The fast growing, drought tolerant, Black Wattle stands proud amongst other woodland trees due to the exceptional range of food and habitat values it extends to a myriad of wildlife. It has also provided a culturally diverse range of Colonial and Aboriginal plant uses. This article will explore its kaleidoscope of attributes by beginning at its roots and following up the tree to the showy, yellow flowers that give way to pods of hard, black seeds.
To begin with, the roots form a symbiotic relationship with mycorrhizal fungi (fungus roots), which produce "yummy" truffles that bettongs, bandicoots and potoroos dig up. Once eaten and digested, their spores are spread far and wide in the marsupials' droppings. Following a hot bush fire, these and buried wattle seeds germinate prolifically in a competition free, environment of newly sterilised soil. A flush of black wattle seedlings, along with other pioneering species colonise the erosion prone soil and supply soil nitrogen from its nitrogen fixing root nodules.
The cracks and crevices in the wattle's bark are home for many insects and invertebrates. The rare Tasmanian Hair Streak Butterfly lays her eggs in these hidey holes. Its caterpillars are often attended by formic acid smelling ants (Iridiomyrmex sp.) that feed off the larva's sweet exudates. Ants herd the larva down the trunk and across the grassy understorey to a White Gum, where they pupate, under the bark crevices' protection.
The raucous Black Cockatoos as well as trout fishermen, strip its outer bark in search of other insects such as longicorn beetles and the Wattle Goat Moth larva. These larvas can tunnel for up to 5 years, within the wood of stressed wattles, developing into high protein snacks sometimes reaching 10 cm in length. The frass ejected out of the tunnels was used by the aborigines to rekindle their precious glowing embers that they carried from camp to camp. The adult grey-brown moths (15cm wing span) can lay from 10 to 30,000 creamy eggs under a mucous covering on the tree's bark, presenting a delicious treat for bark gleaning birds. Insect feeding birds such as Thornbills, Black Headed and Strong Billed Honey Eaters gorge on defoliating insects such as the greenish dome shaped Leaf beetles (Chrysomelids) and Fireblight beetles. The latter leave a characteristically reddish brown, scorched appearance after attacking the wattles. Birds even feed on the itchy to touch caterpillars of small moths, which web the wattle leaves together. They also peck open the large brown galls, which form in response to fungi aggravating the wattle's bark. Their reward is the tiny native wasp larva, which live inside.
Early last century, the bark was the basis of a thriving tannin industry, which could extract up to 45% tannic acid from its pulped bark. Within ten years, the wattles had been extensively logged in close proximity to colonial townships causing a rapid deforestation of the woodlands. These tannins continue to be used today for tanning, plywood, particleboard adhesives and antiseptics. Expansive plantations of black wattle in S. Africa have replaced our Tasmanian trees as suppliers to world-wide markets. The sad legacy of these wattle plantations has been a new S. African forest weed invader!
The Aborigines soaked the outer bark in wooden troughs near an open fire to extract decoctions, which they applied to aching joints and as antiseptics to cuts. The inner bark was split into lengths for coarse string. Baskets were woven for collecting shell fish, whilst bindings were made for fixing their flintheads onto spear shafts.
The wattle's flexible branches were used by the Aborigines to form lean-tos or half-dome huts, by covering them with bark sheaths, coarse foliage or even possum or roo skins. The early colonial "wattle and daub" huts were constructed using a wattle framework, clad with clayey mud. As a craft wood for fine furniture, black wattle compares directly to black wood (Acacia melanoxylon).
The colonists burnt the wood for both cooking and the fine white ash residue. A sheet and clothes whitener, as well as'lye' for soap making, were formed from the ash. Soap was produced by combining the lye with fat cut from meat and then perfumed with herbal extracts such as lavender oil.
The amber coloured sap that oozed from damaged trunks was an essential commodity to the aboriginals, necessitating their need to carry a supply when on walkabout. To do this, they would mix molten sap with burnt mussel shells or coarse ashes to form tennis ball sized wads. Only the lighter coloured sap was prized as a food or drink. It was often dissolved in water with a dash of sweet wattle flower nectar to produce a quenching drink. The darker sap, blended with fine ash formed filler for plugging holes in water carrying vessels or bark canoes. Interestingly, early Sydney confectioners used the lighter sap as a base for a flavoured chewing gum.
As mentioned earlier, a variety of birds are attracted to this wattle. The protein rich nectar that pools in their leaf axils is fed to young nestlings or stored in hives or nests by bees and ants. When these stores or 'Honey-pots' were discovered, they provided the ultimate Mars Bar for the aborigines! The black wattle flower provides nitrogen rich pollen which acts as an energy source for honey eaters such as Wattle Birds, Yellow Throated Honey Eaters and New Holland Honey Eaters as well as worker bees and ants. By being part of the natural system, the aboriginals, understood that the timing of the wattles' flowering coincided with the prime eating condition of the kangaroos, following spring grazing on the succulent, native grasslands. They would prepare by sharpening spears and firing the grasslands to herd the mobs for easy hunting.
"Hill-topping" sites are a Midland's landscape feature consisting of isolated woodland remnants, dominated by black wattle, amongst the lower sea of exotic pastures. These sites are critical habitat sites for male butterflies. Their spiralling flight patterns attract females for mating and before lying eggs on nearby vegetation. These remnants are recognised as crucial to preserving the diversity of butterfly species and bird species.
Seeds were highly prized by the aboriginals who would grind them into polysaccharides and protein rich flour prior to baking flat bread. More recently the jet setting traveller enjoys "wattle seed" biscuits as part of the bush tucker revolution. Ants aid the wattles' natural regeneration by collecting and burying their seeds. They feed on the fleshy, oil rich seed stalks. These little stores of hard seeds may germinate only after a hot fire followed by a soaking rain.
Black Wattle is not just another native tree. Celebrate Wattle Day on September 1st by growing and enjoying one. The reward of observing its fascinating interrelationships with the wildlife justifies the effort.
Phil Watson