El suelo como factor ecológico en el desarrollo de la vegetación en el centro-oeste del Brasil

Abstract

In the vast phytogeographic region of the campos cerrados (Grassland with scattered tortuous trees) of central Brazil, it is common to find, in scattered areas appearing as islands, true forest associations, palm savannahs, and other types of associations, where the typical plants of cerrado do not occur. In order to find out if the distribution of the cerrado and of these other types of association might be related to some edaphic factor, the authors studied the vegetation and the soil of ten different areas in a region of uniform climate between Lagoa Santa and Belo Horizonte, State of Minas Gerais. Three of these areas were covered with cerrado, three with grass pasture and Acrocomia palm, two with forest, one with pasture and isolated trees, and one with a type of vegetation designated as campo sujo (secondary association). The following results were obtained: The cerrado association or rather the typical plants of cerrado (Qualea, Kielmeyera, Caryocar, etc.) were found only in acid soils (pH between 4.2 and 4.6), very poor in exchangeable bases, chiefly in calcium.

The forest and the grassland with Acrocomia or isolated trees (former forests) were found only in soils with a pH above 5.0, and relatively rich in calcium. The typical plants of these associations were not found in the cerrados.

Seedling of black beans (Phaseolus vulgaris) grown in samples of the cerrado and sujo soils showed marked symptoms of calcium deficiency, generally dying 2 to 4 weeks after germination. In samples of the palm savannah and forest soils, the growth of beans was normal. After adding calcium carbonate to the cerrado and sujo soils, the growth of the seedlings was also normal. The authors conclude that the distribution of cerrado within its phytogeographic region is apparently controlled by the soil more than by any other ecological factors. The cerrado plants are apparently tolerant to soils low in calcium content and with low pH, where typical forest trees and good forage plants cannot grow. Liming is probably the most recommendable treatment for improving the soil and thereby bettering conditions for agricultural and animal husbandry practices in cerrado areas.