Tree ferns are important elements of tropical forests, mainly because they are common and provide microhabitats for epiphytic plants. Due to their ecological importance, the aim of this study was to evaluate population structure, distribution, and influence of environmental variables on tree ferns in the state of Santa Catarina, southern Brazil. All tree ferns with a diameter at breast height ≥ 10 cm on 418 sampling units (SUs) systematically distributed throughout the study area were measured (total sampled area of 153.4 ha). Population structure was evaluated through classical phytosociological parameters and the relationships among dominance and environmental variables were evaluated through multiple linear regression models. Dicksonia sellowiana presented the greatest importance value among all species (IV = 13.19 %), followed by Alsophila setosa (IV = 4.37 %) and Cyathea phalerata (IV = 2.71 %). Altitude and mean rainfall of the driest quarter were significantly related to the dominance of D. sellowiana in most of the SUs. The mean temperature of the driest quarter and aspect were significantly related to the dominance of Cyatheaceae. Our study demonstrates that tree ferns are important elements of forest communities in the state of Santa Catarina.

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Tree ferns are common elements in subtropical Atlantic Forest, sometimes reaching more than half of dominance at forest sites. Climate change could impact the distribution and diversity of tree ferns, hence impacting the ecological processes provided by them. We investigate the impacts of future climate changes in the potential distribution of tree fern species, as well as in the α- and β-diversity. Our first hypothesis (H1) is that warmer climate in the future will increase the distribution of Cyatheaceae species and decrease the distribution of Dicksoniaceae species. Due to a larger number of Cyatheaceae than Dicksoniaceae, the richness will tend to increase. However, the increase in richness might lead to homogenization, consequently decreasing β-diversity (H2). To test these hypotheses, we used distribution models to predict the potential species distribution in the present and future. Then, we calculated the changes in potential distribution areas, α-, and β-diversity components between scenarios. Finally, we assessed the impact of these changes within Protected Areas. We found that Dicksoniaceae distribution tends to shrink in the future, while half of Cyatheaceae tend to lose distribution. Species richness tends to decrease in the future, as well as β-diversity. At least 43% of the sites tend to have their species richness reduced, while only 26% of sites tend to gain species. Our results suggest that species associated with cold environments will lose suitable areas and are more threatened. Richness tends to decrease mainly in sites with high precipitation seasonality. Furthermore, the tree ferns assemblage tends to homogenize.