White-Sand Vegetation of Brazilian Amazonia

This paper describes a distinctive vegetation type occurring on white-sand soils which are scattered throughout the region. Although essentially homologous throughout Amazonia, white-sand vegetation is known locally by various terms: to avoid confusion, exclusive use of the single term Amazon is proposed. The caatinga is distinguished from other regional vegetation types by its white-sand soil, scleromorphic physiognomy, and unusual floristic composition. Possible origins of the white-sand soil include: in-situ weathering, alluvial deposition, or podzolization. The scleromorphic physiognomy of the caatinga indicates a lack of nutrients and/or periodic water deficiencies in the soil. Extreme edaphic conditions and the insularity of these sites have probably acted as powerful selective forces, generating a biota characteristically low in diversity and high in endemism. Numerous endemic species may currently face extinction due to widespread burning of caatinga vegetation. Repeated fires on white-sand sites result in the effective arrest of succession; subsequent mining of these sites for sand eliminates any possibility of vegetational reestablishment. Alternative benefits of the caatinga in its intact state are considered.