The influence of environmental factors on biological soil crust: from a community perspective to a species level approach

Questions: Environmental factors have been identified as strong modulators of plant community distribution and diversity, especially in arid and semi-arid ecosystems. Despite recent advances in the ecology of biological soil crusts (BSC) from a community perspective, much remains unknown at the species level. Do environmental factors at different scales influence species richness, diversity and composition of BSC communities? At the species level, what are the main predictors for species occurrence and frequency? Location: A geographic gradient from southeast to central Spain. Methods: In a geographic gradient, we characterized BSC communities based on species richness and diversity, species composition and species frequency. Using generalized linear mixed models (GLMMs) and multivariate analyses we evaluated the effect of precipitation, type of soil substrate, presence of shrubs and presence of Stipa tenacissima on community attributes. Results: Precipitation positively influenced species richness and diversity, but had little effect on BSC occurrence at the species level. Type of substrate was a strong predictor for species composition, occurrence and frequency, gypsiferous soils being those with higher species richness and diversity. At the local scale, S. tenacissima had more effect on species occurrence and frequency, while shrub presence was a poor predictor of community attributes. Conclusions: Environmental factors influence BSC diversity predominantly at a large scale, while local-scale factors influence both community diversity and species distribution.