As soon as the name She-oak is mentioned, as is the case with the Gum tree, any fair dinkum Aussie knows exactly what plant you are talking about. But few would know that these strange and mysterious trees possess both real and imaginary powers and maybe one of over 40 species in Australia and the South Pacific.
The She-oak family (Casuarinacece) is a highly evolved family and is closely related to no other. They have achieved specialisation in isolated conditions such as exposed, sandy coastal foreshores, riverbanks, dry grassy woodlands, desolate rocky sites or swampy riparian flats.
This article deals mainly with Drooping She-oak (Allocasuarina verticillata), but reference will be made to some of its brothers including the Black She-oak or Bull-oak (Casuarina littoralis) and some mainland species.
Its generic name Casuarina or Allocasuarina ("Allo"meaning like the casuarina) refers to the fine filamentous branches, which resemble the cassowary's quills. It is also noted that early Australians referred to casuarinas as Australian "Pines". The verticillata in Allocasuarina verticillata relates to the whorled arrangement of the very reduced leaves around the stem, (as in bike spokes). The word She-oak comes from the recognition by the early colonial craftsmen that an inferior (in their opinion) oak grain could be achieved by cutting the she-oak logs on the quarter (a specialised saw milling technique) and using the wood for crafting etc.
An architect could not have done a better job of designing these plants for the extreme environmental conditions in which they thrive.
The long drooping branches consist of myriads of finer branchlets. The leaves are reduced to ribs on the branchlet, which end in leaf teeth. These reduced leaves occur in whorls located at the evenly spaced joints along the branchlets. These green branchlets perform the same food-making role (photosynthesis) as the leaves, but save on water losses, by reducing transpiration.
The trees are endowed with a tough corky, corrugated bark, ideal as a protective shield from the abrasive, sand laden coastal winds.
The trees have two distinct forms, either male or female (dioecious). The male tree has long reddish flowers at the ends of its branchlets, which pollinate the rusty red, globular flowers on the female tree. The female's flowers are designed to hang well out to catch the wind born pollen grains that wafts pass from the nearby male. The production of pollen can be so prolific that they often produce a reddish carpet of pollen under the trees.
The fruit resembles brown cones with valves (look like little beaks) opening to produce shiny black seeds.
The cones can be assisted to release the seed, by selecting ones that have closed valves, and storing them in a paper bag for a few weeks, until the beaks open to release the seed.
Botanists use the number of reduced leaves in the whorl and the distance apart of each branchlet joint, as clues to tell the 40 odd she-oaks apart. However, telling them apart can be made a fun activity where the Dropping She-oak occurs in close proximity to the Bull-oak.
Have the youngsters pick a cone from each tree and roll the cone over the backs of their hands. They will never have any problems separating the two, blindfolded! The She-oak cone has sharp beaks and is unpleasantly prickly, while the bull-oak's beaks are soft.
While they have these ripe cones in their hands they can extract a sample of seed from each of them. The She-oak will have black shiny ones while the bull-oak will provide dull greyish brown seeds. The latter is typical of only 6 species, now being the only true Casuarina species while most others fall into the Allocasuarina category.
Of course, they can also see the drooping verses the upright forms of the two species, but they can also get a clue from the type of rock they are growing. Closer examination of the rock and associated soil reveals that dolerite derived soils regularly grow the She-oak, whilst just over the way where sandstone or mudstone derived soils occur, the bull-oak will prosper.
The exception is the sandy coastal soils of the hind dunes, where the she-oak happily survives.
The mysticism of She-oaks relates to the Tahitians, who believed that they arose from the warriors who died in battle, killed by clubs or spears made from its very hard wood. The warriors hair became the foliage and their blood oozed forth once more as the red sap.
However, for the colonists, they saw the superstition and mythical nature of the tree in its ability to support the parasitic mistletoe, since it commonly sprawls over and sometimes smoothers this tree.
The Australian southern states mistletoe (Amyema sp.) has a remarkable ability to mimic the host she-oak so much so that they are very hard to tell apart.
The authenticity of the suspect plant is given away by watching the mistletoe bird feeding on its glutinous berries. The seed passes through the bird's unusual gizzard in 30 minutes and lodges on another She-oak branch. Its green shoot then suckers into the bark, with the help of its enzymes, that breakdown the bark and wood.
A broad range of nectar feeding birds pollinates the mistletoes. These include unlikely species such as the cuckoo-shrikes, ravens, cockatoos, shrike thrushes and even wood swallows. They also provide nutritious fruits for the birds to feed on, which is a separate activity to the dispersal role that the mistletoe bird performs.
As a landscape plant for the gardens or streetscapes, the public either like them or loathe them. Their ability to flourish in dry coastal sites and attract native birds should guarantee a strong following.
However even though some do not favour them, many like their wind breaking, screening and erosion control abilities. They also possess an expansive, dense root system, which binds the sandy soils, whilst restricting only but the toughest of plants from surviving, the dry, low light conditions under their canopy.
They form a low maintenance, naturally mulched and weed free location under their canopy. This is ideal for the lazy gardener, as it provides a retreat for relaxing on a hot summers day within its soft luminous shade. Remember to create the opportunity by early removal of the young tree's lower branches (formative pruning), which will keep the area underneath open and accessible.
The She-oak roots have developed a symbiotic relationship with mycorrhiza fungi. This enables she-oaks to fix their own nitrogen and tap into the nutrient exchange system offered by the dense mat of this fungal mycelium attached to their roots.
Not only does this give the She-oak its tolerances to tough conditions, but it also provides the ready-made food source for a number of our little furry friends (bandicoots, potoroos, bettongs).
Their truffle fruiting bodies provide a nutritious treat, following their important bioturbation process, used in their endeavours to uncover the buried truffles. The truffles pass through the gut of the animal which pre treats the spores ready for germination once dispersed. Their droppings with these spores are advantaged even more if they are placed on soil recently sterilised following a local wildfire.
The She-oak's life history is a construct of the fire regime to which it has been subjected. A fire regime is made up of the frequency of the firing (years between successive fires), the season of the fire and the intensity of the fire (relates to the amount of fuel available and moisture levels in the soil and surrounding air).
The She-oak is an excellent example of how an individual plant's life history changes depending on the fire regime applied. The response mostly relates to the intensity of the fire as described below.
So what does this fire ecology information tell us?
She-oak trees, which are killed by hot fires, shed their seed. These will only stay viable for less than 3 months in the soil. With suitable conditions, prolific germination occurs after a hot fire on the sterile nutrient rich ash bed. (Provided that the harvester ants do not grab them first).
Once successfully germinated, the dense mass of seedlings crowd out other native plants, which may germinate. It needs to be remembered that, young She-oaks need to have at least 5 to 7 years of growth before they start to produce seed bearing cones and at least 10 years before they have a reasonable number of cones in their canopy.
If no further hot fires occur the She-oak community dominates the area once again. If two hot fires occur within 7 years then the She-oak woodland will be replaced by a grassy woodland.
It needs to be recognised that many of today's prominent She-oak woodlands were originally grassy woodlands, containing a few She-oaks. These open grassy woodlands were managed primarily for hunting purposes by the local aboriginals tribes, using frequent fires to produce green pick. Where aboriginal firing practises have ceased, some of these woodland communities have slowly become dominated by She-oaks.
A good example is "She-oak Reserve" or Rosny Point Foreshore Reserve" (30 hectares) located in the prime riverside position on the opposite side of the Derwent River to Hobart city. Early landscape paintings from the late 1800's show open grassy woodland, with a few She-oaks in the sub-canopy under scattered white and blue gums. Today's blanketing She-oak woodland is a response to a change from the traditional aboriginal fire regime for the area, to the current "no burn" policy.
If the land managers, in consultation with the people of Hobart, wished to revert back to this original landscape, then all that is required is two hot burns spaced within a seven-year period!
The craft wood potential of the hard, beautifully grained, reddish timber was recognised by early settlers. Its attributes ensured an export market to the mother country. Here it was treated as a prized wood, only to be used sparingly on highly prized projects. Small artefacts such as document boxes or inlaid features in fine quality furniture were crafted from this imported She-oak.
The strength of the wood proved useful to colonists for crafting axe handles and other tool handles.
Today the wood has once again been recognised for its qualities to the point where a few plantations of She-oaks have recently been planted. These plantations also benefit the apiary industry as the flowers' pollen attracts honeybees, which produce a distinctive tasting honey.
She-oak was also noted for its firewood property of burning very hot, leaving a pure white ash bed. This white ash proved ideal as a sheet whitener, prior to commercial whiteners.
This ash also comprised the major component in soap, forming the "Li" or alkali which, when mixed with animal fat (Sheep or Roo origins) and scented with rose water, chemically combined to form real true blue soap.
She-oak was popularly used for making spears. The inner bark and sapwood shavings were soaked in water and the liquid gargled for toothaches.
Aboriginal tribes used the She-oak trunks for attracting grubs. The trunk was dumped into creeks and rivers to attract grubs. These were harvested and eaten raw or cooked.
The young She-oak cones were chewed to promote salvia in dry mouths, as they travelled long distances through the hot, dry landscape.
Exudates collected from the trunk were chewed or melted with warm water to form a jelly prior to eating.
Like them or loathe them, they are intriguing trees, which help to provide a sense of place within our Aussie bush landscape. Finally, one of the most pleasant natural sounds is that of the wind murmuring through the swaying canopies of a clump of she-oak trees. A place for relaxation!
Phil Watson
