Pre-Columbian cherry picking by the New York Times

A few weeks ago, the NYT published an article about pre-Columbian Amazonia. The journalist reported the discovery of pre-Columbian geometric ditches in the Brazilian Acre. These were actually discovered a decade ago and were already described in a book edited by Pärsinnen et al (2003) and again by Pärsinnen et al (2009) in Antiquity, who called them “geoglyphs”. Till today, no one knows what those ditches were excavated for. As Pärsinnen et al. (2009) say: “The function, or functions, of the geoglyphs remain a mystery”. However, the author of the NYT article says that this discovery shows that Amazonia was densely populated in pre-Columbian times and is “potentially upending the conventional understanding of the world’s largest tropical rain forest”.

But, how can we draw conclusions about how pre-Columbian Amazonia looked like on the basis of something that we don't even know what it is?

I can already hear the answer of those who are pushing for the idea of a densely populated Amazonia: it is not only the geoglyphs! What about the terra preta? And the high productive agriculture of the raised fields? And the complex societies of the upper Xingú?

Well, all these archaeological features have one thing in common: they are found in sites that cover a very small and often peripheral part of Amazonia. But, let’s explore these arguments one by one.

Terra preta:

Terra preta is an organic anthrosol that is found in small patches (normally less than 2 hectares) distributed on the bluffs of large Amazonian rivers. Terra preta indicates the presence of pre-Columbian settlements. But it does not say how many people were living there at any given time or how complex those groups of people were from a social point of view. Many publications put together terra preta and terra mulata under the same label of Amazonian Dark Earth (ADE) and then speculate about large areas of high productive soils. But Terra preta properties cannot be extended to terra mulata (which, for example, has far less phosphorous compared with terra preta and lacks the pottery). As I have already discussed here and here, the claims about terra preta being the product of intentional transformation of soil for high productive agriculture have no scientific basis. Glaser and Birck (in press), who are among the greatest experts of the geochemical properties of terra preta, say in their latest paper “there is no scientific evidence indicating that forgotten agricultural techniques for large scale soil fertility improvement are responsible for terra preta genesis.”

Raised fields:

The high productivity of raised field agriculture in South America has never been demonstrated. I wrote a paper about this last year (Lombardo et al. 2011) were it is shown that raised fields in the Bolivian Amazon (which is, by far, the place with the highest amount of raised fields in Amazonia) were built to avoid water logging during periods of extreme precipitations. They were not a pre-Columbian green revolution but a means to adapt and survive in an unfriendly environment.

The Upper Xingú (Heckenberger, 2003):

In the upper Xingú, as Meggers (2003) puts it, the “clear evidence” of complex and large societies is anything but clear: “Heckenberger et al. state that domestic remains cover about 50 to 60% of the ditched areas and would represent 10 to 24 houses with 12 to 16 occupants each, but provide no archaeological evidence for these estimates.”[...] “Heckenberger et al. assert that “Xinguano cultivation and land management…provides a viable alternative” to modern clear-cutting strategies, but they do not describe them.” […] “Even if Heckenberger et al.'s analysis were acceptable, it would have no bearing on the controversy over the pre-Columbian existence of dense settlements and complex social organization in Amazonia. Like other regions with ditches, causeways, and mounds (the Llanos de Moxos, Bolivia; Acre and Marajó, Brazil; and the western Llanos, Venezuela), the Upper Xingu is environmentally and geographically peripheral to the rainforest. “

This last quote is probably the most important. In fact, even if we consider all the archaeological sites as evidence of pre-Columbian complex societies, they are all located in the peripheral regions of Amazonia or along the river floodplains called varzea, the belt of seasonally flooded areas that flanks the Amazonian rivers. Varzea accounts for only the 2% of the Amazon Basin. The problems of extrapolating from these few sites to the whole Amazonia have been extensively discussed by Bush and Silman (2007) and more recently by McMichael et al (2011) and Barlow et al (2011). Based on lake sediments and charcoal distribution analyses, these researchers conclude that human disturbance in Pre-Columbian Amazonia was localized. As Mark Bush, from the Florida Institute of Technology, clearly states: “It is very unlikely that the majority of Amazonia was strongly impacted by human activity.” (PDF of his talk here). In the words of Barlow et al. (2011): “We therefore urge caution before presuming that findings from a few well studied regions can be extrapolated to the entire Amazon, and reject the idea that the pristine myth has been thoroughly debunked by archeological evidence. Instead, we suggest that the influence of historical peoples occurred along gradients, with high impacts in settlements and small and scattered Amazonian Dark Earths, moderate impacts where enrichment planting occurred or where forests were affected by anthropogenic wildfires, and finally a largely imperceptible footprint from subsistence hunting and resource extraction across vast tracts of Amazonian forests that are far from permanent settlements and navigable rivers ”.

How is it possible that the NYT’s journalist, while writing his piece, didn’t bump into any of these papers?

William Woods, a geographer at the University of Kansas, is quoted by the NYT saying: “If one wants to recreate pre-Columbian Amazonia, most of the forest needs to be removed, with many people and a managed, highly productive landscape replacing it”. But, I think that before the scientific community accepts the idea that Amazonia was a highly productive anthropogenic landscape we need far more evidence than rectangular ditches in the Acre and patches of anthrosol.

Post scriptum

All this 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. If, as some authors suggest, there was considerable human disturbance in pre-Columbian Amazonia, then we can conclude that Amazonia is highly resilient and that the current degradation of its ecosystems may be reversible. On the other hand, if this resilience is overestimated, then mistaken policies can lead to irreversible loss of biodiversity and ecosystem services (Bush and Silman, 2007). Understanding the extent of pre-Columbian human disturbance of Amazonia is a prerequisite in order to assess the possible influence that post-contact re-forestation had on global climate. 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. 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, 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. More on this here.

References

-Bush, M. B., and Silman, M. R., 2007, Amazonian exploitation revisited: ecological asymmetry and the      policy pendulum: Frontiers in Ecology and the Environment, v. 5, no. 9, p. 457-465.
-Glaser, B., and Birk, J. J., In Press, State of the scientific knowledge on properties and genesis of     Anthropogenic Dark Earths in Central Amazonia (terra preta de Índio): Geochimica et Cosmochimica Acta.
-Heckenberger, M. J., Kuikuro, A., Kuikuro, U. T., Russell, J. C., Schmidt, M., Fausto, C., and Franchetto, B., 2003, Amazonia 1492: pristine forest or cultural parkland?: Science, v. 301, p. 1710-1714.
-Lombardo, U., Canal-Beeby, E., Fehr, S., and Veit, H., 2011, Raised fields in the Bolivian Amazonia: a prehistoric green revolution or a flood risk mitigation strategy?: Journal of Archaeological Science, v. 38, no. 3, p. 502-512.
-Meggers, B. J., 2003, Revisiting Amazonia Circa 1492: Science, v. 302, p. 2067.
-Pärssinen, M., Schaan, D., and Ranzi, A., 2009, Pre-Columbian geometric earthworks in the upper Purús: a complex society in western Amazonia: Antiquity, v. 83, p. 1084-1095.

-McMichael, C., Bush, M., Piperno, D., Silman, M., Zimmerman, A., & Anderson, C. (2011). Spatial and temporal scales of pre-Columbian disturbance associated with western Amazonian lakes The Holocene, 22 (2), 131-141 DOI: 10.1177/0959683611414932
-Barlow, J., Gardner, T., Lees, A., Parry, L., & Peres, C. (2011). How pristine are tropical forests? An ecological perspective on the pre-Columbian human footprint in Amazonia and implications for contemporary conservation Biological Conservation DOI: 10.1016/j.biocon.2011.10.013