Grass-tree (Xanthorrhoea semiplana, Liliaceae) facilitation of the endangered pink-lipped spider orchid (Caladenia syn. Arachnorchis behrii, Orchidaceae) varies in South Australia

Abstract

We examined the role of the grass-tree Xanthorrhoea semiplana F.Muell. canopy in the survival of the nationally endangered orchid Caladenia (syn. Arachnorchis) behrii Schltdl. at three sites in the northern Adelaide region. We compared grazing and pollination of the flowering orchids within and away from the grass-tree canopy. Grass-trees generally provided significant protection from grazing, but orchids protected by grass-trees experienced reduced pollination for 2 out of 5 years. The net effect of these interactions, as measured by seed set, varied across years. When grazing pressure is high, orchids may benefit from grass-tree protection (facilitation), but under low grazing pressure, it is more probable that orchids set seeds away from grass-trees than under their canopy. Grazing pressure probably does not decrease in view of habitat fragmentation the importance of fragments as wildlife refuges. Therefore, factors affecting the survival of grass-trees, such as Phytophthora cinnamomi, may also affect orchid survival. Kangaroos which are often assumed to be responsible for most grazing in the Adelaide Hills are not the only predators of orchids, and a culling program has so far not resulted in a decrease of grazing pressure for the orchids. Translocation and fencing programs should examine the role of facilitative plants and grazers before spending precious conservation resources.

A Comprehensive Study of Orchid Seed Production Relative to Pollination Traits, Plant Density and Climate in an Urban Reserve in Western Australia

“…Sudden decline of local populations can occur in habitats which are in good condition. Grazing animals such as kangaroos observed in other studies [56,57] were rare at the study site. However, suspected symptoms of virus infection were sometimes observed before plants disappeared.…”

Recognising fuzzy vegetation pattern: the spatial prediction of floristically defined fuzzy communities using species distribution modelling methods

“…Over half (61 of 107) of the species analysed had a significant ( P < 0.05) indicator value for a particular community, indicating that the classification encompassed a large proportion of variation in the vegetation. A number of the species with high indicator values are of particular interest to management, including species of Xanthorrhoea , which provide key habitat to plants and animals (Petit & Dickson ; Frazer & Petit ; Swinburn et al. ) and Leptospermum continentale and Pteridium esculentum , which are important fire fuel elements (McCarthy et al.…”

Fire as a tool to manage pollination services

“…Although this tentative model is yet to be tested, it is interesting to consider the underlying mechanisms. Petit and Dickson (2005) found that the pollination rate of a sexually-deceptive orchid decreased as the amount of vegetation within close proximity increased, which they attributed to increased difficulty for pollinators in locating orchid flowers. In the heathy woodland system studied in the present paper, vegetation structure is low in the early post-fire environment, gradually increasing to a maximum in mid successional stages, and then declining again late in succession (Cheal 2010;Brown 2013).…”