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Desire for fire: how is it that the devastation of a wildfire can also trigger the flowering of a beguilingly beautiful orchid?

WHEN WE THINK OF FIRE, we often picture scenes of devastation; burnt-out homes and blackened, bare landscapes. But fire also brings life to many species and many plants have adapted to use periodic fires as a reproductive tool. Take, for example, the magnificent mountain ash (Eucalyptus regnans) in Victoria that regenerates only from seed. While fire will kill a mature mountain ash, it will also provide the perfect conditions for its seeds to germinate.

When land is stripped of its original vegetation by fire, flood or glaciation, an area of bare ground does not remain devoid of flora and fauna. The area is rapidly colonised by a variety of species that subsequently modify the area. These changes in the environment may, in turn, allow additional species to become established. So fire can also increase the number of a particular species present in a community.

Changes in fire frequency can have a negative impact on the recurrence of species. Herbs requiring light and space may disappear if grasslands are allowed to flourish without regular fire. Wilsons Promontory in Victoria and Tasmania's Friendly Beaches have seen plant communities change from floristically diverse heathland to dense tea-tree scrubland because of reduced fire frequencies.

Flowers from Flames

The existence of some orchid species can be greatly influenced by the presence and frequency of fire. Many Australian species use fire and other disturbances as stimulation tools for flowering, and there are a few orchids that can only be found flowering in an area that has been recently burnt.

The lizard orchid (Burnettia cuneata) is a leafless terrestrial orchid that is rarely seen above ground. Found in south-eastern Australian swamp and heathlands and damp buttongrass moorlands, the orchid only flowers for one or two days after hot summer fires.

The orchid survives in the intervening period by teaming up with a mycorrhizal fungus. The fungus attaches itself to the root system of the orchid, penetrating it with fine, hair-like growths called hyphae. The hyphae then grow out into the soil, acting like an extension of the root system and increasing the plant's ability to extract nutrients from the soil. In return, the orchid provides the fungus with energy to survive. The lizard orchid reproduces solely from seed and the pollinator of the species is unknown.

Found in New South Wales, Victoria, South Australia, Tasmania and King and Cape Barren Islands, the tiny caladenia (Caladenia pusilla) is so named for its small flowers, often just eight millimetres across. That's as small as your little fingernail! Existing mainly in heathlands and occasionally in open forests, flowering of the tiny caladenia is promoted by fire. Flowering occurs because the orchid takes advantage of the extra light and nutrients becoming available after other plants have died. The species is thought to be self-pollinating throughout its Tasmanian range because some flowers do not fully open.

Found only in Tasmania, the rainbow sun orchid (Thelymitra polychroma) was first identified in 1997. The species was discovered in burnt heathland that was still in the early stages of regrowth. It is thought that flowering is strongly fire-dependent, as the species has not been found in nearby unburnt habitats that were otherwise the same. Flowering occurs on relatively cool windy days in late October and November.

Kirsten Saunders is ACF's Campaign Administration Assistant.
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Author:Saunders, Kirsten
Publication:Habitat Australia
Geographic Code:8AUST
Date:Apr 1, 2003
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