The effects of geomorphology and associated soil properties on biological soil crust abundance and distribution

Background/Question/Methods

Biological soil crusts can be patchy and vary in community composition, abundance and distribution according to abiotic and biotic ecological gradients.  Only a few studies have investigated how multiple environmental drivers (vegetation, soil chemical and physical properties, geomorphology) simultaneously influence crust ecology.  Our objective was to test if a geomorphic approach that is linked to soil properties can be used to explain patterns of biological soil crust distribution on an alluvial piedmont landscape in the Mojave Desert.  Standard community ecological and geomorphic methods were used to characterize land surface components (functional groups of plants and biological soil crust types, physical components) of three geomorphic surfaces of differing ages. 

Results/Conclusions

Significant differences in total crust and crust functional group abundance and diversity were observed between the geomorphic surfaces.  Geomorphically young alluvial deposits had greatest crust cover and functional group diversity, with abundance and functional group diversity decreasing with geomorphic age.  Preliminary results also showed that cyanobacterial and micro-algae community composition and biomass differed based on geomorphology, with diversity and biomass decreasing with geomorphic age.  This trend could be attributed to altered physical land surface properties, such as decreased micro-topography and increased surface rock density, which are linked to soil property changes such as increasing alkalinity and vesicular horizon development.  In conclusion, we found that, at least in the Mojave Desert, a geomorphic classification of the landscape can help elucidate patterns of crust abundance and community composition and potentially be linked to variation in ecological function.