Diversity of dry forest epiphytes along a gradient of human disturbance in the tropical Andes

Disturbance effects on dry forest epiphytes are poorly known. How are epiphytic assemblages affected by different degrees of human disturbance, and what are the driving forces? An inter-Andean dry forest landscape at 2300 m elevation in northern Ecuador. We sampled epiphytic bryophytes and vascular plants on 100 trees of Acacia macracantha in five habitats: closed-canopy mixed and pure acacia forest (old secondary), forest edge, young semi-closed secondary woodland, and isolated trees in grassland. Total species richness in forest edge habitats and on isolated trees was significantly lower than in closed forest types. Species density of vascular epiphytes (species per tree) did not differ significantly between habitat types. Species density of bryophytes, in contrast, was significantly lower in edge habitat and on isolated trees than in closed forest. Forest edge showed greater impoverishment than semi-closed woodland and similar floristic affinity to isolated trees and to closed forest types. Assemblages were significantly nested; habitat types with major disturbance held only subsets of the closed forest assemblages, indicating a gradual reduction in niche availability. Distance to forest had no effect on species density of epiphytes on isolated trees, but species density was closely correlated with crown closure, a measure of canopy integrity. Microclimatic changes but not dispersal constraints were key determinants of epiphyte assemblages following disturbance. Epiphytic cryptogams are sensitive indicators of microclimate and human disturbance in montane dry forests. The substantial impoverishment of edge habitat underlines the need for fragmentation studies on epiphytes elsewhere in the Tropics.