Comparison of floristic changes on vegetation affected by different levels of soil erosion in Miocene clays and Eocene marls from Northeast Spain

Abstract

Increased soil erosion on Eocene marls from N Aragon (NE Spain) tends to reduce vegetation cover and plant species number, but little is known about its effect in the neighbouring Miocene clays. In this study, the vegetation of strongly eroded areas on Miocene clays was analysed in terms of erosion intensity and compared with Eocene marls. Releves were carried out on uniform patches of vegetation affected by different levels of erosion. The degeneration of vegetation cover explained 34% of the variation in species number as opposed to 48% in marls, and a clear pattern of species replacement through the destruction of the vegetation cover was not observed. Approximately 25% of the species decreased significantly and 4% increased, as opposed to 47% and 0% in marls, respectively. Erosion on marls may be more severe (more disturbance) and less stressing for vegetation (more water availability) than on clays. The few species that colonized intermediate degeneration stages and highly eroded sites were more common in non-eroded areas in drier bioclimatic belts. Thus, the degeneration of vegetation by soil erosion favoured the establishment of xeric species. The ecological range of erosion-resistant species was not wider than non-resistant species. Overall, increased soil erosion selected for different plant species in marls than in clays.