Factors driving trait-convergence linked to leaf economic spectrum in tropical ferns

Environmental filters, competition, and phylogenetic relationships play crucial roles in determining plant functional patterns across different environmental scenarios, scales, and taxa. Patterns of functional convergence and divergence are crucial to understand trait-environment interactions and plant coexistence, which must consider multiple drivers partitioning the ecological, environmental, and evolutionary processes, an integrative approach explored in this study. We analyzed leaf trait convergence and divergence among co-occurring tropical fern species, the relationship between functional and taxonomic components, and the role of local environmental conditions on functional patterns. We established 22 plots in three forest remnants of northeastern Brazil and measured key leaf economic spectrum (LES) traits (leaf area – LA, specific leaf area – SLA, leaf dry-matter content – LDMC) in fern assemblages and quantified local environmental conditions (edaphic variables, basal area of trees, and rock cover). Functional trait convergence dominated the fern assemblages for all LES traits. We found a significant phylogenetic signal for LDMC. The increases in fern species richness show an association with an increase in convergence for LA, whereas changes in fern floristic composition were associated with convergence in LDMC. Regarding the local abiotic factors, increases in soil bases and pH were related to functional convergence in LA, and soil rock cover led to a divergence in SLA. For instance, divergence in LA occurred in poor assemblages and under more acid soils, while divergence in SLA occurred in heterogeneous environments. We conclude that multiple drivers affect fern functional patterns at fine scales in the tropical forest.