Scientific approaches to Australian temperate terrestrial orchid conservation
Mark C. BrundrettTerrestrial Ecosystems Branch, Policy and Coordination Division, EPA Service Unit, Department of Environment, PO Box K822, Perth, WA 6000, Australia and Faculty of Natural and Agricultural Sciences, School of Plant Biology, The University of Western Australia, Crawley, WA 6009, Australia. Email: brundrm@cyllene.uwa.edu.au
Australian Journal of Botany 55(3) 293-307 https://doi.org/10.1071/BT06131
Submitted: 21 June 2006 Accepted: 23 October 2006 Published: 18 May 2007
Abstract
This review summarises scientific knowledge concerning the mycorrhizal associations, pollination, demographics, genetics and evolution of Australian terrestrial orchids relevant to conservation. The orchid family is highly diverse in Western Australia (WA), with over 400 recognised taxa of which 76 are Declared Rare or Priority Flora. Major threats to rare orchids in WA include habitat loss, salinity, feral animals and drought. These threats require science-based recovery actions resulting from collaborations between universities, government agencies and community groups.
Fungal identification by DNA-based methods in combination with compatibility testing by germination assays has revealed a complex picture of orchid–fungus diversity and specificity. The majority of rare and common WA orchids studied have highly specific mycorrhizal associations with fungi in the Rhizoctonia alliance, but some associate with a wider diversity of fungi. These fungi may be a key factor influencing the distribution of orchids and their presence can be tested by orchid seed bait bioassays. These bioassays show that mycorrhizal fungi are concentrated in coarse organic matter that may be depleted in some habitats (e.g. by frequent fire). Mycorrhizal fungi also allow efficient propagation of terrestrial orchids for reintroduction into natural habitats and for bioassays to test habitat quality.
Four categories of WA orchids are defined by the following pollination strategies: (i) nectar-producing flowers with diverse pollinators, (ii) non-rewarding flowers that mimic other plants, (iii) winter-flowering orchids that attract fungus-feeding insects and (iv) sexually deceptive orchids with relatively specific pollinators. An exceptionally high proportion of WA orchids have specific insect pollinators. Bioassays testing orchid-pollinator specificity can define habitats and separate closely related species. Other research has revealed the chemical basis for insect attraction to orchids and the ecological consequences of deceptive pollination. Genetic studies have revealed that the structure of orchid populations is influenced by pollination, seed dispersal, reproductive isolation and hybridisation. Long-term demographic studies determine the viability of orchid populations, estimate rates of transition between seedling, flowering, non-flowering and dormant states and reveal factors, such as grazing and competition, that result in declining populations.
It is difficult to define potential new habitats for rare orchids because of their specific relationships with fungi and insects. An understanding of all three dimensions of orchid habitat requirements can be provided by bioassays with seed baits for fungi, flowers for insects and transplanted seedlings for orchid demography. The majority of both rare and common WA orchids have highly specific associations with pollinating insects and mycorrhizal fungi, suggesting that evolution has favoured increasing specificity in these relationships in the ancient landscapes of WA.
Acknowledgements
Andrew Brown and Steve Hopper provided valuable comments and information. I also particularly thank the following people: Andrew Batty and Professor Sivasithamparam at the University of Western Australia. I gratefully acknowledge the many colleagues, students and volunteers who have collaborated with me in orchid research: Kingsley Dixon, Eric Bunn, Keran Keys, Bob Dixon and Siegy Krauss at the Botanic Gardens and Parks Authority; postgraduate students: Nura Abdul Karim, Jeremy Bougoure, Margaret Collins, Sofi Mursidawati, Belinda Newman; honours students: Yumi Bonnardeaux, Ailsa Scade, Erin Wright, Danika Collins; and Andrew Brown, Jillian Stack, Beth Laudon and others at the Department of Conservation and Land Management. Volunteers of the West Australian Native Orchid Study and Conservation Group, Friends of Kings Park and Kings Park Master Gardeners. Funding was provided by ARC, The Botanic Gardens and Parks Authority, ALCOA World Alumina Inc., The National Heritage Trust and Lotterywest.
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