Achyranthes arborescens (Chaff Tree, Soft-wood)

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)

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

Achyranthes arborescens (Chaff Tree, Soft-wood)

2. National context

This species is endemic to Norfolk Island and not currently listed under the EPBC Act or State legislation.

3. How judged by TSSC in relation to the EPBC Act criteria.

TSSC judges the species to be eligible for listing as critically endangered under the EPBC Act. The justification against the criteria is as follows:

Criterion 1 - Decline in numbers

Since European settlement 80% of the native vegetation on Norfolk Island has been cleared. A significant decline in population numbers is inferred due to the extensive land clearing, unrestricted grazing and significant habitat degradation. There has been widespread establishment of large populations of invasive weed species and high levels of seed predation by rats. Whilst it is possible that the population decline since European settlement could be as high as 80%, there is, however, a lack of information about generation times and no quantitative data is available for recent rates of decline.

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

Criterion 2 - Geographic distribution

The species is very restricted in its geographic distribution, the extent of occurrence being 2.3ha (0.023km2). The population is considered severely fragmented, none of the four subpopulations containing more than 40 individuals. Continuing declines in the number of mature individuals, number of subpopulations, extent of occurrence, area of occupancy, and quality of habitat are projected due to the vulnerability of small populations to stochastic disturbance events (including cyclones), limited recruitment resulting from predation of seeds by rats, grazing by cattle and competition from exotic weeds. The species is adapted to moist forest conditions and is therefore susceptible to unfavourable climate change (projected increases in the incidence of drought and extreme rainfall events that cause physical damage).

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

Criterion 3 - Population size and decline in numbers or distribution

The total number of mature individuals is 57 and the population is considered to be severely fragmented, no subpopulation containing more than 40 individuals. Continuing declines in the number of mature individuals, number of subpopulations, extent of occurrence, area of occupancy, and quality of habitat are projected due to the vulnerability of small populations to stochastic disturbance events (including cyclones), limited recruitment resulting from predation of seeds by rats, grazing by cattle and competition from exotic weeds. The species is adapted to moist forest conditions and is therefore susceptible to unfavourable climate change (projected increases in the incidence of drought and extreme rainfall events that cause physical damage).

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

Criterion 4 - Population size

The total number of mature individual plants recorded in surveys is 57.

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

Criterion 5 - Probability of extinction in the wild

There is no quantitative data available against this criterion.

4. Conclusion

The total number of mature plants, 57, is low and the total population is considered to be severely fragmented, none of the four subpopulation containing more than 40 individuals. The geographic distribution is precarious for the survival of the species and is very restricted, having an area of occurrence of 2.3ha (0.023km2). Continuing declines in the number of mature individuals, number of subpopulations, extent of occurrence, area of occupancy, and quality of habitat are projected due to the vulnerability of small populations to stochastic disturbance events (including cyclones), limited recruitment resulting from predation of seeds by rats, grazing by cattle and competition from exotic weeds. The species is adapted to moist forest conditions and is therefore susceptible to unfavourable climate change (projected increases in the incidence of drought and extreme rainfall events that cause physical damage). The species is eligible for listing as critically endangered under criteria 2 and 3.

5. Recommendation

TSSC recommends that the list referred to in section 178 of the EPBC Act be amended by including in the list in the critically endangered category: Achyranthes arborescens (Chaff Tree, Soft-wood)