Multiscale effects on biological soil crusts cover and spatial distribution in the Monte Desert

Abstract

Biological soil crusts (BSC) play diverse roles in arid and semi-arid ecosystems such as increasing soil fertility and reducing soil loss due to aeolian and hydric erosion, but they are very sensitive to disturbances. These attributes point to the relevance of BSC for soil conservation and restoration. In order to use BSC for restoration of degraded soils, we need to understand the ecological drivers of BSC. In this study, we analyzed the effect of environmental factors on BSC cover at different spatial scales in the central Monte Desert (Argentina), including landform, slope, aspect, vascular plants, and disturbance intensity. We evaluated the effects of different factors with linear mixed effect models, comparing the adjustment of models of different complexity, which included different number of factors. First, at the landscape scale, we analyzed BSC cover in two geomorphological units with different soils, topography, and vegetation. BSC cover was higher in the old riverbed, which has a higher proportion of fine clay soil particles, than in the aeolian plain. Disturbance effects were apparent in the old riverbed, showing increasing BSC cover at higher distances from settlements, and BSC located both, under and outside plant canopies. At the mesoscale, we found no differences of BSC cover in dune flanks and inter-dune valleys of the aeolian plain. Finally, at the microscale, BSC patches of higher surface cover were found in association with vascular plants (Larrea divaricata, Bulnesia retama, Lycium sp.), on mounds, and in microsites of southern exposure and high slopes. Our findings suggest that BSC develop preferentially associated with vascular plants, which generate mounds and sloped microsites with southern exposure, where lower irradiances reduce desiccation in these extremely dry environments.