Geomorphic agents versus vegetation spreading as causes of badland occurrence in a Mediterranean subhumid mountainous area

Previous evidence on the chief role of physical weathering on badland development in the Vallcebre area (South Eastern Pyrenees) led to the study of the amounts of energy available for the main geomorphic agents, and to analyze the results in the light of the patterns of vegetation cover acid species distribution, in order to explain both the occurrence of these badland forms and their preference fur north-facing (shady) hillslopes. Results showed that the weathering potential provided by freezing is about two orders of magnitude greater than rainfall kinetic energy, and that the former strongly depends on hillslope aspect. The study of vegetation demonstrated that vegetation is poorer in cover and species composition on shady hillslopes than on sunny ones, spontaneous revegetation of these surfaces being restrained by cold thermal conditions rather than by water availability. These results show that the occurrence of these badland areas depends on montane climatic attributes that control geomorphic and biological processes, and that are different from those that promote the occurrence of badlands in dry Mediterranean areas. The preference for northern aspects provides evidence for these differences. (C) 2000 Elsevier Science B.V. All rights reserved.