Spatial signatures in biological soil crust communities and their drivers

Background/Question/Methods

Ubiquitous to drylands, biological soil crusts (BSCs) are understood to mediate ecosystem function via the redistribution of water in space. Changes in cover and configuration of these highly sensitive soil communities to exogeneous factors likely mean that the functional role of BSCs changes significantly with conditions. Despite our growing understanding of BSC biogeography, we have little understanding of how they organize at small scales, as BSC patches are often square centimeters in area. A hierarchical multiple linear Bayesian model was created to elucidate the driving factors determining the spatial metrics of BSCs and surrounding vegetation. This model utilized remotely sensed satellite data, soil samples, and high resolution unmanned aerial vehicle (UAV) imagery taken at 26 sites throughout the American Southwest.

Results/Conclusions

Preliminary posterior distributions suggest that aridity, soil calcareousness, and slope aspect are the most significant drivers of metrics describing BSC cover and configuration. Aridity showed the greatest effect size on late successional dark-mixed BSCs, which play key roles for nitrogen fixation and soil moisture. Dark-mixed BSCs exhibit abrupt changes in proportional cover and patch complexity along the aridity gradient, suggesting non-linear response to changing climate and a critical role of water exchange at patch edges. Slope also is exhibited to increase clustering in these landscapes, further highlighting the importance of BSCs in ecohydrological exchange. Results of this study suggest that the spatial traits, and therefore ecological function, of BSCs are highly sensitive to changes in aridity and that conserving these soil communities is urgent in the face of ongoing climatic change.