Velvet Boronia (Boronia hippopala)

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)
13 April 2005

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

Boronia hippopala (Velvet Boronia)

A review of the Boronia group in eastern and northern Australia was undertaken in 2003 (Duretto 2003). Prior to this review, six species of Boronia were recognised in Tasmania (i.e. B. anemonifolia, B. citriodora, B. nana, B. parviflora, B. pilosa, and B. rhomboidea). The 2003 revision identified a total of 15 taxa for Tasmania with nine endemics, including Boronia hippopala. Following this revision, surveys were commissioned to verify both the distribution and the population parameters of a number of Boronia species, including Boronia hippopola. These surveys were undertaken during August to December 2003. Numbers of mature plants were determined either through direct counts or by estimates of plant density and areas of occupancy.

2. Description

Velvet Boronia is a woody shrub that grows to 2 m high. Velvet Boronia grows within Eucalyptus pauciflora-dalrympleana woodland, typically at the margins of marshes occupied by wet heath and scrub. Its preferred habitat is characterised by gentle slopes with moderate to poor drainage and a high surface rock cover. It occurs in association with Micrantheum hexandrum, Leptospermum lanigerum, L. scoparium, Callistemon viridiflorus, Banksia marginate, Epacris sp. Aff. Virgata 'Dukes Marsh', Pultenaea gunnii and Tetratheca pilosa and the undershrub Hibbertia serpyllifolia.

3. National context

Velvet Boronia is endemic to Tasmania, being known only from the upper catchment of St Pauls River in Tasmania's Eastern Tiers. Prior to the 2003 review, the distribution of the species was poorly known and it was considered to consist of eight plants known from a single roadside site.

Velvet Boronia is now known from three populations with an estimated total number of mature individuals between 6000-9000. The three known sites are: Horseshoe Marsh, 10 hectares and 1-2000 mature individuals; the north western margins of Dukes Marsh, 2 hectares and 1-2000 mature individuals; and south of the Dukes River, 10 hectares and 4-5000 mature individuals.

About 60% of the total population occurs in the Mt Puzzler Forest Reserve (i.e. all plants that occur south of Dukes River) with the remaining 40% on State Forest within informal reserves, either streamside reserves or flora/forest health special management zones. The Horseshoe marsh population occurs on State Forest with the majority of plants occurring within an existing management zone for Phytophthora cinnamomi. This zone was established due to the presence of other threatened plant species including Epacris exserta (now Epacris sp. Aff. Virgata 'Dukes Marsh') and Acacia axillaris.

Velvet Boronia has been nominated for listing under the Tasmanian Threatened Species Protection Act 1995. The Tasmanian Threatened Species Scientific Advisory Committee has not yet made a decision on the conservation status of the species.

EPBC Act criteria.

TSSC judges the species 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.

Potential threats to this species are considered to be possible infection from the plant pathogen Phytophthora cinnamomi, an inappropriate fire regime, permanent flooding, and activities that either directly disturb known sites (e.g. road works and maintenance) or alter its hydrology (e.g. upstream or upslope activities in the upper catchments of the St Pauls River and Dukes River that increase runoff or sediment loads).

The actual level of susceptibility of Velvet Boronia to Phytophthora cinnamomi is, at this stage, unknown. However, the susceptibility of other Boronia species to Phytophthora cinnamomi has long been recognised. Phytophthora cinnamomi can be spread by dispersing independently through very moist but well aerated soil aided by water, wildlife and human activities such as road building and maintenance. Previous advice from experts suggest that fire, or frequent fires, can create conditions conducive to an increased abundance and spread of Phytophthora cinnamomi. Fire reduces organic matter in the soil and associated soil micro-flora/fauna that can have a suppressive effect on Phytophthora cinnamomi. Fire also reduces the vegetation cover and allows soil temperature and water availability to rise, facilitating an increase in the pathogen. The movement of fire fighters and associated machinery is a secondary mechanism aiding the spread of Phytophthora cinnamomi.

Velvet Boronia has a very small proportion of younger plants, typically in disturbed areas. This is considered to reflect the last major fire in the area that occurred approximately twenty years ago. Too frequent fire is considered to be detrimental to the survival of the species. Conversely, should long periods occur between suitable fire events, plants may become senescent with soil-stored seed becoming unviable.

The species occurs adjacent and down slope of roads and disturbance to the species habitat may occur from road works and maintenance. The species may also be at risk from disturbance to the hydrology of its habitat from upstream or upslope activities (e.g. activities upstream that alter site water levels or cause increased runoff and sediment loads).

While a number of potential threats have been identified, there is insufficient evidence to indicate what level of historical decline the species may have undergone or that a decline is likely in the immediate future. There is insufficient quantitative data available against this criterion. Therefore, the species is not eligible for listing under this criterion.

Criterion 2 - Its geographic distribution is precarious for the survival of the species and is very restricted, restricted or limited.

Velvet Boronia is currently estimated to have an extent of occurrence of 12.6 km² and an area of occupancy between 20-25 hectares. It is known to occur in three populations: Horseshoe Marsh, 10 hectares and 1-2000 mature individuals; the north western margins of Dukes Marsh, 2 hectares and 1-2000 mature individuals; and south of the Dukes River, 10 hectares and 4-5000 mature individuals. Targeted surveys of similar habitat in the region have failed to locate any additional populations.

While the species has a restricted geographic distribution, and is known from only three populations, there is insufficient evidence to indicate that this geographic distribution is, in itself, precarious for the survival of the species. Potential threats to this species are considered to be possible infection from the plant pathogen Phytophthora cinnamomi, an inappropriate fire regime, permanent flooding, and activities that either directly disturb known sites (e.g. road works and maintenance) or alter its hydrology (e.g. upstream or upslope activities in the upper catchments of the St Pauls River and Dukes River that increase runoff or sediment loads).

There is insufficient evidence to indicate that the existing population of Velvet Boronia is subject to a continuing decline or extreme fluctuations in population numbers. About 60% of the total population occurs in the Mt Puzzler Forest Reserve (i.e. all plants that occur south of Dukes River) with the remaining 40% on State Forest within informal reserves, either streamside reserves or flora/forest health special management zones. The Horseshoe marsh population occurs on State Forest with the majority of plants occurring within an existing management zone for Phytophthora cinnamomi. This zone was established due to the presence of other threatened plant species including Epacris exserta (now Epacris sp. Aff. Virgata 'Dukes Marsh') and Acacia axillaris.

The geographic distribution, while restricted, is not considered precarious for the survival of the species as the species is well protected in reserves, is under no immediate threat and appears not to be subject to an ongoing decline. Therefore, the species is not eligible for listing under this criterion.

Criterion 3 - The estimated total number of mature individuals is very low, low, or limited, and: (a) evidence suggests that the number will continue to decline at a very high, high, or substantial rate; or (b) the number is likely to continue to decline and its geographic distribution is precarious for its survival.

Velvet Boronia has an estimated total number of mature individuals between 6000-9000. The number of mature individuals is not very low, low, or limited.

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

Criterion 4 - The estimated total number of mature individuals is extremely low, very low or low.

Velvet Boronia is now known from three populations with an estimated total number of mature individuals between 6000-9000. The three known sites are: Horseshoe Marsh, 10 hectares and 1-2000 mature individuals; the north western margins of Dukes Marsh, 2 hectares and 1-2000 mature individuals; and south of the Dukes River, 10 hectares and 4-5000 mature individuals. However, the total population of Velvet Boronia is geographically very restricted, occurring in only three populations contained within the one catchment with an estimated an area of occupancy of between 20-25 hectares.

Velvet Boronia has a very restricted area of occupancy and occurs at only three locations. It is considered to be prone to the effects of human activities as the plant commonly occurs downslope of roads. Potential threats to the species include infection from the plant pathogen Phytophthora cinnamomi; an inappropriate fire regime; permanent flooding; roadwork and maintenance and alteration of site hydrology (e.g. from upstream or upslope activities that increase runoff and sediment loads).

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

Criterion 5 - Probability of extinction in the wild

There is no quantitative data available against this criterion. Therefore, the species is not eligible for listing under this criterion.

5. Conclusion

Velvet Boronia occurs in three populations within a very restricted geographic distribution. It is known from three sites in the upper catchment of the St Pauls River in Tasmania's Eastern Tiers. Potential threats to the species and its habitat include infection with the plant pathogen Phytophthora cinnamomi, an inappropriate fire regime, permanent flooding, direct disturbance from road works and maintenance, and activities that alter the species site hydrology (e.g. upstream and upslope activities that increase runoff and sediment loads). The species is eligible for listing as vulnerable under criterion 4.

6. Recommendation

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

  • Boronia hippopala (Velvet Boronia)

Conservation Advice

Velvet Boronia is a woody shrub that grows to 2m in height. It occurs within Eucalyptus pauciflora-dalrympleana woodland often at the margins of marshes occupied by wet heath and scrub. It is endemic to Tasmania, being known only from the upper catchment of the St Pauls River in Tasmania's Eastern Tiers (North Tasmania NRM region).

Key threats to the Velvet Boronia include: infection from the plant pathogen Phytophthora cinnamomi, an inappropriate fire regime, permanent flooding, disturbance from road works and maintenance; and alterations to its site hydrology (e.g. from upstream or upslope activities that increase runoff and sediment loads).

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

  • protection of known sites from direct or indirect disturbance due to road works or maintenance; permanent flooding, and alteration to its site hydrology from upstream and upslope activities that may increase runoff and sediment loads;
  • establishment of appropriate protocols to minimise possible infection and spread of the plant pathogen Phytophthora cinnamomi;
  • investigation, development and implemention of an appropriate fire management regime for sites where the species is known to occur;
  • investigation of the feasibility of extending the Mt Puzzler Forest reserve to include sites where Velvet Boronia occurs at Horeshoe Marsh and relevant portions of Dukes Marsh.

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.

A Recovery Plan is not yet in place for this species. A national Threat Abatement Plan exists for the plant pathogen Phytophthora cinnamomi: 'Threatened Abatement Plan for Dieback Caused by the Root-rot Fungus Phytophthora cinnamomi, Commonwealth of Australia 2001."

Priority for the development of recovery plan: Low.

Publications used to assess the nomination

Duretto, M.F. (2003) Notes on Boronia (Rutaceae) in eastern and northern Australia. Muelleria 17, 19-135.

Schahinger, R. (2004) Distribution and Conservation Status of the Tasmanian Endemic Shrubs Boronia gunnii, Boronia hemichiton and Boronia hippopala. Report to the Threatened Species Unit, Department of Primary Industries, Water and Environment, Hobart, Tasmania.