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

1. Scientific name (common name) Hoya australis subsp. oramicola (a vine)

2. Description Hoya australis subsp. oramicola is an evergreen, perennial vine with succulent leaves that grow to approximately 10cm long. Its flowers are cream coloured and fleshy, with flowering recorded during March and July. Fruiting occurs three to four months after flowering.

3. National Context Hoya australis subsp. oramicola is endemic to the Northern Territory. The subspecies is restricted to coastal monsoon vine thicket communities on Bathurst and Melville Islands, where it is known from four localities (Kerrigan et al 2004). The subspecies is currently listed as vulnerable under the Northern Territory Territory Parks and Wildlife Conservation Act 2000.

4. How judged by the Committee in relation to the EPBC Act criteria. The Committee judges the subspecies to be eligible for listing as vulnerable under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 – It has undergone, is suspected to have undergone or is likely to undergo in the immediate future a very severe, severe or substantial reduction in numbers. Hoya australis subsp. oramicola is endemic to the Northern Territory. The subspecies is restricted to coastal monsoon vine thicket communities on Bathurst and Melville Islands, where it is known from four localities (Kerrigan et al 2004). Very little data on abundance is available for this subspecies. Russell-Smith (1992) records this subspecies as common at Lubra Point on Bathurst Island and uncommon at Condor Point on Melville Island. Russell-Smith (1992) has characterised adult population sizes of common rainforest species as large if greater than 50 individuals were present. Based on these figures, the population size of this subspecies has been estimated at 350-700 mature individuals, however this estimate is highly speculative and surveys to quantify population size are crucial (Kerrigan et al 2004). Very little is known about the threatening processes impacting this subspecies. There is evidence in the literature however, which indicates that the subspecies habitat, monsoon forests, are vulnerable to disturbance from cyclones, cattle, buffalo, pigs, and dry-season wildfires (Panton 1993 and Russell-Smith et al 1992). Due to a lack of historical survey information, there are no quantitative data available to indicate past trends in the population size of the species, nor any evidence of threats currently impacting on the species which could lead to a decline in numbers in the immediate future. Therefore, there are no quantitative data available to assess the species against this criterion.

Criterion 2 –Its geographic distribution is precarious for the survival of the species and is very restricted, restricted or limited. Hoya australis subsp. oramicola is endemic to the Northern Territory. The subspecies is found only on Bathurst and Melville Islands, where it is known from four localities (Kerrigan et al 2004). The extent of occurrence of Hoya australis subsp. oramicola is estimated to be 4800 km2 and the subspecies area of occupancy is estimated to be 24 km2. Survey effort has been adequate to support the estimate of extent of occurrence, based on extensive surveys on the Tiwi Islands and rainforest habitats across the Top End (Fensham and Woinarski 1992, Russell- Smith 1991 and Woinarski et al 2000). Nevertheless, there is no quantitative data available to assess past declines in the subspecies extent of occurrence or area of occupancy. Very little is known about the threatening processes impacting this subspecies. There is evidence in the literature however, which indicates that the subspecies habitat, monsoon forests, are vulnerable to disturbance from cyclones, cattle, buffalo, pigs, and dry-season wildfires (Panton 1993 and Russell-Smith et al 1992). The coastal vine thicket communities, in which the subspecies occur, are unlikely to be directly affected by proposed forestry activities on the Tiwi Islands (Woinarski et al 2000). Nevertheless, large scale clearing of adjacent woodlands may impact upon local hydrology and provide opportunities for invasion by weedy species, particularly if adequate buffer zones are not established and maintained (Kerrigan et al 2004). In conclusion, although the geographic distribution of Hoya australis subsp. oramicola is restricted, it is not precarious to its survival. Therefore, the species is not eligible for listing under this criterion.

Criterion 3 – The estimated total number of mature individuals is limited to a particular degree and: (a) evidence suggests that the number will continue to decline at a particular rate; or (b) the number is likely to continue to decline and its geographic distribution is precarious for its survival. The population size of Hoya australis subsp. oramicola is estimated at 350-700 mature individuals, however this estimate is highly speculative (Kerrigan et al 2004). Due to a lack of historical survey information, there are no quantitative data available to indicate past trends in the population size of the species, nor any current evidence to suggest that the subspecies will continue to decline at a particular rate. Therefore, there are no quantitative data available to assess the species against this criterion.

Criterion 4 – The estimated total number of mature individuals is extremely low, very low or low. The population size of Hoya australis subsp. oramicola is estimated at 350-700 mature individuals, however this estimate is highly speculative (Kerrigan et al 2004). Nevertheless, the estimated total number of mature individuals is low. Therefore, the species is eligible for listing as vulnerable under this criterion.

Criterion 5 - Probability of extinction in the wild There are no quantitative data available to assess the species against this criterion.

5. CONCLUSION Hoya australis subsp. oramicola is endemic to the Northern Territory. The subspecies is found only on Bathurst and Melville Islands, where it is known from four localities. Very little is known about the threatening processes impacting this subspecies. There is evidence in the literature however, which indicates that the subspecies habitat, monsoon forests, are vulnerable to disturbance from cyclones, cattle, buffalo, pigs, and dry-season wildfires (Panton 1993 and Russell-Smith et al 1992). The population size of Hoya australis subsp. oramicola is low and is estimated at 350-700 mature individuals.

The species is eligible for listing as vulnerable under criterion 4.

6. Recommendation The Committee recommends that the list referred to in section 178 of the EPBC Act be amended by including in the list in the vulnerable category: Hoya australis subsp. oramicola (a vine)

Associate Professor Robert J.S. Beeton Chair Threatened Species Scientific Committee

Publications used to assess the nomination Fensham, R.J. and Woinarsi, J.C.Z. (1992). Yawulama: the ecology and conservation of monsoon forest on the Tiwi Islands, Northern Territory. Report to DASET. (Consevation Commission of the Northern Territory: Darwin). Forster, P.I. and Liddle, D.J. (1996) Hoya. Flora of Australia 28: 231-237. Holtze (2005) Darwin Herbarium specimen database. (NT Department of Infrastructure Planning and Environment, Darwin.) Gibbons, A. (2003) Recovery plan for threatened plants of the Tiwi Islands in the Northern Territory of Australia.. Northern Territory Department of Infrastructure, Planning and Environment, Darwin. Kerrigan, R., Cowie, I., Baker, R. (2004) Threatened species information sheet, Hoya australis subsp. oramicola. (Darwin Herbarium, Department of Infrastructure, Planning and Environment, NTG) Liddle, D.T., Russell-Smith, J., Brock, J., Leach, G.J. and Connors, G.T. (1994) Atlas of the vascular rainforest plants of the Northern Territory. Flora of Australia Supplementary Series No. 3, ABRS, Canberra. Russell-Smith, Jeremy (1991) Classification, species richness, and environmental relations of monsoon rain forest in northern Australia. Journal of Vegetation Science 2.259-278. Russell-Smith, J. (1992). Plant populations and Monsoon Rain Forest in the Northern Territory, Australia. Biotropica 24(4): 471-487. Russell-Smith, J.,and Bowman, D.M.J.S. (1992). Conservation of monsoon rainforest isolates in the Northern Territory. Biological Conservation 59: 51-63. Woinarski, J., Brennan, K., Hempel, C., Firth, R. and Watt, F. (2000) Biodiversity Conservation on the Tiwi Islands: Plants, vegetation types and terrestrial vertebrates on Melville Island. Unpublished report Parks and Wildlife Commission of NT, Palmerston.