Cerrado Vegetation in Brazil: An Edaphic Gradient
1977
Lopes, A. S. | Cox, F. R.
The vegetation in central Brazil is a tropical savanna called “cerrado” that varies from pure grassland to a nearly closed canopy of medium height trees overlying grass. Since forest is the expected climax vegetation there, several theories have been given to explain the types of grassland present. The more promising of these involve differences in soil properties, but only a few sites have been used for evaluation. To study these relaships in more detail and yet cover the bulk of the region, 518 composite topsoil samples were collected from a 600,00 km² area. Laboratory characterizations included pH, exchangeable A1, nutrient levels (including micronutrients), organic matter content, particle size distribution, and color. The relationships between type of vegetation and differences in soil properties were evaluated statistically, primarily by correlation and regression. A positive gradient was found between the density and height of woody vegetation and the following soil properties: pH (H₂O), pH (KC1), exchangeable Ca, Mg, and K, and extractable P, Zn, Cu, and Mn. As the percent of A1 saturation increased there was a decrease in density and height of woody vegetation. Neither exchangeable A1, particle size distribution, nor organic matter content showed a consistent gradient with the vegetative measure. There was a tendency for more dense stands of vegetation to occur on dark, reddish brown topsoil; while less dense stands occurred on brown to dark brown topsoils. The results suggest that the types of vegetation present in the region may best be explained by differences in soil properties, and it is recommended that soil Al be expressed by percentage Al saturation, rather than by its absolute value, in these relationships.
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