Data from: Deciphering terrestrial fern community assembly — what does the combination of functional and phylogenetic trends reveal about their environmental preferences?

Questions: Our study focuses on the following questions: 1) Do the climatic and edaphic conditions of the southern Brazil Atlantic Forest impact terrestrial ferns' functional diversity, and if so, is it influenced by phylogenetic structure? 2) Which morphological functional traits are most relevant for terrestrial ferns in response to climatic and edaphic changes, and do these relationships originate from the past or just recent days? And 3) If there are trait-environment relationships, what adaptive mechanisms can be inferred from them?

Study site: Subtropical Atlantic Forest, comprehending Rio Grande do Sul, Santa Catarina, and Paraná, Brazil.

Method: We analyzed nine morphological traits related to resistance, competitive advantage, and reproductive success. All traits were analyzed with and without phylogenetic correction, to compute multi-trait functional diversity using the standardized effect size of mean functional distance and functional composition via the community-weighted mean. Both metrics were weighted by the absolute frequency of species within sites. Subsequently, we identified the most influential climatic or edaphic drivers based on linear models. To assess the significance of trait-environment relationships, we employed permutational null models.

Results: The functional diversity of terrestrial ferns correlates with rainfall, but when accounting for phylogenetic structure, this relationship shifts and an association with temperature arises. Similarly, competitive and reproductive traits were associated with nitrogen content and rainfall, respectively. However, most of the morphological traits vary independently of edaphic and climatic factors, regardless of the considering or not phylogenetic structure. Few traits, specifically related to resistance and competition, were dispersed across the phylogeny and were not linked with any factor evaluated, leaving the question of their true determinants unanswered.

Conclusions: Combining functional and phylogenetic information on terrestrial ferns indicates that species morphology response highly depends on the scale observed. Our analyses demonstrate that climatic factors are the primary drivers of trait diversity in terrestrial ferns within the Subtropical Atlantic Forest, influencing most evaluated traits. Soil characteristics, while not the main determinant for terrestrial species strategies, significantly influence competitive traits and select specific clades. These findings may help predict the distribution of terrestrial ferns amidst the increasing trend of land use and cover changes in the Atlantic Forest domain.