Biotic and abiotic effects on biocrust cover vary with microsite along an extensive aridity gradient

Abstract

Biocrusts are globally distributed and important for sustaining critical ecosystem functions. Little is known about their continental drivers and how smaller-scale microsite differences might affect biocrusts along aridity gradients. This limits our ability to manage biocrusts effectively under drier climates. We collected data on biocrust cover, biotic (plants, litter, grazing intensity) and abiotic (soil texture, soil stability and integrity) attributes from four microsites (trees, shrubs, grasses, open) at 150 sites along an extensive aridity gradient in eastern Australia. At the sub-continental scale, average biocrust cover increased with declining litter cover, and crust cover became more variable with increasing aridity. Biocrust cover was greatest in open microsites and least under trees, and differences were related to the effects of soil texture, vegetation and grazing intensity, which either increased or declined with increasing aridity. Our study reveals that biotic and abiotic effects on biocrust cover vary at different spatial scales along an aridity gradient. Predicted increases in aridity in eastern Australia will likely enhance biocrust cover whereas microsite-level effects are likely to be driven by land management actions such as vegetation removal and overgrazing.