|Issue Date||Summer 2008|
|Number of Articles Online||1 Articles|
|Download Print Version||Newsletter40.pdf|
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|Title||A Species on the Brink: Saving the Miena Cider Gum|
Eucalyptus gunnii ssp. divaricata (the Miena Cider Gum) is endemic to Tasmania, with its distribution restricted to the edge of frost hollows in open woodland in the Great Lakes region on the Central Plateau. The species, listed as Endangered at both state and national levels, entered into a severe and rapid decline in the late 1990's, resulting in the extinction of at least one of the wild populations, and death of all mature adults in some populations. The dead populations, which can be seen from the Lakes Highway, make a dramatic sight, with the spreading branching pattern typical of the species, completely exposed by a lack of any foliage. Standing beneath the skeletal canopy of these spreading trees is a reminder of just how precarious a species' existence can be. The decline of Eucalyptus gunnii ssp. divaricata is thought to be a result of changing climatic conditions with the taxon unable to cope with the warmer drier conditions being experienced in the Central Highlands. The decline appears to be most severe in disturbed populations, and in populations showing the most extreme characteristics of the species.
Eucalyptus gunnii ssp. divaricata, while one of Tasmania's most frost resistant eucalypts, is very susceptible to drought stress and browsing pressures. The leaves of Eucalyptus gunnii ssp. divaricata are highly palatable (more so than most other eucalypts) and are favoured by possums, stock, and deer as well as a range of insects. Following recovery from drought stress the regrowth is very nutrient rich, making it even more palatable to browsers and this is exacerbated by pressure from insect populations which have increased due to warmer winters. Stock grazing, increased fire frequency and the application of fertilisers in many populations, have also increased the nutrient content of regrowth, further increasing palatability resulting in spiralling declines from which populations do not appear to be able to recover.
Fortunately, seed was collected from the two populations, representing the most morphologically extreme form of Eucalyptus gunnii ssp. divaricata, which have suffered the worst decline. This seed, collected between the late 70's and the early 90's, has now been germinated, and we have 500 seedlings of Eucalyptus gunnii ssp. divaricata almost ready to plant. Some of these seedlings will be planted into the two wild populations from which the seed was collected. There are presently no mature individuals setting seed in either population and no seed is held in the canopy. The only hope for survival of these populations is to encourage growth of repressed seedlings currently present in the understorey, and to establish new seedlings. Seedlings planted into the wild will be caged to prevent browsing pressure and monitored. Caging seedlings has been shown to be effective in the wild, with caged seedlings showing higher survival and growth rates than uncaged seedlings.
In addition to planting seedlings into the wild populations, ex situ conservation plantings will be established on private land at Bothwell, Kellevie and Granton. These plantings will provide insurance against the potential extinction of this species even if decline continues in the wild populations. Once mature, the conservation plantings will provide an invaluable source of seed, so that future attempts can be made to re-establish Eucalyptus gunnii ssp. divaricata in the wild. Additionally, these trees may aid future research into the species, for example by providing foliage for genetic analysis.
If you would like to be involved in establishing the conservation plantings, or in planting and caging seedlings into the wild populations please contact
- Threatened Plant Action Group Coordinator, Catriona Scott on 62336692 or email Catriona.Scott@dpiw.tas.gov.au
Photo: farmer Rae Young and threatened Species botanist Wendy Potts planting Eucalyptus gunnii ssp. divaricata seedlings. Courtesy Simon de Salis