The impact of moderate to marginal land suitability on prehistoric agricultural production and models of adaptive strategies for Easter Island (Rapa Nui, Chile)

Journal of Anthropological Archaeology 25 (2006) 290–317 www.elsevier.com/locate/jaa

The impact of moderate to marginal land suitability on prehistoric agricultural production and models of adaptive strategies for Easter Island (Rapa Nui, Chile) Geertrui Louwagie

a,c,* ,

Christopher M. Stevenson b, Roger Langohr

a

a

c

Ghent University, Laboratory of Soil Science, Krijgslaan 281-S8, 9000 Ghent, Belgium b Virginia Department of Historic Resources, Richmond, Virginia 23221, USA School of Biological and Environmental Science, College of Life Sciences, University College Dublin, Belfield, Dublin 4, Ireland Received 16 March 2005; revision received 17 October 2005 Available online 9 January 2006

Abstract Land evaluation was applied to assess the productivity of sweet potato, taro, yam, sugar cane, and banana during the prehistoric period on Rapa Nui (1500–1700 AD). Pedological and ethno-archaeological fieldwork enabled an estimation of prehistoric data. Twelve soil profiles distributed over four sites, Akahanga, La Pe´rouse, Tepeu, and Vaitea, were selected as land evaluation units. Six soil types, classified following the traditional Rapanui soil capability classification, served as test units. The land evaluation model took spatial and temporal precipitation variability, along with anthropogenic response, into account. Easter Island temperature and precipitation were assessed as close to optimal for sweet potato, rather moderate for banana and almost marginal for taro, yam and sugar cane. Dominant other limiting factors for moderate to marginal suitability were nutrient availability associated with andic soil properties and water availability following temporary precipitation deficit. Technical and organisational responses to these variables could have included lithic mulch, land use planning and supervision of food production. These adaptive strategies would have reduced the effect of climate variation and spread the risk of decreased yields. This rationale allows an understanding why prehistoric Rapanui people continued to produce well above the subsistence minimum, even under moderate or marginal production conditions.  2005 Elsevier Inc. All rights reserved. Keywords: Easter Island; Prehistoric (1500–1700 AD); Land evaluation; Agricultural production; Polynesian cultigens; Ethno-archaeology; Climate variability; Soil nutrient deficiency; Technical and organisational adaptive strategies; Lithic mulch

Over the past decades, there has been an ongoing debate about the rapid decline in socio-political complexity of the Easter Island society around 1680 AD (Renfrew and Bahn, 1996, p. 251). The topic has mainly been discussed by archaeologists and palaeo-botanists (Flenley and Bahn, 2003; *

Corresponding author.Fax: +353 1 7161102. E-mail address: [email protected] (G. Louwagie).

Flenley et al., 1991; Orliac and Orliac, 1998a), who have approached the topic from their discipline-specific knowledge base. Others have discussed the matter within the broader framework of the fate of other Polynesian islands in the Pacific Ocean (Kirch, 2000; Rolett and Diamond, 2004) or even from a worldwide historical perspective (Ponting, 1991, pp. 1–7; Tainter, 1988, p. 71).

0278-4165/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jaa.2005.11.008

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317

Rapa Nui was settled ca. 700 AD and over the next thousand years it emerged into a chiefdom society with a highly ranked lineage present in each of the regional territories. The emergence of ranking and complexity is revealed by architectural symbols of elevated status such as costly elite stone dwellings and increasingly elaborate and large temple complexes adjacent to elite precincts. However, pinpointing the exact time period of decline in this complexity is difficult. Deeply imbedded in the literature is the date of 1680 AD based upon the analysis of oral histories by Me´traux (1940). Additional support for this late 17th century date is present in three lines of archaeological evidence. The first is a general shift in the settlement pattern that includes the abandonment of interior agricultural field systems geared towards surplus production that were under elite management (Stevenson, 1997). A drop in resource use suggests a decline in the overall capabilities of elite personnel. Second, artificially constructed refuge caves, with no prior use, appear within residential sites. The appearance of these caves likely correlates with the occurrence of island warfare and has been dated by obsidian hydration to post 1650 AD (Rorrer, 1998). Lastly, terminal construction phases dating at a few centrally placed temples such as ahu Heki’i show that final architectural additions occurred at ca. 1600 AD, or slightly later (Martinsson-Wallin, 1998), and reflect the end of the megalithic building tradition. A central theme of the discussion goes back to the question of whether the origin of the collapse was natural or anthropogenic. Deforestation has been suggested as the main anthropogenic trigger for a radical transformation of the once flourishing Easter Island society (Flenley and Bahn, 2003; Flenley et al., 1991; Mieth and Bork, 2003; Renfrew and Bahn, 1996, pp. 251–252; Rolett and Diamond, 2004). Mann et al. (2003) provide evidence for the island’s forest clearance starting abruptly around ca. 1200 AD and perceive this event as an indicator of an economy that switched from a predominantly hunter-gatherer to a dryland farming society. They obviously do not link this shift to the society’s decline and leave it open whether this change was triggered for climatic reasons. Feeding the anthropogenic cause, Dumont et al. (1998) suggest that Amerindians contributed to the cultural collapse of the island, based on plant and animal microfossil identification in a core from the Rano Raraku crater lake. Furthermore, the topic of agricultural landscape transformation and its impact on socio-polit-

291

ical evolution has been raised, mainly based on archaeological settlement data (Stevenson et al., 1999). However, there has also been a remarkable shift in perspective that hypothesises a climatic reason behind the societal organisational restructuring. Several authors have suggested an abrupt climatic change, such as the effects of the Little Ice Age with concomitant cooler weather and severe droughts (Hunter-Anderson, 1998; McCall, 1993, 1995) or merely a prolonged period of extreme drought (Orliac and Orliac, 1996, 1998a,b, 1999) to explain the collapse of the Rapanui culture. However, climatologists find insufficient data to support the Little Ice Age hypothesis (MacIntyre, 2001b) or a significant impact from the El Nin˜o Southern Oscillation (ENSO) (Genz and Hunt, 2003; MacIntyre, 2001a,b) or the Interdecadal Pacific Oscillation (IPO) (Gosai et al., 2002) on Easter Island climate. Until now, this combination of climatic and anthropogenic causes have been merely hypothesised but not investigated. On an island where agriculture played a fundamental economic role in the past (Stevenson and Haoa, 1999; Stevenson et al., 1999), we believe that it is necessary to focus on the links between the environmental constraints to crop production, agricultural production strategies that minimise these constraints, and the effects of these factors on the socio-political organisation. In this article, we compare archaeological settlement data with land evaluation results for staple crops (sweet potato, taro, yam, sugar cane, and banana) using twelve land units distributed over four sites (Akahanga, La Pe´rouse, Tepeu, and Vaitea) (Fig. 1). Through the description and analysis of climatic and soil characteristics, we are able to determine the suitability of these land units for the growth of mentioned staple crops. These sites were occupied between approximately 1100 and 1800 AD. Agricultural production and response to environmental variability Economic production systems must adapt to limiting conditions within the immediate environment by the implementation of strategies that reduce risk and/or increase output (Leach, 1999; Morrison, 1994). In many cases, one of the most influential factors affecting agricultural production systems is the amount of available moisture that permits, or prevents, farmers from using otherwise favourable land. Other non-cultural factors may include tem-

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Fig. 1. Location of investigated land evaluation units (LEU), including auger profiles (P) as reference and test units, on Easter Island (altitude lines every 100 m).

perature stress, limited nutrient availability, excess of toxic nutrients, soil drainage, plant pests or unfavourable topographic conditions. These limiting factors may be temporally variable or relatively stable over time. Soil quality can be linked to the soil’s natural ability to function (inherent) or depend on its management (dynamic) (Karlen et al., 1997; USDA, 2004). Rapa Nui may be characterised as an environment with several significant environmental limitations, some of which became increasingly important over time. A number of factors can be identified and include: (i) a strongly isolated island environment of limited surface area and concomitant limited land resources, including at initial settlement large trees and a shrub undergrowth that were likely cleared by the end of the 16th (Flenley, 1996) or the mid 17th century (Orliac and Orliac, 1998a, 1999; Mann et al., 2003). As plant cover was removed, wind velocities increased, and evapotranspiration increased to the high levels that are present today. (ii) a subtropical climate with a buffering oceanic character, characterised by a summer–dry season and unpredictable moisture surpluses or deficits due to important climatic variability (Hunt and Lipo, 2001);

(iii) extensive areas with shallow soils and large basalt rock outcrops; (iv) soils that are well drained; and (v) a volcanic island with a substantial amount of soils that have andic soil properties and a weathering sequence that ultimately results in limited phosphorus and potassium availability (Louwagie, 2004, p. 258). Under such high-risk conditions characterised by climatic variability and marginal conditions, cultural and technical responses aimed at ‘‘variance minimisation’’ (Allen, 2004) can be introduced to maintain adequate levels of production to meet subsistence and political needs. Sufficient food was especially important in the maintenance of the annual feasting cycle and the investment in temple infrastructure so important in political legitimisation. It is our general hypothesis that regions such as Rapa Nui will develop increasingly rigid social hierarchies to cope with problems of crop production. This can be manifested in several ways. The first is through the direct management of production by the placement of chiefly representatives, or overseers, within the field systems (Stevenson, 1997). It is unlikely that production of food beyond the immediate subsistence needs was completely volun-

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317

tary and direct supervision was thus required. This need for supervision would have led to the emergence of a large group of supervisors accountable to the higher-ranking elite. The strength of social hierarchy is also evidenced by greater investment in community and religious megalithic architecture. Such is the case on Rapa Nui where temple complexes and elite dwellings located at regional centres became increasingly complex between 1300 and 1550 AD and energetically expensive to build (e.g., Stevenson et al., 2005). Along with this increasing complexity in sociopolitical structure, new technical improvements were incorporated in the agricultural system, such that it had a resilient and sustainable character that could tolerate environmental fluctuations. This is evidenced by: (i) lithic mulch management, whereby the soil surface is covered with rock or coarse fragments, to overcome temporary water deficit (Louwagie, 2004, pp. 205–226; Louwagie and Langohr, forthcoming 2006; Maxwell, 1995; Stevenson et al., 1999) and with a side effect of increased soil temperature (Allen et al., 1998); and (ii) rotation patterns to maintain soil chemical fertility (Louwagie, 2004, pp. 205-226; Louwagie and Langohr, forthcoming 2006). It is also evident from past settlement pattern studies that Rapa Nui farmers capitalised on regional environmental differences. Rapa Nui experiences a strong elevation- and aspect-dependent rainfall pattern whereby upland regions in the centre part of the island can have up to twice the annual moisture of lowland coastal areas (see below: Climate). Numerous small domestic house pavements, cooking areas and rock alignments are found in association with spatially extensive rock gardens in the centrally located Vaitea region. Radiocarbon and obsidian hydration dating of a few upland house sites indicate a temporally restricted use of the region between approximately 1300 and 1700 AD (Stevenson et al., 2002). In this paper, it is our goal to determine how the island climate and soil characteristics can have structured the strategies directed toward variance minimisation. Were the soils of Rapa Nui adequate in nutrients on an island-wide basis to grow sweet potato, taro, yam, sugar cane, and banana? Did nutrient-deficient regions limit the types of crops

293

that could be grown in certain areas? Did the occurrence of soils with reduced capability limit the overall production capacity of Rapa Nui farmers? Does the state of the island soils alter the debate between climatic versus anthropogenic reasons for the eventual decline in complexity? We will evaluate these questions through application of the land evaluation process. Land evaluation Land evaluation procedure and model According to the Food and Agriculture Organization of the United Nations (FAO, 1976), land evaluation is the process of assessing land performance for specific purposes. A schematic representation of the activities in the land evaluation procedure is given in Fig. 2 (adapted after FAO, 1976, p. 28). This framework constitutes the basis for a qualitative land evaluation model, integrating physical, socio-economic, and socio-cultural parameters. Interviews with farmers provided insight into the driving forces of prehistoric Rapanui land performance (Louwagie, 2004, pp. 205–226; Louwagie and Langohr, forthcoming 2006). Priority was given to older respondents (eight of ten), seen in their rich knowledge of traditional (versus modern or presentday) farming systems. Climatic conditions (extreme cold, drought, etc.), staple crop characteristics (planting and harvesting date, crop development stages, yield, etc.) and soil characteristics and management practices (weed and disease control, fertiliser application, etc.) were registered. Special attention was paid to local soil classification names reflecting the traditional societal perception of and response to the land. On Rapa Nui these names refer to vaguely defined, rather subjective soil characteristics. Samples were taken to check the traditional names with soil characteristics that could be analytically determined (pH, content of organic carbon, nitrogen, and cations). Mentioned traditional Rapanui soil capability classification was used as a reference and test framework to develop crop production criteria for ‘‘good soils,’’ especially with respect to nutrient availability. When the traditional classification was not distinctive or detailed enough, additional promoting and constraining factors for crop production were identified and introduced into the model. The land evaluation model was developed along the spatial and temporal variability axes in three phases:

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INITIAL Objectives Data and assumptions

LAND UTILISATION TYPES

LAND USE REQUIREMENTS and LIMITATIONS

Iteration

Improvements

LAND EVALUATION UNITS

COMPARISON of LAND USE with LAND Matching Socio-economic analysis Sustainability

LAND QUALITIES

LAND SUITABILITY CLASSIFICATION

Iteration

Fig. 2. The land evaluation procedure (FAO, 1976, p. 28).

Phase 1. A climatic suitability assessment considering Rapa Nui as one single area, regardless of precipitation variability over the island. Phase 2. A static land suitability classification, in which climatic and soil characteristics were considered for each land evaluation unit, thus taking spatial variability into account. Phase 3. A dynamic land suitability classification, in which (i) climate variability and possible (ii) anthropogenic soil management responses were considered. The impact of spatial and temporal variability was thus estimated. In phases two and three, four suitability classes, corresponding with four severity levels, were defined in accordance with the FAO-framework: S1, highly suitable (severity level 1: no limitation); S2, moderately suitable (severity level 2: moderate limitation); S3, marginally suitable (severity level 3: severe limitation); and N, not suitable (severity level 4: very

severe limitation). The parametric boundaries of the land suitability classes are based upon the traditional soil capability classification (TSCC). Details of the latter are elaborated in Louwagie (2004) and Louwagie and Langohr (forthcoming 2006). Table 1 shows the link between the traditional Rapanui soil capability classification and the land suitability classes in the land evaluation model for the prehistoric Rapanui context. By comparing land qualities (LQ’s) with land use requirements (LUR’s), land suitability classes were determined (Fig. 2) according to the maximum limitation method. In the latter case, the severest limiting LUR/LQ (i.e., with the highest-numbered (1–4) suitability class) determines the final suitability class and interactions between LQ’s are neglected (Rossiter, 1990, 1996; Rossiter and Van Wambeke, 1997). The maximum limitation method was chosen, because of the limited insight into interaction and weight of the land characteristics and qualities con-

Table 1 Prehistoric Rapanui land suitability classes, severity levels and relative yield indices, based on the traditional Rapanui soil capability classification, with classes and relative yield indices, and comparable to the land indices of Sys et al. (1993) Traditional Rapanui soil capability classification

Prehistoric Rapanui land suitability classification

Sys et al. (1993)

Class

Relative yield index

Class

Severity level

Relative yield index

Land index

100 80 60–50 20

S1 S2 S3 N

1 2 3 4

100–81 80–56 55–21 20–0

100–75 75–50 50–25 25–0

Oone Oone Oone Oone

hatu reherehe mararı´a rautu´

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sidered in the prehistoric Rapanui context. The land suitability subclass code is attributed according to the most limiting LQ and eventually sheds light on choices for land improvement (e.g. lithic mulch management). In case calculated values corresponded to threshold values between classes, the most favourable class was attributed. Within the context of dynamic land suitability, climate variability was considered in terms of precipitation variability. Next to the reference situation, scenarios were calculated for extreme drought and excess precipitation. Anthropogenic response to climate and climate variability, and eventual ensuing water deficit, was evaluated by assessing the impact of lithic mulch management on water availability. The eventual side effect of increasing soil temperature was not elaborated here. Land evaluation data Site location (land evaluation units, LEU’s) Easter Island is located 3700 km West of Santiago de Chile (Chile) at W10926 0 (longitude) and S2710 0 (latitude) (Fig. 1). It has a triangular shape, based on the presence of three extinct volcanoes: Poike, Rano Kau, and Maunga Terevaka. The surface is approximately 170 km2 in size and the elevation ranges between 0 and 506 m at Maunga Terevaka. Four sites, comprising twelve land evaluation units (LEU’s), were investigated in detail: Akahanga (AK1, AK2, and AK3), La Pe´rouse (LP1, LP3, LP4, and LP6), Tepeu (TP3) and Vaitea (VA2, VA3, VA4, and VA8) (Fig. 1). Additional hand auger observations on seven locations spread over three sites and representing six traditional soil capability classes were performed and were situated on the footslopes of small volcanic vents located parallel with the southeast coast of the island: Mata Henga (002, 003), Maunga Roa (1.1, 004, 005, and 006) and Maunga Te Kahu Rea (1.2) (Fig. 1). Within the model, these were used as reference and test units. Landform and soils (land qualities, LQ’s, and land characteristics, LC’s) Substratum and parent material mainly consist of tephra, i.e., volcanic material ejected from a vent during an eruption and transported through the air, and/or lava flows. The eruptions produced large portions of basic volcanic rocks, in the region indi-

295

cated as Terevaka basalt (Baker, 1998; Baker et al., 1974; Charola, 1997), that are limited to the central part of the island where they cover about two thirds of the island. Rocks of intermediate and siliceous composition cover about one third of the landmass, especially the periphery of the island (Charola, 1997; De Paepe and Vergauwen, 1997). The studied sites lie on the slopes of the Maunga Terevaka volcano, the youngest of the three major volcanoes on the island. It erupted for the first time some 300,000 years ago in the Rano Raraku area and a younger volcanic episode, with Rano Aroi as the largest crater, produced great quantities of basaltic lava (Baker, 1998; Baker et al., 1974; Fischer and Love, 1993). The last large lava flow in the evolution of Maunga Terevaka occurred towards the (south)west side and is estimated to have happened only 2000–3000 years ago; it was emitted by a small cone called Maunga Hivahiva (Baker, 1998; Baker et al., 1974; Charola, 1997). The weathering of this tephra results in soil material with andic soil properties that contains significant amounts of short-range ordered minerals, such as halloysite, imogolite, allophane, ferrihydrite, and aluminium–humus complexes. These soils are characterised by low bulk density, mostly silt loam or finer textures, high organic matter content, variable charge surfaces, and high phosphate retention capacity. With advanced weathering, decreasing potassium availability is expected in the allophanic soils (Utami, 1998, p. 290). Using the BASIC-software (Van Wambeke, 1985) on the climatic data from Mataveri (see below), Easter Island proves to have a typic udic soil moisture regime and an isothermic soil temperature regime. According to WRB (1998) and USDA (1999) soil classification systems, TP3 and VA4 were classified as Hyperdystri-Silandic and Hyperdystri-Aluandic Andosols or Typic Hapludands; AK1, AK2, and AK3 as Silti-Pachic, Silti-Endosodic, Silti-Hyposodic Phaeozems or Andic Hapludolls; LP4 as SiltiPachic Phaeozem or Typic Hapludoll; LP6 as SiltiLuvic Phaeozem or Typic Argiudoll; LP1 and VA3 as Hyperdystri-Silandic and Ferrali-Silandic Cambisols or Andic Dystrudepts; VA2 and LP3 as Hyperdystri-Humic and Hyperdystri-Umbrihumic Cambisols or Andic and Humic Pachic Dystrudepts; VA8 as Humi-Episkeletic Leptosol or Lithic Udorthent. The detailed landform and soil information base is provided in Louwagie (2004). In this article we only reproduce those data needed in the land evaluation process (Tables 4–9).

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Several analytical methods were used in the soil characterisation process. The pHH2O-values of the soil samples were measured using a soil/liquid suspension ratio of 1/5, after 1 h suspension. Contents of organic carbon (OC) and available phosphorus ((P2O5)a) were determined following, respectively, the ISO 10694 (1995) and Olsen et al. (1954) method. The exchangeable sodium percentage (ESP) identifies to which degree the exchange complex is saturated with sodium (Na) and is given by: ESP = Na/CEC · 100, with CEC, the cation exchange capacity. Cation exchange capacity (Metson method) and the exchangeable cations K and Na (atomic emission flame spectrometry) were determined using ammonium acetate (pH 7) and following the NF X 31-130 and NF X 31-108 norms (AFNOR, 2004).

the root zone by deep percolation. Based on our own ethno-archaeological research (Louwagie, 2004, pp. 205–226; Louwagie and Langohr, forthcoming 2006) and estimates of deep percolation on the island (Hauser, 1998, p. 218), effective precipitation ratios (a), were assessed at 0.40 in summer and 0.60 in winter; intermediate values were calculated for spring and fall. Precipitation patterns on Easter Island exhibit both spatial and temporal variability. According to Norero (1998, p. 140) elevation and slope aspect mainly determine the spatial precipitation variability. With reference to the Mataveri climatic station, the annual precipitation is empirically expressed as P ðZ; X Þ ¼ ½1 þ 0:0016  ðZ  41Þ  f ðX Þ  P M ; with P (Z, X), precipitation (mm) at location with elevation Z and slope aspect X, PM, precipitation (mm) at the climatic station of Mataveri, and f (X):

P, ET, ET/2 (mm)

Climate (land qualities, LQ’s, and land characteristics, LC’s) For the Easter Island context, it is assumed that present-day climate is comparable to that of the 1500–1700 AD period. Simulations with the ECBILT-CLIO-model (Goosse et al., 2004) indeed support this hypothesis (personal communication Goosse). Present-day monthly data of precipitation and temperature for the climatic station at Mataveri (elevation: 41 m) are given in Fig. 3 (FAO, 1985). Calculation of decade data was conducted according to the algorithm of Gommes (1983). The effective precipitation (Pe = a · P) excludes the precipitation (P) lost by surface runoff or to

X

NW W

SW S

SE

NE

N

f (X) 1.15 1.02 0.69 1.00 1.12 1.00 0.89 1.02 Following this formula, annual precipitation values for the distinct LEU’s, with precipitation ratios ranging between 0.974 and 1.38, vary between 1063 and 1503 mm under reference climatic conditions (PM = 1091 mm). Schanz’s (1964) unpublished precipitation data at Mataveri and Vaitea are in line with this equation. Temporal cycles of drought and excess precipitation result in annual oscillations of 1000 mm around the mean annual precipitation at the Mataveri cli-

180

30

150

25

120

20

90

15

60

10

30

5

0

E

T (˚C)

296

0 Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Time P

ET

ET/2

Tmean

Tmax

Tmin

Fig. 3. Average monthly precipitation (P), evapotranspiration (ET) (modified Penman method) and mean (Tmean), minimum (Tmin) and maximum (Tmax) temperature (T) at Mataveri (series of at least 30 years for P, series of 10 years for the other parameters) (FAO, 1985).

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the evapotranspiration (Fig. 3). The latter theoretical period was checked with local data obtained through ethno-archaeological research (Louwagie, 2004, pp. 205–226; Louwagie and Langohr, forthcoming 2006) and proved to be coherent with the interview data. Duration of the crop growth period and crop development stages was based on the information drawn from the questionnaires and adapted according to the existing literature for the five specific crops (Doorenbos and Kassam, 1979; FAO, 1996; FAO, 2000; Landon, 1991; MCD-RF, 1991; Norman et al., 1995; Raemaekers, 2001; Rehm and Espig, 1991; Sys et al., 1993; Wilson, 1977). An overview of the selected crop growth period characteristics (length, start, end, length of crop development stages) is given in Table 2. As sweet potato has a shorter crop growth cycle than the other crops, two crop growth cycles per year were considered. The start of the first growth period (GP1) coincides with the theoretical starting date (1st of February); the end of the second crop growth period (GP2) coincides with harvest in summer, meeting a higher demand in food in those months with several social events or festivities according to the questionnaires. Table 3 provides the crop coefficients (kc) for the discrete crop development stages and for the midseason (MS) and at harvest (H) adapted for the specific Easter Island conditions according to the formula: kc Adj = kc (RH = 45%, u2 = 2 m s1) + [0.04 · (u2  2)  0.004 · (RHmin  45)] · (h/3)0.3 (Allen et al., 1998, pp. 121, 125), with RH, relative humidity, u2, wind speed at 2 m height and h, crop height. Average values for root and tuber crops are indicated for taro and yam, as precise values were not available. Leaf area index (LAI) (Sys et al., 1993, pp. 186–189; Wilson, 1977), harvest index (Hi) (Sys et al., 1993, pp. 186–189;

matic station (McCall, 1995). The ECBILT-CLIOmodel (Goosse et al., 2004) indeed suggests important climate variability with comparable probabilities for either extreme drought or excess precipitation over the considered time period (personal communication Goosse). Taking the average annual of 1091 mm (FAO, 1985) as a reference, extreme drought scenarios of 591 mm, fitting with the hypothesis of Little Ice Age impact, with a possible decrease in precipitation down to about 500 mm (MacIntyre, 2001b), and extreme precipitation levels of 1591 mm were assumed. It is worthwhile mentioning that McGregor and Nieuwolt (1998, p. 310) distinguish between climatic variability when changes occur at annual or decadal scale and climate change at long (changes greater than 20,000 years) or at short term (changes between 100 and 20,000 years). Crops (land utilization types, LUT’s) Based upon ethnographic evidence, such as Englert (1974) (1885–1965 AD), McMillan Brown (1996) (start 20th century) and Me´traux (1957) (1934–1935 AD), and archaeo-botanical studies (Orliac and Orliac, 1996, 1998a,b, 1999; Yen, 1988), sweet potato (Ipomoea batatas), taro (Colocasia esculenta), yam (Dioscorea alata), sugar cane (Saccharum officinarum), and banana (Musa sp.) were the rain-fed staple crops on prehistoric Rapa Nui. Sweet potato was considered to be the dominant staple crop in the food production system. Theoretical calculation of the crop growth period was based on the FAO-concept (Kowal, 1978), using the climatic data at Mataveri (FAO, 1985). The Easter Island crop growth period starts on the first of February and ends on the sixteenth of January in the next calendar year and roughly coincides with the period when precipitation exceeds half of

Table 2 Crop growth periods characteristics (length, start, end, and length of crop development stages) for the selected land utilisation types (LUT) adapted to Easter Island conditions (multiple sources, see Louwagie, 2004) LUT

Sweet potato Taro Yam Sugar cane Banana

Length (d)

GP1 GP2

Date (d)

Total

I

CD

MS

LS

Start

End

150 150 300 300 360 360

40 40 60 60 30 60

40 40 120 120 50 90

40 40 90 90 220 120

30 30 30 30 60 90

1 1 1 1 1 1

30 30 30 30 30 30

FEB AUG FEB FEB FEB FEB

JUN DEC NOV NOV JAN JAN

GP1/GP2, growth period 1 and 2; I, initial stage; CD, crop development stage; MS, mid-season stage; LS, late-season stage; AUG, August; FEB, February; JUN, June; NOV, November and DEC, December.

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Table 3 Crop-specific characteristics (LAI, Hi, kc, MERD, p, and ky) for the selected land utilisation types (LUT) adapted to Easter Island conditions (multiple sources, see Louwagie, 2004) LUT Sweet potato Taro Yam Sugar cane Banana

GP1 GP2

LAI

Hi

kc I

kc MS

kcAdj H

kcAdj MS

kc H

MERD (m)

p

ky

4.0 4.0 4.0 4.0 5.0 5.7

0.55 0.55 0.55 0.55 0.25 0.20

0.50 0.50 0.50 0.50 0.40 0.50

1.15 1.15 1.10 1.10 1.25 1.10

0.65 0.65 0.95 0.95 0.75 1.00

1.07 1.10 1.04 1.04 1.19 1.05

0.60 0.61 0.89 0.89 0.74 0.98

1.0 1.0 1.0 1.0 1.5 0.7

0.65 0.65 0.65 0.65 0.65 0.35

1.1 1.1 1.1 1.1 1.2 1.3

GP1/GP2, growth periods 1 and 2; LAI, leaf area index; Hi, harvest index; kc, crop coefficient; kc Adj, adjusted crop coefficient; MERD (m), maximum effective rooting depth; p, soil water depletion fraction; ky, yield response factor; I, initial stage; MS, mid-season stage; and H, harvest.

Wilson, 1977), maximum effective rooting depth (MERD) (Allen et al., 1998, pp. 163–165), soil water depletion fraction (p) adapted for ETc according to p = p (ETc = 5 mm d1) + 0.04 · (5  ETc) with 0.1 6 p 6 0.8 (Allen et al., 1998, p. 162) and yield response factor (ky) (Doorenbos and Kassam, 1979; Sys et al., 1991a, p. 261) are also indicated. Again, approximate values were used for taro and yam. The latter characteristics are used to calculate crop response on water deficit (see Table 12: matching tables with LUR’s). Database (LQ’s and LC’s) The chosen diagnostic land qualities in the prehistoric Rapanui context were: water availability (w), nutrient availability (n), and alkalinity (a). Each land quality comprises a set of diagnostic land characteristics, which determine the severity or limitation level of the land quality. Water availability (w) was assessed based on (i) climate- and crop-specific water availability (WAc), (ii) soil-specific plant available water (PAW), (iii) soil depth (SD), and (iv) landform and topographic position (LTP). Nutrient availability (n) was assessed based on (i) pHH2O, (ii) organic carbon content (OC), (iii) available phosphorus ((P2O5)a) and (iv) exchangeable potassium (K). The degree of alkalinity (a) was estimated by means of the exchangeable sodium percentage (ESP). Anthropogenic response to water deficit was evaluated by assessing the impact of lithic mulch management on water availability by introducing a land quality called climate-, crop-, and management-specific water availability: WAcm. The concomitant severity level was indicated as: wm, and the resulting land suitability class as: LSCm.

Tables 4–9 list the land evaluation data at the distinct land evaluation units for reference, extreme dry and excess precipitation conditions. The climatic water balance (WAc), i.e., the water availability based on climatic and crop characteristics, is estimated as: WAc (%) = 100 + [(Pe  ETc)/ ETc · 100], where [(Pe  ETc)/ETc · 100], represents the climatic water surplus or deficit as defined by Thorntwaite (1948), with Pe, effective precipitation and ETc, crop evapotranspiration. Effect of lithic mulch on the water availability (WAcm) was considered through a reduction in evapotranspiration over the crop growth period (Cerda`, 2001; Doolittle, 1998; Lightfoot, 1994; Mather, 1974). The latter was assessed at 20% for 100% surface cover with coarse fragments (SCF) (after Allen et al., 1998); SCF-data are given in Table 17. The effective reduction in evapotranspiration is proportional to the fraction of the soil surface covered by lithic mulch. Landform and topographic position (LTP) and soil depth (SD) were determined during field observations. Saprolite within the Easter Island soilscape is regarded as a root-limiting layer, as roots do not easily penetrate this dense, weathered bedrock with no pedality. For calculation of soil physical and chemical characteristics, the procedure as elaborated by Sys et al. (1991b) was followed and adjusted or completed where necessary. For all soil characteristics, except ESP, soil profiles were divided in equal sections and to each section a weighting factor was attributed. The factors depend on total soil depth and the highest weight is applied to the surface horizon (Table 10). Missing data for particular horizons were taken from adjacent horizons with the same master soil horizon symbol (A, B, C or transitions).

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317

299

Table 4 Land evaluation data for reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions of the first crop growth period of sweet potato (GP1) (optimal rooting depth = 1.0 m) for the nineteen land evaluation units (LEU) LEU WAc (%) WAcm (%) WAc (%) WAcm (%) WAc (%) WAcm (%) PAW SD LTP (mm m1) (m) PM = 1091 mm PM = 591 mm PM = 1591 mm

pHH2O OC (%)

(P2O5)a K ESP (mg kg1) (cmolc kg1) (%)

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

5.9 6.1 6.2 5.9 5.8 6.2 6.0 6.6 6.3 6.3 5.3 5.2 6.5 5.5 6.2 5.8 5.6 5.2 5.4

286 310 175 97 114 128 46 385 48 43 33 130 94 152 59 51 38 32 15

81 80 85 85 81 81 81 84 77 77 77 77 77 82 90 106 108 108 108

81 80 85 85 81 81 82 84 80 80 82 78 84 100 90 106 108 115 132

41 40 42 42 41 41 41 42 38 38 39 39 39 41 45 53 54 54 54

41 40 42 42 41 41 41 42 40 40 41 39 42 50 45 53 54 58 66

122 121 127 127 122 122 122 127 115 115 116 116 116 122 135 158 163 163 163

122 121 127 128 122 122 123 127 120 120 124 117 126 149 135 158 163 173 198

180 204 180 199 201 173 201 197 169 204 206 201 167 151 205 197 170 198 49

1.00 1.00 1.00 1.00 0.40 1.00 0.45 1.65 0.97 1.12 0.85 2.00 0.54 1.05 0.73 1.85 0.83 0.41 0.24

LO LO IN-LO IN-LO LO LO LO LO UP UP UP LO IN-UP IN-UP LO UP LO IN-LO

2.46 2.32 2.24 2.70 3.61 3.31 1.93 1.82 1.23 1.46 3.47 2.44 2.76 0.99 6.84 3.81 4.20 7.44 10.0

0.39 0.76 0.20 0.56 0.71 0.35 0.14 0.93 0.41 0.59 0.08 0.24 1.04 1.00 0.19 0.05 0.10 0.10 0.08

1 2 2 2 1 2 1 5 26 13 3 3 4 9 2 2 <1 <1 1

WAc, climate- and crop-specific water availability; WAcm, climate-, crop-, and management-specific water availability; PAW, soil-specific plant available water; SD, soil depth; LTP, landform and topographic position; LO, lower, IN, intermediate, and UP, upper part of slope; pHH2O, pH in water; OC, organic carbon; (P2O5)a, available phosphorus; K, exchangeable potassium; ESP, exchangeable sodium percentage. Table 5 Land evaluation data for reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions of the second crop growth period of sweet potato (GP2) (optimal rooting depth = 1.0 m) for the nineteen land evaluation units (LEU) LEU WAc (%) WAcm (%) WAc (%) WAcm (%) WAc (%) WAcm (%) PAW SD LTP (mm m1) (m) PM = 1091 mm PM = 591 mm PM = 1591 mm

pHH2O OC (%)

(P2O5)a K ESP (mg kg1) (cmolc kg1) (%)

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

5.9 6.1 6.2 5.9 5.8 6.2 6.0 6.6 6.3 6.3 5.3 5.2 6.5 5.5 6.2 5.8 5.6 5.2 5.4

286 310 175 97 114 128 46 385 48 43 33 130 94 152 59 51 38 32 15

47 47 50 50 47 47 47 49 45 45 45 45 45 48 53 62 63 63 63

47 47 50 50 47 48 48 49 47 47 48 46 49 58 53 62 63 67 77

24 24 25 25 24 24 24 25 22 22 23 23 23 24 26 31 32 32 32

24 24 25 25 24 24 24 25 23 23 24 23 25 29 26 31 32 34 39

71 71 74 74 71 71 71 74 67 67 68 68 68 72 79 93 95 95 95

71 71 74 75 71 71 72 74 70 70 72 69 74 87 79 93 95 101 116

180 204 180 199 201 173 201 197 169 204 206 201 167 151 205 197 170 198 49

1.00 1.00 1.00 1.00 0.40 1.00 0.45 1.65 0.97 1.12 0.85 2.00 0.54 1.05 0.73 1.85 0.83 0.41 0.24

LO LO IN-LO IN-LO LO LO LO LO UP UP UP LO IN-UP IN-UP — LO UP LO IN-LO

2.46 2.32 2.24 2.70 3.61 3.31 1.93 1.82 1.23 1.46 3.47 2.44 2.76 0.99 6.84 3.81 4.20 7.44 10.0

0.39 0.76 0.20 0.56 0.71 0.35 0.14 0.93 0.41 0.59 0.08 0.24 1.04 1.00 0.19 0.05 0.10 0.10 0.08

1 2 2 2 1 2 1 5 26 13 3 3 4 9 2 2 <1 <1 1

See Table 4.

Plant available water (PAW) was determined based on the USDA-texture class (USDA, 1993, pp. 136–140), using the conversion as mentioned

in Sys et al. (1991b, p. 208). Mean plant available water (mm m1) was calculated over the effective rooting depth, applying weighting factors with

300

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Table 6 Land evaluation data for reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions of taro (optimal rooting depth = 1.0 m) for the nineteen land evaluation units (LEU) LEU WAc (%) WAcm (%) WAc (%) WAcm (%) WAc (%) WAcm (%) PAW SD LTP (mm m1) (m) PM = 1091 mm PM = 591 mm PM = 1591 mm

pHH2O OC (%)

(P2O5)a K ESP (mg kg1) (cmolc kg1) (%)

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

5.9 6.1 6.2 5.9 5.8 6.2 6.0 6.6 6.3 6.3 5.3 5.2 6.5 5.5 6.2 5.8 5.6 5.2 5.4

286 310 175 97 114 128 46 385 48 43 33 130 94 152 59 51 38 32 15

70 70 74 74 70 70 70 73 66 66 67 67 67 71 78 91 94 94 94

70 70 74 74 70 70 71 75 69 69 71 68 73 86 78 91 94 100 115

35 35 37 37 35 35 35 36 33 33 34 34 34 35 39 46 47 47 47

35 35 37 37 35 35 35 36 35 35 36 34 37 43 39 46 47 50 57

105 104 110 110 105 105 105 109 100 100 101 101 101 106 118 137 141 141 141

105 104 110 111 105 106 106 109 104 104 107 102 110 130 118 137 141 150 172

180 204 180 199 201 173 201 197 169 204 206 201 167 151 205 197 170 198 49

1.00 1.00 1.00 1.00 0.40 1.00 0.45 1.65 0.97 1.12 0.85 2.00 0.54 1.05 0.73 1.85 0.83 0.41 0.24

LO LO IN-LO IN-LO LO LO LO LO UP UP UP LO IN-UP IN-UP — LO UP LO IN-LO

2.46 2.32 2.24 2.70 3.61 3.31 1.93 1.82 1.23 1.46 3.47 2.44 2.76 0.99 6.84 3.81 4.20 7.44 10.0

0.39 0.76 0.20 0.56 0.71 0.35 0.14 0.93 0.41 0.59 0.08 0.24 1.04 1.00 0.19 0.05 0.10 0.10 0.08

1 2 2 2 1 2 1 5 26 13 3 3 4 9 2 2 <1 <1 1

See Table 4. Table 7 Land evaluation data for reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions of yam (optimal rooting depth = 2.0 m) for the nineteen land evaluation units (LEU) LEU WAc (%) WAcm (%) WAc (%) WAcm (%) WAc (%) WAcm (%) PAW SD LTP (mm m1) (m) PM = 1091 mm PM = 591 mm PM = 1591 mm

pHH2O OC (%)

ESP (P2O5)a K (mg kg1) (cmolc kg1) (%)

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

5.9 6.1 6.2 5.9 5.8 6.2 6.0 6.6 6.3 6.3 5.3 5.2 6.5 5.5 6.2 5.8 5.6 5.2 5.4

286 310 175 97 114 128 46 385 48 43 33 130 94 152 59 51 38 32 15

70 70 74 74 70 70 70 73 66 66 67 67 67 71 78 91 94 94 94

70 70 74 74 70 70 71 75 69 69 71 68 73 86 78 91 94 100 115

35 35 37 37 35 35 35 36 33 33 34 34 34 35 39 46 47 47 47

35 35 37 37 35 35 35 36 35 35 36 34 37 43 39 46 47 50 57

105 104 110 110 105 105 105 109 100 100 101 101 101 106 118 137 141 141 141

105 104 110 111 105 106 106 109 104 104 107 102 110 130 118 137 141 150 172

180 204 180 199 201 173 201 194 169 203 206 198 167 151 206 188 170 198 49

1.00 1.00 1.00 1.00 0.40 1.00 0.45 1.65 0.97 1.12 0.85 2.00 0.54 1.05 0.73 1.85 0.83 0.41 0.24

LO LO IN-LO IN-LO LO LO LO LO UP UP UP LO IN-UP IN-UP — LO UP LO IN-LO

2.46 2.32 2.24 2.70 3.61 3.31 1.93 1.82 1.23 1.46 3.47 2.44 2.76 0.99 6.84 3.81 4.20 7.44 10.0

0.39 0.76 0.20 0.56 0.71 0.35 0.14 0.93 0.41 0.59 0.08 0.24 1.04 1.00 0.19 0.05 0.10 0.10 0.08

1 2 2 2 1 2 1 6 26 13 3 3 4 9 2 2 <1 <1 1

See Table 4.

depth as mentioned in Table 10. The effective rooting depth is equal to the optimal rooting depth, i.e., 1 m for sweet potato and taro, 1.5 m for sugar cane and banana and 2 m for yam, unless a root-limiting layer is present.

The soil fertility characteristics were calculated over the top 0.50 m, taking the thickness of the different horizons into account and attributing weighting factors for different depths according to Table 10. This decision was taken because planting pits,

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317

301

Table 8 Land evaluation data for reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions of sugar cane (optimal rooting depth = 1.5 m) for the nineteen land evaluation units (LEU) LEU WAc (%) WAcm (%) WAc (%) WAcm (%) WAc (%) WAcm (%) PAW SD LTP (mm m1) (m) PM = 1091 mm PM = 591 mm PM = 1591 mm

pHH2O OC (%)

(P2O5)a K ESP (mg kg1) (cmolc kg1) (%)

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

5.9 6.1 6.2 5.9 5.8 6.2 6.0 6.6 6.3 6.3 5.3 5.2 6.5 5.5 6.2 5.8 5.6 5.2 5.4

286 310 175 97 114 128 46 385 48 43 33 130 94 152 59 51 38 32 15

47 46 49 49 47 47 47 48 44 44 45 45 45 47 52 61 63 63 63

47 46 49 49 47 47 47 48 46 46 48 45 49 57 52 61 63 67 76

23 23 24 24 23 23 23 24 22 22 22 22 22 24 26 30 31 31 31

23 23 24 25 23 23 24 24 23 23 24 23 24 29 26 30 31 33 38

70 69 73 73 70 70 70 73 66 66 67 67 67 71 78 91 94 94 94

70 69 73 74 70 70 71 73 69 69 71 68 73 86 78 91 94 100 114

180 204 180 199 201 173 201 195 169 203 206 198 167 151 206 187 170 198 49

1.00 1.00 1.00 1.00 0.40 1.00 0.45 1.65 0.97 1.12 0.85 2.00 0.54 1.05 0.73 1.85 0.83 0.41 0.24

LO LO IN-LO IN-LO LO LO LO LO UP UP UP LO IN-UP IN-UP — LO UP LO IN-LO

2.46 2.32 2.24 2.70 3.61 3.31 1.93 1.82 1.23 1.46 3.47 2.44 2.76 0.99 6.84 3.81 4.20 7.44 10.0

0.39 0.76 0.20 0.56 0.71 0.35 0.14 0.93 0.41 0.59 0.08 0.24 1.04 1.00 0.19 0.05 0.10 0.10 0.08

1 2 2 2 1 2 1 6 26 13 3 3 4 9 2 2 <1 <1 1

see Table 4.

Table 9 Land evaluation data for reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions of banana (optimal rooting depth = 1.5 m) for the nineteen land evaluation units (LEU) LEU WAc (%) WAcm (%) WAc (%) WAcm (%) WAc (%) WAcm (%) PAW SD LTP (mm m1) (m) PM = 1091 mm PM = 591 mm PM = 1591 mm

pHH2O OC (%)

ESP (P2O5)a K (mg kg1) (cmolc kg1) (%)

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

5.9 6.1 6.2 5.9 5.8 6.2 6.0 6.6 6.3 6.3 5.3 5.2 6.5 5.5 6.2 5.8 5.6 5.2 5.4

286 310 175 97 114 128 46 385 48 43 33 130 94 152 59 51 38 32 15

53 53 56 56 53 53 53 55 50 50 51 51 51 54 60 69 71 71 71

53 53 56 56 53 54 54 55 53 53 54 52 56 66 60 69 71 76 87

27 26 28 28 27 27 27 28 25 25 26 26 26 27 30 35 36 36 36

27 26 28 28 27 27 27 28 26 26 27 26 28 33 30 35 36 38 44

80 79 84 84 80 80 80 83 76 76 77 77 77 81 89 104 107 107 107

80 79 84 84 80 80 81 83 79 79 82 77 83 99 89 104 107 114 131

180 204 180 199 201 173 201 195 169 203 206 198 167 151 206 187 170 198 49

1.00 1.00 1.00 1.00 0.40 1.00 0.45 1.65 0.97 1.12 0.85 2.00 0.54 1.05 0.73 1.85 0.83 0.41 0.24

LO LO IN-LO IN-LO LO LO LO LO UP UP UP LO IN-UP IN-UP LO UP LO IN-LO

2.46 2.32 2.24 2.70 3.61 3.31 1.93 1.82 1.23 1.46 3.47 2.44 2.76 0.99 6.84 3.81 4.20 7.44 10.0

0.39 0.76 0.20 0.56 0.71 0.35 0.14 0.93 0.41 0.59 0.08 0.24 1.04 1.00 0.19 0.05 0.10 0.10 0.08

1 2 2 2 1 2 1 6 26 13 3 3 4 9 2 2 <1 <1 1

see Table 4.

with loose consistence and having a depth between 0.3 and 0.5 m, were observed at several LEU’s. The method is opposed to that of Sys et al. (1993) who consider only the top 0.25 m. The depth over

which the nutrients were calculated (0.50 m) responds to the depth where the main rooting system of sweet potato (0.20–0.30 m), taro (0.15– 0.40 m), sugar cane (0.15–0.40 m), and banana

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Table 10 Weighting factors (Sys et al., 1991b) Total soil depth (m)

Number of equal sections

Weighting factors (from top to bottom)

>1.25 1.00–1.25 0.75–1.00 0.50–0.75 0.25–0.50 0.25

6 5 4 3 2 1

2.00–1.50–1.00–0.75–0.50–0.25 1.75–1.50–1.00–0.50–0.25 1.75–1.25–0.75–0.25 1.50–1.00–0.50 1.25–0.75 1.00

Remark. For calculating soil characteristics, soil profiles were divided in equal sections and to each section a weighting factor was attributed. The factors depend on total soil depth and the highest weight is applied to the surface horizon.

(0.20–0.60 m) occurs (Louwagie, 2004). Even though yam tubers can grow much deeper (1.0– 2.0 m), it was assumed that nutrient uptake mainly occurred in the upper 0.50 m. The exchangeable sodium percentage (ESP) was evaluated by taking the highest value within the optimal rooting depth or the effective rooting depth, if a limiting layer was present. Matching tables or land use requirements (LURs) Climatic crop requirements for the considered land use requirements (LUR’s) are given in Table 11. Matching tables for other land characteristics are given in Table 12. As the relative yield indices (cf. Table 1) from the traditional Rapanui soil capability classification and the elaborated prehistoric land evaluation model are comparable to those defined by Sys et al. (1993) for corresponding classes, the matching tables were based on the crop requirement tables given in Sys et al. (1993). Where

insufficient, additional references were consulted; the first author elaborated crop response to natural water deficit and anthropogenic water management. Crop response on climatically determined water deficit (WAc) had to be assessed for the specific Easter Island environment, to attribute severity levels. Water availability of 100% or more means that all the water required for maximum evapotranspiration is available. This value would then correspond to optimal suitability (S1). Water-limited production potential (WPP) was used to check the effect of water deficit on the different LUT’s over the distinct LEU’s, including the test units. Relative yield (RY) was assessed by relating the WPP to the radiationthermal production potential (RPP), i.e., the maximum attainable yield determined by the photosynthetic ability of the crop cultivar and the radiation, irrespective of water stress. WPP- and RPP-calculation were based on the FAO-three-level hierarchy crop growth model (Allen et al., 1998; Kowal, 1978). Subsequently, a linear regression between the dependent variable, relative yield (RY), and the water availability (WAc), here considered to be the independent variable, was established. For sweet potato, the two crop growth periods were considered, which explains the higher amount of observations. For sugar cane, WPP was not calculated for the test units, as the maximum effective rooting depth for water uptake (MERD = 1.5 m) was largely exceeding the sampled profile depth of the test units (0.6 m). Regression equations for taro and yam were not calculated, because of the lack of precision in the selected crop coefficients (kc), and the uncertainty in the soil water depletion fraction (p). Both parameters are necessary to adequately

Table 11 Climatic crop requirement table for the considered land utilisation types (LUT) LUT

Latitude

Sweet potato

N40–S32

T ( C)

Annual P (mm) Opt

Min

Reference

Opt

N40–S32

750–1000 650–1500 750–1250

500 400 500

24 22–32 18–28

Wilson (1977, p. 196) Sys et al. (1993, p. 158) FAO (1996)

Taro

N30–S30 N35–S18

2000–2500 1800–2700

1750 1000

21–27 21–28

Wilson (1977, p. 196) FAO (1996)

Yam

N20–S20 N23–S20

1000–1500 1000–2000

600 700

30 22–32

Wilson (1977, p. 196) FAO (1996)

Sugar cane

N35–S35

1500–2000

1000

24–37

FAO (1996)

N31–S31

1500 to >1800 1200–3600

1000 650

18 to >22 23–33

Sys et al. (1993, p. 24) FAO (1996)

Banana

P, precipitation; T, temperature; Opt, optimum; Min, minimum.

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303

Table 12 Matching tables giving threshold values (UTV, upper threshold value; LTV, lower threshold value) of diagnostic land characteristics (LC) for the different land utilisation types (LUT) to determine land suitability classes (LSC) (multiple sources, see Louwagie, 2004, pp. 377– 384) LQ

Water availability (w)

LC

UTV LTV

UTV LTV

UTV LTV

UTV LTV

UTV LTV

Ib

Ce

Da

So

Ms

WAc (%), WAcm (%)

128 102 70 26

102 70 26 0

128 102 70 26

102 70 26 0

128 102 70 26

102 70 26 0

125 100 69 25

100 69 25 0

136 109 75 27

109 75 27 0

S1 S2 S3 N

PAW (mm m1)

210 125 85 50

125 85 50 0

210 150 125 85

150 125 85 0

210 125 85 40

125 85 40 0

210 140 85 50

140 85 50 0

210 150 125 85

150 125 85 0

S1 S2 S3 N

SD (m)

2.00 0.75 0.50 0.20

0.75 0.50 0.20 0.00

2.00 0.75 0.50 0.20

Landform and topography

Nutrient availability (n) pHH2O

OC (%)

(P2O5)a (mg kg1)

K (cmolc kg1)

Alkalinity (a)

LSC

ESP (%)

8.2 5.5 5.0 4.5

5.5 5.0 4.5 <4.5

6.6 5.5 4.9 4.3

>3.0 2.0 1.0

2.0 1.0 0.0

>3.0 2.0 1.0

650 225 95 25 3.50 0.65 0.35 0.15 0 15 20 >25

225 95 25 0 0.65 0.35 0.15 0.00 15 20 25

0.75 >1.25 0.50 1.00 0.20 0.75 0.00 0.50

0.80 >1.00 0.50 0.75 0.25 0.50 0.00 0.25

Lower part (LO) of slope Intermediate part (IN) of slope Upper part (UP) of slope 5.5 7.0 5.5 7.5 4.9 5.5 5.1 5.5 4.3 5.1 4.8 5.0 4.0 4.8 <4.8 4.5

650 225 95 25

2.0 1.0 0.0 225 95 25 0

3.50 0.65 0.35 0.15 0 10 15 >20

1.00 >1.25 0.75 0.80 0.50 0.50 0.00 0.25

0.65 0.35 0.15 0.00 10 15 20

>3.0 2.0 1.0 650 225 95 25 3.50 0.65 0.35 0.15 0 4 8 >16

2.0 1.0 0.0 225 95 25 0 0.65 0.35 0.15 0.00 4 8 12

>1.5 1.0 0.6 650 225 95 25 3.50 0.65 0.35 0.15 0 10 15 >20

5.5 5.0 4.5 4.0

7.5 5.6 5.2 4.5

1.0 0.6 0.0

>2.4 1.5 0.5

225 95 25 0 0.65 0.35 0.15 0.00 10 15 20

650 225 95 20 3.50 0.65 0.35 0.15 0 4 8 >16

0.75 0.50 0.25 0.00

S1 S2 S3 N

5.6 5.2 4.5 4.0

Upgrade Neutral Neutral S1 S2 S3 N

1.5 S1 0.8 S2 0.0 S3 225 95 20 0 0.65 0.35 0.15 0.00 4 8 12

S1 S2 S3 N S1 S2 S3 N S1 S2 S3 N

Ib, Ipomoea batatas, sweet potato; Ce, Colocasia esculenta, taro; Da, Dioscorea alata, yam; So, Saccharum officinarum, sugar cane; Ms, Musa species, banana; LC, land characteristics, legend see Table 4.

calculate the WPP. The equation obtained for sweet potato was used instead. Table 13 lists regression equations, squared regression coefficients (R2) and number of observations (n) for the different LUT’s. The concomitant threshold values necessary to attribute land suitability classes are calculated according to the levels defined for the Rapanui land suitability classification (Table 1) and listed in the matching tables for the respective LUT’s (Table 12). With respect to additional water supply due to surface runoff, the water availability severity level

or subclass of lower positions along slopes was upgraded with one level or class. Results Climatic suitability To assess the island-wide climatic suitability, the Easter Island precipitation and temperature data (Fig. 3) were compared with the crop-specific climatic requirements (Table 11). According to the cli-

304

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Table 13 Relative yield (RY) for three land utilisation types (LUT) in function of climate- and crop-specific water availability (WAc), latter calculated with mentioned maximum effective rooting depth (MERD) LUT

MERD (m)

RY = f(WAc)

R2

n

Sweet potato Sugar cane Banana

1.0 1.5 0.7

RYIb (%) = 0.7813 · WAc (%) RYSo (%) = 0.7985 · WAc (%) RYM. (%) = 0.7357 · WAc (%)

0.91 0.89 0.86

38 12 19

Ib, Ipomoea batatas, sweet potato; So, Saccharum officinarum, sugar cane; Ms, Musa species, banana; R2, squared regression coefficient; and n, amount of observations.

matic requirements by Sys et al. (1993) the Easter Island climate for sweet potato production is assessed as moderately suitable during the first crop growth period (February–June) (GP1) (Louwagie, 2004; Louwagie and Langohr, 2002) and as marginally suitable during the second period (August–December) (GP2) (Louwagie, 2004). This is due to a moderate to severely limiting mean temperature over the crop growth period. Nevertheless, mean temperature over the distinct crop growth periods still falls within the optimum temperature range as mentioned in the widely used Ecocrop 1-database (FAO, 1996) and is thus considered to be optimal. Annual precipitation is not limiting for sweet potato. Easter Island temperature during the crop growth period for taro (February–November) is at the lower limit of the optimum temperature range of 21–28 C. Mean annual precipitation at Mataveri (1091 mm) is far below the required optimum of 1800–2700 mm, but still above the required minimum of 1000 mm. Easter Island temperature during the crop growth period of yam (February–November) is expected to be marginal when compared to the optimum temperature range of 22–32 C. Mean annual precipitation is estimated to be optimal or slightly limiting, as compared to the required 1000– 2000 mm for optimal growth. The Easter Island climate has also marginal precipitation and temperature conditions for sugar cane growth. Temperatures recorded over the year fit with optimal conditions for banana. Sys et al. (1993, p. 23) mention a minimum precipitation of 1000 mm and attribute an S3-class when the annual precipitation is below 1250 mm. Annual precipitation is however assessed as slightly limiting, as the Ecocrop 1-database (FAO, 1996) agrees upon an optimum ranging between 1200 and 3600 mm and a minimum of 650 mm. Altogether, we might expect moderate suitability for banana.

Concluding, Easter Island climate is at the edge of optimal climatic conditions for sweet potato, rather moderate for banana and almost marginal for taro, yam and sugar cane. Static land suitability Table 14 provides a matrix of land suitability classes and subclasses for all the considered LEU’s and LUT’s under reference (PM = 1091 mm), but LEU-specific annual precipitation, and assuming no lithic mulch management. Annual precipitation as assessed for the distinct LEU’s, with precipitation

Table 14 Annual precipitation (P) and land suitability classes and subclasses for distinct land evaluation units (LEU) and different land utilisation types (LUT) for reference precipitation (PM = 1091 mm at Mataveri) LEU P (mm) LUT Ib

Ce

Da

So

Ms

S2n S2w S3n S2n S3w S2n Nn S2n Na S3n/w Nn S3n S3n/w S3n S3n Nn Nn Nn Nn

S2n S2w S3n S2n Nw S2n Nn/w S2a/n Na Na Nn S3n S3n/w S3a/n S3n/w Nn Nn Nn/w Nn/w

S2n/w S2w S3n S2n/w S3w S2n/w Nn S2w Na S3n/w Nn S3n S3n/w S3w S3n/w Nn Nn Nn Nn/w

S2n/w S2w S3n S2n/w S3w S2n/w Nn S2a/w Na Na Nn S3n S3n/w S3a/w S3n/w Nn Nn Nn Nn/w

GP1 GP2 1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

1124 1115 1177 1177 1124 1124 1124 1171 1063 1063 1075 1075 1075 1133 1253 1464 1503 1503 1503

S2n S1 S3n S2n S3w S2n Nn S2n Na S3n Nn S3n S3n S3n S3n Nn Nn Nn Nn

S2n/w S2w S3n S2n S3w S2n/w Nn S2n/w Na S3n/w Nn S3n S3n/w S3n/w S3n/w Nn Nn Nn Nn

Ib, Ipomoea batatas, sweet potato; Ce, Colocasia esculenta, taro; Da, Dioscorea alata, yam; So, Saccharum officinarum, sugar cane; and Ms, Musa species, banana.

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ratios ranging between 0.974 and 1.38, varies between 1063 and 1503 mm. Except for one LEU, AK3, and two test LEU’s, Oone hatu ‘uri (1.2), good black soil, and Oone mararı´a (004), barren soil, there are no differences between the different LUT’s at land suitability class level. This means that the LEU’s have comparable land qualities for the considered staple crops. At subclass level however, differences between the LUT’s appear, mainly with regard to water availability (w). The latter mainly corresponds to differences in the water balance of effective precipitation over crop evapotranspiration during the respective crop growth periods and the ensuing crop response. Within this context, the second crop growth period of sweet potato (August–December) is much less favourable than the first one (February–June). Important water deficits are also noticed for the perennial crops, sugar cane and banana. In case of yam, requiring a deeper soil for optimal root and tuber development, soil depth has a major impact in attributing a higher severity level to the w-subclass. With respect to nutrient availability (n), pH and OC-content are the only soil characteristics that follow crop-specific requirements. With respect to this, OC-content is exceptionally decisive in attributing the n-subclass for the LEU’s AK1 and LP6. Alkalinity (a) is decisive at subclass level in case of crops that are (i) moderately, as taro and sugar cane, to (ii) highly sensitive, as yam and banana, to soil alkalinity. In some cases lower land suitability classes are attributed to the test units as would be expected from their name attributed according to the traditional soil capability classification. In case of the first crop growth period of sweet potato (February–June), Oone hatu (‘uri), good (black) soil (1.2), is attributed an S1-class. For the other LUT’s, water availability is slightly limiting due to an unfavourable climatic crop-specific water balance. It should be mentioned here that Oone hatu (‘uri) is traditionally seen as a good soil with respect to nutrient availability, but prone to water deficiency. LEU 1.1 additionally has slightly limiting K-content. Oone reherehe, poor soil (003), is in the traditional soil capability classification indicated as moderately capable. This soil type is, except for sugar cane and banana, attributed an S2-class with subclass n, indicating moderate limitations with respect to nutrient availability. Both P2O5- and Kcontents are responsible for this shortage. It appears that water availability is additionally limiting for the

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perennial crops sugar cane and banana. Oone mararı´a, barren soil (004), has the specific characteristic of shallow depth, containing common small rock fragments and is traditionally seen as a moderately to marginally capable soil. Except in case of yam, where threshold values for soil depth are more severe than for the other crops, the Oone mararı´a soil type was attributed an S3-class, with subclasses indicating severe limitations of water and nutrient availability. Oone (hatu) mea, red soil with andic properties (002), is especially detrimental to crops with high nutrient demands. This soil type is attributed an S3class with subclass n, due to marginal K-content. Considering intra-site variability, the Vaitea site gives the most coherent picture, as opposed to Akahanga that shows marked variability with respect to limiting land qualities for crop growth. The LEU’s on Vaitea, located in the centre of the island on the slopes of Maunga Terevaka and at about 2 km from Rano Aroi, form a relatively coherent group and mainly show limiting nutrient availability. The LEU’s are considered unsuitable (N-class), dominantly as a consequence of their exchangeable potassium values being below the critical level of 0.15 cmolc kg1; in VA8 available phosphorus content is below the critical level within the 0.50 m control section too. Two LEU’s, VA4 and VA8, have additional limitations with respect to water availability as a consequence of their limited soil depth for deep-rooting crops as yam, sugar cane and banana. With respect to limiting K-content, LP1 belongs to this group too. The La Pe´rouse site, located about 1 km inland from the north coast is, except for LP1, indicated as moderately suitable (S3-class) for crop growth. The LEU’s, however differ at subclass level. Limiting land qualities are in all cases nutrient availability and in some cases water availability. Only LP3, with a soil depth of 2 m, has for none of the considered LUT’s severe limitations with respect to water availability. Thanks to its position at the lower part of the slope, LP3 receives additional runoff and gets an upgrade of the w-subclass. In LP4, shallow soil depth of only 0.54 m additionally restricts water availability for taro and yam. The land characteristics responsible for marginal nutrient availability differ between the LEU’s. LP1 and LP3 have severe limitations due to low K-content; LP4 has marginal P2O5-content and LP6 has marginal OC-content for tuber crops. With respect to marginal conditions for nutrient availability, TP3, located at less than 500 m from the coastal

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cliffs bordering the west side of the island and probably consisting of relatively recent volcanic ash, can be adjoined to this group. AK3, located about 500 m inland from the southeast coast, is comparable to LP4 with respect to nutrient availability. The studied LEU’s at the Akahanga site show the highest diversity with respect to land suitability and limiting land qualities. A site-specific phenomenon is however the relatively high ESP, resulting in alkalinity problems for moderately to highly sensitive crops. The high Na-content results from (i) ocean spray and/or (ii) weathering of the substratum. The substratum at Akahanga indeed is more differentiated and has concomitant relatively high Na2Ocontent (Unpublished data De Paepe). Na-content moreover decreases from bottom to top, a typical gradient in favour of the weathering hypothesis. Especially AK2 shows severe limitations for all the evaluated LUT’s. The same applies to LP6 that also has severe limitations for crops that are sensitive to high exchangeable sodium, as yam and banana. An additional effect results from the fact that relatively high Na-contents can facilitate clay dispersion. Parallel oriented, microlaminated, slightly dusty clay coatings were observed in the field in AK2 and AK3 and their presence (locally up to 20%) was confirmed by micromorphological observations; in LP6, only few (2–5%) clay coatings of the same type were observed in thin section (Louwagie, 2004). Dynamic land suitability: climate variability Extreme drought (PM = 591 mm) Table 15 provides a matrix of annual precipitation variability and land suitability classes and subclasses for all the considered LEU’s and LUT’s under extreme drought (PM = 591 mm). Under extreme drought (PM = 591 mm), differential annual precipitation values over the distinct LEU’s range between 576 and 814 mm. Extreme drought conditions are especially constraining for taro and sugar cane, which require a minimum of 1000 mm precipitation. Also yam and banana, with minimum precipitation requirements around 650 mm, reach their limit. Sweet potato on the other hand copes well with drought, as it only needs a minimum of 500 mm. Ethnographic reports indeed mention that cultivation of taro and yam is neglected in drought periods so that they are apt to die out; to the contrary, sweet potato can be a reliable food because of the tolerance for dry conditions (McMillan Brown, 1996, p. 181).

Table 15 Annual precipitation (P) and land suitability classes and subclasses for distinct land evaluation units (LEU) and different land utilisation types (LUT) under extreme drought (PM = 591 mm at Mataveri) LEU P (mm) LUT Ib

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

609 604 637 637 609 609 609 634 576 576 583 583 583 614 679 793 814 814 814

GP1

GP2

S2n/w S2w S3n S2n/w S3w S2n/w Nn S2n/w Na S3n/w Nn S3n S3n/w S3n/w S3n/w Nn Nn Nn Nn

S3w S3w S3n/w S3w S3w S3w Nn S3w Na/w Nw Nn/w S3n/w Nw Nw S3n/w Nn Nn Nn Nn

Ce

Da

So

Ms

S2n/w S2w S3n S2n/w S3w S2n/w Nn S2n/w Na S3n/w Nn S3n S3n/w S3n/w S3n/w Nn Nn Nn Nn

S2n/w S2w S3n S2n/w Nw S2n/w Nn/w S2a/n/w Na Na Nn S3n S3n/w S3a/n/w S3n/w Nn Nn Nn/w Nn/w

S3w S3w S3n/w S3w S3w S3w Nn S3w Na/w Nw Nn/w S3n/w Nw Nw S3n/w Nn Nn Nn Nn/w

S3w S3w S3n S2n/w S3w S3w Nn S2a/w Na/w Na/w Nn/w S3n/w Nw Nw S3n/w Nn Nn Nn Nn/w

See Table 14.

Water availability (subclass: w) has become the dominant limiting crop production factor in almost all cases. Land suitability classes commonly reflect LUT-specific water balance (precipitation over evapotranspiration) requirements. Nutrient availability, eventually combined with limited rooting depth, remains the limiting factor at the site of Vaitea and in LP1. LEU’s are all classified as unsuitable for the considered LUT’s. Alkalinity remains the dominant limiting factor in AK2, consequently resulting in an N-class. Optimal conditions for crop production (class: S1) are not represented any longer. In accordance with LUT-specific water availability being the most determining land characteristic for land suitability, extreme drought results in the most diverse picture when grouping the LEU’s according to the attributed class for the different LUT’s. Excess precipitation (PM = 1591 mm) Table 16 provides a matrix of annual precipitation variability and land suitability classes and subclasses for all the considered LEU’s and LUT’s under excess precipitation (PM = 1591 mm). Under excess precipitation (PM = 1591 mm), differential annual precipitation values over the distinct LEU’s range between 1550 and 2192 mm. The occur-

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317 Table 16 Annual precipitation (P) and land suitability subclasses and subclasses for distinct land evaluation units (LEU) and different land utilisation types (LUT) under excess precipitation (PM = 1591 mm at Mataveri) LEU

P (mm)

LUT Ib

1.1 1.2 002 003 004 005 006 AK1 AK2 AK3 LP1 LP3 LP4 LP6 TP3 VA2 VA3 VA4 VA8

1639 1627 1716 1716 1639 1639 1639 1708 1550 1550 1568 1568 1568 1652 1827 2135 2192 2192 2192

GP1

GP2

S2n S1 S3n S2n S3w S2n Nn S2n Na S3n Nn S3n S3n S3n S3n Nn Nn Nn Nn

S2n S1 S3n S2n S3w S2n Nn S2n Na S3n/w Nn S3n S3n/w S3n S3n Nn Nn Nn Nn

Ce

Da

So

Ms

S2n S1 S3n S2n S3w S2n Nn S2n Na S3n Nn S3n S3n S3n S3n Nn Nn Nn Nn

S2n S1 S3n S2n Nw S2n Nn/w S2a/n Na Na Nn S3n S3n/w S3a/n S3n/w Nn Nn Nn/w Nn/w

S2n S1 S3n S2n S3w S2n Nn S1 Na S3n/w Nn S3n S3n/w S2n/w S3n Nn Nn Nn Nn/w

S2n S1 S3n S2n S3w S2n Nn S2a Na Na Nn S3n S3n S3a S3n Nn Nn Nn Nn/w

See Table 14.

rence of extremely humid conditions could be constraining for sweet potato, which requires a precipitation optimum between 650 and 1500 mm, but still thrives with annual precipitation varying between 650 and 1500 mm (Table 11; Sys et al., 1993). Nutrient availability has become the dominant limiting crop production factor. Water availability remains the limiting factor in shallow profiles (e.g., VA8, VA4), especially for deep-rooting crops as yam, sugar cane and banana. Alkalinity remains problematic in soils with high exchangeable sodium percentage (e.g., AK2, AK3, and LP6). Altogether inherent soil characteristics are decisive in the spatial land suitability pattern under conditions of excess precipitation. Grouping the LEU’s according to attributed land suitability classes gives the most coherent picture over the different LUT’s, moving practically almost from land suitability to land capability, i.e., from crop-specific to general groups. Dynamic land suitability: anthropogenic response to climate variability Table 17 indicates shifts in land suitability classes and subclasses for all the considered LEU’s and LUT’s as a consequence of lithic mulch under refer-

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ence (PM = 1091 mm), extreme drought (PM = 591 mm) and excess precipitation conditions (PM = 1591 mm); the observed prehistoric garden type is indicated as well. Altogether, the effect of lithic mulch management on land suitability class and/or subclass level is not very pronounced. In the reference situation and under excess precipitation, increasing water availability as a direct result of lithic mulch management results in either (i) no upgrade of the w-severity level when other land characteristics as soil depth or plant available water, are too limiting to allow for an upgrade, or when the increase occurs within the same class, or (ii) an upgrade of the w-severity level, however not reflected in the subclass, as other land qualities are more limiting, or (iii) an upgrade of the w-severity level, so that water availability is no longer the most limiting factor. Under excess precipitation, mentioned effects of lithic mulch management were especially noticed in case of the second crop growth period of sweet potato taro (however not resulting in a different subclass) and sugar cane, under reference climatic conditions also for taro. These data eventually sustain the hypothesis that taro and sugar cane considerably contributed to a more balanced and diverse diet under excess precipitation. However, accepting this hypothesis implies that people would have been hardly aware or even unaware of the limiting nutrient availability status, an inherent soil quality of the LEU’s in question. It is indeed not unrealistic to consider that people adapted to or lived with consequences of environmental pressure or even degradation without being aware of it, as e.g., mentioned by Ponting (1991, p. 401) with respect to the long-term decline in Mesopotamia or the relatively rapid collapse of the Maya and Rapanui culture. Latter author indicates such behaviour as tolerant or resilient. On the other hand, lithic mulch has proven to be most effective in case of (i) extreme drought and (ii) crops that are grown under less favourable conditions. This is (intentionally) the case (i) for the second growth period of sweet potato because of socio-economic reasons, or (ii) for crops with an all-year-round crop growth cycle, as sugar cane and banana. In a similar vein, Kirch (2000, p. 318) mentions deliberate cropping cycle intensification on other Polynesian islands; lithic mulch management could be interpreted as such too. The data further confirm lithic mulch management as an adaptive agricultural strategy at locales with important crop growth period moisture deficits. Accord-

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Table 17 Prehistoric garden types and effect of lithic mulch (SCF, %) on land suitability classes and subclasses for distinct land evaluation units (LEU) and different land utilisation types (LUT) under reference (PM = 1091 mm), extreme dry (PM = 591 mm) and excess precipitation (PM = 1591 mm) conditions LEU

003 005 006 AK2 AK3 LP1 LP3 LP4 LP6 VA4 VA8

Prehistoric garden type

— — — — — Low density boulder garden Edge of boulder garden Edge of household garden Lithic mulch garden Edge of boulder garden Boulder garden

SCF %

2 2 5 20 20 30 5 40 90 30 90

Land suitability classes and subclasses when subject to lithic mulch effect PM (mm) = 1091

591

Ce

Ib

1591

GP1

GP2

— — — — — — — S3n — — —

— — — — — — — — — — —

— — — — — — — — S3n/w — —

So

Ms

— — — — — — — — S3w — —

— — — — — Nn — S3n/w S3a/w — —

Ib

So

GP1

GP2

— — — — — — — — — — —

— — — — S3n — — S3n — — —

— — — — — — — S3n — — —

SCF (%), surface coarse fragments; PM, precipitation at Mataveri climatic station; Ib, Ipomoea batatas, sweet potato; Ce, Colocasia esculenta, taro; Da, Dioscorea alata, yam; So, Saccharum officinarum, sugar cane; and Ms, Musa species, banana.

ing to Giambellucca (1991, in McGregor and Nieuwolt, 1998, p. 265), severe droughts may last between 19 and 32 months at the local island scale, thus affecting one to two crop growth cycles of about a year. Lithic mulch management must have enabled farmers to overcome periodical droughtlinked water shortage, improving water availability to levels as provided by regular rainfall patterns. It appears to be an effective strategy to limit the risks linked to climate variability. The possible side effect of temperature should not be neglected here. Moreover, given the apparent absence of long-term food storage facilities on prehistoric Rapa Nui, ongoing food production must have been of the utmost importance. The locally widespread use of this strategy (e.g., La Pe´rouse, Akahanga), to optimise crop growth conditions for sweet potato, sugar cane and banana could also reflect the importance of a balanced prehistoric diet, both in terms of energy availability and diet diversity. Coverage of land evaluation data with archaeological settlement data The carrying capacity on an island-wide scale is impossible to assess because the land evaluation units are not linked to land mapping units, which allow extrapolation to a larger area. Nevertheless, locating the evaluated LEU’s on the map delineat-

ing 16th century territorial subdivisions on Rapa Nui enables us to discuss the data in a socio-economic context. Fig. 4 gives the model as proposed by Stevenson (2002) based on the distribution of large ceremonial platforms (ahu). This model is considered to give a good approximation of lineage land holdings. An overlay of the 16th century territorial subdivisions with the spatial distribution of the LEU’s shows that (i) LEU’s 1.1, 1.2, 004, 005, and 006 (TSCC), the Akahanga site and the Vaitea site belong to the Akahanga territory, (ii) LEU’s 002 and 003 (TSCC) belong to the Vaihu territory, (iii) the La Pe´rouse site belongs to the Heki’i territory and (iv) the Tepeu site belongs to the Tepeu territory. The Akahanga territory In the Akahanga territory, twelve LEU’s were evaluated. As the territory spreads over an area with differing elevation from 0 to 500 m, high precipitation variability is represented, with estimated annual precipitation values varying between 1063 and 1503 mm over the different units (PM = 1091 mm). Under reference climatic conditions, their land suitability varies from highly to moderately suitable at the footslope of Maunga Te Kahu Rea, located about 1 km land inward from the south coast, to

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309

Fig. 4. Proposed model of territorial subdivisions on Rapa Nui in the 16th century (Stevenson, 2002).

unsuitable on the slopes of Maunga Terevaka (Vaitea), located in the north of the territory. Under extreme drought, land suitability at the footslope of Maunga Te Kahu Rea (LEU’s 1.1, 1.2, 004, and 005) is only moderately to marginally suitable, and water availability has become an important (additional) limiting factor. At Vaitea, nutrient availability still prevails as the most limiting factor to the extent that these LEU’s are evaluated as unsuitable. As mentioned above, inherent soil characteristics determine the land suitability pattern under extreme humidity. Even though the LEU’s at Vaitea have favourable elevation (160–190 m) and slope aspect (southeast) to receive considerable amounts of precipitation (2135–2192 mm), nutrient provision, especially potassium, is unfortunately such that these LEU’s are classified as unsuitable for crop growth. However, this territory exhibits high land suitability variability over a relatively large area compared to the other territories. Food supply is expected to have been sufficient over this land holding. Archaeological data indeed show that even sites as Vaitea (Stevenson et al., 2002), with unsuitable land, or AK2 (Stevenson and Cristino, 1986), with severe limitations due to high sodium content, show evidence of dense prehistoric settlement and extensive gardens. Fig. 5 illustrates the latter at the Vaitea site where the rectangular houses appear to be remains of elite manager houses (Stevenson et al., 2005). Their well-spread distribu-

tion over this infertile part of the Akahanga territory provides evidence for managed agricultural production. The Vaihu territory The Vaihu territory contains two LEU’s that represent the Oone hatu mea (002) and Oone reherehe (003) soil types. Under reference climatic conditions (PM = 1091 mm) and for all the considered LUT’s, Oone reherehe, poor soil, was evaluated as moderately suitable and Oone mea, red soil with andic soil properties, as marginally suitable. Both soil types have restrictions in terms of nutrient availability. In this territory, the substratum is partially composed of more intermediate, more siliceous rock as compared to the Akahanga and Heki’i territories where basalt rock dominates (covering basalt sensu stricto and hawaiitic basalt substratum) (Unpublished data De Paepe). Unfortunately, no detailed chemical analysis of the substratum was available for this site, so that an eventual effect on the nutrient provision could not be assessed. This picture is also valid under excess precipitation (PM = 1591 mm). Under extreme drought (PM = 591 mm), water becomes an additional restraining factor. Land suitability assessment is only based on two point observations here. An adequate soil map is indispensable to verify whether these data can be extrapolated over the relatively small area of this territory.

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Fig. 5. Prehistoric gardens, rectangular houses and studied land evaluation units (LEU’s)* at Vaitea, located in the Akahanga territory (the LEU’s show a limited distribution over the site as the pedological fieldwork only ran over one season as opposed to two successive seasons of archaeological survey; they are concentrated in the area that was excavated in 2001).

The Heki’i territory The Heki’i territory is represented with four LEU’s that are marginally suitable (LP3, LP4, and LP6) to unsuitable (LP1) for the considered LUT’s under reference precipitation (PM = 1091 mm). Limitations are due to limited nutrient and water availability. As this territory lies parallel to the coast at low elevation, estimated annual precipitation is relatively low (around 1100 mm). Water availability is expected to be a restraining factor over the entire Heki’i territory. LEU’s as LP4 and LP6 indeed shift from marginal to unsuitable land under extreme drought (PM = 591 mm). Accordingly, one of the

clearest examples of lithic mulch management within the studied LEU’s is situated at La Pe´rouse (Stevenson and Haoa, 1999), more specifically at LP4 and LP6, with 40 and 90% coverage, respectively. This strategy appears to be an adaptive response, especially to conditions of extreme drought; the average food supply is, despite this strategy, expected to be marginal in the Heki’i territory. The Tepeu territory The Tepeu territory is poorly represented in terms of evaluated land units. Crop growth conditions for the considered LUT’s are marginal with

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respect to nutrient and water availability, under the different climatic scenarios. Restricted potassium and phosphorus availability in TP3 are linked to andic soil properties. As the Tepeu territory roughly coincides with the triangular area where the most recent lava flow occurred and that is characterised by soils developed in volcanic ash deposits, it is assumed that this territory has an overall marginal suitability and concomitant marginal food supply. Unfortunately, the Tepeu district is largely unsurveyed and estimates of the number of archaeological sites and gardens cannot be stated.

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0.25 m of the soil. Periodical burning of the grass cover probably started from the moment grazing became important on the island. However, as compared to this, chemical degradation is much more severe upon land clearing and burning of the primary vegetation when organic carbon and bound nutrients are easily lost through leaching. 4. We only have access to crop requirement data for present-day cultivars. Crop-specific parameters for prehistoric cultivars remain enigmatic. It is expected that prehistoric cultivars yielded less compared to the modern varieties.

Discussion and conclusions The goal of this study is to look at the interaction between the climatic factors and soil characteristics to assess their suitability for the growth of Polynesian cultigens on Rapa Nui between 1500 and 1700 AD. Prior to this assessment, we were cognizant of the fact that the land evaluation model for prehistoric Rapa Nui was applied to present-day physical data. Applying land evaluation procedures to a past context requires us to be aware of the following limitations when drawing our conclusions: 1. A past database, if available, is often not detailed enough or at least highly hypothetical. 2. With regard to climate, no high-resolution palaeo-environmental data exist for the last four hundred years and reference was made to the present-day situation; however it is assumed comparable to prehistoric conditions. 3. Accurate past soil characteristics are difficult to assess. Soils may have changed since the 16– 17th century Polynesian occupation. Physical soil degradation is witnessed by increased erosion on the island since the introduction of grazing sheep (from 1872 to 1985) and cattle (in the 1970s) (McCall, 1995) with ensuing overgrazing, especially on slope positions. Where present, buried soil horizons are the consequence of (i) volcanic activity (AK3, LP3, TP3, and VA3) or (ii) settlement (VA2). Lack of volcanic activity over the past 2000 years (Charola, 1997) and settlement data (surface prospection) between 1300 and 1700 AD on the Vaitea site (Stevenson et al., 2002) provide the evidence that the present-day surface at the studied LEU’s corresponds to that of the 1500–1700 AD period. Intensive grazing also brings an important soil faunal activity of earthworms and dung beetles in the upper 0.10–

With these factors in mind, the island-wide climatic suitability assessment, assuming average climatic conditions being constant over the island and all other land qualities being optimal, would at maximum allow for: 1. an S1-class for sweet potato, 2. an S2- or S3-class for taro, depending on the sitespecific annual precipitation, with 1000 mm as an absolute minimum, 3. an S2- or S3-class for yam, due to limiting temperature over the growth period, 4. an S2- or S3-class for sugar cane, depending on the site-specific annual precipitation, with 1000 mm as an absolute minimum, and as an effect of limiting temperature, 5. an S2-class for banana. Maximum attributed land classes under average, reference precipitation conditions (PM = 1091 mm) varying in function of elevation and slope aspect, are: 1. an S1-class for sweet potato, 2. an S2-class for taro, however also on LEU’s with precipitation slightly above the required minimum where we rather expect an S3-class (e.g. AK1 and TSCC-test units: 1.1, 1.2,Oone hatu ‘uri; 003, O. reherehe; 005, Oone hatu ‘urimararı´a), 3. an S2-class for yam, 4. an S2-class for sugar cane, however also on LEU’s with precipitation slightly above the required minimum where we rather expect an S3-class (e.g., AK1 and TSCC-test units: 1.1, 1.2, Oone hatu ‘uri; 003, O. reherehe; 005, Oone hatu ‘uri-mararı´a), 5. an S2-class for banana.

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From this point of view, the elaborated model seems a little too optimistic for taro and sugar cane at those LEU’s that receive marginal annual precipitation. The land evaluation conducted in this study learned that today, soils are generally only moderately to marginally suitable for the staple crops that the prehistoric Rapanui society relied upon. In contrast to the initial expectations, problems of soil nutrient availability associated with andic soil properties, rather than soil water availability, became highly important in the evaluation procedure. This soil status did not develop after erosion of a fertile forest soil that may have been present before deforestation (Mieth and Bork, 2003; Renfrew and Bahn, 1996, p. 252). The exposure of less fertile soil horizons is certainly possible, and investigated soil profiles in this research reflect multiple past volcanic events where erosion can uncover less fertile strata. However, these events already predate human occupation on the island and, except for some presentday short-distance sheet erosion on some LEU’s at Akahanga and La Pe´rouse, no evidence of erosion was detected on the studied sites. Particular sites, such as Vaitea, are considered unsuitable due to insufficient nutrient availability, with exchangeable potassium and eventually available phosphorus as the most limiting soil characteristics. Based on field investigations and literature data on the island, Mikhailov (1999) also mentions soil fertility problems, including limited available phosphorus. Other LEU’s in the area of Akahanga are assessed as unsuitable because they suffer from too high exchangeable sodium percentages, originating most probably from weathering of the Na2O-rich substrate with some possible ocean spray. How did the combination of nutrient-deficient soils and variable rainfall affect agricultural production on Rapa Nui? We propose there were responses to these variables in both the technical and organisational spheres of production and these would have included modifying the landscape through lithic mulching and land use planning by matching crop growth areas to land utilisation types. These strategies would have reduced the effects of climate variability and prevented additional decreases in crop yields. In addition to higher rainfall in the upland regions, portions of these areas were attractive because of the rugged lava flows that create a dissected topography. Environmental barriers to wind,

be they natural stone outcrops, or artificial earthworks (Ladefoged et al., 2003), are very effective in reducing evapotransporation and raising the overall amount of available moisture. The rugged topography of the Vaitea region contains many small, protected depression positions with pockets of deeper soils that were cultivated. The nearby basalt outcrops also provide the raw materials for the production of lithic mulch and small wind-deflecting boulders that cover the landscape. Still, the current study learns that land at Vaitea is classified as unsuited for the staple crops of the 1500– 1700 AD period as a result of low potassium and phosphorus availability. Yet the archaeological evidences for crop cultivation is extensive throughout a 400-year period (1300–1700 AD). The higher rainfall levels, coupled with lithic mulching, would have raised yields but the low nutrient availability calls for extensively used agricultural fields with a likelihood of considerable plant spacing and frequent fallow periods. The possible side effect of increased soil temperature might also explain why even at Vaitea, where land suitability is assessed as very severely limited due to nutrient deficiency, lithic mulch was applied. The presence of small temples (ahu) and chiefly compounds within the Vaitea region attests to a managerial presence (Stevenson and Haoa, 1998; Stevenson et al., 2002). It is likely that these marginal lands were used for production above the household level that would support seasonal feasting and corporate building projects. Yields for these activities may have been lower than optimum and possibly have involved a high investment of labour. Based on the latter hypothesis, a near-constant supervision may have been necessary for initially clearing new fields, weeding and clearing, and transport of foods to lowland regions at the needed times. This fits with the earlier-formulated organisational strategies and would have strengthened the bureaucratic structure of the chiefdom but the level of investment in community projects would have been low and over the longer term. In general, the climatic and nutrient data suggest that the economy would have focused on the sweet potato. In lowland locations, this tuber could have withstood most of the extremes in moisture fluctuation and produced a viable crop twice annually. However, the overall quantity of tubers would have varied depending upon soil fertility. The lack of nutrients may have spurred the early introduction of artificial fertilisation practices where organic

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refuse was added to the soil, albeit that hard evidence for the latter are missing so far. On soils which allowed adequate rooting depth, the addition of lithic mulch would have raised the available moisture (WAcm) by about 20–25% in the case of 90% surface cover (Tables 4–9). This technique seems especially beneficial during the second crop growth period of sweet potato (August–December) (Table 17). The climatic parameters also suggest that taro and yam were not particularly reliable at lowland locations. Both of these tubers are at the lower limit of their moisture tolerance levels under average conditions and, like the sweet potato, would produce even lower yields on nutrient-poor soils. The excavation of deep planting pits covered with lithic mulch to contain these tubers may have been sufficient to grow these plants in good years. It is more likely however, that taro and yam predominated at upland locations in areas of deeper soils to increase their overall productivity. Rainfall variability was probably responsible for temporal shifts in the crop and dietary pattern. In periods of excess precipitation, crops such as taro and sugar cane had more favourable growth conditions and could contribute to a more balanced and diverse diet. Increased yields would have allowed greater production. Within the context of prehistoric territorial divisions, this situation probably supported prosperous food exchange and social co-operation. However, in case of extreme drought, food availability and diversity must have periodically dropped. Despite additional management response to temporary crop water stress such as lithic mulching, people were likely living at the edge of sustainability, at least periodically. Our current assessment of general production capability depends on how much area was effectively used for agriculture. In that sense, land availability might have compensated for the limited production potential of the Easter Island environment. The subsistence rationale of spreading risk over several environments, rather than aiming at optimal yields from a single location, fits within this context. Especially within a situation of significant climate variability, characterised by annual oscillations in precipitation, temperature and wind, yield fluctuations must have called for risk allocation as a preferred strategy for sustained food security. This hypothesis is formulated under the assumption of climate variability, characterised by annual or decadal oscillations, rather than (dramatic) climate

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change, occurring at time scales of 100 years or more. The rationale of minimising environmental variation through technical and organisational buffers, such as spreading, and thus minimising risk through the use of different environments, allows an understanding why prehistoric Rapanui people continued to produce well above the subsistence minimum, even under moderate or marginal production conditions. This ability to tolerate and maintain production beyond that of household needs, even under severe environmental limitations, argues that effects of extreme drought could be tolerated, at least over short periods. It is our hypothesis that a combination of an already inherent limitation in nutrient availability, eventually over time exacerbated by continued crop growth, and succeeding years of climatic stress resulted in reduced yields. There were limited options to such a situation. At its apex, the Rapanui culture probably faced a large population and restricting environmental factors that probably limited the amount of additional land available for agriculture. This situation eventually undermined the productive capability of a society that relied upon a few staples augmented by smallscale fishing and chicken husbandry. Such a situation eventually precipitated a crisis of organisation in the late 17th century that resulted in the replacement of a failed ideology (religion) and resourceneedy political organisation. Acknowledgments We acknowledge the following authorities and institutions that facilitated our research activities on Easter Island during the February 2001 and February 2002 scientific missions: Sr. Enrique Pakarati Ika, Governor; Sr. Angel Cabeza, Executive Secretary, ‘‘Consejo de Monumentos Nacionales de Chile,’’ Santiago; the ‘‘Consejo de Patrimonio Rapa Nui’’; the ‘‘Museo Antropolo´gico Padre Sebastian Englert’’; the ‘‘Corporacio´n Nacional Forestal (CONAF)’’; the ‘‘Servicio Agrı´cola y Ganadero (SAG)’’ and the ‘‘Sociedad Agrı´cola y de Servicios Isla de Pascua Ltda. (SASIPA).’’ We are also grateful to Sra. Sonia Haoa and all the respondents to the ethno-archaeological study for their co-operation and interest: Sr. Luis Avaka Paoa, Sr. Juan Cha´vez Haoa, Sra. Luisa Fati, Sr. Nicolas Haoa (Senior), Sr. Juan Haoa Hereveri, Sra. Maria Auxilia Hereveri Pakomio, Sr. Juan Hey, Sr. Alberto Hotus Cha´vez, Sra. Maria Kristina Manutomatoma

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Pakarati, Sr. Omar Castillo, Sra. Evi Pakarati Tepano, Sr. Rodrigo Paoa Atamu and Sr. ‘‘Kipi’’. References AFNOR, 2004. E´valuation de la qualite´ des sols—volume 1: me´thodes d’analyse chimique. Association Franc¸aise de Normalisation. Allen, M.S., 2004. Bet-hedging strategies, agricultural change, and unpredictable environments: historical development of dryland agriculture in Kona, Hawaii. Journal of Anthropological Archaeology 23, 196–224. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration—Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56. Food and Agriculture Organization of the United Nations, Rome. Baker, P.E., 1998. Petrological Factors Influencing the Utilization of Stone on Easter Island. In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Easter Island in Pacific Context, South Seas Symposium, Proceedings of the Fourth International Conference on Easter Island and East Polynesia, August 5– 10, 1997, University of New Mexico, Albuquerque. The Easter Island Foundation Occasional Paper 4. Bearsville and Cloud Mountain Presses, Los Osos, CA, pp. 279–283. Baker, P.E., Buckley, F., Holland, J.G., 1974. Petrology and geochemistry of Easter Island. Contributions to Mineralogy and Petrology 8, 127–139. Cerda`, A., 2001. Effects of rock fragment cover on soil infiltration, interrill runoff and erosion. European Journal of Soil Science 52, 59–68. Charola, A.E., 1997. Death of a moai. Easter Island statues: their nature, deterioration and conservation. Easter Island Foundation Occasional Paper 4. Cloud Mountain Press and Bearsville Press, Los Osos, CA. De Paepe, P., Vergauwen, I., 1997. New Petrological and Geochemical Data on Easter Island. Rapa Nui Journal 11, 85–93. Doolittle, W.E., 1998. Innovation and diffusion of sand- and gravel-mulch agriculture in the American Southwest: a product of the eruption of Sunset crater. Quaternaire 9, 61–69. Doorenbos, J., Kassam, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper 33. Food and Agriculture Organization of the United Nations, Rome, p. 193. Dumont, H.J., Cocquyt, C., Fontugne, M., Arnold, M., Reyss, J.-L., Bloemendal, J., Oldfield, F., Cees, L., Steenbergen, C.L.M., Korthals, H.J., Zeeb, B.A., 1998. The end of moai quarrying and its effect on Lake Rano Raraku, Easter Island. Journal of Paleolimnology 20, 409–422. Englert, P.S., 1974. La tierra de hotu matu’a. Historia y etnologı´a de la Isla de Pascua. Editorial Universitaria, Santiago de Chile, p. 276. FAO, 1976. A Framework for Land Evaluation. FAO Soils Bulletin 32. Food and Agriculture Organization of the United Nations, Rome, p. 72. FAO, 1985. Agroclimatological data. Latin America and the Caribbean. FAO Plant Production and Protection Series 24. Food and Agriculture Organization of the United Nations, Rome. FAO, 1996. Ecocrop 1. Crop Environmental Requirements Database. Software, FAO Software Library, Land and Water

Development Division, Food and Agriculture Organization of the United Nations, Rome. FAO, 2000. Ecocrop. . Plant Production and Protection Division, Food and Agriculture Organization of the United Nations, Rome. Fischer, S.R., Love, C.M., 1993. Rapanui: The Geological Parameters. In: Fischer, S.R. (Ed.), Easter Island Studies, Contributions to the History of Rapanui in Memory of William T. Mulloy. Oxbow Monograph 32. Oxbow Books, pp. 1–6. Flenley, J.R., 1996. Further evidence of vegetational change on Easter Island. South Pacific Study 16 (2), 135–141. Flenley, J., Bahn, P., 2003. The Enigmas of Easter Island. Island on the Edge. Oxford University Press, Oxford, p. 256. Flenley, J.R., King, A.S.M., Teller, T., Prentice, M.E., Jackson, J., Chew, C., 1991. The late quaternary vegetational and climatic history of Easter Island. Journal of Quaternary Science 6, 85–115. Genz, J., Hunt, T.L., 2003. El Nin˜o Southern Oscillation and Rapa Nui prehistory. Rapa Nui Journal 17 (1), 7–14. Gommes, R.A., 1983. Pocket computers in agrometeorology. FAO Plant Production and Protection Paper 45. Food and Agriculture Organization of the United Nations, Rome, p. 140. Goosse, H., Masson-Delmotte, V., Renssen, H., Delmotte, M., Fichefet, T., Morgan, V., van Ommen, T., Khim, B.K., Stenni, B., 2004. A late medieval warm period in the Southern Ocean as delayed response to external forcing? Geophysical Research Letters 31 (6), L06203, doi:. Gosai, A., Salinger, J., Mullan, B., 2002. The Interdecadal Pacific Oscillation—Pacific Climate Shifts. Island Climate Update 21–June 2002. , consulted 09/07/2003. Hauser, Y.A., 1998. Localizacio´n y Caracterizacio´n Morfolo´gica, Geolo´gica y Geote´cnica de Eventuales Sitios para la Captacio´n, Almacenamiento y Distribucio´n de Agua de Riego en Isla de Pascua (Capı´tulo 8). In: Ingenierı´a Agrı´cola Limitada (Ed.), Diagno´stico para el desarrollo integral de Isla de Pascua: proyecto piloto de riego en cultivos hortofrutı´colas, V Regio´n, Tomo I, Diagno´stico de situacion actual. Departamento de Estudios, Comisio´n Nacional de Riego, Repu´blica de Chile. Hunt, T., Lipo, C.P., 2001. Culture elaboration and environmental uncertainty in Polynesia. In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Pacific 2000, Proceedings of the Fifth International Conference on Easter Island and The Pacific. The Easter Island Foundation. Bearsville Press, Los Osos CA, pp. 103–115. Hunter-Anderson, R.L., 1998. Human vs climatic impacts at Rapa Nui: Did the people really cut down all those trees? In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Easter Island in Pacific Context South Seas Symposium, Proceedings of the Fourth International Conference on Easter Island and East Polynesia, August 5–10, 1997, University of New Mexico, Albuquerque. The Easter Island Foundation Occasional Paper 4. Bearsville and Cloud Mountain Presses, Los Osos, CA, pp. 85–99. ISO 10694, 1995. Soil quality—determination of organic and total carbon after dry combustion (elementary analysis). , consulted 23/12/2003.

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317 Karlen, D.L., Mausbach, M.J., Doran, J.W., Cline, R.G., Harris, R.F., Schuman, G.E., 1997. Soil quality: a concept, definition and framework for evaluation. Soil Science Society of America Journal 61 (1), 4–10. Kirch, V.P., 2000. On the Road of the Winds. An Archaeological History of the Pacific Islands before European Contact. University of California Press, Berkeley, p. 424. Kowal, J., 1978. Agro-ecological zoning for the assessment of land potentialities for agriculture. In: Land evaluation standards for rainfed agriculture, Report of an Expert Consultation, October 25–28, 1977, Rome. FAO World Soil Resources Report 49. Food and Agriculture Organization of the United Nations, Rome, pp. 13–23. Ladefoged, T., Graves, M., McCoy, M., 2003. Archaeological evidence for agricultural development on Kohala, Island of Hawai’i. Journal of Archaeological Science 30, 923–940. Landon, J.R. (Ed.), 1991. Booker Tropical Soil Manual. A Handbook for Soil Survey and Agricultural Land Evaluation in the Tropics and Subtropics. Longman Scientific & Technical Harlow, England, p. 474. Leach, H.M., 1999. Intensification in the Pacific. Current Anthropology 40, 311–321. Lightfoot, D.R., 1994. Morphology and ecology of lithic-mulch agriculture La Pe´rouse area (Easter Island, Chile). Geographical Review 84, 172–185. Louwagie, G., 2004. Palaeo-environment reconstruction and evaluation based on land characteristics on archaeological sites. Case study I: Verrebroek ‘‘Dok’’ and Doel ‘‘Deurganckdok’’ (Belgium, Province of East-Flanders). Case study II: Easter Island (Chile). Unpublished Ph.D. dissertation, Faculty of Sciences, Ghent University, p. 399. Louwagie, G., Langohr, R., 2002. Testing land evaluation methods for crop growth on two soils of the La Pe´rouse area (Easter Island, Chile). Rapa Nui Journal 16 (1), 23–28. Louwagie, G., Langohr, R., forthcoming 2006. Traditional perspectives on agriculture from Rapa Nui (Easter Island, Chile). In: Denham, T.P., Iriarte, J., Vrydaghs, L. (Eds.), Rethinking Agriculture: Archaeological and Ethnoarchaeological Perspectives. One World Archaeology, UCL Press, London. MacIntyre, F., 2001a. ENSO, climate variability, and the Rapanui: Part I. the basics. Rapa Nui Journal 15 (1), 17–26. MacIntyre, F., 2001b. ENSO, climate variability, and the Rapanui: Part II. oceanography and Rapa Nui. Rapa Nui Journal 15 (2), 83–94. Mann, D., Chase, J., Edwards, J., Beck, W., Reanier, R., Mass, M., 2003. Prehistoric destruction of the primeval ssoils and vegetation of Rapa Nui (Isla de Pascua, Easter Island). In: Loret, J., Tanacredi, J. (Eds.), Easter Island. Kluwer Academic/Plenum Publishers, New York, pp. 133–153. Martinsson-Wallin, H., 1998. Excavations at Ahu Heki’i, La Perouse, Easter Island. In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Easter Island in Pacific Context, South Seas Symposium, Proceedings of the Fourth International Conference on Easter Island and East Polynesia, August 5–10, 1997, University of New Mexico, Albuquerque. The Easter Island Foundation Occasional Paper 4. Bearsville and Cloud Mountain Presses, Los Osos, CA, pp. 171–177. Mather, J.R., 1974. Climatology: Fundamentals and Applications. McGraw-Hill Book Company, New York, p. 412. Maxwell, T.D., 1995. The use of comparative and use of engineering analyses in the study of prehistoric agriculture.

315

In: Teltser, P.A. (Ed.), Evolutionary Archaeology: Methodological Issues. University of Arizona Press, Tucson, pp. 113–128. McCall, G., 1993. Little ice age: some speculations for Rapanui. Rapa Nui Journal 7, 65–70. McCall, G., 1995. Rapanui (Easter Island). In: Pacific Island Year Book. Fiji Times Ltd., Suva, Fiji. , consulted 23/05/1997. MCD-RF, 1991. Me´mento de l’agronome. Collection ‘‘Techniques rurales en Afrique.’’ Ministe`re de la Coope´ration et du De´veloppement, Re´publique franc¸aise, p. 1635. McGregor, G.R., Nieuwolt, S., 1998. Tropical Climatology. An Introduction to the Climates of the Low Latitudes. John Wiley, Chichester, p. 339. McMillan Brown, J., 1996. The Riddle of the Pacific. Adventures Unlimited Press, Kempton, Illinois, USA. Me´traux, A., 1940. Ethnology of Easter Island. Bernice P. Bishop Museum Bulletin 160. Honolulu. Me´traux, A., 1957. A Stone-Age Civilization of the Pacific. Andre Deutsch Limited, London, p. 249. Mieth, A., Bork, H.-R., 2003. Diminution and degradation of environmental resources by prehistoric land use on Poike peninsula, Easter Island (Rapa Nui). Rapa Nui Journal 17, 34–41. Mikhailov, I.S., 1999. Soils of Rapa Nui (Easter Island). Eurasian Soil Science 32, 1177–1180. Morrison, K.D., 1994. The intensification of production: archaeological approaches. Journal of Archaeological Method and Theory I, 111–159. Norero, Sch. A., 1998. Aspectos Clima´ticos y Ecofisiolo´gicos de Isla de Pascua (Capı´tulo 4). In: Ingenierı´a Agrı´cola Limitada (Ed.), Diagno´stico para el desarrollo integral de Isla de Pascua: proyecto piloto de riego en cultivos hortofrutı´colas, V Regio´n, Tomo I, Diagno´stico de situacion actual. Departamento de Estudios, Comisio´n Nacional de Riego, Repu´blica de Chile. Norman, M.J.T., Pearson, C.J., Searle, P.G.E., 1995. The Ecology of Tropical Food Crops. Cambridge University Press, Cambridge, p. 430. Olsen, S.R., Cole, C.V., Watanabe, F.S., Dean, L.A., 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. U.S. Department of Agriculture Circular 939, 1–19. Orliac, C., Orliac, M., 1996. Arbres et arbustes de l’ıˆle de Paˆques. Composition et e´volution de la flore depuis l’arrive´e des Polyne´siens. Rapport interme´diaire, Compte-rendu de la Mission arche´ologique a` l’ıˆle de Paˆques, Octobre-Novembre 1995, Ministe`re des Affaires Etrange`res/CNRS/Consejo de Monumentos/Conaf. Orliac, C., Orliac, M., 1998a. The Disappearance of Easter Island’s Forest: Over-exploitation or Climatic Catastrophe? In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Easter Island in Pacific Context, South Seas Symposium, Proceedings of the Fourth International Conference on Easter Island and East Polynesia, August 5– 10, 1997, University of New Mexico, Albuquerque. The Easter Island Foundation Occasional Paper 4. Bearsville and Cloud Mountain Presses, Los Osos, CA, pp. 129-134. Orliac, C., Orliac, M., with the collaboration of Peartree, E., Wattez, J., 1998b. Composition et e´volution de la flore de l’ıˆle

316

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317

de Paˆques du 14e`me au 17e`me sie`cle. Rapport novembre 1998, CNRS/Ministe`re des Affaires Etrange`res. Orliac, C., Orliac, M., 1999. Evolution du couvert ve´ge´tal a` l’ıˆle de Paˆques du 15ie`me au 19ie`me sie`cle. In: VargasCasanova, P., (Ed.), Easter Island and East Polynesian Prehistory. Instituto de Estudios de Isla de Pascua, Facultad de Arquitectura y Urbanismo, Universidad de Chile, pp. 195– 200. Ponting, C., 1991. A Green History of the World. The Environment and the Collapse of Great Civilizations. Penguin Books Ltd, Harmondsworth, Middlesex, England, p. 430. Raemaekers, R.H. (Ed.), 2001. Crop Production in Tropical Africa. Directorate General for International Co-operation, Ministry of Foreign Affairs, External Trade and International Co-operation, Brussels. Rehm, S., Espig, G., 1991. The Cultivated Plants of the Tropics and Subtropics. Cultivation, Economic Value, Utilization. Institute of Agronomy in the Tropics (IAT), University of Go¨ttingen. Verlag Jose Margraf, Stuttgart, p. 552. Renfrew, C., Bahn, P., 1996. Archaeology. Theory, Methods and Practice. Thames and Hudson, London, p. 608. Rolett, B., Diamond, J., 2004. Environmental predictors of preEuropean deforestation on Pacific islands. Nature 431, 443– 446. Rorrer, K., 1998. Subsistence Evidence from Inland and Coastal Cave Sites on Easter Island. In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Easter Island in Pacific Context, South Seas Symposium, Proceedings of the Fourth International Conference on Easter Island and East Polynesia, August 5–10, 1997, University of New Mexico, Albuquerque. The Easter Island Foundation Occasional Paper 4. Bearsville and Cloud Mountain Presses, Los Osos, CA, pp. 193–198. Rossiter, D.G., 1990. ALES: a framework for land evaluation using a microcomputer. Soil Use and Management 6, 7– 20. Rossiter, D.G., 1996. Discussion paper. A theoretical framework for land evaluation. Geoderma 72, 165–190. Rossiter, D.G., Van Wambeke, A.R., 1997. Automated Land Evaluation System (ALES). ALES Version 4.65 User’s Manual. SCAS Teaching Series T93-2 Revision 6, Department of Soil, Crop & Atmospheric Sciences, Cornell University, Ithaca, New York, p. 280. Schanz, K., 1964. Informe sobre el clima de la Isla de Pascua. Unpublished report, p. 8. Stevenson, C., 1997. Archaeological Investigations on Easter Island. Maunga Tari: An Upland Agricultural Complex. The Easter Island Foundation. Bearsville and Cloud Mountain Presses, Los Osos CA. Stevenson, C.M., 2002. Territorial Divisions on Easter Island in the Sixteenth Century: Evidence from the Distribution of Ceremonial Architecture. In: Ladefoged, T.N., Graves, M.W. (Eds.), Pacific Landscapes, Archaeological Approaches. The Easter Island Foundation. Bearsville Press, Los Osos, CA, pp. 211–229. Stevenson, C.M., Cristino, C., 1986. The residential settlement history of Easter Island’s Southern Coastal Plain. New World Archaeology 7 (1), 29–38. Stevenson, C.M., Haoa, S., 1998. Prehistoric Gardening Systems and Agricultural Intensification in the La Perouse Area of Easter Island. In: Stevenson, C.M., Lee, G., Morin, F.J. (Eds.), Easter Island in Pacific Context, South Seas Sympo-

sium, Proceedings of the Fourth International Conference on Easter Island and East Polynesia, August 5–10, 1997, University of New Mexico, Albuquerque. The Easter Island Foundation Occasional Paper 4. Bearsville and Cloud Mountain Presses, Los Osos, CA, pp. 205–213. Stevenson, C., Haoa, S., 1999. Diminished Agricultural Productivity and the Collapse of Ranked Society on Easter Island. Archaeology, Agriculture and Identity. Kon-Tiki Museum, Oslo. Stevenson, C.M., Wozniak, J., Haoa, S., 1999. Prehistoric agricultural production on Easter Island (Rapa Nui), Chile. Antiquity 73, 801–812. Stevenson, C.M., Ladefoged, T., Haoa, S., 2002. Productive strategies in an uncertain environment: prehistoric agriculture on Easter Island. Rapa Nui Journal 16, 17–22. Stevenson, C.M., Ladefoged, T., Haoa, S., Guerra Terra, A., 2005. Managed Agricultural Production in the Vaitea Region of Rapa Nui, Chile. In: Stevenson, C., Ramirez, J.M., Morin, F., Barbacci, N. (Eds.), The Ren˜aca Papers, Proceedings of the 6th International Conference on Easter Island and the Pacific. The Easter Island Foundation. Bearsville Press, Los Osos, CA, pp. 125–136. Sys, C., Van Ranst, E., Debaveye, J., 1991a. Land evaluation. Part I. Principles in land evaluation and crop production calculations. Lecture notes, International Centre for PostGraduate Soil Scientists, State University Gent, p. 274. Sys, C., Van Ranst, E., Debaveye, J., 1991b. Land evaluation. Part II. Methods in land evaluation. Lecture notes, International Centre for Post-Graduate Soil Scientists, State University Gent, p. 247. Sys, C., Van Ranst, E., Debaveye, J., Beernaert, F., 1993. Land evaluation. Part III. Crop requirements. Lecture notes, International Training Centre for Post-graduate Soil Scientists, University Ghent. Agricultural Publications 7. General Administration for Development Cooperation, Brussels, p. 199. Tainter, J.A., 1988. The Collapse of Complex Societies. Cambridge University Press, Cambridge, p. 250. Thorntwaite, C.W., 1948. An approach toward a rational classification of climate. Geographical Review 38, 55–94. USDA, 1993. Soil Survey Manual. United States Department of Agriculture Handbook 18. Soil Survey Division Staff, United States Department of Agriculture, p. 437. USDA, 1999. Soil Taxonomy. A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Agriculture Handbook 436. Natural Resources Conservation Service, United States Department of Agriculture, p. 869. USDA, 2004. What is Soil Quality? Soil Quality—Managing soil for today and tomorrow. , consulted 27/04/2004. United States Department of Agriculture. Utami, S.R., 1998. Properties and Rational Management Aspects of Volcanic ash Soils from Java, Indonesia. Unpublished Ph.D. dissertation, Department of Geology and Soil Sciences, Faculty of Sciences, University of Gent, p. 388. Van Wambeke, A., 1985. Asia Soil Moisture Regimes. SMSS Technical Monograph, 9. Wilson, L.A., 1977. Root Crops. In: Alvim, P., de, T., Kozlowski, T.T. (Eds.), Ecophysiology of Tropical Crops. Academic Press, New York, pp. 187–236. WRB (FAO, ISRIC, ISSS), 1998. World Reference Base for Soil Resources. World Soil Resources Reports 84. Food

G. Louwagie et al. / Journal of Anthropological Archaeology 25 (2006) 290–317 and Agriculture Organization of the United Nations, Rome, p. 88. Yen, D.E., 1988. Easter Island Agriculture in Prehistory. The Possibilities of Reconstruction. In: Vargas, P.C. (Ed.), Pro-

317

ceedings of the First International Congress Easter Island and East Polynesia, 1984, Hanga Roa, Easter Island, Volume I. Archaeology. Instituto de Estudios Isla de Pascua, Facultad de Arquitectura y Urbanismo, Universidad de Chile, pp. 59–81.