Swamp She-oak - profile

Indicative distribution

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Key:

known

predicted

The areas shown in pink and/purple are the sub-regions where the species or community is known or predicted to occur. They may not occur thoughout the sub-region but may be restricted to certain areas. ( click here to see geographic restrictions). The information presented in this map is only indicative and may contain errors and omissions.

Scientific name: Casuarina obesa

Conservation status in NSW: Endangered

Commonwealth status: Not listed

Profile last updated: 14 Oct 2024

Description

The Swamp She-oak is a much-branched shrub or small tree, 3 to 15 metres tall (though most plants in NSW are less than 8 metres), with deeply-fissured, corky bark. The branchlets are up to 30 centimetres long and 2 to 3 millimetres in diameter, with the leaves reduced to about 16 minute teeth that circle each joint. Each segment between the slightly spreading teeth are 8 to 14 millimetres long. The flowers are small, the male ones are produced in a dense spike 5 to 6 centimetres long on the ends of the branchlets. The fruits are clustered in a cone 10 to 20 millimetres long.

Distribution

The Swamp She-oak is widespread in southern Western Australia and plants from this population are widely planted (including in NSW) for agroforestry, particularly in salt-effected areas, and as a street tree. The eastern population is much more restricted with only scattered occurrence in the Wimmera and Mallee in Victoria, and one occurrence, at Lake Benanee in New South Wales. The NSW population, consisting of only male plants was first discovered in 1951, but was believed to have been cleared prior to 1979 (and hence considered extinct in NSW). In 1999, it was confirmed to still occur at the site, although as all plants are females it is believed this is a different population. The plants occur at three discrete locations along just over a kilometre of the north-western shoreline of the lake, to the south west of the original population.
A recent record from near Moama in the South West Plains Botanic Division has not been confirmed.

Habitat and ecology

Requires moist, slightly saline soils. Potential habitats include shorelines of permanent, ephemeral or relict lakes. These systems may be freshwater or saline-influenced judging by the present distribution of the species.
In NSW, associated species include River Red Gum (Eucalyptus camaldulensis), Black Box (E. largiflorens) and River Cooba (Acacia stenophylla) with the understorey dominated by grasses and sedges.
Flowering time is not known in NSW. Flowers are seldom seen in Victorian populations but have been recorded throughout the year in Western Australia.
Recent surveys at Lake Benanee populations report suckering of Casuarina obesa (although suckers were heavily browsed by stock, rabbits and kangaroos).
Seedlings of Casuarina obesa in Western Australia have been found to be highly tolerant of saline waterlogged conditions.
Plants can develop an unusual thickness of the branchlets and exceptionally large fruits, characters that are due to insect and fungal infection affecting particular stands. NSW populations have also recently suffered from borer attack, possibly associated with drought conditions in recent years.
Segregation of male and female stands of the species occurs.
Population sizes across the range of the species vary from one plant to over 200 trees scattered in groups of three to six; has been observed growing in extensive thickets; some trees are very old and apparently healthy.

Regional distribution and habitat

Click on a region below to view detailed distribution, habitat and vegetation information.

Riverina

Threats

Serious lack of regeneration due to heavy grazing of suckers, and soil compaction retarding potential suckering or seedling recruitment.
Salination of sites, with increasing irrigation developments and less frequent natural flooding.
Invasion of exotic species such as Onion Weed (Asphodelus fistulosus), which has changed community composition and out competed regeneration.
Physical damage to plants; rabbit burrowing has undermined root systems, stock has caused mechanical damage to trees, with broken limbs and dieback evident.
Dieback and senescence in remaining populations is a concern.
Reproductive viability of remaining populations is a concern.
Clearing of stands for cropping and agricultural development.
Water management at Lake Benanee may influence the survival of this species. Until recently the lake had been permanently flooded but has recently been drained and then re-filled as part of water-saving operations. There may be changes to the water management regime of Lake Benanee in future years.

Recovery strategies

A Saving Our Species conservation project is currently being developed for this species and will be available soon. For information on how you can contribute to this species' recovery, see the Activities to assist this species section below.

Activities to assist this species

Facilitate regeneration by excluding stock, rabbits, kangaroos and humans from the population.
Undertake weed control in habitat areas.
Promote active revegetation of trees by planting seedlings from local seed stock, transplanting root suckers; a site Lake Benanee has been recommended as suitable for active revegetation.
Monitoring of the health of the trees is needed to determine impacts of flooding/drying cycle and this should influence the management of water within Lake Benanee.
Conduct seed germination trials.

Information sources

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992) Plants of Western New South Wales. (Inkata Press, Sydney)
Cupper, M.L. and Sluiter, I.R.K. (1999) A report on the status of Swamp Sheoak (Casuarina obesa Miq. in Lehm.) in south-western New South Wales. Report to NSW NPWS. (Ogyris Pty Ltd., Mildura)
Jessop, J.P. and Toelken, H.R. (eds.) (1986) Flora of South Australia. Part I. (South Australian Government Printing Division, Adelaide)
Lehmann, J.G.C. (1845) Casuarina obesa Miq. Plantae Preissianae 1: 640.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennet, E.M., Lander, N.S and Macfarlane, T.D. (1987) Flora of the Perth Region. Part 1. (Western Australian Herbarium and Department of Agriculture, Perth).
Margules and Partners Pty Ltd, P. and J. Smith Ecological Consultants and Department of Conservation, Forests and Lands, Victoria (1990) River Murray riparian vegetation study (Murray-Darling Basin Commission, Canberra)
Ogyris Pty. Ltd. (2008) A Report on the Purported Ill-Health of Casuarina obesa Miq. in Lehm. at Lake Benanee, Southwest New South Wales - November 2008. Report to NSW Department of Water and Energy.
Porteners, M. and Robertson, G. (2003) Threatened Plants in Western New South Wales: Information Review. (NSW NPWS, Hurstville)
Pressey, R.L., Cohn, J.S. and Porter, J.L. (1990) Vascular plants with restricted distributions in the Western Division of New South Wales. Proceedings of the Linnean Society of New South Wales 112: 213-227
Van der Moezel, P.G., Watson, L.E., Pearce-Pinto, G.V.N. and Bell, D.T. (1988) The response of six Eucalyptus species and Casuarina obesa to the combined effect of salinity and waterlogging. Australian Journal of Plant Physiology 15(3): 465-474
Walsh, N.G. and Entwisle, T.J. (1998) Flora of Victoria; Volume 3, Dicotyledons Winteraceae to Myrtaceae. (Inkata Press, Melbourne)
Wilson, K.L. and Johnson, L.A.S. (1989) Casuarinaceae. In: George, A.S. (ed) Flora of Australia vol. 3 pp. 100-189. (Australian Government Publishing Service, Canberra)
Wilson, K.L. and Johnson, L.A.S. (2000) Casuarina. Pp. 508-510, 624 in Harden, G.J. (ed) Flora of New South Wales. Volume 1. Revivsed Edition. (University of New South Wales Press, Sydney)