A Geographical Method for Anthrosol Characterization in Amazonia: Contributions to Method and Human Ecological Theory

Abstract

4.1 Introduction This paper focuses on methodological and theoretical aspects of research to characterize the degree of pedological modification of terra preta dó ındio or Indian Black Earth, a class of anthrosols known in the recent literature as Amazonian dark earths (Woods and McCann 1999). Research was carried out along the Rio Negro, a blackwater region renowned for its oligotrophic (nutrient-poor) status and for the constraints these conditions place on the productivity of terrestrial, aquatic, and human ecosystems. For the blackwa-ter terra firme environments where it is found, Black Earth represents an anomaly both ecologically and culturally. Its high nutrient and soil organic matter (SOM) contents contrast with the characteristics of the highly weath-ered soils that predominate in the region. Furthermore, both contemporary agricultural practices on Black Earth and the density and/or duration of set-tlements presumably required to form Black Earth are anomalous for theo-retical models that draw strong linkages between specific ecological condi-tions, shifting agriculture, and low population density in terra firme environments. The first contribution of this paper is methodological. A geographical method for characterizing Black Earth site distribution and the degree of pedological modification of these sites are presented. Interviews with local residents and systematic sampling procedures were employed to determine the spatial distribution of anthrosols along perennial waterways. Composite sampling, test pits, and total phosphorus determinations were used to deter-mine the degree of soil modification at these sites. Possible applications of these geographical methods are discussed. Additional contributions of research are theoretical. Analysis of the spatial patterns of human settlements permits the identification of preferred sites of Amerindian occupation and an improved understanding of the ability of these oligotrophic environments to sustain sedentary populations. Further-more, the generation of indices of site development allows for important associations to be drawn between preferred areas of residence and the pat-tern of critical resources that may have sustained these inhabitants.