3.5 Acacia perangusta (C.T. White) Pedley
Acacia perangusta is endemic to south east Queensland. It is known from two disjunct localities approximately 240 km apart. A. perangusta has been recorded from the Maryborough - Hervey Bay area and from Rochedale, Victoria Point, Mt Cotton and Beenleigh in the Greater Brisbane area. It has been recorded from SF 1294 (Fty 1705) SF 682 (Fty 1579), SF 215 (Fty 821) and Springwood Conservation Park. No information is available on population sizes. Current or perceived threats to the continued survival of A. perangusta are considered to be loss of habitat, an inappropriate fire regime and grazing of domestic cattle.
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 perangusta was originally described as a variety of the common species A. fimbriata (Brisbane golden wattle) (White 1939). In his revision of the Acacias of Queensland Pedley (1978) raised this variety to the rank of species. The botanical description of Acacia perangusta is as follows:
Shrub or small tree up to 6 m tall; branchlets reddish, slender, angular, glabrous. Pulvinus ca 0.5 mm long; phyllodes linear, apex acute or occasionally obtuse, 3-7.5 cm x 0.11-0.16 cm, 20-55 times as long as broad, glabrous, midnerve prominent; gland small but projecting from margin, 0.7-1.4 cm from base. Heads of 9-12 flowers in glabrous axillary 15-20-branched racemes, axis 2.5-3 cm long, peduncles 2-2.5 mm long; flowers lime-yellow, (4-) 5-merous, rather widely spreading. Pods slightly constricted between seeds and raised over them alternately on each side, 7.5 cm x 0.5 cm, glabrous and slightly glaucous; seeds longitudinal (Stanley & Ross 1983). For a more detailed description refer to Pedley (1978).
Acacia perangusta is clearly closely related to and is often confused with A. fimbriata. However, A. perangusta differs from A. fimbriata in having narrower glabrous phyllodes with the gland further from the phyllode base, glabrous flowers and narrower pods (Pedley 1978).
3.5.3 Current conservation status
Acacia perangusta is presently listed on the schedule of the Queensland Nature Conservation Act 1992 as “vulnerable wildlife”. The species has been assigned a national conservation status of V (vulnerable) by ANZECC (1993). It is also listed on Schedule 1 Part 2 (vulnerable) of the Commonwealth Endangered Species Protection Act 1992.
Acacia perangusta was not surveyed during the present study. Details from Queensland Herbarium specimens of A. perangusta are listed in Appendix 1.4. Twenty specimens of A. perangusta have been collected from two disjunct localities approximately 240 km apart. As far as can be ascertained, this distribution pattern is natural and is not related to habitat reduction or fragmentation from human activity. It has been recorded from the Maryborough - Hervey Bay area (5 specimens), and from Rochedale, Victoria Point, Mt Cotton and Beenleigh in the Greater Brisbane area (15 specimens).
Two specimens from the Brisbane area are from Daisy Hill State Forest (SF 215 Fty 821) and one from Springwood Conservation Park. The remaining twelve specimens are either from roadsides, freehold land or other land of unknown tenure. Daisy Hill State Forest is now a non-commercial forest and is presently managed by the Department of Natural Resources for recreational use. A. perangusta was noted as common at the site of collection in Daisy Hill State Forest in 1993.
Four of the five specimens from the Maryborough - Hervey Bay area have insufficient information to accurately locate the collection site. Butler and Neate (1996) reported that the distribution of A. perangusta in the Toogoom area is discontinuous and confined to forest remnants, road verges, fence lines, unimproved freehold land and on crown land utilised for extractive industries. It is not reported to occur in any conservation reserve in this area. A. perangusta is known from two state forest sites:
1) SF 1294 (Fty 1705) - Lenthall’s Dam. This site was first recorded in February 1997. Recently it has been reported that A. perangusta is relatively common on the ridge north of the dam wall in eucalypt open-forest near a vine thicket community (J. Aridis, Department of Natural Resources). This species is also reported on freehold land downstream of the dam wall along the Burrum River (Moran 1997).
2) SF 683 (Fty 1579) This site is not vouchered, although specimen AQ587996 may have come from this site. Butler and Neate (1996) reported that A. perangusta is relatively common within the State Forest.
In the Toogoom area, A. perangusta has been observed on ridges and slopes with gravelly thin topsoils (less than 30 cm deep) over lateritic rock layers (Butler and Neate 1996). The vegetation tends to be open-forests dominated by Eucalyptus siderophloia. Other tree species present included Corymbia citriodora, C. intermedia and Lophostemon suaveolens.
In the Brisbane area A. perangusta has been recorded on undulating terrain with gravelly/sandy soil, sandstone ridges and on alluvial soils along creek banks. The vegetation structure is a woodland or open-forest. The more frequent tree species recorded are Eucalyptus tindaliae and Corymbia henryi. Other tree species recorded at the sites include E. carnea, E. planchoniana, E. fibrosa and E. microcorys.
Acacia perangusta is a perennial shrub reaching 6 m high. The longevity of individual plants is unknown. The main method of reproduction is by sexually produced seeds. Butler and Neate (1996) reported A. perangusta can produce abundant seed within 2 to 3 years of germination. The species is known not to be capable of resprouting from the stem base or other underground organs.
Flowering has been observed from June to September. No pollinators have been reported for A. perangusta. However studies of pollinators of other Acacia species indicate they are primarily insect pollinated (Bernhardt 1989). Fruits have been recorded in October. 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).
Most Acacia species release their seed from the mature pods in a dormant state. Heating of the soil during the passage of a fire is the primary mechanism for breaking seed dormancy and allowing germination. With these seed characteristics, A. perangusta would accumulate a persistent seedbank in the soil during inter-fire periods. The length of viability of seed in the soil is unknown.
Individuals of A. perangusta have been observed to be killed by fire (Butler and Neate 1996). Fire is a major environmental factor in Australia, particularly in dry sclerophyll forest. Different intensities, frequencies and seasonal occurrences of fire will effect the population dynamics of this species. Although little is known about the fire ecology of A. perangusta it is suggested that fire plays an important role in the recruitment pattern of this species.
It has been noted that A. perangusta responds to soil disturbance and seedlings are grazed by domestic cattle (Butler and Neate 1996).
There have been in the past large tracts of habitat cleared for urban and agricultural development. Clearing of habitat for urban development is continuing to occur in the Maryborough - Hervey Bay and Brisbane areas.
Butler and Neate (1997) reported that in the Maryborough-Hervey Bay area that A. perangusta is subjected to grazing by cattle and suggested that this has severely depleted the population of A. perangusta.
The limited knowledge about the effect of fire and 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 seedlings to flower and replenish the soil seedbank. Soil needs to be heated sufficiently during fires to break seed dormancy to allow germination after fires.
3.5.8 Management, research actions and conservation measures
Survey work is required to determine which populations remain and what would be the appropriate course of action for conserving the species. In the southern end of its distribution there are within the vicinity of presently vouchered sites a number of local council reserves that need to be investigated.
Most of the populations in the southern part of its range are near or within urban areas. Future management of these habitat remnants will be important to the long term survival of the species in this part of its range.
It is important to understand how A. perangusta responds to differing fire regimes in its habitat. Research is required into the fire ecology, reproduction biology and the population dynamics of the species.
Monitoring and research are also required to determine the long term effect of grazing of domestic stock on the species’ ability to maintain a viable population.