The physical environment of rupestrian grasslands (campos rupestres) in Brazil: Geological, geomorphological and pedological characteristics, and interplays

Abstract

The Rupestrian Grassland is a vegetational complex with grassy to shrubby formations that occur throughout the high mountains of Brazil, usually formed by structurally resistant rocks, little affected by late tectonics, and strongly eroded and weathered under long term geological stability. RGC is closely associated with high altitude landsurfaces, in which several factors have a determinant role: (1) extreme oligotrophy, and acid, nutrient-depleted parent materials; (2) resistance to weathering and erosion (chemical and physical); (3) constant wind exposure; (4) intense fire regime. Variations of RG phytophysiognomies are basically due to soil depth (edaphic factor), drainage and landscape stability and evolution. Landforms (geomorphological attributes) affect the RGC at continental scales (high landsurfaces), regional scales (regional landforms, such as escarpments, valleys, slopes) and local scales (soil depth, stoniness, rockiness, drainage). The most common occurrence of RGC in Brazil is on Quartzite and metarenites, followed by canga and other Fe-rich substrates, igneous rocks and metamorphics, hence displaying a high diversity of substrates, with a major trait of extreme soil oligotrophy and acidity, and crucial variations in soil depth. The occurrence of well-documented areas of RG on Granitic and gneissic terrains imply that even richer rocks, submitted to long term weathering and erosion, can lead to similar soils on Highlands, where rock outcrops are also common (e.g. Caparaó, Itatiaia, Brigadeiro, Serra dos Órgãos). RGC can occur immersed in different domains (Atlantic Forest, Caatinga, Cerrado), regardless of present day climates, since it represents an edaphic climax of long-term development. The widespread distribution of comparable RGC, from Amazonia (Carajás, Roraima, Pacaás Novos, Cachimbo) to the Central Plateau (Santa Barbara, Ricardo Franco, Pirineus) and Northeastern and Southeastern Brazil (Caparaó, Espinhaço, Sincorá, Jacobina, Itatiaia, Serra dos Órgãos, Brigadeiro, Carangola) raises the unresolved question of phylogenetic ancestry, age and similarities (floristic, structural) between those isolated islands of Rupestrian vegetation. These aspects are central to the evolution of Brazilian Biomes, representing key issues to resolve the late Quaternary Refuge Theory controversy, and test the validity of island biogeographical isolation theories.