The distribution of vascular epiphytes over gradients of light and humidity in north‐east Australian rainforest

Abstract

Microclimatic conditions have a strong influence on the distribution of vascular epiphytes, among which orchids often occur in sunnier and more drought-prone situations than ferns. However, very few studies have looked at the distribution of ferns and orchids in Australian tropical rainforests. By using transmitted light measurements at the locations of individual epiphytes and vapour pressure deficit from the canopy and base of host trees, we were able to determine the patterns of light and humidity in the rainforest environment, and the responses of ferns and orchids to variation in the physical environments. We surveyed five sites, ranging from 800 to 1180 m in elevation in the lower montane rainforests of north-east Australia. Data loggers recorded the vapour pressure deficit (VPD) at the forest floor and canopy of each site. Light was correlated with height within the host tree and VPD differed significantly over position in the host tree and elevation. There was a strong partitioning of taxonomic groups over the light and VPD gradients. Orchids occurred in environments that had higher mean light levels and mean daily maximum VPD (27% and 0.43 kPa, respectively) than ferns (21% and 0.28 kPa). There was also strong microclimatic partitioning of species within taxonomic groups, suggesting that microclimatic factors play an important role in the realized niche spaces of epiphytes within the tropical Australian rainforest. Thus, the tested ecological generalizations made on tropical rainforest epiphytes apply in Australia.

The contributions of lightning to biomass turnover, gap formation and plant mortality in a tropical forest

“…Our field observations suggest that the delayed mortality of these epiphytes resulted from desiccation or tree fragmentation, rather than the direct effects of lightning. Although surviving epiphytes on dead trees probably experience premature deaths, desiccation‐resistant epiphytes on surviving trees could benefit from the increase in light availability over the short term (Sanger and Kirkpatrick 2017). Therefore, lightning probably influences epiphyte community composition by creating habitat heterogeneity.…”

A review of Australian tree fern ecology in forest communities

“…The wet tropics of Australia is an area with the greatest richness of epiphytic species in Australia (Sanger & Kirkpatrick 2015), yet there are few studies on epiphytes on tree ferns in Australian tropical forests (Wallace 1981; Cummings et al . 2006; Frieberg & Turton 2007; Sanger & Kirkpatrick 2015; Sanger & Kirkpatrick 2017a,b,c). Of these few studies, only Wallace (1981) mentions tree ferns with epiphytes and in one situation – Cyathea hosting the epiphyte Fieldia australis .…”

Leaf economics in a three‐dimensional environment: Testing leaf trait responses in vascular epiphytes to land use, climate and tree zone

“…Climate, land use and vertical distribution within trees all affect epiphyte species composition, frequently in parallel and interacting ways (McCune, 1993; Sanger & Kirkpatrick, 2017). Major taxonomic groups show clear partitioning in response to abiotic conditions (Richards et al., 2020; Zotz, 2007).…”