The central role of soil in shaping terrestrial ferns’ assemblage composition, but not taxonomic diversity, in subtropical Atlantic forests

Understanding the uneven fern distribution is crucial for predicting future changes in their diversity and composition. Here, we explore major subtropical Atlantic Forest' physiognomies, addressing the following questions: 1) Is the current classification of subtropical Atlantic Forest’ physiognomies consistent with variations in fern assemblage composition and taxonomic diversity? 2) What are the main drivers shaping terrestrial ferns taxonomic diversity and species composition across the subtropical Atlantic Forest’ physiognomies? To answer these questions, we surveyed 34 sites across the subtropical Atlantic forests, 14 from data generated here and 20 from the literature. Then, evaluated patterns of taxonomic diversity (Simpson diversity and species richness) and assemblage composition at a regional scale. Our results indicate that assemblage composition and taxonomic diversity vary highly across these physiognomies. However, a substantial shift occurs between dense rainforests/dry forests and coastal woodlands to others. The main driver of taxonomic diversity was rainfall seasonality. In contrast, soil cationic exchange capacity, annual rainfall, and clay content were the main factors influencing community composition. Therefore, our study captures some consistent patterns, but they provide only a partial view due to sampling gaps. Nevertheless, expanding quantitative sampling remains essential for a more comprehensive understanding of fern distribution across the Atlantic forests.

Keywords:
Atlantic Forest; cationic bases; climate extremes; fern ecology rainfall; Southern Brazil; terrestrial ferns