People and environment in pre-Columbian Amazonia: two new proxies

What was the extent of human occupation and environmental impact in the pre-Columbian Amazonia?

This question has been at the center of much of the research on pre-Columbian Amazonia since Betty Meggers published her paper ‘Environmental Limitation on the Development of Culture’ (1). The reconstruction of the Amazon’s past is based on evidence obtained from the study of the present landscape, sediments and archaeological remains. These ‘evidences’ are called proxies. Pollen is a proxy for past vegetation, tree rings are proxies for past climate variability, CO2 stored in the ice cores is a proxy for past levels of atmospheric CO2 and so on.

Paleo-ecologists, geographers, archaeologists etc. trying to understand the region’s past have first to look for proxies (this means going to the field and taking samples of lacustrine sediments and/or soils, or going into the mountains after morains and other glacial deposits); then they have to interpret the data gathered and assess their significance (to what extent does this data represent a local or regional event?): we can say that past values of CO2 inferred from ice cores are proxies for past global concentrations of CO2 because the atmosphere is well mixed, but we cannot say that the extent of a moraine in a particular valley indicates past global temperature or precipitations, because local conditions in that valley could have been (and very likely were) different from the conditions of a similar valley in the other hemisphere. As the process involves different stages, datasets and interpretations, it is not uncommon for researchers to disagree on the conclusions. This has often been the case with regards to Amazonia.

In this post, I will try to provide a brief overview of the proxies (and their interpretations and significance) that have been used to infer the extent of the impact pre-Columbian populations had on Amazonia and the contribution of a recent paper published in Science (2) to our understanding of the region’s past.

The first proxies

When Betty Meggers wrote ‘Environmental Limitation on the Development of Culture’ in the fifties (1), there was not much data on Amazonia. At that time scientists relied considerably on anthropological studies of modern indigenous communities and on written documentation left by the first explorers. The fact that the ‘modern’ indigenous population in Amazonia was limited to small nomadic and semi-nomadic groups was attributed to environmental constraints: unfertile soils and frequent floods. As Amazonian soils cannot support large and stable populations in modern times, it was thought that, also in the past, Amazonia was inhabited by small groups of hunters and gatherers. In contrast, written reports from the first explorers described large and rich societies with plenty of food and gold. Myths such as El Dorado arose on the basis of these reports. However, as the written reports contained some statements that were clearly false, such as the existence of blond women warriors with only one breast (the “Amazonas” from whom the river and the region took their names), these historical documents were often disregarded and the consensus within the scientific community was that Amazonia in the past only hosted small nomadic groups that did not have a significant impact on the environment. 

The discovery of the “lost cities”

In the last 30 years, when more funding, interest and technology became available to spur archaeological research, scholars started to find new evidence of pre-Columbian complex societies in those very places where Megger’s model of environmental determinism predicted that they shouldn’t be. The discovery of raised fields and monumental mounds in the Bolivian Amazon (3,4), the geometric ditches in the Acre (5), the terra preta sites, the earthworks in the upper Xingù (6), the mounds in the Marajo islands, were far more reliable proxies than ‘modern indigenous communities’ and ‘old written reports’. More importantly, these discoveries suggested that Betty Meggers’ model was wrong. Archaeologists (actually, in most cases, North American Anthropologists) started speculating about the significance of these discoveries and how they challenged the theory of environmental determinism. Archaeological evidence showed that environmental constrains did not limited cultural evolution in Amazonia because human intelligence overcame them. People built highly productive raised fields that were able to produce tons of Maize per hectare on a continuous basis (without fallow periods); people transformed infertile oxisols in extremely rich terra preta allowing the production of food surpluses that permitted the rise of large and complex societies all over Amazonia. Pre-Columbian Amazonia was now seen by many as a “cultural parkland” (6) and an “anthropogenic cornucopia” (7). Pre-Columbians practiced agroforestry to such an extent that they contributed to the modern patterns of Amazonian biodiversity. Some geographers, paleoecologists and climatologists speculated about the large impact that pre-Columbians had on world climate: As Amazonia was densely populated, then it was also extensively de-forested. Following the discovery of the Americas in 1492, 95% of the original population died because of the spread of the diseases brought by the Europeans. The sharp decrease in population meant the abandonment of the agricultural fields and the re-growth of the rainforest. The forest absorbed huge amounts of CO2 from the atmosphere and, because of this, contributed to trigger the Little Ice Age…

The latest paradigm shift

The above reconstructions, although exciting, have been considered too extreme by some scholars, including myself (4,8); because there is insufficient paleoecological data or archaeological evidence to support them. The main problems with the reconstructions of pre-Columbian Amazonia as an “anthropogenic cornucopia” are related to the interpretation and significance of the proxies taken into account. Although it is a fact that there are thousand of hectares of raised fields in the Bolivian Amazon (the proxy) it is not clear how they were used and how productive they were (the interpretation). Moreover, there is no basis for assuming that similar levels of landscape modification took place elsewhere in Amazonia (the significance or scope). The same is true for other proxies. For instance, terra preta. On what basis do we interpret terra preta as an improved agricultural soil? We all agree that within the Amazon basin there is evidence of past complex society, but can we extrapolate from a few sites to the whole of Amazonia? Till now, the most important argument against the “anthropogenic cornucopia” theory has been the lack of data supporting it. As Betty Meggers said, it is all about wishful thinking. But, a few days ago, a new paper by McMichael et al. (2) added two new proxies to the debate: charcoal and phytoliths. They are actually not new at all, but, for the first time, extensive parts of the Amazonian rain forest have been sampled for the presence of these two proxies. Charcoal is a proxy for fire and phytoliths are a proxy similar to pollen, phytoliths tell us which kinds of plants were cultivated (if any). Both of them have local significance because you can find them only in the very place were the fire or the plants were. But, as McMichael et al. sampled many spots in the Amazon rain forest (247 soil cores collected from 55 locations) , their results are now of regional significance. This is the first time that we have a dataset obtained from the random sampling of an extensive part of Amazonia, rather than mere generalizations of data obtained from small and selected archaeological sites. Based on the analysis of charcoal and phytoliths, McMichael et al. concluded that most of Amazonia was “predominantly occupied by relatively small and shifting human populations during the pre-Columbian era”. This opens up a great and fascinating perspective for future studies. If, as Meggers said more than half a century ago, environment matters: what are the environmental opportunities that allowed the rise of complex societies in some sites such as the Llanos de Moxos in the Bolivian Amazon?

There is still much to be learnt about human-environment interactions in pre-Columbian Amazonia. The Llanos de Moxos, with its great amount, diversity and spatial variability of earthworks, is a promising site for future research.

1) B. J. Meggers (1954). Environmental Limitation on the Development of Culture American Anthropologist  
2) McMichael CH, Piperno DR, Bush MB, Silman MR, Zimmerman AR, Raczka MF, & Lobato LC (2012). Sparse pre-Columbian human habitation in western Amazonia. Science (New York, N.Y.), 336 (6087), 1429-31 PMID: 22700926  
3) Lombardo, U., Prümers, H. (2010). Pre-Columbian human occupation patterns in the eastern plains of the Llanos de Moxos, Bolivian Amazonia Journal of Archaeological Science, 37 (8), 1875-1885  
4) Lombardo, U., Canal-Beeby, E., Fehr, S. and Veit (2011). Raised fields in the Bolivian Amazonia: a prehistoric green revolution or a flood risk mitigation strategy? Journal of Archaeological Science, 38 (3) 5) Pärssinen, M., Schaan, D., and Ranzi (2009). Pre-Columbian geometric earthworks in the upper Purús: a complex society in western Amazonia Antiquity, 83  
6) Heckenberger MJ, Kuikuro A, Kuikuro UT, Russell JC, Schmidt M, Fausto C, & Franchetto B (2003). Amazonia 1492: pristine forest or cultural parkland? Science (New York, N.Y.), 301 (5640), 1710-4 PMID: 14500979  
7) Erickson, C. L (2008). Amazonia: the historical ecology of a domesticated landscape in Handbook of South American archaeology, edited by H. Silverman and W. H. Isbell  
8) Lombardo, U., May, J-H. and Veit, H. (2012). Mid- to late Holocene fluvial activity behind pre-Columbian social complexity in the south-western Amazon basin The Holocene

The extent of human disturbance in pre-Columbian Amazonia

Understanding the extent to which pre-Columbian peoples altered and deforested the Amazon basin is key in order to assess i) the impact that pre-Columbians had on global climate during the Holocene [Dull et al., 2010] and ii) the resilience of the Amazon rainforest to human disturbance [Bush and Silman, 2007]. The first point is essential to our understanding of the major drivers behind climate fluctuations during the Holocene, and hence to help predict future fluctuations. The second point is important to inform conservation and development policies in Amazonia. Unfortunately, the scarcity of archaeological and paleoecological data from the Amazon Basin has favoured the proliferation of “reconstructions of the past” that are hard to test.  Some of these theories have reached broad audiences thanks to the echo provided by popular media and books [Mann, 2005]. New archaeological findings that suggest the existence of complex societies in pre-Columbian Amazonia have led some researchers to define the Amazon Basin as a “manufactured landscape” or an “anthropogenic cornucopia” [Balée and Erickson, 2006; Erickson, 2008].  There are 3 different lines of research that can help assess whether or not these reconstructions are accurate. One is to focus on those regions that host important archaeological remains and study the evidence of complex societies. This work is already being carried out by some archaeologists such as Heiko Prümers. The second area of research is to examine if and how the development of complex societies in the region were influenced by local environmental constraints and opportunities. This is the kind of work that I am carrying out in the Llanos de Moxos and  hope to discuss in another post quite soon J (briefly introduced here…). Another area of research that can help us understand the Amazon’s past is to test if the level of human disturbance associated with the sites where evidence of complex societies has been discovered can be extrapolated to the rest of the Amazon basin.  A milestone paper that looks at the latter, and that has been often cited in this blog, is Bush and Silman (2007).

A few weeks ago, The Holocene published on-line a new paper that delves deep into this question, providing interesting new data [McMichael et al., 2011].  McMichael et al. test the hypothesis that human disturbance was widespread in the Amazon Basin during pre-Columbian times (as some authors have suggested). If this hypothesis is true and the disturbance was widespread then, the authors argue, the sites where permanent settlements were likely to have established should show sedimentary evidence of that disturbance. Hence, they cored lakes (considered by the authors as preferred settlement sites) and sampled soils in the vicinity of the lakes and looked at charcoal and phytoliths. They found that charcoal record was discontinuous and localized. They then concluded, based on the sedimentary evidence: “Our data suggest that while all of the settings examined were occupied or used, the halo of influence around each was limited. It should not be assumed that intensive landscape transformations by prehistoric human populations occurred throughout Amazonia or that Amazonian forests were resilient in the face of heavy historical disturbance”. The paper suggests that pre-Columbians developed into complex societies and substantially altered their environment in those areas where environmental conditions were favourable. They predict that these sites can be found along the main rivers and in those parts of the Amazon Basin that are characterized by a strong seasonality (like the Llanos de Moxos).

In my opinion this paper is a beautiful piece of Science and I invite you to read it!

References:

Balée, W., and C. L. Erickson (2006), Time, complexity and historical ecology, in Time and complexity in historical ecology: studies in the neotropical lowlands, edited by W. Balée and C. L. Erickson, pp. 1-17, Columbia University Press, New York.

Bush, M. B., and M. R. Silman (2007), Amazonian exploitation revisited: ecological asymmetry and the policy pendulum, Frontiers in Ecology and the Environment, 5(9), 457-465.

Dull, R. A., R. J. Nevle, W. I. Woods, D. K. Bird, S. Avnery, and W. M. Denevan (2010), The Columbian Encounter and the Little Ice Age: Abrupt Land Use Change, Fire, and Greenhouse Forcing, Annals of the Association of American Geographers, 100(4), 755-771.

Erickson, C. L. (2008), Amazonia: the historical ecology of a domesticated landscape, in Handbook of South American archaeology, edited by H. Silverman and W. H. Isbell, pp. 157-183, Springer, Berlin.

Mann, C. C. (2005), 1491 New revelations of the Americans before Columbus, Vintage books, New York.

C. H. McMichael, M. B. Bush, D. R. Piperno, M. R. Silman, A. R. Zimmerman, & C. Anderson (2011). Spatial and temporal scales of pre-Columbian disturbance associated with western Amazonian lakes The Holocene : 10.1177/0959683611414932

Less than 1% of Amazonia is made of Terra Preta. Is that enough?

I’ve just read a review written by William Balée (2010) about the book ‘Amazonian Dark Earths: Origins, Properties, Management’. Balée considers that the discovery of Terra Preta is proof that people in pre-Columbian Amazonia, rather than adapting to environmental conditions, ‘created’ the environment they inhabited. This allowed the development of complex societies in the region regardless of environmental constraints (such as poor soils, floods, lack of protein...). People overcame all these problems by creating Terra Preta. This is an extract from Balée’s introduction: “This contribution refutes, in essence, the adaptationist view of Amazonian indigenous societies […]. It is intriguing that this refutation takes place in light of what constitutes less than 1% of the forested part of the region’s surface soils (Woods and Denevan 3.1:1). That small fraction, nevertheless, like the difference in DNA between humans and chimpanzees, takes on profound significance in terms of understanding […] agriculture, population, and settlement in the prehistory of the region.”

Can we really consider this 1% like the difference in the DNA between humans and chimpanzees?

An answer to this question is given by Bush and Silman (2007): “The hypothesis of widespread Amazonian landscape management is based on analyses of archaeological sites and the assumption that there was a large pre-contact Amazonian population (> 10 million people). A caveat must be applied to these data, and indeed all of the data that we have to date about human disturbance in the Amazon, which is that they are derived from just a few locations, and do not represent either a systematic or a randomized sampling design. There is no ecological component predicting which forest was most likely to be occupied. Was disturbance spread evenly across all of Amazonia or concentrated near human habitation? Is it safe to extrapolate results from sites where we know human habitation occurred to the rest of Amazonia? Ecologists are familiar with problems of scale. […] extrapolating observations from dot maps can be dangerous, especially when the dots represent discrete activities of limited spatial extent (eg terra preta formation).”

It is striking how scholars can have such differing views at such a basic methodological level! (-:

Another interesting point is where that 1% is found: terra preta sites (the “dots” Bush and Silman are talking about) are found along the courses of the major Amazon rivers (fig. 1).

Figure 1 Terra preta sites. From Glaser (2007)

The preference for settling along rivers would seem to indicate that environmental conditions (in this case closeness to fish protein and waterways) did in fact condition the development of pre-Columbian societies. If we consider terra preta as evidence of the existence of large permanent settlements established by complex societies, then its spatial distribution along major rivers would suggest precisely that social complexity developed where environmental conditions were good. And, as so many archaeologists and anthropologists have stressed before me, there is no basis to infer that large permanent settlements were also established in other areas further away from rivers, where environmental conditions would have been tougher. 

P.S.

I have just discovered a new post in the Blog of Neves about the same issue. have a look (in Portuguese): http://arqueologiadaflorestatropical.blogspot.com/

William Balée (2010). Amazonian Dark Earths Tipití: Journal of the Society for the Anthropology of Lowland South America


Bush, M., & Silman, M. (2007). Amazonian exploitation revisited: ecological asymmetry and the policy pendulum Frontiers in Ecology and the Environment, 5 (9), 457-465 DOI: 10.1890/070018


Glaser, B. (2007). Prehistorically modified soils of central Amazonia: a model for sustainable agriculture in the twenty-first century Philosophical Transactions of the Royal Society B: Biological Sciences, 362 (1478), 187-196 DOI: 10.1098/rstb.2006.1978

Pre-Columbian raised field agriculture: a review

A new paper on raised field agriculture was published on line last week in the journal Ecological Engineering. The title, “Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today”, is a bit misleading. You would think it is just another paper claiming that the re-habilitation of raised field agriculture will provide means for sustainable, highly productive, flood/drought proof, politically correct and environment friendly tropical agriculture… but it is not. Instead, it is a good review of all the relevant literature about pre-Columbian raised field agriculture.

The paper, by Renard D., also includes valuable references to raised fields in Asia and is co-authored by a diverse and interdisciplinary group of researchers, including Bruno Glaser, a soil scientist who is among the most prominent world experts of terra preta, archaeologists that have long worked on pre-Columbian raised fields and ecologists. However, in my opinion, its conclusions fall short.

The main point of the paper, with which I fully agree, is that raised fields are found in a variety of environments that differ with respect to almost everything: you find raised fields in all kind of soils; you find them in the Amazon basin and in the Andes; you find them in permanent swamps/lakes and in seasonally flooded/dry savannahs. Therefore, it is very likely that, in different places/conditions, fields were managed in different ways. The paper examines almost all the theories and hypothesis that have been put forward about raised fields. However, while it becomes clear that some of these hypothesis are contradictory, such as the need (or no need) of fallow periods, Renard et al., regrettably, do not take positions. Having noticed all the differences between the fields, I would have concluded that their only common trait is that they improved the drainage and I would have therefore stressed that drainage is the defining aspect of raised field agriculture (see this)…but they do not conclude that, and I would be interested to know why.

They do conclude, and again, I fully agree with them, that before we start to rehabilitate raised field agriculture in real-life situations today, we should fill the huge gaps we still have in our understanding of how pre-Columbian raised field agriculture may have worked. I do hope Oxfam and the other NGOs promoting raised field agriculture in lowland Bolivia today read the paper and take on board its main recommendations.
 - Thanks to Anna for telling me about the paper.

Una nueva revisión de los estudios sobre agricultura en camellones

Un nuevo artículo sobre agricultura en camellones acaba de ser publicado en la revista Ecological Engineering. El titulo del artículo hace referencia al papel que los camellones pueden tener como herramienta productiva y sostenible. Sin embrago, no es el típico articulo que nos cuenta como, gracias a la rehabilitación de camellones, se puede revolucionar la agricultura tropical. Más bien, se trata de un artículo que hace un buen resumen de todo lo más importante que ha sido producido por la comunidad científica sobre el tema. Este trabajo incluye también referencias a los camellones de Asia. En la interdisciplinaria lista de autores, encabezada por Renard D., también encontramos a Bruno Glaser, un pedólogo experto mundial de terra preta, arqueólogos con años de experiencia trabajando en camellones y ecólogos.  Sin embargo, en mi opinión, en sus conclusiones se quedan cortos.

El punto principal del artículo, con el cual estoy totalmente de acuerdo, es que los camellones aparecen en una grande variabilidad de sitios y condiciones medioambientales: los encontramos en los más diferentes tipos de suelos; en la cuenca del Amazonas igual que en las regiones Andinas; en lagos igual que en pampas sujetas a ciclos de inundación y sequía. Entonces es muy probable que en diferentes sitios y condiciones los campos fueran manejados de manera distinta. El artículo hace el elenco de todas las teorías e hipótesis que se han hecho sobre la agricultura de camellones. Pero, en todos esos casos donde las hipótesis se contradicen (como por ejemplo sobre la posibilidad que los camellones se puedan cultivar de manera continuativa, sin dejarlos descansar) los autores no toman nunca posición. Una vez que queda claro que hay una gran diversidad de contextos geográficos donde se encuentra los camellones y que seguramente hubo distintos manejos,  yo diría que la única característica común a todo tipo de camellones y en todo sitio es que mejoran en drenaje. Pero Renard D. et al., no llegan a esta misma conclusión, y me interesaría saber el porqué.

Ellos concluyen su artículo afirmando que antes de montar proyectos de rehabilitación de camellones que involucren las comunidades locales, se deben llenar todos los grandes vacíos que todavía existen en nuestro conocimiento de cómo los camellones estuvieron funcionando. Y yo no podría estar más de acuerdo con esta conclusión. Espero que Oxfam y las otras ONGs que están involucradas en proyectos de rehabilitación con comunidades indígenas y campesinas, lean este artículo y lo tomen en cuenta.

D. Renard, J. Iriarte, J.J. Birk, S. Rostain, B. Glaser, & D. McKey (2011). Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today Ecological Engineering