Diuris tricolor, the Pine Donkey Orchid population in the Muswellbrook local government area - endangered population listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the population of the orchid Diuris tricolor Fitzg., the Pine Donkey Orchid, in the Muswellbrook local government area as an ENDANGERED POPULATION in Part 2 of Schedule 1 of the Act. Listing of endangered populations is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Diuris tricolor Fitzg . (synonyms  Diuris sheaffiana Fitzg.,  Diuris colemaniae Rupp) (family Orchidaceae) is not currently listed as an endangered species in Part 1 of Schedule 1 or a critically endangered species in Part 1 of Schedule 1A and as a consequence populations of this species are eligible to be listed as endangered populations.

2. Diuris tricolor Fitzg. is an endemic Australian orchid that has been described by Jones (1993) as follows: "Terrestrial herb. Leaves 1-3, linear, 20-30 cm long, 3-4 mm wide, conduplicate. Raceme 20-40 cm high, 2-6 flowered. Flowers bright yellow to orange, speckled with red to purple and white markings on the labellum and dorsal sepal, 2.5-3 cm across. Dorsal sepal ovate, 7-15 mm long, 4-11 mm wide, erect. Lateral sepals 15-65 mm long, 1-3 mm wide, deflexed, parallel or crossed. Petals widely divergent; lamina ovate or elliptic, 5-14 mm long, 3-10 mm wide; claw 2-7 mm long, expanded into the lamina. Labellum 7-12 mm long; lateral lobes linear to narrow-cuneate, 3-4.5 mm long, 1.5-2.5 mm wide, margins crenulate; midlobe ovate when flattened, 6-9 mm wide, ridged along midline; callus of 2 broad ridges 4-4.5 mm long. Flowers Sept.-Nov."

3. Diuris tricolor is found in New South Wales and Queensland. In New South Wales, populations of the species occur on the northern tablelands, central tablelands, north western slopes and central western slopes (Jones 1993).

4. Diuris tricolor is found in sclerophyll vegetation (Jones 1993) on flats or small rises, on a range of substrates including sandy or loamy soils derived from granite, porphyry, laterite or alluvium (DEC 2005).

5. The Muswellbrook LGA population of Diuris tricolor comprises the large-flowered form of the species (which also occurs at several other locations).

6. The population of Diuris tricolor in the Muswellbrook local government area (LGA) comprises a number of occurrences, ranging from a few scattered individuals to a few thousand individuals (B Holzinger, pers. comm.). The area of occupancy of the population is less than 50 km2 in the Muswellbrook LGA. Therefore, the geographic distribution of the population is estimated to be highly restricted.

7. The population of Diuris tricolor in the Muswellbrook LGA is at the eastern limit of the geographic range of the species. All other populations of the species are located west of the Great Dividing Range. The distance of the Muswellbrook LGA population to the nearest population of the species to the west is c. 100 km. Therefore the population in the Muswellbrook LGA is disjunct and at the limits of its geographic range.

8. The habitat of Diuris tricolor in the Muswellbrook LGA has been fragmented by past land clearing. The population continues to be threatened by both small-scale clearing (e.g. rural dwellings, maintenance of roadsides and easements, etc.) and broad-scale clearing associated with open-cut coal mining and residential subdivision. 'Clearing of native vegetation' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

9. A number of sites in the Muswellbrook LGA, at which Diuris tricolor is known to occur, are fragmented and degraded patches of native vegetation, exposed to invasion by weeds such as  Chloris gayana (Rhodes Grass),  Eragrostis curvula (African Love Grass) and  Hyparrhenia hirta (Coolatai Grass). These exotic grasses compete with  D. tricolor for space and light and may threaten its persistence at several sites. Invasion of native plant communities by exotic perennial grasses listed as a Key Threatening Process under the Threatened Species Conservation Act.

10. The population of Diuris tricolor Fitzg. in the Muswellbrook LGA is eligible to be listed as an endangered population as, in the opinion of the Scientific Committee it is facing a very high risk of extinction in New South Wales in the near future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

Clause 19

The population is facing a very high risk of extinction in New South Wales in the near future as, in the opinion of the Scientific Committee, it satisfies any one or more of the following paragraphs and also meets the criteria specified in the following clause:

(a) it is disjunct or near the limit of its geographic range.

Clause 21

The geographic distribution of the population is estimated or inferred to be highly restricted and:

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

(i) an index of abundance appropriate to the taxon, or
(ii) geographic distribution, habitat quality or diversity, or genetic diversity; or

Associate Professor Lesley Hughes
Chairperson
Scientific Committee

Proposed Gazettal date: 27/4/07
Exhibition period: 27/4/07 - 22/6/07

References: 

DEC (2005) 'Threatened species, populations and ecological communities of New South Wales.' Accessed on 19/09/05.

Jones DL (1993) Diuris. In 'Flora of New South Wales'. (Ed. GJ Harden) pp. 138-145. (New South Wales University Press: Kensington)