Eucalyptus gunnii subsp. divaricata (Miena Cider Gum)

Advice to the Minister for the Environment and Heritage from the Threatened Species Scientific Committee (TSSC) on Amendments to the list of Threatened Species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)

1. Scientific name, common name (where appropriate), major taxon group

Eucalyptus gunnii subsp. divaricata B.M. Potts ms. (Miena Cider Gum)

2. National Context

The Miena Cider Gum is endemic to the Tasmanian Central Plateau. It is currently being considered for listing as endangered under Tasmanian legislation. It is not currently listed under the EPBC Act.

3. How judged by TSSC in relation to the EPBC Act criteria

TSSC judges the Miena Cider Gum to be eligible for listing as endangered under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 - Decline in numbers

The Miena Cider Gum is estimated to have a generation length of at least 100 years and to have undergone a substantial reduction in numbers. In early 1999 the decline in numbers over the past 5 to 100 years was calculated to be 30% based on approximately 20 years of field research. Since 1999 researchers have indicated that the number of dead mature trees has increased due particularly to the effect of drought, however, a revised estimate of the rate of decline has not been determined. A substantial reduction in numbers is expected in the future as mature trees continue to die and likely inbreeding effects (reduced seed set and fitness) contribute to reduced recruitment. A range of processes are thought to contribute to limited recruitment and the decline in health and death of mature trees including frequent burning of the vegetation to reduce shrub frequency, grazing from sheep, rabbits and native marsupials, the clearing of trees for road work and raising hydro-electric lake levels, felling of mature trees for seed collection and drought. Further research is required to determine the magnitude, significance and impact of the individual threats. An estimate of the rate of future decline in numbers was calculated in early 1999 to be 30% over the next 5 to 100 years.

Therefore, the species is eligible for listing as vulnerable under this criterion.

Criterion 2 - Geographic distribution

The geographic distribution of the Miena Cider Gum is restricted, the extent of occurrence being 1600km2 and area of occupancy being 40 - 50ha. It is known from five locations, three of which contain approximately 50 mature individuals, another approximately 500 and the largest approximately 1000 mature individuals.

As the population has fragmented and the distance between mature trees within the sub-populations has increased, due to the death of many mature trees, the rate of self-fertilisation is expected to increase and inbreeding effects are likely to be manifest in the population. Inbreeding is expected to result in reduced seed set, and reduced survival and vigour of seedlings. An unquantified decrease in seed production has been reported from the largest sub-population and regeneration over the past two decades is reported to be limited. Seedlings of the Cider Gum (E. gunnii) resulting from self-fertilisation have been observed to show inbreeding depression in the form of reduced vigour and survival. The fitness of juveniles is particularly important to successful recruitment as the seedlings frequently experience severe climatic conditions (frost and drought) in addition to other threats discussed below.

Historic and ongoing declines have been observed in the extent of occurrence, area of occupancy, number of locations and number of mature individuals. A number of threats have been identified as contributing to limited recruitment and declines in the health and death of mature trees including frequent burning of the vegetation to reduce shrub frequency, grazing from sheep, rabbits and native marsupials (particularly the Brushtail Possum Trichosurus vulpecula), the clearing of trees for road work and raising hydro-electric lake levels, felling of mature trees for seed collection and drought. Whilst the Miena Cider Gum is one of the most frost resistant Eucalypts, it is considered to be the most drought sensitive of the Eucalypts with which it occurs. Unfavourable (warmer, drier) climatic conditions are reported to have prevailed over the past decade, the general drought conditions experienced on the Central Plateau have been reported to have been particularly severe during 1999-2000. There may also be a long term climatic trend toward hotter, drier conditions, as have been experienced over the past decade that would adversely impact the surviving populations that are adapted to cold, frosty, wet conditions. Succulent new growth is highly palatable to the Brushtail Possum that is reported to have increased in numbers in the Central Plateau region over the past decade. At the site of the largest sub-population juveniles are often associated with roadside margins where they are vulnerable to destruction during road maintenance or widening. Some threats (burning, stock grazing and seed collection) have been reported not to be operating at the same intensity as previously. Further research is required to determine the magnitude, significance and impact of the individual threats. At this stage no individual threat can be identified as the primary cause of declines, the combination of a number of threats is likely to continue to result in limited recruitment and contribute to declines in the health and death of mature trees.

Therefore, the species is eligible for listing as endangered under this criterion.

Criterion 3 - Population size and decline in numbers or distribution

Whilst the total number of trees and seedlings has been estimated to number in excess of 10,000, less than 2,000 have been estimated to be setting seed. Evidence from field research conducted over the past two decades indicates declines in the order of 30% may be experienced over the next 5 - 100 years, the generation length being at least 100 years. The range of threats that have been attributed to the observed and projected declines have been detailed under criterion 2.

Therefore, the species is eligible for listing as endangered under this criterion.

Criterion 4 - Population size

The total number of trees and seedlings has been estimated to number in excess of 10,000, however, less than 2,000 have been estimated to be setting seed.

Therefore, the species is not eligible for listing under this criterion.

Criterion 5 - Probability of extinction in the wild

There is no quantitative data available against this criterion.

4. Conclusion

The geographic distribution of the Miena Cider Gum is restricted and precarious to the survival of the species. It has an extent of occurrence of 1600km2 and area of occupancy of 40 - 50ha. It is known from five locations. Due to fragmentation of the population, and increased distances between mature trees, inbreeding effects are expected and are likely to be manifest in the population in the form of reduced seed set and fitness of juveniles. In combination with other threats, inbreeding effects contribute to reduced recruitment.

Ongoing declines are expected in the extent of occurrence, area of occupancy, number of locations and number of mature individuals. A range of threats have been identified as contributing to past and future declines in recruitment, health and death of mature trees including frequent burning of the vegetation to reduce shrub frequency, grazing from sheep, rabbits and native marsupials, the clearing of trees for road work and raising hydro-electric lake levels, felling of mature trees for seed collection and drought. Further research is required to determine the magnitude, significance and impact of the individual threats.

Whilst the total number of trees and seedlings has been estimated to be in excess of 10,000, less than 2,000 have been estimated to be setting seed. Evidence from field research conducted over the past two decades indicates declines in the order of 30% may be experienced over the next 5 - 100 years. The species is eligible for listing as endangered under criteria 2 and 3.

5. Recommendation

TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by
including in the list in the endangered category:

Eucalyptus gunnii subsp. divaricata B.M. Potts ms. (Miena Cider Gum)

Conservation advice

The Miena Cider Gum only occurs on the Tasmania Central Plateau (South Tasmania NRM region). It is known from five locations.

Key threats to the Miena Cider Gum include: frequent burning; grazing sheep, rabbits and native marsupials (e.g. brushtail possums); clearing for roadwork; flooding; seed collection; and drought.

The priority recovery and threat abatement actions required for this species are:

  • restrict site access (e.g. fencing) or implement other controls to reduce grazing pressure from sheep and rabbits;
  • prevent direct physical disturbance to the species and its habitat (e.g. clearing, flooding); and
  • prevent illegal seed collection.

This list does not encompass all actions that may be of benefit to this species, but highlights those that are considered to be of the highest priority at the time of listing. Longer term issues that should be considered in broader landscape, regional and or recovery planning include an appropriate fire management strategy.

'Threat Abatement Plan for Competition and Land Degradation by Feral Rabbits' was published in 1999. No Recovery Plan is currently in place for the Miena Cider Gum.

Priority for the development of recovery plan: Low