Reduced growth and survival of vascular epiphytes on isolated remnant trees in a recent tropical montane forest clear-cut

Forest fragmentation can negatively affect tropical epiphyte diversity, but the processes leading to such impoverishment are insufficiently understood. Due to a lack of experimental studies, the relative influence of dispersal constraints vs. growth conditions remains particularly controversial. This paper addresses the fate of late juvenile and adult vascular epiphytes in response to severe forest disturbance in montane southern Ecuador. Plant growth and survival on trunks and lower branches of isolated remnant trees was studied for the first three years following clear-cutting. Overall epiphyte mortality was substantially increased on remnant trees (72% over 3 years) relative to undisturbed forest (11%). Mortality on remnant trees was higher during the first year (52%) than during the second (20%) and third year (26%). Pteridophytes and dicots suffered higher losses than monocots. Plants surviving on remnant trees generally showed a marked negative growth regarding maximum leaf length, whereas the annual increment in leaf number varied more strongly among taxa (families). The present study provides the first field-experimental evidence for the adverse effects of forest disturbance on the performance of later, well-established life stages of vascular epiphytes. The results suggest that growth conditions may often be a more important predictor of epiphyte diversity in disturbed habitats than dispersal constraints. Similar plant responses can be expected to occur along forest edges. Therefore, the retention of scattered green trees, narrow strips or small fragments of forest are unlikely to be sufficient management tools for the conservation of epiphyte diversity in tropical landscapes. Waldfragmentierung kann tropische Epiphytendiversität beeinträchtigen, doch die zugrundeliegenden Prozesse sind unklar. Nicht zuletzt durch das Fehlen experimenteller Studien bleibt insbesondere der Einfluss von Ausbreitungslimitierungen gegenüber Wachstumsbedingungen kontrovers. Die vorliegende Arbeit untersucht die Folgen einer Waldrodung für spätjuvenile und adulte Wuchsstadien vaskulärer Epiphyten in den Anden Südecuadors. Hierzu wurde das Schicksal individueller Pflanzen auf Stämmen und niedrigen Ästen isolierter Reliktbäume über die ersten drei Jahre nach der Waldrodung verfolgt. Epiphyten auf Reliktbäumen zeigten deutlich höhere Sterblichkeitsraten (im Mittel 72% über drei Jahre) als in ungestörtem Wald (11%). Die Sterblichkeit auf Reliktbäumen war im ersten Jahr höhe