Vegetation pattern in arid sand dunes controlled by biological soil crusts along a climatic gradient in the Northern Negev desert

Abstract

Vegetation cover and biomass production in drylands are largely controlled by rainfall amounts on a regional and global scale. However, soil water availability on the small-scale is influenced by hydrological processes, soil types and surface properties. In the sand dunes of the north-western Negev biological soil crusts built up by cyanobacteria, green algae, mosses and soil lichens play an important role for the ecosystem processes. They are changing the surface properties. We investigated the vegetation in response to geo-ecological parameters and biological soil crusts along a rainfall gradient from 170 mm to 78 mm. In the interdunes the vegetation cover was 26-30% and showed no significant difference along the climatic gradient. Vegetation cover on the dune crests depends on the sand mobility and decreases towards the more arid parts. The biological crusts limit infiltration and counteract on the rainfall gradient. Therefore, no differences in the vegetation cover were detected and on the mesoscale level the biomass index was negatively correlated to the annual rainfall. Sand mobility and surface stability are important parameters determining the vegetation pattern. Surface properties like crust and fine material are key factors for the hydrological processes and control water redistribution on the micro-scale and, thus, vegetation pattern.