Dear Delphine Renard and Doyle McKey,
Having read your comments on my post, I think I was wrong with my critiques. I focused on specific technical details and overlooked the key issue. I will try to address that now.
A key controversy surrounding raised field agriculture is whether they were built as an opportunity (to produce more per unit of land and unit of work) or as a necessity (to gain marginal lands, regardless of increased labor costs per unit of production). This is the key point that needs to be addressed before raised field agriculture can be put forward as an alternative for today.
We can imagine 3 different pre-Columbian scenarios.
1) Population increased (or climate changed) and people had to gain marginal land for agriculture. In this scenario, raised field agriculture required more work for unit of production compared with slash and burn agriculture but served to increase the amount of overall arable lands and feed more people (this is Boserup’s idea).
2) Building raised fields required less work than practicing slash and burn agriculture. Pre-Columbians chose to cultivate the savannah instead of the forest. In this case they just build raised fields because it was easier than clearing the forest with stone axes (this is Denevan’s idea).
3) Raised fields were more productive per unit of land AND required less work per unit of production than slash and burn agriculture. Raised field agriculture triggered population growth and permitted the development of large complex societies despite poor soils (this is Erickson’s idea).
The archaeological and geomorphologic evidence in the Bolivian Amazon suggests that the most plausible scenario is likely to be the first one; because a) raised fields are built in forested areas and b) the model proposed where fertility is increased thanks to water logged between the fields is not applicable in Moxos (as I explain in my last paper)
You say “We think it likely that the need for a fallow period [in raised fields] was variable among these systems, depending on soil fertility”. But this doesn’t change the argument because the underlying fertility was there also for the agriculture without the raised fields! The need for fallow periods is the same for raised fields than for other forms of agriculture. If you have good fertile soils, why would you build raised fields, transforming (and losing) half of the good land into canals? The existence of raised fields in places where there were fertile sediments is itself evidence that fields were built to improve the drainage (as fertility was already there). In other words, to transform marginal lands subject to floods into agricultural surface.
When considering the idea of re-introducing raised field agriculture today, we have to bear in mind that people now have metal tools and mechanical saws. Clearing the forest is far easier than it was in the past and, on the whole, population density in the Amazon is very low. There is no doubt that today clearing forest is far cheaper than building raised fields (10 people can clear 1 hectare of forest in a couple of days).
Those who propose raised field agriculture have to demonstrate that they can get more output per unit of work than with slash and burn agriculture. Till now I haven’t seen any figures, experiment or theoretical model backing this. On the other hand, after 40 years of proposing the re-introduction of raised field agriculture, this technology hasn’t been adopted by indigenous people or any other group of farmers.
Coming back to your paper, the question I wish you had addressed in your conclusions is: are raised fields a necessity arising from population pressure or an opportunity to produce more with less effort? I think we have plenty of evidence to support the former and very little to support the idea that the regions where we find raised fields experienced a pre-Columbian Green Revolution :-)