Through Amazonian Eyes: The Human Ecology of Amazonian Populations

5. Savannas

Savannas The upland savannas are characterized by two distinct and strongly marked seasons, each about six months in duration. These areas, known as cerrado in Brazil and as llanos in Colombia and Venezuela, have considerable differences in hydrologic conditions. The llanos are commonly poorly drained, whereas the cerrados are more often than not well-drained. The Brazilian cerrados occupy an area of 180 million hectares, while the llanos occupy about 120 million hectares (Sanchez 1977: 537). Figure 33 illustrates the areal distribution of the savannas in northern South America. By the end of the Cenozoic, and principally during the Pleistocene, important climatic changes took place in South America. Temperatures seem to have declined by about 4 or 5 degrees C, the climate became drier, and the savannas extended into many areas previously and currently occupied by tropical forests (Hammen 1972; Haffer 1969: 133). Areas currently without a definite dry season may have been the few regions that were able to preserve tropical forests during the Pleistocene, such as the areas between the Jurua River and the Upper Orinoco, which are believed to have served as Pleistocene refugia (Haffer 1969: 132). These areas may be important not only in understanding the past but also in forecasting what might happen should deforestation of the tropical forests lead to increasing dryness. The Brazilian savannas have numerous limitations to their agricultural use because of their extreme acidity, high aluminum saturation, and low nutrient and cation exchange capacity; during the dry season, plants can be stressed by the lack of moisture unless they have deep tap roots. Without irrigation and fertilization, agriculture over most of these areas is highly precarious and uncertain. The upland savannas are crisscrossed by numerous rivers, along which grow gallery forests. Native Amazonians have found in these areas a habitat that has permitted a good life based upon swidden agriculture and productive hunting and collecting. The savannas are more advantageous for hunting not necessarily because they have more animal biomass but because better visibility facilitates the work of the hunter and the patchy ecotones and strong seasonality make predicting the behavior of game easier than in upland forests. The most important environmental pressures that influence the strategies of human populations in this habitat are the cycles of heavy rain and extreme dryness, the nutritional limitations of the soil, the presence of numerous and dispersed ecotones, and the lesser productivity of fishing. 118 SAVANNAS 119 ,-- Amazon \.", Basin Figure 33. Upland savannas of Amazonia (from Goedert 1985: 15 and Prance 1978: 215). Characterization of the Savannas When we think of the Amazon we think of the lush tropical forests and rarely of the savannas. Nevertheless, large expanses of savanna can be found throughout the basin, and those habitats are no less important to native populations than the forested environments that receive the bulk of the attention . The savannas cover an area 1.8 million square kilometers in Brazil and may be found in the basins of the Middle and Upper Tocantins, Araguaia , Irirf, Xingu, and Tapaj6s. Others are found in the south of Rondonia and in the northern parts of Mato Grosso and Roraima. These habitats were called "marginal" by the authors in the Handbook ofSouth American Indians because of the apparent limitations of the savannas for agricultural production and the seeming lack of interest in crop nurturing by populations in the region at the time they were first ethnographically observed (Steward 1939-1946). The agricultural potential of the 120 SAVANNAS savannas differs significantly from that of the upland forests and the floodplains . The practice of swidden cultivation involves problems not present in either of the two other habitats under traditional conditions. The mean annual temperatures in the savannas vary between 20 and 27 degrees C. Generally, rainfall is in the range of 800 to 2,000 millimeters annually, with periods of dryness lasting three to seven months. The deficit in moisture in the Brazilian central plateau between May and September can be as high as 491 millimeters (Lopes and Cox 1977). Eighty percent of the rain falls in January, February, and March in the cerrados and in July, August , and September in the llanos. Brief periods of up to three weeks without rain in the rainy season, called veranicos, can have severe negative results in an area with high evapotranspiration and a low capacity for water retention in excellently drained soils (Goedert 1985). Insolation is very high in the region...