Lepidorrhachis mooreana - critically endangered species listing

NSW Scientific Commitee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the palm Lepidorrhachis mooreana (F. Muell.) O.F.Cook as a CRITICALLY ENDANGERED SPECIES in Part 1 of Schedule 1A of the Act. Listing of Critically Endangered species is provided for by Part 2 of the Act.

 

The Scientific Committee has found that:

 

1. Lepidorrhachis mooreana (F. Muell.) O.F.Cook (family Arecaceae, subfamily Arecoideae) is described by Green (1994) as a: “Palm with sturdy trunk to 2m tall; leaf scars 1-2 cm apart. Leaves stiff, arcuate, 1-1.5 m long; petiole stout, 20-30 cm long; pinnae 25-40 cm long. Inflorescence 30-50 cm long, spreading stiffly, with 100 or more ultimately slender branches. Male flowers developing first; petals c. twice as long as sepals; anthers dorsifixed; pistillode cylindrical. Female flowers cream-coloured, 8 mm long. Fruit c. 1 cm diam., red.” As is typical for Arecoideae, individuals are monoecious, but the species is unusual within the subfamily in that inflorescences contain flowers of one sex only, rather than both sexes, with both male and female inflorescences occurring on a single plant (Baker and Hutton 2006). Flowering is generally from August to December (Baker and Hutton 2006) with fruits maturing in subsequent years. It is likely to be insect pollinated, but pollinators are unknown. A plant may have mature fruits, developing fruits and flowers present at the one time.

 

2. Lepidorrhachis mooreana is from a monotypic genus and is endemic to New South Wales. It is only found on Lord Howe Island, where it is known as the Little Mountain Palm.

 

3. On Lord Howe Island, Lepidorrhachis mooreana is restricted to the cloud forest vegetation at the summits of Mt Gower and Mt Lidgbird (Pickard 1983, Harris et al. 2005, Baker and Hutton 2006), where it occurs above an elevation of approximately 740 m (Baker and Hutton 2006). On the 27 ha summit plateau of Mt Gower, L. mooreana is most abundant on small ridge tops and slopes rather than lower slopes and small gullies (Auld et al. 2010). The species was not seen on the northern half of the summit of Mt Lidgbird during survey work for Auld et al. (2010) and it is likely that it is not abundant or widespread on this mountain summit. The summit of Mt Lidgbird is very narrow and there is little suitable habitat for L. mooreana. All known locations occur within the Lord Howe Island Permanent Park Preserve.

 

4. Lepidorrhachis mooreana has a very highly restricted geographic distribution. The area of occupancy and extent of occurrence for L. mooreana are estimated to be 8 km2, based on 2 x 2 km grid cell, the scale recommended for assessing area of occupancy by IUCN (2010).

 

5. There have been no comprehensive estimates of the population size in Lepidorrhachis mooreana. Where the species is abundant on the summit of Mt Gower, Auld et al. (2010) found densities ranging from 1200 to 3400 mature plants per hectare. Assuming L. mooreana occupied half of the summit plateau, this would equate to between 16,000 and 47,000 mature plants on Mt Gower. However, the introduced Black Rat (Rattus rattus) can destroy all the fruits that are produced by L. mooreana (Auld et al. 2010). Because over 90% of the habitat of the species is currently impacted by Black Rats most of the palms on Mt Gower are currently not successfully reproducing. In assessing the conservation status of species, IUCN (2010) recommends that estimates of mature individuals should not include those that never produce new recruits. An estimate of the mature population size that can reproduce is more likely to be an order of magnitude less than 16,000 - 47,000. Hence, a very large reduction in population size is inferred based on the decline in the quality of the habitat for L. mooreana on Mt Gower.

 

6. The major threats to Lepidorrhachis mooreana are impacts by the introduced Black Rat (Rattus rattus) and a changing climate. Black Rats were introduced to Lord Howe Island after a shipwreck in 1918 (Billing and Harden 2000) and spread across the island. Black Rats can destroy all the annual seed crop of L. mooreana (Auld et al. 2010), and may also consume leaves of seedlings, juveniles and adult palms. Moore (1966) and Pickard (1980) have reported that successful fruit production in L. mooreana is negligible unless the fruits are protected from Black Rats. Typically L. mooreana establishes a juvenile bank of palms on the forest floor (Auld et al. 2010). The loss of fruits to Black Rats prevents the establishment of the juvenile bank of palms and hence, leads to a lack of long-term recruitment in L. mooreana (Auld et al. 2010). As L. mooreana is confined to the cloud forests on the summits of Mt Gower and Mt Lidgbird, any changes to the onset, magnitude and duration of cloud cover in summer under a changing climate could adversely affect the species. ‘Predation by the Ship Rat Rattus rattus on Lord Howe Island’ and ‘Anthropogenic Climate Change’ are listed as Key Threatening Processes under the Threatened Species Conservation Act 1995.

 

7.The Lord Howe Island Board carries out a baiting program to reduce the numbers and impacts of Black Rats. Black Rats are known to impact on seed production in the four endemic palms on the island (Pickard 1980). On Mt Gower, some 7% of the summit has been baited to reduce the impacts of rats (Auld et al. 2010). This baiting has been effective in allowing successful maturation of Lepidorrhachis mooreana fruits and recruitment of seedling plants in the baited areas. The population structure in baited versus non baited areas varies markedly in terms of juvenile plants (Auld et al. 2010). Baiting has led to successful palm recruitment in both L. mooreana and a co-occurring palm species (Hedyscepe canterburyana, the Big Mountain Palm) on the summit of Mt Gower. Ongoing control or eradication of rats has been recommended by Auld et al. (2010) for the long-term conservation of both these mountain palms.

 

8. Lepidorrhachis mooreana (F. Muell.) O.F.Cook is eligible to be listed as a Critically Endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2010:

 

Clause 6 Reduction in population size of species

The species has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time frame appropriate to the life cycle and habitat characteristics of the taxon:

(a) a very large reduction in population size,

based on the key indicator:

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

 

Clause 7 Restricted geographic distribution and other conditions

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

(a) very highly restricted,

and:

(d) a projected or continuing decline is observed, estimated or inferred in either of the key indicators:

(a) an index of abundance appropriate to the taxon, or

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

 

Dr Richard Major

Chairperson

Scientific Committee

Proposed Gazettal date: 15/04/11

Exhibition period: 15/04/11 - 10/06/11

 

References:

 

Auld TD, Hutton I, Ooi MKJ, Denham AJ (2010) Disruption of recruitment in two endemic palms on Lord Howe Island by invasive rats. Biological Invasions 12 3351-3361

 

Baker WJ, Hutton I (2006) Lepidorrhachis. PALMS 50, 33-38.

 

Billing J, Harden B (2000) Control of introduced Rattus rattus L. on Lord Howe Island. I. The response of mouse populations to warfarin bait used to control rats. Wildlife Research 27, 655–658.

 

Green PS (1994) Flora of Australia Vol. 49 Oceanic Islands 1. (Australian Government Printing Service: Canberra).

 

Harris R, Cassis G, Auld TD, Hutton I (2005) Patterns in floristic composition and structure in the mossy cloud forest of Mt Gower summit, Lord Howe Island. Pacific Conservation Biology 11, 246–256.

 

IUCN Standards and Petitions Subcommittee (2010) ‘Guidelines for Using the IUCN Red List Categories and Criteria Version 8.1.’ Prepared by the Standards and Petitions Subcommittee in March 2010.(http://intranet.iucn.org/webfiles/doc/SSC/RedList/RedListGuidelines.pdf)

 

Moore HE (1966) Palm hunting around the world. IV Lord Howe Island. Principes 10, 13–21.

 

Pickard J (1980) The palm seed industry of Lord Howe Island. Principes 24, 3–13.

 

Pickard J (1983) Vegetation of Lord Howe Island. Cunninghamia 1, 133–266.

Page last updated: 15 April 2011