Trigwell's Rulingia (Rulingis sp. Trigwell Bridge) 2003-2008

Interim recovery plan no. 148
Gillian Stack and Andrew Brown
Department of Conservation and Land Management, WA, 2003

1. Background

History

Rulingia sp. Trigwell Bridge was first collected from private property by R. Smith in 1989 and is still the only known wild population known. Plants grow in cracks on a lateritic ridge in an area that was used for grazing sheep until 1992. As just two wild plants are known a translocation project coordinated by the South West Region Threatened Flora Recovery Team (SWRTFRT) is underway and includes putting plants back into the wild population and up to six other self-sustaining populations in areas of similar habitat. Research into the fire response of Rulingia sp. Trigwell Bridge seed has confirmed that fire stimulates germination of the species. This knowledge has been used during germination trials in two new translocated populations (Populations 4T and 5T).

Due to the extremely small population size, restricted distribution and threats associated with growing in a specialized habitat, Rulingia sp. Trigwell Bridge was declared as Rare Flora in November 1993, and ranked as Critically Endangered in September 1995.

Description

A full taxonomic description for the species has been prepared by Dr. Gordon Guymer, Senior Botanist, Queensland Herbarium, however, as the species has not yet been formally described, it is not currently available.

Rulingia sp. Trigwell Bridge is a small shrub up to 1.5 m tall and 1 m wide with branches and leaves covered in star-shaped hairs that are typical of other species in the genus. The narrow stipules are deciduous and the upper stipules are divided into thin lobes. The terminal flowers are creamy white, and petals are equal or shorter in length than the sepals. The broad-based petals embrace the stamens and the upper portion of the petals forms a ligule (Brown et al. 1998).

Distribution and habitat

Rulingia sp. Trigwell Bridge is endemic to Western Australia where it is known from a single wild population in the West Arthur area over a range of less than 1 km. New translocated populations are being established near the known population.

In its natural state the species is found on a lateritic ridge supporting open low jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) woodland, with two mature plants growing in small fissures in the rock. It is not known whether this is the species' preferred habitat or if these plants have survived because they were less accessible to grazing animals, including sheep and rabbits. Associated species include Banksia grandis, Xanthorrhoea preissii, Macrozamia riedlei, Sollya heterophylla and Acacia pulchella.

Native plant species at the translocation sites are largely the same as taxa associated with the wild population, but soils differ in being laterite rich rather than an exposed laterite ridge. Translocated plants appear to be surviving well at these new sites.

Biology and ecology

In 1995 staff from the Botanic Garden and Parks Authority (BGPA) conducted research to determine seed viability and seed production capability of the two natural plants. They found that 60% of flowers produce capsules, with an average of 6.5 seeds per capsule. This results in a seed production capacity of approximately 5000 seeds. Laboratory analysis of the collected seeds indicated 100% germination in a nutrient enriched medium.

Fire research has been conducted by Wellington District in 2000, 2001 and 2002. Results suggest that a high intensity burn of greater than 50°C for a duration of more than ten minutes is needed for optimum germination of Rulingia sp. Trigwell Bridge seed in the field. There were indications that soil-stored seed was still present and viable after at least seven years.

Threats

Rulingia sp. Trigwell Bridge was declared as Rare Flora in November 1993 and ranked as Critically Endangered (CR) in 1995. It currently meets World Conservation Union (IUCN, 2000) Red List Category 'CR' under criteria A1c; B1ab(iii)+2ab(iii); C2a(i); D as there has been an estimated population size reduction of 90%; the extent of occurrence is estimated to be less than 100 km2 and the area of occupancy less than 10 km2; the species is known to exist at a single wild location with a continuing decline in the quality of habitat and the single known population contains fewer than 50 mature individuals.

The species is currently known from one adult and two juvenile plants in single known natural population, and several hundred plants in five translocated populations. In its natural state the species appears to have very specific habitat requirements with the low number of extant plants and its restricted distribution being a major threat to its survival. Other threats include a lack of recruitment in the natural population, poor genetic diversity, inappropriate fire regimes, grazing and weeds.

  • Restricted distribution is a serious threat to Rulingia sp. Trigwell Bridge as a single event such as clearing, disease or senescence could result in the extinction of the natural population. However, it is hoped that translocated populations will become self-sustaining and contribute to the long-term survival of the species.
  • Lack of natural recruitment threatens this species. The reasons for this low level of recruitment are not certain, but may include an absence of high-intensity fire needed to germinate soil-stored seed.
  • Poor genetic diversity is likely to result from the low number of plants in the wild population. There are now just two adult plants in the wild population and this represents an extremely limited gene pool (although there may be additional genetic variation in the soil-stored seed bank). Low genetic diversity reduces the species' ability to adapt to changes in its environment.
  • Inappropriate fire regimes may affect the viability of populations. It is known that seed of Rulingia sp. Trigwell Bridge germinates following fire and the soil seed bank would rapidly be depleted if fires recur before juvenile plants reach maturity and replenish the soil seed bank. Conversely, it appears from fire research that occasional high intensity fires are needed for reproduction of the species. Population 1 is protected from fire by the surrounding exposed rock, and through the low fuel levels associated with the habitat.
  • Grazing by rabbits (Oryctolagus cuniculus), sheep, kangaroos and 'twenty eight' parrots (Barnardius zonarius semitorquatus) has previously been a major threat to Population 1. Steps have been taken to reduce this threat, and annual rabbit control is required. Insects also impact Rulingia sp. Trigwell Bridge and populations may require protection from this threat.
  • Weed invasion is a minor threat to Population 1. Weeds suppress early plant growth by competing for soil moisture, nutrients, and light. However, as Population 1 occurs on rocky exposed habitat there are relatively few weeds. Those that are there are readily managed by hand weeding.
Pop. No. & Location Land Status Year/No. plants Condition Threats
1. NE of Boyup Brook Private Property 1995 4
1998 1 (2)
2001 3
2002 2
Moderate Lack of natural recruitment, inappropriate fire regimes, weeds, grazing
1T. NE of Boyup Brook Private Property 1998 49
2001 42
2002 41
Healthy Inappropriate fire regimes, weeds, grazing poor recruitment
2T. NE of Boyup Brook Nature Reserve 1998 89
2001 46 (18)
2002 37 (73)
Healthy Inappropriate fire regimes, grazing, firebreak maintenance, weeds
3T. ESE of Collie Proposed Conservation Park 1998 40
2001 54
2002 52
Moderate Inappropriate fire regimes, grazing, poor recruitment
4T. S of Darkan Nature Reserve 2001 (17)
2002 (5)
Healthy Inappropriate fire regimes, grazing
5T. Conservation Park 2002 (223) Healthy Inappropriate fire regimes, grazing

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 Rulingia sp. Trigwell Bridge comprises:

  • the area of occupancy of the wild population;
  • the area of occupancy of translocated populations;
  • areas of similar habitat within 200 metres of known populations, i.e. open jarrah and marri woodland associated with laterite (these provide potential habitat for natural population expansion);
  • corridors of remnant vegetation that link populations (these are necessary to allow pollinators to move between populations); 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).

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 for wild and translocated populations is habitat critical and that all populations are important.

Benefits to other species/ecological communities

There are no threatened ecological communities in the immediate vicinity of Rulingia sp. Trigwell Bridge. However, recovery actions put into place for the species will benefit the remnant bushland habitat in which it occurs.

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 Rulingia sp. Trigwell Bridge 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.

Social and economic impacts

The implementation of this recovery plan is unlikely to cause significant adverse social and economic impacts. Although the single natural population of the species occurs on private property, the landowner is working closely with DCLM in providing protection and a ringlock fence was erected around the population in1992 and nursery grown plants have been translocated back into the area. Four of the five translocated populations are on Conservation reserves.

Evaluation of the Plan's Performance

The Department of Conservation and Land Management (DCLM), in conjunction with the Recovery Team will evaluate the performance of this IRP. In addition to annual reporting on progress with listed actions and comparison against the criteria for success and failure, the plan is to be reviewed within five years of its implementation.

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 Rulingia sp. Trigwell Bridge 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.