Recreating the Country blog
Blackwood, Acacia melanoxylon
Riparian Wattles – think black, think silver and think swamp.
Victoria’s waterways are great places to visit. Whether they are wide flowing rivers or small dry creek beds they are exhilarating to explore.
Here are some snapshots of my own memories of walks along river/creek banks;
The edges of our creeks and rivers are where you will find plants that are unique to moist environments. These are plants that have adapted to wet feet during times of flooding and to extreme dry seasons a few months later. They deserve our admiration because they somehow thrive in spite of these dramatic climate contrasts.
Three remarkable riparian wattles
There are three remarkable wattles that grow on waterways that I regularly visited on seed collecting expeditions and they’re easy to remember - think black, think silver and think swamp.
The Blackwood and the Silver Wattle, Acacia dealbata are often found sharing a river bank. You can see them together at Morrisons on the Moorabool River 7km north of Meredith in central Victoria. In this deep and mysterious valley they grow on the river flat and provide the understorey and tall shrub layers under a canopy of River Red Gums.
The Swamp Wattle, Acacia retinodes forms a low shrub layer under River Red Gums at the very pretty Pitfield’s reserve on the Woady Yallock River, 15km NW of Rokewood.
These wattles illustrate how nature builds structural layering into vegetation, a critically important strategy to maximise safe habitat for wildlife. Click here and scroll down to read about structural layering in vegetation
The tallest of this trio is the Blackwood, Acacia melanoxylon;
Commonly pronounced melon-ox-a-lon
It’s all Greek – melas = black; xylon = wood.
Literally it translates as ‘black wood’ and it describes the deep brown/black colour of the heart wood of mature trees. The outer layer of the heartwood is called the xylem. This is where water is carried from the roots, up the trunk to the leaves. Tall trees like the taller Blackwoods have a long way to lift water from their roots to nourish the leaves and new growth.
Some Human context
The adaptable Blackwood
The Blackwood has a very wide distribution from northern Queensland right down the east coast to Tasmania. It also occurs naturally in the Mt Lofty region of SA.
It is a hardy, dense, strong, long lived wattle that makes an excellent fire retarding windbreak on farms. Its best suited to moist soils and damp gullies.
Choosing the right provenance for your planting is important because they vary greatly in drought tolerance and size, from forest giants to bushy tall shrubs (see below). Ideally choose Blackwoods indigenous to the planting site as they will be well adapted to the local climate and soil.
Blackwood’s are well known for producing a hard, dense timber for making beautiful furniture, benchtops, cupboard doors and veneers. It is described as one of the world's finest furniture timbers.
The timber most suitable for cabinetry is usually harvested from Blackwood’s growing in higher rainfall areas where the trees grow tall and straight. In the wet forests of the Otway Ranges and Tasmania, Blackwood’s live well over 150 years and can grow into 30m tall forest giants.
In lower rainfall well drained soils and moist gullies, Blackwood’s may live up to 100 years and are a much smaller tree (10m – 12m). They have closer growth rings and are prized for making personalised furniture. Blackwood’s growing in low rainfall dry woodland areas along waterways grow to a similar size and age. The Morrison's Blackwoods described above fit into this category.
This medium sized form is ideal as a street tree because it is strong, dense, shady and long lived. It has the added advantage of needing very little maintenance.
There are also smaller Blackwood’s that have adapted to the heavy soils and exposure to the climate extremes of the basalt plains. These trees have a hard life, live up to 25 years and reach 5 – 7m tall. They’re gnarly wood is prized for craft work.
Wood-workers take care
Blackwood saw-dust is a recognised lung, eye and skin irritant. I met a cabinet maker near Portland who had a small shed full of dried and numbered Blackwood planks that he was keen to sell. He had harvested the logs himself from trees that had been cut down under powerlines on a nearby roadside. The logs had been slabbed and were ready for use in his workshop. Sadly he found that the saw-dust from the Blackwood irritated his normally healthy lungs causing asthma, even when he worked with a dust extractor.
The perfect paddock tree - the benefit of clumps
The hardiness and longevity of the Blackwood makes it an ideal paddock tree. It also hosts nitrogen-fixing Rhizobium bacteria (like all wattles) that improve soil fertility. This benefits surrounding trees, crops and native grasslands. Its tough bark is resistant to damage from stock and the trees provide excellent shade.
To hasten the development of significant habitat for wildlife as well as excellent shelter for stock, plant new paddock trees in groups of five with a spacing of 3 – 5 metres between each tree.
Group planting like this multiplies and accelerates the ecological services these new paddock trees provide. The tree clump will have many of the benefits of a single 50 – 75 year old mature tree in only 10 – 15 years.
When these Blackwood's mature beyond 15 years some can be thinned for their valuable timber to make room for the remaining trees to develop a more robust form.
The Blackwood’s pale yellow to white flowers grow in clusters and appear from September – November in the southern states and November – March in Queensland.
In south-east Queensland the Blackwood supports many native butterfly larvae - the tailed emperor, silky hairstreak, imperial hairstreak, stencilled hairstreak and large grass-yellow butterflies.
Its dense foliage also provides shelter for many birds. It offers protected nesting areas and produces copious quantities of seed.
This seed is popular food for Cockatoos, Rosellas, Wattlebirds, various honeyeaters, King Parrot and the Bronzewing Pidgeon.
Ants also harvest Blackwood seed for the oil rich aril and take the seeds underground where they will remain viable for centuries
Small birds like the Grey Fantail and Superb Fairy Wren glean insects from Blackwood leaves.
The glands at the base of the Blackwood leaves (phyllodes) produce a sugary sap during flowering that attracts a variety of birds including silvereyes, honeyeaters, treecreepers, spinebills and thornbills. This entices them to the tree to help with pollination.
Sugar Gliders also harvest the nourishing protein rich sap by wounding the trunk to encourage it to bleed. The Gliders defend the Blackwoods within their territory from other families of Sugar Gliders.
Sugar Gliders also feed on the sap of Black Wattle, Acacia mearnsii, Silver Wattle and Lightwood, Acacia implexa
Blackwood has a rich history of use by indigenous Australians;
The bark of the Blackwood is soaked in hot water to produce an analgesic solution. This will ease pain when rubbed into sore muscles or used to bathe painful rheumatic joints.
The leaves have been used as a natural soap. Take some fresh leaves, add a little water and rub hands together vigorously until the foam forming saponins are released. These natural chemicals will clean your hands.
Blackwood twigs and bark were used to stun fish, making them easy to catch.
The thick sap from the trunk was used as an adhesive to join pieces of Blackwood to craft strong weapons and tools. These include spear-throwers, boomerangs, clubs and shields. The inner bark was used to make a strong string.
Caution – Cleaning Blackwood seed creates a fine dust that is very irritating to the lungs.
Like other wattles, Blackwoods are easy to gerninate from seed using the boiled water treatment described at the end of the ‘Black Wattle’ story.
The seed is very distinctive as it is encircled by an orange aril. It is also very convenient to collect as it often hangs on trees for months with the seed-pods fully open as if advertising its availability.
Refer to a section at the end of 'Acacias' for a simple method of inoculating wattle seedlings for more vigorous and healthy trees.
Removing the aril
I have found that Blackwood seed is easier to treat and to sow if the aril is removed.
After the seed is separated from the pods most of the arils will still be attached. To remove them, wearing leather gloves and a dust mask, rub the seeds vigorously between your hands until most of the arils are dislodged. Winnow the seed pouring it from bucket to bucket in a light breeze. The lighter arils will blow to the side leaving the cleaned seeds ready to package in a Zip-lock bag.
Remember to record the species name, collected location and the date of collection on the bag for future reference. Other valuable information to record; tree size, soil type, drainage, exposure and the number of plants in the seed collection sample as a guide to its genetic diversity.
Paddock trees: benefits on farms
Silver Wattle, A. dealbata
We have all been in the presence of something in nature that is truly breathtaking. We’ve felt its magnificence and we’ve sensed its yawning reach back into history tugging at our imaginations.
This article is about the ancient paddock trees that dot our rural and urban landscapes. They are a feature of our living environment, solid, very old and undemanding. They are reminders of what once was here before we came. Sometimes they are very rare examples of trees that are found nowhere else on the planet.
Picture yourself driving through the Australian countryside and your view is an endless expanse of open paddocks. The distant horizon is only interrupted by a random scattering of old trees. They are the lone trees that are the singular remains of the original vegetation. A vegetation that was a diverse mix of plants that once clothed this countryside, unbroken, from South Australia through Victoria and north into Queensland.
These are the paddock trees and viewed from the roadside they seem unremarkable. They are like a group of strangers in an old photograph, interesting but without a story to connect us. They are just old trees, inconsequential and irrelevant to our busy lives. But are they?
In truth these paddock trees are an enduring and vital part of our timelessness view. They have been part of this landscape for thousands of years since the end of the last ice age and possibly before it began. They are an important feature throughout the world. In different countries they have different names - isolated trees, pasture trees, remnant trees and people have always valued them for their antiquity and for the shade they provide.
Ecology of paddock trees
Now we know that they are much more than shady and historic icons.
In an ecological sense they support many other life forms.
They are the high rise apartments, B&B’s, supermarkets and hardware stores for thousands of insects, birds, mammals, reptiles and amphibians.
‘Large old trees frequently contain hollows, which are places where over 300 of our frog, reptile, bird and mammal species sleep, rear young, seek shelter from the weather or evade predators’.
(Gibbons & Lindenmayer – Respecting our Forest Veterans, Nature Australia, winter 2003)
In 2000, a study in W.A & NSW of insects living in paddock trees added to our appreciation of the diversity of life that they support.
Researchers, Majer and Recher found 1,600 distinct insect species in 40 trees. This is almost the total species of birds, mammals, reptiles and frogs found on the entire Australian continent.
They also found an average of 16 species of bird frequenting these trees. Another study of insects under paddock trees found a greater diversity and numbers closest to the trees where leaf litter was deepest. This was linked to higher levels of organic matter and nutrients under the trees.
Paddock trees are also ‘stepping stones’ for the annual migration of many insect and bird species. Woodland birds move between larger patches of remnant vegetation, flying from old tree to old tree. Paddock trees allow these bird populations to migrate and remain viable in areas where they would otherwise become rare or extinct.
Threatened species like the Superb Parrot, the Squirrel Glider, Brush-tailed Phascogale and a number of species of micro-bats have also been recorded living in and feeding on the pollen, nectar, seed and insects in paddock trees.
Researcher Dr Andrew Bennet and colleagues from Deakin University describe the remarkable strategy of Box-Ironbark trees growing on poor soils. While most eucalypts flower in spring providing an oversupply of nectar, the box and ironbark’s flower in winter when there is a shortage.
This stimulates mass migrations of Lorikeets and honeyeaters that travel huge distances for the winter feast. The endangered Swift Parrot flies annually across Bass Strait in June to southern Victoria to feed on the nectar of the Yellow Gum/White Ironbark. This benefits the trees as the faeces of these birds, mammals and countless insects feeding on the flowers and leaves greatly enriches the soil, enabling the paddock trees to prosper on otherwise poor leached soils.
A keystone landscape feature
A paddock trees isolation adds significantly to its importance to the local ecology. They are an oasis in the open landscape and a refuge in an exposed and windswept paddock. The critical connectivity they provide across an open landscape is more beneficial when the trees are closer, within ‘line of site’ for birds. This is ideally a tree spacing of between 20 – 100 meters.
The benefit to our nation of protecting and restoring scattered paddock trees is immense. Many of them are eucalyptus trees with a lifespan of 400 – 500 years and sometimes much longer. This remarkable longevity provides a continuity of resources, a thread of familiarity and certainty that the local wildlife have relied on for millennia.
Biologists describe old paddock trees as keystone features on our landscape. And like the keystones supporting stone arches in a centuries old cathedral, they are understated but they are vital. Take the keystones away, the arches will crack and the cathedral will crumble. Take the paddock trees away, the diverse web of life that they have supported for centuries will wither and the whole ecology will collapse.
Protecting paddock trees is part of the climate change solution
Big trees make it rain
Under paddock trees the microclimate is cooler and wetter. This is partly because of the shade and wind shelter the trees provide. Though it’s also because old trees are very good at intercepting rainfall and making the most of it. This is part of the trees water cycle and it climaxes with the release of water vapour from the tree’s leaves back into the atmosphere.
If there are enough big trees then inland clouds can form. This is because cool air moving across the landscape is pushed up by the big trees and cooled as it rises. This rising, moist, cool air condenses forming water droplets. These water droplets may then fall on the surrounding landscape as rain.
Unfortunately large scale clearing of paddock trees and the original mixed vegetation that connected them across the broader landscape, has dramatically reduced this creation of inland rainfall. This is illustrated by the observations of Indigenous Australians;
In northern Queensland, the first Australians called old paddock trees ‘water trees’. This recognised their essential role in maintaining the hydrological balance of the broader landscape. They observed that permanent water holes became dry, as did the grassy landscapes, when the old trees were lost because of clearing and mismanagement.
'Without the water trees, our water will start to find it hard to stay on country to play its role of supporting life'.
Victor Steffensen, Fire Country
Big trees absorb more carbon
In January 2014, The Conversation reported a study of 403 species of old trees in tropical and temperate Australia. William Morris from Melbourne University proved that large old trees grow faster and absorb carbon dioxide more rapidly than younger trees.
‘We now know that the biggest trees are the most valuable as both carbon stores and carbon sinks. If a manager’s goal is to maximise carbon uptake, then maintaining larger trees may be an efficient way to do so.’
Paddock trees need our protection
This is a snapshot of the extraordinary web of life supported by paddock trees. They stand alone and in isolation, an integral part of forgotten and diverse plant systems. Remarkably and stoically they manage to hold the shrunken remains of past ecologies together, with a dignity and beauty that deserves the gratitude of a nation.
Studies indicate they are not being replaced and that they are dying at a rate of 2% each year.
Clearly they need our protection. Click here to read the abstract of a recent Australian National University study on paddock tree decline. Their decline and restoration is the topic of part 3.
The science of Tree Hugging
In Iceland people are being encouraged to hug a big tree to combat feelings of loneliness and isolation. Hugging a tree increases levels of the hormones oxytocin, dopamine and serotonin, helping us bond with the tree and making us feel calmer and happier. Since we can no longer hug each other, perhaps the time has come to start hugging our old paddock trees as a gesture of our heartfelt thanks.
Click here to read the delightful story,
'How River Red Gums came to be - a dreamtime story'
Paddock trees continues next month;
Part 2 - The benefits of paddock trees on farms
Part 3 - Restoring paddock trees and fostering the next generation
Send in a picture of your favourite paddock tree and I'll put it here for all to admire. Do you have a personal story about your tree?
Thanks to Kaye, Murray and Grace for photos of amazing paddock trees.
Murray added these insights into his family's connection with two paddock trees;
Here are a couple of Manna gums we have, the first we call the "swing tree", as it is only an easy walk from the house, and ever since my now teenage children were young, it has hosted a swing. I've had to replace the swing a few times, but the tree goes on. It's a great spot to sit and watch the sunset, or have a campfire.
The second we call the " faraway tree", after the Enid Blyton story. There are at least half a dozen hollows, reminding us of the tree in the story and all its residents.
Grace added - This is what we call “Grandmother Tree”, such a blessing to have on our little property. Currently having a drink from flooded Mt Emu Creek. Unfortunately she doesn’t look healthy this year, so I’ve taken seed to propagate. Blessings
Stephen Murphy is qualified in Geology and Environmental Management and has been a nurseryman and a designer of natural landscapes for over 30 years. He loves the bush, supports Landcare and is a volunteer helping to conserve local reserves.