Conclusions
Our results document that local-scale biotic processes, such as
facilitation by the shrubs, are important determinants of diversity
patterns. In general, shrubs are known to provide refugee for species in
harsh conditions, such as high aridity or overgrazing. Furthermore, we
argue that the discrepancy in the literature on changes in plant-plant
interactions may be partially explained by differences in plant life
strategies of species in the conditions of the combined effect of biotic
(grazing) and abiotic (aridity) stress. Therefore, in the arid region,
drought-escaping species like ephemerals and ruderals (R-selected) and
species tolerating stress (S-selected) but avoiding herbivory are highly
dependent on the facilitation under the canopy of shrubs. However, in
sites without severe aridity, canopy of the target shrub protected
competitive species (C-selected) in the conditions of high grazing
intensity (low aridity/high grazing). On the contrary, on sites without
intensive grazing and severe aridity (low aridity/low grazing),
facilitative effects of the shrub turned to neutral or even competitive.