Effect of slope aspect on soil and vegetation properties along an aridity transect

This study has investigated the effect of south- and north-facing hillslopes (SFS and NFS, respectively) on soil and vegetation properties along a climatic transect that covers four climatic zones: Mediterranean, semiarid, arid, and extreme-arid. The results indicate that differences between NFS and SFS in organic matter and soil moisture contents were significantly higher in the Mediterranean zone than in any other site along the climatic transect, particularly at the end of the rainy season. Both soil properties were higher on NFS than on SFS. Similarly, differences between the opposite hillslopes in species richness along the climatic transect were found significant only in the Mediterranean zone, where species richness was higher on the SFS than on the NFS. However, species diversity on SFS was significantly higher than that on NFS at all sites, except for the semiarid zone, where no significant difference between aspects was found. Species diversity on SFS changed along the climatic transect at an almost linear rate, while on NFS there was a sharp increase from the extreme-arid zone to the semiarid zone, followed by a decline moving towards the Mediterranean zone. Vegetation cover along the climatic transect was higher on NFS than on SFS, except for the extreme-arid zone, where no significant difference was found. The general conclusions are: (a) The most significant differences in soil and vegetation properties between NFS and SFS are found in the Mediterranean zone, mainly at the end of the rainy season; in the semiarid, arid, and extreme-arid zones the differences are small and generally negligible, (b) The spatial and seasonal differences on SFS are smaller than those on NFS.