Anthropogenic control of late-Holocene landscapes in the Cuzco region,Peru

Abstract

The rise of complex Andean cultures is tied to increasingly sophisticated use of natural resources and infrastructural development. Considerable debate surrounds the extent to which these societies were forced to respond to changing climates or whether their modifications to the landscape minimized climate impacts. Here, we present a region-wide perspective of paleoecological changes around Cuzco, Peru using three lake sediment records. We investigate whether vegetation shifts in the three records occurred simultaneously, and explore whether such changes were due to climatic conditions or human activities, or both. A new paleoecological record from Lake Huaypo reveals a transition from Amaranthaceae (i.e. quinoa) cultivars to maize at c. 2800 cal. yr BP. This agricultural change is also documented at two other Andean lakes: Marcacocha (Chepstow-Lusty A (2011) Agro-pastoralism and social change in the Cuzco heartland of Peru: A brief history using environmental proxies. Antiquity 85: 570–582) and Pacucha (Valencia BG, Urrego DH, Silman MR et al. (2010) From ice age to modern: A record of landscape change in an Andean cloud forest. Journal of Biogeography 37: 1637–1647). Wetter climatic conditions are inferred to be a leading cause behind the change from Amaranthaceae to maize cultivation. At 1300 cal. yr BP, a rapid increase in Andean forest pollen types, especially Alnus, is observed at Huaypo, with similar changes occurring at Marcacocha at c. 1000 cal. yr BP and at Pacucha at c. 500 cal. yr BP. Drier paleoclimatic conditions at the time and the importance of Alnus, a species well-known for its ability to grow quickly and its widespread use for fuel and timber, suggest that the expansion was due partly to agroforestry. The Huaypo paleoecological record reveals that the practice of agroforestry first began during the Wari Period, and then continued through the Late Intermediate Period and period of Incan rule.

Keywords

agriculture agroforestry anthropogenic landscapes fossil pollen quinoa

Introduction

Within the Andes, abrupt or extreme climate events, including regional warming and protracted droughts, have been implicated as some of the major factors leading to the cultural collapse of the Tiwanaku and Wari (Abbott et al., 1997; Binford et al., 1997; Shimada et al., 1991; Thompson et al., 1985), as well as the widespread expansion of the Incan empire (Chepstow-Lusty et al., 2009). However, accounts advocating the role of climate in either the development or collapse of cultures often include only one paleoecological record, or a small number of temporally limited archaeological sites, restricting the ability for spatial and temporal extrapolation. Similarly, focusing on a single climatic event may oversimplify the process of environmentally induced cultural change (Diamond, 2009). Here, we compare three paleoecological lake sediment records in the Cuzco region that span the last 4000 years. This section of the Andes, during this time period, was extensively occupied and modified by human activity (Bauer, 2004; Covey, 2008b). We investigate whether the ecological impact of societies through time was similar within the Cuzco region, and, thus, whether climate or humans had greater control over changing land-use patterns.

Within South America, the Inca are one of the most heavily studied cultures, largely due to their role as the wealthiest and most recognizable group encountered by Europeans. Despite lasting less than 140 years (ad 1400–1532; 550–418 cal. yr BP), the Incan empire is often cited as the culture that transformed Andean landscapes. Engineering feats such as terracing mountainsides, road-building, and monumental architecture are iconic of Incan landscapes. Social organization, such as forcing conquered groups to cultivate maize or trees for tribute payments, also contributed to the manufactured landscapes of the Inca (Bauer, 2004; Garcilaso de la Vega, 1966 [1609]; Hastorf, 1993; Hastorf et al., 2005; Johanessen and Hastorf, 1990). In contrast to the Incan legacy, that of an earlier culture, the Wari, is poorly known. No historical records of the Wari exist, and what is currently known of them is derived from archaeological investigations. Studies of the Cuzco region of southern Peru, the epicenter for Incan societal development, have begun to reveal the foundational importance of Wari cultural developments (ad 600–1000; c. 1350–950 cal. yr BP) (Bauer et al., 2010; Covey, 2008a). Rather than developing unique agricultural techniques, the Inca may have simply built upon existing practices developed by the Wari, or possibly even earlier societies (Bauer, 2004; Covey, 2008a, 2008b).

Plant domestication and agriculture had been present in the Andes of southern Peru for at least 6000 years before the rise of the Wari (Pearsall, 2008). In the Bolivian Andes, just south of Lake Titicaca, the domestication of the cold-hardy, highland cultivar, quinoa (Chenopodium quinoa Willde), appears to have occurred by at least 3500 years ago (Aldenderfer, 1999, 2008; Bruno and Whitehead, 2003; Pearsall, 2008), and paleoecological studies from southern Peru confirm high abundances of Amaranthaceae pollen by this same time, if not slightly earlier (Chepstow-Lusty et al., 1996; Valencia et al., 2010). Although agricultural innovation can be linked to food supply and population growth (Pearsall, 2008), it can also provide for ritual or shamanistic functions (Hastorf, 1993; Hastorf and Johannessen, 1993). In the Cuzco region, archaeological and paleoecological evidence both suggest that between c. 950 and 450 cal. yr BP (ad 1000–1400), termed the Late Intermediate or Killke Period, maize became increasingly important economically and culturally (Bauer, 2004; Branch et al., 2007; Covey, 2008a, 2008b; Hastorf, 1993; Hastorf and Johannessen, 1993). No isotopic studies have been carried out within the Cuzco region itself, and so indications of the dietary importance of maize prior to ad 1000 come largely from paleoecological records. Maize pollen first appears in the lake sediment of Marcacocha c. 2700 cal. yr BP (Chepstow-Lusty et al., 1996, 1997, 2003) and at Pacucha c. 3000 cal. yr BP (Valencia et al., 2010). Because maize pollen grains are quite large (generally 58–99 µm when mounted in silicone, but reaching 108 µm when mounted in glycerine (Holst et al., 2007; Whitehead and Langham, 1965)) and do not disperse far, their presence in lake sediment records is believed to be a reliable indicator of local maize cultivation or processing.

Agroforestry and protection of forest resources were Incan adaptations to a chronic shortage of wood in the Cuzco and Junin regions (Chepstow-Lusty and Winfield, 2000; Hastorf et al., 2005; Johanessen and Hastorf, 1990; Pachacuti Yamqui, 1950 [1613]); Sherbondy, 1986). By 650 cal. yr BP (ad 1300), many barren and probably previously cleared (or uncolonised) Andean mountainsides were planted with a variety of Andean forest species, to control soil erosion and provide constant sources of wood for fuel and tribute payments to the Inca elite (Johanessen and Hastorf, 1990; Pachacuti Yamqui, 1950 [1613]; Sherbondy, 1986). The trees used included cold-adapted, high-altitude trees such as Polylepis and Buddleja, in addition to Andean forest types such as Alnus and Escallonia resinosa (Hastorf et al., 2005; Johanessen and Hastorf, 1990).

Climate has been implicated in nearly all phases of human cultural development, from imperial expansions to collapses around the world (i.e. Diamond, 2009). An academic debate has arisen over whether climate or human initiatives underlay the rise and fall of Andean cultures (e.g. Binford et al., 1997; Erickson, 1999; Kolata et al., 2000), particularly as extreme climate events have become a hot topic in scientific and popular media. The consolidation of power and territorial expansion of the Wari and Incan civilizations have been linked to exploitation of climatic conditions (Chepstow-Lusty et al., 2009; Moseley, 2001). The Wari may have exploited an extended period of drought in the mid to late 6th century ad (1388–1356 cal. yr BP) by introducing their adaptive techniques of irrigation and terraced agriculture to expand their territorial control (Branch et al., 2007; Kemp et al., 2006; Moseley, 2001; Shimada et al., 1991). Likewise, the Inca may have capitalized on a period of sustained warming, that crossed a threshold from c. ad 1100, to expand their empire after c. ad 1400 (550 cal. yr BP; Chepstow-Lusty et al., 2009). However, purely climate-driven interpretations of cultural change have been challenged as ‘premature’ with regard to the chronology of events (Isbell, 2008) and referred to as ‘neo-environmental determinism’ (Erickson, 1999). Instead, some have viewed the entire Holocene as essentially unnatural (i.e. dominated by anthropogenic influence) and highlight the capability of Andean civilizations to adapt successfully to environmental fluctuations (Balee and Erickson, 2006; Denevan, 2001; Erickson, 1999). In this view, human society was in control of their development, rather than subject to the whims of climatic change. Therefore, a question for paleoecologists and archaeologists alike arises: at which point, if ever, do these central Andean cultures attain control of the landscape and overcome climatic challenges?

Here, a new paleoecological record from Lake Huaypo, 20 km northwest of Cuzco, is presented and contrasted with two other regional records, those of Lakes Marcacocha (Chepstow-Lusty et al., 1996, 1997, 2003, 2009) and Pacucha (Hillyer et al., 2009; Valencia et al., 2010). The three sites provide a regional perspective of changes in both climate and human activity around Cuzco, without interruption, over the past 4000 years.

Study site

Lake Huaypo (13°24′31.87″S; 72°7′59.01″W; 3500 m elevation; Figure 1) is located on the Eastern Cordillera of the Peruvian Andes. The lake consists of two basins joined by a shallow shelf, which currently supports marsh vegetation on the northern and southern edges and is typically covered in 0.5–1 m water (Figure 1). The southwestern basin gently slopes to a maximum depth of 5 m. The northeastern lake basin has a maximum depth of 18 m, with steep slopes near the deepest portion. The longest diameter across the two basins is approximately 3 km, and each basin is approximately 0.75 km across the shortest diameter.

Figure 1.

Huaypo map and bathymetry. Huaypo (H) is located 20 km northwest of Cusco (C), west of the Urubamba River valley. The lake consists of two basins (middle right) separated by a shallow shelf. The sediment core was taken from the deeper basin at a depth of 14 m. The steep slopes of the lake basin prevented coring from the deepest portion of the lake. Other paleoecological and paleoclimate sites mentioned in the text include: Tigre Perdido (TP), Pacucha (P), Marcacocha (M), and Quelccaya (Q). This photo of Lake Huaypo was taken in July 2009 facing southeast, providing a view of the slopes at the southern side of the lake with small remnant forest patches and also includes the modern agropastoral landscape that primarily surrounds Huaypo. Photo courtesy of Christopher LaDrew.

Huaypo is a hypersaline lake with no modern inlets or outlets, though it does receive limited water supply from local springs. On the northern shore of Huaypo, there is a knoll reaching an elevation of 3700 m that supports secondary regrowth forest, including introduced Eucalyptus, among cleared agricultural fields. A steeper knoll to the south of the lake, situated between the two basins, has a maximum elevation of 3825 m a.s.l. The modern landscape is a mosaic of forest patches on the steepest terrain, with cultivated fields on gentler slopes. The watershed around Huaypo is relatively flat, and is heavily modified by humans for agricultural and pastoral purposes. Huaypo’s watershed extends c. 10 km in all directions around the lake to draining landscapes with maximum elevations of c. 4300 m. Huaypo is centrally located between the Incan cities of Cusco to the southeast and Ollantaytambo to the northwest, both 20 km distant. Before Incan rule, the region was influenced primarily by the Wari, and experienced less-unified local government during the Qotakalli (ad 200–600; 1750–1350 cal. yr BP) and Killke periods (ad 1000–1400; 950–550 cal. yr BP) (Bauer, 2004; Bauer et al., 2010).

The modern puna landscape around Huaypo is rich in Asteraceae, Plantago, Brassicaceae, and Ericaceae, and includes modern cultivars such as those in the Solanaceae and Fabaceae families. Maize is currently grown in wetter regions to the southeast of the lake in the Pampa de Anta. Introduced populations of Eucalyptus also surround the lake, testifying to the heavily altered nature of this modern landscape. The modern treeline forms around 3200–3300 m, but this is hypothesized to have been artificially lowered by centuries, even millennia, of pastoralism and burning (Ellenberg, 1979; Wille et al., 2002). Elsewhere in the southern Peruvian Andes, evidence of a higher natural treeline is found in remnant patches of upper montane forest that include Asteraceae, Buddleja, Clethra, Ericaceae, Escallonia, Podocarpus, Rubiaceae, and Weinmannia up to 3600 m elevation (M Bush, personal observations, 2005). A dense understorey is often formed by a wide variety of terrestrial ferns. These upper montane forest taxa, which can tolerate fairly dry conditions, would also probably have been found around Huaypo prior to human clearance. Patches of cold-adapted Polylepis woodland may also have existed above the treeline around Huaypo. The genus Alnus has one native Andean species, A. acuminata H.B.K., which is common in upper montane forests (Gentry, 1993). This Andean species is also typical of disturbed areas or along river banks and is prized for human use because of its ability to grow fast and straight and fix nitrogen (Furlow, 1979). In an elevational transect study, Alnus was observed to be a dominant tree and pollen type within a southern Peruvian montane forest between 2300 and 2800 m elevation (Weng et al., 2004b), though it was much less common above 2800 m elevation. Nevertheless, Alnus currently grows from the Sacred Valley (2800 m elevation), north of Cuzco, to elevations of ~3300–3400 m (A Chepstow-Lusty, personal observations, 2009), which is also the common altitudinal limit for high-quality maize production in the area, as shown at Marcacocha.

Huaypo is located close to two previously published paleoecological records from the Cuzco region (Figure 1). Pacucha (13°35′26″S, 73°19′42′W, 3095 m elevation) is a large lake in the Andahuaylas region directly west of Cuzco. The paleoecological record from Pacucha spans nearly 25 kyr, and is described in Hillyer et al. (2009) and Valencia et al. (2010). In contrast, Marcacocha (13°13′S, 72°12′W, 3355 m elevation) is a recently infilled small lake basin, with a paleoecological sediment record spanning 4200 years. This site has been described in Chepstow-Lusty (2011) and Chepstow-Lusty et al. (1996, 2009).

Materials and methods

In August 2005, a sediment core was raised from the deepest portion of Lake Huaypo (Figure 1). The cores were raised using a Colinvaux-Vohnout piston corer (Colinvaux et al., 1999) from an anchored platform in approximately 16.5 m of water. The core was split, described (Figure 1) and photographed for high-resolution digital imagery at the University of Florida Department of Geological Sciences, using a GEOTEK core logger. The chronology of the Huaypo record was based on seven ¹⁴C accelerator mass spectrometry dates on bulk sediment, taken at locations containing sufficient organic material. An eighth radiocarbon date sample was submitted for analysis in the summer of 2011 to assess the modern hard water error in the lake, because the sediment core contained sections with relatively high calcium carbonate percentages. The eighth date sample consisted of a modern submerged aquatic plant (Myriophyllum sp.). Dates were calibrated on OxCal 4.1 using the IntCal09 calibration curve (Bronk Ramsey, 2009; Reimer et al., 2009). Ages were determined by linear interpolation between calibrated radiocarbon ages, using the mean age as the mid-point, from 0 to 310 cm depths and using a polynomial best-fit line from 310 to 791 cm depths.

Sediment subsamples (0.5 cm³) for pollen and charcoal analysis were prepared using standard procedures (Faegri and Iversen, 1989) and then mounted on microscope slides in glycerine. A total of 88 subsamples were taken to provide an average temporal resolution of c. 50 years (distances between samples ranged from 2.5 to 20 cm). During pollen preparation, samples were spiked with exotic Lycopodium tablets, containing a known number of spores, to allow pollen concentrations to be calculated (Stockmarr, 1971). Each sample was counted using a Zeiss photomicroscope under either 400× or 630× magnification. Pollen identification was based on comparison with reference samples from the Neotropical Pollen Library collection at the Florida Institute of Technology, the Neotropical Pollen Database (Bush and Weng, 2006), and published works (Heusser, 1971; Hooghiemstra, 1984; Markgraf and D’Antoni, 1978). Counts of 300 pollen grains were made, excluding aquatic taxa. In the case of low pollen concentrations, counts were terminated after reaching 2000 Lycopodium spores. Some analyzed pollen samples, particularly those in which Zea mays had not been found, were filtered with a 60 µm mesh and reanalyzed to search for Zea grains. The filtered pollen samples were mounted on slides using glycerine and were scanned under 400× magnification on a Zeiss photomicroscope. From this group of filtered samples, maize pollen grains were identified at 10, 105, 110, 120, 165, 260, and 530 cm depths. All grains counted as Zea were >80 µm in diameter. Microcharcoal counts were also made from the pollen slides, counting the number of charcoal particles greater than 5 µm in length per 50 Lycopodium spores.

Loss-on-ignition was performed on 0.5 cm³ sediment samples at 2 cm intervals for the top 2 m, and then at 10 cm intervals for the rest of the core to provide a c. 30–60 yr resolution for organic and bulk carbonate content. The samples were weighed in dry crucibles, and then weighed again after 12 h at 105°C (to determine mass of water loss), 4 h at 550°C (inorganic matter mass), and 2 h at 950°C (carbonate mass) (Heiri et al., 2001).

Data were analyzed using the program R, version 2.11.1, including the functions within the PaleoMAS packages (Correa-Metrio et al., 2010). The detrended correspondence analysis within PC-Ord 5 (McCune and Mefford, 1999) was performed using 43 pollen types, all of which reached an abundance of 0.5% in at least one sample and were present in at least ten counted samples (after Birks, 1998). Similar filtering and analytical procedures were applied to the pollen data from Lakes Pacucha and Marcacocha.

Results

Stratigraphy and chronology

The Huaypo B sediment stratigraphy reveals several distinct sections of sediment deposition within the core (see Figure 3). Sediment consisted of large sections of unlaminated, dark organic gyttja, with several discrete sections of lamination, varying in coloration. Within the first and third meters of the core, several layers of gypsum, or calcium sulfate, were present, ranging from 1 to 9.5 cm in thickness. Gypsum, a mineral commonly found in hypersaline waters, is typically formed under highly evaporative conditions, and also when waters warm, as gypsum becomes less soluble as temperatures increase. The deepest 3.5 m of the sediment core consisted of marbled sediments, possibly indicative of turbulent water flows at the bottom depths of the lake during the first thousand years of its formation.

Calibrated radiocarbon results from the bulk sediment samples indicated the 8 m core from Lake Huaypo spanned approximately 4500 years (Figure 2; Table 1). Around c. 2800–3000 cal. yr BP, several ¹⁴C dates within the core provided nearly simultaneous ages, i.e. within the 95% error range. These ¹⁴C dates were obtained from 154 to 400 cm sediment depth. The close radiocarbon dates probably result from very rapid sedimentation, which could have occurred because of more intense or frequent precipitation events at the time, or also may be related to human activity increasing the vulnerability of the watershed to erosion and hence the amount of sediment carried into the lake. The radiocarbon date received for the modern aquatic plant sample was greater than modern (with modern representing ad 1950), indicative of a lack of hard water error within the lake. Though the amount of hard water error may fluctuate through time (i.e. Grimm et al., 2009), the date at 57 cm (1287±26 cal. yr BP), which had only 0.58% bulk carbonate, is viewed as a reliable age. The remainder of the radiocarbon dates occurred within sections of the sediment core where calcium carbonate abundances were higher (7–15%). However, with the lack of a modern hard water error and the general agreement in chronologies between Huaypo and regional records around c. 3000 cal. yr BP, we consider hard water error to have been minimal throughout the length of this record.

Figure 2.

Huaypo calibrated radiocarbon dates and age model. The calibrated age ranges of dates from 154, 263, 310, and 400 cm depths overlap, indicating a period between c. 2800 and 3000 cal. yr BP in which a large amount of sediment was rapidly deposited. The base age indicates the lake formed c. 4540 cal. yr BP.

Table 1.

Radiocarbon dates and calibrated ages for Huaypo sediment core. Calibration of radiocarbon ages was performed using OxCal 4.1 and the IntCal09 calibration curve (Bronk Ramsey, 2009; Reimer et al., 2009). The calibrated range includes the 2σ ranges on either side of the mean.

Lab code	Depth(cm)	Description	¹⁴ C yr BP(± 1 σ)	δ ¹³ C	Cal. range (cal. yr BP)
OS-72688	31	Bulk sediment	1120±30	−24.50	960–1076
OS-64836	57	Bulk sediment	1360±30	−20.18	1265–1310
OS-72624	154	Bulk sediment	2840±30	−15.10	2863–3064
OS-64837	263	Bulk sediment	2910±25	−29.00	2959–3160
OS-64827	310	Bulk sediment	2870±25	−25.05	2889–3076
OS-64838	400	Bulk sediment	2730±25	−25.19	2765–2873
OS-72688	751	Bulk sediment	3930±30	−25.34	4257–4496
OS-90296	NA	Submerged aquatic	>Modern	−16.03

Figure 3.

Huaypo stratigraphy and loss-on-ignition results by depth (cm). Variations in Huaypo sediment types are shown alongside the percentages of sediment organic matter and calcium carbonate. The seven age ranges (calibrated) are also shown at the appropriate core depth. Gypsum layers are identified by the gray bars. Detailed description of the sediment core shows regions of unlaminated, solid gyttja interrupted by distinct laminated sections. The laminated sections differed in sediment coloration. Discrete layers of gypsum were prevalent in the first and third meters of the core. Marbled sediments made up the base of the sediment core.

Multivariate analysis

The pollen record from Huaypo included 84 terrestrial pollen types. Observation of the pollen spectra, as well as the detrended correspondence analysis (DCA) output (Figures 4 and 5; SOM Figure 1, available online), indicated that three primary pollen zones existed within the paleoecological record, with boundaries at 1265 cal. yr BP (55 cm depth) and 2845 cal. yr BP (165 cm depth).

Figure 4.

Multivariate analysis of Huaypo pollen record; Biplot of Axes 1 and 2. The DCA output of Axes 1 and 2 revealed a clear polarization of the younger samples (<1265 cal. yr BP; circles) from the rest of the record. Along Axis 2, samples from the interval 1265 to 2845 cal. yr BP (squares) were found at the positive end, while the oldest core samples (2845 to 4540 cal. yr BP; triangles) were located at the negative end.

Figure 5.

Huaypo paleoecological record. The complete fossil pollen record is provided with black lines indicating the separation between pollen zones and gray bars delineating gypsum laminae in the lake sediment. Pollen concentration is given as number of grains per cm³, microcharcoal as number of charcoal fragments per cm³, Zea as number of grains counted per sample, and the remaining pollen taxa as percent abundance. Aquatic taxa (i.e. Cyperaceae, Isoetes, Myriophyllum, and Alismataceae) and spores were both calculated as % abundance relative to the pollen sum, though neither of them were included within the sum itself.

The DCA of the pollen record from Huaypo differentiates the youngest samples (modern to 1265 cal. yr BP) from the oldest samples along Axis 1 (Figure 4). A plot of the taxon scores on Axes 1 and 2 indicated the positive end of Axis 1 is driven primarily by montane forest types, such as Alnus, Dodonaea, Acalypha, and Moraceae/Urticaceae (SOM Figure 1). Whereas the negative end of Axis 1 was dominated primarily by the influence of puna types, i.e. Poaceae, Plantago, Rubiaceae (likely high-altitude herbs), and Asteraceae, Axis 2 was more influential in separating samples from 1265 to 2845 cal. yr BP from the samples found at the base of the core. This separation appears to be driven by dominant agricultural types, as Zea mays is at the positive end and Amaranthaceae (quinoa-type) and Ambrosia are at the negative end of Axis 2.

Local pollen zones

HUA-1 (792–165.1 cm depth; 4540–2845 cal. yr BP; pollen concentration 7000–36,250 grains/cm³)

Organic-rich (~40%) sediments with the highest pollen concentrations of the core had the lowest CaCO₃ concentrations. The pollen spectra were dominated by very high abundances of Poaceae (>50%) and the lowest abundance of Andean forest types of the entire core (<10%). High abundances of Amaranthaceae and Ambrosia pollen occurred in HUA-1. Identification of individual pollen grains with a scanning electron microscope indicated the pollen grains from the Amaranthaceae family were probably derived from the agricultural types, most likely that of quinoa (B Valencia, personal observations, 2011; SOM Figure 2, available online), though the Amaranthaceae family also includes salt-tolerant species that may have naturally inhabited the Huaypo catchment area (though there is no evidence of them currently). Intermediate abundances of Cyperaceae probably reflected the low lake levels at this time and a marshy shoreline colonized by sedges. Intermediate concentrations of charcoal were observed in HUA-1. Three gypsum layers were deposited at 244–253.5 cm (2881–2886 cal. yr BP), 230–237.5 cm (2875–2878 cal. yr BP), and 226–227 cm (2873–2874 cal. yr BP). Though the gypsum layers ranged in thickness from 1 to 11 cm, these layers may represent only short time periods (i.e. 1–5 years) as a result of the rapid sedimentation rate suggested by the radiocarbon dates. All three layers were deposited close to the transition between HUA-1 and HUA-2.

HUA-2 (165–55.1 cm depth; 2845–1265 cal. yr BP; pollen concentration 2880–17,750 grains/cm³)

In this interval, pollen concentrations decline slightly from previous levels, while charcoal concentrations increase to their highest levels within the core. Charcoal concentrations also become more variable. The sediment became slightly less organic and more variable than in HUA-1, as concentrations of carbonate increased (7.4%). Zea mays (maize) pollen is found at the beginning of the zone. As maize appeared in the record, Amaranthaceae and Ambrosia abundances declined sharply. Poaceae abundances declined slightly, while Andean forest type abundances slowly increased. Cyperaceae abundances reached their lowest levels in the core (<5%), though become more prominent at the top of the zone. Within HUA-2, two gypsum layers were deposited at the beginning of the zone at 212.5–216 cm (2867–2869 cal. yr BP) and 198–209 cm (2860–2865 cal. yr BP), and two thick layers of gypsum were deposited near the end of the zone at 60.5–71 cm (1334–1509 cal. yr BP) and 79.5–90 cm (1638–1814 cal. yr BP).

HUA-3 (55–0 cm; 1265–modern; pollen concentration 3060–19,450 grains/cm³)

The lowest pollen concentrations of the core coincide with reduced charcoal abundances. Both organic matter and carbonate concentrations remained relatively low compared with the rest of the core. With regard to agricultural pollen types, maize remained present throughout this zone, and Amaranthaceae abundances were extremely low. The most prominent change within this pollen zone was the rapid increase in the abundance of Andean forest pollen types, especially Alnus, Acalypha, and Moraceae/Urticaceae. Cyperaceae abundances remained relatively low, with the exception of a very large peak in abundance at 813 cal. yr BP (25 cm depth). Three thin bands of gypsum were deposited within HUA-3 at 7–9 cm (188–257 cal. yr BP), 16–19 cm (500–605 cal. yr BP), and 28–29 cm (917–952 cal. yr BP).

Discussion

During the mid-Holocene Thermal Maximum, the Central Andes was gripped by prolonged droughts between c. 9000 and 4400 cal. yr BP. The end of the dry events appear to have begun earlier in Peru than Bolivia, c. 4800 cal. yr BP, (Abbott et al., 2003; Hillyer et al., 2009; Valencia et al., 2010), and the onset of ponding at Huaypo at 4500 cal. yr BP is entirely consistent with the regional record. In the southern Andes, the peak of this dry period was one of human abandonment and has been termed the zone of archaeological silence (Nuñez et al., 2002). However, in Peru, less extensive dry periods may have produced ‘microsilences’ in which human absence at arid sites was more local and ephemeral (Dillehay, 2002; Nuñez et al., 2002). At Huaypo, which would probably always have been wetter than the Altiplano, human occupation is suggested at the base of the record. The prevalence of quinoa-type Amaranthaceae cultivars within zone HUA-1 (2845–1265 cal. yr BP) shows a reliance on cold- and dry-adapted crops during this interval. Ambrosia co-occurred with Amaranthaceae, increasing and decreasing in tandem. The only native species of Ambrosia in the Cuzco area (A. arborescens) is a weedy shrub associated with disturbed ground and terrace stabilization that can grow into a small tree if allowed (Chepstow-Lusty et al., 1996, 2003; Tupayachi, 1993).

This agricultural record during HUA-1 (4540–2845 cal. yr BP) is set amid a puna grassland landscape, with high abundances of Poaceae and low abundances of Andean forest taxa. Intermediate levels of charcoal indicate that fire was influencing the landscape, though the extent to which this was a blend of natural versus anthropogenic burning cannot be evaluated. Lower lake levels could have produced focusing of pollen grains within the lake basin and hence high pollen concentrations. Furthermore, inferred seasonal drying may have promoted increased flammability of the catchment vegetation.

The incorporation of maize into early Horizon agriculture

At the beginning of HUA-2, c. 2845 cal. yr BP, the first maize pollen is documented in the Huaypo sediments, concurrent with a marked reduction in Amaranthaceae abundance. Amaranthaceae cultivars are adapted to highland climatic conditions, and would have typically grown at Huaypo’s elevation (3500 m a.s.l.). Maize is believed to have an upper altitudinal limit of ~3550 m a.s.l., though the practice of pushing maize into locations just beyond optimal environmental conditions was common (Hastorf, 1993). It is important to note the basic difference in pollination biology between maize and Amaranthaceae. We have been conservative in identifying maize pollen. Our prior studies of modern Andean grasses revealed no species producing pollen that exceeded 70 µm when mounted in glycerine (M Bush, unpublished data, 2005). A size cut-off in combination with a characteristic surface pattern and annulus, used to identify maize of 72 µm (e.g. Pope et al., 2001; Whitehead and Langham, 1965) was probably reasonable, but we have adopted a minimum size of 82 µm before identifying the grain as coming from Zea mays. The large grains of Zea pollen are almost all trapped in the tassels of the male inflorescence, and very few travel more than 10 m from the parent plant via the wind (Jarosz et al., 2003) and would be limited to fluvial transport within the confines of the watershed. To find any maize pollen at all in lake sediment suggests substantial cultivation, or at least processing, of maize near the lake. In contrast to maize, Amaranthaceae produce copious amounts of pollen that is easily dispersed. Thus the measures of Zea and Amaranthaceae are essentially independent of one another, i.e. finding two or three Zea grains in an extended count has no real impact on the percentage of Amaranthaceae pollen found.

During what appears to have been a phase of increased moisture availability between c. 3000 and 1300 cal. yr BP, the abundance of Andean forest taxa remained low, possibly because of temperature restrictions. The shift from quinoa-type cultivars to maize at c. 2845 cal. yr BP was synchronous with reduced concentrations of pollen and organic matter and a marked decline in Cyperaceae, probably caused by an expanding lake flooding the wetland. The gypsum layers deposited at the end of HUA-1 (4540–2845 cal. yr BP) occurred simultaneously with decreases in organic matter, indicative of short periods of aridity just before the transition to wet conditions at c. 3000 cal. yr BP (Figure 3). Microcharcoal abundance increased slightly despite the apparent rise in moisture availability. A later peak in pollen concentration c. 1800–2100 cal. yr BP, coincident with the largest charcoal peak of the record, is inferred to reflect a drier event, which is also reflected in the Cyperaceae peaks at Marcacocha (Chepstow-Lusty et al., 2003).

Maize generally needs c. 500–800 mm of precipitation during the growing season (Brouwer and Heibloem, 1986), whereas quinoa is more drought-adapted, successfully growing in environments with an average of 285 mm of precipitation during the growing season (Vacher, 1998). Thus, the transition to wetter conditions at c. 3000 cal. yr BP may have introduced just enough moisture to allow cultivation of maize around Huaypo. The onset of wetter conditions also allowed for a slow expansion of trees and shrubs typical of the Andean forest near the elevation of Huaypo at 3500 m. Rather than an abrupt colonization by these taxa, the pollen record revealed a slow march between 2845 and 1265 cal. yr BP in HUA-2, for example, the slow increase in the pioneer forest genus Alnus and the continuous, though still low (<5%) pollen presence of other forest types, such as tree genera from the Moraceae/Urticaceae, Juglandaceae and Ulmaceae families. Whether the plant types were surrounding the lake, or simply expanding populations just downslope, their increasing abundance indicates increasingly favorable environmental conditions were slowly appearing (i.e. wetter and possibly warmer) around Huaypo during this time. Charcoal abundance, having slightly increased through this time span (2845–1265 cal. yr BP), does not fit the pattern reflected in the rest of the paleoecological proxies of a wetter climate. This proxy, though, probably reflected the increasing level of human dominance within the landscape surrounding Huaypo, rather than climatic changes in the region.

Comparisons of key pollen types from Huaypo, Pacucha, and Marcacocha fossil pollen records reveal strikingly similar patterns of vegetation change, all shifting from highland crops to maize cultivation c. 2845 cal. yr BP (Figure 6). Similar to changes observed at Huaypo, quinoa-type and Ambrosia pollen abundances dropped at c. 3000 cal. yr BP. Further north in the central Andes, similarly high abundances of Ambrosia and Amaranthaceae pollen types are contemporaneously observed at Laguna Baja (Hansen & Rodbell 1995). At Laguna de Chochos, the arrival of Amaranthaceae and Ambrosia pollen types, though remaining at low levels, indicate possible human occupation and agriculture on a more modest scale between c. 6000 and 3000 cal. yr BP (Bush et al., 2005). Between c. 2700 and 2000 cal. yr BP at Marcacocha, maize pollen was rare and discontinuous while Amaranthaceae abundance remained high, suggesting local climatic conditions may have been unfavorable for its sustained presence prior to c. 2000 cal. yr BP. As Marcacocha is located in a tributary at 3350 m altitude above the Urubamba Valley at 2800 m, maize cultivation may have only been successful during periods of climatic amelioration (i.e. increased warming, with water being less of a limiting factor at this site), or may only have been attempted when population pressures demanded it.

Figure 6.

Cuzco-region comparison of pollen records. Pacucha (black), Marcacocha (dark gray), and Huaypo (light gray) displayed nearly synchronous ecological shifts regarding primary cultivars and Andean forest taxa. Amaranthaceae, Ambrosia, and Alnus are all provided as % abundances. Zea mays is provided as pollen counts. Asterisks indicate ¹⁴C dates for each lake record. The cultural stratigraphy follows Bauer (2004).

Gypsum layers are absent in the lower part of HUA-2 and may indicate a continuation of wetter climatic conditions after 2845, with a shift to drier conditions at c. 1850 cal. yr BP, causing high evaporative conditions and two extensive periods of gypsum deposition (Figure 3). Coastal Peruvian archaeological records indicate that at 3000 cal. yr BP a ~3000 yr period of strong El Niño events ended (Sandweiss et al., 2001). As such events typically bring drought to the central and southern Andes, such a transition in interannual climate variability may have made environmental conditions more favorable for maize. In northern Peru, an isotopic record from Tigre Perdido cave also provides support for overall wetter conditions in the central Andes beginning at c. 3000 cal. yr BP (Figure 7; van Breukelen et al., 2008). Interestingly, δ¹⁸O at Tigre Perdido becomes more enriched, indicative of drier conditions, between c. 2200 and 1650 cal. yr BP, when maize pollen is lacking in the Huaypo pollen record though present at Marcacocha (which may have been less water-limited).

Figure 7.

Regional paleoclimate comparison. Key pollen types from the Huaypo lake sediment record (a) are displayed with various Peruvian paleoclimate records. The δ¹⁸O (b) and accumulation records from the Quelccaya ice core (Thompson et al., 1985) are shown in (c), and the Tigre Perdido δ¹⁸O record (van Breukelen et al., 2008) in (d).

This agricultural transition also provides strong evidence of an important cultural shift to dietary dependence on maize, away from the original Andean highland crops. At c. 2845 cal. yr BP, the sharp decline in Amaranthaceae abundance indicates that this crop was virtually abandoned as a dietary staple, in preference for maize, which is more productive and calorie-rich (Finucane, 2009; Piperno, 2006; Wernke and Whitmore, 2009). Quinoa continues to appear in the pollen records for centuries after the appearance of maize, but at markedly reduced abundances. Such findings support the hypothesis that maize became a dietary staple during the Middle Formative Period (1500–500 bc; 3450–2450 cal. yr BP) as has been suggested by Finucane (2009). Other archaeological investigations from the region indicate that villages began to increase in size concurrent with this shift, and social hierarchies developed shortly thereafter (Bauer, 2004; Bauer et al., 2010). Pampa de Anta, just to the west of Huaypo, appears to have been a center of political power during the Qotokalli cultural phase, which may explain why Huaypo shows the most continuous presence of maize (Bauer, 2004).

Andean forest recovery

Nearing the end of the HUA-2 local pollen zone (2945–1266 cal. yr BP), organic matter and Cyperaceae abundances became increasingly variable, probably due to fluctuating lake levels. At 1300 cal. yr BP, a simultaneous decline of charcoal concentration and expansion of Andean forest types, particularly Alnus, occurred very rapidly at Huaypo. Fire virtually disappeared within the landscape and forest taxa responded vigorously to the new conditions. The event occurred rapidly, though successively, at all lakes; first at Huaypo at 1265 cal. yr BP, followed by Marcacocha at c. 900 cal. yr BP, and finally at Pacucha at c. 500 cal. yr BP. The sequence of Alnus expansion at the three lake sites is opposite to that which would be expected based on each site’s elevation.

The rapid Andean forest expansion could have been a result of reaching an ecological tipping point in non-flammability (i.e. becoming too wet to burn extensively) or from human influence. Within the Huaypo sediment core, no gypsum deposition occurred at the beginning of this transition, suggesting initially wet climatic conditions around 1300–1200 cal. yr BP (Figure 4). Regional isotopic paleoclimate records also indicate that climatic conditions were wet during the initial altitudinal rise in Andean forest types at Huaypo, though episodes of aridity were observed later in these regional records, especially between 1100 and 600 cal. yr BP (Figure 7) (Thompson et al., 1985; van Breukelen et al., 2008). In Huaypo, gypsum deposition only occurs c. 700–600 cal. yr BP, when Quelccaya also displays a period of aridity. The moist environmental conditions at 1300 cal. yr BP would have generated ample fuel for fires, whether natural or anthropogenic. As the climate regime became drier (Thompson et al., 1985; van Breukelen et al., 2008), a contraction of Andean forest taxa would be expected, opposite to what has been observed at Huaypo, and failing to support the role of climate in the rapid increase in forest taxa. Though warming could have produced an upslope shift in Andean forest taxa, fluid inclusion analysis at Tigre Perdido failed to indicate any change in temperatures since the mid Holocene (van Breukelen et al., 2008). However, such long-distance comparisons of different proxies from different paleoenvironmental archives should be treated with caution. Nevertheless, the rapid rise in Andean forest pollen types was driven primarily by the rise in one tree taxon, Alnus. From what is known of the distribution of Alnus in the Peruvian Andes, the high-elevation environmental conditions surrounding Huaypo (3500 m a.s.l.) should not have supported such a large population of this Andean forest species (Weng et al., 2004b). Therefore, the primacy of a known cultivar for timber in this woodland resurgence, lends support to the role of humans in driving this change.

Throughout the central Andes, rapid peaks in Alnus have also occurred around the same time (Weng et al., 2004a). Several lakes on the Junin plain of Peru exhibited rapid increases in Alnus abundance around 1000 cal. yr BP, though the chronologies are restricted by limited radiocarbon dates in the sediment cores (Hansen and Rodbell, 1995; Hansen et al., 1984, 1994). On the western slopes of the Ecuadorian and Peruvian Andes, similar peaks in Alnus pollen have been observed between 1300 and 1000 cal. yr BP (Hansen et al., 2003; Weng et al., 2006). Each of these sites lies above the typical altitudinal zone in which A. acuminata is found (Furlow, 1979; Gentry, 1993; Weng et al., 2004b). Since A. acuminata produces copious pollen, the Alnus peaks may have represented pollen blown upslope from nearby populations at lower altitudes undergoing significant expansion. Nevertheless, an increase in the establishment of A. acuminata at higher elevations and expansion of downslope populations could have been encouraged and even actively managed by local peoples. In a study of carbonized wood remains from pre-Incan and Incan (ad 1300–1530; 650–420 cal. yr BP) archaeological sites, Hastorf et al. (2005) inferred active forest management or harvesting of >40 woody taxa. In Incan times, specific wood types, including Alnus, were more intensively used (Hastorf et al., 2005), though no archaeological wood use has been studied prior to 850 cal. yr BP. The paleoecological evidence presented here, based on pollen, lend support for the upslope migration and potential management of Andean forest taxa, especially Alnus by c. 1265 cal. yr BP, nearly 650 years before archaeological studies have indicated. Independent archaeological evidence examining carbonized wood remains is still lacking from the Cuzco area and is required to confirm the presence of in situ populations of A. acuminata at these altitudes and at such an early period. In addition, other plant macroremains in the lake sediments, such as winged seeds or leaves, would validate the presence of Alnus close to Huaypo and should be investigated using cores closer to the lake shore. The initial expansion of Alnus at Marcacocha was attributed to climate amelioration (specifically warming) during the ‘Medieval Climate Anomaly’ (i.e. Chepstow-Lusty et al., 2003, 2009). However, the Alnus peak at Huaypo and several other Andean lakes occurred prior to the beginning of the ‘Medieval Climate Anomaly’ and, therefore, cannot be attributed to these climatic influences alone.

Chepstow-Lusty and colleagues (1998, 2003, 2009) have suggested that Alnus expansion at Marcacocha initially was a natural upslope colonization due to warming from ad 1100, with continued expansion as the Inca and their predecessors managed Alnus trees for agroforestry. In part, this hypothesis is due to the existence of written historical records describing Incan cultural activities and the coincident timing of the Incan empire and the Alnus peak at Marcacocha (Chepstow-Lusty and Winfield, 2000). However, its colonization at Huaypo at 1265 cal. yr BP, prior to Incan cultural influence near Cuzco, suggests that the practice of agroforestry was initiated during the Wari period. Moist climatic conditions may have assisted the expansion of Alnus and other Andean forest types, but the rapidity of the Alnus expansion and its continuation through later periods of aridity is consistent with active human manipulation of Alnus populations. Interestingly, at c. 1100–1000 cal. yr BP, slight declines are observed in the Alnus pollen abundance at Huaypo, concurrent with the collapse of the Wari, and this may indicate a lapse in active management or a population decline of Alnus due to a period of aridity. The practice of agroforestry was maintained and continued after the Wari civilization collapsed by Cuzco-area residents that later became the Inca. Andean stable oxygen isotope records from Quelccaya and Lake Pumacocha both indicate a period of aridity throughout much of the Late Intermediate Period (790–450 cal. yr BP) (Bird et al., 2011; Thompson et al., 1985). At Huaypo, the nearly continuous cultivation of maize and maintenance of Andean forest trees through this period of greater aridity suggests that the Wari and subsequent peoples at this lake were capable of adapting to such climatic conditions through terracing and irrigation technologies. At Pacucha during the late Intermediate Period, local rule was controlled by the Chanka, a loosely unified culture that was conquered by the Inca ~500 cal. yr BP (Bauer et al., 2010). The Alnus peak at Pacucha was delayed compared with that at Huaypo and Marcacocha. Alnus abundance peaked at 500 cal. yr BP, simultaneous with Incan conquest over the Chanka and indicative of a rapid encouragement of agroforestry around Pacucha after the Inca took over local control.

Notably, at all three Cuzco-region lake sites, a decrease in Alnus is experienced at the time of Spanish conquest. Typically, at this time in history, changes in charcoal concentration are often looked to as a clear sign of a rapid decline in the native Andean population; however, no noticeable change occurred within the Huaypo charcoal record. Instead, the dip in Alnus provides evidence of what historical records describe as a period of intense deforestation, because the Spanish created an insatiable need for wood for fuel and construction (Chepstow-Lusty and Winfield, 2000; Hastorf et al., 2005; Sherbondy, 1986). The written records also report a resumption of agroforestry practices by the Spanish at the end of the 16th and beginning of the 17th centuries (Sherbondy, 1986), which is confirmed by increases in Alnus pollen abundance at all three lakes.

Conclusions

Paleoecological records reported here show that with the rise of the Wari came a coincident increase in human modification and control over the landscape. One reason behind this cultural development appears to have been the reliance on maize as a primary cultivar and form of subsistence for at least 1400 years prior to Wari cultural expansion. The irrigation and terracing technologies initially developed by the Wari allowed for near-continuous maize agriculture for many centuries, until faced with a protracted drought c. ad 1000. Though the Wari civilization itself collapsed, the presence of maize indicates human occupation continued at Huaypo.

Taken together, the paleoecological records at Huaypo, Marcacocha, and Pacucha indicate that the arrival of maize as a primary subsistence crop in the Cuzco region depended on favorable climatic conditions. This transition was a crucial step in the evolution of Andean cultures in southern Peru, providing an efficient supply of calories (in terms of caloric output for energy input) for the expanding populations. Particularly for cultures such as the Wari, reliance upon maize in diet and ritual was influential in their expansion into the Cuzco area. Later environmental stresses, such as periods of prolonged aridity, could be coped with, using a variety of new agricultural technologies initiated by the Wari and maintained by the Incan empire. Though the Wari civilization proper did not survive protracted drought conditions c. 1000 cal. yr BP, human occupation throughout the Cuzco area benefited from their agricultural advances. Based on the three paleoecological records, the level of human influence over the landscape can be shown to have increased dramatically within the past two millennia. Though the Incan empire has been estimated to have supported between 6 and 14 million people at its height (McEwan, 2006), the interruption of their reign by the Spanish conquistadors prevents us from answering whether or not this high population was sustainable.

Footnotes

Acknowledgements

The authors would like to thank two anonymous reviewers for their input, Dolores Piperno and Crystal McMichael for their comments on the manuscript and Jean-Francois Jeuland for maize pollen assistance.

Funding

This research was supported by grant DEB-0742301 from the National Science Foundation. NASM was supported by the National Science Foundation Graduate Research Fellowship Program and the NSF GK-12 program.

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Supplementary Material

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Anthropogenic control of late-Holocene landscapes in the Cuzco region,Peru

Abstract

Keywords

Introduction

Study site

Materials and methods

Results

Stratigraphy and chronology

Multivariate analysis

Local pollen zones

HUA-1 (792–165.1 cm depth; 4540–2845 cal. yr BP; pollen concentration 7000–36,250 grains/cm3)

HUA-2 (165–55.1 cm depth; 2845–1265 cal. yr BP; pollen concentration 2880–17,750 grains/cm3)

HUA-3 (55–0 cm; 1265–modern; pollen concentration 3060–19,450 grains/cm3)

Discussion

The incorporation of maize into early Horizon agriculture

Andean forest recovery

Conclusions

Footnotes

Acknowledgements

Funding

References

Supplementary Material

HUA-1 (792–165.1 cm depth; 4540–2845 cal. yr BP; pollen concentration 7000–36,250 grains/cm³)

HUA-2 (165–55.1 cm depth; 2845–1265 cal. yr BP; pollen concentration 2880–17,750 grains/cm³)

HUA-3 (55–0 cm; 1265–modern; pollen concentration 3060–19,450 grains/cm³)