Green Hill Thomasia (Thomasia sp. Green Hill) Interim Recovery Plan 2003-2008

Interim Recovery Plan No. 132
Val English
Department of Conservation and Land Management, WA, 2003

1. Background

History

An interim Recovery Plan was drafted for Thomasia sp. Green Hill in 1999 (Evans and English 1999). This document is based on that plan and includes additional information compiled since 1999.

Thomasia sp. Green Hill was first officially collected in 1972, several kilometres south of New Norcia. This population could not be relocated during flora surveys in 1993 and 1994, and the species was not located during extensive floristic surveys conducted in the region by T. Griffin during 1990-1992. In September 1995 a survey was conducted specifically for Thomasia sp. Green Hill in the New Norcia area, and a collection was made in an area of remnant vegetation on private property. This consisted of two small subpopulations (13 and 8 plants respectively), separated by a distance of 1.5 km. This remains the only known population, but has increased in size to 18 and 81 plants respectively.

A Thomasia specimen collected by D. W. Giminez in 1923 appears very similar to the above taxon. Following a taxonomic review of Thomasia, this specimen may be identified as Thomasia sp. Green Hill.

Description

Thomasia sp. Green Hill is a low shrub approximately 40 cm in height with multiple stems that grow from a rootstock. The leaves are flat, narrowly elliptic, 10-13 mm long and 5 mm wide. The inflorescences are racemes of about three flowers. The ribbed calyx is mauve with a reddish purple base. The calyx is approximately 7 mm long, and is divided for less than half its length into five obtuse arching lobes. The rounded petals and anthers are dark purple-black.

Distribution and habitat

Thomasia sp. Green Hill is endemic to Western Australia and is apparently confined to the New Norcia area. It is known from only one population, consisting of two subpopulations, with a total of 99 plants. The subpopulations grow approximately 1.5 km apart but within the same remnant bush block and on the same brown clayey sand over laterite, in open Eucalyptus wandoo woodland. Associated taxa include Grevillea sp., Melaleuca radula, Melaleuca scaberula, Glischrocaryon sp., Hibbertia hypericoides, Allocasuarina campestris, Calothamnus sp., Eucalyptus wandoo, and Stylidium species.

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 Thomasia sp. Green Hill 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 any 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

There are no other known threatened species or communities that occur in the habitat of Population 1. However, recovery actions implemented to improve the quality or security of Thomasia sp. Green Hill Population 1 are likely to improve the condition of its bushland habitat.

Social and economic impacts

The implementation of this recovery plan is unlikely to cause significant adverse social and economic impacts. The only known population of Thomasia sp. Green Hill occurs on private land and the landholders are amenable to managing the habitat of the species for conservation. Recovery actions refer to continued liaison between stakeholders with regard this area.

Evaluation of the Plan's Performance

The Department of Conservation and Land Management, in conjunction with the Moora District 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).

The critical habitat for Thomasia sp. Green Hill comprises:

  • the area of occupancy of the known population;
  • areas of similar habitat within 200 metres of the known population, i.e. brown clayey sand over laterite in open wandoo woodland (these provide potential habitat for natural range extension);
  • remnant vegetation that links subpopulations (this is necessary to allow pollinators to move between subpopulations);
  • 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

Very little is known about the biology and ecology of the genus Thomasia or about Thomasia sp. Green Hill. Thomasia sp. Green Hill is known to have the ability to regenerate from rootstock after grazing, and probably also following fire.

There is no information about pollinators, but work on germination rates of seed collected from both subpopulations indicates the viability of the seed produced is high. The germination rate was initially tested using boiling water and resulted in only 20-40% germination, but subsequent testing with a treatment of nicking the seed coat resulted in 100% germination.

The species is difficult to propagate from cuttings, although some clones appear to have better strike rates than others.

Threats

Thomasia sp. Green Hill was declared as Rare Flora the Western Australian Wildlife Conservation Act 1950 in October 1996 and ranked as Critically Endangered (CR) in November 1998. It is also listed as Endangered under the EPBC Act. It currently meets World Conservation Union (IUCN 2000) Red List category 'CR' under criterion B1ab(iii)+2ab(iii) (IUCN 2000), as it consists of one population with a small number of adult plants, with declining quality of the habitat. The species exists in a bush block in New Norcia and the main threats are weed invasion, fire, firebreak maintenance, chemical drift, grazing and a lack of genetic diversity.

  • Weed invasion is a threat to adult plants and seedlings at both subpopulations. Weeds suppress early plant growth by competing for soil moisture, nutrients and light. Thomasia sp. Green Hill occurs on the edge of the bush block adjacent to farmland and the site is therefore prone to weed invasion from nearby pasture.
  • Inappropriate fire regimes may affect the viability of populations, as seeds of Thomasia sp. Green Hill probably germinate 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 disturbances such as fire are needed for reproduction of this species.
  • Firebreak and fence maintenance activities threaten plants that are growing close to the firebreak and fenceline. Vehicles turning, grading, chemical spraying and other maintenance activities could affect both subpopulations of Thomasia sp. Green Hill.
  • Chemical drift or leaching of herbicide and fertiliser applications on adjacent farmland have the potential to impact both subpopulations of Thomasia sp. Green Hill.
  • Grazing by kangaroos was impacting on this species in late winter 1999, but the impact of grazing declined following rapid growth of the plants in spring of that year.
  • Grazing by sheep is a potential threat to both subpopulations if the fenceline between the pasture and the bush block is not maintained.
  • Genetic diversity of the species is limited as there are only 99 plants of this species. Genetic diversity is required to provide a species with the ability to adapt to changing conditions, such as climate.
Summary of population information and threats
Pop. No. & Location Land Status Year/No. plants Condition Threats
1a. SW of New Norcia Private (East) 1995 13
1998 16
1999 18(2)
Good Weed invasion, fire, firebreak maintenance, grazing
1b. SW of New Norcia Private (West) 1995 8
1998 50+
1999 81
Good Weed invasion, fire, firebreak maintenance, chemical drift, grazing

Guide for decision-makers

Section 1 provides details of current and possible future threats. Any on-ground works (clearing, firebreaks, roadworks etc) in the immediate vicinity of Thomasia sp. Green Hill 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.