Wednesday, 19 December 2012

Trinidad 2013?

The Llanos de Moxos, in the Bolivian Amazon, are a fascinating site. Full of archaeological remains, striking and diverse tropical fauna and flora and many indigenous cultures. The Llanos covers about 150.000 km2 of seasonally flooded savannah. For many years it has been largely neglected by the scientific community, only a handful of researchers have worked in the area. Fortunately, things are now beginning to change. In the last half a decade several new researchers (including myself) have decided to study this fascinating region. As far as I know, there are now several ongoing research projects in the LM. I list here those that come to mind:

A few weeks ago, whilst reading a post on John Walker’s blog, I thought it would be great if we could all meet next summer in Trinidad,Beni. Actually, Last year I already talked about organising some kind of meeting among the ‘Moxos researchers’ with Marcos Michel, currently Director of la Direccion General de Patrimonio Cultural of the Bolivian Government, and with other people from the Governación del Beni, and all seemed very keen with the idea. It would be great to share some of our work and experiences among ourselves, but also among local researchers and interested parties. There are plenty of Benianos who are passionate about the  past of the LM and some areperforming their own research (such as Ricardo Bottega in Trinidad or Jaime Bocchetti in Santa Ana de Yacuma). It could be really interesting to engage in an exchange of ideas and experiences between “cientificos gringos” and Bolivianos!
If you like the idea and want to get involved you could do 2 things: 1) if you know of other ongoing projects in the Llanos de Moxos you could send the link of this page to those involved and send me their names (so that I can add them to the list). 2) Let me know when would be the best time for you to have the meeting in Trinidad, considering that it would have to be during the dry season (June-October). Keep in mind that there is a conference on Amazonian archaeology in Ecuador from the 7 to 14 of September, so we should avoid overlapping. Although I am not entirely sure if the conference has been confirmed.
Cheers, and I hope to see you in Trinidad next summer!

Friday, 24 August 2012

How lake-like was Lake Pebas?
What did the long-lived lake complex in (nowadays) western Amazonia look like during the Miocene?
First a bit of context…
The geological history of Amazonia has been profoundly influenced by the uplift of the Andes, which started during the Paleogene, about 65 to 34 million years ago (Ma). When the Andes reached the elevation of approximately 2000 meters, they caused massive rains because they stopped the movement of the clouds from east to west. This huge increase in precipitation resulted in very high erosion rates in the eastern side of the Andes and changed the sedimentation regime in the Andean foreland and in Amazonia. At the same time, subsidence exceeded sediment input creating swamps and lakes.
The thickness of the deposited sediments reached more than 1000 meters. It is not clear if this happened between 23 and 10 Ma, due to the mechanism described above (Hoorn et al. 2010a,b); or between 9 and 4.5 Ma, due to a reduction in the subduction angle of the Nazca plate in the Central Andes that shifted the sedimentation area eastward (Latrubesse et al. 2010). Nowadays these sediments constitute what is known as the Pebas (Solimões in Brazil) formation, which outcrops in several areas of Peru and Brazil. What did Amazonia look like during this period? The most accepted hypothesis suggests that a huge system of lakes and wetlands formed in the foreland basin: the so-called lake Pebas. It would seem that Lake Pebas was connected with the Caribbean Sea. The instability of this connection would contribute to explain the high diversity of fresh water fish with marine ancestors that now live in the Amazon river system (Hubert and Renno, 2006). You can find an in depth analysis of how the geological history of South America shaped modern day Amazonia and its biodiversity in Hoorn et al. (2010a).
Two weeks ago I was in Iquitos-Peru for the Tropical Rivers 2012 conference, where we were taken on a guided excursion along the river Amazon and shown, by Dr. Latrubesse, an outcrop of the Pebas formation located a few hours by boat from Iquitos (fig. 1). This outcrop holds clear indications (such as cross-bedding and climbing ripples) that it was formed in a fluvial depositional environment.

Fig 1 Outcrop of the Pebas formation near Iquitos-Peru

According to Latrubesse, the sediments of the Pebas formation are fluvial and there is no stratigraphic evidence of the thick and widespread lacustrine sediments that should be expected if a huge lake the size of the Mediterranean Sea had been present in Amazonia for 10 million years. Moreover, Latrubesse claims that there is no evidence of tidal influence in the fossil record of the Pebas formation. More on Latrubesse’s reconstruction of lake Pebas can be found in Latrubesse et al. (2010).
My impression is that the discussion about the existence of lake Pebas is more a matter of definitions than a sedimentological problem. As a matter of fact, I cannot see much difference between the “large wetland of shallow lakes and swamps” described by Hoorn et al. (2010a) and the “avulsive rivers associated with megafan systems, flood basins (swamps, lakes, internal deltas and splays) and soils developed on flat dry areas” described by Latrubesse et al. (2010). In both cases, the resulting sedimentary record would be characterized by low energy fluvial deposition and back-swamp lakes. It seems to me that the whole discussion is about how “lake-like” the Pebas lake/wetland actually was. On the other hand, it is not clear that Hoorn and Latrubesse are talking about the same thing when referring to Pebas. Latrubesse et al. say that Pebas was deposited in the late Miocene in a fluvial environment while Hoorn et al. (2010b) say that the Pebas is a Middle Miocene to early Late Miocene (~16 to 11.3 Ma) deposit characterized by lake-embayment and swamp systems. But, Hoorn et al. (2010b) also define a Late Miocene fluvial-tidal-dominated wetland phase (~11.3 to 7 Ma) called “Acre phase” which, again, would be pretty similar to   Latrubesse's reconstruction.
Quite more striking is the disagreement with respect to the connection that the Pebas lake/wetland might have had with the Caribbean Sea. While Latrubesse is quite certain that “there is no evidence of a marine environment in the fossil record” other authors state that the connection with the marine environment is well supported by the paleontological evidence (see references in Hoorn et al. (2010a)).
What do you think? Do you agree with me that the sedimentological record of the scenario proposed by Hoorn et al. (2010a,b) would be pretty much the same as that proposed by Latrubesse et al. 2010? And how would you explain such a discrepancy in the interpretation of the paleontological record? The paleontological record is also key to assess when (Middle or Late Miocene?) the Pebas (Acre?) formation was deposited.
Hoorn et al. (2010a). "Amazonia Through Time: Andean Uplift, Climate Change, Landscape Evolution, and Biodiversity." Science 330(6006): 927-931.
Hoorn et al. (2010b). “The development of the Amazonian mega-wetland (Miocene; Brazil, Colombia, Peru, Bolivia)” in Hoorn and Wessenligh Eds. Amazonia: landscape and species evolution
Hubert and Renno (2006) “Historical biogeography of South American freshwater fishes.” Journal of Biogeography 33: 1414–1436
Latrubesse et al. (2010). “The late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system” Earth-Science Reviews 99: 99-124. 

Hoorn et al (2010). Amazonia Through Time: Andean Uplift, Climate Change, Landscape Evolution, and Biodiversity Science DOI: 10.1126/science.1194585
Latrubesse et al (2010). The late Miocene paleogeography of the Amazon Basin and the evolution of the Amazon River system Earth-Science Reviews DOI: 10.1016/j.earscirev.2010.02.005

Tuesday, 3 July 2012

Arqueologia da Floresta Tropical: Betty J. Meggers (1921-2012)

Arqueologia da Floresta Tropical: Betty J. Meggers (1921-2012): Texto extraído do site                                                            Betty J. Meggers (19...

Wednesday, 20 June 2012

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

Monday, 30 April 2012

Effects of the expanding agriculture frontier in the Bolivian Amazon

ResearchBlogging.orgLast week, a paper published in Nature spurred a lot of debates on the internet about the future of agriculture and our ability to feed the 9 billion people that the world will have in 2050. One important aspect related to this debate is the availability of agricultural land. However, people do not always have a clear idea of what expanding the agriculture land means. Here an example of what is happening in one of the most biodiversily rich places of the world: the Bolivan Amazon. Let’s just have a look at a few Google earth’s images of the Lake Peroto in the Llanos de Moxos (dep. of Beni in the Bolivian Amazon).
Image taken the 17 of May 2003. Land use is extensive cattle ranching. Typical floating vegetation (locally called “yomomo”) is growing along the shores of Lake Peroto.

Image taken the 20th of Nov 2004. Land use is extensive cattle ranching. It is the end of the dry season, and the water level is extremely low. In the greenish areas inside the lakes water is almost completely evaporated. This is normal in the Llanos de Moxos, where seasonality can be extreme
Image taken the 2nd of July 2009. Land use is extensive cattle ranching. We are at the beginning of the dry season, water level is quite high, the water is clearly visible.
Image taken the 8th of August 2011. Land use is extensive cattle ranching plus industrial agriculture. 70 hectares of land in the surroundings of the lake have been used to produce rice.

What happened to the lake in 2011? Now the lake is almost completely covered with vegetation... Is it dry? Or is it the first effect of land use change: eutrophication? Based on my personal experience of having been working in the Llanos de Moxos for more than 10 years now and based on the fact that the nearby Lake Suarez is full of water (photo below) on the 15 of August 2011, I would conclude that Lake Peroto is in process of eutrophication.
Lake Suarez. Image taken the 15th of August 2011. The lake is full.

Industrial agriculture in the Beni is already causing deforestation and threatening archaeological sites (see this). Now it is also affecting lake ecology. Is industrial agriculture what people in the Beni really need? Does this kind of agriculture make any sense in a place with a density population of 1 person per square kilometre? Here, a very important part of the population lives in indigenous communities whose subsistence depends on local natural resources. What will happen to them in ten years’ time if these resources are depleted?

Seufert V, Ramankutty N, & Foley JA (2012). Comparing the yields of organic and conventional agriculture. Nature PMID: 22535250

Wednesday, 14 March 2012

A story of people and rivers in the Amazon of 5000 years ago
This time I will tell you about a story that began in the Mid-Holocene (5000 years ago) and is set in the Bolivian Amazon. More precisely in the south-eastern part of the Llanos de Moxos seasonally flooded savannah, in what we call the Monumental Mounds Region MMR (Fig. 1).  Here, between 400 and 1400 AD, pre-Columbians built hundreds of monumental earth mounds, known locally as “lomas”. These earth mounds are planned, complex buildings made by one or more pyramids built on top of elevated platforms (Fig. 3-3).  Monumental mounds can be up to 20 meters high and can cover up to 30 hectares. In the MMR there are more than 350 of these pre-Columbian buildings.
Figure 1 The Llanos de Moxos, the MMR (yellow
box) and the paleo-courses of Río Grande (pink lines). 
During the early Holocene (between 11.000 and 5.000 years ago) this portion of Amazonia was relatively dryer than today, inundations were less frequent and rivers transported few sediments. During these stable climatic conditions there was no deposition of fluvial sediments in the savannahs and soils were forming all over the Llanos de Moxos. 

Mid- Holocene: Río Grande built the landscape

But things changed a lot during the Mid-Holocene, between 5 and 4Ky BP. The Rio Grande (pink lines in Fig. 1) entered in a period of frequent avulsions and high sedimentation, probably triggered by a climate change towards wetter conditions. As a result, in the South-eastern LM, it formed a ­fluvial distributary system (FDS) (Fig. 2-1). Suddenly, the landscape was transformed into a large swamp, dominated by something similar to an interior delta. This FDS deposited several levees, crating relief at a local scale (Fig. 2-2), and a sedimentary lobe, creating relief at a regional scale (Fig. 2-3). The former soils were buried and the landscape became a mosaic of patches of savannahs closely interwoven and sometimes enclosed by forested paleo-levees.

Late Holocene: pre-Columbians transformed the landscape

In the MMR, the lobe deposition favoured the development of a complex pre-Columbian society by increasing the region’s agricultural potential. Firstly, it created a convex-up topography, which greatly reduced its susceptibility to ­flooding; secondly, the construction of the elevated ­fluvial levees significantly improved drainage conditions at the local scale. Furthermore, the Río Grande also provided relatively younger sediments derived from its Andean catchment that are rich in nutrients. Thus, the Río Grande removed the two biggest obstacles faced by tropical agriculture in the rest of Amazonia: severe waterlogging and poor soils. But the Río Grande’s job was not perfect: fl­uvial levees enclosed patches of ­floodplain, resulting in ponding and pronounced waterlogging. Thus pre-Columbian people had to transform the landscape through the construction of a drainage system in order to further improve agricultural conditions (Fig. 3-1).

The network of canals had a significant impact on the edaphology of the MMR: it pushed the forest-savannah boundary towards the savannah, eventually increasing the area of well-drained, usable land. The inhabitants of the MMR were very lucky because they also had several lakes placed on the top of the sedimentary lobe. Building canals that transported the water from the lakes to the agricultural fields (Fig. 4), they were able to perform agriculture even during the dry season.
The spatial overlap (Fig. 3-2) between the monumental mounds and the area of deposition of the sedimentary lobe created by the Río Grande during the mid- to late Holocene  suggests that good edaphic conditions favoured the emergence of the monumental mounds culture (Fig. 3-3).

The ­fluvial landscape created by Río Grande was probably an important factor behind the emergence of the monumental mounds culture in the South-eastern LM, as it provided favourable environmental preconditions in terms of soils, nutrients and drainage characteristics. Pre-Columbians additionally modified and improved their environment by building a network of drainage canals.
Figure 4 (a) Drainage canal (A–B) and irrigation canal (C–D) 
built along topographic slopes. (b)The C–D canal in detail;
 the irrigation canal linking Lake San José to the Cotoca mound 
joins pre-existing natural channels. Coring in the middle of 
the canal shows that the bed of the canal is only 50cm below 
the present bed (which is about 50 cm below the modern savannah). 
Therefore, this canal was at most 1 meter deep but went through a slope 
of 3 meters. The only possible function of such a canal was irrigation.

You can find more on this story in my latest paper published on-line in the journal “The Holocene”. It is entitled “Mid- to late-Holocene fluvial activity behind pre-Columbian social complexity in the southwestern Amazon basin” and can be found here. 

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 DOI: 10.1016/j.jas.2010.02.011

Umberto Lombardo, Jan-Hendrik May, & Heinz Veit (2012). Mid- to late-Holocene fluvial activity behind pre-Columbian social complexity in the southwestern Amazon basin The Holocene

Friday, 24 February 2012

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.


-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.
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Monday, 20 February 2012

The Climate War
Climate is changing. This is like an obvious conclusion if you are old enough to remember how it was only 20 or 30 years ago. Non c'è più la mezza stagione” (“There are no more middle seasons” which is the Italian equivalent of “Things are not what they used to be”) is one of the most used expression when travelling on the train in Italy, like a mantra used to start any conversation.

Less commonly accepted among the general public is that the cause of this change towards a warmer climate is CO2 (and other greenhouse gases) we humans release into the atmosphere. It is not uncommon to hear people say this is not true. Many, not only in the USA, think that “the left-wing political agenda is behind the global warming (GW) hoax”. What is quite surprising is that among scientists there is not such a controversy. All climatologists (but a few outliers…) agree on the fact that anthropogenic gases are responsible for the GW. So, how is it possible that we have such a schizophrenic society in which scientists and the general public have different opinions on scientific issues? If the public do not base their opinion about science on what scientists say, where do those opinions come from?

Well, there is now a very interesting book on sale that explains it all. The Hockey Stick and the Climate Wars: Dispatches from the Front Lines, by Michael Mann. Mann is a climatologist who has been involved, for the last 10 years, in the big battle that is being fought between scientists, on one side, and conservative journalists, politicians and corporations on the other side. I really enjoyed reading it for several reasons: you get quite a good understanding of how Science works; you end up learning a lot about climatology and you get a thorough historical reconstruction that provides you with a fair answer to the questions above. If you have sufficient economic means, you can take one of the basic principles of science (nothing is “true”, everything is under scrutiny) and sell it to the public as “they don’t know what they are talking about”.

I strongly recommend the book. If you are a scientist or you already know enough about climate science, this book can offer you a valuable historical reconstruction of one of the saddest examples of what happens when Science falls under political intimidation. If you belong to those who still do not have a clear idea about what is going on with the so called “climategate”, or who call themselves “sceptical”, this book can give you a precise idea of what the “climategate” actually is and will make you far less “sceptical”. On the other hand, if you believe that GW is a liberal hoax, don’t buy the book. Science is not for “believers”. Science is for the real sceptical, who can change idea once enough evidence is provided.


The Hockey Stick and the Climate Wars: Dispatches from the Front Lines by Michael E. Mann

Mann, M., Bradley, R., & Hughes, M. (1998). Global-scale temperature patterns and climate forcing over the past six centuries Nature, 392 (6678), 779-787 DOI: 10.1038/33859