Wednesday, 13 July 2011

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. 

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

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


  1. When this subject has come up in the past among those who have knowledge and views it is often pointed out that it is the Terra Mulata that indicates large populations. These areas are vast, away from the rivers, and confirmed by aerial mapping of the raised bed fields where the Terra Mulata is found. A phrase often heard is that it is an area the size of France.

    The discussion then devolves into debate about the reason for raised beds and how this could have been related to the Terra Mulata creation.

    There is data, but its interpretation is varied.

  2. Back 40, as far as I know, terra mulata is found in the surrounding on the terra preta sites and formed because of the burning and manuring associated to agriculture. It is completely new to me that there are raised bed fields associated with terra mulata. Can you please provide any bibliographic reference for this?