3.3 Acacia baueri Benth. subsp. baueri
The distribution of Acacia baueri subsp. baueri occurs from Bundaberg to Sydney. In Queensland A. baueri subsp. baueri is restricted to the coastal plain not more than 20 km from the coast with a range along the coast of approximately 320 km and with an area of occurrence of approximately 6,400 km2. It has been recorded from SF 581 SA 1 (Beerwah) and from Burrum Coast, Mooloolah River, Cooloola and Moreton Island National Parks, and from Pine Ridge Conservation Park. No information is available on population size. Current or perceived potential threats to the continued survival of A. baueri subsp. baueri are considered to be loss of habitat and inappropriate fire regimes.
3.3.2 Species description and identification
The genus Acacia is widespread throughout the tropical and subtropical regions of the world (excluding Europe) with approximately 1200 species (Mabberley 1997). In Australia it comprises approximately 900 species of shrubs and trees, which are widely distributed throughout the continent with a large range of foliage and flower types.
Acacia baueri Benth. was formally described in 1842 from material collected somewhere along the east coast of Australia. The species belongs to the section Lycopodiifoliae which are a very distinctive group within the Acacias as they have their phyllodes arranged in regular whorls along the stem.
There are two subspecies of A. baueri, A. baueri subsp. baueri and A. baueri subsp. aspera. A. baueri subsp. aspera is chiefly known from the Blue Mountains, New South Wales and is not considered in this report. The botanical description of Acacia baueri subsp. baueri is as follows:
Erect shrub less than 0.5 m tall; branchlets terete, glabrous or with indumentum of sparse to moderately dense antrorse white hairs, sometimes tuberculate. Stipules up to 0.8 mm long, often absent; pulvinus 0.4-0.6 mm long; phyllodes 6-8(9) per whorl, very rarely scattered, straight or recurved in upper half, or only at apex, mucronate, slightly laterally compressed, 0.7-1.6 cm x 0.05-0.1 cm, glabrous or occasionally tuberculate, or with scattered white hairs similar to those of branchlets, obscure longitudinal nerve on each side of phyllode. Heads of 10-15 flowers, peduncles 0.2-1.5 cm long; receptacle pubescent; bracteoles ca 1 mm long with few hairs; flowers golden-yellow, 5 merous. Pods linear, sessile, up to 2.5 cm x 0.2-0.3; glabrous or with extremely sparse appressed hairs mainly at base, seeds longitudinal, more or less cylindric, 4-5.5 mm x 2-2.5 m. (Stanley & Ross 1983). For a more detailed description refer to Pedley (1972). For an illustration see Morrison and Davies (1991).
Acacia baueri subsp. baueri is a very distinctive Acacia with its phyllodes in whorls of 6 to 9 along the stem. For this reason it is unlikely to be confused with any other species within its range in Queensland.
3.3. Current conservation status
Acacia baueri is presently listed on the schedule of the Queensland Nature Conservation Act 1992 as “vulnerable wildlife”. It is also listed on Schedule 1 Part 2 (vulnerable) of the Commonwealth Endangered Species Protection Act 1992. The species has not been assigned a national conservation status by ANZECC (1993)
3.3.4 Distribution and abundance
Acacia baueri subsp. baueri was not surveyed during the present study. Acacia baueri subsp. baueri occurs from Bundaberg to Sydney. In Queensland A. baueri subsp. baueri is restricted to the coastal plain not more than 20 km from the coast with a range along the coast of approximately 320 km from just south of Bundaberg to Burleigh Heads on the Gold Coast.
Details from Queensland Herbarium specimens of A. baueri subsp. baueri are listed in Appendix 1.2. Twenty-four specimens have been collected from approximately 16 sites. Nine of the earliest records (prior to 1970) give only a general locality which is inadequate to accurately relocate the collection site.
A. baueri subsp. baueri is recorded from Kinkuna and Woodgate sections of the Burrum Coast N.P. (3 records), Mooloolah River N.P. (1 record), Cooloola N.P. (1 record) and Moreton Island (1 record) N. P., and Pine Ridge Conservation Park(1 record). The species is also recorded from Fraser and North Stradbroke Islands. A. baueri subsp. baueri has been recorded on a roadside embankment from State Forest Scientific Area within SF 561 (Fty 1655) (1 record). Although not recorded A. baueri subsp. baueri is highly likely to be present in Noosa N.P. Recently A. baueri subsp. baueri has been recorded at the Tugun Refuse Tip (Gold Coast).
There is no information available on population sizes, however, it is generally reported as being rare or occasional at collection sites.
A. baueri subsp. baueri is restricted to the coastal lowlands mostly on infertile, often seasonally waterlogged sandy soils in heathlands, shrublands and low open woodlands. Other species most commonly recorded at the collection sites included: Banksia aemula, Banksia serrata, Banksia oblongifolia, Eucalyptus racemosa and Eucalyptus umbra.
At the recent recorded site at the Tugun Refuse Tip it is growing on a low isolated rise in a broad dune swale with sapric sandy soil. The vegetation is a heathland. The common shrub and ground species included: Banksia oblongifolia, Baeckea frutescens, Leptospermum semibaccatum, L. whitei, Leucopogon leptospermoides, Lepyrodia interrupta, Caustis recurvata, Restio tenuiculmis and Stylidium graminifolium.
A. baueri subsp. baueri is a perennial shrub up to 0.5 m high. The longevity of individual plants is unknown. The main method of reproduction is by sexually produced seeds. The species is not known to be capable of resprouting from the stem base or other underground organs.
Flowering has been recorded from February to May, August and October to December. A. baueri subsp. baueri may flower at most times of the year, but the principal flowering season is spring to early summer. No pollinators have been reported for A. baueri subsp. baueri. However studies of pollinators of other Acacia species indicate they are primarily insect pollinated (Bernhardt 1989). Fruits have been recorded from June to October and December. The fruit splits soon after maturing, releasing the seed. It is not known if the opening of the capsule forcibly ejects the seed or whether the seeds just fall to the ground. The seed has a fleshy attachment on the outside of the seed coat. It is suggested that such attachments promote secondary dispersal by ants (Berg 1975).
When released from the mature pods, seeds are dormant. As with most hard-seeded leguminous species, this dormancy is due to seed coat impermeability. The genus Acacia contains numerous species whose germination is promoted by heat from fire. With these seed characteristics A. baueri subsp. baueri would accumulate a persistent seed bank in the soil during inter-fire periods. The length of seed viability in the soil is unknown.
Fire is a major environmental factor in Australia, particularly in dry sclerophyll forest. Different intensities, frequencies and seasonal occurrences of fire will affect the population dynamics of this species. Although little is known about the fire ecology of A. baueri subsp. baueri, it is suggested that fire plays an important role in the recruitment pattern of this species.
There have been in the past large tracts of potential habitat cleared for urban development, especially on the Gold and Sunshine Coast. Clearing and drainage of habitat for urban development is continuing to occur especially in the south of its range on the Gold and Sunshine Coasts.
The limited knowledge about the effect of fire and this species’ response makes it difficult to assess the total impact of varying fire regimes. However, too frequent a fire regime would certainly lead to a gradual decline in the population. Sufficient time would be required between fires to allow new seedlings to flower and replenish the soil seedbank. Sufficient soil heating is also needed during fires to break seed dormancy and allow germination after fires.
3.3.8 Management, research and conservation measures
Additional survey work is required to determine what populations are left and what would be the appropriate course of action for conserving the species. Information on population sizes, fecundity and general ecology is required. Areas worthy of investigation include any remnant wallum vegetation on the Gold and Sunshine Coast, and coastal wallum country between Maryborough and Tin Can Bay.
Gold Coast City Council should be encouraged to preserve the remnant heathland on the Tugun Refuse Tip Reserve. The Pine Ridge Conservation Park presently offers the most secure habitat of A. baueri subsp. baueri in the Gold Coast region. The population should be assessed and monitored.
Fire intensity, frequency and seasonality are important factors in determining the long term population levels of most hard-seeded leguminous species. It is important to understand how A. baueri subsp. baueri responds to differing fire regimes in its habitat. Research is required into the fire ecology, reproduction biology and the population dynamics of this and other Acacia species.