“Predicting pre-Columbian anthropogenic soils in Amazonia”

“Predicting pre-Columbian anthropogenic soils in Amazonia” is the title of a recent paper by McMichael et al. published in Proceeding of the Royal Society B. It is not open access but you can read the abstract here. In this paper McMichael et al. present a predictive model for the presence of Terra Preta in Amazonia.  The model predicts the likelihood of finding Terra Preta sites in any given spot within Amazonia.  In general, I liked the idea behind the paper. These models give us an objective basis for further research and discussions. It is thanks to this kind of work that we can go beyond subjective views about the extent of human impact in pre-Columbian Amazonia and start to formulate hypothesis that, through survey and measurement, can be later tested. The first important result of this paper is that, given the data available, we can now estimate that terra preta is likely to be found only in a 3.2% of the forested areas of Amazonia. This is far less than other previous estimates (Erickson, 2008).

However, I find the discussion of McMichael et al. a bit disappointing with regards to two points. The first is the meaning they give to the presence of terra preta; the second is the reasons they give to explain the absence terra preta outside of Brazil.

What is terra preta? Is it the result of permanent settlement where people cooked and dumped food remains for centuries, eventually causing the enrichment of the soil in with charcoal, phosphorous, organic matter and the rest of elements used to define terra preta? Or is it the result of soil management techniques aimed at improving fertility and agricultural potential? McMichael et al. seem to imply that terra preta is the latter: the result of soil fertility enhancement. They say: “The lack of terra pretas in western Amazonia may be because the Andean-derived soils of western Amazonia did not require nutrient enrichment… [the bold is mine]”. However, this kind of interpretation of terra preta being the result of Pre-Columbian agricultural intensification has been challenged by many authors. Neves & Petersen (2006) discovered that at the Hatahara occupation site (close to Manaus) pre-Columbians actually used terra preta to build burial mounds, which is a strange use for an agricultural soil that took centuries to form. Of course, we cannot exclude that pre-Columbians took advantage of the fertile terra preta for their gardens associated to their homes; in the same way that they could have taken advantage of the fertility of pre-existing middens (see Arroyo-Kalin, 2012 for a discussion on this).But this does not mean that people intentionally created terra preta for agriculture!

Recently, Glaser & Birck (2012) concluded their review about the state of the scientific knowledge about the properties and genesis of Anthropogenic Dark Earths in Central Amazonia saying: “there is no scientific evidence indicating that forgotten agricultural techniques for large scale soil fertility improvement are responsible for terra preta genesis”. 

This leads us to my second concern: what does it mean when no terra preta is found? Here, McMichael et al. suggest that the lack of terra preta indicates that people decided to produce food in some other way, due to cultural and/or environmental reasons. They say: “[In the Llanos de Moxos] instead of terra preta formation, large societies sustained themselves by using techniques such as fish weirs and raised-field agriculture”. But, is it cultivating little gardens that large societies sustained themselves? I think the answer is no. In fact, pre-Columbians living in terra preta sites performed agriculture in the surrounding area, eventually forming terra mulata sites. Terra mulata sites are far larger than terra preta ones. Terra mulata sites do not contain pottery and are far less fertile than terra preta ones, but still, they are richer in organic matter than the normal Amazonian oxisols (more on this here). It is terra mulata that formed because of ancient agricultural use, not terra preta.

The main problem we face when tackling the question of terra preta is its definition. The definition that is generally given to terra preta coincides with the description of the geochemistry of a midden (From Wikipedia: an old dump for domestic waste which may consist of animal bone, human excrement, botanical material, vermin, shells, sherds, lithics, and other artifacts and ecofacts associated with past human occupation) and there are middens everywhere in the world! As a consequence of this, terra preta sites are now appearing everywhere... We should also keep in mind that the whole terra preta concept is rooted in the context of the big surprise that the first researchers had when they found black organic sediments in the middle of Amazonian heavily weathered soils. In fact, terra preta is often defined (and mapped in the field) in relation to the surrounding soil (Fig. 1). In my view, there is not much that actually differentiates terra preta from other occupation horizons elsewhere. I have seen several places in the Bolivian Amazon that, because of the colour of the soil, concentrations of P, Ca, charcoal etc., would fit quite well into the definition of terra preta (see for example this). It is just that they are not called terra preta, yet :- ). It could be that the absence of terra preta sites outside Brazil is merely the result of researchers giving these kinds of soils/deposits different names in different regions, such as “middens” or “occupation horizons”.

Figure 1: oxisol left, terra preta right (from Wikipedia)

I think that the, otherwise excellent, paper by McMichael at al. could have benefited from incorporating into their model a database of terra mulata sites, instead of terra preta sites. Or, even better, if they had used a database of pre-columbian occupations, including the archaeological sites known outside of Brazil. This would have provided a more reliable tool for modelling pre-Columbian agriculture (if a terra mulata database had been used) or settlements patterns (if a database of archaeological sites had been used) within the Amazon basin; and for modelling pre-Columbian disturbance of the natural environment.

References
 McMichael CH, Palace MW, Bush MB, Braswell B, Hagen S, Neves EG, Silman MR, Tamanaha EK, & Czarnecki C (2014). Predicting pre-Columbian anthropogenic soils in Amazonia. Proceedings. Biological sciences / The Royal Society, 281 (1777) PMID: 24403329

Erickson, C.L. (2008). Amazonia: the historical ecology of a domesticated landscape In: H. Silverman, W.H. Isbell (Eds.), Handbook of South American archaeology. Springer, Berlin, pp. 157-183 DOI: 10.1007/978-0-387-74907-5_11

Neves, E.G., & Petersen, J.B. (2006). Political economy and pre-Columbian landscape transformations in Central Amazonia In: W. Balée & C.L. Ericksonl (Eds.),Time and complexity in historical ecology. Columbia University Press, New York, pp. 279-309

Arroyo-Kalin, M. (2012). Slash-burn-and-churn: Landscape history and crop cultivation in pre-Columbian Amazonia Quaternary International, 249, 4-18 DOI: 10.1016/j.quaint.2011.08.004

Glaser, B., & Birk, J.J. (2012). State of the scientific knowledge on properties and genesis of Anthropogenic Dark Earths in Central Amazonia (terra preta de Índio) Geochimica et Cosmochimica Acta, 82, 39-51 DOI: 10.1016/j.gca.2010.11.029

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

Review of Betty J. Meggers‘ review of the Handbook of South American Archaeology

Betty J. Meggers has been working in Amazonian archaeology for more than 50 years. She has recently published a review of the Handbook of South American Archaeology, which is of great relevance to all of us working on the paleoecology of Amazonia during the Holocene. You can download her paper here.

The paper discusses 3 fundamental aspects of the South American archaeology: i) how contemporary Amazonian archaeologists’ interpretation of the archaeological record has been biased by the abandonment of the classical archaeological methods of pottery analysis; ii) the origin of new world pottery and iii) the relationship between environmental conditions and cultural development in Amazonia.

Classical archaeologists spent months on end drawing and analysing thousands of pieces of pottery. In the first part of her paper, Meggers explains why this meticulous work is a fundamental step in scientific archaeology: “Pottery can be decorated using an essentially unlimited number of techniques and motifs without affecting the utility of the vessel, making independent duplication of identical decoration unlikely”. Therefore, the analysis of pottery’s details and decorations allows us to distinguish diffusion (cultural aspects which are transmitted form one cultural group to another) form independent invention, where a cultural trait arises spontaneously in a given population. According to Meggers, some of the authors of the Handbook omit this important task, undermining the strength of their interpretation of archaeological records

Pottery analysis is the criteria that Meggers uses to discuss, in the second part of her paper, the origin of new world pottery. Many archaeologists that have contributed to the Handbook believe that pottery was independently invented in Amazonia. In Meggers’ view, the similitudes between Japanese Jomon pottery and the Valdivia pottery (which is the oldest pottery in America, dating 6000 BP) are too many to be the result of some form of “cultural convergence”. Moreover, she highlights that the period of Valdivia pottery coincides with a catastrophic volcanic eruption in Japan, which could have pushed groups of Japanese fishermen towards the American coasts. Hence, these Japanese fishermen would have influenced the pottery of early Americans. .

In the Handbook, Amazonia is depicted as a “manufactured landscape” or “anthropogenic cornucopia”. In the third part of her paper, Meggers assesses whether or not such descriptions of Amazonia are supported by the archaeological evidence. She shows that the evidence is actually very weak: the idea of widespread human occupation of pre-Columbian Amazonia is not supported by pollen, phytolith and charcoal analysis, which indicate that vast areas of Amazonia have never faced human disturbance; no systematic archaeological excavation has ever been performed that supports the assumption that large permanent settlements were common in Amazonia; many of the earthworks often cited in support of the “manufactured landscape” idea are concentrated in the Llanos de Moxos, which are ecologically quite different from the tropical rainforest that covers most of the Amazon basin; there is no evidence suggesting that ADE was created for intensive agriculture or to exclude that slash and burn agriculture was a common practice among pre-Columbian people.

Despite the fact that the bibliography of Meggers’ paper is not as large as it could have been, it can still serve as a good introduction to the archaeology of Amazonia for anyone who wants to get into the heart of the current debates.

Betty J. Meggers (2011). Handbook of South American Archaeology reviewed by Betty J. Meggers Revista de Antropología Chilena, 43 (1), 147-157

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

New data about Amazonian Dark Earth (ADE).

The Journal of Archaeological Science has just published a new study on ADE. The study, of Birk et al. is entitled: “Faeces deposition on Amazonian Anthrosols as assessed from 5b-stanols”. I have just read it and this is my very first impression:

The new data are extremely interesting. The authors look at the presence of coprostanol (a marker for faeces) in Amazonian Dark Earth (ADE). They have found a clear change in the index used to asses different sources of stanols, when comparing samples from the topmost 10 cm with samples coming from a depth of 30-40 cm. It seems that litter degradation is responsible for this change. Moreover, it also seems that the normal indexes used to assess the human origin of the stanols do not work very well in Amazonia. This paper is going to be a valuable reference to similar studies performed in Amazonia in the future.

Natural Oxisol on the left; Terra preta on the right

However, while Birk et al. correctly notice that one of the most debated topics about ADE is its origin, they do not do very much to assess why the faeces were there and what is their meaning from an archaeological point of view. ADE is found in two different forms, terra preta and terra mulata. Terra preta is darker, contains more organic matter, P and charcoal and also contains lots of fragments of ceramic. Terra mulata is like a light version of terra preta, it contains more nutrients and charcoal compared with “natural” soils from the surroundings, but less compared to terra preta. Moreover, in the terra mulata sites there is no pottery. Terra preta is found in small patches of about 1 hectare and terra mulata if found surrounding the terra preta sites. Terra mulata can cover as much as 200 hectares. An interpretation could be that terra preta resulted from settlements while terra mulata resulted from agriculture. If this thesis was correct, the high fertility of terra preta would be a side effect of human waste disposal and not the intentional result of land fertilization. In the case of terra mulata, if we assume it has been produced by agricultural use, fertilization must have been intentional. In this case, it would have been very important to see if there is any coprostanol in terra mulata! But the study did not look at terra mulata. Many scholars talk about ADE as synonymous of terra preta, without making a distinction with terra mulata, despite the fact that the differences between the two are key to understanding the past of Amazonia (estimating past population density, the region’s carrying capacity, the levels of social complexity achieved, pre-Columbian settlement patterns, the extent of the human impact on pre-Columbian forest etc.)

Birk et al. only compared samples from 4 terra preta sites with samples from natural soils. I think they missed a great occasion. If they had also looked at 4 samples from terra mulata sites they might have been able to shed new light on the matter. Perhaps they did look at terra mulata and just decided to publish the results in a second paper…keeping us waiting GRRRR J

Birk, J. J., Teixeira, W.G., Neves, E.G., & Glaser, B. (2011). Faeces deposition on Amazonian Anthrosols as assessed from 5β-stanols Journal of Archaeological Science, 38 (6), 1209-1220 : doi:10.1016/j.jas.2010.12.015

Terra preta

Terra preta, also known as Amazonian Dark Earth (ADE), is a really interesting phenomenon. ADE is an anthropogenic soil, mostly found in Brazilian Amazonia, characterized by its dark colour. The ADE’s colour derives from the high amount of charcoal and organic matter contained. It is actually the high quantity of charcoal and organic matter that “defines” terra preta. The incomplete combustion of wood produces charcoal with highly aromatic humic substances, which, once oxidized, a process that takes centuries, increase the soil’s ability to hold nutrients and hence its fertility. Terra preta is a very good soil for agriculture because it is rich in nitrogen, phosphorus, potassium and calcium. The major source of the incomplete combusted charcoal is cooking fire (Glaser et al. 2001)

From an archaeological point of view, should be quite clear what terra preta is: the result of a prolonged human occupation of a site where people have cooked and dumped wastes for hundreds of years. But, many archaeologists do not agree with this interpretation, for them terra preta was “created specifically for permanent farming” (Erickson 2008). It is the evidence of intensive pre-Columbian agriculture! I have read several papers on this topic: while many of them give for granted the “intensive agriculture” interpretation none of them provide archaeological evidence to support it. Because of all the speculations that have been done on the terra preta phenomenon, everybody now is looking for terra preta in its study site!! We have reached the extreme of scholars who said “With the exception of low levels of organic matter and charcoal, Johannes Lehmann (personal communication, 2004) favorably compares the Mound Inventory sample [in the Llanos de Moxos – Bolivian Amazon] to those of anthropogenic ADE found in Brazil” (Erickson & Balee 2006:200-201). How is that possible that you can call something “terra preta” if there is no charcoal and no organic matter??

The reason for this attachment to the productive aspect of terra preta is simply because it is sexy. We can learn from the past; we can establish development projects with indigenous communities and they can re-discover their own ancient agriculture; thanks to terra preta, intensive agriculture in the Amazon can be sustainable etc.

Yes, we have to admit that the terra preta rhetoric is cool. But, should science be driven by the coolness of its conclusions?

Ref.

Erickson, C.L. (2008): Amazonia: the historical ecology of a domesticated landscape. - In: Silverman, H. & W. Isbell (eds.): Handbook of South American Archaeology. - New York: Springer: 157-183.

Erickson, C.L. & W. Balée (2006): The historical ecology of a complex landscape in Bolivia. - In: Balee, W. & C.L. Erickson (eds.): Time and complexity in historical ecology. New York: Columbia University press: 188-233.

Glaser, B., Haumaier, L., Guggenberger, G. & W. Zech (2001): The “Terra Preta” phenomenon: a model for sustainable agriculture in the humid tropics. - In: Naturwissenschaften 88(1): 37-41.