by Phil Watson

(an update of his previous article "In appreciation of the common Black Wattle")

Photograph by John and Marion Simmons, courtesy of Launceston Field Naturalist Club

Acacia mearnsii
First impressions can often belie a richer story-the humble black wattle (Acacia mearnsii) may not be considered a tree of distinction or renowned; however, this ferny-leaved woodland species has a few surprises under its bark which may change many walkers' hasty judgement. Beyond their striking beauty when festooned in late spring with golden blooms and their extraordinary array of food and habitat values, they possess a fascinating range of vital historical cultural uses. Allied to this is their crucial role in the leather industry, ensuring that colonists and bushwalkers alike remained well shod with hard wearing boots. Other curious associations, which this article will explore, include their cryptic mutually beneficial (symbiotic) relationships with fungi, moths, wasps and their connection with Errol Flynn via truffles and bettongs.

Tannin supplies--crucial for the emerging leather industry
Early last century, with the infant colony's imported supply of boots and shoes rapidly diminishing, the footwear industry began to mushroom. The key requirements were reliable supplies of tannin, soft leather for the uppers and tougher leather for the soles.

It was soon established that black wattle was the panacea for tannin supplies, given that approximately forty five per cent tannic acid could be extracted from the pulped bark. Kangaroo and wallaby skins were eminently suitable for the soft leather uppers, but superior sole leather proved the most elusive component being subject to the fickle pastoral industry for supply of cattle hides.

Due to a constant need for freshwater, tanneries were sited on waterways and rivulets close to towns large enough to also supply a substantial labour force. In Hobart, tanneries including Blundstones Pty. Ltd and Campbell and Minchin, Saddlers and Leather Goods (their sign can still be seen on the comer of Elizabeth and Bathurst Streets) became established along the Newtown and Cascades rivulets. In Richmond tanneries spread along the Coal River, the best known of these being the McGowan's tannery.

With some of these tanneries boasting over 100 pits and the pressing call to maintain a steady supply of black wattle bark, the leather industry became major employers for the fledgling towns.

Woodcutters, fellmongers and curriers
The tanning process deserves a closer look. It generally began when the teams of hard- working woodcutters stripped the bark from 7 to 10 year old trees during the September to February period when the sap is freely flowing. They used a chiselling technique starting from the base and moving upwards along the trunk. The dried bark was then crushed and added to water in tanning pits which enabled various styles of tannin liquor to be brewed.

Selected skins were de-fleshed and scraped by fellmongers in readiness to be immersed for a few days in the pits. Once tanned and dried the hides were prepared by curriers in accord with the use of the leather. It was from these humble beginnings that Blundstones, the oldest continuous tannery in the southern hemisphere, manufactured their legendary 'Blundstone 208' bush walking boots. Unfortunately besides the enduring legacy of highly polluted and often toxic waterways, the burgeoning tanning industry also decimated all the black wattle stands within close proximity to colonial townships. This
was compounded by the ongoing deforestation of woodlands with mushrooming demand for firewood and building supplies.

Today black wattle is grown commercially world-wide, particularly in southern Africa, not only for tanning soft leather but other bark extracts as the basis of resins, thinners, and adhesives. The timbers are used for building materials, charcoal for fuel and pulp for paper, whilst rural African communities rely heavily on it for fuel and building. Interestingly, its botanical name derives from a species collected and described by De Wilderman in the late nineteenth centaury from a cultivated specimen in Kenya which he assumed was indigenous. He named it after a compatriot American botanical collector
Edgar Alex Mearns (1856-1919). The sad legacy of these wattle plantations is that the African forests are plagued by black wattle weed invader!

Black wattles host their own miniature food web
What would life be without mutually beneficial and enduring friendships? Nature appreciation, exploring and bushwalking, stand proud as an excellent means or framework to foster relationships and to enhance health and wellbeing, somewhat akin to the multiple roles performed in nature by the black wattle.

Every black wattle hosts numerous mutually beneficial (symbiotic) fungal relationships. The most visually obvious example for bushwalkers relates to the black wattle's association with the dark ball-like fungal galls (Urymycladium sp.) that decorate the outer branches of older trees.
Fungal gall on acacia mearnsii
These galls provide a cosy home for moth caterpillars which feed on the fungal spores and in return disperse their spores when the larvae metamorphose into moths. However many larvae never make it to the moth stage as a result of predatory ichneumoid wasps which use sonar guided proboscises to inject their eggs into the caterpillar. The wasp eggs hatch producing a multitude of smaller larvae that voraciously feed inside the large caterpillar parasitising them completely. Curiously the food chain does not terminate here as bark gleaning native birds such as Black faced cuckoo shrike, Shrike thrush and the Strong billed honey eater peck open the galls, to be rewarded with either the succulent caterpillars or wasp larvae.

Black wattle and vegetable caterpillar fungi get on fine together
Less conspicuous are the many underground symbiotic relationships that are played out in the subsoil, well protected from the many passing foot prints. Most remarkable of these is the relationship between a dormant moth caterpillar and the dark and fawn vegetable caterpillar fungi (Cordyceps gunnii and
C. hawkesii
). These fungal bodies survive close to the surface within the black wattle's roots zone. They appear briefly as 100mm tall, club-like mushrooms in the ground litter layer prior to bursting and dispersing their spores. They develop from a parasitised moth caterpillar, the body of which becomes crammed with the mycelium as the fungi completely invade the moth's tissue. Intriguingly these fungi are closely related to the species at the centre of the lucrative Tibetan and Nepalese vegetable caterpillar fungi harvesting industry. As their primary income earner currently valued at $80,000 per kilogram, the local cultural minority tribes have harvested them for millenniums from alpine wildflower meadows.
They are highly prized for their aphrodisiac properties and feature prominently in Chinese medicine.

Black wattle and ants maintain a good working relationship!
Ants are not just smelly little creatures that bite bush walkers if they camp on, sit down in or walk across their well-defined territory. From the black wattle's perspective they are actually a major aid to their survival. Attracted by the nutritious, fleshy, oil-rich seed stalks (elaisomes or arils) attached to the black wattle's hard seedcases (testa), ants collect and bury the seeds. By doing this they inadvertently provide an important service to support the potential for the seeds to germinate. These little piles of stored seeds are buried by the ants at around two centimetres under the surface ensuring they are protected from being burnt during a hot fire. However the intense heat is able to penetrate sufficiently to crack the seed coating to enable germination following a soaking rain. From a bush regeneration perspective low-intensity burns are not hot enough to crack these buried wattle seeds along with the many other bush pea species. Hot burns not only crack these seeds, but also deliver competition-free ash beds of sterilised soil to support germination. Refreshingly, one of the first green flushes visible in the starkness of a burnt woodland landscape is the feathery green leaves of black and silver wattle seedlings. The rhizobium bacteria housed within the root nodules of these young wattles also inject precious nitrogen supplies into the soil, aiding the re-colonisation of the landscape.

Taking an opportunity to pry into the cracks and crevices within the tough outer bark of the black wattle will reveal trails of little black ants, as well as a plethora of healthy diminutive fellas thriving in their humble yet cosy niches. The caterpillar of the rare Tasmanian hair-streak butterfly (Pseudamenes chlorinda) is one such insect which has hatched from eggs deposited under the bark's hidey holes. These caterpillars exude a sweet liquid which attracts the attention of little formic-acid-smelling ants (Iridiomyrmex sp.) that most bushwalkers would have smelt when enjoying a well earned rest. These ants nurture the caterpillars in return for their exudates, protectively herding them, like cows, down the trunk and across the grassy understorey to the white gum (Eucalyptus viminalis). Here under the bark on the northern side, they pupate into colourful butterflies characterised by hair-streak-like extensions on the base of their wings.

Acacia mearnsii flower buds     Flower Buds