Interaction intensity along the stress gradient
For all three indices (cover, richness, and Shannon diversity), RII was higher in the arid compared to the semi-arid climatic region (Figure 2). The RII indices for species’ cover, species’ richness and Shannon diversity were all positive on both the LG and HG sites in the arid region, indicating a facilitative effect of the target shrub,Artemisia kopetdaghensis (Figure 2; Appendix A). However, the response of RII to the grazing intensity varied with climatic conditions. A significant facilitation (expressed by the positive RII values) was recorded in the semi-arid region for species’ cover and richness, but only on the HG sites. The RII values for species’ covers were negative for the LG sites in the semi-arid region, indicating competition rather than facilitation by the dominant shrub (Figure 2; Appendix A). The RII values for Shannon diversity on the HG and LG sites in the semi-arid region and the RII values for species’ richness on the LG sites in the semi-arid region did not significantly differ from zero, indicating neutral interactions (Figure 2).