Epiphytes are integral to tropical forests yet little is understood about how succession proceeds in these communities. As trees increase in size they create microhabitats for late-colonizing species while maintaining microhabitats for early colonizing species in the small branches. Epiphyte succession may follow different models depending on the scale. At the scale of the entire tree, epiphytes may follow a species accumulation model where species are continuously added to the tree as trees increase in size. At the scale of one zone on a branch (e.g., inner crown), they may follow the replacement model of succession seen in terrestrial ecosystems. Assuming tree size as an indicator of age, I surveyed epiphytes in 61 Virola koschnyi trees of varying size (2.5 cm – 103.3 cm dbh) in lowland wet tropical forest in Costa Rica. I documented the spatial distribution of epiphytes within tree crowns. The replacement model would predict an increase in species richness and a predictable change in epiphyte communities in a particular crown zone as trees increased in size. The species accumulation model would predict in increase in species richness and abundance with tree size as well as a nested community structure of small trees nested within large trees.
Results/Conclusions
Epiphyte richness and abundance increased with tree size, and epiphyte community composition followed the predictions of the species accumulation model at the scale of the entire tree crown; epiphyte communities in small trees were nested subsets of those in large trees and epiphyte communities became more similar to the largest trees over time. Furthermore, epiphyte species in small trees were replaced by mid- and late-successional species in the oldest parts of the tree crown, which followed the predictions of the replacement model of succession. However, epiphyte species in small trees dispersed towards the younger branches as trees increased in size resulting in epiphyte communities in small trees being more similar to the outer crown of large trees than the inner crown of large trees. Thus, epiphyte succession followed a replacement model in particular zones within tree crowns but a species accumulation model at the scale of the entire tree crown.