Spatial ecology and host diversity of three arboreal plants from Lord Howe Island

Abstract

In canopy ecology, it has long been understood that different guilds of arboreal plants have different spatial distributions and degrees of host specificity. Here, we present a case study looking at how within-crown spatial niche and host specificity vary between three very different morphologies of arboreal plant on Lord Howe Island, interpreting these in terms of different water acquisition strategies. We quantify within-crown spatial niche and created a null model to test host specificity in three species with very different water acquisition strategies (a mistletoe, an orchid and a detritus-collecting fern). The mistletoe had greater host specificity than the two epiphyte species, and was restricted to thinner branches. The fern occurred further from the outer crown than the other species including on the trunks of host trees, and was the only species to show no indication of host specificity. Differences in distribution are consistent with differences in water acquisition strategy, providing an initial link between traits and spatial distribution, a potentially fruitful avenue of future research.

The invasion of non-native epiphyte Platycerium bifurcatum in Auckland’s urban forest canopy

“…Urban ecosystems are complex, have an array of surfaces that are not available in natural ecosystems, and may not be indicative of establishment potential in native forests. However, P. bifurcatum appears not to be constrained by establishment surface: this fern will establish on a range of surfaces from exposed scoria walls through to the shade of the sub-canopy, from broad urban street tree branches to narrow, vertical stems and has been recorded on Cordyline australis, Eriobotrya japonica, and Metrosideros excelsa elsewhere in New Zealand (Heenan et al 2004;Dawes et al 2020;Brownsey et al 2021;Wu 2023). In Indonesia, P. bifurcatum has been recorded growing naturally on 14 different species (of 12 families) at Purwodadi Botanic Garden (Solikin 2014).…”

“…Astelia spp., ferns, orchids) creating novel habitats in the canopy for native and non-native epiphytes, invertebrates, and invasive mammals (Wilson 1996;Pemberton 2003;Innes et al 2018;Allen et al 2021). Further, studies from Lord Howe island in the native range of P. bifurcatum show that this taxa can establish on stems as small as 8 cm in diameter in the understory suggesting that New Zealand's rich small tree flora and palm understorey could provide ready suitable establishment surfaces in native forests (McGlone et al 2010;Dawes et al 2020).…”

“…Dense colonies are effective in overcoming the various stressors of the epiphytic habit and individual ramets of P. bifurcatum can express different frond morphologies (on the basis of vertical position in the colony) thereby performing different functions for the colony (Burns 2021). Colonies can establish on vertical surfaces in the understory and mid-canopy and are not constrained by phorophyte taxa as an establishment surface (Solikin 2014;Dawes et al 2020). As an attractive, ornamental taxa, this fern has been introduced to gardens around the world and is an invasive weed in Florida, South Africa, and Hawai'I (Wilson 1996;Pemberton 2003;Jones et al 2020).…”