Meta-community structure of vascular epiphytes in a temperate rainforest

I quantified the occurrence of all vascular plant species inhabiting 43 Thuja plicata Donn ex D. Don trees in a temperate rainforest in British Columbia, Canada, to test whether (i) epiphyte species richness increased with tree diameter, and (ii) epiphyte distributions showed evidence for nestedness, checkerboard distributions, or compartmentalization. Nine vascular plant species were observed growing epiphytically. One species ( Polypodium glycyrrhiza Eat.) is an obligate epiphyte, while the remainder typically occurred on the forest floor. Smaller host trees (<0.5 m in diameter) lacked vascular epiphytes, and species richness increased with host diameter. No evidence for nested or checkerboarded distributions was observed. However, epiphyte distributions were compartmentalized, owing to five similar shrub species that tended to co-occur jointly, generating sharp turnover in species composition between host trees with and without shrubs. The lack of co-occurrence patterns indicative of interspecific interactions among epiphytes indicates that the epiphyte meta-community is structured stochastically from species that normally grow terrestrially.