3.4 Acacia grandifolia pedley
Acacia grandifolia is endemic to south east Queensland where it occurs in an restricted area between Mundubbera, Coalstoun Lakes and Proston in the Burnett Pastoral District. It covers a range of approximately 100 km and encompasses an area of occurrence of approximately 4200 km2. It has been recorded from six State Forests as well as along road verges, freehold and leasehold land. It is not recorded in any conservation reserve. No quantitative information is available on population sizes. However, anecdotal evidence indicates that it is common within its restricted range. The species is not threatened by extinction in the short to medium term. However, the species may be potentially threatened in the long term by clearing for agricultural development, grazing of domestic cattle and inappropriate fire regimes.
3.4.2 Species description and identification
The genus Acacia is placed in the family Mimosaceae. 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 grandifolia Pedley was formally described in 1978 from material collected in the Mundubbera area (Pedley 1978). The botanical description of Acacia grandifolia is as follows:
Tree up to ca 8 m tall; branchlets stout angular with dense whitish indumentum of erect hairs, extending to pulvinuses and peduncles. Pulvinus 6-10 mm long; phyllodes more or less straight, asymmetrically elliptic, 9-15 cm x 2.5-5 cm, ca 3-4 times as long as wide, up to 7.5 cm wide and twice as long as wide on young plants, indumentum of spreading hairs, 3(-4) longitudinal nerves more prominent than the rest, secondary nerves widely spaced, strongly anastomosing; gland basal, large. Spikes in pairs in upper axils, peduncles thick, 5-8 mm long, velvety; spikes dense, 5-10 cm long, rachis velvety; flowers golden-yellow, 5 merous. Pods flat, 6 cm x 0.6 cm; tomentose; seeds shining, longitudinal, ca 4 mm x 2 mm, rather thick; funicle pale yellow. (Stanley & Ross 1983). For a more detailed description refer to Pedley (1978).
Acacia grandifolia is closely related to and resembles A. longispicata and A. crassa (L. Pedley pers. comm.). A. grandifolia can be distinguished from these species by having broad phyllodes that are 3 to 4 times as long as wide with very conspicuous vein reticulum on the phyllode, and the nerve islands less than 3 times as long as wide. The other two species have narrower phyllodes that are 4 to 18 times as long as wide with a vein reticulum that is not very conspicuous and the nerve islands more than 3 times as long as wide.
Acacia grandifolia Pedley is presently listed on the schedule of the Queensland Nature Conservation Act 1992 as “vulnerable wildlife”. However, a change in the conservation status is pending, from Vulnerable to Rare on the Queensland schedule. 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 grandifolia was not surveyed during the present study. A. grandifolia is endemic to south east Queensland. It occurs in a restricted area between Mundubbera, Coalstoun Lakes and Proston in the Burnett Pastoral District. It covers a range of approximately 100 km and encompasses an area of occurrence of approximately 4200 km2.
Details from Queensland Herbarium specimens of Acacia grandifolia are listed in Appendix 1.3. There are 28 specimens which have been collected from approximately 19 sites. Another 46 sites are recorded in the CORVEG database. The species is known from 6 State Forest areas (SF 210 Fty 702, SF 249 Fty 1693, SF 220 Fty 9980, SF 132 Fty 1348, SF 255 Fty 1025, SF 1344 Fty 1534) and on Brian Pastures Research Station. It is also recorded from leasehold land and road verges in the area. It has not been recorded in any conservation reserve. There is one record from the Dawson Range near Dingo approximately 250 km NW of the Mundubbera district. This record is based on juvenile material that is atypical of this species and needs to be confirmed when more material becomes available.
There is no quantitative data on population sizes. Originally A. grandifolia was considered to be an uncommon species within a narrow range. However, in recent times it has been found to be locally common and very abundant within the area (T. Ritchie pers. comm., P. Grimshaw pers. comm.).
Acacia grandifolia grows in hilly terrain on hillslopes of varying aspects and slope, hillcrests, gullies and plains on usually shallow well drained soils, sandy loam to clay loam in texture derived from sandstones and acidic volcanics. The vegetation is tall woodland or open-forest with a range of floristic associations. The most frequently recorded tree species are Eucalyptus crebra, Corymbia citriodora, C. trachyphloia and E. exserta.
3.4.6 Life history and ecology
Acacia grandifolia is a small tree reaching 8 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 observed from July to October. No pollinators have been reported for A. grandifolia. However studies of pollinators of other Acacia species indicate they are primarily insect pollinated (Bernhardt 1989). Fruits have been recorded from October to November. 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).
Seeds are dormant when released from the mature pods. 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. grandifolia 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 effect the population dynamics of this species. Although little is known about the fire ecology of A. grandifolia it is suggested that fire plays an important role in the recruitment pattern of this species. There is no quantitative information available on this species’ fire requirements.
Anecdotal evidence indicates that this species proliferates in areas of disturbance. It is reported to been transported in gravel used in maintenance of road verges within its present range (P. Forster pers. comm.). Pedley (1978) commented that grazing of domestic cattle may restrict the establishment of Acacia seedlings.
In recent years the species has been observed to be very common at a number of localities within its restricted range. The species’ continued existence in the wild in the short to medium term does not appear to be threatened. However, with no populations within areas set aside for the conservation of the natural habitat, the species may be potentially threatened in the long term by the management of its habitat for other uses.
Populations on freehold and leasehold land are potentially threatened by clearing for agricultural development and by grazing of domestic cattle.
The species appears to respond favourably to some degree of habitat disturbance. However there is no information on the effect of varying levels of habitat disturbance.
The occurrence of fire in the habitat of A. grandifolia should not be viewed as being incompatible with the long term survival of the species. However the lack of ecological information about this species response to fire makes it impossible to assess what would be an appropriate level of frequency and intensity for the long term benefit of the species. If fires are too frequent, the plants will have insufficient time to build-up a soil seedbank to replace plants that have been killed in the fires, and this will lead to population declines.
3.4.8 Management, research and conservation measures
No populations are known to be in conservation reserves. Negotiations should be undertaken with landowners or Department of Natural Resources to reserve at least some of the population.
It is important to understand how A. grandifolia responds to differing fire regimes in its habitat. Research is required into the fire ecology, reproduction biology and the population dynamics of the species.
The effect of grazing of domestic stock of the population dynamics of A. grandifolia needs to be assessed if grazing on crown land continues in areas where this species grows.