Procesos erosivos intensos en las áreas marginales de la Depresión del Ebro y el Pirineo : Interpretación de los patrones de la vegetación

This article reviews the current knowledge about erosion processes in badlands and other strongly eroded areas in the northern half of Aragón (Spain), from the Middle Ebro Basin to the Pyrenees. The four most extensive lithologies with the strongest erosion processes were selected: pure gypsum from the Central Ebro Valley, Miocene clays from Hoya de Huesca and Somontano, Eocen marls from the Prepyrenees and Eocen flysch from the Pyrenees. The climate of each substratum was studied, as well as the most important edaphic and lithological characteristics in arder to explain the erosion processes. Sorne information about erosion rates and vegetation characteristics from each substratum were included. Also vegetation patterns in these areas and their interactions with erosion processes and other factors were interpretted. Very strong differences between the lythologies were found. Pure gypsum has high infiltration and low erosion rates, but the ion exportation by dissolution is high. These characteristics and the low annual rainfall mean that the vegetation has to resist a high water stress. The vegetation pattern is very uniform and topography is the most important factor to explain this. However, in the gullies of eocen marls, infiltration is very low anderosion rates are very high. These strong erosion processes cause formation of a mosaic with stable, depositional and eroded areas in close proximity to each other. This implies that the vegetation is very heterogeneous in small spatial scales, and typically there is a "species mixture". Generally, Miocen clays are characteristic between eocen marls and pure gypsum, and the characteristics of eocen flysch are usually similar to eocen marls.