Human vs Climatic Impacts at Rapa Nui or, Did the People Really Cut Down All those Trees?

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Proceedings of the Fourth InternationalConference on

Easter Islandand East Polynesia

University of New MexicoAlbuquerque, 5-10 August 1997

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Proceedings of the Fourth International Conferenceon Easter Island and East Polynesia

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85

Human vs Climatic Impacts at Rapa Nui: Did the People Really Cut DownAll those Trees?

RosalindL. Hunter-Anderson

IntroductionThat the now mostly treeless, grass-covered Pacific

island, called Rapa Nui by its people, once supportedpalms and other woody vegetation has been known sinceSelling's identification of microscopic pollen in paleo-sediment cores taken during the Norwegian Archaeologi¬cal Expedition (Heyerdahl and Ferdon 1961). This intrigu¬ing botanical find was later corroborated by John Flenleyand his associates (Flenley and King 1984; Flenley et al.1991), who analyzed the sediments in longer cores ob¬tained from three of the island's volcanic craters, RanoAroi in the north, at 410 m elevation; Rano Kau in thesouthwest, at 110 m, and Rano Raraku in the southeast, at75 m (Figure 1).

The cores, some of which extend some 37,000 yearsinto the past, contained pollen, spores, and charcoal parti¬cles that reflect, albeit obliquely, Rapa Nui's previouslandscapes. Detailed analysis of these data yielded theimage of an island once covered by a palm forest, trans¬

formed over a relatively short time, ca. 1000 years, into thegrassland Rapa Nui is today. The last part of this landscapechange coincided with human occupation, which prompted

Flenley and his associates to suggest a scenario connectingthe actions of the Rapanui people with the decline and finaldecimation of the island's forest and its replacement bygrasses (Flenley et al. 1991; Bahn and Flenley 1992; seealso Diamond 1995).

The Human-Impact ScenarioAccording to this scenario, when people first settled

the island ca. 1550 BP (before present), Rapa Nui wasthickly forested, except for its highest elevations. Thedominant tree was very like Jubaea chilensis, the statelywine palm of Chile, which can reach a height greater than80 ft and a diameter greater than 4 ft (Hortis 3rd 1976).Woody shrubs and small trees were also present, as were

various grasses, some which are now extinct.Rapa Nui's first settlers brought with them

several tropical Pacific cultigens and domesticanimals, including chickens. In addition, theyintroduced a small rat, whose significance will beapparent shortly.

Immediately upon settlement, the peoplebegan to remove the native palms, using fire tomake room for gardens. Trees were cut for fire¬wood, canoes and other wood-consuming activi¬ties such as transporting and erecting Rapa Nui'sfamous stone images upon platforms.

The human population increased over time,and so did the burning and felling of the large,native palms. As the deliberate deforestation con¬tinued unabated, the palm trees became rare andserious erosion and soil exhaustion ensued. Tomake matters worse, the imported rats ate thepalm fruits (as did the people), which severelydiminished the regeneration of the trees and con¬tributed to their demise. Owing to human and rat

activities, by 500 BP, the forest had all but disappeared,and an extensive grassland had taken its place.

The authors enlivened this scenario with a psycho-anthropological ingredient, implying that, just like theresource-extracting enterprises of the commercial worldtoday, indigenous subsistence fanning and fishing societiescontinuously exploit the natural resources of their environ¬ment until they are totally depleted, without regard to the

RANO KAU

RANO RARAKU

Figure 1. Map showing coring sites (from Flenley et al. 1991).

5

86 Rosalind Hunter-Anderson

long- and short-term consequences of their actions. Thus,if subsistence farmers need to clear forested land forgardens, they clear continuously until all the forested landhas been cleared and all the natural vegetation has beendestroyed. Suppose they need wood for firewood and formaking canoes; they continue to fell trees until all havebeen wiped out. The driving force accounting for thisbehavior is genetically inborn human selfishness (Bahnand Flenley 1992:86). At Rapa Nui, this "selfish-gene"-driven behavior was what decimated and exhausted theentire native palm population and all previously fertileland.

As the last palm tree was felled, no more timber wasavailable for firewood and building ocean-going canoes,and no more tree trunks were available for statue trans¬portation. Without the palms, people had to rely upongrasses to fuel their earth-ovens, and the statue-buildingcustom had to be abandoned. As the last canoe on theisland wore out, people could no longer engage in oceanfishing. In the absence of fish, they relied upon chickens,which became so valuable that they were kept in stonehouses so as to prevent their theft.

Unable to escape from the island, people started tofight, and some resorted to cannibalism and living incaves.The prominence of fighting led to the rise of a birdman cultwhich emphasized the physical prowess of young warriors,and that was the state of affairs when the first Europeansarrived in the late 18thcentury.

In the remainder of this paper Ipresent my misgiv¬ings about this scenario and suggest an alternative, geo-climatic understanding of the late Holocene decline ofRapa Nui's palms. Let me begin with the scenario'spsycho-anthropological fantasies about subsistence agri¬culture and its alleged ill-effects upon the environment.

Subsistence Agriculture

As an anthropologist who has been studying indige¬nous farming and fishing practices in Micronesia for over15 years, and who is familiar with the pertinent literatureon the subject, Ican attest to the patent falsehood of theportrayal of subsistence farming in the scenario. Irealizethat the image of subsistence-level societies depleting,ruining, and exhausting their environments through relent¬less resource exploitation is common in the speculativesections of the archaeological and related literature, partic¬ularly in the Pacific (e.g., Kirch 1984; Dodson 1992;Steadman 1995).

Yet despite its pervasiveness in that literature, theimage is not borne out by ethnographic reality. Rather itappears to be a product of the imagination of people whoproject their personal experience with human/natural re¬source relationships characteristic of modern commercialsocieties, upon an unfamiliar world (to them) of indige¬nous subsistence-level societies.

In modern commercial societies, where many if not

all human-natural resource relationships are shaped by

economic specialization, the behavior of most naturalresource-extracting enterprises, such as mining, fishing,and logging firms is dictated by economic (not ecological)considerations. In order to survive, pay creditors, meetpayroll, remain profitable, and so forth, they continuouslyextract the target resource until it is depleted, irrespectiveof undesirable consequences to others. For someone grow¬ing up in the modern commercial milieu, witnessing theunabated extraction of natural resources by industry is adaily experience. This experience becomes so internalizedthat it is projected by default upon the unfamiliar world ofsubsistence economies.

However, the facts gathered by objective and focusedgeographical, botanical, and ethnographic studies showthat subsistence farmers actually implement an extensiverepertory of practices and customs which are designed toinsure that nothing is removed from the environment inquantities exceeding the rate of natural rejuvenation.1Sub¬sistence agricultural practices which have been shown toprevent soil loss and to enhance soil nutrient status includefallowing, mulching, terracing, and crop rotation; for nu¬merous and interesting details, see Conklin (1957), Kun-stadter (1978), Zinke et al. (1978), Sabhasri (1978), andRuthenberg (1980). With respect to the human-impactscenario's claims regarding the use of fire in deforestationand other inaccurate assumptions about subsistence farm¬ing, consider the following contrary observations.

FireSubsistence farmers use fire with great caution and

sometimes not at all, depending upon the crops to begrown and the natural setting of the garden plot. Uplandrice swiddens planted in the forest require an even andthorough burning of the slash, in order to immediatelyrelease nutrients into the soil and to provide full sun to thefast growing seedlings. In tuber-dominated swiddens, theuse of fire is very limited or entirely absent, as Iwill showin a moment. Even where the burning of slash must bethorough, as in the rice swiddens of the Lua' of northwest¬ern Thailand, farmers cut fire breaks along the edge of theplot to be burned to prevent the fire in one plot fromspreading into adjacent fallow fields, and they avoid cut¬ting or burning trees on ridge tops, narrow gullies, bound¬aries between cultivation zones, and the edges of water¬courses (Zinke et al. 1978:140).

The Lua' case is not typical of small Pacific islandfarming systems because it involves rice grown as a staple.In the Pacific islands, tubers such as taro, yams, and sweetpotatoes are the dominant crops, and their cultivation doesnot involve thorough and complete burning prior to plant¬ing. For example, in preparing a forest garden in Yap, ahigh volcanic island in the western Carolines, the slash isburned but not whole trees, which are left standing to serveas supports for the yam vines (Hunter-Anderson 1983,1991). Fire may be applied to the base of some of thelarger trees, shocking the leaves off, which lets in light for

6

Human vs Climatic Impacts at Rapa Nui 87

the short time needed by the immature plantings. Afteractive harvesting ceases in 1-2 years, the tree stumps in theplot have already sprouted and recovery of the forest hasbegun, augmented by roots and seeds from adjacent fallowplots. This maintains the correct conditions for Cyr-tosperma chamissonis, grown in nearby pits; unlike Colo-casia esculenta, this aroid requires the dappled sun of theforest.

In the preparation of mound-gardens in the grassyuplands of northern Sumatra, fire is not used at all; asimple turning under of the surface layer with grass rhi¬zomes intact is sufficient to provide a nutritious plantingmedium for rice and the other crops grown in these opensettings (Sherman 1980). In Yap, sweet potato mound-gardens in the non-forested interior savanna are treated inthe same manner (Hunter-Anderson 1983; 1991).

Enhancement of NaturalEcosystems

Subsistence farming involves practices that actuallyenhance the natural vegetation, both in forests and ingrassy areas, by augmentation. For example, since Yapwas settled over two thousand years ago (Gifford andGifford 1959; Intoh and Leach 1985), the natural forestshave been converted into "agro-forests" by selectiveculling and adding cultivars needed for house and canoeconstruction, medicine, and-artifacts as well as for food(Falanruw 1994).

Similar forest management practices have been ob¬served elsewhere in Micronesia (Hunter-Anderson 1991).As in the African savanna (Fairhead and Leach 1996),deliberate and systematic planting of useful trees andshrubs is practiced in Yap's savannas, for example, innewly settled areas, and along pathways to provide shadeand coconuts. The net effect of these practices is to in¬crease the diversity and quantity of woody vegetationwhere, without human intervention, grasses, ferns, andother low herbaceous vegetation tend to prevail (Hunter-Anderson 1983, field obs. 1980-1990).

ManagingErosionandMoistureAvailability

In seasonally wet climatic regimes, subsistence farm¬ers minimize erosion of slopes by channeling excess water

away from plots (Hunter-Anderson 1983, 1991); they alsolay logs across slopes, build terraces from dirt and rocks,and plant along slope contours (Kunstadter et al. 1978). Insloping Lua' plots, such techniques result in negligible soilerosion rates; recent studies show soil loss to be 1.15 mmper ten years, or 11.5 cm per millennium (Zinke et al.1978:153). In warm, dry regimes, and here Rapa Nui isexemplary, several techniques to maximize the moistureavailable to cultigens and to prevent wind-sun-burn havebeen recorded (Metraux 1940). These include plantingbananas, Sophora trees and other crops in mulchedpits andcrevices fed by runoff or underground fresh water seepsand flows, and building up rock walls around vulnerableplants. Deep planting of Colocasia esculenta (taro) in open,

rocky soils is another measure taken to reduce moistureloss and heat stress.

PalmWood UsesCanoes

Next Iwish to address the scenario's assertions re¬garding the uses of palm wood. For example, it is claimedthat the Rapanui felled the native palms to provide lumberfor making canoes. This is dubious in light of the Pacificethnographic record which indicates that palm wood isgenerally avoided for building canoes. The preferred woodis from dicotyledonous trees, such as breadfruit(Artocarpus altilis) and mahogany (Calophyllum inophyl-lum)~ The near-universal avoidance of palm wood appearsto relate to its high specific gravity. John Tamagyron, anexperienced canoe builder from Yap, told me recently(pers. comm. 1997) that coconut palm wood (niu inYapese, Cocos nucifera)3 is not used for canoe hulls be¬cause it does not float well (it is "too heavy"). Sailingcanoes must be made of the lightest wood possible since aheavier wood hull is harder for the wind to push. The woodof the dicots such as breadfruit and mahogany floats well,does not become waterlogged, and is strong—yet it can beadzed into a variety of shapes quite precisely. Repairs areeasily made on dicot wood canoes; the damaged part issimply cut out and a custom-shaped piece is fitted in. Thiscannot be done with palm wood due to its splinteringfracture pattern, according to the Yapese.

Given the properties of palm wood, and if the RapaNui palm was similar to Jubaea chilensis, the assumptionthat Rapa Nui was an exception to the rule of Pacific islandcanoe building is especially problematic. According toGurley and Liller (1997), the tough outer bark of Jubaeachilensis is extremely hard (like ivory or bone) and verythin (5 mm). These attributes would make it impossible toshape the logs by adzing, and canoe hulls hollowed out

from palm logs would quickly break up in the ocean.Where dicot wood is rare or the available dicot trees

are small, people still prefer this kind of wood over palm;they build the hulls from patches and slats, cutting andfitting the pieces together over a light frame (see Haddonand Hornell 1975 for examples). Rapa Nui is a highvolcanic island that supports suitable dicot trees, for exam¬ple, Thespesiapopulnea (mako 'iin Rapa Nui), a relativelylarge coastal tree that grows to 60 ft (Hortis 3rd 1976), andSophora toromiro, which is a small tree recently extinct butpresent throughout prehistoric times and called toro-miroby the Rapanui.

According to Rapanui wood carvers such as TitoHotu and others (pers. comm. 1997), palm wood "sinks"and would not be suitable for a canoe; these expertsexplained that mako'iwood probably was used for canoessince it swells and contracts with heat and cold withoutcracking and is relatively light and easy to work yet strong.The trunk of toromiro reportedly grew to 20 inches indiameter; according to Cook, it grew as big around as a

7


man's thigh (Metraux 1940:16), clearly big enough for apatchwork canoe. According to the few extant descriptionsof indigenous Rapanui canoes (Haddon and Hornell1975:96-103), they were of the patchwork type—madefrom fitted pieces (type of wood unspecified).

Movingthe StatuesIntriguing but also dubious is the scenario's sugges¬

tion that palm trees as tall and large as Jubaea chilensiswere cut down, with destructive frequency, to assist in thetransport of stone statues. If palm logs were used as rollersor levers, they need not have been used once and thendiscarded, but rather saved for re-use in future transportepisodes. Re-using the logs would have reduced the rate ofpalm felling to a non-destructive level, but regardless ofre-use patterns, the frequency of transport episodes wasprobably far too low to have had any effect upon the totalpalm population, considering the number of statue-bearingplatforms ever built on the island.

To estimate how often statues were transported andset upon platforms, we can take the high estimate of 300built platforms, obtained from archaeological surveys(Bahn and Flenley 1992:147) and then multiply 300 plat¬forms by 3, which is an estimate of the average number ofstatues set upon a platform. The product is 900 statue-

moving events. If the practice of statue emplacement uponplatforms prevailed from AD 750-1680, that is, for about930 years, then, on average, there were about 1.03 statue-

moving events per year during this time. The rate of statuequarrying and emplacement upon platforms seems to haveincreased later in prehistory, but, if so, all the more reasonto expect that the logs used for one transportation eventwere re-used in the same year or adjacent years. ThatJubaea chilensis logs last for several years is indicatedfrom the investigations of Gurley and Liller (1997); onelog which had lain dead in the forest for 20 years exhibiteda density between 200 and 540 kg/m. If such long-lastinglogs were harvested for statue transportation, they couldhave been curated and re-used for long periods, postponingthe cutting of more trees and reducing overall tree con¬sumption.

The use of logs as rollers or rails for moving theheavy monoliths is questionable considering that there isample ethnographic evidence that cultural practices aregenerally congruent with the principle of least effort (seeZipf 1949). Accordingly, the prehistoric Rapanui wouldhave kept monolith transport effort to a minimum byengaging in this behavior as infrequently as possible whileusing the lightest materials that would suffice to accom¬plish their goals. Put simply, they would refrain fromencumbering the already-difficult task of handling thelarge stones by also cutting down and bringing into posi¬tion very large and heavy logs every time a monolith hadto be moved.

InOceania the usual methodof moving heavy objectsis to drag them over a layer of slick organic material such

as grass, palm fronds, or small bamboo stems; large andheavy logs, canoes, and stones are moved using thismethod.

Raising a heavy object upon log rollers or runnersseems unnecessary when it could be dragged along theprepared ground surface without them. The number ofpeople doing the dragging may have been large, but thatwould not make the work harder, it would make it easier!While the reasons cannot be discussed here, due to spacelimitations, the participation of many people in such socio¬political events is desirable (see Hunter-Anderson and Zan1996), and modern researchers' preoccupation with mini¬mizing the number of participants in stone-moving events,through technological solutions, reflects an ignorance ofethnographic reality in the Pacific.

FirewoodCutting down live palm trees for firewood, as sug¬

gested in the scenario, is quite unlikely given knownethnographic practices and the archaeological record. Car¬bonized fragments of palm endocarps have been found inRapa Nui's earth-oven features, whereas no palm wood hasbeen identified in these contexts, to my knowledge.4This isin keeping with practices elsewhere in the Pacific, wherethe usual cooking fuels are the dry husks and shells ofcoconuts, as well as dead branches and rotten tree trunks ora variety of trees. In contrast, live tree trunks and branchesare reserved for the construction of permanent structures,such as houses, and for making smaller objects like bowlsand boxes. Dicot trees are used for these purposes becausecoppicing does not kill the trees; in fact the injury stimu¬lates regrowth. Straight trunks of monocots like betel nutand coconut palm may be uspd for house posts and floor¬ing, but usually the trees are not cut down until they havestopped bearing. After the wood posts have rotted and needreplacing, they may be chopped up and burned as fuel.Because the frequency of building wood structures isconsiderably lower than the frequency of cooking events,the destruction of trees—whether monocots or dicots—forconstruction purposes generally does not exceed their rateof regeneration.

Earliest SettlementPerhaps because the scenario's validity depends

greatly upon a relatively early date for first human settle¬ment of the island, its authors ignored the ambiguitysurrounding the timing of this event. They based theirestimate for human arrival upon the radiocarbon date fromPoike Ditch of AD 386±100 years (ca. 1570 BP), sampleK-502, reported by Smith in Heyerdahl and Ferdon(1961:394). This date is considered unreliable by modernstandards and lacks a clear cultural association; other veryearly dates suffer from similar problems (Spriggs andAnderson 1993; Skj0lsvold 1996). Acceptable radiocarbondates suggest a more realistic estimate for initial settlement

8


is the last half of the first millennium AD, or even thebeginning of the second millennium AD, which wouldbring it into line with the initial settlement dates of Hawai'iand New Zealand (Spriggs and Anderson 1993).The accu¬rate dating of Rapa Nui settlement is critical because manyof the paleo-sedimentary data (reviewed below) cited asindicating palm decline come from sediments that appearto have been deposited between 600 BC and AD 750 (2600and 1200 BP). That is, these data show that forest declinehad started and was going on not only before the realisticdate of first human settlement but even before the datefavored in the scenario.

Patterns inthe Paleo-Sediment DataThe paleo-sedimentologists have assumed that the

charcoal particles in the cores signify human-set fires andthat simultaneous decline in palm pollen counts and in¬crease in grass pollen counts, as well as a parallel temporalshift from mostly large-diameter grass pollen to mostlysmall-diameter grass pollen, indicate human disturbance to

the vegetation. However, inspection of the core profiles (ofpalynomorph frequencies and percentages) indicates thatthese patterns are not really clear, nor does the dating ofthe cores support a direct associationwith human actions.

charcoal to be detected first, with counts increasing upwardin the core. A pre-1500 BP onset of fire would eliminatehuman causation in this case also.

At Rano Raraku, in the upper portion of the RRA3core (Flenley et al. 1991:Figure 18), charcoal particles,while present and "clearly abundant" (ibid. 107), were notcounted in this core, so the timing of onset of fires at ornear this site remains unknown.

A possible source of pre-human fires at Rapa Nui isvolcanic eruptions. According to geological estimates, therelatively young lava flows in the southeastern portion ofthe island "are unlikely to be more than two or threethousand years old and could conceivably be appreciablyyounger" (Baker quoted in Flenley et al. 1991:85).5 Thistime frame generally coincides with the onset of charcoaldeposition at Rano Aroi and Rano Kau, although no vol¬canic ash layer was observed in the cores from these sites.6

PalmPollenDecline, Grass PollenIncreaseConcerning the simultaneous onset of palm pollen

decline and grass pollen increase, in the RRA3 core fromRano Raraku, the shift begins at about 0.90 m, a positionon the core that dates to ca. 480 BP. But this observation

CharcoalParticlesIn the AROI core from Rano Aroi,

charcoal particles are first detected at ca.1.6 m (Flenley et al. 1991: Figure 19).On the age-depth graph (ibid. Figure 10),1.6 m on the core dates to 2600 BP. Notonly is this date for the onset of fires in ornear the catchment too old for humancausation, the consistent presence ofcharcoal particles upward through thecore (increasing from less than 50 at 1.6m to ca. 100 particles near the top) isunexpected at this remote site, whichlacks any archaeological evidence of in¬tensive agriculture or habitation. On theother hand, the charcoal in the core maynot be prehistoric at all, deriving insteadfrom modern disturbances to the uppermeter of the core (ibid. 91-92), with thelower counts representing particles thatpenetrated downward into older sedi¬ments.

At Rano Kau, charcoal particles were relatively abun¬dant at the base of the KAU1 core and were presentupward through the core to the top, with some gaps due to

low recovery rates (Flenley et al. 1991: Figure 20). Thebase, according to the age-depth graph (ibid. Figure 11),dates to ca. 1500 BP. The high basal counts suggest aneven earlier onset of fires in or near this catchment, sincethe usual pattern, as at Rano Aroi, is for small amounts of

Borehole — RRA 2 RRA 3number

- 7 65011209 000±15C

35 260+980-870

7701WC13 B10± IMS

60 80

Distance from bank (metres)

LIVING RHIZOMES

E3COARSE DETRITUS

VOLCANIC ASH

200 c.210

FINE DETRITUS

0CLAY L MUD

Figure 2. Profile of four cores from Rano Raraku (from Flenley et al. 1991).

may be spurious because just below this date, at 1.10 m,the normal deposition of organic detritus was interruptedby a 10 cm-thick layer of in-washed silt and sand (Flenleyet al. 1991:91) (Figure 2).

The interruption effectively erased the palynomorphdeposition history between 1.10 and 1.20 m, spanning atleast 400 years, according to the age-depth curve for thiscore (Henley et al. 1991: Figure 9). The age-depth curve

9


(Figure 3) assumes a relatively rapid and unchanging rate

of deposition at this site, which permitted the analysts toignore the four consecutive dates below the interruption(SRR 2427, SRR 2426, SRR 1679, and SRR 1553). Ifthese dates are valid, and the deposition rate was slower inthis part of the core, then the interruption masks a verylarge portion of deposition history at the site, namely, thelast half of the Holocene! The nearest date below theinterruption at 1.20 m is 7770 BP (at 1.65 m), and the nextthree are 8060 BP (at 2.10 m), 11300 BP (at 3.65 m), and

AGE-DEPTH GRAPH, RRA3 CORE

co

o

>>o*

"Oc0iflDojC

ito»<

36-

32"

28-

24-

210 Pb rate

SRR"

SRR"SRR*1554

SRR- 2420

f SRR-

SRR- / 1585

2428 '

8I

10i

12

Depth im)

Figure 3. Age-depth curve RRA3 (from Flenley et al. 1991).

11970 BP (at 4.7 m).Ambiguities in the dating of these deposits prevent an

accurate estimate of when the palms began to decline andthe grasses to increase. These changes may have started asearly as the mid-Holocene, or, if the age-depth curve iscorrect, as late as 900 BP. One way to clear up thisambiguity would be to analyze the palynomorphs from theRRA4 core, taken far from the bank where no erosion lensinterrupts the deposition sequence (Figure 2).

In the AROl core from Rano Aroi, no decline inpalm pollen can be seen in sediments dating to the last1,500 years nor indeed during the entire Holocene (Flenleyet al. 1991: Figure 19) (Figure 4).

Figure 4 shows a small increase in palm pollen at1.70 m, dated ca. 2100 BP; thereafter palm pollen countsresume their previous lows upward through the core. Grasspollen also shows no distinct rise and is relatively abundantthroughout the Holocene sediments, which encompass the

upper 3 m. However, the dating of these deposits is am¬biguous. According to Flenley et al. (1991:91-92), rootsmay have contaminated all the dating samples, producingtoo-recent dates throughout the core. If the 2100 BP datefor the brief rise and then resumption of low counts ofpalm pollen is correct, this event took place too early tohave been caused by human activity, and if the 2100 BPdate has been contaminated with modern roots, as Flenleyet al. (1991) suspect, an even stronger case can be made for

332> ÿ<U LOV«J "

if <J°V

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111>0ÿ 750-••O

*»R-1T91

)4440ÿ noo

SRR-2421

37110ÿ UOO-1040 i_i i i i » <

SO JO 10

Fig. 4: Profile segment from Rano Aroi (alt. ca. 425m) bore¬hole 1 (from Flenley et al. 1991).

non-human agency.At Rano Kau, beginning ca. 1350 BP, the upper 7.5 m

of the KAU1 core shows a pattern of simultaneous palmpollen decline and grass pollen rise (Flenley et al.1991:Figure 20) (Figure 5).

However, palynomorphs of any kind were scarce inthis record, creating data gaps that put the robustness of the

10


pattern in doubt. Assuming it is reflective of a vegetationchange, and human actions were responsible, forest clear¬ance must have been intensive prior to 1350 BP to haveeffected such major changes in the vegetation near thesite.7 Yet there is no archaeological evidence for such earlyactivities. Rano Kau, overlooking steep ocean cliffs, wasnot the site of an early settlement, and the annual cere¬

monies at Orongo on its south flank began after the cessa¬tion of stone platform and statue construction in the late1600s (McCall 1979; Stevenson 1986).

S

Irt llf// /

3 -

BW-Mll

iooo,,,\±TQw\ÿ W»-24;

1040

Fig. 5: Rano Kau profile segment (alt. ca. 110m) borehole 1(from Flenley et al. 1991).

Large-Diameter and Small-Diameter Grass PollenFlenley and King (1984:49) suggested that the large-

diameter grass pollen, which is prevalent in the Pleistocenelevels of cores from Rano Aroi and Rano Raraku, signifiescooler temperatures. This interpretation was dropped in1991, when deliberate deforestation was invoked to ex¬plain the temporal trend from mostly large-diameter to

mostly small-diameter grass pollen. Nonetheless, the dis¬appearance over time of large-diameter grass pollen is not

clearly associated with human occupation or actions. In theAROI core from high and remote Rano Aroi, where there

is no archaeological evidence for early settlement nor foragricultural activity within or near the catchment, this trendis the most pronounced. At Rano Raraku, non-humancauses for changes in grass types are indicated as well;large-diameter grass pollen is relatively abundant in thelower portion of the RRA3 core but essentially disappearsfrom the record after a volcanic ash layer was deposited at

5.2 m, dated to ca. 14,000 years ago. Small-diameter grasspollen, barely present prior to the volcanic activity, doesnot become abundant until the uppermost meter, which isyounger than 480 BP and extends into modern times.

The pattern of grass-pollen-size changes at RanoRaraku suggests two independent causes, one associatedwith volcanic activity, and the other related to conditionsin late prehistoric and historic times. The latter cause,giving rise to small-diameter grass pollen after 480 BP,occurred too late to be correlated with initial human settle¬ment and deforestation, and the former cause is unrelatedto human actions.

The KAU1 core from Rano Kau, with its relativelyshort record of 1,500 years and sparse palynomorphs, doesnot cover the late Pleistocene period when large-diametergrass pollen is dominant at the other sites. From the base ofthe core at 9.8 m, upward to 4 m, dated ca. 1000 BP, grasspollen of any kind is rare and that which is present haslarge diameters. At 4 m, a gradual shift begins, lasting until500 BP, when the record stops at 1.8 m due to a lack ofpollen. The shift is from very low counts of large-diametergrass pollen and practically no small-diameter grass pollento relatively high counts of medium- and small-diametergrass pollen. Along the core, the segment without pollen is40 cm long. Pollen was again countable at 0.20 m, inmodern deposits, which yielded very high counts of small-diameter grass pollen and practically no large-diameterforms. Flenley et al. (1991) speculate that the majority ofsmall-diameter grasses represented in the top 20 cm of thecore were historically introduced types which came toRapa Nui along with the horses, cattle and sheep that havebeen present for over 100 years. Thus the case for destruc¬tive prehistoric human impacts based upon the record ofgrass pollen grain size at Rano Kau is quite weak.8

ErosionWhenever addressing soil erosion, the scenario is so

fixated on the idea that it must have been caused by forestclearance that the normal and natural conditions underwhich soil loss occurs are ignored (Wischmeier and Smith1978).' The physical evidence for erosion in the cores ismore simply accounted for by water-saturation and slump¬ing of soils, from heavy or prolonged rainfall, earthquakes,and a climatically determined open vegetation—factorsconsistently known to cause soil loss on steep slopes.Episodes of soil erosion were inferred in the coring analy¬ses when narrow lenses of terrestrial materials were seenbetween layers of organic detritus that make up the bulk ofthe cores. In fact the stratigraphic positioning of these

11


erosion lenses does not support human causation. Forexample, according to Flenley et al. (1991:89), a 10 cm-thick erosion lens of silt, sand and gravel was observed inthe Rano Raraku RRA3 core at 1.10-1.20 m (Figure 2).

The authors believe this lens washed into and accu¬mulated at the bottom of Rano Raraku's lake during theconstruction and removal of stone statues, when "such anamount of human activity as partially or totally to destroythe vegetation nearby" (Flenley et al. 1991:106) was takingplace. However, the radiocarbon date obtained from mate¬rial within the lens is 6850 BP, clearly before any humanactivity. This anomalous early date was explained as con¬tamination from old carbon in the soil and rocks of thelens. The 480 BP date, just above the lens, in the detrituslayer into which it protrudes, is the one assumed to becorrect; according to the age-depth graph for this core(Figure 3), at 1.10-1.20 m the sediments would have beendeposited ca. 1200 BP. Although 1200 BP may be withinthe human occupation period, it is far too early for the peakin the quarrying of stone for platforms and statues, whichoccurred several centuries later.

BOREHOLE

IIHO: usrno«rri

»H0! >MKIN: ISOIt 210: 100

"HMO.tOOO

IHUO.I IOC

vertical exaggeration 2-5 x

p uo*i no

30 40 50

Distance from bank (metres)

ÿ LIVINGRHtZOMfS

¥ ¥ V» *

SEDGEFEAT

w/ / /

C0AASEdetains

FINE iCOARSEDETRITUS

Figure 6. Rano Aroi cores diagram (from Flenley et al. 1991).

The erosion lenses in the cores at Rano Aroi alsohave dating problems (Figure 6). In the AROI core, thelower lens lies between sediments dated 28670 BP and34440 BP, and the upper one lies between sediments dated7680 BP and 10960 BP, making an association with humanactivity impossible. Flenley et al. (1991:92) state that eventhese dates may be too recent due to contamination frominverted floating mats of vegetation. At Rano Kau (Figure5), no erosion lens was detected in the cores, although thearchaeological remains of an extensive agricultural terracesystem are still visible on the slopes of this crater (Ferdon

1961; McCoy 1976, 1978). If forest clearance for quarry¬ing and for gardens to support those living at the quarrywere indeed the cause of soil erosion at Rapa Nui, thereshould have been several lenses at Rano Kau.

BiologicalProblemsPalmAnalogs

There are also problems with biological aspects of thescenario. For example, the selection of Jubaea chilensis asthe likely analog for the Rapa Nui palm is incongruent withpaleontological standards for identifying fossil life forms.

The assessment of Dransfield et al. (1984) is that theRapa Nui palm pollen morphology indicates only that itwas a member of the cocosoid tribe, and that the fossilpollen could, not be distinguished from that of Cocosnucifera, the coconut palm. Despite the similarities be¬tween Jubaea chilensis endocarps and the similarly sizedand shaped subfossil endocarps found at Rapa Nui(Dransfield et al. 1984), in the absence of the inflorescenceand flowers, it was "not possible to indicate whether theEaster Island palm is an extinct species of Jubaea or

whether it represents a distinctgenus" (Dransfield et al. 1984:751).

Equating the Rapa Nui palmwith Jubaea chilensis ignores the sig¬nificant environmental differencesbetween coastal Chile and tiny, iso¬lated Rapa Nui well over 2,000 milesaway. The specific climatic differ¬ences between the two environmentsand the implications of these differ¬ences for their floras will be dis¬cussed later. Here Isuggest a moreappropriate analog for the Rapa Nuipalm is Juania austialis (Mart.)Drude (Hortis 3rd 1976). Thought bySkottsberg (1925) to have derivedfrom a tropical American ancestor,this palm is endemic to the Juan Fer¬nandez Islands (Skottsberg 1956; andsee Steussy et al. 1984), which arelocated 1800 miles southeast of RapaNui, at about the same latitude asSantiago, Chile, but 400 miles fromthe mainland. The flora of Juan Fer¬

nandez Islands is classified in a different botanicalprovince from that of coastal Chile, reflecting long isola¬tion (Takhtajan 1986). The fruits of Juania austialis aresimilar to those of Jubaea chilensis and to those inferredfrom the subfossil endocarp found at Rapa Nui. Reachinga height of 25 ft, Juania australis is much smaller thanJubaea chilensis,and like Rapa Nui's palm, Juania australisevolved in the absence of mammals. Flenley et al. (1991)did consider the woody composites from the Juan Fernan¬dez Islands as analogs for Rapa Nui's extinct composites;why they did not consider Juania australis as a more likely

|> ii MOWNCUT

12


analog than Jubaea chilensis fov Rapa Nui's extinct palm ispuzzling.

In the absence of genus-level resolution in the iden¬tity of Rapa Nui's palm pollen, the possibility remains thatmore than one cocosoid genus or species is represented,but has not been detected, in the sediments, particularly inthose deposited during the prehistoric human occupationwhen Cocos nucifera may well have been cultivated, aswere other Indo-Pacific cultigens brought from the west.

Given this possibility, the palm pollen frequencies trackedalong the cores could represent a more complex picture ofpalm abundance and extinction in the upper sediments thanthat depicted in the scenario.

Palm root casts have been observed in lowland soilsexposed at Poike and "on the north side of the road fromVaitea to 'Anakena" (Bahn and Flenley 1992:90), also at

Maunga Tari (Stevenson 1997); the size of the trees whichthe root casts "lined with carbon" (ibid. 87) represent is not

known, nor have these features been dated. Maybe they arefrom coconut trees, maybe not. That the root casts havesurvived into the present suggests that palms have beengrowing on the island relatively recently.

Although the scenario depicts a treeless island whenEuropeans arrived in the late 1700s, the historic recordsuggests that Rapa Nui was not completely treeless. Forexample, Captain Cook observed "woods" in the distance(Cook cited in Flenley et al. 1991). While some of these"woods" may have been banana plantations, they alsocould have included small clusters of other cultivated trees

including toro-miro, whose pollen is present in the upperlevels of the cores at all three sites. Late in the followingcentury Pedro Toro Hurtado, a Chilean resident of RapaNui for four years, observed a number of areas that hebelieved had once supported small forests (Toro 1893 inMcCall 1979:123). The actual constituents of these forestenclaves remain unknown. Toro attributed their demise to

sheep and cattle introduced in the 1870s. The woods seenby Cook and the forest enclave remnants seen by Torosuggest the historically introduced grazers and browsershave been highly effective in maintaining the nearly tree¬

less landscape of today, as Flenley et al. (1991:87) recog¬nized.

RatEffectsAnother biological problem in the scenario is its

suggestion that the Polynesian rat contributed to thedemise of Rapa Nui's now-extinct native palms. Thisproposal was made in the context of the inference thatRapa Nui's palm was very similar in biology to the Chileanwine palm, Jubaea chilensis. Yet, in Chile, rats actuallyhelp in the reproduction of Jubaea chilensis. According to

Grau (1996), in the northern part of Jubaea chilensis 'sgeographical range, two species of mountain rats, Abro-coma benettimuirayiand Otodon degus, eat the fruits, andtheir gnawing stimulates germination of the embryo. Thusthe introduced Polynesian rats' gnawing on the fruits of the

Rapa Nui palm, if the tree was very similar to Jubaeachilensis,would not have prevented, but rather would haveassisted in, its regeneration.

ClimateA climatic cause for palm decline was not considered

in any detail by Flenley et al. (1991:109), who cited a lackof reliable data for the reconstruction of climate during thelast 1,500 years. Bahn and Flenley (1992) dismissed cli¬matic causation using the following reasoning. The periodspanning the late Pleistocene through the mid-Holocenewas marked by major climatic fluctuations— from the cold,arid late Pleistocene to the hot, moist mid-Holocene. Palmtrees on Rapa Nui managed to survive these fluctuations;therefore, palm trees with such a survival record would notdisappear during a single drought in the late Holocene.First, it is completely possible that trees requiring a mini¬mum amount of moisture would survive fluctuations inavailable moisture, as long as it did not fall below theirrequired minimum, but would be wiped out completelyduring a single period in which the amount of moistureneeded did indeed fall below that minimum. Tree extinc¬tion events due to long drought periods during the lateHolocene are not unknown; for example, such an extinc¬tion event is recorded at four paleontological sites in theSierra Nevada (Stine 1994). But more importantly, thecoring data are too ambiguous to favor an interpretation ofradical over gradual decline in palms. A single drought iscertainly not the only climatic condition whose emergencecould have caused a decline in palms.

The issue here is not reconstructing climate but iden¬tifying the causes of palm decline, the increase in grasses,and the presence of fire, all of which have been directlyinferred from the coring data. Human subsistence andother cultural practices do not leave remnants in paleo-sediment cores; therefore it is an even situation: The coresmay lack data for reliable climatic reconstruction but theyalso lack data for reliable reconstruction of cultural prac¬tices. The question remains, which type of factors, naturalor cultural, were responsible for palm decline, grassesincrease, and the presence of fire inferred from the coringdata?

The cores actually do contain some clues as to cli¬matic trends during the last 1,500 years, if we start a littlefarther back in time than that arbitrary cutoff point. Thethree climatic ratios devised by Flenley et al. (1991:109-110) to reconstruct pre-1500 BP climate indicate a coordi¬nated climatic shift ca. 3000 BP, which has implicationsfor the survival of palms and trees generally. The ratio oftrees and shrubs to herbs and pteridophytes indicates mesicvs stressful conditions for the trees; the ratio of grasses toferns indicates dry vs moist conditions; and the ratio ofwoody composites to palms indicates cool vs warm condi¬tions (Figure 7).

All of t!iese ratios at Rano Aroi, the climatically-most-sensitive site, show a shift at ca. 3000 BP, toward

13


warmer, more stressed conditions for trees and more moistconditions favorable for ferns and aquatics within thecrater lakes. The close coordination in the timing of thesechanges suggests Rapa Nui's climate had changed in thelast half of the Holocene, and the effects were becomingevident by ca. 3000 BP.

Isuggest these data indicate that the climate wasbecoming more variable—that is, climatic fluctuations intemperature and moisture were wider and more frequent.The steady continuation of these trends until no more dataare available at Rano Aroi, ca. 1500 BP, suggests that theywere on-going when people first settled Rapa Nui. Theimplication of the late-Holocene shift toward increasingclimatic variability is that prehistoric human actions hadnothing to do with the origin of these trends, which areclearly evident by ca. 3000 BP, and that they had nothingto do with their continuance either. Like the vegetation, thepeople must have been adjusting to the variable climate asthey worked to make their island livable. The reason theprehistoric record stops at 1500 BP at Rano Aroi is becausethe upper meter was disturbed in the 1920s by teams ofbullocks which were used to drag the soil around inattempts to make a small dam (Flenley et al. 1991:91).

Let us look again at the record from Rano Kau,whose KAU1 core covers the 1,500-year period in ques¬tion and for which Flenley et al. (1991:109) offered avegetation history—despite their reluctance to reconstructclimate from these same data (Figure 5). The rapid deposi¬tion of detritus which makes up most of the core's first 10meters began by at least ca. 1500 BP and yielded littlepollen of any kind, as noted previously. Human distur¬bance to the vegetation on the steep slopes of the craterwas cited to explain the declines in tree and shrub pollen,

the increase in grass pollen, and the consistent presence ofcharcoal particles from the base to the top of the core.However, given the climatic trends of increasing climaticvariability as indicated in the climatic-indicator ratios atRano Aroi (Figure 7), climate change on-going since atleast 3000 BP is more likely the cause for these observa¬tions at Rano Kau. An already open vegetation was becom¬ing more open and grassy, and susceptible to fire duringhot, dry periods when spontaneous combustion of deadvegetation at ground surface, in the presence of nearly pureoxygen from super-respiring plants could occur, and/orduring volcanic eruptions. Rainfall more readily ran offinto the crater lakes during rainy episodes. Henley et al.suggested that the thick organic detritus in the cores fromthis site indicates that the surface at Rano Kau was swampythroughout the deposition period. This is consistent withRano Aroi's ratio showing increasing moisture available toferns and aquatics, plant forms that are well-represented inthe KAU1and KAU2 cores from Rano Kau.

A Geo-Climatic ModelThe above discussions are sufficient to motivate con¬

sideration of a geo-climatic model to explain the demise ofRapa Nui's palms. This is in line with McCall's (1993,1994a) suggestion that climatic deterioration characterizedby prolonged and severe droughts during the Little IceAge, broadly from ca. 600-50 BP, or AD 1350 to thepresent century (Grove 1988; Dansgaard et al. 1969;Thompson et al. 1986), prompted the cultural changesreflected in the archaeological record by the late AD1600s. While McCall's focus was upon cultural adjust¬ments, mine here is upon the vegetative ones. Both seembest accounted for climatically. Like McCall, Iam nottechnically trained to create detailed climatic models, but Ican suggest that such a model for Rapa Nui should includethe geo-climatic measure called the Temperateness Index(TI) formulated by geographer H. P. Bailey in 1964 (seealso Axelrod 1967).

The Temperateness IndexThe TI of a given locality indicates the degree to

which mild climatic warmth is evenly distributed through¬out the year (Figure 8). Based on a complex formula usingglobal data, the TI is calculated from a locality's averageannual temperature and its average annual range of temper¬ature, and this result is compared to non-deviating idealtemperature of 57°F. The maximum TI is standardized at100. In effect, the lower a locality's TI, the more theclimate deviates from constant moderate warmth on a dailyand yearly basis. The Pacific coast of Chile is within thesupertemperate climatic zone, that is, locales within thiszone have a TI greater than 65. These supertemperatelocales contrast with more inland settings where tempera¬tures deviate more radically from the ideal.

The present range of Jubaea chilensis, from 30° -40°S latitude, and its wild distribution, which is from 30° -

CUMATE RATIOS, RANOAROI

AR0 ARO ARO

o too

STRESSED ---MESIC

100

—ÿ MOIST

100

WARM

Soure* FUnlayO

Figure 7. Three climatic ratios (from Henley et al. 1991).

14


36°S latitude (Gurlcy and Liller 1997), are within thissupertemperate zone.

The TI has significant biological implications in thatit appears to control diversity of flora, at least on thecontinents; locales with a high TI tend to support a diverseflora (and fauna), and they exhibit a commingling of plantsand animals which otherwise do not occur in the samegeographical area. Highly temperate localities today sup¬port mixtures of tropical and Holantartic or Holartic forms,as well as trees normally seen only in high latitudes or highaltitudes, such as conifers (for several examples, see Axel-rod 1967).

The effects of supertemperateness can be seen inFigure 9, which shows Jubaea chilensis growing alongsidedesert forms such as the Boojum-like tree on the right, andlarge pine trees. In coastal southern California, anothersupertemperate zone, the same diversity of flora is typical,especially where water is regularly supplied. The largetrees in these high-TI settings have put much of theirenergy into structure as opposed to reproduction, manifest¬ing a pattern of slow replacement and individual longevity.But these characteristics can be their downfall under condi¬tions of less climatic evenness and a competitive regimethat favors faster-growing and faster-reproducing formslike grasses.

Rapa Nui's cores indicate a decline in plant diversitywhich could reflect a reduction in the TI over time. InRano Raraku's RRA3 core (Flenley et al. 1991: Figurel8),a decline in the diversity of trees and shrubs is evident by

the onset of the Holocene, when six of the nine majorgenera and family groups tracked in the core have disap¬peared (Macaranga comp., Trema, Urticaceae/Moraceae,Myrtaceae Psidium sim., Coprosma, Sapindus), leavingonly palms, Sophora, woody composites, and Triumfetta.Between ca. 7000 and 500 BP, the woody composites andTriumfetta dropped out. Among the grasses, four of thelargest-diameter forms were gone by the end of the Pleis¬tocene and two more large-diameter forms dropped outbetween ca. 7700 and 1200 BP.

In the Rano Aroi AROl core (Flenley et al. 1991:Figure 19), three of the ten tree and shrub groups(Rubiaceae, Myrtaceae undiff., and Umbelliferae comp.)tracked in the core were gone by the end of the Pleistocene,and between ca. 7680 and 2000 BP, Coprosma, Acalyphacomp., and Sophora dropped out, leaving palms, Trium¬fetta, and Macaranga comp. Among the grasses, the twolargest-diameter forms were gone by the end of the Pleis¬tocene and two more of the large-diameter forms haddropped out by 2000 BP. The KAU1 core from Rano Kaucovers too short a time period to discern whether thepattern seen in RRA3 and AROl is also evident at this site,but comparable data are not presented for the longer KAU2core (Flenley 1993: Figure 2), whose base was dated to9130 BP. However, palms declined between ca. 1600 BPand 900 BP; the woody composites were gone by ca. 1500BP and Triumfetta by ca. 900 BP.

It appears that the changes in climate, reflected in thepost-3000 BP ratios at Rano Aroi, had effectively reduced

TEMPERATENESS OF THE CONTINENTS

PACIFIC

INDIANOCEAN

OCEANOCEAN

CATEGORY GEOGR.R£V..OCT.,1«fl4

SupertemperateTemperateSubtemperate'IntemperateExtreme

M100)

Figure 8. Continental temprateness distribution; the coast of Chile is in the supertemperate catagory (Bailey 1964).

15


Rapa Nui's Temperateness Index, if we accept the abovedeclines in plant diversity as evidence.10 Suppose thiscontribution to a reduction in climatic temperateness weremore frequent and longer droughts, hotter summer temper¬atures and colder winter temperatures occurred. Underthese more variable conditions, all occurring prior to hu¬man settlement, the Rapa Nui palm would have had diffi¬culty competing with faster-growing and faster-reproducing forms such as grasses.

Presently Rapa Nui's TI is 51— barely within thetemperate group, and far from supertemperate Santiago,Chile, whose TI is 67. Locales with a TI of ca. 50 aretypically dominated by grasses. In California these localesare in the great central valley classified by Kuchler asnatural grasslands (Espenshade 1990). Rapa Nui's presentsparse flora and lack of large trees may be due largely to itspresently low TI, interacting with the island's small sizeand extreme isolation, as earlier botanists had suspected(Skottsberg 1956; Van Balgooy 1971) and as predicted bybiogeographic theory (MacArthur and Wilson 1967; Pimm1991). For example, see Figure 10, in which the smallerand more isolated islands support less diverse floras.

Under more temperate conditions in the Pleistoceneand early Holocene, a relatively diverse flora, including theslow-growing, slow-reproducing Rapa Nui palm, couldhold its own despite late Pleistocene aridity. During suchtimes the palm could retreat to low¬land settings out of the wind andwhere soil moisture was greatest. Amajor global warming took place atmid-Holocene, peaking ca. 6,500years ago (Imbrie and Imbrie 1979;Goodess et al. 1992). After thispeak, present climates became es¬tablished in the circum-Pacificarea, including those affected bythe El Nino/La Nina weather sys¬tem with its alternating droughtsand excessive rainfall episodes(McGlone et al. 1992; Markgraf1992; Sandweiss et al. 1996).

In an alternative, geo-climaticscenario for Rapanui, people ar¬rived at Rapa Nui on the crest ofthe last wave of eastward humanradiation into the Pacific ca. 1000BP, a "population pulse" associatedwith the favorable conditions of theLittle Climatic Optimum that pre¬vailed from ca. 1200 to 600 BP (Figure 11). They found amostly grass-covered island with few beaches; swampy,high-elevation calderas; and few trees and shrubs, growingin protected lowland locales. At first, the climate wasfavorable, and tropical cultigens could be grown withmoderate success. The population increased, and settle¬ment was extended into the interior, and ocean voyaging

Figure 9. Santiago garden with Jubaea chilensis, conifers,and desert palms (from Bahn and Flenley 1992).

was still a part of the culture. The native palms were on thedecline but never actually went extinct. With the coolerweather and severe droughts of the Little Ice Age (Figure11), the coconut trees failed to bear and even the heartiertoromiro trees became less common and harder to raise.Sweet potatoes (Ipomoea batatas), obtained from the main¬land, became the most important food crop since theycould tolerate a wide range of temperatures, and goodharvests were possible when the rains were adequate

1000

o>100

10

A LPT

_1_

30 100 10002

island area km

10000 100000

Figure 10. Relation between island size and number of flowering plant genera; islands be¬low the line are all very isolated; Rapanui is marked by a triangle and the letter E (from Coxand Moore 1980).

(especially during El Nino episodes). Nonetheless popula¬tion declined due to an overall reduction in agriculturaloutput, and many cultural adjustments had to be made.

Ocean voyaging ceased, not because people had nocanoes but because it was too hazardous to sail, andbesides, their nearest neighbors at Pitcairn and Hendersonhad withdrawn to larger islands farther west due to adverse

16


NZ Glacial Variationadvance—retreal

AD 2000

ClimaticOptimum

Little Ice Age

AD 1000

AD/BC 0

BCIOOO

BC 2000

BC 3000 2760

Figure 11.Paleo-climatic fluctuations over the last 5000years as indicated by advances and retreats of New Zealandglaciers (from Leach and Leach 1979).

growing conditions on these marginal islands. The Rapanuifocused upon increasing the fertility of themselves andtheir crops. Without adequate rainfall to support interiorsettlement, people congregated mainly along the southerncoast where sweet potato harvests were best. They contin¬ued to gather shellfish and pursue inshore marine re¬sources, but chickens became an important dietary compo¬nent. Starvation and skirmishes were not unknown, but thepeople continued to live on their crops, as best they could.

In the late 1700s, with the Little Ice Age in fullswing, initialEuropean encounters were devastating for thealready-reduced population (for details see McCall 1994b,1997). During the ensuing century, the Europeans not onlytook people away from their home island, they introducedmany destructive animals, including rabbits, cows, horses,sheep, goats, and pigs. While useful as food, the animalswere allowed by the European ranchers to roam all over

the island, whereas the people were not. Restricted in theirmovements and by their small numbers, thanks to slaveraids, new diseases and other adverse consequences ofoutside contact, the Rapanui could not protect the vulnera¬ble trees and saplings from the depredations of the alienbeasts. The net effect upon the landscape was to furtherincrease the proportion of grasses and to decrease theproportion of already-scarce trees. The Europeans offeredto alleviate the suffering of the few remaining people,allowing them to emigrate, but many refused to leave andcontinued to plant their crops; after all, it was their islandand it had supported them for nearly a millennium.

In 1984, and again in 1991, paleo-sedimentologistsannounced that the ancient Rapanui were to blame for theloss of the island's native palms and for the radical trans¬formation of a former paradise island into a barren waste¬land (a year later the accusations were repeated in thepopular press by Bahn and Flenley. In 1991, a Pacificgeographer compiled strong evidence for environmentalcauses (climate, sea level fluctuations, seismicity, soils,etc.) of present landscapes throughout Oceania (Nunn1991),corroborating a cultural anthropologist's deductions(McCall 1979) that an extended drought had prompted thelate prehistoric cultural changes at Rapa Nui (McCall1993, 1994a). In 1997 another anthropologist, lately fromGuam, asks, in light of the pertinent ethnographic, archae¬ological, climatological, biological, geological, paleo-sedimentological and historical facts, which story is moreplausible, and which would you buy?

Footnotes1 One might object that ethnographic observations on estab¬

lished subsistence-level societies do not apply to the early settlersof the Pacific islands, assuming people behave more recklesslywhen they are in a 'pioneering' phase than after they have settleddown and "learned" to better manage the resources of their newlocale (see Diamond 1976). Yet it seems odd to suppose thatpeople who had successively occupied the remote Pacific islandsover a time span of some 2500 years would not have"remembered" the lessons learned during this time (not to men¬tion the lessons learned in the Asian homeland) and "applied"them at Rapanui! Similar thinking permeates the literature onocean-voyaging (e.g., Irwin 1992), in which it is presumed thatthe future settlers of the remote Pacific islands had to first learn tosail and hone their skills in a "voyaging nursery" before theycould sail out into the Pacific, along the lines of a child having tolearn to crawl before he can walk and run. The analogy may beappealing, but that does not make it appropriate to culturalsystems!

Footnotes2 The only recorded case of palm wood being used for an

entire canoe is on tiny Arorae, a low coral island in the andsouthern Gilberts (Kiribati) (Alexander 1902:727). It is unknownif these canoes were used in the open ocean, or whether they were

sailing canoes.The word niu throughout the Pacific (i.e., the myriad

Austronesian languages of Polynesia, Micronesia, and Melane-

17


sia) refers only to Cocos nucifera and is not a general term for"palm," as asserted by Bahn and Flenley (1992: 86). For Polyne¬sians and others to have a general term for "palms" would be likethe Eskimo having one term for "snow"! That the Rapanui referto the tree glyphs in the Rongorongo script by the term niusuggests, therefore, that these symbols signify Cocos nucifera,regardless of their vague similarities with the profile of someJubaea chilensis palms (see Bahn and Flenley 1992: Figures56-58).

4 Orliac and Orliac (1997) have found a shift from woodyto grassy fuels used in prehistoric hearths and earth-ovens at

Rapanui, beginning ca. AD 1650. This change in cooking fuel istwo centuries later than when deforestation was supposedlycomplete, according to the scenario!

5 For older rocks, K/Ar dating can be used, but accuratedating of recent lavas is not yet possible, hence their age must beestimated from their physical condition including chemical con¬tent, density, morphology and other aspects.

6 A lens of volcanic ash was recorded in all four cores fromRano Raraku. It occurred between sediments dated ca. 1197 and1888 BP respectively (Flenley et al. 199: Figure 6).

7 In a preliminary publication of the K.A02 core, takenfarther from the bank, Flenley (1993) suggests that initial humandisturbance to the vegetation in and near this catchment isindicated by a decline in palm pollen and rise in grass pollen thatbegan ca. 1650 BP. A shift at this time implies that humansettlement was earlier, by some 300 years, than the estimateassumed in the scenario. Although charcoal particles were ob¬served in KA02, counts are not given, so the timing of the onset

of fires cannot be estimated from this core.8 Grass pollen diameters are not given for the KA02 core

(Fienley 1993).9 As Nunn (1991, 1994) reminds us, natural processes do

not simply stop operating because people are present; contrary to

the common assumption, human actions do not supersede suchprocesses, rather they take place within this larger physicalcontext.

10 Normally, in long paleosediment cores, pollen diversityincreases upward due to better preservation in the more recent

sediments (Cummings pers. comm. 1997). The opposite patternseen in the long cores from Rapanui is therefore provocative andrequires an explanation.

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Diamond, J. 1995. Easter's End. Discover the WorldofScienceMagazine, August:62-69.

Dodson,J., ed. 1992. The Naive Lands. Longman Cheshire,Melbourne.

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Human vs Climatic Impacts at Rapa Nui or, Did the People Really Cut Down All those Trees?

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