National recovery plan for Zieria lasiocaulis

NSW National Parks and Wildlife Service, 2002
ISBN 0 731 36892 4

1. Current conservation status

Zieria lasiocaulis J. A. Armstrong ms is known from nine locations restricted to an area of about 20 square kilometres. These populations are located in Willi Willi National Park, north-west of Port Macquarie on the mid-north coast of New South Wales (NSW). The species is naturally restricted with a total population estimated at 20,000 to 25,000. The largest population of about 20,000 plants occurs over about one hectare.

Z. lasiocaulis is currently listed as Endangered (Schedule 1) on the NSW Threatened Species Conservation Act 1995 (TSC Act) and the listed as Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).

Z. lasiocaulis has been classified by Briggs and Leigh (1996) as 2V, which means it occurs over a geographic range of less than 100 km and is at risk of disappearing from the wild over a period of 20-50 years through continued depletion. A more appropriate classification is 2VCat. This specifies that 1000 plants or more are known to occur within a conservation reserve and the total known population is reserved.

2. Description

2.1 Taxonomic description

The manuscript name Zieria lasiocaulis as described by Armstrong (2002) is used in this recovery plan since a published description of the taxon was not available at the time of plan preparation. It is also described by Armstrong (1991) under the name Zieria species N.

The following description has been adapted from Armstrong and Harden (2002) and Armstrong (2002):

Z. lasiocaulis is a tall shrub or small tree up to six metres in height. The young branches are hairy between the decurrent leaf bases, and most parts of the plant are dotted with oil glands which result in plants having a strong, though not unpleasant, aroma. Leaves are opposite and usually 3-foliolate, with the central leaflet elliptic to oblanceolate, four to six cm long and one to two cm wide, more or less glabrous, and with entire margins. Inflorescences are axillary, many-flowered and shorter than the leaves. The four white petals are 3.5-4 mm long and hairy to more or less glabrous, and the calyx lobes are and about one mm long. The fruit are hairless, dotted with oil glands, and lack an appendage. Seeds are usually black, about 2.3 mm long and 1.3 mm broad. Z. lasiocaulis flowers from late autumn to spring, and fruits in summer.

Z. lasiocaulis is similar in general appearance to the more widespread Z. arborescens ssp. arborescens and Z. southwellii, but can be distinguished by the pubescence, primarily of long simple hairs, on young growth.

2.2 Taxonomic significance

The genus Zieria in the family Rutaceae consists of at least 44 species, mainly occurring in eastern Australia, and one species in New Caledonia (Armstrong 1991).

Many species of Zieria, including Z. lasiocaulis, occur as highly localised endemics. Of the 43 Australian species, 13 are listed as endangered and eight as vulnerable under the Commonwealth EPBC Act. Twenty seven species of Zieria are considered to be rare or threatened by Briggs and Leigh (1996).

In NSW, 13 of the 35 species of Zieria are listed as endangered, four as vulnerable and one as an endangered population on the schedules of the TSC Act.

3. Distribution

3.1 Current and historical distribution

Z. lasiocaulis is endemic to NSW, and is known from about nine locations restricted to an area of approximately 20 square kilometres near Mount Banda Banda and Marowin Mountain on the mid-north coast of NSW (Figure 1).

There are no historical records for Z. lasiocaulis outside the current range, suggesting that it has evolved and persisted with a naturally very restricted distribution.

 Locations of populations of Zieria lasiocaulis.

Figure 1: Locations of populations of Zieria lasiocaulis.

3.2 Tenure

All populations of Z. lasiocaulis occur within Willi Willi National Park.

Part of the area of occurrence of Z. lasiocaulis (previously Banda Banda Flora Reserve) is included in the 'Central-Eastern Australian Rainforest World Heritage Area' (DASET 1992).

4. Ecology

4.1 Habit

Z. lasiocaulis is a tall shrub or small tree up to six metres in height (Armstrong 2002).

4.2 Reproductive biology

Vegetative reproduction

Vegetative reproduction by either root suckering or sub-surface epicormic outgrowths occurs in some species of Zieria. Armstrong (2002) reports that Z. lasiocaulis does not vegetatively reproduce, however, a few shoots arising from the base of old plants of Z. lasiocaulis were seen at one location (P. Gilmour pers obs).

Breeding system

Z. lasiocaulis is probably outcrossing and self-compatible. It is generally considered to be an obligate seeder (regenerating from seed only) (Armstrong 2002). Highly variable pollen viability responses are reported, with plants at Mount Banda Banda displaying very low pollen viability (Armstrong 2002).

Flowers are produced in late winter or spring and fruit is produced in summer. Plants were recorded flowering at four years of age. This is based on the Marowin Mountain population which was burnt about January 1994 (A. Marshall pers comm). Plants that germinated following the fire were flowering profusely when surveyed in November 1998. Flowers are bisexual, and pollination is most likely by pollen- and nectar-seeking beetles (Armstrong 2002). Small native bees and several species of beetle were observed on flowers at the Marowin Mountain population (P. Gilmour pers obs).

Seed dispersal

Seeds are released explosively from the mature fruit, and possess an ant-attracting elaisome which may result in short distance dispersal by ants (Armstrong 2002; Smith 1989). Most ant dispersal of seeds is over a short disance (Gomez and Espadaler 1998).

Germination and recruitment

A number of different germination and recruitment strategies were observed in the field, all of which appear to have resulted from some form of disturbance. Many populations occur on roadsides or in areas where logging has disturbed the soil. The largest population occurs on the summit and southern ridge of Marowin Mountain in recently burnt areas. A smaller population was observed in an area that had burnt 12 to 18 months before inspection (P. Gilmour pers comm).

An interesting aspect of the Marowin Mountain site is the fact that small seedlings and young plants are present almost five years after the fire event. This may indicate that the 1994 fire did not stimulate the entire seed-bank to germinate, and some seed was able to delay germination. Such a strategy would maximise the possibility of Z. lasiocaulis recruiting after fire.

South-east of the summit of Marowin Mountain a small population of about 50 seedlings occurs in a natural gap caused by a tree fall. There were no mature plants of Z. lasiocaulis observed in this clearing or within the surrounding forest (the nearest mature plants observed were at least 200 metres away). In this case germination may have been stimulated by exposure of soil to direct sunlight and consequent heating.

Armstrong (2002) suggests that Zieria species generally have short seed viability, but field observations of populations of Z. lasiocaulis suggest a persistent soil seed-bank. A study by Auld et al. (2000) showed evidence that Zieria involucrata has a persistent soil seed-bank of between one to two decades. Research is required into the seed-bank dynamics of Z. lasiocaulis to determine the longevity and relative importance of soil-stored seed, and the importance of disturbance for stimulating germination.

Fire response

Plants of Z. lasiocaulis are probably killed by fire (Armstrong 2002), although if basal shoots can occur (see Vegetative reproduction section above) it is possible that individuals could survive low intensity fires. Germination of seed may be stimulated by appropriate fire regimes.

4.3 Population structure

Results of population monitoring undertaken to date has plants in a range of maturity classes ranging from seedlings through to senescent. Comparison with earlier survey data apparently shows aging of plants in the population, with some sites changing from all seedlings to all immature plants.

There are no data on the longevity of individuals, but it is estimated at 20 to 30 years, based on the approximate age of eucalypt regrowth at sites where mature Z. lasiocaulis occur (P. Gilmour pers comm).