|The Fragile Tropics of Latin America: Sustainable Management of Changing Environments (UNU, 1995)|
|Part 4 : The semi-arid north-east|
|White sand soils in north-east Brazil|
White sand soils are amongst the most infertile of the generally infertile tropical soils. They are composed mainly of quartz sand, and support a distinctive vegetation. This, varying from open savanna to closed forest, is characterized, by pronounced sclerophylly, low diversity, and high endemism. Forests on white sand soils are reported from several humid tropical regions of the world and are variously designated: Amazon caatinga or campinarana in Amazonia (Anderson, 1981); wallaba forest or muri-bush in Guyana, and heath forest, kerangas or padang, in Borneo.
As shown in figure 11.1, extensive areas of white sand soils and related vegetation (white sand formations) are present in Amazonia, occurring in the Rio Negro basin, in Serra do Cachimbo on the Pará-Mato Grosso boundary, on the Chapada dos Parecis in Rondônia and along the Atlantic coast near the mouth of the Amazon, as well as in Maranhão. Small patches are present in many other parts of Amazonia.
Amazonian white sand soils occur under diverse geological and geomorphological conditions. They are found on the low uplands (called terra firme), mainly composed of arenaceous sediments; on natural levees in a floodplain (várzea); sand ridges or dunes in a coastal lowland (restinga); and on plateaux (chapadas) of Cretaceous sandstone, or on hill areas of granitic rocks (Whitmore and Prance, 1987).
White sand soils also cover a considerable area of North-East Brazil, or the Nordeste. The objective of this paper is: (1) to clarify the distribution of white sand soils in North-east Brazil;(2) to examine their characteristics and genetic processes; and (3) to consider the influence of deforestation on their formation.