4000 years of human impact and vegetation change in the central Peruvian

Andes - with events parallelling the Maya record?

A. J. CHEPSTOW-LUSTY, K.D. BENNETT, V.R. SWITSUR & A. KENDALL"

A lake-sediment sequence from Marcacocha in the central Peruvian Andes provides a well-dated and continuous vegetation record from an area rich in Inca and pre-Inca

remains over the last 4000 years. Climatic changes in this record at A D 1-100 and AD 900- 1050 seem to be broadly contemporaneous with major arid events from Lake

Chichancanab, Mexico, affecting the Maya civilization and corroborated by the Quelccaya and Huascaran ice cores in Peru.

Recording the human presence in the central Andes Most civilizations in the world probably had their kick-start subsequent to the bizarre acci- dent of cultivating cereals -wheat, rice, maize or millet. In the Andes, a major centre for the origin of numerous cultivated plants (Vavilov 1926; 1992) including potatoes, it may instead have been a diverse array of tubcrs imd pseudo- cereals that led to an early population expan- sion. It was not until much later that maize arrived from Central America to ,supplement and probably to replace many of these indig- enous crops.

The central Andes was the centre of the Inca empire which stretched from southern Colom- bia to central Chile, AD 1290-1537; the end- point of a whole series of civilizations, chiefdoms and kingdoms which have left ar- chaeological remains all through the Andes (Keatinge 1988; Bruhns 1994). There were no historical records until the arrival in 1532 of the Spanish who caused the collapse of the Inca civilization, including the loss of sophisticated farming systems and the introduction of Eura-

sian doniesticated animals. Even in the historical period from 1532 to the present, reliable docu- mentation is largely missing prior to 1850. When only archaeological remains are studied for human impact on the landscape, the record is invariably disjunct in time and space, and fre- quently compounded by the problem of dat- ing events precisely.

Continuous records are needed to document these changes accurately in this area across this time-interval. Well-dated sequences obtainable from lakes within major areas of archaeologi- cal importance can provide continuous records of vegetation and climatic changes, and anthro- pogenic impact, such as at Marcacocha.

The Marcacocha sequence The Patacancha Valley (Peruvian central An- des: 13"13's, 72"12'W, altitude 3300 m), con- taining the infilled lake at Marcacocha, is located within the central area of the Pan-Andean civi- lizations (Keatinge 1988; Bruhns 1994). Reput- edly once a sacred lake according to the local people, its potential palaeo-ecological signifi- cance was recognized by the Cusichaca Trust,

* Chepstow-Lusty 8r Bennett, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, England. Switsur, Godwin Laboratory, Free School Lane, Cambridge C132 ~ K S , England. Kendall, The Cusichaca Trust, Springfields, 62 High Street, Belbroughton. Stourbridge DY9 9511, England.

Keceived 15 December 1995, revised 14 April 1996, accepted 5 July 1996.

ANTIQUITY 70 (1996): 824-33

4000 YEAKS OF HUMAN IMI’ACX AND VEGETATION CIIHNGE IN THE CENTRAL PERUVIAN ANDES H25

FIGUI~E 1. Location o/ Loguna Murcucochtr 011 the /Zl/iplQ170 of soil t h e m Peru relative to the Quulccnya ice cap. Lake Titicaca a n d major Inca cifies.

directed by Ann Kendall; preliminary analy- sis cstablishcd that it contained 8 m of sediments (Tim Holden pers. comm. 1989). The valley is a niinor tributary of the Urubamba river, ex- tending from the confluence at Ollantaytambo (2800 m), once a major Inca city, up to a pass at 4500 m, c. 1 2 k m to the north (FIGIJRES 1 & 2) . It is today heavily cultivated and almost completely deforested. Wooded remnants are mostly secondary, introduced types, even grow- ing on Inca terrace systems, but fragments of native woodland occur in steep-sided ravines. The infilled lakc of Marcacocha, only 40 ni in diameter and located 100 m east of the Pata- cancha river, remains wet in the dry season and it probably formed as a nivation hollow at the end of the last Ice Age.

Previous investigations of the Holocene record of the central Arides, providing a regional scheme for vegetational change, unfortunately have mostly come from above the forest limit at altitudes greater than 4000 m, in Peru at Lagunas Junin, Tuctua, Pomacocha, Jeronimo (Hansen et ( 7 1 . 1984; Hansen et al. 1994), and in Bolivia (Graf 1981). The tree-line at this al-

titude is c. 3900 ni (Ellenberg 1979) , but at Marcacocha the forest has been largely replaced by scrubland communities.

Only Laguna Paca (Hansen et al. 1994) at 3600 m altitude offers a broad, but valuable comparison with Marcacocha (altitude 3300 m]. Laguna Paca lies near the town of Jauja, close to the archaeological site of Pancan in the val- ley of the Mantaro River in the province of Junin, with cultivation up to the lake-shore. The Mantaro River valley and Junin plain have been a focal area for studies investigating the early domestication of plants and have provided abundant ethnobotanical remains (e.g. Pearsall 1980; 1988; Hastorf 1988). Laguna Paca only has a single calibrated radiocarbon date at the base of the sequence at 5303k90 BP, from which all the other dates have been interpolated. Another site at Laguna Baja has provided a vegetation record from the eastern Andes of northern Peru (Hansen & Kodbell 1995) below the tree-line at 3575 m, revealing possible in- dication of anthropogenic activity after 5000 BP. As at Laguna Paca, the time control is not well constrained, and it is in addition rcmoved

826 A.J. CHEPSTOW-LIJSTY, K.D. BENNETT, V.R. SWITSUR & A. KENDALL

from the centre of the Pan-Andean civilization. Lithic material from Manachaque Cave near Laguna Baja with radiocarbon dates c. 4200 BI’ perhaps corroborate the hypothesis that settle- ment and agricultural disturbance were under way near by, as disturbance indicators corre- spond with the lowest representation of the tree Alnus in the pollen record.

Methods Two overlapping series of cores were obtained using a Livingstone piston corer, 5 cm in di-

FIGLIKE 2. Marcacocha, Patacancha Valley, Peru, 12 km north of Ollantnytaiiibo. Ancient terraces and high slope field systems in the background, a maize field in the fore- gro u 11 d .

ameter, from the centre of Marcacocha. The sediment was analysed for fossil pollen, loss on ignition, magnetic properties, and radiocar- bon age determinations, to provide data on lo- cal environmental change. The basal 2 m of the sediments cored, well-rounded gravels of flu- viatile origin, are palynologically barren. Five samples were taken from the upper 6 m of lake muds at approximately equal intervals and sig- nificant vegetation events for bulk radiocarbon dating. They provide an internally consistent series, producing a precise chronostratigraphy

4000 YEARS OF HIJMAN IMPACT AND VEGETATION CHANGE IN THE CENTRAL PERUVIAN ANDES 8 2 7

depth (m) laboratory uncalibrated calibrated reference determination age (EP)

(b.p.1

1.10-1.18 Q-2917 620k50 595+35 240-2.18 Q-2918 1460k50 1340f40 3.10-3.18 Q-2919 1805550 1730+70 4.78-4.86 Q-2920 2245150 2230+60 6.10-6.18 Q-2921 3650+60 3980285

TABLE 1. Bulk radiocarbon dotes of samples at Marcacocha.

and have been calibrated using the program CALIB 3.0 (Stuiver & Reimer 1993a) (TABLE 1). The sediment accumulation was greatest in the central part of the core. Low pollen concentra- tions, because most of the plants in the surrounding

vegetation have poor pollen production and dispersal characteristics, resulted in samples being counted approximately every 30 cm. Additionally, charcoal and total pollen concen- trations were estimated every 8 cm. Pollen of trees is scarce or absent for much of the record, although the region is clearly capable of supporting forest growth in the absence of agriculture. There are only a few grains in any one sample of poten- tially long-distance, high pollen-producing taxa such as Podocarpus and Ephedra.

Results The vegetation record of Marcacocha was di- vided by numerical zonation procedures (Birks & Gordon 1985) intothree zones (FIGURE 3): full results will be published later.

AD

-t

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FIG~JRE 3 . Vegetation and charcoal record at Marcucocha covering over 4000 years. The lithology at Marcacocha consists of homogenous highly organic lake muds deposited relatively slo~uly, except for the rapidly deposited silty horizons, indicated b y arrows. The shaded circles indicate the calibrated radiocarbon dates (see TABLE 1). The taxa illustrated are shown as percentages oj'the total pollen and spores. Infilled dots represent < 0.5%. Significant Andean crops may be represented by the families Chenopodiaceae and Cruciferae, associated with weeds in the Compositae, including Ambrosia. The 3 major zones were calculated according to Birks Li Gordon (1985).

828 A J. CHEPSTOW-LUSTY, K.D. BENNETT, V.R. SWITSlJR & A. KENDALL

Zone m-1 (>Zoo0 BC-C. A D 100) indicates that forests had already been removed and major agriculture was probably being prac- tised. Pollen types in the families Chenopo- diaceae/Amaranthaceae (Chenolilms), which are difficult to distinguish, may include hardy crops such as the pseudo-cereals. quinoa and canihua (Chenopodium quinoa and C. pallidi- caule). These plants are generally considered to he adapted to cold, seasonally dry condi- tions. This is consistent with the Laguna Paca record and with macrofossil evidence from the Junin area ( Hansen P t al. 1994; Pearsal 1980; 1983) confirming cultivation ahout 4000 BP. According to Pearsal(1980), there <ire nine spe- cies of Chenopodium and several of Amaranthus in the Junin area. The Cruciferae may be de- rived from incipient cultivars of the crop maca, Lepidirim meyenii , one of the hardiest crops in the world (Natural Resource Council 1989). Pearsal (1988) records Lepidirim root remains 3000 BC to AD 500-600 at Panalauca cave in the Junin area. The high proportion of Compo- sitae pollen may represent agricultural weeds, or shrubs indicating secondary growth. Ambrosia, a herb within the Compositae, is an excellent indicator of soil disturbance in the New World and is very prominent in this in- terval. This family comprises 33% of the flora in the Patacancha Valley today (Carter 1988). The high proportion of grasses (Gramineae) may indicate conditions favourable to supporting abundant livestock, such as camelids. An in- crease in sedges (Cyperaceae) towards the end of this interval suggests the lake was gradually infilling and the margins encroaching. Through- out this interval, charcoal concentrations are generally very high, reflecting regular burning, possibly to maintain the quality of the pasture, and the valley was clearly subject to agricul- tural pressure.

Zone m-2 (C. A D ZOO-AD 10.501 begins after a sharp influx of silty deposits and high charcoal conLentrations; these perhaps indicate flooding of the river and excess soil erosion during a sudden event such as a flash flood. Two species in the genus Plantago, es- pecially F! rigida type (Hansen et al. 1994; Hoog- hiemstra 1983) increase, suggesting that the climate had become colder. In the regional veg- etation synthesis from the lakes in the Junin area, Hansen P t al. (1994) indicate a similar

cooling between 3000 and 1000 BP (chronolo- gies poorly constrained). These changes are consistent with Seltzer & Hastorf's (1990) study from the Junin area, where peat samples de- posited after the glacier retreated at Quebrada Anas give an age of c. AD 680. Since peat in- ception may occur within 1000 years after gla- cial retreat, the timing of the initiation and longevity of this glacial phase is highly specu- lative -but it did occur before AD 680. Wright (1984) reports a suggested glaciation prior to 1100 BP for the western cordillera of the cen- tral Peruvian Andes.

At Marcacocha, pollen perhaps indicative of the crops, including quinoa, and associated weeds decline, suggesting a reduction of agri- cultural productivity in the Patacancha Valley. Towards the top of this zone, the climate may have begun to become warmer and drier, and farming was attempted again, including possi- bly cultivation of the extremely cold-tolerant tuber, maca (Cruciferae). There is little sign of quinoa cultivation; the increase in grasses pre- ceded by another possible flash-flood may re- flect overgrazing, when expanded use of agricultural fields at lower elevations forced pastures to higher altitudes. The Compositae most likely represent shrubs regenerating in an environment less intensively utilized. The low abundance of Ambrosia may provide clear evi- dence of limited agricultural activity.

The beginning of Zone 171-3 (AD 1050-AD 19941 correlates with the arrival of Alnus after AD 1050 at Marcacocha when the climate switched to comparatively warmer and drier conditions, but with no marked soil erosion event. This AInus rise is clearly shown also at Laguna Paca (Hansen et 01. 1994), where the dating is less precise. Alnus today survives as a riverine species in the Patacancha Valley, and in rare scattered patches on the hillsides. Important for its wood and in Andean traditional medicine (Chiclote et al. 1985), it may also have been a vital tree in stabilizing soil erosion in the past. The em- phasis which the Inca placed on terracing, and the Quechua word mallki meaning both the (planted) tree and a dead ancestor (Sherbondy 1986), make one think they were aware of the role of trees in preventing soil erosion. Forests were state property and damaging them was punished, with a special authority, inallki kamayoc, enforcing regulations (Wickes & Low-

4000 YEAKS OF HIJMAN IMPACT AND VEGETATION CHANGE IN THE CENTRAI, PERUVIAN ANDES 829

derniilk 1938). The Patacancha Valley terraces and canals were created at least from AD 1000 onwards (Ann Kendall pers. comm.); in par- ticular it was intensely terraced during the Inca period, AD 1290-1534, and there are no indi- cations of soil erosion in the record. There is no evidence that post AD 1000 the climate be- came moister because of the appearance of Aliiiis (Hansen eta] . 1994). Between AD 1100 and 1500, precipitation remained low (Thompson et al. 1988) and irrigation systems using melt water became highly developed. Quinoa cultivation begins again, but less pronounced than earlier, or at least Cheno/Ams are present indicating drier conditions. Quinoa was probabli j ust one of many crops including potatoes and ocu, but these latter crops do not produce wind-dispersed pollen. Reduced charcoal production in this interval may indicate a reduction in burning and changes in farming techniques, emphasized by the low abundance of Ambrosia.

Between AD 1550 and 1650, there appears to have been large-scale clearance of the Alnus, following the fall of Ollantaytambo in AD 1537, the final stronghold of Inca resistance to the Spanish. There was a high demand for construc- tion and firewood for towns, mines and iron- works; according to Ansion (1986), the daily wood consumption of a Spaniard equalled that of an Indian for a month. Cultivation of quinoa may even have been suppressed by the Span- ish, due to its association with ancient rituals (Simmonds 1990). Irrigation technology disap- peared, possibly as knowledge faded with the blending of cultures and limited manpower to maintain these systems (Kendall 1992). The increase in Cruciferae (maca?) after the Alnus declines may indicate this crop was being grown as tribute payments to the Spanish or that the climate was in fact becoming cooler. This is speculative; soon after the conquest, the Span- ish found their livestock reproducing poorly in the highlands, and the Indians recommended maca -with results so remarkable they were noted by Spanish chroniclers. Colonial records from 200 years ago indicate tribute payments of roughly 9 tons of macu demanded in the Junin area alone (National Research Council 1989). The terraces of the Patacancha Valley contin- ued to be farmed; the quantity of crops most certainly reduced, whilst varieties and compo- sition may have changed. Marcacocha, remem- bered locally as a small lake 40 years ago, is

today infilled and blanketed by a wetland plant community, dominated by rushes (Juncus).

Maize pollen grains have been found in a scattering of samples between 502 cm depth, approximately 2500 years ago and at 30 cm depth, approximately 150 years ago. Maize pollen grains are large at 70p, and exception- ally poorly dispersed, so it is not impossible that maize has been cultivated in the Patacancha Valley even earlier. At Laguna Paca (Hansen et al. 1994), pollen of maize and other agricul- tural indicators are recorded from 2000 BP. Currently, maize is cultivated adjacent to the infilled lake of Marcacocha, at its extreme alti- tude in the valley. Further up, tubers such as potatoes become dominant. A site with many buriel chambers adjacent to the lake on the low promontory of Juchuy Aya Orqo is being exca- vated. It is expected to have occupations dat- ing over 2700 years from c. 800 BC until the 16th century AD. Carbonized maize and quinoa grains have been uncovered (Emily Dean pers. comm.), with associated pottery of the Late Intermediate Period (c. AD 1000 to 1440).

Correlation with the Quelccaya and Huascaran ice-cores? The Quelccaya ice-core in southern Peru pro- vides a detailed record of precipitation, tem- perature and dust fluxes over the last 1500 years (Thompson et al. 1986; 1988). The first of two dust events in the Quelccaya ice-core, with a peak intensity at c. AD 620, is attributed to major agricultural activity by the Tiwanaku state es- pecially around Lake Titicaca; i t may correlate with a silty-charcoal rich influx between AD 600 and 700 at Marcacocha (FIGURE 4). The second dust event (AD 920), occurring when the climate switched to drier conditions caus- ing the rapid decline of the Tiwanaku State (Ortloff & Kolata 1993), may be linked with the beginning of Zone m-3 (AT) 1050-1994) when Alnus became established. There is a signifi- cant decrease in mean precipitation A D 1000- 1400 in the Quelccaya ice-core, as well as a temperature increase, estimated from the oxy- gen isotopes at 0.5-1"C. This temperature rise AD 1000-1400 is known in Europe as the Me- dieval Warm Epoch (Lamb 1965). Vegetation changes, such as the colonization of Alnus, naturally lag behind the climatic changes. Al- though the climate around Marcacocha today is markedly seasonal (with the dry season be-

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4000 YEAKS 01' HIJMAN IMPACT AND VEGETATION CHANGE IN THE CENTRAL PERUVIAN ANDES 831

tween May and September), the Patacancha river, flowing from snow meltwater deposited above 5000 m, provides a vital year-round wa- ter supply, exploited by irrigation canals built into the sides of the Patacancha Valley and still present today. The drought which destroyed the economic basis of the Tiwanaku State may have been less damaging in this area.

The 'Little Ice Age', a global phenonienon (Grove 1985) clearly shown in the Quelccaya ice-core AD 1490-1900, may have had a pro- found effect in the region. This is the time in the valley when A l n u s starts to disappear rap- idly, probably as a combination of climatic fac- tors and changing land-use practices.

The Huascaran ice-core from the north-cen- tral Andes of Peru (Thompson et al. 1995) pro- vides a palaeocliniatic history spanning the Late Glacial stage and Holocene over 15,000 years. The largest dust peak of the last 10,000 years - which exceeds the average background level by 9 times, and the only other prominent peak (9000 years ago) by almost 3 times - occurs 2000 years ago, at a time of progressive cool- ing. At Marcacocha at AD 1 climatic change begins with a silty, charcoal rich layer as a re- sult of flash-flooding and perhaps inappropri- ate farming techniques, followed by the establishment of cold-favouring Plantago spp. Warming in the Huascaran ice-core record ap- pears to occur when Alnus became established, and the Little Ice Age is in addition clearly documented, corresponding with the marked decline of Alnus .

Parallel climatic events between Marcacocha, Peru and Lake Chichancanab, Mexico? Sediment composition and oxygen isotopes provide a continuous climate proxy record from Lake Chichancanab in Yucatan, Mcxico (Hodell et al. 1995) and evidence of climatic deteriora- tion in the Maya region during the terminal Classic period. Two major events centred at AD 1 and AD 900 are seen in the sulphur content record - used as a proxy for evaporitic gyp- sum, and hence aridity - which appear to be broadly contemporaneous with the dramatic vegetation shifts at Marcacocha at AD 1-100 and AD 950-1050 (FIGURE 4). The oxygen-isotope record at Chichancanab also supports the tim- ing of these events. The intense arid event at AD 1 in Mexico appears to correspond with the

silty-charcoal rich layer at Marcacocha, pre- empting the plants favouring colder conditions, and temporally correlated with the dust layer from the Huascaran C2 ice-core. The highest subsequent peak in the sulphur content record at Chichancanab centred on AD 900, when drought may have caused the collapse of the Classic Maya, may be linked to initiating Alnus growth at Marcacocha at AU 1050, expectedly lagging behind the climatic events when it be- came warmer. And this may be contempora- neous with the major dust peak in the Quelccaya ice-core centred on AD 920, thought to corre- late with the collapse of the Tiwanaku civili- zation around Lake Titicaca.

Laguna Punta, also in the Yucatan, provides a high-resolution oxygen-isotope record span- ning 3500 years (Curtis et al. 1996). Millennial- scale changes are clearly shown at c. 1785 BP and c. 943 BP (AD 1051) and this interval was drier than the periods before or after.

Discussion The matching events seen in the Quelccaya and Huascaran ice-cores and the Marcacocha lake sediments indicates that the Marcacocha events are local expressions of regional forcing fac- tors (FIGURE 4). These events are not only re- gional, for strong responses at AD 1-100 and AD 900-1050 are broadly contemporaneous between both Central and South America (FIG- URE 4). The Huascaran ice-core reveals a pro- gressive cooling which began almost 6000 years ago; at 2000 years ago a threshold was passed which led to a minor glaciation. This event is contemporary with a drought in Mexico. At La Yeguada in Panama, Piperno et al. (1991) dem- onstrate a decline in agriculture after 2000 R P ,

which may have occurred only as a result of loss of soil fertility, but may have a climatic aspect. With both Mexico and Peru experienc- ing droughts at c. AD 1000, one cannot rule out the involvement of El Nifio events; the Andes has a variable and unpredictable climate with El Niiio years causing drought on the Altiplano (Philander 1989), and after a few years of sus- tained aridity and over-exploitation of limited and fragile resources this could cause long-last- ing effects. There is strong evidence that coastal Peru was effected by a series of disastrous El NiAo years around AD 1050 (T. Heyerdahl pers. comm.). In California, Stine (1995) radiocar- bon dated the outer growth rings of trees growing

832 A.J. CHEPSTOW-LIJSTY, K.D. BENNETT, V.R. SWITSLJR & A. KENDALL

below the present water level, killed when the water rose at the end of a drought. He found evidence of two dry periods: one from c. AJI 800 to 1100 and another from c. AD 1200 to 1350. Chumush cemetries in southern Califor- nia from AD 1100 to 1300 reveal a marked in- crease in damaged skulls, arrow injuries and disease as water levels dropped, and hence resources diminished (Fischman 1996). Hydro- gen-isotope ratios of lake organic matter from Lake Kalamazoo, southwestorn Michigan (Krishnamurthy et al. 1995) indicate a shift from a warm, dry period to a cold period at 2000 years ago, and a warming trend since 1000 years ago. More records within and outside the New World are needed to confirm t,he correlation between these major climatic events centred on AD 1 and AD 1000. and better modelling to grasp how they are related.

Today the Andes in Peru are deforested; exotic trees, especially Eucalyptus globulus, are be- ing planted to halt soil erosion. The last 4000 years in Peru has seen climatic fluctuations devastating agricultural systems that could not adapt as rapidly, combined with soil erosion resulting from complete tree lass. Improved terracing and irrigation technology correspond with a series of kingdoms and chiefdoms lead- ing to the rise ofthe Inca c. AD 1290-1537. Soil erosion was reduced. Large areas of the high- lands were described by early Spanish colo- nists as barren and with only patches of forest (e.g. Diez de San Miguel 1567). After their ar- rival, the understanding of the environment and technology was lost, and there was further de- forestation.

References AYSICIN, 1. 1086. El d j o l J - el hosque en lo .iociednd Andinn.

Lima: lnstituto Nacional Forestal y Faiina-FAO. UIRKS. H.J.B. & A.D. GORDON, 1985. Numericml methods in

Quaiernurj~ pollen nnul-vsis. Londnn: Academic Pr RIIIIHNS. K. 1994. Ancicril South Americo. Cambridge!:

bridge lfniversity Press. CAIITER, S. 1988. The vegetation of the Patamncha Valley, i n

A. Kendall (cd.) , Tl7r: Potnconcho I'rrojert 1987-19RX. Unpublished report, The Cusidiaca Trust.

CHI(:LO'I'F, J.P.,D.O. VlDAl.,R.J. Ji\P&E.B. ClilTNi. 1985. Apuntt,s s o h a1gunn.s especim forestales nntivos de la sierrn Perim n n. I,i ma : Minis t eri o de Agrii: ill t ura , Inst i t n t o Nacional Forestal y Fauna.

CilxlIs, J.13.. D.A. HCII IEL~~ & M. BICNNKR. 1996. Climate vari- ability nn thi: Yucatan Peninsula (Mexico] during the past 3500 years, and implications lor May" cultural evolu- tion, Quotrrnary Research 46: 37-47.

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The ancient terraces are still farmed today in the Patacancha Valley, but probably on a much smaller scale; maize and potatoes now appear the main staples in this valley. The irrigation technology of the Inca has largely disappeared, so that fewer people can subsist in these areas. There are now attempts to renew this irriga- tion technology by the Cusichaca Trust in its rural development programme in the Patacancha and other valleys (Kendall 1992).

In the Andes, civilization may have taken off for biogeographical reasons alone, being such a major centre of diversity for so many poten- tial plants and animals for domestication. In these high mountains, with their fragile ecol- ogy and harsh conditions, technology can help humans survive but not cope with sustained climatic extremes. And even in the lowlands of Mexico, the collapse of the Maya reminds us civilization is not secure. High resolution records of vegetation and human impact can provide a framework for placing and linking discontinuous archaeological events of Andean and Maya civilizations within a proxy-climatic continuity.

AcknoM,ledgeiifents. We would like to thank the Cusichaca Trust archaeo1ogic:al group for their assistance at Marcacocha, Sandra Echegaray our guide, Andrew Gerrard (Godwin Laboratory, Canihridge) for the radiocarbon dating and Jill Dye for assistance with preparation. Steve Boreham, Rob Early, Bill Sillar and Simon Haberle provided stimulating dixussions. Chris Glaister, Linda Heusser and Charles Turner gave vital advice for fine sieving and Godwin's oxidation technique. We are grateful to useful reviews by Christine Hastorf and an anonymous reviewer. This work was sup- ported by NERC research grants GR9/804, GR9/02178'X, the Montgomery Trust and the British Ecological Society.

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