An endangered tree fern increases beta-diversity at a fine scale in the Atlantic Forest Ecosystem

Some species make substantial contribution to habitat heterogeneity, supporting species coexistence. Dicksonia sellowiana Hook., an endangered tree fern, is a known phorophyte for epiphytes, has the potential to be such a taxon. We tested the hypothesis that D. sellowiana increases plant diversity in Brazilian Restinga forest, a biodiversity hotspot, by augmenting the habitat heterogeneity at a fine scale. To do this we quantified α-diversity and β-diversity in three habitat types: on the tree fern trunks, immediately beneath the trunks and away from the trunks. In total, 40 ferns were sampled. Overall we recorded 2602 individuals belonging to 61 phanerophyte species in 30 families. The number of individuals sampled varied among habitats but rarefaction showed that richness did not differ. In contrast, species composition varied markedly amongst habitats. Both statistical approaches detected high levels of β-diversity, particularly between the species found in the vicinity of the fern, and those in the samples away from the trunks. Indicator species analysis was used to identify the species characteristic of the different habitats. About 30% of the species were exclusively found in “away plots”, 17% were exclusively “below plots” and 15% were found only on the trunks, 13% were found on the trunks and below them, 12% on “bellow” and “away plots”, 10% of species occurred in all areas and 3% were found on trunks and “away plots”. Our results lead us to conclude that the endangered fern D. sellowiana plays an important role in promoting habitat heterogeneity within the Restinga forest. As this iconic species is threatened, its overexploitation may lead to impoverishment of plant communities. Conservation effort towards both the area and this species are crucial to maintaining Restinga plant diversity.