Abstract:
The impact of human disturbance on colonisation dynamics of vascular epiphytes
is poorly known. We studied abundance, diversity and floristic composition of epiphyte
seedling establishing on isolated and adjacent forest trees in a tropical montane landscape. All
vascular epiphytes were removed from plots on the trunk bases of Piptocoma discolor. Newly
established epiphyte seedlingswere recorded after 2 years, and their survival after another year.
Seedling density, total richness at family and genus level, and the number of families and genera
per plot were significantly reduced on isolated trees relative to forest trees. Seedling assemblages
on trunks of forest trees were dominated by hygrophytic understorey ferns, those on
isolated trees by xerotolerant canopy taxa. Colonisation probability on isolated trees was
significantly higher for plots closer to forest but not for plots with greater canopy or bryophyte
cover. Seedling mortality on isolated trees was significantly higher for mesophytic than for
xerotolerant taxa. Our results show that altered recruitment can explain the long-term impoverishment
of post-juvenile epiphyte assemblages on isolated remnant trees.We attribute these
changes to a combination of dispersal constraints and the harshermicroclimate documented by
measurements of temperature and humidity. Although isolated trees in anthropogenic landscapes
are considered key structures for themaintenance of forest biodiversity inmany aspects,
our results show that their value for the conservation of epiphytes can be limited.We suggest
that abiotic seedling requirementswill increasingly constitute a bottleneck for the persistence of
vascular epiphytes in the face of ongoing habitat alteration and atmospheric warming.
