The dynamics of Terra Preta

Abstract

This research explores human-environmental interactions in a nutrient-poor (oligotrophic) environment, the blackwater ecosystems of Amazonia. I focus in particular on the modifiability of ecosystem properties by traditional groups and the enhancement of subsistence options within these "anthropogenic" landscapes. The cooccurrence of naturally-occurring terra firme soils (Latosols) and Indian Black Earth, a more fertile anthrosol resulting from the semi-permanent settlement of Amerindian groups, provides a unique opportunity for analyzing: 1) the role of anthropogenic modifications of the environment in conditioning human adaptive processes, and 2) the plasticity of human-environmental interactions within nutrient-poor environments. Two years of cognitive, behavioral and biophysical data collection among caboclo families farming both Indian Black Earth and non-anthropogenic Latosols provides the groundwork for the analysis. My inquiry into the role of the anthropogenic environment in conditioning human adaptive processes includes a characterization of the anthropogenic environment and an identification of distinctive adaptive processes resulting from environmental differences. To research the plasticity in humanenvironmental interaction, I analyzed the degree to which pedology and cultivation systems on Black Earth depart from the "referent" Latosol cultivation system (plasticity as practice and outcome), as well as the factors that constrain and enable this divergence (plasticity as theoretical construct). Both quantitative (soil sampling, botanical quadrants, time allocation studies, frame analysis) and qualitative (soil horizon descriptions, semistructured interviews, participant observation) methods were employed.|Results show how anthropogenic modifications of the environment condition cognitive, behavioral and biophysical manifestations of adaptive process. This is true for ethnopedological domains, perceptions of productive opportunities and differences, cropping associations, nutrient management activities and fallow dynamics. Secondly, both the ecosystem and associated subsistence manifestations exhibit significant plasticity in distant blackwater environments. While soil fertility varies geographically, average values of exchangeable calcium, available phosphorus and Base Saturation are invariably the most plastic parameters and similar crops may be grown in Black Earth and non-anthropogenic soils in each setting. This suggests that divergent uses result from other, non-biophysical factors. Evidence that Black Earth becomes important as traditional diets change, exotic crops become available and market influences take hold suggest that important historical contingencies (technological, political-economic, cultural) underlie the plasticity of human-environmental interactions. Yet environmental constraints are also evident in the inability of contemporary groups to form Black Earth, in the constraints posed by an oligotrophic environment on intentional or fortuitous soil enhancement and in cultivation-induced soil degradation. The Structuration Model of Human Ecosystems was developed to explicate this ension between ecological praxis and ecosystem constraints in human ecosystems.