Elsevier

Quaternary International

Volume 312, 29 October 2013, Pages 109-119
Quaternary International

Human–environment interactions in pre-Columbian Amazonia: The case of the Llanos de Moxos, Bolivia

https://doi.org/10.1016/j.quaint.2013.01.007Get rights and content

Abstract

The reconstruction of past environmental and historical events is much needed in Amazonia, a region at the centre of heated debates about the extent of pre-Columbian human disturbance of the natural ecosystems. Important aspects of this debate are to establish to what extent the rise of social complexity was influenced by the local geo-ecology; and what productive strategies were adopted in order to sustain these societies. The Llanos de Moxos (LM), in the Bolivian Amazon, is a vast floodplain made up of a variety of geo-ecological sub regions that host many different types of pre-Columbian earthworks. Therefore, it offers an excellent opportunity to compare different kinds of archaeological landscapes and their relationship to different pre-Columbian cultures and environmental settings. This paper analyses the links between pre-Columbian earthworks and the local geo-ecology in two regions of the LM: 1) the platform field region (PFR) in the north of Santa Ana de Yacuma, where the highest concentration of raised fields has been documented, and 2) the monumental mounds region (MMR) south and east of Trinidad, where >100 pre-Columbian monumental mounds are found. The study draws from remote sensing and GIS analysis, field work in the Bolivian lowlands, and laboratory analysis. Differences in the way people transformed the landscape in the PFR and MMR seem to respond to differences in the local geo-ecology of the two sites. The results also suggest that environmental conditions exerted an important, though not exclusive, control over the levels of social complexity that were reached in different areas of the LM.

Introduction

The extent of human occupation and environmental impact in pre-Columbian Amazonia has been at the centre of much of the research on human–environment interactions since Betty Meggers (1954) published her paper ‘Environmental Limitations on the Development of Culture’. Since then, evidence of pre-Columbian complex societies in Amazonia, here considered sensu stricto (Eva et al., 2005, Fig. 1a), has been reported in the upper Xingú River (Heckenberger et al., 2003, 2008), Marajó Island (Meggers, 2001b; Schaan, 2008), the confluence between the Tapajós and the Amazon rivers (Neves and Petersen, 2006), the Acre region (Pärssinen et al., 2009) and the Llanos de Moxos (LM) (Erickson, 2000a, 2008; Prümers, 2009; Lombardo and Prümers, 2010). Likewise, evidence of pre-Columbian anthropogenic soils and agricultural technologies has been described in several locations within Amazonia (Michel, 1997; Denevan, 2001; Erickson, 2008; Arroyo-Kalin, 2010, 2012; Lombardo et al., 2011a, Lombardo et al., 2011b; Glaser and Birk, 2012; Rostain, 2012). Following these discoveries, there is now a general consensus among researchers that complex societies did form in some areas of Amazonia. Social complexity is here understood as the combination of subsistence intensification, political integration and social stratification following population growth (Johnson and Earle, 2000). However, whether or not the whole of pre-Columbian Amazonia was densely inhabited has remained highly controversial (Meggers, 2001a, 2003, 2010; Bush and Silman, 2007; Barlow et al., 2012). While some scholars believe that large settlements were limited to areas with favourable environmental conditions and human disturbance was localized (Denevan, 1996; Bush and Silman, 2007; Barlow et al., 2012; McMichael et al., 2012a), others suggest that social complexity developed regardless of environmental constraints and opportunities and that human disturbance in Amazonia was ubiquitous (Balée and Erickson, 2006; Erickson, 2008; Clement and Junqueira, 2010).

This debate has important implications for our understanding of the resilience of Amazon ecosystems and the scale of deforestation in pre-Columbian Amazonia. Understanding how resilient Amazon ecosystems are can help inform present and future development and conservation policies for the region (Meggers, 2001a; Willis and Birks, 2006; Bush and Silman, 2007). If, as some authors suggest, there was considerable human disturbance in pre-Columbian Amazonia (Heckenberger et al., 2007; Erickson, 2008; Clement and Junqueira, 2010) and an important part of the modern rainforest is secondary, then we can conclude that Amazonia is highly resilient and that the current degradation of its ecosystems may be reversible. However, if Amazonia's resilience is overestimated, then mistaken policies can lead to irreversible loss of biodiversity and ecosystem services (Bush and Silman, 2007). The reconstruction of pre-Columbian settlement patterns is a prerequisite in order to assess the possible influence that post-contact re-forestation had on global climate (Dull et al., 2010; Nevle et al., 2011). It has been estimated that pre-Columbian population in Amazonia fell by 95% after the spread of diseases that followed the arrival of the Spaniards (Denevan, 1992). This sharp fall in population would have meant that large areas under cultivation before the conquest were abandoned and re-colonized by the rainforest. As Amazonia is one of the largest terrestrial players in the global carbon cycle (Grace, 2004), it has been suggested that the reforestation that followed the conquest could have sequestrated enough CO2 from the atmosphere to become an important factor in triggering the Little Ice Age (Faust et al., 2006; Nevle and Bird, 2008; Dull et al., 2010; Nevle et al., 2011).

A recent turning point in this debate has been the publication of new data on phytoliths and charcoal distribution which suggest that most of western Amazonia was occupied by relatively small and shifting human populations (McMichael et al., 2012b). This reconstruction has been strengthened by the observation that during the last two millennia the charcoal records derived from lake sediments in the Americas follow a similar pattern to that of the rest of the world, suggesting that it was global climate that influenced fires and not anthropogenic fires that influenced global climate (Power et al., 2013).

In light of these new studies, it would therefore appear that the development of complex societies was restricted to specific areas where environmental conditions were most favourable. In Amazonia, it has been argued that favourable locations for the rise of complex societies are to be found in areas of marked seasonality, which favours slash and burn agriculture (Bush and Silman, 2007), along the bluff of the major rivers (Denevan, 1996) or close to the Andes, where fertile alluvium created good conditions for agriculture (Lombardo et al., 2012). However, within these macro areas, human occupation patterns are not homogeneous (see Lombardo et al., 2011b), suggesting that other factors, such as site-specific environmental conditions, could have favoured or hindered cultural evolution.

In order to gain a better idea of the kind of human–environment interactions that existed in pre-Columbian Amazonia and the extent of human disturbance, we need to disentangle the influence that large scale environmental factors had on the development of complex societies, such as climate or proximity to the Andes, from local environmental constraints and opportunities. The Llanos de Moxos, a seasonally flooded savannah that covers much of south-western Amazonia, is an ideal site for this kind of study because it is made up of a diverse set of geo-ecological sub regions that host a rich array of pre-Columbian earthworks: canals, causeways, fish weirs, raised fields and monumental earth mounds (Erickson, 2008; Lombardo and Prümers, 2010; Lombardo et al., 2011a). These earthworks are unevenly distributed in the LM (Fig. 1); some types of earthworks are present in some areas, whilst absent in others (Denevan, 1966; Lombardo et al., 2011b). The LM therefore offers an excellent opportunity to compare different kinds of cultural landscapes and assess their relationship to different pre-Columbian cultures and environmental settings. The study of the LM is particularly relevant as its archaeological landscape has often been presented as evidence that Amazonia was once densely populated by complex societies (Stahl, 2004; Erickson, 2008; Mann, 2008).

In this paper we analyse the links between pre-Columbian earthworks and the local environmental settings in the platform field region (PFR) in the north of Santa Ana de Yacuma, where the highest concentration of raised fields has been documented, and in the monumental mounds region (MMR) south and east of Trinidad, where >100 pre-Columbian monumental mounds are found (Fig. 1b). Following a similar approach as in Walker (2011), it is here hypothesised that if differences in water regime and soil fertility exist between the PFR and the MMR, these differences are likely to have shaped variations in productive strategies, types of earthworks built for agriculture and ultimately the levels of social complexity achieved in pre-Columbian times. On the other hand, if such differences do not exist, then we may assume that earthwork diversity within the LM could have cultural and ethnic explanations and cultural evolution here was independent from the local geo-ecology.

Section snippets

The Llanos de Moxos (LM)

The LM covers an area of 150,000 km2 in northeastern Bolivia, in the southern part of the Amazon basin. It is located between 12°S and 16°S. The region is drained by three major rivers, the Mamoré River, which crosses the central plains, and the Beni and Iténez Rivers, in the northwestern and the northeastern margins of the LM respectively. These three rivers converge with the Madre de Dios River to form the Madeira River, which is a tributary of the Amazon River. The landscape of the LM is

Geomorphology and edaphology of the PFR

The platform fields region (Fig. 2a) is located in a recently uplifted region (Hanagarth, 1993; Dumont and Fournier, 1994). This neo-tectonic activity has been responsible for the counter clockwise movement of the Beni River (Dumont, 1996) which has left several paleo-valleys and inactive meander belts. These paleo courses are now occupied by underfit rivers, such as the Omi and Yruyañez, along which a great number of raised fields is found (Walker, 2004). Topographic profiles I and II of Fig. 2

Geomorphology and edaphology of the MMR

In the MMR (Figs. 1 and 2b), the landscape is characterized by the presence of savannahs closely interwoven with forested levees of paleo-rivers. The levees of these paleo-rivers are responsible for the elevated areas on top of which forest grows. As shown in Fig. 3, the height difference between the paleo-levees and the savannah can be more than 3 m. Forests growing on the paleo-levees account for approximately 25% of the MMR's land cover. In addition to the formation of the paleo-levees, the

Discussion

The PFR and MMR present some similarities and important differences. Both regions are crossed by paleorivers and are free from river overflows. However, the two regions differ in soils, relief and the presence of water bodies. In the PFR, hydromorphic soils with a low CECeff and high aluminium toxicity are associated with an almost flat landscape characterized by a concave profile and limited local relief. On the other hand, in the MMR, more fertile soils with thicker organic epidedons are

Conclusions

The archaeological and geoarchaeological evidence from Amazonia suggest that pre-Columbian population densities followed gradients of large scale environmental variables such as climate and proximity to the Andes. At this large spatial scale, the anomalous high density of pre-Columbian earthworks in the LM can be explained by its marked seasonality, which facilitated forest clearing, and the abundance of fertile sediments inherent to the Andean foreland. However, at a smaller regional scale,

Acknowledgments

The present work has been funded by the Swiss National Science Foundation (SNSF) grant N° 200021-122289 and 200020-141277/1 and performed under authorization N° 017/2012 issued by the Unidad de Arqueología y Museos (UDAM) del Estado Plurinacional de Boliva. We thank Dr. M.R. Michel López from the Ministerio de Culturas and our Bolivian counterpart Dr. J.M. Capriles for their support. We thank the Sirionó people, the communities of Villa Banzer, Miraflores and Perotó, Mr. F. Böheme, Mr. Bauser,

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