction of unknown palm pollen PHILIPPINES Tinian 20° HAWAIIAN ISLANDS COLOMBIA 0° ECUADOR PAPUA NEW GUINEA SOLOMON ISLANDS SAMOA FIJI Mo’orea Tahiti TONGA VANUATU PERU Tubuai Rimatara NEW CALEDONIA Lord Howe Norfolk Raoul NEW Tawhiti Rahi ZEALAND AUSTRALIA 20° Rapanui Rapa CHILE 40° 120° 140°E 160° 120° 140° 160° 180° 100°W 80° Fig. 1. Geographic distribution of the Arecoideae subfamily of the Arecaceae. Tribes, subtribes and genera within these subfamilies having Pacific oceanic islands representatives are listed 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 by humans to many tropical islands. Oceanic islands with Holocene palaeoecological records showing a decline or extirpation of this subfamily are also indicated. glacial expansion and other major climatic changes. The extirpation and extinction of terrestrial biota on Pleistocene atolls and islands must have occurred many times following complete inundation during the postglacial marine transgressions. Estimates of from Kerguelen, a sub-Antarctic island in the Indian Ocean, represents the only Pleistocene record of a tree extinction from an oceanic island (Phillipe et al., 1998). A 2 m section of wood found in a glacial moraine suggests that this species survived throughout CHINA JAPAN Minami Daito CORYPHOIDEAE Liviston adecline Pritchardia Pritchardia extirpation TAIWAN Laysan A UNITED STATES of AMERICA SOLOMON Naturalised Pritchardia ISLANDS MEXICO HAWAIIA N I SLAND S 20 ° PHILIPPINES VANUATU F IJI COLOMBI A Galapagos Is 0° ECUADO R PAPU A NE W GUINE A A SAMOA TONGA NEW CALEDONI A A USTRALI A COOK ISLANDS Atiu Tua mot uA rchip elag o PERU Society Is Mangaia Rimatara Tubuai Aus tral Arc hipe lago 20° CHIL E NEW ZEALAND 40° 120° 140°E 160° 180° 160° 140° 120° 100°W 80° Fig. 2. Geographic distribution of the Coryphoideae subfamily of the Arecaceae. This subfamily is only represented on Pacific oceanic islands by the genera Livistona and Pritchardia (see Table 2). Oceanic islands with Holocene palaeoecological records showing a decline or extirpation of these genera are also indicated. Inset A shows the current distribution of naturalised Pritchardia. 2551 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 CHINA UNITED STATES of AMERICA JAPAN CALAMOIDEAE Metroxylon decline Metroxylon extirpation NYPOIDEAE CEROXYLOIDEAE CEROXYLOIDEAE decline TAIWAN MEXICO 20° HAWAIIAN ISLANDS PHILIPPINES COLOMBIA 0° ECUADOR PAPUA NEW GUINEA SOLOMON ISLANDS SAMOA FIJI TONGA PERU VANUATU NEW CALEDONIA 20° AUSTRALIA Juan Fernandez Is CHILE NEW ZEALAND 40° 120° 140°E 160° 180° 160° 140° 120° 100°W 80° Fig. 3. Geographic distribution of the Calmoideae, Nypoideae and Ceroxyloideae subfamilies of the Arecaceae. Tribes, subtribes and genera within these subfamilies having Pacific oceanic islands representatives are listed in Table 2. Oceanic islands with Holocene palaeoecological records showing a decline or extirpation of these subfamilies are also indicated. interglacial and interstadial sea-levels are known for the late Pleistocene Pacific from a series of dated uplifted-coral terraces in the Huon Peninsula, Papua New Guinea (Chappell et al., 1996). The closest series of uplifted terraces in the oceanic Pacific islands that provide any indication of Pleistocene sea-level come from the Fijian Archipelago (Nunn and Omura, 1999) and bathymetric mapping indicates substantial inundation of these islands during the latest marine transgression (Gibbons and Clunie, 1986). A mid-Holocene (4000–6000 yr cal BP) sea-level rise of up to w2 m in the central Pacific (Dickinson, 2001) is known to have inundated atolls of the Tuamotu Archipelago (French Polynesia; Pirazolli and Montaggioni, 1986). However, fossil evidence for plant extinctions on atolls has not become available due to the lack of depositional settings that retain terrestrial organic matter following marine inundation. One characteristic of oceanic island floras as opposed to other organisms is that they are extremely vagile and can rapidly colonise new Table 3 A comparison of palm diversity based on the numbers of genera and species globally and for the Pacific islands inclusive of oceanic and continental fragments. Global generac Calamoideae 21 1 Nypoideaea Coryphoideae 46 Ceroxyloideaeb 8 Arecoideae 108 a Global speciesc Ratiod Pacific generac Pacific speciesc Ratiod 620 1 455 42 1250 39.5 1 10 5 11.6 9 1 35 1 121 4.5 1 7 1 3.8 2 1 5 1 32 The Nypoideae is monogeneric and monotypic. 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. b landforms and rapidly re-colonise frequently disturbed environments (Carlquist, 1996). Plant endemism is very low on atolls, thus the gradual inundation by rising sea-levels would at most extirpate plants indigenous to tropical coasts. Radiometric dating of volcanic deposits on Raoul, in the Kermadec Group (New Zealand) has revealed that the island was periodically buried by large volumes of ejecta throughout the late Pleistocene and Holocene (Worthington et al., 1999). The Denham Bay caldera erupted w2200 yr cal BP and the ejecta volume was comparable in magnitude to the 1883 Krakatau eruption. This eruption must have resulted in total biological sterilisation of the island, even of buried plant propagules. Large trees on Raoul (Sykes, 1977) have colonised and in most cases re-colonised the island since this eruption including: Pseudopanax arboreus (Araliaceae), Rhopalostylis baueri (Arecaceae), Corynocarpus laevigatus (Corynocarpaceae), Aristotelia cf. serrata (Elaeocarpaceae), Homalanthus polyandrus (Euphorbiaceae), Pisonia umbellifera (Nyctaginaceae), Pittosporum crassifolium (Pittosporaceae), Melicope ternata (Rutaceae), Melicytus ramiflorus (Violaceae) and the endemic species Myrsine kermadecensis (Myrsinaceae) and Metrosideros kermadecensis (Myrtaceae). The seed source for most of these trees may have come from neighbouring islands in the Kermadec Group (115– 160 km from Raoul), mainland New Zealand (950–1000 km from Raoul) 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 extirpation on oceanic Pacific islands comes from Rapanui where both archaeobotanical 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 the timing of floral demise and human colonisation. At low taxonomic levels, as exhibited in the faunal extinction record (Steadman, 2006), plant extinctions on Rapanui are concentrated in certain families 2552 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Table 4 Palaeoecological records of Pritchardia decline and/or extinction from oceanic island sites in the Pacific (arranged according to latitude). A summarised palynological record of Maunutu, listed in bold is presented in Fig. 5. Site Island Decline or extirpation Age for palm decline or extirpation (yr cal BP)/reference Age of initial human colonisation (yr cal BP)/reference Reference Laysan Laysan, Hawaiian Islands, U.S.A. Kaua’i, Hawaiian Islands extirpation <5000 and after 1822 AD 1822 AD/Rauzon, 2001 Athens et al., 2007 <1200 1200/Burney et al., 2001 Burney et al., 2001 O’ahu, Hawaiian Islands Decline and/or extirpation; Extirpation ¼ Athens et al., 1992 O’ahu, Hawaiian Islands O’ahu, Hawaiian Islands O’ahu, Hawaiian Islands Extirpation Extirpation Extirpation ¼ ¼ ¼ 1200/Tuggle and Spriggs, 2000 ¼ ¼ ¼ O’ahu, O’ahu, O’ahu, O’ahu, Extirpation Extirpation Extirpation Extirpation ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ Athens and Ward, 1996 Athens and Ward, 1993 Athens and Ward, 1995 Athens et al., 2002 Decline ¼ Denham et al., 1999 Extirpation <1500 Extirpation <1500 Extirpation Extirpation Extirpation <2500 ¼ <900 Extirpation <900? 1000/Weisler et al., 2006 1200/Anderson and Sinoto, 2002 1100/Kirch and Khan, 2007 ¼ ¼ 900/Prebble and Wilmshurst, in press 900? h   Ma a’ulepu Makauwahia ‘Uko’a Maunawili Kawai Nui Fort Shafter Flats Kapunahalab Hamakua Liliha Kalaeloa (Ordy Pond)  Ohi’apilo Temae Te Roto Veitatei Tamarua West Maunutu (Fig. 5) Mihiurac a b c Hawaiian Hawaiian Hawaiian Hawaiian Islands Islands Islands Islands Moloka’i, Hawaiian Islands Mo’orea, Society Islands, French Polynesia Atiu, Cook Islands Mangaia, Cook Islands Mangaia, Cook Islands Rimatara, Austral Islands, French Polynesia Tubuai, Austral Islands, French Polynesia Athens and Ward, 1997 Hammatt et al., 1990 Athens et al., 1992 Parkes, 1997 Parkes, 1997 Ellison, 1994 Ellison, 1994 Prebble and Wilmshurst, in press; Prebble and Porch, unpublished data Prebble and Porch, unpublished data; Fossil pollen and fruit identified. Fossil pollen and palm root concretions identified. Only fossil fruit identified; pollen yet to be examined ¼ As above. Table 5 Palynological records with signatures of human impact showing the decline and/or extinction of diagnostic palm pollen (excluding Pritchardia) from oceanic islands of the Pacific. Summarised palynological records of the sites listed in bold are presented in this paper. Approximate age for initial palm decline (yr cal BP) Decline or extinction Reference 5500 <1000a Macphail et al., 2001 Lord Howe, Australia 250 <200 extirpation or extinction decline Dodson, 1982  , Japan Minami Daito 7500 <1500 decline Kuroda, 1996 3500 <2000 a extirpation Ward, 1988; Athens et al., 1996 3800 <2000a extirpation Athens et al., 1996 9300 <3000a decline Athens and Ward, 2004 6000 4300 6000 a <3000 <3000a <2500a decline decline decline 35 000 <2000a extinction 6000 <5000b 5500 a extirpation or extinction decline Southern, 1986 Southern, 1986 G. Hope and J. Stevenson, pers. comm.. e.g. Dransfield et al., 1984; Flenley et al., 1991; Mann et al., 2008 G. Hope and J. Stevenson, pers. comm.. Macphail et al., 2001 Taxa Site(s) Island cf. Hedyscepe canterburyana (Rhopalostylidinae type) Howea spp. Norfolk, Australia Metroxylon cf. amaricarum Kingston Common Old Settlement Beach Swamp  Minami Daito lagoon Yela Metroxylon cf. amaricarum Okat Metroxylon cf. amaricarum IARII Laguas Livistona cf. chinensis Metroxylon cf. vitiensis Metroxylon cf. vitiensis Metroxylon cf. vitiensis Vunimoli Bonotoa Sari Paschalococos disperta Most lake calderas Sari cf. Pinanga sp. (Arecoideae type) Rhopalostylis cf. baueri Rhopalostylis cf. baueri Rhopalostylis cf. sapida Kingston Common Denham Bay (Fig. 8) Tawhiti-rahi Kosrae, Federated States of Micronesia Kosrae, Federated States of Micronesia Guam, Mariana Islands Viti Levu, Fiji Viti Levu, Fiji Vanua Levu, Fiji Rapanui, Chile Viti Levu, Fiji Norfolk, Australia Raoul, Kermadec Group, New Zealand Poor Knight Islands, New Zealand Approximate age range encompassed in record (yr cal BP) <1000 300 2200c/w300a decline 700 <300–200a,d extirpation Prebble and Wilmshurst, unpublished data 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 data for 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). 2553 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 and genera. The extirpation of representatives of entire plant families on Rapanui is very high when considering that very few records of this nature exist on other oceanic Pacific islands. Aside from Rapanui and excluding palms, the extinction or extirpation of plant families on oceanic islands (Table 1) has only been recorded on the remote islands of Rimatara (French Polynesia), Laysan (Hawaiian Islands) and the Juan Fernandez Islands (Chile). Plant family extinctions can be attributed to the Malesian floral attenuation from the west continental islands to the east oceanic islands which has reduced large families and genera often to single representatives as is demonstrated by the tree flora of Raoul. Such a pattern could be enhanced by selective human exploitation of trees for fuel, timber or forest 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 the extinction of Rubiaceae trees on Rapanui seems more surprising given the high rate of diversification on islands that has resulted in numerous Hawaiian Island endemics adapted to different ecological conditions (e.g. Psychotria, Nepokroeff et al., 2003). Preferential selection by invasive alien herbivores and seed predators of trees with edible fruits or seeds must also have influenced these extinction patterns as has been proposed for the Hawaiian Islands and Rapanui (Athens et al., 2002; Hunt, 2007). For the Hawaiian Islands, the suggestion of rat-induced plant extinction through seed and flower predation was made on the basis of declines 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 are designated as subfamilies in the most recent phylogenetic classification (Asmussen et al., 2006; Dransfield et al., 2008). Each subfamily has developed independently from a purported Cretaceous origin for the family, with distinct morphologies, reproductive habits, dispersal patterns, and ecological and environmental parameters (Dransfield et al., 2008). Palms are primarily confined to equatorial and tropical regions with increasing species diversity in areas of high humidity, high rainfall and fertile soils (Svenning et al., 2008). However, palms were once geographically more widespread than at the present, and fossils have been found in most regions of the world (Harley 2006). All the five subfamilies (Calamoideae, Nypoideae, Coryphoideae, Ceroxyloideae and Arecoideae) have representatives in the oceanic Pacific islands (see Table 2). Based on recent accounts of the Pacific palm floras (Dowe and Cabalion, 1996; Doyle and Fuller, 1998; Hodel and Pintaud, 1998; Dowe, 2002; Dowe and Chapin, 2006; Hodel, 2007; Trénel et al., 2007; Pintaud and Baker, 2008), we established the distribution ranges for the systematic groupings of the palm subfamilies (Figs. 1–3) providing a biogeographic outline for interpreting palaeoecological records of palm decline, extinction or extirpation (Table 3). 3.2. Palaeoecological records We review the palaeoecological studies carried out on a variety of late Quaternary sedimentary deposits from the oceanic Pacific islands with palm fossils represented and contribute summaries of previously unpublished results. Most records are published or are available from the Indo-Pacific Pollen Database held at The Australian National University (Hope et al., 1999). Most records are of Holocene age and are derived from a variety of swamp deposits with rich organic sediments. As the fossil record of Pritchardia has been examined by a number of authors (Athens et al., 2002; Hunt, 2007) we briefly summarise the available Holocene records for this genus (Table 4). We also examine palynological records from oceanic Pacific islands that reveal palm pollen types which show either palm decline (Table 5) or no apparent decline (Table 6). In an attempt to explain palm decline or lack of palm decline in response to human impact on oceanic Pacific islands, we present five swamp records preserving palm pollen, which reveal aspects of Table 6 Extant or extinct fossil palm pollen types found in palaeoecological deposits from the oceanic islands of the Pacific. Morphological descriptions follow the terminology of Punt et al. (2007). Micrographs of a number these fossil pollen types are presented in Fig. 4. Genus Aperture Exine Numbers of extant oceanic island species Oceanic island distribution Systematic reference Cocos asymmetric monosulcate, rarely trichotomonosulcate asymmetric monosulcate asymmetric monosulcate symmetric monosulcate disulcate intectate, thick (w7 mm) 1 (C. nucifera) Tropical Pacific Thanikaimoni, 1970; Jagudilla-Bulalacao, 1997 finely scabrate 1 (H. canterburyana) finely scabrate 2 (H. belmoreana, H. forsteriana) Lord Howe (Australia) Norfolk (Australia) Lord Howe (Australia) rugulate, finely rugulate-striate reticulate 1 (J. australis) Juan Fernandez Islands (Chile) zonosulcate spinose-tectate, spines with swollen bases finely rugulate rugulate verrucate or gemmate granular, areolate, fossulate or minutely reticulate 1 (N. fruticans) Hedyscepe Howea Juania Metroxylon (not M. sagu) Nypa Paschalococosa symmetric monosulcate cf. Pinanga variable Pritchardia Rhopalostylis asymmetric monosulcate, occasionally trichotomosulcate asymmetric monosulcate finely reticulate to clavate 5 (M. amicarum, M. paulcoxii, M. salomonense, M. vitiense, M. warburgii) Harley and Baker, 2001 Harley, 1999, Dransfield et Republic of Palau/Federated States Harley, 1999, of Micronesia. Fiji, Samoa, oceanic Dransfield et Solomon Islands, Vanuatu Oceanic Solomon Islands and Harley, 1999, Mariana Islands Dransfield et 2006, al., 2008 2006, al., 2008 2006, al., 2008 0 (P. disperta) Extinct Dransfield et al., 1984 1 (P. insignis); probable extinction on Vanua Levu, Fiji. P. insignis Philippines to Caroline Islands 28 (23 from the Hawaiian Islands; 5 from other Pacific Islands: P. thurstoni; P. pacifica, P. vuylstekeana P. pericularum, P. mitiaroana) Republic of Palau/Federated States of Micronesia Hawaiian Islands; oceanic Fiji; Tonga, French Polynesia, Cook Islands Ferguson et al., 1983; Harley, 2006 Selling, 1948; Dransfield and Ehrhart, 1995; Harley, 1999, 2006 2 (R. baueri, R. sapida) Norfolk (Australia), Kermadecs, Poor Knights (New Zealand) Cranwell, 1953 a Endocarps, wood charcoal and phytoliths have also been described (e.g. Dransfield et al., 1984; Cummings, 1998; Orliac, 2003; Horrocks and Wozniak, 2008; Delhon and Orliac, in press). 2554 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Table 7 Palaeoecological 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 or extirpation Age for initial palm decline (yr cal BP) Extant indigenous palm genera with monosulcate pollen Affinity for monosulcate palm pollen types based on phytogeographic relationships Reference Tinian, Northern Marianas, U.S.A. Tahiti, Society Islands, French Polynesia Mo’orea, Society Islands, French Polynesia Rapa, Austral Archipelago, French Polynesia Rimatara, Austral Archipelago, French Polynesia Viti Levu, Fiji Hagoi <4000 Cocos? Arecoideae (not Cocos), Vaihiria Decline or extirpation extirpation <1000 Cocos? Arecoideae, (not Cocos), Coryphoideae Athens and Ward, 1998 Parkes et al., 1992 Temae extirpation <4500 Cocos? Arecoideae (not Cocos), Coryphoideae Parkes, 1997 Tukou (Fig. 5) extinction or extirpation <500 None Arecoideae (not Cocos) This paper Maunutu (Fig. 6) extinction or extirpation <500 Cocos? Arecoideae (not Cocos) Voli Voli decline or extirpation <5500 Arecoideae (not Cocos) Viti Levu, Fiji Bonotoa decline <3500 Balaka, Calamus, Cocos, Cyphosperma, Hydriastele, Neoveitchia, Physokentia, Veitchia ¼ Viti Levu, Fiji Vunimoli <3500 ¼ Arecoideae, Coryphoideae Prebble and Wilmshurst, in press Hope et al., 1999, G. Hope pers. comm. Southern, 1986; Hope et al., 1999 Southern, 1986 <7000 ¼ Arecoideae, Coryphoideae Rhopalostylis Arecoideae (not Cocos) Viti Levu, Fiji Norfolk, Australia decline or extirpation Tagamaucia decline or extirpation Kingston extirpation or Common extinction <800 palm decline, extirpation or extinction that occurred prior to European arrival. In most of the palynological studies presented, indirect signals of human arrival include increased concentrations of charcoal particles and associated vegetation changes. The chronologies of initial human colonisation established for the oceanic islands examined rely on archaeological data in combination with palynological changes indicating human impact. We present records with both pre-human colonisation and human impact contexts and show how a range of proxies provide a reliable means of highlighting background ecological change and the downstream ecological consequences of human colonisation including palm decline and extinction. In the palynological records presented, sediment cores were generally sampled at regular intervals and processed for palynomorphs using standard procedures as described by Moore et al. (1991). We have chosen to present records where all samples have been spiked in the initial processing step with exotic Lycopodium spores to allow palynomorph and charcoal particle concentrations to be calculated. The concentrations of Arecaceae type pollen, and key indicator taxa (e.g. exotic and disturbance taxa) were obtained by counting pollen and spores as a ratio of the added exotic Lycopodium spores (Stockmarr, 1971). In most cases the concentrations of microscopic charcoal fragments were obtained by counting as a ratio of the added exotic Lycopodium spores (per cm3). Other methods include counting charcoal fragments as a proportion of the total particle Arecoideae, Coryphoideae Southern, 1986; Hope et al., 1999 Macphail et al., 2001 sum or counting the aerial coverage of fragments on a prepared microscope slide. For each of the studies presented, radiocarbon dates were calibrated using the program CALIB Version 5.0 (Stuiver et al., 2005) and are presented in Table 5. The main sedimentary characteristics of each record are described in Table 6. The percentages of the main vegetation types (trees and shrubs, herbs, ferns and fern allies) and the concentrations of Arecaceae pollen types, key indicator taxa, charcoal particles and total palynomorphs were placed into stratigraphic diagrams for comparison using the program C2 Data Analysis Version 1.4 (Juggins, 2005). The stratigraphy of each record presented is divided into three zones (pre-human, initial human impact and recent human impact where applicable), defined on the basis of the main vegetation signals, charcoal particle concentrations, and the presence of exotic taxa introduced first at initial human colonisation, and later by Europeans. 3.3. Historical data We also review the palaeoecological studies carried out on very recent sediments which document the decline of palms after European colonisation of a number of islands. We focus on two islands (Raoul, Kermadec Group, New Zealand) and Robinson Crusoe (Juan Fernandez Islands, Chile) which show sharp responses to human impact. These records have been retrieved from the IndoPacific Pollen Database and previously unpublished datasets. Table 8 Islands with palaeoecological records used in the present study indicating their isolation and timing of initial colonisation. Also includes the continental islands of Fiji. Location Nearest continental landmass/distance (km) Nearest large oceanic island/ distance (km) Rapa, Austral Archipelago, French Polynesia Rimatara, Austral Archipelago, French Polynesia Viti Levu, Fiji Vanua Levu, Fiji Robinson Crusoe, Juan Fernandez Islands, Chile Raoul, Kermadec Group, New Zealand New Zealand/3600 Raivavae/520 New Zealand/3200 Rurutu/150 New Caledonia/1150 New Caledonia/1150 South America/520 Vanua Levu/60 Viti Levu/60 Alexander Selkirk/180 New Zealand/950 Macauley, Kermadec Group, New Zealand/120 Island area Maximum elevation above Age of initial human colonisation (yr cal BP)/reference sea-level (m) (km2) 38 650 8 80 10 400 5600 93 1300 1000 920 30 520 750/Kennett et al., 2006 850/Prebble and Wilmshurst, in press 3000/Nunn, 2007 3000/Nunn, 2007 After 1574 AD/Woodward, 1969 600/Anderson, 2001 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 since European colonisation of islands is also obtained from historical botanical survey data. These surveys not only record the decline of palms but often identify the ecological mechanism for decline, usually resulting from a range of human impacts. 3.4. Taxonomic and phytogeographic affinity of the fossil pollen types The morphology of the fossil palm pollen is described following the 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 structure for distinguishing genera and in some cases species. Morphological descriptions follow the terminology of Punt et al. (2007). Based on the morphological descriptions of each diagnostic fossil type (Table 7) or unknown palm types (Table 8), taxonomic and phytogeographic affinities for fossil types from each palynological record are proposed. 4. Results and discussion 4.1. Oceanic Pacific island palm phytogeography Fig. 4. Micrographs A and B: Arecoideae type pollen from Core 6 160 cm, Tukou Swamp, Rapa, French Polynesia. C and D: Arecoideae type pollen from Core 1 Transect 2 185 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. G and H: cf. Pinanga (Arecoideae) type pollen from Core 1 410 cm, Sari Swamp, Vanua Levu, 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 Pritchardia fruit from Mihiura Swamp, Tubuai, French Polynesia. L: Fossil Pritchardia fruits Mihiura Swamp Core 2 (350 cm), Tubuai, French Polynesia. Palms on oceanic Pacific islands follow the general trends of habitat preferences as do those in nearby areas such as Malesia and Southeast Asia, being found mostly in mesic terrestrial environments in complex rainforest associations. Table 3 provides a comparison of global diversity of palms, with those occurring on the oceanic Pacific islands. Overall, there is less diversity with regard to genera and the numbers of species in genera than for palms globally. The most diverse and widespread subfamily is the Arecoideae which has representatives in most archipelagic groups from the Solomon Islands, south to New Zealand, and east to French Polynesia (Fig. 1). A confounding factor is that the relatively low ratio of species to genera (i.e. levels of anticipated speciation) in the Arecoideae in the oceanic Pacific islands is related to the presence of monotypic or small genera in the area. The second most diverse subfamily is the Coryphoideae (Fig. 2), which has widespread distribution from the Solomon Islands through Vanuatu, New Caledonia, Fiji to French Polynesia and Hawaii, but not to the islands to the south of New Caledonia, nor to the east of French Polynesia. Apart from the monotypic Pritchardiopsis on New Caledonia, the Coryphoideae in the western oceanic Pacific islands is represented by a few outlier species in the species rich genera of Licuala and Livistona, genera that have their greatest diversity to the west in Malesia and Australia. Conversely, the genus Pritchardia, with 26 species, is an example of a genus with high levels of speciation and island endemism. Pritchardia is most diverse on the Hawaiian Islands with 24 species, most of which are endemic to single islands in that archipelago and known by small populations. Otherwise, the genus has three widespread outlier species occurring in Fiji and Tonga (P. thurstonii), the Cook Islands and French Polynesia (P. mitiaroana), and known only from unequivocally wild populations (P. pritchardia) but otherwise widespread as an adventive and cultivated plant in the oceanic Pacific islands (Hodel, 2007). The third most diverse subfamily is the Calamoideae (Fig. 3) which is represented by two genera, of which Calamus is most diverse in Malesia and southeast Asia (with about 360 species) and extends to Fiji in the Pacific (with a single widespread species). The second genus, Metroxylon (7 spp.), has its greatest diversity in the western oceanic Pacific islands from Solomon Islands east to Samoa and north to Micronesia (with 6 spp. endemic to the oceanic islands), and with one species shared with Malesia to the west. The 2556 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Table 9 Palaeoecological 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 Fig. 5 Tukou C6; Prebble, unpublished Fig. 6 Fig. 7 Fig. 8 Rapa, Austral Archipelago, French Polynesia Lab code OZH282 UCIG6015 UCIG6014 Rimatara, Austral Archipelago, French Polynesia Maunutu C1T2; Prebble and WK17008 Wilmshurst, in press WK17009 WK22538 WK22539 Robinson Crusoe, Juan Fernandez Islands, Chile La Piña JFRC-PI; Haberle, OZF279 unpublished data OZF280 Raoul, Kermadec Group, New Zealand Denham Bay X06/8; Wilmshurst WK21624 and Prebble, unpublished data WK21625 oceanic Pacific distribution of the monogeneric and monotypic Nypoideae and the Ceroxyloideae (Fig. 3) is anomalous as they are only represented by Nypa fruticans (restricted to the Marianas and Kosrae, Federated States of Micronesia), and Juania australis (restricted to Robinson Crusoe of the Juan Fernandez Islands, Chile), respectively. The predominant phylogenetic relationships of oceanic Pacific islands palms are with taxa in New Guinea and Malesia, and to a lesser extent Australia, North America and South America. Relationships with Australian palms lie primarily in the landmasses of Gondwanan origin, such as New Caledonia and New Zealand, and there is otherwise a biogeographic disjunction between Australia/ New Caledonia/New Zealand, and the oceanic Pacific islands archipelagos to the north and east. There is also a disjunction between French Polynesia, which is the eastern limit of Malesiancentred diversity attenuation and the oceanic Pacific islands that lie close to South America: namely J. australis on Robinson Crusoe, Juan Fernandez Islands, Chile, which has its closest affinity with taxa from South America. 4.2. Pre-Quaternary fossil records of oceanic Pacific island palms The fossil record of palms is rich and widespread and has been summarised by Harley (2006). Palm floras originated in wet-tropical regions as early as the mid-Cretaceous. This tropical affinity has meant that fossil records of palms have been used as an important indicator of changing past climatic conditions, particularly for the Oligocene–Miocene cooling (Morley, 2000). These records also show that the palm flora of the African continent and Indian subcontinent was considerably more diverse than at present (Harley and Morley, 1995; Pan et al., 2006; Harley, 2006). The earliest palm fossils in Australia have been dated to the early Palaeocene, and with other significant records from the early Eocene and late Oligocene (Greenwood and Conran, 2000), although putative palm pollen types have been found almost continuously across all stratigraphic ages. Most Australian palm fossils have not been assigned to extant taxa. Those that have been assigned identities include macrofossils and fossil pollen of Nypa Depth (cm) 14 120–122 210–212 210–212 75–77 105–107 125–127 275–277 44–45 90–95 33 37 840 2190 2465 500 918 930 1941 555 1410 101 146 C age BP 1s 70 140 30 35 32 35 35 30 40 30 30 Method Calibrated age range 2s BP AMS AMS AMS AMS AMS AMS AMS AMS AMS AMS AMS 569–904 1738–2465 2346–2697 470–544 722–905 728–907 1717–1920 505–553 1179–1343 0–253 0–269 (as Nipa and Spinizonocolpites) found in Eocene deposits from a number of locations in Australia (Pole and Macphail, 1996). A specimen from Pliocene deposits in New Zealand has been assigned to the genus Cocos (C. zeylandica) because of the distinctive and characteristic three pores in the endocarp (Berry, 1926; Couper, 1952). Other fossil pollen types including Arecipites (also Arecipites cf. Rhopalostylis sapida), Palmidites and Dicolpopollis (Metroxylon affinity) appear in Australia and New Zealand after the Upper Eocene (Raine et al., 2008). These records indicate that many palms probably arrived in New Zealand after the break-up of Gondwana and were available for dispersal before the emergence of the main oceanic archipelagos in the Pacific. Fossil records of palms from oceanic islands of the Indian Ocean exist for the drowned Tertiary islands of Ninetyeast Ridge including Arecipites and Spinizonocolpites (Kemp and Harris, 1975), and for the sub-Antarctic island, Kerguelen described as Monosulcipollenites minimus Levet-Carette (Harley, 2006). However, considering that the first oceanic islands in the Pacific, outside of Gondwana, emerged in the Eocene, fossil records fail to indicate the timing or position 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. Given that most oceanic islands are in the West Pacific and are of late Miocene to Pliocene (10–1.8 ma) age, from the configuration of islands it can be assumed that the direction of plant dispersal should follow a west to east direction (Carlquist, 1996). Very few Miocene deposits have been described from oceanic Pacific islands. The drill cores from Eniwetok Atoll (Leopold, 1969), described above, reveal Livistona type palm pollen. One of the few Pliocene deposits of value for fossil palm research is a shallow lignite seam located at Arahu at the northeast head of Ha’urei Harbour on Rapa at around 200 m in elevation. This represents one of only two lignite deposits in the oceanic island Pacific, the other located at Babeldaob in Palau (Federated States of Micronesia). The Arahu deposit, like at Babeldaob, formed prior to the erosional dissection of a former lake caldera that now forms the harbour on the southeast side of the island. Cranwell (1964) examined some of the Arahu lignite collected in 1934 for its Table 10 Palaeoecological records from the islands used in the present study. Presented is a summary of the main sedimentary characteristics of each record. Figure Site Elevation above sea-level (m) Type of deposit Depth of record below surface (cm) Pre-human sediments Initial human impact sediments Fig. 5 Tukou C6 0–3 0–240 Maunutu C1T2 La Piña JFRC-PI Denham Bay X06/8; 2–4 0–750 (250 presented) Pandanus leaf and wood peat overlying estuarine sands and silts Pandanus and Acrostichum leaf peat Organic silts and clays Fig. 6 Estuarine backswamp formed behind an alluvial delta Moat-swamp behind raised limestone shelf Forest hollow Organic silts 0–150 Juania leaf peat Organic clays 45 Organic clays and silts with fine organic lenses Organic silts and clays Fig. 7 Fig. 8 650 3–5 Backswamp formed behind volcanic beach sands Analyst M.Prebble Estuary Swamp forest Initial human impact Recent human impact 1738-2465 yr cal BP 2346-2697 yr cal BP 240 220 200 180 160 140 80 100 60 40 20 120 569-904 yr cal BP Depth (cm) 0 e Ar co e ea id T e yp (n C ot a nd Pa o oc s nu s) -i s ou en ig d n sw am p st re fo tre e C er yp ac e ea a Po ce ae > 40 m ic ro ns C o ol ca si a e sc L e ul w ud nt ig a- ia in tr -i l Po le r nt na nd sp e or u od c u od ed ce d cu lti w ge n d ee co nc en tra tio n/ cc C ha rc oa lp ar l tic e co nc e ra nt tio n/ cc T e re s an d ru sh bs bs er H s rn Fe an d rn fe al lie s n Zo es Summary proportional data Pre-human Herbs Fig. 5. Palynomorph concentration and summary proportional data for Core 6 from Tukou Swamp, Rapa, French Polynesia. Results are plotted against depth and radiocarbon ages. Selected taxa are presented including Arecaceae 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. M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 2557 palynological potential identifying some ‘palmoid’ grains, indicative of an island-based extinction of the Arecaceae, given the current lack of any indigenous palms on Rapa. Prebble (in press) undertook further examination of the Arahu lignite seam, but failed to locate any Arecaceae type pollen. Taccaceae pollen was identified which has a distinct sulcus with even margins, very similar to many palm pollen grains, including Pritchardia (Selling, 1948). Also identified were high proportions of sedges (Cyperaceae), Zingiberaceae, Myrtaceae, Piperaceae, Sapindaceae, and Rubiaceae of a type comparable to the endemic Coprosma rapensis. Cranwell (1964) also identified a few grains of the gymnosperm genus Dacrydium (not of the New Zealand species D. cupressinum), which she considered to be a contaminant. This could also have been derived from a wind blown dispersal during the late Miocene following the pacific expansion of Dacrydium into areas such as New 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 oceanic Pacific islands is limited by the number of available terrestrial organic sedimentary deposits. The main Pleistocene deposits recording palms are from the Hawaiian Islands and Rapanui where large lake calderas preserve organic sediments. From the Hawaiian Islands, fossil palm (cf. Pritchardia) stems found near sea-level at Aliapa’a Kai salt lake on O’ahu date from 100 000 yr BP (Lyon, 1930) indicate that palms were abundant on the islands during the Pleistocene (Carlquist, 1980; Cuddihy and Stone, 1990; Athens, 1997). From the palynological record of Ka’au Crater, O’ahu, (460 m above sea-level), Hotchkiss and Juvik (1999) show that Pritchardia palms were locally abundant around 35 000 yr cal BP but declined during the Last Glacial Maximum (LGM). Pritchardia responded quickly to rising precipitation levels and temperature after the LGM with the highest palm pollen representation recorded throughout the Lateglacial. Palm pollen decreased in the early Holocene as other wet forest taxa including Metrosideros (Myrtaceae) increased in abundance. A number of Pleistocene palynological records from the caldera lakes of Rapanui show large proportions of palm pollen representing 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 subtropical and tropical climates indicate warmer conditions. Palm pollen is dominant in sediments radiocarbon dated to 32 000– 35 000 yr cal BP but declined during the LGM where in some sections pollen is poorly preserved. The late Pleistocene sequences from Aroi and Rano Raraku vary but palm pollen generally increases by the end of the Lateglacial. Macrofossil evidence of Rhopalostylis is recorded from the Hutchison formation on Raoul in the Kermadec Group, New Zealand (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 andesite and pyroclastic flows have been recorded on Raoul, the oldest dating to 1.4 ma and the most recent at 2200 yr cal BP (Worthington et al., 1999). Most of these eruptions must have resulted in total biological sterilisation of the island including Rhopalostylis which may have re-colonised the island several times in the Pleistocene and Holocene. 4.4. Holocene fossil records of oceanic Pacific island palms Declines and/or extirpations of nine taxa recognisable from distinctive fossil palm types have been recorded from upward of 40 sedimentary deposits located on 19 different oceanic islands Fig. 6. Palynomorph concentration and summary proportional data for Core 1 Transect 2 from Maunutu Swamp, Rimatara, French Polynesia. Results are plotted against depth and radiocarbon ages. Selected taxa are presented including the Pritchardia type, Arecaceae pollen and other Arecaceae type. Percentages are derived from the total palynomorph sum and the diagram is zoned on the basis of pre- and posthuman impact vegetation changes. Analyst M. Prebble M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Depth (cm) 2558 (Tables 4 and 5). Of these records 18 deposits from nine islands show a decline or extirpation of the genus Pritchardia (Table 4). Palm extirpations are recorded on 11 islands, although some of these records may represent species extinctions. Rapanui is the only island with fossil deposits recording a palm species extinction, of the genus Paschalococos, which was described as a distinct taxon based on the differences of subfossil endocarps to similar species (Dransfield et al., 1984; Zizka, 1991). Descriptions of the designated pollen types are given in Table 6 with micrographs of the main types presented in Fig. 4. A further 10 pollen records from seven islands reveal the decline, extirpation or extinction of palms, which can only be designated as Arecaceae pollen and at best described to subfamily (Table 7). Considerably more systematic observations of both micro- and macrofossils are required in order to confirm any generic or species affinities. Using Holocene palaeoecological records from five different oceanic Pacific islands (Table 8) we present a range of palynological data which are intended to represent palm extirpation or decline on human impacted sites utilising a range of reliable proxies for initial human impact. The radiocarbon chronologies and general characteristics of each sedimentary archive are described in Tables 9 and 10, respectively. We attempt to show how palms have responded to ecological changes prior to human impact, primarily sea-level change. We firstly examine sites on small and remote oceanic islands including Rapa and Rimatara in the Austral Archipelago (French Polynesia), which currently have no surviving indigenous palms. 4.4.1. Tukou Core 6, Rapa, Austral Archipelago, French Polynesia Tukou marsh (Fig. 5) lies on the south side of the broadest river delta and associated estuarine mud flats of Ha’urei Harbour. Such marshes are typical of coastal embayments where organic sediments have accumulated over inorganic silts and clays since sealevel stabilisation within the last 4000 yr cal BP. The marsh is comprised of mostly exotic weed vegetation. Abandoned Colocasia esculenta (Araceae) agricultural terrace features surround the marsh and lie 50 cm or more above the marsh surface. Tukou Core 6 is positioned in the centre of the marsh records more than 2500 yr cal BP of vegetation change. The pre-human zone between 2500–800 yr cal BP is characterised at the base by the presence of Arecoideae pollen, Cyperaceae pollen and high proportions of fern spores indicative of an alluvial or estuarine coastline. By around 1000–1500 yr cal BP a Pandanus (Pandanaceae) swamp forest has developed at the site. After around 800 yr cal BP, in the initial human impact zone, Pandanus pollen concentrations decline steeply in response to increasing Poaceae and Cyperaceae pollen, charcoal particle concentrations and the initial appearance of Colocasia pollen after 800 yr cal BP. Arecoideae type pollen is not represented in this zone suggesting that either palm populations were always very low or initial human impact was severe, causing rapid palm decline. No indigenous palms survive on Rapa and there are no historical records of palms apart from the probable recent introduction of C. nucifera (Arecoideae). The few coconut trees that survive on Rapa do not set mature fruit presumably in response to the subtropical climate. In his ethnography of Rapa, Stokes (m.s.) recorded from informants in 1920 a local tradition referring to Haari rohutu, a palm goddess represented by an idol figure wrapped in palm fiber. Unfortunately, no traditions refer to a palm tree or its demise. The close association between the eventual absence of most coastal lowland forest taxa in the recent human impact zone and the first appearance of European weeds suggests coastal swamp forest including palm had long since disappeared by initial European colonisation in 1814 AD (Ellis, 1831). 2559 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Table 11 Examples 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 for initial human colonisation (yr cal BP) Approximate age range encompassed in record (yr cal BP) Extant indigenous palm genera with monosulcate pollen Affinity for palm pollen types excluding C. nucifera Reference Yap, Federated states of Micronesia Totoya, Fiji Fool 3500 3500 Clinostigma, Cocos?, Hydriastele, Ponopi Arecoideae Dodson and Intoh, 1999 3500 2200 Balaka, Cocos?, Veitchia Arecoideae, Coryphoideae Viti Levu, Fiji Dravawal, Jigojigo, Keteira, Lawakile, Udu, Yaro Voli Voli FV VOL 1 3500 6000 Arecoideae, Coryphoideae Viti Levu, Fiji Nadrala 3500 2200 Balaka, Calamus, Cocos, Cyphosperma, Hydriastele, Neoveitchia, Physokentia, Veitchia ¼ Viti Levu, Fiji Nadrau 3500 2300 ¼ Arecoideae, Coryphoideae Vava’u, Tonga Vava’u, Tonga Avai’o’vuna Ngofe 3000 3000 4500 6000 Cocos?, Pritchardia, Veitchia Cocos?, Pritchardia, Veitchia Arecoideae, Coryphoideae Arecoideae, Coryphoideae Clark and Cole, 1997; Clarke et al., 1999 Hope et al., 1999; G. Hope pers. comm. Hope et al., 1999, G. Hope pers. comm.. Southern, 1986; Hope et al., 1999 Fall, 2005 P. Fall, pers. comm. 4.4.2. Maunutu, Rimatara, Austral Archipelago, French Polynesia According to Dickinson (2001), Rimatara is one of six makatea type islands of the Cook–Austral groups of islands that consist of an annular limestone plateau that surrounds a degraded volcanic bedrock core. A unique characteristic of makatea islands is the extensive sediment-filled and waterlogged depressions that extend out like a moat, between the inner rim of the annular limestone and the base of the inland volcanic core. Most of these ‘moat deposits’ are covered with swamp vegetation. Maunutu swamp on Rimatara provides one example of a palaeoecological record from a moatswamp similar to those examined on Mangaia (Ellison, 1994) and Atiu (Parkes, 1997), both makatea islands in the Cook Islands. Further descriptions of this record can be found in Prebble and Wilmshurst (in press) (Fig. 6). The 7.5 m C1T2 record (2.3 m shown in Fig. 6) shows more than 3000 yr cal BP of palm decline and probable extirpation. The pre-human zone, between 900–2000 yr cal BP, is dominated by Pandanus pollen and Acrostichum (Pteridaceae) fern spores. The high concentrations of Pandanus pollen indicate a swamp forest with a fern understorey. The initial appearance of Colocasia pollen from the introduced horticultural crop, the decline of Pandanus pollen and high concentrations of charcoal particles in C1T2 after 800 yr cal BP indicate that the Pandanus swamp forest was burnt-off in the processes of establishing Colocasia cultivations along the most inland areas of Maunutu swamp. Additional disturbance indicators including Poaceae pollen and Dicranopteris (Gleicheniaceae) spores provide additional support for initial human impact on Rimatara. More recent human impacts are indicated by the presence of Commelina diffusa (Commelinaceae) a weed introduced after 1822 AD (Ellis, 1831), which now Arecoideae, Coryphoideae dominates the swamp vegetation along with other introduced weeds. Like on Rapa, no indigenous palms survive on Rimatara and there are no historical or ethnographic records of palms apart from the probable introduction of C. nucifera. Only one Arecoideae pollen type (Fig. 4 plates A and B), similar to that described from Rapa, is found in the pre-human sediments. Pollen from an extinct or extirpated cf. Meryta spp. (Araliaceae) was identified, representing a family extinction on Rimatara. Very few low-pollen producing taxa are identified in samples where extremely high concentrations of Pandanus pollen and Acrostichum spores dominate the record. Three Arecaceae pollen types including a Pritchardia type, Arecoideae type (Fig. 4 plates C and D) and one degraded palm type (similar to the Arecoideae type) within the initial human impact zone and are recorded in high concentrations at around 750 yr cal BP. The later two types are not recorded in the recent human impact zone. The close association between the decline of Pritchardia type palm pollen and the first appearance of European weeds suggests palm extinction took place soon after European contact in 1822 AD. A number of plant species have declined since this time, probably as a result of direct browsing by European stock animals (e.g. goats), including a Myoporum (Myoporaceae) recorded historically but not in the most recent botanical surveys (Meyer et al., 2004; see Table 1.). C. nucifera pollen is only recorded in the recent human impact zone and is probably a recent human introduction given the lack of diagnostic coconut pollen from any pre-human sediments. We discount the human introduction of Pritchardia and other palms to the island, particularly given the pre-human record of Arecoideae type pollen. Table 12 Critically endangered oceanic Pacific island palms from the IUCN list 2007. Taxa Island Numbers in wild Main threats Carpoxylon macrospermum Pelagodoxa henryana Pritchardia affinis P. aylmer-robinsonii P. hardyi P. kaalae P. limahuliensis P. munroi P. napaliensis P. schattaueri P. viscosa Aneityum, Tanna and Futuna, Vanuatu Unknown Hawai’i, Hawaiian Islands Nihoa, Hawaiian Islands Kaui’i, Hawaiian Islands O’ahu, Hawaiian Islands Kaui’i, Hawaiian Islands Molokai, Hawaiian Islands Kaui’i, Hawaiian Islands Hawai’i, Hawaiian Islands Kaui’i, Hawaiian Islands ? Unresolved, may be no wild populations 60 2 30 150 100 1 or 2? 90 12 4 habitat loss habitat loss, invasive alien species natural disasters invasive alien species invasive alien species, natural disasters invasive alien species invasive alien species invasive alien species invasive alien species invasive alien species, natural disasters 2560 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Table 13 A 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 Green, 1994; Sykes, 1977 Juania australis Juan Fernandez Islands, Chile 15 Pritchardia spp. Hawaiian Islands 25 Metroxylon vitiense Livistona chinensis Oceanic island Fiji Minami Daito, Japan Feral animal browsing and habitat clearance Feral animal browsing and habitat clearance Feral animal browsing and habitat clearance Agricultural development Urban and agricultural development 16 >10 Henderson et al., 1995; Sanders et al., 1982 Chapin et al., 2004 McClatchey et al., 2006 Dowe, 2001 4.5. Holocene records of Pritchardia decline and/or extirpation 4.7. Recent declines of oceanic Pacific island palms In addition to the palm pollen sequence from Maunutu on Rimatara, several records of Pritchardia decline have been analysed from the Hawaiian Islands (see Athens, 1997; Athens et al., 2002; Burney et al., 2001; Hunt, 2007 for a summary), three records from the Cook Islands and one further macrofossil (fruit) record from Tubuai, also in the Austral Archipelago (Table 4). A single undated profile from Mihiura swamp on Tubuai revealed Pritchardia type fruits (Fig. 4 plates K and L) at depths ranging from 3.2 to 3.8 m, probably from a pre-human sedimentary context. The widespread decline of Pritchardia species on the Hawaiian Islands has also been documented in archaeobotanical sequences and further evidence from both fruit and trunk macrofossils indicates that Pritchardia was one of the most abundant trees prior to human settlement on Kauai (Burney et al., 2001) as it probably was on other Hawaiian islands (Athens et al., 2002). Palynological records from most islands in the Hawaiian Archipelago have recorded declines of Pritchardia pollen from pre-human sediments in which palm pollen often comprises up to half of the pollen within the palynological assemblages (Table 4; Fig. 2). Accumulated historical and palaeoecological evidence indicates that on most oceanic island archipelagos palms were more widespread. Historical botanical survey data provide the greatest number of plant extinction records by virtue of the large amount of data. From the most recent IUCN Red List (IUCN, 2007), the majority of recorded plant extinctions to 2007 are from the oceanic Pacific islands, Madagascar and the Mascarene Islands (Maunder et al., 2002), especially the Hawaiian Islands and French Polynesia from which botanical surveys have accumulated large datasets over the last 100 years. When examining palms (Table 12), the IUCN considers four genera (12 species) from the oceanic Pacific islands to be critically endangered. However, the significance of these endangered species is difficult to assess. The historical distribution of palms recorded is complicated by human impacts which mostly preceded any empirical botanical or ecological studies. The initial impact of early Europeans on oceanic Pacific islands was not often recorded before any systematic botanical observations. Sandalwood, for example, was exploited from many oceanic Pacific islands during the 19th century for the perfume trade that resulted in ecological degradation of island vegetation (Shineberg, 1967; Wester, 1991). The impact of the introduction of exotic animals including rats, pigs and goats and invasive plants upon initial European colonisation has had massive consequences for island floras. Declines are best known for representatives of the Hawaiian Island Pritchardia (e.g. Chapin et al., 2004), but a number of studies now show that representatives of other genera have showed population declines predominantly in response to exotic invasive species (Table 13). Palaeoecological records provide one means of assessing historical impacts on vegetation in the absence of botanical observations, allowing the scale of forest decline to be assessed as well as detecting incidents of fire and the invasion of exotic plants (Haberle, 2003; Prebble and Wilmshurst, in press). The following two palaeoecological records from two different oceanic Pacific islands highlight how palms have declined following European colonisation. 4.6. Holocene palynological records with no apparent declines in Arecaceae palm pollen A few palynological sites from oceanic Pacific islands (Table 11) show that despite strong signatures of human impact including increases in disturbance indicators such as Poaceae pollen and charcoal particles, there is no apparent decline in Arecaceae pollen. Many palms may maintain population structure despite disturbance events by a range of ecological and biological mechanisms. The primary reason for survival on larger and less remote islands including Tonga will be the size of palm populations and their widespread distribution but also their level of dependence on extant animal seed dispersers and pollinators. Adaptation to a wide-range of soils’ substrates and hydrological regimes, having non-specialised seed dispersal or being resilient to fire may be other important factors in predicting palm survival (Vormisto et al., 2004). Some palms may respond positively to human colonisation including C. nucifera. Although not discussed in this paper, macrofossil remains of C. nucifera nuts, exceeding the age of initial human colonisation, have been described from Aneityum in Vanuatu (Spriggs, 1984). Also several pollen records show that C. nucifera was present on some islands prior to human arrival (e.g. Laysan, Hawaiian Islands; Athens et al., 2007). However, the pollen record of C. nucifera is unequivocal, in that most pollen types are poorly described. It has been proposed that C. nucifera were initially domesticated in Southeast Asia and then introduced by humans to many islands with indigenous populations of wild type indigenous trees, but also to other islands without indigenous coconut (Harries, 1978; Harries et al., 2004). 4.7.1. La Piña, Robinson Crusoe (Masafuera), Juan Fernandez Islands, Chile Bosque La Piña (Fig. 7) lies at around 600 m on the southeast slopes of Robinson Crusoe, an oceanic island situated w600 km from 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 accumulation overlying relatively inorganic basal clays. From around 1500– 1200 yr cal BP, J. australis palm pollen is recorded in very high concentrations (up to 10 000 000 grains per cm3) indicating highly localised pollen deposition. The consistent rise in fern spores (including Blechnum and Histiopteris incisa) and charcoal particles at around 25–30 cm indicate initial human impact on the island, taking place sometime after 1574 AD. At this time concentrations of Juania pollen drop to the low levels recorded in the organic sections of the core and suggest rapid palm forest clearance following increased burning. Ferns cc n/ n/ tio tio en al s s ne Zo rn s Fe er bs H Tr ee s an an d d fe sh rn ru b le rti c pa al rc o ha C li e s nc co co or e sp n lle Po Bl ec hn an d um ty in er is pt tio is H tra tra en nc l) ci pe sa (s m al lm -p a is ra l st au ia an Ju 0 10 Initial human impact 20 After 1574 AD 30 40 505-533 yr cal BP Depth (cm) 50 1179-1343 yr cal BP 60 70 80 90 Pre-human 100 110 120 130 140 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 cc Summary proportional data Analyst S. Haberle Fig. 7. Palynomorph concentration and summary proportional data for Core 1 from Bosque La Piña Swamp, Robinson Crusoe, Chile. Results are plotted against depth and radiocarbon ages. Selected taxa are presented including Juania 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. 2561 2562 Summary proportional data en nc al s rn ru b Zo ne s an rn s Fe er bs s Tr ee H an d d fe sh d an n lle Po lie s co or e sp m >5 0 al C ha rc o pt tio is H tra en co ic -f sa ci in er is <5 0 e ea ac Po ro n er n -h s ro n ic m rm ke er os id ro s M et eu Ps nc er b s si en ec ad re u bo ar x na pa do an al om H s dr us ly po irp us xt th -e lia te to Ar is an ed at m al -p is yl st lo pa ho 0 2 4 6 8 10 Forest regeneration post 1970? 12 Depth (cm) 16 18 20 22 24 Shrub and fernland 26 28 Initial European impact 14 30 0-253 yr cal BP 32 34 0-269 yr cal BP Pastoral grasses 36 38 40 Pre-European impact ? 42 Analyst M. Prebble 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 including Rhopalostylis 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. M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 R tio tra n/ tio cc n/ cc Trees and shrubs M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 Historical records of human activity on the island (Woodward, 1969) reveal that goats were introduced upon initial European discovery in 1574. Weeds such as Rumex acetosella were introduced along with more stock animals in 1740. This was followed in the 1890s by the introduction of Eucalyptus and Pinus timber trees. The subsequent invasion of these exotic species followed repeated burning of indigenous forest resulted in the rapid decline of palms. 4.7.2. Denham Bay, Raoul, Kermadec Group, New Zealand The Denham Bay (Fig. 8) core is situated approximately 200 m from the shoreline of the main bay on the west side of Raoul, an oceanic island situated w970 km off the coast of mainland New Zealand. The swamp is built up behind beach sands and is currently covered with sedges and grasses and surrounded by expanding Metrosideros forest. Organic clays and silts with fine organic lenses overly basal clays with lower concentrations of pollen and spores. Based on two recent radiocarbon ages, taken at the core base, this short 42 cm record only captures up to 250 yr cal BP of vegetation change on the island. As Raoul was initially colonised by Polynesians around 700 yr cal BP and probably abandoned soon after the main faunal resources had been exhausted (Anderson, 2001), this core does not provide any indication of initial human colonisation of the island. Rhopalostylis palm pollen (Fig. 4 plates I and J) is abundant in the basal zone of the core along with Pseudopanax (Araliaceae) and Homalanthus (Euphorbiaceae) pollen and may represent preEuropean impact vegetation. Spikes in charcoal particles and Poaceae pollen appear above this zone (pastoral grass zone) in association with the rapid displacement of forest taxa. This zone is followed by a prolonged period of fern dominance (fern zone). These changes may represent initial European settlement of the island beginning in 1814 at Denham Bay following the establishment of a whaling station on the island. Goats and pigs were introduced on the island sometime before 1836 in the process of expanding the whaling station (Straubel, 1954). Sheep were brought on to the island in 1883–84 after the cessation of the whaling industry and large tracts of low elevation forest were cleared for pasture. In the upper part of the core Rhopalostylis and Metrosideros re-enter the record in greater abundance. The expansion of these taxa followed the end of farming practices in the mid-1900s and the eradication of feral goats and pigs in the 1970s (Sykes and West, 1996). Rhopalostylis has survived throughout recent historical impacts on the vegetation of Raoul re-colonising areas previously cleared for agriculture. The Denham Bay palynological record shows that prior to the expansion of European settlement on Raoul, Rhopalostylis was probably more abundant and may have dominated the coastline of the island. This palm re-colonised the island after the 2200 yr cal BP Denham Bay eruption that resulted in decimation of the islands biota. Seeds were probably sourced from Norfolk (Australia) and dispersed by birds, most likely parrots and pigeons. No bird dispersal of palm fruits from distant islands has been recorded on Raoul, although R. sapida seedlings have been found on Tawhiti Rahi in the Poor Knights islands (Fig. 1) dispersed by birds more than 20 km from mainland New Zealand (West, 1999). 4.7.3. Palms unknown in wild as indicators of island extirpation There are a number of palm species in the oceanic Pacific islands that are thought to have otherwise originated in the region but have never been recorded or collected in an unequivocal wild state. Among these is Pelagodoxa henryana (Arecoideae) which was first described from Nuku Hiva, Marquesas, French Polynesia from a grove apparently associated with cleared land near a village. Brown (1931) noted the occurrence of Pelagodoxa from Raivavae, Austral Archipelago, French Polynesia and assumed that this palm was transported to the island from 2563 Nuku Hiva. This species is also known from adventive populations in Vanuatu and the Solomon Islands (Dowe and Chapin, 2006). The closest relatives of P. henryana occur in New Guinea (Stauffer et al., 2004). Other species of unknown provenance include Pritchardia pacifica, which is most likely to have originated in Fiji, but no wild populations presently occur there (Hodel, 2007). This species is very widely cultivated in the oceanic Pacific islands, and is adventive and naturalised on many islands (Dowe and Cabalion, 1996). A further two Pritchardia species, P. pericularum and P. vuystekeana were described from cultivated plants in Herrenhausen Gardens, Germany, though their provenance was recorded as the Tuamotu Archipelago. However, no species matching the descriptions of either of these have been recorded or collected there, and the only Coryphoid palm species that occurs there, P. mitiaroana on Makatea, bears little resemblance to either taxa (Hodel, 2007). It is probable that the wild populations of the four abovementioned species have been extirpated. 5. Conclusions We have examined the available fossil records and more recent historic evidence showing declines, extirpation or extinction of palms from the oceanic Pacific islands. Palaeoecological records of the genus Pritchardia provide the best evidence for human-mediated extirpation with three island records situated outside its modern distribution. In many of the palaeocological records examined extinctions or extirpations are identified by monosulcate pollen indicative of the palm family but not diagnostic of higher orders beyond subfamily. In these records extirpation or extinction is determined by the modern absence of extant palms with this pollen type. Further systematic microscopy is being conducted to determine the generic affinity of these fossil types, now possible for many genera of the Arecaceae using electron microscopy (Dransfield et al., 2008). A number of palaeoecological records show the prevailing ecological trends both before and after human colonisation. Pleistocene records, from Rapanui and O’ahu (Hawaiian Islands) show that palms responded quickly to rising precipitation levels and temperature after the LGM, but declined in the Holocene as other wet forest taxa became more abundant (Flenley et al., 1991; Hotchkiss and Juvik, 1999). There is no evidence to suggest that palms approached extinction following abrupt regional climate change events recorded from a range of climate proxies elsewhere in the Pacific. Prior to human impact, changing island insularity associated with geological activity and fluctuating sea-levels are the most likely causes of abrupt palm decline or extirpation. The probable extirpation of Pinanga from the coastal lowlands of Vanua Levu, Fiji by around 5000 yr cal BP may have resulted from rising sea-level. Several late Holocene palaeoecological records from a number of islands reveal strong evidence for human-mediated palm decline and extinction. In most records a close correspondence exists between evidence for rapid forest clearance indicated by increased charcoal particles and declines in pollen of forest taxa, including palms. Some records also reveal the rapid invasion of introduced weed species, further indication of human-mediated habitat modification. 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, palms probably occupied prime soils preferred for C. esculenta cultivation by the Polynesian population. The selective impact on large trees, including palms, occupying large tracts of productive land was inevitable and essential for sustained island colonisation. On larger and less remote islands extinctions or extirpations are rare despite the abundant evidence for substantial vegetation change following 2564 M. Prebble, J.L. Dowe / Quaternary Science Reviews 27 (2008) 2546–2567 initial human colonisation. The decline of the lowland and coastal palm genus, Metroxylon, on the large islands of Fiji, may represent the combined effects of changing coastlines following mid–late Holocene sea-level fluctuations that left coastal palm populations more vulnerable to initial human impact at around 3500 yr cal BP. Historical records of human activity on the oceanic Pacific islands reveal that feral animals and invasive weeds introduced since European colonisation have had a profound impact on palm populations. Long-term botanical survey data and ecological studies have revealed for many oceanic island palms that every aspect of the ecology and biology of palms has been affected by invasive species. Such effects include, seed predation, disruption of pollination and seed dispersal and direct damage from herbivores. These studies have also shown that the invasion of exotic species has continued following repeated burning of indigenous forest resulting in the rapid decline of palms. The historically documented ecological disruption caused by invasive alien species and the direct human modification of indigenous forest habitats leaves few other plausible mechanisms that could explain extinction events, both now and in the past. From this review of evidence for palm declines on oceanic Pacific islands we conclude the following: 1. The diversity of palm lineages in the oceanic Pacific islands drops with the increasing remoteness of islands. 2. Fossil pollen records of palm declines, extirpations and extinctions are biased towards more remote oceanic islands. 3. Little unequivocal fossil evidence is available to suggest that late Quaternary plant extinctions, namely of palms, occurred on oceanic islands prior to human colonisation. However, extinctions can be inferred on the basis of changing island insularity associated with geological activity and fluctuating sea-levels (i.e. marine inundation of islands). 4. Palm species now absent on oceanic Pacific islands were widespread and locally abundant. In addition, palms may have been predisposed to extinction given their size (<10 m in height) and slow reproductive rates. 5. Palms often dominate environments with high humidity, high rainfall and fertile soils, but on remote oceanic islands these areas were preferred for crop cultivation at initial human colonisation suggesting that palms were predisposed to human-mediated extinction. 6. Long-term ecological data of islands only recently colonised by humans suggests that the loss of seed dispersers and pollinators following human colonisation has also contributed to palm decline and extinction. Acknowledgements We thank a number of people for freely sharing their datasets: G. Hope, D. O’Dea, J. Stevenson, S. 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