What happened in the Americas during the Pleistocene-Holocene transition?

Pinter et al., on a paper recently published in Quaternary Science Reviews, have reviewed several studies about the changes in vegetation and fire patterns in the Americas between 13.000 and 8.000 yr BP. The transition from the Pleistocene to the Holocene saw a climate change that marked the end of the last glaciation. During the Holocene, the ice melted, the see level raised and, of course, the vegetation changed. Therefore, the changes in paleoecological records of this period - like pollen and charcoal in lake sediments – have been interpreted as exclusive evidence of climate change. However, the problem is that during this same period of climatic change, people colonized America and also transformed the environment. We know that people can have a negative impact on the environment. Pinter et al. report several examples: “In Australia, human colonization ca 50,000–45,000 BP was accompanied by extinction of 90% of large fauna and the rapid decline of rainforest gymnosperms and other fire-intolerant plant taxa and by sharp increases in charcoal […] Tasmania was colonized 5–10 kyrs later than mainland Australia, and megafaunal extinctions and fire-driven devegetation and erosion also occurred 5–10 kyrs later.”

Why should it have been any different in America? People used fire and hunted large herbivores, maybe bringing them to the extinction. The extinction of the megafauna and the use of fire had an important impact on the vegetation. So, the main conclusion of their review is that climate is not the “universal independent variable” determining environmental change. People also played an important role.

But where and when? And here comes the importance of archaeological research and the study and reconstruction of past human-environment interactions. We need to set the geographical and chronological limits of human presence in the Americas in order to be able to interpret the paleoecological archives with any accuracy. This is extremely important in the Amazon Basin, where evidence of early human occupation is scarce. We need to address a fundamental question: Were there no people living in Amazonia 10.000 yr. BP or have we simply been unable to find their archaeological remains yet?

Pollen from Moxos

The group of Quaternary palaeoecology – University of Edinburgh – has recently published a paper on the Review of Palaeobotany and Palynology. The paper, “Characterisation of Bolivian savanna ecosystems by their modern pollen rain and implications for fossil pollen records” addresses an important question: how well do pollen assemblages represent the composition of the vegetation in Beni's seasonally flooded savannah? Answering this question is a pre-condition to the correct interpretation of the fossil pollen records.

Imagine you have a lake surrounded by grass and the forest is 10 km away. If you measure the pollen (using pollen traps) in the grassland right by the lake shore, you will get almost only grass pollen. And what type of pollen would you expect to find in the middle of the lake? As the lake is surrounded by grassland, the obvious answer would be grass pollen…but, Jones et al. have actually found a lot of forest pollen. The reason is that the travel distance of pollen depends on the reproductive strategies of each kind of vegetation. If a tree relies on wind for spreading its pollen, that pollen will travel a long distance from the tree. On the contrary, plants that rely on more complex strategies for pollination, like using insects, will be under-represented in the lake. Understanding these pollen/vegetation relations is key to the correct interpretation of the pollen records in lacustrine sediments.

I think, and hope, that quite soon we will see a paleo-environmental reconstruction of the Llanos de Moxos based on pollen record from lakes around Trinidad. I am very curious to see whether we are able to differentiate those changes in the pollen profile caused by natural events from man-induced changes in the last 2500 years

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.

10 days to my first step on USA and, guess what? I’m scared!

I am going to California for the 76^th congress of the SAA. Being my first time in the USA, my girlfriend warned me: “…me dijo la ali que para entrar en los EEUU tienes que llenar un formulario online 48 horas antes de viajar, sino no te dejarán entrar […] también me recordó la Karen que las ciudades americanas no son como las europeas, que uno no puede andar por donde le da la gana a las tantas de la noche, que hay que ir con un poco de cuidado, si puedes dejar el pasaporte en el hotel y salir con el carnet de identidad mejor, por si te roban. También me recordó que San Francisco es la ciudad de EEUU con más homeless, porque el clima es bueno y la seguridad social es mejor que en otras ciudades - por lo tanto muchos homeless migran ahí. Bueno, que lo tengas en mente, que San Francsico no es Barcelona o Pisa o Berna vale???”. Ok, that is just because she loves me and she is a bit overprotective…but then I got a nice present: The Rough Guide to California. Well, I started reading it and…. see what is written in the “basics” chapter: “Hitchhiking: In Southern California, standing anywhere near a highway is an invitation for a quick death”! And, on page 36: “If the police do flag you down, don’t get out of the car, make any sudden moves, or reach into the glove compartment, as the cops may think you have a gun. Simply sit still with your hands on the wheel; when questioned, be polite and don’t attempt to make jokes.”

I stopped reading the guide. Come on!!! I grew up in Sicily, I have lived in Bolivia, Ireland the UK, …USA can't be that bad right?…

Now, I have just watched this video on youtube and I can’t believe it. Is it really like that? Should I fear the police more than San Francisco’s homeless?

The importance of maize

Maria Bruno has recently published a very interesting paper where she presents the results of the analysis of carbonized plant remains from the site of Loma Salvatierra, in the Llanos de Moxos region of Bolivia (Department of Beni). The most common crop encountered was maize, but she also tentatively identified chili pepper, sweet potato, jack bean, peanuts, squash, and cotton.
Maria's work suggests that in the mounds region of the eastern Llanos de Moxos maize was the most important crop (together with yucca) in sustaining the large population that seems to have inhabited this area. What is striking is that there are no raised fields here! Have those who provided the scientific background for this anything to say?

Ref:

Bruno, M. C. (2010). Carbonized Plant Remains from Loma Salvatierra , Department of Beni , Bolivia. Zeitschrift für Archäologie Außereuropäischer Kulturen, 3, 151-206.

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, 1875-1885. Here