White-sand Ecosystems in Amazonia

Vegetation on sandy soils, ranging from open grasslands and shrublands to closed-canopy, thin-trunked forests, can be found in patches throughout the Amazon. Despite variation in names, appearance, ecological correlates, and suggested origins, these 'white-sand ecosystems' (WSE) share distinctive characteristics and biological communities. Here, in the first Amazon-wide review of WSE, we review the variation in WSE and the factors underlying this variation. We present the most comprehensive Amazon-wide map to date of WSE and calculate their total area. We find that WSE are still not completely mapped, and we use biological correlates as a proxy to indicate where white-sand vegetation patches likely occur. Through our synthesis of the literature, we find that key factors, such as geologic origin, soil characteristics, hydrology, and fire regimes, vary widely and have differing impacts in different regions on vegetation structure and on floral, faunal, and fungal species composition. Although studies of WSE have increased dramatically in recent years, WSE in many parts of the Amazon remain understudied, and there is little synthesis of the interaction of factors across different areas. In response, we suggest priorities for future research. Finally, we find that WSE are inadequately protected and, where accessible, are regularly mined for sand, logged, or burned and cleared for agriculture. We argue that due to their island-like distribution patterns and resultant complex metapopulation dynamics, their extremely slow recovery after disturbance, and their important contributions to basin-wide diversity patterns and ecosystem services, WSE should be given special consideration in conservation efforts to ensure their persistence in Amazonia.