Abba Bell (Darwinia sp. Williamson) interim recovery plan 2003-2008

Interim recovery plan no. 139
Gillian Stack & Val English
Department of Conservation and Land Management, Western Australia, 2003

1. Background

History

G.J. Keighery ¹ made the first collection of Darwinia sp. Williamson from the base of the Whicher Range in November 1991. N. Gibson ² and other botanists undertook floristic and vegetation surveys of the Swan Coastal Plain in 1994 (Gibson et al. 1994) but located no additional populations of the species. A hot fire burnt through the population in 1993 and resulted in the death of almost all the mature individuals. Approximately 100 D. sp. Williamson seedlings were noted at that site during a survey in 1994, and some of these plants flowered in 1995.

Dieback disease caused by the plant pathogen Phytophthora cinnamomi is known to exist in the vicinity of Darwinia sp. Williamson. The taxon is presumed to be susceptible to this pathogen, as this is a characteristic of many Myrtaceous species. Susceptibility tests are being conducted but are incomplete at this stage. The site was first sprayed with phosphite in 1996, and this action is ongoing. The Department's Blackwood District staff assess the effectiveness of this treatment by monitoring local key dieback indicator species (personal communication, R. Smith ³).

An Interim Recovery Plan was developed for the species in 1999 (Stack et al. 1999). Information accumulated since that plan was completed has been incorporated into this plan and this document now replaces Stack et al. (1999). This IRP will be implemented in conjunction with the IRP for the 'Shrublands on southern Swan Coastal Plain Ironstones' (English 1999) and with IRPs for other Critically Endangered taxa that occur at the same locality (Brachysema papilio, Lambertia echinata subsp. occidentalis and Petrophile latericola).

Description

Darwinia sp. Williamson is an erect or sometimes spreading shrub, up to 70 cm tall by 40 cm wide, and often uses other shrubs for support. The green linear leaves, 3 to 5 mm long, are triangular in cross section, are crowded at the ends of branches, and bend backwards. This feature of the leaves distinguishes the species from the similar Darwinia oederoides. The inflorescence is nodding or (in young plants) rarely erect. The flowers are enclosed by red and green bracts that are arranged in several rows. The ribbed floral tube is brown, 3 mm long, with small triangular calyx lobes. The petals are about 1 mm long, and there is a red, curved style, 10 to 16 mm long (Brown et al. 1998).

Distribution and habitat

Darwinia sp. Williamson is known from a single wild population (Population 1) at the base of the Whicher Range, in a winter-wet area of shrubland on shallow red clay over ironstone. The ecological community in which the species grows ('Shrublands on southern Swan Coastal Plain Ironstones') was ranked as Critically Endangered in 1995. These ironstone soils are highly restricted in distribution. There are a total of 13 occurrences of this species-rich plant community located on seasonal wetlands on ironstone and heavy clay soils on the Swan Coastal Plain near Busselton (English 1999). D. sp. Williamson has been translocated into two recently purchased areas that contain ironstone soils with vegetation in variable condition.

Much of the species diversity in the community comes from annuals and geophytes. Typical and common native species are the shrubs Kunzea aff. micrantha, Pericalymma ellipticum, Hakea oldfieldii, Hemiandra pungens and Viminaria juncea, and the herbs Aphelia cyperoides and Centrolepis aristata (Gibson et al. 1994). Other associated species include Hakea varia, Loxocarya magna and Chamelaucium roycei.

There are six additional Declared Rare Flora (DRF), three of which are also ranked Critically Endangered, that occur on the ironstone soils in the vicinity of Darwinia sp. Williamson. These are Brachysema papilio (CR), Lambertia echinata subsp. occidentalis (CR), Petrophile latericola (CR), Dryandra nivea subsp. uliginosa (Endangered), Dryandra squarrosa subsp. argillacea (Endangered) and Chamelaucium roycei ms (Vulnerable).

The IRPs for all of the Critically Endangered flora that occur near Darwinia sp. Williamson will be complementary to, and implemented in conjunction with, the IRP for the 'Shrublands on southern Swan Coastal Plain Ironstones' (English 1999).

¹ Greg Keighery, Principal Research Scientist (botany), the Department's Science Division, Wildlife Research Centre
² Neil Gibson, Senior Research Scientist (botany), the Department's Science Division, Wildlife Research Centre
³ Russell Smith, Ecologist, Phosphite Program, The Department's Environmental Protection Branch, Bunbury

International Obligations

This plan is fully consistent with the aims and recommendations of the Convention on Biological Diversity, ratified by Australia in June 1993, and will assist in implementing Australia's responsibilities under that Convention. However, as Darwinia sp. Williamson is not listed under any international agreement, the implementation of other international environmental responsibilities is not affected by this plan.

Role and interests of indigenous people

There are no known indigenous communities interested or involved in the management of areas affected by this plan. Therefore no role has been identified for indigenous communities in the recovery of this species.

Habitat critical to the survival of the species, and important populations

Given that this species is listed as Critically Endangered it is considered that all known habitat is habitat critical. In addition all populations, including translocated populations, are considered important to the survival of the species. Recovery actions include survey for further populations that would lead to the identification of additional habitat critical.

Benefits to other species/ecological communities

Population 1 is located within an occurrence of a Threatened Ecological Community (TEC) listed as Endangered under the EPBC Act, and Critically Endangered in Western Australia. Other listed flora also occur in the wider habitat of Population 1 of Darwinia sp. Williamson (Gastrolobium papilio (previously Brachysema papilio), Lambertia echinata subsp. occidentalis, and Petrophile latericola). All of these taxa are listed as Critically Endangered in Western Australia and Endangered under the EPBC Act. Recovery actions implemented to improve the quality or security of the habitat of Darwinia sp. Williamson Population 1 are likely to improve the status of the TEC in which this population is located, and also that of other listed flora that occur in the wider habitat.

Social and economic impacts

The implementation of this recovery plan is unlikely to cause significant adverse social and economic impacts. There are mineral leases over the area that contains population 1a of Darwinia sp. Williamson (refer Table 1), however, a mine proposed for immediately adjacent to the habitat of this species has been approved by all relevant authorities conditional upon specified environmental commitments made by the mining company. Recovery actions refer to continued liaison between stakeholders.

Evaluation of the Plan's Performance

The Department of Conservation and Land Management, in conjunction with the South West Region Threatened Flora Recovery Team will evaluate the performance of this recovery plan. In addition to annual reporting on progress against the criteria for success and failure, the plan is to be reviewed within five years of its implementation. Any changes to management / recovery actions made in response to monitoring results will be documented accordingly.

Critical habitat

Critical habitat is habitat identified as being critical to the survival of a listed threatened species or listed threatened ecological community. Habitat is defined as the biophysical medium or media occupied (continuously, periodically or occasionally) by an organism or group of organisms or once occupied (continuously, periodically or occasionally) by an organism, or group of organisms, and into which organisms of that kind have the potential to be reintroduced (Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)).

The critical habitat for Darwinia sp. Williamson comprises:

  • the area of occupancy of the known population;
  • occurrences of ironstone habitat currently containing translocated plants of this species (populations 2T and 3T) which may in time become self-sustaining populations;
  • areas of similar habitat within 200 metres of wild and translocated populations, i.e. winter-wet areas of shrubland on shallow red clay over ironstone (these provide potential habitat for natural range extension);
  • corridors of remnant vegetation that link wild and translocated populations (these are necessary to allow pollinators to move between populations and are usually road and rail verges);
  • the local catchment for the groundwater and surface water that feeds the wetland habitat in which the species occurs; and
  • additional occurrences of similar habitat that do not currently contain the species but may have done so in the past (these represent possible translocation sites).

Biology and ecology

Little is known about the biology and ecology of Darwinia sp. Williamson. The species appears to be killed by fire, although one adult plant was recorded as surviving the 1993 fire. Darwinia species are generally considered to be fire-sensitive with post-fire regeneration occurring mainly from seed. Approximately 100 seedlings germinated after the 1993 fire, and a few of these flowered in October 1995. The species is likely to be dieback susceptible as this is a characteristic of many Myrtaceous species.

A number of Darwinia species are cultivated for their ornamental bell-like flower heads. Propagation of Darwinia species is achieved through cuttings, as seed germination is often low even under generally favourable conditions (Turnbull and Doran 1987). Further investigation of germination techniques is necessary. The germination rate of this species has ranged from 60 to 86% initially, and was 31% after one year in storage (unpublished data A. Cochrane 4). Like most Darwinias, this species propagates well from cuttings, with strike rates generally above 50% and often as much as 90% (personal communication A. Shade 5).

Threats

Darwinia sp. Williamson was declared as Rare Flora under the Western Australian Wildlife Conservation Act 1950 in October 1996 and was ranked as Critically Endangered (CR) in November 1998. It is also listed as Endangered under the EPBC Act. It currently meets IUCN Red List Category 'CR' under criteria A4ce; B1ab(iii)+2ab(iii); C2a(ii) (IUCN 2000), as it is only known from a single population comprised of approximately 100 mature individuals, with continued decline in the quality of the habitat. The main threats are disease, inappropriate fire regimes, mineral sand exploration and extraction, changes to hydrology, water-logging and salinity, weeds, rabbit grazing, and impacts such as high wind speeds that occur as a consequence of proximity to cleared land.

  • Disease is a serious threat to Population 1. Phytophthora is known to occur in the vicinity of the species, and Darwinia sp. Williamson is suspected to be susceptible to this plant pathogen. As this is the only in situ population, protecting the habitat from dieback is imperative. There have also been deaths of the DRF species Dryandra nivea subsp. uliginosa at the locality, and these are likely to have been caused by canker (probably Armillaria luteobubalina). The susceptibility of Darwinia sp. Williamson to this second pathogen is unknown.
  • Inappropriate fire regimes would affect the viability of the population, as Darwinia sp. Williamson appears to be an obligate seeder that germinates following fire. If this is the case, the soil seed bank would rapidly be depleted if fires recurred before regenerating or juvenile plants reached maturity and replenished the soil seed bank. However, it is likely that occasional fires are needed for reproduction of the species.
  • Mineral sand extraction has been approved within privately owned land adjacent to the area of State Forest which contains Population 1. Potential impacts include major modification of the hydrology of the area, and the proponent has installed an artificial recharge system to help maintain current hydrology and several piezometers for monitoring purposes.
  • Mineral sand exploration and extraction leases exist over the area of State Forest in which Darwinia sp. Williamson occurs.
  • Water-logging and salinity are becoming threats on the ironstone soil type on which Darwinia sp. Williamson occurs (Tille and Lantzke 1990). Extensive clearing for agriculture in the area is likely to have increased surface runoff and recharge of the groundwater. Neither waterlogging nor salinity are immediate threats, but require monitoring. Hirschberg (1989) measured levels of salinity in the groundwater in the area, and found the water near this population to be reasonably fresh.
  • Weeds are an established problem at the translocation sites. These partially cleared areas were purchased by the Department in 1999, and are being rehabilitated. Weeds suppress early plant growth by competing for soil moisture, nutrients and light. They also exacerbate grazing pressure and increase the fire hazard due to the easy ignition of high fuel loads, which are produced annually by many grass weed species.
  • Rabbits are a threat to the translocated populations through selectively grazing seedlings and young growth.
  • Environmental stress including strong winds as a consequence of proximity to cleared land is a threat at Population 2T. Lack of native vegetation increases wind and heat exposure increasing susceptibility to desiccation and reducing plant vigour.

4 Anne Cochrane, Manager, the Department's Threatened Flora Seed Centre
5 Amanda Shade, Horticulturalist, Botanic Garden and Parks Authority

Summary of population information and threats
Pop. No. & Location Land Status Year/No. plants Condition Threats
1. Whicher Range State Forest 1991 Common
1992 27
1993 1
1994 1 (ca100)
1997 5 (ca100)
2002 100+
Healthy Disease, inappropriate fire regimes, mineral sands exploration and extraction, waterlogging and salinity
2T. Whicher Range(Oates Rd) Nature Reserve 2001 (328) 49 Disease, inappropriate fire regimes, waterlogging and salinity, weeds, rabbits, strong wind, drought
3T. Whicher Range(Negus’ Block) Nature Reserve 2001 (68) 32 Disease, inappropriate fire regimes, waterlogging and salinity, weeds, rabbits, kangaroos

Numbers in brackets = number of juveniles. Pop.No.T = a translocated population.

Guide for decision-makers

Section 1 provides details of current and possible future threats. Any on-ground works (clearing, mining firebreaks, roadworks etc) in the immediate vicinity of Darwinia sp. Williamson will require assessment. On-ground works should not be approved unless the proponents can demonstrate that they will not have an impact on the species, its habitat or potential habitat, or on the local surface or groundwater catchments such that hydrology of the wetland habitat of the species would be altered.