Dual community assembly processes in dryland biocrusts communities

1.  Biocrusts are critical components of drylands where they regulate a wide range of ecosystem functions, however, their response to the worldwide phenomenon of shrub encroachment and to livestock grazing, the most extensive land use in drylands, are not well studied. Grazing by livestock and increases in shrub cover could influence biocrust communities directly via trampling or shading, or indirectly, by altering biotic interactions amongst biocrust taxa. The extent of these changes in biocrust cover, diversity and composition are poorly known. 2.   We used linear models and structural equation modelling to examine the direct effects of grazing and shrubs on biocrust community composition and the indirect effects mediated by changes in species interactions. 3.   Biocrust richness and cover increased with increasing shrub cover at the site level. This pattern occurred despite the negative response we found (lower cover and richness) under shrub patches vs open areas, which wa...