Do changes in grazing pressure and the degree of shrub encroachment alter the effects of individual shrubs on understorey plant communities and soil function?

1. Shrub encroachment has dramatically altered the structure and functioning of many dryland ecosystems worldwide. While positive effects of shrubs on their understorey are commonly found (patch-level effects), these effects can be either positive or negative when scaled up to the community or landscape level (landscape-level effects). These contrasting results are likely to be caused by differences in the degree of shrub encroachment or grazing pressure among studies. No study has addressed the relationship between the patch-level effects of shrubs and the degree of shrub encroachment (i.e., their density or cover) within the landscape, and how this relationship is influenced by grazing. 2. We examined how differences in grazing pressure and the degree of shrub encroachment, as measured by shrub cover, influences patch-level effects of shrubs on multiple soil and plant attributes (plant density, biomass and similarity between shrub-open areas, and soil stability, nutrient cycling, and ...