Pre-Columbian agricultural landscapes, ecosystem engineers, and self-organized patchiness in Amazonia

Doyle McKey; Stéphen Rostain; José Iriarte; Bruno Glaser; Jago Jonathan Birk; Irene Holst; Delphine Renard

doi:10.1073/pnas.0908925107

Edited by Olga F. Linares, Smithsonian Tropical Research Institute, DPO AA 34002-9998, FL, and approved January 21, 2010 (received for review August 9, 2009)

Abstract

The scale and nature of pre-Columbian human impacts in Amazonia are currently hotly debated. Whereas pre-Columbian people dramatically changed the distribution and abundance of species and habitats in some parts of Amazonia, their impact in other parts is less clear. Pioneer research asked whether their effects reached even further, changing how ecosystems function, but few in-depth studies have examined mechanisms underpinning the resilience of these modifications. Combining archeology, archeobotany, paleoecology, soil science, ecology, and aerial imagery, we show that pre-Columbian farmers of the Guianas coast constructed large raised-field complexes, growing on them crops including maize, manioc, and squash. Farmers created physical and biogeochemical heterogeneity in flat, marshy environments by constructing raised fields. When these fields were later abandoned, the mosaic of well-drained islands in the flooded matrix set in motion self-organizing processes driven by ecosystem engineers (ants, termites, earthworms, and woody plants) that occur preferentially on abandoned raised fields. Today, feedbacks generated by these ecosystem engineers maintain the human-initiated concentration of resources in these structures. Engineer organisms transport materials to abandoned raised fields and modify the structure and composition of their soils, reducing erodibility. The profound alteration of ecosystem functioning in these landscapes coconstructed by humans and nature has important implications for understanding Amazonian history and biodiversity. Furthermore, these landscapes show how sustainability of food-production systems can be enhanced by engineering into them fallows that maintain ecosystem services and biodiversity. Like anthropogenic dark earths in forested Amazonia, these self-organizing ecosystems illustrate the ecological complexity of the legacy of pre-Columbian land use.

Footnotes

¹To whom correspondence should be addressed. E-mail: doyle.mckey{at}cefe.cnrs.fr.
Author contributions: D.M., S.R., J.I., B.G., J.J.B., and D.R. designed research; D.M., S.R., J.I., B.G., J.J.B., I.H., and D.R. performed research; S.R., J.I., B.G., J.J.B., I.H., and D.R. analyzed data; and D.M., S.R., J.I., and B.G. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
*Most of the occupation sites appear to have been abandoned 800–400 years ago, but scattered reports document the rare use of these techniques by Amerindians into colonial times (28). Early European accounts describe the practice of raised-field agriculture by Otomac Indians in Venezuela (66) and by Tainos in Hispaniola (67), who constructed small mounds using wooden tools similar to the Arauquinoid shovel found in Suriname (37). In recent years, immigrants from Suriname (Saramaka) and from Haiti have constructed small, localized areas of raised beds in similar habitats, often in close proximity to pre-Columbian complexes. Exploiting the opportunity for comparative study of a time series, we included some of these modern analogs in our study of ecological processes.
This article contains supporting information online at www.pnas.org/cgi/content/full/0908925107/DCSupplemental.