A simple classification of soil types as habitats of biological soil crusts on the Colorado Plateau, USA

Question: Can a simple soil classification method, accessible to non-experts, be used to infer properties of the biological soil crust (BSC) communities such as species richness, evenness, and structure? Location: Grand Staircase-Escalante National Monument, an arid region of the Colorado Plateau, USA. Methods: Biological soil crusts are highly functional soil surface communities of mosses, lichens and cyanobacteria that are vulnerable to soil surface disturbances such as grazing. We sampled BSC communities at 114 relatively undisturbed sites. We developed an eight-tier BSC habitat classification based upon soil properties including texture, carbonate and gypsum content, and presence of shrinking-swelling clays. We used simple structural equation models to determine how well this classification system predicted the evenness, richness, and community structure of BSC relative to elevation and annual precipitation. Results: We found that our habitat classification system explained at least 3.5 x more variance in BSC richness (R-2 = 0.57), evenness (R-2 = 0.59), and community structure (R-2 = 0.34) than annual precipitation and elevation combined. Gypsiferous soils, non-calcareous sandy soils, and limestone-derived soils were all very high in both species richness and evenness. Additionally, we found that gypsiferous soils were the most biologically unique group, harboring eight strong to excellent indicator species. Conclusions: Community properties of BSCs are overwhelmingly influenced by edaphic factors. These factors can be summarized efficiently by land managers and laypeople using a simple soil habitat classification, which will facilitate incorporation of BSCs into assessment and monitoring protocols and help prioritize conservation or restoration efforts.