Amazon savannas: living fossils? Some reflexions

Abstract

Mosaics of forest and savannas are common in Amazonia, as in other parts of South America. They vary in physiognomy, complexity and shape of distribution, and their origin is still a matter of debate. Edaphic, climatic and hydrological factors, as well as fire, have been suggested. A further explanation involves paleoclimatic changes; shifting climatic belts, would have induced natural replacement of savanna and forest. The present study adds pedological and geomorphologic evidence in favour of the hypothesis. The area of study is the Brasilian state of Roraima, where the mosaics have an apparently random distribution, uncorrelated to environmental aspects. The presence in such areas of (1) several levels of groundwater ironstone, (2) erosional surfaces covered by ironstone fragments and by pebbles of milky quartz, both under forest and savanna, (3) polycyclic profiles with stonelines and (4) both vegetation types in similar types of soil and relief, all indicate the former occurence of forests in present savanna areas, and vice-versa