Australian forest profiles: Casuarina
The family Casuarinaceae occurs naturally in Australia, Southeast Asia and the Pacific and comprises four genera and 90 species. Australia has 66 species in three genera: six in Casuarina, 59 in Allocasuarina and one in Gymnostoma. Commonly called she-oaks (and sometimes oaks) because of the similarity of their timber to that of European oaks, casuarinas are a distinctive part of many Australian coastal and riverine landscapes.
The word ‘casuarina’ is derived from the Malay word for cassowary, kasuari, and is a reference to the similarity of the tree’s drooping branches to the feathers of the bird. Casuarinas also bear a resemblance to pine trees, with needle-like foliage and woody fruits. The foliage, however, is not composed of true leaves but rather of green, jointed branchlets that function like leaves. The true leaves are tiny, tooth-like structures protruding from around the top of each joint.
Only some casuarina species form forest communities1; others are too short or sparsely distributed to be classified as forest. Most casuarina forests are low in height, sometimes with a dense, shrubby understorey. The tallest casuarina forests occur along rivers, where trees can grow to more than 20 metres.
Casuarina forests occur as woodlands or open forests over more than 2.2 million hectares and make up about 1.5% of Australia’s total forest area.
Table 1 shows that the total area of casuarina forest increased by nearly a quarter of a million hectares between 2003 and 2008, mainly as a result of improved mapping in the Northern Territory. The table also shows that more than 800 000 hectares of casuarina forest classified in 2003 in an ‘unknown’ crown cover class has been reclassified as either woodland or open forest, and that a large area of forest previously classified as open forest is now classified as woodland.
Where are Australia’s casuarina forests?
Casuarina forests occur in all states and territories of Australia (Table 2). Its largest expanse occurs in a band from the semi-arid zone in South Australia through western New South Wales and into Queensland (Figure 1). Significant forests are also found in coastal New South Wales. Belah (Casuarina cristata) forests have the widest distribution, growing in habitats ranging from stony slopes to heavy clay soils.
Common inland species include belah and river she-oak (C. cunninghamiana), which often occur in association with acacias and eucalypts. Coast she-oak (C. equisetifolia) occurs in pure stands on coastal fore-dunes in eastern Australia and, in less exposed sites, also in association with coastal banksias. Pure stands of the rock she-oak (Allocasuarina huegeliana) are found on granite soils and outcrops in Western Australia. Because it is more resistant than local eucalypts to drought, drooping she-oak (A. verticillata) forms pure stands on very dry sites in Tasmania.
Figure 1: Casuarina forest distribution, 2008
| Woodland | Open | Closed | Unknown crown cover | Total | |
|---|---|---|---|---|---|
| Casuarina 2003 | 359 | 871 | 0 | 809 | 2,039 |
| Casuarina 2008 | 2,082 | 191 | 0 | 0 | 2,274 |
| Note: Crown cover is the area of ground covered by tree canopies, ignoring overlaps and gaps within individual canopies. It is usually measured from above using aerial photographs or other remote sensing imagery. In Australia, woodland has a crown cover of 20–50%, open forest a crown cover of 50–80%, and closed forest a crown cover of greater than 80%. Sources: NFI (2003), MIG (2008). |
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Ownership and management
New South Wales contains 52% of Australia’s casuarina forests, South Australia 30% and Victoria 6% (Table 2). About 45% of the casuarina forest estate occurs on leasehold land, 37% in nature conservation reserves and 13% on private land. Less than 5% is located in multiple-use public forests or on other crown land.
| Tenure | ACT | NSW | NT | Qld | SA | Tas. | Vic. | WA | Australia |
|---|---|---|---|---|---|---|---|---|---|
| Leasehold land | 42 | 918,135 | 34,408 | 20,165 | 13,427 | 0 | 0 | 20,036 | 1,006,213 |
| Multiple-use forests | 0 | 8,362 | 0 | 2,575 | 0 | 0 | 19,988 | 0 | 30,925 |
| Nature conservation reserves | 207 | 109,850 | 15 | 3,486 | 629,681 | 619 | 71,641 | 8,747 | 824,246 |
| Other crown land | 0 | 20,685 | 3,986 | 960 | 5,273 | 97 | 3,033 | 35,497 | 69,531 |
| Private land | 0 | 104,608 | 75,079 | 28,801 | 21,470 | 700 | 36,506 | 18,093 | 285,257 |
| Unresolved tenure | 0 | 5,922 | 284 | 5,366 | 1,078 | 0 | 0 | 0 | 12 650 |
| Total | 249 | 1,167,562 | 113,772 | 61,353 | 670,929 | 1,416 | 131,168 | 82,373 | 2,228,822 |
| Note: Totals may not tally due to rounding. The six forest tenure categories above are defined at MIG (2008, ppxvii–xviii). Source: NFI (2003), MIG (2008) |
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- Australian Capital Territory:
- Casuarina cunninghamiana (river she-oak).
- New South Wales:
- C. cristata (belah), C. cunninghamiana, C. glauca (swamp oak), C. pauper, Allocasuarina leuhmanii (buloke), A. verticillata (drooping she-oak), A. littoralis (black oak).
- Northern Territory:
- A. decaisneana, C. equisetifolia (coast she-oak).
- Queensland:
- A. leuhmannii, C. cristata, C. equisetifolia, A. torulosa (forest oak), A. littoralis, C. cunninghamiana, C. glauca, G. australianum (Daintree pine).
- South Australia:
- A. verticillata, C. pauper, A. decaisneana, A. luehmannii.
- Tasmania:
- A. verticillata, A. littoralis.
- Victoria:
- C. pauper and/or A. luehmannii, A. verticillata.
- Western Australia:
- C. cristata, A. huegeliana, A. decaisneana, C. obesa, A. fraseriana (Western Australian she-oak).
Values and uses
Wood
The wood of some casuarina species is used in flooring, cabinetmaking and other ornamental woodworking. The Western Australian she-oak (Allocasuarina fraseriana), for example, is used for making furniture and forest oak (A. torulosa) is used to make roof shingles. The quantity of wood available for such purposes is small because the resource is limited and the products are expensive and keenly sought after.
Coast she-oak is used for timber, poles, pulpwood and mulch and is also reputed to be an excellent fuelwood because it is relatively smokeless when it burns. It also produces high-quality charcoal. Belah is often used for fence posts and firewood.
Environmental
Casuarina forests are important for biodiversity, supporting a wide range of vertebrate and invertebrate fauna. The glossy black cockatoo (Calyptorhynchus lathami), which is endangered in parts of its range, depends on seeds of the forest oak and black oak (A. littoralis) as its primary food source.
In many agricultural areas, drainage and flood mitigation measures undertaken mostly during the period 1960–1990 caused a decline in casuarina forests along creeklines and watercourses.
Casuarina vegetation communities associated with swamps and rocky outcrops have been relatively protected from interference and many occur within conservation areas. Even these, however, are threatened by increased waterlogging and salinity as a result of clearing and the fragmentation of upland forests.
Coastal development and urbanisation are also affecting casuarinas in wetlands and in the zone just above high tide.
Casuarinas such as belah are often used in reforestation because of their value as windbreaks and in soil reclamation and erosion control. They are also planted in many other countries for these purposes – including in the United States (especially California and Hawaii), China, Egypt, India and New Zealand.
Indigenous uses
Indigenous people traditionally use the hard wood of she-oaks for making boomerangs, shields and clubs. In Wyrie Swamp, South Australia, archaeologists found a 10 000-year-old boomerang made of she-oak wood. Young shoots are chewed to reduce thirst, and cones are also eaten.
Other uses
The foliage of some species, such as river she-oak and belah, is used as fodder for stock during drought. Casuarina bark has been used in tannin production.
Atmospheric nitrogen fixation
Casuarina roots fix atmospheric nitrogen through nodules that contain specially adapted symbiotic actinomycete bacteria of the genus Frankia. Because of this, casuarinas can grow on nutrientpoor soils and in other marginal environments, such as granite outcrops or sandy soils.
References and further reading
Boland D, Brooker M, Chippendale G, Hall N, Hyland B, Johnston R, Kleinig D, McDonald M and Turner J (2006). Forest Trees of Australia, 5th edition, CSIRO Publishing, Melbourne.
Doran J and Turnbull J (eds) (1997). Australian Trees and Shrubs: Species for Land Rehabilitation and Farm Planting in the Tropics, ACIAR Monograph No 24, Australian Centre for International Agricultural Research, Canberra.
Gurumurthi K, Nicodemus A and Siddappa (eds) (2001). Casuarina Improvement and Utilization, Institute of Forest Genetics and Tree Breeding, Coimbatore, India.
Marcar N and Crawford D (1995). Trees for Saltland: A Guide to Selecting Native Species for Australia, CSIRO Press, Melbourne.
Midgley S, Turnbull J and Johnston R (eds) (1983). Casuarina Ecology, Management and Utilization, CSIRO, Melbourne.
MIG (Montreal Process Implementation Group for Australia) (2008). Australia’s State of the Forests Report 2008, Bureau of Rural Sciences, Canberra.
NFI (National Forest Inventory) (2003). Australia’s State of the Forests Report 2003, Bureau of Rural Sciences, Canberra.
Wilson K and Johnson L (1989). Casuarinaceae. Flora of Australia, Volume 3, Australian Government Publishing Service, Canberra.
Website
www.daff.gov.au/forestsaustralia