Epiphyte community development throughout tree ontogeny: an island ontogeny framework

Aim Epiphytes are a conspicuous feature of numerous forests, yet they are poorly understood compared with terrestrial plants. Theoretical frameworks have helped bridge this gap; however, important questions relating to epiphyte community development have yet to be answered. For example, at what point in tree ontogeny do epiphytes first establish? Do epiphyte communities develop uniformly, or is there variation among host trees? Methods In this study, we build upon Darwin's geological theory of island ontogeny to explore changes in epiphyte species richness throughout the life span of their respective host trees. Based on the general features of island ontogeny, we predict that there are three stages of epiphyte community development: (i) an initial stage where host trees are devoid of epiphytes because they lack sufficient architectural and physiological characteristics suitable for epiphyte establishment, (ii) a second stage where trees acquire epiphytes as adults and continue to do so into maturity, and (iii) a final stage where epiphyte communities progress through a period of species decline following host tree mortality. To test our model predictions, we censused epiphyte communities on 371 host trees from six New Zealand tree species. We first assessed the relationship between epiphyte species richness and host tree diameter. We then tested whether relationships between epiphyte species richness and host tree diameter varied between host species. Results and conclusion Results were consistent with model predictions. Our investigation found variation in the ontogenetic stage at which host trees become favourable for epiphyte establishment. Moreover, the rate at which epiphyte species richness increased with host tree diameter varied among host species. Our findings indicate that an island ontogeny framework is useful for guiding investigations on epiphyte community development.