Microclimatic patterns correlate with the distribution of epiphyllous bryophytes in a tropical lowland rain forest in Costa Rica

Quantitative analyses of the factors driving the distribution of bryophytes in the phyllosphere of tropical rain forests are rare. In this study we sampled epiphyllous bryophytes on two leaves of each of 57 individuals belonging to four phorophyte species (Asplundia pittieri, Carludovica drudei, Costus laevis and Dieffenbachia concinna) at three adjacent, but microclimatically varied sites in the Esquinas forest, Costa Rica. Microclimatic parameters and phorophyte identities were correlated to differences in cover, diversity and species composition of bryophyte assemblages by means of Kruskal-Wallis tests, non-metric multidimensional scaling and indicator species analysis. High relative humidity and in particular daily fluctuations in relative humidity proved to be the most important factors for epiphyll distribution suggesting severe constraints of epiphyll colonisation by pronounced humidity fluctuations. Differences in air temperature and light availability as well as phorophyte identity were only weakly correlated with bryophyte cover and diversity. However, species composition of epiphyllous assemblages was related to all microclimatic variables as well as to phorophyte identity. The strong response of epiphyllous bryophytes to even subtle microclimatic variations suggests that undisturbed forest canopies and their control on microclimate may be essential for the development of epiphyll communities.