Dispersal and establishment of vascular epiphytes in human-modified landscapes

The ongoing destruction of old-growth forests puts tropical forest species under great pressure because of the resulting habitat loss. A pre-requisite for the maintenance of a viable metacommunity in a fragmented landscape is the connectivity between habitable patches. We experimentally studied four vital steps of epiphyte dispersal in different habitat types in western Panama. (i) Seed falling velocity (Vterm) is known to correlate with long-distance dispersal via convective updraft. All measured Vterm of bromeliad and orchid seeds fell into a range of velocities with a high chance of long-distance dispersal. (ii) We quantified attachment success of bromeliad seeds as a function of bark rugosity with >30 common tree species in the region. Even fine bark structure allowed effective attachment. (iii and iv) Successful establishment is achieved when a seed germinates and a plantlet grows and survives. Germination success and early establishment of four bromeliad species did not differ between isolated trees, teak plantations or secondary forest patches. Microclimatic differences between habitat types were marginal and neither germination nor establishment correlated significantly with annual precipitation. The findings suggest a large capacity for dispersal and successful early establishment for these anemochorous species. A potentially regenerating forest may receive considerable input from sources such as pasture trees and in this way gain structural complexity, which also greatly enhances its value for other forest organisms.