Journal of Archaeological Science 34 (2007) 1e9http://www.elsevier.com/locate/jas

Testing the sustainability and sensitivity to climatic change of terraceagricultural systems in the Peruvian Andes: a pilot study

Nicholas P. Branch a,*, Rob A. Kemp a, Barbara Silva a, Frank M. Meddens a,Alan Williams a, Ann Kendall b, Cirilio Vivanco Pomacanchari c

a Department of Geography, Royal Holloway, University of London, Egham Hill, Egham, Surrey, TW20 0EX, UKb 2 Spinner’s Court, 55 West End, Witney, Oxon, OX8 6NJ, UK

c San Cristobal de Huamanga National University, P.O. Box 220, Ayacucho, Peru

Received 15 November 2005; received in revised form 3 March 2006; accepted 16 March 2006

Abstract

The results of an integrated geoarchaeological and palaeoecological pilot study of a prehistoric agricultural terrace and nearby mire basin arepresented. They reveal two stages of terrace construction for the cultivation of Zea mays during the Middle Horizon (615e695 AD) and late,Late Intermediate Period (1200e1400 AD). These stages were strongly associated with evidence for vegetation succession, destabilisation anderosion of the surrounding landscape, and changes in mire surface wetness. The reasons for agricultural terrace abandonment and/or reconstruc-tion are uncertain, with only circumstantial evidence for climatically induced agricultural change.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Peru; Agricultural terrace; Mire basin; Geoarchaeology; Pollen stratigraphy; Radiocarbon dating

1. Introduction

Palaeoclimatic reconstructions based upon ice-core data in-dicate that Periods of short-term climate change have occurredover the past 2000 years in the Peruvian Andes [37,47e49].These changes probably represent a response to variations inthose factors influencing the dominant weather system inthis mountainous region e.g. Intertropical Convergence Zone(ITCZ) and El Nino Southern Oscillation (ENSO). Accordingto the ice-core records, they were extreme, spatially variableevents, which deviated markedly from the present-day cold-semi arid climate, the consequences of which were fluctua-tions between colder/wetter and warmer/drier conditions (seealso [10,16,24,42,43]). In the central Peruvian Andes, the im-pact of these extreme variations in precipitation and/or temper-ature on the terrestrial environment remains unclear, althougha small number of important palaeoecological studies of lakes

* Corresponding author. Tel.: þ44 1784 443405; fax: þ44 1784 472836.

E-mail address: n.branch@rhul.ac.uk (N.P. Branch).

0305-4403/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jas.2006.03.011

and mire basins have started to record the possible responseof the landscape and vegetation cover (e.g. [9,11e15,21e23,36]). To complement these studies, archaeological evidencein Peru suggests that some prehistoric civilisations may havedeveloped subsistence strategies to ensure their survival duringPeriods of aridity such as between 600 and 700 AD (MiddleHorizon, Table 1) when the Wari people created innovativeand highly efficient agricultural systems [17,51]. In contrast,climate change may have caused the demise of some civilisa-tions and their economy. For example, the decline of thecoastal Moche culture (near Trujillo) from 100e700 AD(Early Intermediate Period, Table 1), and the Tiwanaku raisedfield agriculture from 950 AD (Middle Horizon) in the Titi-caca Basin [3,5,34,35,44,46] have both been attributed toa failure to respond to short-term climatic deterioration. Inthe Colca Valley, northwest of Arequipa, detailed investiga-tions of terrace systems have identified three phases of aban-donment, between (i) 540e730 AD (shift from non-irrigatedto irrigated systems due to regional aridity), 1040e1490 AD(abandonment of some higher altitude irrigated terraces, rea-sons unknown though possibly in response to a drier climate),

2 N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

1530e1720 AD (demographic changes caused by disease andsocial reorganisation) [17]. Although there were undoubtedlysocial-political-economic reasons for the rise or fall of thesecultures [18,50], there is a body of multi-proxy data, fromboth archaeological and geological archives, which demon-strate that climate change may have been one of the primaryforcing factors initiating cultural change [3]. These changesprobably included social unrest, political instability and eco-nomic collapse, which settlement and agricultural abandon-ment represent in the archaeological record [39].

1.1. Research rationale

Agricultural terraces are a highly visible landscape feature inthe Peruvian Andes, with some of the most notable exampleslocated within the Cuzco and Ayacucho regions (Fig. 1). Vari-ous individuals and non-governmental organisations (NGOs)have advocated the need to rehabilitate these and other tradi-tional farming methods in order to create a more sustainable ag-ricultural system, and thus longer lasting socio-economicstability [28,30,33,52]. Recent implementation of a trial pro-gramme of Inca terrace restoration and traditional farming inthe Cuzco and Ayacucho regions by the Cusichaca Trust, anNGO with a long history of rural development in Peru, hasled to increased production of cash crops and personal wealth,reduced hunger and improved individual prestige (e.g. [28]).Technological information obtained from associated archaeo-logical excavations of Middle Horizon (Wari; 500e1000AD), Late Intermediate Period (1000e1438 AD) and Late Ho-rizon (Inca; 1438e1533 AD) agricultural terraces has under-pinned the development of this programme, and permittedrecording of their structural organisation and development, in-cluding irrigation and drainage characteristics, and the physicalproperties and composition of the soil infilling the terrace. Sin-gle or multiple palaeosols within vertical sections of the ter-races exposed during archaeological excavations suggested,however, Periodic reconstruction possibly following abandon-ment and/or failure of the agricultural system. These observa-tions stimulated a collaborative science-based investigation tounderstand in detail the land-use and pedo-sedimentary historyof the terraces in the Ayacucho region, and to test the hypothesisthat the terrace agricultural systems were sometimes unsustain-able during extended Periods of drought.

Table 1

Generalised cultural chronology for the Peruvian Andes

Cultural Period Approximate chronology

Republican Period 1826 ADepresent

Colonial Period 1533e1826 AD

Late Horizon 1438e1533 AD

Late Intermediate Period 1000e1438 AD

Middle Horizon 500e1000 AD

Early Intermediate Period 200 BCe500 AD

Early Horizon 800e200 BC

Initial Period/formative 2000e800 BC

Pre-ceramic 4000e2000 BC

Archaic 10,000e4000 BC

2. Study area: Cultural and environmental context

The area chosen for the pilot study was the Chicha-SorasValley (near Andahuaylas in the Ayacucho region), centredon the village of Pampachiri (S 14 �110 W 73 �320), which islocated 125 km southwest of Andahuaylas and 500 km north-west of the Colca Valley (Fig. 1). Pampachiri (3364 m asl) hasa mean annual precipitation of 1000 mm with April to Novem-ber, and December to March, being the dry and wet season,respectively. There are, however, substantial variations in pre-cipitation from year to year [27]. Diurnal temperatures (mean7e10 �C) vary considerably with frequent frosts particularlyduring the dry season. Although arable and pastoral agricul-ture is important for the local inhabitants, farming is onlya moderately significant component of the local economy atpresent. Grazing and tuber (potato and ulloco) crops predom-inate above 3400 m asl, whilst maize, quinoa and tarwi are themain crops cultivated on lower-altitude terraces irrigated fromnatural sources (tributaries)eartificial irrigation channels arerare [27]. The dominant rock types in the area are basalt andtuffdmost of the soils appear to have formed in unconsoli-dated fluvial or mass movement deposits comprising mixturesof these lithologies. The vegetation cover comprises sub-punagrassland/shrubland (ca. 3300e3900 m asl), with isolatedPolylepis trees.

The earliest known evidence for human occupation of theChicha-Soras valley and its hinterland coincides with the startof the Pre-ceramic (4000e2000 BC), followed by occasional

Fig. 1. Location of the Chicha-Soras Valley and other locations mentioned in

the text.

3N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

sites with ceramics related to the Muyu-Moqo C-D style of theInitial Period (2000e800 BC). There is no archaeologicalevidence for human occupation of the Chicha-Soras valleyduring the Early Horizon (800 BCe200 AD) or Early Interme-diate Period (200 BCe500 AD), although the possibility ofhuman activity in the valley during this time cannot be ruledout [8,27,34]. The Middle Horizon (500e1000 AD) was char-acterised by the creation of extensive irrigated terrace agricul-tural systems within the Chicha-Soras valley mainly by theWari civilisation for the cultivation of Zea mays [26,31].This occurred during a time of major military expansionacross the Peruvian Andes, which included the developmentof major towns and villages. Settlement in the Chicha-Sorasvalley was confined to small habitation sites located near tothe terraces, which were possibly occupied only on a seasonalbasis [27]. The collapse of the Wari in the Chicha-Soras valleymay have been associated with some demographic changes, assuggested by ceramic styles; however, unlike other major val-leys that were abandoned e.g. Ayacucho, Chicha-Soras settle-ments continued to be occupied, but it remains unclear whateffect these demographic changes had on the agricultural sys-tem. The onset of the Late Intermediate Period (1000e1438AD) witnessed the continuation of terrace cultivation (Chankaculture) associated with nearby small settlements that werealso probably only occupied on a seasonal basis; whilst athigher altitude numerous corrals were constructed for pastoralfarming. These small sites were probably linked politicallyand economically, at least at a local scale, with larger settle-ments, which comprised both towns and villages locatedmainly on mountainsides and hilltops. Although there is eth-nohistorical evidence to suggest conflict with Inca populationstowards the end of this Period, there is also some archaeolog-ical evidence indicating new terrace construction and in-creased production in more marginal agricultural areas, e.g.steep slopes [27]. The Inca Empire (Late Horizon) imposedits control on the area from 1438 to 1533 AD, which initiateda Period of further terrace construction. In conclusion, the eth-nohistorical and archaeological data suggest that the culturalhistory of the Chicha-Soras valley was characterised by settle-ment continuity, with small habitation sites located near toagricultural terraces from the Middle Horizon onwards.However, due to the absence of a precise chronological modelfor the timing and duration of settlement and agriculture prac-tices, it remains unclear whether the number of settlementsand terraces increased or decreased during, or between, eachcultural Period as a response to political factors or short-term environmental change.

3. Materials and methods

Using a combined palaeopedological/sedimentological,palaeoecological and archaeological approach, the projectconcentrated on a site where a number of buried palaeosolswere observed within terrace sections in close proximity toa mire basin less than 2 km to the south of the village of Pam-pachiri. The terraces were provisionally dated to the Wari cul-tural Period (500e1000 AD) because of pottery typology and

terrace structure. This pilot study involved the recovery of coresamples from the basin, and the archaeological excavation ofan agricultural terrace (Tocotoccasa) located within 20 m ofthe mire edge (Fig. 1).

3.1. Terrace excavation and pedo-sedimentary studies

The terrace form was described and a representative loca-tion chosen for excavation. A trench (ca. 1 � 10 m) at right an-gles to the terrace wall was excavated by hand from the fronttowards the back of the terrace. A 1-metre wide profile withinthe terrace section was described using the pedological termi-nology of Hodgson [25]. Bulk samples were taken at 5-cmvertical intervals, air-dried and the <2-mm fraction analysedfor pH (water), percentage of organic carbon [1], total phos-phate and available phosphate [29].

3.2. Mire basin sampling and palaeoecological studies

By traversing the mire basin with an Eijkelkamp gouge set(3 cm diameter), records were made of the sub-surface sedi-mentary architecture. From the deepest point of the basin,core samples were obtained using a Russian peat sampler(semi-circular, 5 cm diameter), and then transported to RoyalHolloway, where they were stored at 2 �C. The lithostratigra-phy of the core samples was described in the laboratory usingthe Troels-Smith method (summarised in [4]). Organic matterestimations were made on samples at 1-cm intervals using theloss-on-ignition method [2]. Samples for pollen analysis wereextracted at 20-cm and 10-cm intervals, and prepared usinga modified version of the procedure outlined in Moore et al.[32], involving dispersion of the samples in 1% sodium pyro-phosphate, sieving through 200-mm and 5-mm mesh sizes, heavyliquid separation using sodium polytungstate (2.0 g/cm3) andacetolysis [6]. For each sample, maximum pollen counts of300 pollen grains and spores were attempted, although in severalsamples the pollen preservation and concentration was verypoor, which prevented high counts being attained. The pollendiagram was produced using TILIA and TILIA*GRAPH[19,20], and subjectively divided into local pollen assemblagezones based on the changes in pollen stratigraphy recorded.The pollen results are presented as a percentage of total pollen(including aquatics and spores because these form a minor com-ponent of the pollen assemblage). The category of ‘‘other taxa’’in the selected taxa pollen diagram comprise those pollen grainsand spores presently unidentifiable due to being corroded, amor-phous, broken or folded, and those taxa of minor importance tothe this study, e.g. Escallonia, Euphorbiaceae, Malvaceae.During the pollen analysis, microscopic charred particles werecounted and are presented on the pollen diagram as a percentageof total pollen. It should be noted that pollen analysis was alsoattempted on the pedo-sedimentary sequence uncovered withinthe terrace. This would have possibly provided important addi-tional information on the local vegetation cover and those culti-vars grown on the terrace surface. Unfortunately, no pollengrains or spores were preserved.

4 N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

3.3. Radiocarbon dating

Seven peat samples were submitted for radiocarbon dating toBeta Analytic Inc., USA and Waikato Radiocarbon DatingLaboratory, New Zealand. Sub-samples from the terrace sectionfor radiocarbon dating were placed on a large sheet of cleanaluminium foil inside a laminar flow cabinet. Within this‘‘ultra-clean’’ environment (filtered air), the sub-sampleswere then sorted with clean fine forceps, and fragments of char-coal isolated, weighed and then stored in clean glass vials. Eachcharcoal fragment was checked using a low-power zoom-stereomicroscope with reflected light. Although minute amounts ofcharcoal were isolated in most samples, only the Ah and bAhhorizons contained significant quantities. Samples of charcoalfrom a single depth within the palaeosol A horizon were sub-mitted to the NERC Radiocarbon Laboratory East Kilbridefor AMS dating. To minimise potential inaccuracies, everyeffort was made to ensure that charcoal submitted for datingwas from sapwood, although due to the small size of the char-coal fragments there remains a possibility that heartwood wassubmitted. All radiocarbon results were calibrated using proce-dures outlined in Stuiver et al. [41] and Bronk-Ramsey [7].

4. Geoarchaeology of the Tocotoccasa terrace

The profile comprises a surface soil at the current terracesurface and two underlying palaeosols with clearly definedbAh horizons marking: (1) the original sloping land surfaceand (2) an earlier horizontal terrace surface (Table 2, Fig. 2).The front terrace wall extends down into the top of the subsoil(3bBw) horizon of the original sloping soil. Support for thesecond palaeosol marking a previous terrace surface, ratherthan a ‘‘natural’’ stabilised surface following deposition ofslope material, is provided by evidence for an earlier truncatedterrace wall foundation immediately in front of, and runningparallel to, its successor. Sandor and Eash [38] noted a similarrange of palaeosols in the Colca Valley terraces, although they

Table 2

Field description of the Tocotoccasa terrace profile

Depth (cm) Horizon Macromorphology

0e10 Ah1 Dark brown (7.5YR 3/2); sandy silt loam;

strong subangular blocky; many roots;

abrupt boundary to

10e20 Ah2 Very dark greyish brown (10YR 3/2); sandy

silt loam; moderate fine subangular blocky

and moderate fine granular; abundant roots;

clear boundary to

20e28/33 AB Very dark greyish brown (10YR 3/2); sandy

silt loam; few very small stones; moderate fine

to medium subangular blocky; many roots;

abrupt boundary to

28/33e41/45 Bw1 Dark brown (7.5YR 3/2)); clay loam; few very

small and small stones; moderate fine to medium

subangular blocky; common roots; abrupt

boundary to

41/45e53/59 Bw2 Dark brown (7.5YR 3/2); sandy silt loam; few

very small and small stones; weak medium

subangular blocky; few roots; sharp boundary to

53/59e75 2bAh Very dark grey (10YR 3/1) with very dark greyish

brown (10YR 3/2) mottles; silty clay loam; strong

fine subangular blocky and strong fine granular;

few roots; one circular infilling (20 cm diameter)

of very dark greyish brown, sandy silt loam, strong

fine subangular blocky and strong fine granular;

abrupt boundary to

75e85/113 2bBt Dark greyish brown (10YR 4/2); sandy silt loam;

few very small and small stones; massive; few clay

coatings around channels; few roots; clear

boundary to

85/113e110/

base

3bAh Very dark greyish brown (10YR 3/2); sandy silt

loam; few very small and small stones, common

large and very large stones (in central part);

massive; one ovoid pocket (30 � 10 cm) of very

dark grey

(10YR 3/1), sandy silt loam, moderate fine

subangular blocky; abrupt boundary to

110/basee

base

3bBw Dark brown (10YR 3/3); sandy loam; common very

small stones, few large stones; massive; rare clay

coatings around channels

Fig. 2. Tocotoccasa terrace profile: results of the organic carbon (%), pH, total phosphate (mg/kg) and available phosphate (mg/kg).

5N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

did not provide a clear explanation of the distinction betweenthem.

Several authors have emphasised the difficulties of datingthe construction, or reconstruction, of agricultural terracesdue to re-working of pottery (typological dating) and charcoal(radiocarbon dating) within terrace fills [17,27,38]. At Toco-toccasa, the only pottery found in the terrace section was oflate, Late Intermediate age (1200e1400 AD). Fifteen sherdsdistributed throughout the Ah and Bw horizons of the surfacesoil provide a minimum age for this phase of terrace construc-tion. The only other sherd, found in the 2bAh horizon of theupper palaeosol, conceivably translocated downward or be-came incorporated during reconstruction of the terrace, andhence does not reflect the age of the first phase of terrace con-struction. The radiocarbon dating provides possible support forthis interpretation (Table 3). Although it was not possible toobtain sufficient charcoal from the 3bAh horizon, a radiocar-bon date from the 2bAh horizon of 615e695 AD suggeststhat provided the charcoal is in situ, the first terrace surfacewas established by the early part of the Middle Horizon.

In terms of the bulk analytical properties of the Tocotoccasaprofile, pH is lowest (6.0) in the Ah horizon with a progressiveincrease with depth (7.4 in the 3bBw) reflecting the superim-position of a contemporary leaching profile across the palaeo-sols and covering materials. Maximum values of organiccarbon occur in the Ah horizon (6%) with expected lowerpeaks in the 2bAh and 3bAh horizons. Total phosphate andplant-available phosphate contents are highest in the Ah and2bAh horizons, whilst the 3bAh horizon registers only back-ground values. This pattern might reflect the effects of manur-ing (fertilising) on the two agricultural surfaces, and itsabsence in the original ‘‘natural’’ soil, since it is generally as-sumed that the fertility of these terrace soils was maintainedby a combination of fallowing and manuring [17].

In conclusion, the geoarchaeological investigation of theTocotoccasa terrace has recorded two stages of terrace con-struction: (1) early Middle Horizon (615e695 AD), and (2)late, Late Intermediate Period (1200e1400 AD). However, itis unclear whether the later reconstruction of the terrace wasan ad-hoc event (i.e. repair during use), or part of a more sys-tematic regional programme of terrace development following

a Period of decline and abandonment or de-intensification. Thegeoarchaeological results indicate that any abandonment, if itoccurred, was unlikely to be due to soil fertility exhaustion;other factors such as climate or social-economic change mayhave been responsible.

5. Palaeoecological investigation of the mire basin

Mineral-rich sediment accumulation in the basin started be-fore 2020e1535 BC and was characterised by the depositionof silty sand (460e428 cm; Fig. 3). Impeded drainage due tolocalised colluviation, which caused blockage of the basin out-let, seems the most likely cause. The pollen record at this timeindicates a vegetation cover dominated by Poaceae and Aster-oideae/Cardueae, suggesting the formation of grassland andshrubland (LPAZ 1; Table 4, Fig. 3). Herbaceous peat forma-tion (428e406 cm) from 2020 to 1535 BC indicates the crea-tion of semi-terrestrial, wetland conditions. The onset of peatformation coincided with the colonisation of Chenopodiaceae/Amaranthaceae on surrounding dry land (LPAZ 2). Peat accu-mulation was interrupted by a Period of mineral-rich sedimentaccumulation (406e375 cm), probably brought about by de-stabilisation of the surrounding slopes and transportation ofsediment into the basin by fluvial or aeolian processes. Thepollen record indicates that this event corresponded once againto the development of grassland and shrubland with areas ofdisturbed ground (LPAZ 2).

The renewal of peat growth (375e273 cm) reflects a Periodof landscape stability between 400e160 BC and 210 BCe70AD, which coincided with the expansion of grassland (Poa-ceae) and the colonisation of the mire surface by Cyperaceae(LPAZ 2; 373e315 cm; Table 4, Fig. 3). There was thena ‘‘gradual’’ increase in the proportion of mineral matterdeposited within the basin (315e273 cm), culminating in theaccumulation of a thick unit of sandy clay (273e242 cm) in-dicative of significant erosion of the adjacent catchment. Theincreased input of mineral matter into the basin undoubtedlycontributed to the formation of open water on the mire surface,which, according to the pollen data, formed suitable habitatsfor the growth of Potamogeton, whilst the basin margin mayhave had inflowing streams (LPAZ 3). Taxa indicative of

Table 3

Radiocarbon dates from the terrace palaeosol and mire basin

Depth (cm) Material Laboratory code Conventional

age (BP)

Calibrated date

(BC/AD); 2 sigma

dC13 & wrt PDB

70 Charcoal SUERC-1531 1368 � 25 615e695 AD �25.2

42e52 Peat Wk-12220 193 � 45 1640e1710 AD �27.9 � 0.2

1720e1890 AD

1910e1960 AD

95e105 Peat Wk-12221 388 � 40 1430e1530 AD �28.3 � 0.2

1540e1640 AD

194e204 Peat Wk-12222 712 � 40 1220e1330 AD �27.5 � 0.2

1350e1390 AD

235e245 Peat Wk-12223 755 � 64 1150e1330 AD �27.0 � 0.2

295e305 Peat Wk-12224 2075 � 60 210 BCe70 AD �28.2 � 0.2

345e355 Peat Wk-12225 2228 � 58 400e160 BC �28.1 � 0.2

417e427 Peat Beta-142326 3460 � 90 2020e1535 BC �24.1 � 0.2

6 N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

Fig. 3. Radiocarbon-dated pollen stratigraphy, organic matter content and microscopic charred particles for the mire basin.

disturbed ground are also abundant, including Plantago sp.,whilst dominating the dryland vegetation were Asteroideae/Cardueae and Chenopodiaceae/Amaranthaceae (especially be-tween 270 and 242 cm). Pollen-stratigraphic indicators of hu-man activity are present in the record for this Period e.g. Zeamays, and therefore it is tempting to suggest that the mineralsedimentation and pollen-stratigraphic changes may be dueto activities such as irrigated terrace construction, cultivation,animal husbandry, and possibly burning (see microscopiccharred particles; Fig. 3) by the Wari people in the valley dur-ing the Middle Horizon (600e1000 AD).

Peat formation at 1150e1320 AD indicates the renewal ofsemi-terrestrial conditions on the basin surface and the stabili-sation of vegetation cover on surrounding slopes with expan-sion of Poaceae (LPAZ 4; Table 4, Fig. 3). Further erosion ofthe surrounding slopes (211e204 cm), however, occurred priorto 1220e1330 AD, possibly correlating with archaeologicalevidence for the construction, or reconstruction, of irrigated ter-races during the Late Intermediate Period (1000e1430 AD).The pollen stratigraphy provides support for this interpretation,with a temporary phase of Zea mays cultivation occurring

during a Period of renewed peat accumulation between 204e198 cm. This event also corresponds to an increase in disturbedground indicators, namely Plantago sp. A shallow freshwaterlake formed subsequently with deposition of organic-rich sedi-ment (gyttja) (198e175 cm). This development may have beenthe consequence of abandonment, albeit temporary, of the LateIntermediate Period irrigated terrace agricultural system, caus-ing reduced interception of surface water and increased waterdepth within the basin, or short-term climate change to wetterconditions. Following lake drainage, peat accumulation hascontinued in the basin to the present day, though interspersedwith phases of mineral sediment accumulation. Unfortunately,the poor pollen preservation between 175 and 140 cm restrictsthe ability to build upon the sedimentological data. Succeedingthis Period, the pollen data record an expansion of Asteroideae/Cardueae, followed by the colonisation of Poaceae, Cyperaceaeand Plantago sp. during a Period of renewed peat formation,and a temporary phase of Zea mays cultivation prior to the onsetof the Late Horizon (LPAZ 5). The presence of mineral sedi-ment from 50 cm indicates further disturbance of the surround-ing slopes, which resulted in an increase in the representation of

Table 4

Summary of the pollen-stratigraphic data from the mire basin

Depth

(cm)

LPAZ

No.

Local pollen assemblage

zone (LPAZ)

Summary of main taxa

470e425 1 PoaceaeeAsteraceae Poaceae ca. 55%; Asteroideae/Cardueae ca. 38%; Podocarpus ca. 16%; Solanaceae ca. 35%

425e315 2 CyperaceaeeAsteraceae-

Chenopodiaceae/Amaranthaceae

Cyperaceae ca. 45%; Asteroideae/Cardueae ca. 30%; Chenopodiaceae/Amaranthaceae ca. 10e36%;

Poaceae ca. 25%; Plantaginaceae ca. 3%; Cruciferae ca. 10%; Potamogeton ca. 4%

315e235 3 PoaceaeeCyperaceaeeAsteraceae Poaceae ca. 25e55%; Cyperaceae ca. 35e10%; Asteroideae/Cardueae ca. 20e30%; Plantaginaceae

ca. 5%; Caryophyllaceae ca. 5%; Chenopodiaceae/Amaranthaceae ca. 10e20%; Solanaceae ca. 15%

235e145 4 PoaceaeeAsteraceaeeZea mays Poaceae ca. 60%; Asteroideae/Cardueae ca. 10e100%; Zea mays ca. 3%; Cyperaceae ca. 5e15%;

Plantaginaceae ca. 5e15%; Solanaceae ca. 3e40%

145e0 5 PoaceaeeCyperaceae-Asteraceaee

Zea mays

Poaceae ca. 50e30%; Cyperaceae ca. 20%; Asteroideae/Cardueae ca. 30%; Zea mays ca. 15%;

Plantaginaceae ca. 5%

7N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

Poaceae, Asteroideae/Cardueae and Cyperaceae, and coincidedwith a phase of Zea mays cultivation sometime after 1720e1890 AD (Colonial Period).

In conclusion, the litho- and pollen-stratigraphic records in-dicate three significant phases of landscape instability, eachcharacterised by the deposition of mineral-rich sediment: (1)after 70 AD, (2) just prior to 1220e1330 AD, and (3) after1720e1890 AD. The precise reason, or reasons, for theseevents remain uncertain, although the overwhelming evidencefor widespread human occupation of the Chicha-Soras Valleyduring the Middle Horizon (600e1000 AD), Late IntermediatePeriod (1000e1430 AD) and Colonial Period clearly suggeststhat human activities, such as agricultural terrace construction,would clearly have had a marked impact on the landscape.Supporting this interpretation is the direct pollen evidencefor Zea mays cultivation during the Wari Period, Late Interme-diate Period and Colonial Period, presumably on terraces sur-rounding the mire basin.

6. Discussion and conclusions

Although there is a paucity of detailed radiocarbon-datedlithological and pollen-stratigraphic records from mire basinsin the central Peruvian Andes, those in existence indicatemarked sub-regional variations in their sedimentological andvegetation histories [23,40]. Key factors that account for thesevariations include fluctuations in the nature of dominantweather systems across the Andes, and also the influence of‘‘localised’’ variations in altitude and aspect, soil status andgeology, and for the Late Holocene in particular, human activ-ity. Providing unequivocal evidence for the influence of short-term climate change on the landscape of the central PeruvianAndes using predominantly sedimentological and pollen datafrom mire basins is problematical therefore, especially in thoseareas with a long history of human occupation. At those siteswhere this approach has been successful, the absence of directarchaeological evidence for human activity in the area duringthe Period of the climatic event undoubtedly permitted a posi-tive signal to be identified, providing an important terrestrialpalaeoclimatic signature independent of, but supported by,the ice core records [15,40]. In contrast, the long history ofhuman occupation and landscape disturbance (e.g. agriculturalterrace construction) in the Chicha-Soras Valley may explainthe difficulties in recognising an unequivocal signal of short-term climate change in the mire, despite having radiocarbon-dated palaeoenvironmental records. At this site, the multiplephases of sedimentological and vegetation change indicatinglandscape instability or changes in mire surface wetness/dry-ness cannot be confidently correlated with known climaticvariations recorded in ice cores [45,49] and the other palae-oenvironmental archives. Indeed, the evidence provided bythe mire basin records suggest a stronger correlation betweenknown periods of human activity based on the archaeologicalrecord, and phases of landscape stability/instability and culti-vation based on the palaeoecological records. In particular, thearchaeological evidence for continuity of occupation of smallsettlements located adjacent to terraces suggests that human

impact on the surrounding landscape was both intensive andextensive from the Middle Horizon onwards. This does not ne-gate the possibility, however, of a linkage between stages ofagricultural terrace construction, abandonment and/or recon-struction and short-term climate change. However, the evi-dence from both the mire basin and geoarchaeological studyof the Tocotoccasa terrace is equivocal in this respect, whichsuggests that the evidence for any ‘‘climatic-induced agricul-tural crises’’ [35] is circumstantial, and cannot be correlatedwith certainty to a post-Wari Period of terrace abandonmentin the Colca Valley of Southern Peru [17]. Indeed, confidentlylinking the multiple phases of sedimentological and vegetationchange in the mire and stages of terrace construction, aban-donment and/or reconstruction with the wider archaeologicalrecord requires an improved chronological model for settle-ment in the valley as a whole. This will enable an integratedcultural and landscape model for the Chicha-Soras valley tobe truly assessed in terms of regional events, such as demo-graphic changes, due to political, social and economic factors.

Nevertheless, integration of the pedo-sedimentary recordfrom the Tocotoccasa terrace and the sedimentological andvegetation records from the adjacent mire basin has permittedthe compilation of a provisional model of landscape changethat should be further tested. Construction of the Tocotoccasaterrace occurred during the early Middle Horizon (615e695AD) with reconstruction taking place during the late, LateIntermediate Period (1200e1400 AD). This history is inagreement with the mire basin archive, which records land-scape disturbance and cultivation during the Middle Horizon(600e1000 AD), and a further period of landscape disturbanceduring/immediately prior to a period of Zea mays cultivationin the Late Intermediate Period (sometime between 1150e1330 AD and 1220e1330 AD). However, the absence ofmaize pollen in the mire record at other times should not ne-gate the possibility that different crops were being cultivatedin the Chicha-Soras Valley, e.g. Chenopodiaceae/Amarantha-ceae and Solanaceae. It is unclear, however, whether abandon-ment of the terraces occurred prior to reconstruction and, if so,the reasons involved (e.g. short-term climate change). Similaruncertainties surround the Period since reconstruction. Was theterrace abandoned soon after reconstruction (as suggested bythe absence of Zea mays pollen in the mire), or were othercrops grown and the terrace continued in use, albeit possiblyin a less intensive episodic manner, until the Spanish arrived?There is certainly clear evidence in the mire basin for land-scape disturbance during the late, Late Intermediate and IncaPeriods (1220e1330 AD to 1430e1530 AD), which continuedafter 1720e1890 AD, when there was a renewal of Zea mayscultivation. Finally, there remains a possibility that, becauseof the sub-sampling resolution adopted in this study, maizepollen may be present in other horizons of the mire basin se-quence, which would suggest greater continuity of cultivation.

Examination of further terrace sections and mire cores inthe Chicha-Soras Valley is under way to test the tentative link-ages identified in this pilot project. In particular, since it ispossible that the reconstruction of the Tocotoccasa terracereflected an ad hoc repair during usage, rather than a more

8 N.P. Branch et al. / Journal of Archaeological Science 34 (2007) 1e9

systematic regional restoration following a period of abandon-ment or de-intensification, it will be important to establishwhether its pedo-sedimentary record can be replicated in otherterrace sections.

Acknowledgements

The authors would like to thank the staff of The CusichacaTrust for logistical support, and the inhabitants of the villageof Pampachiri for their hospitality, during the field investiga-tions. The project was funded by NERC small research grantno. NER/B/S/2001/00256, and NERC Radiocarbon Dating Al-location 991.1002. The authors would like to thank Archaeo-Scape, Royal Holloway Geography Department, for a grantto purchase the radiocarbon dates from Beta Analytic INCand Waikato Radiocarbon Dating Laboratory. B.S. contributedinformation to this paper during her NERC/ESRC studentship(award no.: R42200034003).

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