Seasonality drives herbaceous community beta diversity in lithologically different rocky outcrops in Brazil

Background and aims – Seasonality exerts strong controlling forces on species diversity in herbaceous species communities, however, this control process remains poorly understood in tropical lithologically different rocky outcrops. We aim to investigate the effect of seasonality and the variability of soil properties on changes in the herbaceous species richness and species composition of two different herbaceous species communities on rocky outcrops in Brazil. We hypothesize that seasonality, determined by variation in precipitation, and soil fertility, determined by variability in nutrient-related soil properties, drives species diversity (i.e., richness and beta diversity) patterns of herbaceous communities at local scale.Methods – To investigate how the variation between dry and wet seasons affects species richness and beta diversity, we studied plots on rocky outcrops of Iron Quadrangle (40 plots, 1 × 1 m) and Carajás (20 plots, 1 × 1 m). Key results – We observed similar richness patterns between seasons, without significant differences between sites, using rarefaction and extrapolation curves. However, we observed significant differences in beta diversity between seasons. Our results indicate that seasonality determines the temporal variation of the herbaceous species composition, but not species richness. Likewise, our tested models indicated that seasonality shape beta diversity in the studied rocky outcrops. Conclusions – The predictable seasonal precipitation is closely related to the community composition on this type of rocky outcrop formation, where there typically is a marked seasonal water deficit pattern, with increased deficit during the dry season. We presume that seasonality is an important driver in determining plant community assembly at local scale on the studied rocky outcrops.