Spatial Signatures of Biological Soil Crusts and Community Level Self-organization in Drylands

While vascular plants in drylands can spatially self-organize and persist under climatic stress through gradual changes in patch attributes, dryland patch dynamics largely assumes bare soil between plants. Biological soil crusts (BSCs) are communities living in the soil surface of drylands and mediate water redistribution in space. BSCs often occur in patches of light cyanobacteria and dark-mixed aggregates; however, little is known about their spatial patterns and dynamics. Here, we investigate spatial attributes of BSC patches, their spatial interactions with vascular plants, and factors that drive variation in these attributes using ultra-high-resolution (1 cm) maps from UAV imagery across three ecoregions of the southwest United States. Our analysis showed that light cyanobacteria BSCs varied most in patch shape complexity with aridity, while dark-mixed BSCs varied most in abundance. The distribution of dark-mixed BSCs was strongly affected by the soil template (texture and calcareousness) and vascular plants. Light cyanobacteria BSCs and woody plants spatially aggregated with aridity, while slope enhanced the spatial association between BSC functional groups. We conclude that light cyanobacteria BSCs can likely persist under stress through patch shape alterations, while dark-mixed BSC patches may have a lower capacity to do so—corroborating that dark-mixed BSC abundance may decline under altered climatic regimes. Light cyanobacteria BSCs may also buffer the effects of aridity for other biota by promoting runoff. BSCs and vascular plants coordinate in space in response to resource availability, suggesting the need to consider self-organization of multiple unique assemblages to better predict dryland response to climate change.