Surface roots as a new ecological zone for occurrence of vascular epiphytes: a case study on Pseudobombax trees on inselbergs

This study aimed to quantify the importance of surface roots as phorophyte ecological zones for vascular epiphytes in the lithophyte tree Pseudobombax. The study was conducted on phorophytes, trees that support epiphytes, in three neotropical granitoid rocky outcrops (inselbergs). We investigated how community composition and abundance of vascular epiphytes differed among different ecological zones and examined habitat associations on Pseudobombax. Based on a census of 90 trees, we found 5896 individual vascular epiphytes attributed to 137 species. Bromeliads and orchids were dominant. Our results show that surface roots represented an important ecological zone as 53% of the diversity and 20% of the total vascular epiphyte abundance were found within this zone. Abundance patterns differed among the zones and the lithophyte species Sinningia speciosa, Selaginella convoluta and Alcantarea patriae were associated with the surface roots. Our results reinforce the importance of the lithophyte tree Pseudobombax for the maintenance of epiphytic diversity in the tropical inselbergs of southeast Brazil, mainly due to its size and architecture. The presence of large surface roots considerably increases the habitat for different epiphytic groups, including species typical of inselbergs. Roots are thus an important ecological zone for epiphytic communities on inselbergs.