The diffusion of unsuccessful innovations: the myth of raised field agriculture

Pre-Columbian raised field agriculture is an extremely interesting topic that we have discussed in this blog before, here, here and here. We call raised fields “any prepared land involving the transfer and elevation of soil above the natural surface of the earth in order to improve cultivating conditions” (Denevan and Turner, 1974). Raised fields have received a lot of attention in studies related to pre-Columbian demography. They have been considered key in allowing dense populations of complex societies to inhabit seasonally flooded regions of South America in pre-Columbian times. Beyond their academic interest, raised field agriculture has also become popular among rural development workers and aid agencies working with small farmers in South America. For more than 30 years now, some archaeologists and NGOs have favoured the “re-introduction” of this pre-Columbian agricultural technique among modern day farmers. In their view, raised fields (which are considered analogous to the Chinampa system in Mexico) represent a promising pro-poor agricultural innovation which is more productive and sustainable than traditional agriculture (which, in the neo tropics is, basically, slash and burn).

A few days ago, Philippe C. Baveye published on-line a thorough debunk of such proposals  (Baveye in press) . It is a comment to a paper by Renard et al (Renard et al., 2012) where the authors advocate for the adoption of raised fields agriculture among modern farmers. The main points that Baveye puts forwards are: 1) There is no evidence that raised fields have supported dense populations in the past; 2) the pre-Columbian Chinampa system is unique. Therefore, it cannot be assumed that the productivity of the South-American raised fields, which are very different from the Mexican Chinampas, was comparable to that of the Chinampas; and 3) the purpose of raised fields was limited to water management:  soil drainage and/or irrigation. We reach very similar conclusions in (Lombardo et al., 2011). It is important to highlight that none of the projects designed to reintroduce raised field agriculture among small farmers in Bolivia and Peru have ever worked (actually, I am not aware of any successful rehabilitation anywhere in the Americas). Local farmers have no idea or knowledge about this ancient practice: this kind of indigenous knowledge was lost hundreds of years ago when the Spaniards got to America. Therefore, besides the technical problems described above, another reason behind this large scale failure is that raised field agriculture has been entirely “invented” by archaeologists and NGOs: the latest example I know of raised field rehabilitation project failures comes from an Oxfam project in the Beni - Bolivian Lowlands. The picture below shows the current state of the raised fields built by Oxfam in 2009, amid an important media coverage and support (for example, see this BBC article).

In 2011 raised fields were also built in the northern Beni.You see the state of the fields during the summer 2012 (photo below).

Hopefully, Baveye’s comment will contribute to make researchers more cautious before proposing the ‘reintroduction’ of raised field agriculture in rural communities.

References

Baveye, Philippe C. (2013). Comment on “Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today” by Dephine Renard et al Ecological Engineering

Denevan, W. M., and Turner, B. L., 1974, Forms, functions and associations of raised fields in the old world tropics: Journal of tropical geography, v. 39, p. 24-33.

Lombardo, U., Canal-Beeby, E., Fehr, S., & Veit, H. (2011). Raised fields in the Bolivian Amazonia: a prehistoric green revolution or a flood risk mitigation strategy? Journal of Archaeological Science, 38 (3), 502-512 DOI: 10.1016/j.jas.2010.09.022

Renard, D., Iriarte, J., Birk, J., Rostain, S., Glaser, B., & McKey, D. (2012). Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today Ecological Engineering, 45, 30-44 DOI: 10.1016/j.ecoleng.2011.03.007

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

RE: Pre-Columbian raised field agriculture: a review

Umberto: Hello again, here goes Delphine Renard and Doyle McKey’s reply to my last post. I am hoping to make this blog an open space for discussion about the Amazon’s past – so I’ll be more than happy to post people’s comments and views on the subjects here reviewed or any other that you might want to put forward for discussion. If you have articles, reviews or announcements you would like to share with other ‘amazonists’ pass them on to me and I will include them in future entries. 

Delphine Renard and Doyle McKey:

Thank you for your interesting comments on our paper. We would like to address two points you made.

First, you consider that some of the hypotheses about functioning of raised-field agriculture are “contradictory” and regret that we don’t “take a position” in these cases.  We see this a bit differently. Some of these hypotheses apply more to some systems and others to other systems. We thus see these hypotheses as complementary rather than contradictory. An example of the difference in our viewpoints is seen, we think, in your criticism that we do not take a position on whether fallows were necessary or not. We do “take a position” on this point. Our “position” includes two points: (1) We think it likely that the need for a fallow period was variable among these systems, depending on soil fertility. The chinampas were built on quite fertile young soils, with volcanic influence and alluvial import. The underlying fertility of this starting material may explain how agriculture can be conducted continuously there. In areas with poorer soils, fallows may have been necessary. Also, pest buildup could well be more rapid in warm lowland sites; escaping pests might thus confer a greater advantage of incorporating fallows in such sites. (2) We think that experimental field studies so far have been of much too short duration to settle the question in any site. As you pointed out in one of your JAS papers, some of these experiments have also had methodological problems that call their results into question.

Secondly, you conclude that better drainage is the only thing all these systems have in common, and wonder why we didn’t conclude the same. We think this view is too narrow, and that different raised-field systems also have other things in common. One of these is the alternation in time and space of aerobic and waterlogged compartments of the ecosystem, which introduces more complexity in nutrient dynamics and could, as we point out in our review, increase nutrient availability to crops. Input of muck from flooded inter-mound areas onto mounds is one way raised-field agriculture could benefit from this, but there are other ways, for example, putting onto mounds mulch from waterlogging-tolerant vegetation that grew in the flooded spaces during a fallow period. We thus think that the mix of waterlogged and aerobic compartments could have been of functional importance in many different raised-field systems.

Finally, we would like to point out that raised fields, like terra preta, are not “magic bullets” for achieving sustainable agriculture, and it is wrong to consider them so. But they could be useful ingredients of solutions. Some of the criticisms leveled at raised-field rehabilitation projects merely reflect paradoxes that we will have to overcome in any attempt to make agriculture ecologically sustainable today—the loss of knowledge and social capital on which such agriculture depends. Transforming agriculture anywhere is going to be difficult. But this doesn’t make it any less necessary, and we don’t think it’s wise to conclude on the basis of studies so far that raised-field agriculture has nothing to offer.   

Pre-Columbian raised field agriculture: a review

A new paper on raised field agriculture was published on line last week in the journal Ecological Engineering. The title, “Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today”, is a bit misleading. You would think it is just another paper claiming that the re-habilitation of raised field agriculture will provide means for sustainable, highly productive, flood/drought proof, politically correct and environment friendly tropical agriculture… but it is not. Instead, it is a good review of all the relevant literature about pre-Columbian raised field agriculture.

The paper, by Renard D., also includes valuable references to raised fields in Asia and is co-authored by a diverse and interdisciplinary group of researchers, including Bruno Glaser, a soil scientist who is among the most prominent world experts of terra preta, archaeologists that have long worked on pre-Columbian raised fields and ecologists. However, in my opinion, its conclusions fall short.

The main point of the paper, with which I fully agree, is that raised fields are found in a variety of environments that differ with respect to almost everything: you find raised fields in all kind of soils; you find them in the Amazon basin and in the Andes; you find them in permanent swamps/lakes and in seasonally flooded/dry savannahs. Therefore, it is very likely that, in different places/conditions, fields were managed in different ways. The paper examines almost all the theories and hypothesis that have been put forward about raised fields. However, while it becomes clear that some of these hypothesis are contradictory, such as the need (or no need) of fallow periods, Renard et al., regrettably, do not take positions. Having noticed all the differences between the fields, I would have concluded that their only common trait is that they improved the drainage and I would have therefore stressed that drainage is the defining aspect of raised field agriculture (see this)…but they do not conclude that, and I would be interested to know why.

They do conclude, and again, I fully agree with them, that before we start to rehabilitate raised field agriculture in real-life situations today, we should fill the huge gaps we still have in our understanding of how pre-Columbian raised field agriculture may have worked. I do hope Oxfam and the other NGOs promoting raised field agriculture in lowland Bolivia today read the paper and take on board its main recommendations.
 - Thanks to Anna for telling me about the paper.

Una nueva revisión de los estudios sobre agricultura en camellones

Un nuevo artículo sobre agricultura en camellones acaba de ser publicado en la revista Ecological Engineering. El titulo del artículo hace referencia al papel que los camellones pueden tener como herramienta productiva y sostenible. Sin embrago, no es el típico articulo que nos cuenta como, gracias a la rehabilitación de camellones, se puede revolucionar la agricultura tropical. Más bien, se trata de un artículo que hace un buen resumen de todo lo más importante que ha sido producido por la comunidad científica sobre el tema. Este trabajo incluye también referencias a los camellones de Asia. En la interdisciplinaria lista de autores, encabezada por Renard D., también encontramos a Bruno Glaser, un pedólogo experto mundial de terra preta, arqueólogos con años de experiencia trabajando en camellones y ecólogos.  Sin embargo, en mi opinión, en sus conclusiones se quedan cortos.

El punto principal del artículo, con el cual estoy totalmente de acuerdo, es que los camellones aparecen en una grande variabilidad de sitios y condiciones medioambientales: los encontramos en los más diferentes tipos de suelos; en la cuenca del Amazonas igual que en las regiones Andinas; en lagos igual que en pampas sujetas a ciclos de inundación y sequía. Entonces es muy probable que en diferentes sitios y condiciones los campos fueran manejados de manera distinta. El artículo hace el elenco de todas las teorías e hipótesis que se han hecho sobre la agricultura de camellones. Pero, en todos esos casos donde las hipótesis se contradicen (como por ejemplo sobre la posibilidad que los camellones se puedan cultivar de manera continuativa, sin dejarlos descansar) los autores no toman nunca posición. Una vez que queda claro que hay una gran diversidad de contextos geográficos donde se encuentra los camellones y que seguramente hubo distintos manejos,  yo diría que la única característica común a todo tipo de camellones y en todo sitio es que mejoran en drenaje. Pero Renard D. et al., no llegan a esta misma conclusión, y me interesaría saber el porqué.

Ellos concluyen su artículo afirmando que antes de montar proyectos de rehabilitación de camellones que involucren las comunidades locales, se deben llenar todos los grandes vacíos que todavía existen en nuestro conocimiento de cómo los camellones estuvieron funcionando. Y yo no podría estar más de acuerdo con esta conclusión. Espero que Oxfam y las otras ONGs que están involucradas en proyectos de rehabilitación con comunidades indígenas y campesinas, lean este artículo y lo tomen en cuenta.

D. Renard, J. Iriarte, J.J. Birk, S. Rostain, B. Glaser, & D. McKey (2011). Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today Ecological Engineering