Long-term dynamics of an epiphyte community – pattern and process

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Tropical rainforests are characterised by an extreme diversity of both species and life forms. The dynamics of these communities and the underlying mechanisms have been the subject of much research in the last decades, with a heavy bias towards trees, globally coordinated by research networks like the Center of Tropical Forest Studies. Other life forms (lianas, epiphytes, hemiepiphytes, understorey shrubs and herbs) have received much less attention with the exception of lianas that have moved into focus of researchers in the last years. In comparison, our knowledge of epiphytes is still very limited, in spite of the fact that this life form frequently trumps soil-rooted vegetation in terms of local species diversity and clearly differs from trees, since crucial structuring factors of tree communities like herbivore and pathogen pressure seem to play no or a negligible role in epiphytes. Observational evidence and the results of first modelling studies suggest that the dynamics of epiphyte communities differ fundamentally in pattern and process from soil-rooted co-occurring plants. Documenting these patterns and reaching an understanding of the underlying processes are the objectives of this study, which is only possible because of two decades of work at the site and the unique research infrastructure of the Smithsonian Tropical Research Institute in Panama. Globally, there is no other study in a tropical forest setting that even remotely covers a similar time span. The project has descriptive, experimental and modelling elements. A census of 0.9 ha of all epiphytes in an undisturbed lowland forest will allow us to follow the community dynamics over more than 20 years. A transplant experiment will investigate the interactive role of host tree species and relative vertical position in the forest for the success of early epiphyte establishment (= initial attachment, germination, growth and survival), and a modelling approach will develop the correct null model to detect host specificity in epiphyte communities with their typical, highly clumped species distributions. The transplant experiment will also be accompanied by a comprehensive analysis of functional traits. This combination of different approaches should lead to substantial progress in our understanding of the composition and long-term dynamics of vascular epiphyte communities.