Patterns of morphological and physiological traits of epiphytes within trees and between elevations in subtropical Australian rainforest

Abstract

Taxonomically dissimilar epiphyte species can have comparable morphological and physiological traits in similar environmental conditions. However, the degree of trait similarity has not been examined in a comparison of bryophytic and vascular epiphytes across elevational and tree gradients. We assess whether epiphyte species that occupy comparable realised niche spaces within host tree and landscape scale gradients have similarities in taxonomy, morphology or physiology. Vascular and moss epiphytes were surveyed within four height zones at five elevations (300-1100 m asl) in the sub-tropical rainforest of Australia. Epiphyte species distributions were agglomeratively classified using Ward’s method. Chi square tests were used to test for differences in the incidences of taxonomic groups, life forms, leaf thickness, photosynthetic pathways and other drought resistant morphologies between these distributional groups. These traits were also tested for correlation with light and humidity. Six groups were identified based on distribution. Vascular epiphytes with CAM, thickened leaves and other drought-mitigating morphologies were common in the groups that occupied the most xeric situations. All drought resistant traits were associated with high light and low humidity. Vascular species with few to no drought-mitigating characteristics were common in groups that occupied moister situations. Moss morphology was less congruent with environmental conditions than vascular plant morphology, suggesting that moss life forms are responding to a different scale of environmental variation.