Soil properties influence plant species abundance and diversity in a California serpentine grassland

One mechanism driving observed species richness values is the passive sampling effect, where more species are expected by random chance as the number of individuals present increases. For a sparsely-populated California serpentine grassland 64 m² plot, models using passive sampling have been shown to explain much of the variability in the abundance and distribution of plant species. Yet the serpentine environment is particularly harsh, and here we evaluate if and how variation in soil conditions can further explain species- and community-level distributions. We find that although the number of species increases with number of individuals sampled, it is also significantly negatively correlated with soil pH and rockiness. While abundances of “generalist” species do not appear to be sensitive to variation in soil properties, abundances of others – Hemizonia congesta luzulifolia, Phlox gracilis, Calycadenia pauciflora, and Hesperolinon micranthum – are negatively correlated with soil pH. We present these results along with analyses exploring the spatial overlap of soil textural heterogeneity, Ca/Mg, K, Ni, Co, and Cr and plant distributions. This study of soil factors on species- and community-level distributions provides important insight on the role of abiotic factors structuring ecosystems. In this plot, both sampling and habitat qualities are necessary to explain diversity gradients.