Eucalyptus aggregata Deane & Maiden (Black Gum) - vulnerable species

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the tree Eucalyptus aggregata Deane & Maiden (Black Gum) as a VULNERABLE SPECIES in Part 1 of Schedule 2 of the Act. Listing of Vulnerable species is provided for by Part 2 of the Act.

 

The Scientific Committee has found that:

 

1. Eucalyptus aggregata Deane & Maiden is described in Hill (2002) as a 'tree to 18 m high; bark persistent, grey to grey-black, fibrous-flaky, throughout. Juvenile leaves opposite or disjunct, elliptic or ovate to broad-lanceolate, dull green. Adult leaves disjunct, narrow-lanceolate to lanceolate, 5-12 cm long, 1-2 cm wide, green, glossy, concolorous. Umbellasters 7-flowered; peduncle terete, 3-4 mm long; pedicels terete, 0-2 mm long. Buds ovoid, 3-5 mm long, 2-3 mm diam., scar present; calyptra hemispherical or conical, shorter than to as long as and as wide as hypanthium. Fruit conical to hemispherical, 2-4 mm long, 3-5 mm diam.; disk flat or raised; valves exserted.'

 

2. Eucalyptus aggregata occurs on the central and southern tablelands of NSW, and in a small disjunct population in Victoria (Brooker & Kleinig 1983; Hill 2002). In NSW, it occurs predominantly in the South Eastern Highlands Bioregion as defined by Thackway & Creswell (1995). The most eastern part of the distribution is located just within the Sydney Basin Bioregion (Thackway & Creswell 1995). The geographic distribution of E. aggregata is moderately restricted. Whilst the extent of occurrence of E. aggregata is currently estimated to be 28 000 km2, within this distribution, the area of occupancy is estimated to be only about 520-580 km2, based on 2 x 2 km grids, the spatial scale recommended for assessing areas of occupancy by IUCN (2008).

 

3. Eucalyptus aggregata is a small to medium-sized woodland tree and grows in grassy woodlands on alluvial soils in moist sites along creeks on broad, cold and poorly-drained flats and hollows (Brooker & Kleinig 1983; Hill 2002). It commonly occurs with E. rubida (Candlebark), E. viminalis (Ribbon Gum), and E. pauciflora (White Sally, Snow Gum), with a grassy understorey of River Tussock Poa labillardieri (Field 2007). Most populations of E. aggregata are located on private land or road verges and travelling stock routes. Much of the habitat of E. aggregata is naturally grassy and relatively arable, and has been utilised historically by pastoralists (Douglas 2009). Consequently there are very few stands of E. aggregata in conservation reserves and the populations that are, tend to be on the edges of former or extant populations (Douglas 2009). Small populations of E. aggregata have been recorded in Tallaganda, Morton, Yanununbeyan, and the Blue Mountains National Parks, and Turallo Nature Reserve.

 

4. There is estimated to be a moderately low number of Eucalyptus aggregata individuals. Compilation of available survey data indicates that 6300 - 8100 mature individuals are scattered across 130 - 150 locations throughout the distribution. A large number of these consist of a few remnant trees in a largely cleared landscape. Field (2007) estimated that only 9% of populations were large populations (>200 adult trees) in continuous woodland vegetation.

 

5. Eucalyptus aggregata grows mainly in frost hollows and flats, and its habitat is therefore naturally patchy in the landscape. However, much of the landscape in the southern tablelands has been cleared or modified for grazing and agriculture, and this may have contributed to a reduction in the size and extent of most E. aggregata populations (Field 2007). Small-scale clearing may pose considerable threats across much of the range of E. aggregata in the future, as farming properties are subdivided for rural-residential use (Douglas 2009). 'Clearing of native vegetation' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

 

6. About 90% of the populations of Eucalyptus aggregata consist of scattered trees on private land or roadsides, and most have little seedling recruitment due to heavy grazing and/or competition from weeds (Field 2007). Blackberry (Rubus spp.), Harding Grass (Phalaris aquatica), Canary Grass (Phalaris canariensis), Cocksfoot (Dactylis glomerata), Willows (Salix spp.) and Scotch Broom (Cytisus scoparius) are particularly problematic weed species that currently co-occur with E. aggregata (Field 2007; Douglas 2009). 'Invasion of native plant communities by exotic perennial grasses' and 'Invasion and establishment of Scotch Broom (Cytisus scoparius)' are listed as Key Threatening Processes under the NSW Threatened Species Conservation Act 1995. Roadside disturbance, weed invasion, grazing and small-scale clearing are likely to result in continuing decline in Eucalyptus aggregata populations.

 

7. Genetic studies have shown that the small remnant populations of Eucalyptus aggregata are showing a high rate of interspecific hybridization, which can be detrimental to the fitness of offspring and increase the risk of local extinction (Field 2007). Increased hybrid production, introgression, and reduced seed production, germination and survivorship of seed cohorts, were observed when E. aggregata trees were within small remnants and exposed to increased pollen swamping from E. rubida and E. viminalis (Field 2007). As the majority of populations of E. aggregata are small and isolated, this is of particular concern. The few large populations are less affected by hybridisation, and their viability is unlikely to be at the same risk (Field 2007).

 

8. The effects of climate change may also pose a significant threat to Eucalyptus aggregata (Douglas 2009). As the habitat of E. aggregata is located in cold frost hollows and flats across the landscape, under conditions of increased average temperatures and possibly lower effective rainfall, the viability of populations could be reduced if the region becomes warmer and drier, as projected under future climate scenarios (Hennessy et al. 2004). This may reduce the suitability of conditions for recruitment and establishment of E. aggregata seedlings. Invasion by seedlings of other tree species, such as E. rubida and E. viminalis, from surrounding forests and woodlands, may lead to increased competition from those species within the habitat of E. aggregata (Douglas pers. comm. July 2008). 'Anthropogenic Climate Change' is listed as a Key Threatening Process under the NSW Threatened Species Conservation Act 1995.

 

9. Eucalyptus aggregata Deane & Maiden is currently not eligible to be listed as an Endangered or Critically Endangered species.

 

10. Eucalyptus aggregata Deane & Maiden (Black Gum) is eligible to be listed as a Vulnerable species as, in the opinion of the Scientific Committee, it is facing a high risk of extinction in New South Wales in the medium-term future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

 

Clause 15

The geographic distribution of the species is estimated or inferred to be:

(c) moderately restricted,

and:

(d) a projected or continuing decline is observed, estimated or inferred in:

(i) an index of abundance appropriate to the taxon,

(ii) geographic distribution, habitat quality or diversity, or genetic diversity.

 

Clause 16

The estimated total number of mature individuals of the species is:

(c) moderately low,

and:

(d) a projected or continuing decline is observed, estimated or inferred in:

(i) an index of abundance appropriate to the taxon,

(ii) geographic distribution, habitat quality or diversity, or genetic diversity.

 

Dr Richard Major

Chairperson

Scientific Committee

 

Proposed Gazettal date: 12/02/10

Exhibition period: 12/02/10 – 09/04/10

 

References:

 

Brooker MIH, Kleinig DA (1983) 'Field Guide to Eucalypts Volume 1'. (Inkata Press).

 

Douglas S (2009) Black Gum, a nationally threatened tree of upland New South Wales and Victoria. Australasian Plant Conservation 17, 18-19.

 

Field DL (2007) The importance of ecological factors in determining the pattern of interspecific hybridization in fragmented landscapes of Eucalyptus aggregata. PhD Thesis, University of Wollongong.

 

Hennessy K, Page C, McInnes K, Jones R, Bathols J, Collins D, Jones R (2004) 'Climate change in New South Wales. Part 1: Past climate variability and projected changes in average climate'. CSIRO Marine and Atmospheric Research, Aspendale, Victoria.

 

Hill KD (2002) Eucalyptus. In 'Flora of New South Wales Revised Edition Volume 2'. (ed Harden GJ) pp 96-164 (University of NSW Press, Sydney).

 

IUCN (2008) 'Guidelines for using the IUCN Red List Categories and Criteria. Version 7.0.' (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland). (http://intranet.iucn.org/webfiles/doc/SSC/RedList/RedListGuidelines.pdf).

 

Thackway R, Creswell ID (1995) An interim biogeographic regionalisation for Australia: a framework for setting priorities in the National Reserves System Cooperative Program. Version 4.0. ANCA, Canberra.

Page last updated: 28 February 2011