Will these gentle giants of Australian parks and gardens stand the test of time even as the climate changes?
In Australia the eucalypts seem to soak up all the publicity, but there’s another native tree that needs a little more love. It’s every bit as majestic and spectacular, planted prolifically in most capital and regional cities and used in art, religion and landscaping.
We’re talking about Moreton Bay fig trees (Ficus macrophylla).
Frolicking beneath the figs in Botanic Park remains a favourite pastime. The sweet figgy scent brings back many memories, from the earliest of days through to the present.
Exploring the outdoors as a child, clambering over the buttress roots, half climbing, half cuddling rough, grey and wrinkly elephant-like lower limbs and trunks.
Dancing at WOMADelaide’s Moreton Bay Stage, by dusk, day and night, swaying and stomping, swooning and snoozing beneath the trees, year after year.
There’s a persistent rumour we can’t pin down that “Moreton Bay Figs grow for 50 years, live for 50 years and then die for 50 years.” If that’s the case, many are at the end of their lives.
These concerns occupy the minds of horticulturalists throughout Australia. It would be a pity if kids in Brisbane, Sydney, Melbourne, Hobart, Adelaide, Perth and Darwin couldn’t grow up with these giants.
In Adelaide, as the annual World Music Festival, WOMAD, circles back again for another year under the massive figs, we pause for thought: How are the trees faring as they age? Are they growing weary or can they go on forever? And what about climate change, what will extra heat and more extreme weather do for their prospects?
The Moreton Bay fig trees (Ficus macrophylla) in Botanic Park in Adelaide were planted in 1874, in the former Police Paddock, as an extension of the existing Fig Tree Avenue in the adjacent Adelaide Botanic Gardens. Then Director Richard Schomburgk wanted the Park laid out in the character of a landscape garden and arboretum, complementing the more formal Adelaide Botanic Garden.
The original Avenue was planted in 1866. (The first director, George Francis had developed an outstanding Ficus collection using specimens from gardens interstate, but he fell ill and then died in 1865.)
Senior Horticultural Curator Karen Smith says the Ficus collection has grown to include 42 species from around the world including 15 from Australia, “mostly Queensland, Northern Territory and a little bit of Western Australia”. Altogether there’s about 100 Ficus trees in the Garden and Park, of various kinds.
Fig Tree Avenue, now named Murdoch Avenue (after a sizable donation sometime this century), is a star attraction. It has featured in movies, such as Shine (1996) based on the life of David Helfgot and was the setting for a spectacular musical laser light show in 2021 and 2022 called Light Cycles.
Having so many Moreton Bay figs planted together in an avenue has enabled them to grow together as a community, with an interlocked canopy and root system.
In tropical environments, where the trees would normally grow, the soil is poor because nutrients are continuously leaching out with heavy rain.
Buttress roots enable better extraction of nutrients at the surface, before they get leached out, while also providing structure to help stop trees falling over.
But here in Murdoch Avenue the trees “don’t have to worry about that”, Smith says, so they haven’t developed the buttress system. (It’s a different story in the Park, where the trees are not so close together and perhaps the soil was not as rich, either).
The trees are more than 150 years old now and they’re still healthy, bar one. The tree at the southern end of the avenue, closest to the restaurant, died about three years ago.
But when Smith started preparing for its removal, she noticed “a new tree had started to grow”. The new seedling dropped into a crevice of the dead tree and started growing as an epiphyte, deriving its moisture and nutrients from the air, rain and debris accumulating around it.
“This will be the first time we’ve ever let this happen, because normally they’re growing in trees [where] we don’t want them to do that, so we remove them,” Smith says.
“So this one’s a total experiment, and he’s just powering on now. In three years [he’s] definitely doubled his height. So yeah, this is just a little experiment of mine, just to see whether it is successful, even though he’s got a lot of competition above him. Whether he actually will make his way up through the rest of the trees [remains to be seen].”
The effect of the interconnected canopy has been likened to that of a Gothic cathedral by Art Gallery of South Australia assistant director Lisa Slade.
“The trees here are Moreton Bay figs that are known for their buttress roots. And it’s the buttressing that really was a breakthrough in Gothic architecture that enabled the spanning of large areas of space,” she says.
“The way it opens up through the centre – the way the light comes through as if there is some sort of stained glass at the end.”
A further 290 Moreton Bay fig trees have been planted throughout the Adelaide Park Lands and Squares under the control of the Adelaide City Council including Adelaide Oval and the surrounding Park Lands where they are as iconic as the cricket itself.
ACC Horticulture Team Leader Matt Jorgensen says planting continues to this day.
“We have planted a total of eighteen over the last four planting seasons, which included four this season,” he says. “We have removed three over the last three years that, for various reasons, have passed their Safe Useful Life Expectancy.”
The Moreton Bay Fig planted at the intersection of Sir Edwin Smith Avenue and War Memorial Drive, North Adelaide is believed to be the oldest specimen outside the Botanic Gardens and Botanic Park, planted in 1875.
“This tree is an amazing specimen and worth a visit,” Jorgensen says.
Brisbane City Council has “several hundred” Moreton Bay Fig trees in its parks city wide, including 120 in the city’s streets, but they “are no longer planted as a street tree”, a council spokeswoman says.
“Brisbane City Council continues to plant Moreton Bay Fig trees as park specimen trees and within Habitat areas,” she says.
“The oldest planted specimen that we know of in the City Botanic Gardens is dated between 1867-1887.
“We don’t have any records if any older planted specimens once existed that no longer do so.”
Curiously, the council provided information about the lifespan of Moreton Bay Fig trees that could not be verified.
“They can live up to 200 years in the wild and in Brisbane we have many within our parks that are already 100 years old,” the spokeswoman says.
“In the wild, they grow for approx. 50 years, sit for 50-100 years, and die for 50 years. This can be much shorter in urban areas depending on their growing environment.”
Unfortunately Brisbane Council couldn’t attribute that fact to any particular source or person!
But it helpfully added: “Moreton Bay Figs are a keystone food resource. They are loved by many animals, birds and insects. Figs attract possums and fruit bats, which eat the new fresh leaves. In one study up to 84 bird species visited one fig tree.”
Wasps pollinate fig trees and there is a specific wasp for each species. The wasp is attracted by a scent, which is designed to only attract the female wasps for that fig species, the council spokesperson added. “The wasps rely on the fig trees to complete their life cycle.”
- Ficus trees prefer slightly acidic soil with a pH of 6 to 6.5
- Inconspicuous flowers bloom in summer
- Orange to brown or purple fruit is fleshy and up to 2.5cm across, edible but not appetising.
- Propagate Moreton Bay fig by cuttings, in winter when the tree is dormant.
- Figs can suffer from root rot, from infection with the water mould Phytophthora, or a fungus such as Ganoderma spp or Phellinus noxius. These last two root rot diseases are the most commonly damaging to Brisbane’s Moreton Bay Fig trees.
The national Director of urban forest advocacy group Treenet, Tim Johnson, disagrees with the 50-50-50 statement, suggesting it might have come only from disgruntled city planners.
“I dispute that the species spends 50 years in each phase – growth, life and death,” he says.
“Many tree species die young following urban development due to drainage changes, soil compaction and contamination/pollution, and surface sealing by road and roof – it’s a function of typical urban design and engineering, not of the tree species.”
He confirmed that the trees in Adelaide Botanic Garden seem in generally good health, despite approaching the ripe old age of 157.
His friend and colleague Dean Nicolle has photographs of a Moreton Bay fig that is 28m around its trunk and buttressing, and still growing. It’s enormous so it seems older.
Johnson is also fond of the Moreton Bay Fig as a street tree and has encouraged council plantings over recent years.
“The Moreton Bay fig is a magnificent tree and one that many council arborists seek to keep planting in appropriate locations, and they actively look for locations to plant them,” he says.
“I can recall planting them in parks in St Marys and Belair while I worked at the City of Mitcham, and others when I was at City of West Torrens.
“I actively sought opportunities to plant large tree species so that they don’t disappear from our skyline totally – as many of the eucalypts are in the eastern suburbs, primarily but not solely from private properties. I’ve spoken with SA council arborists in recent months who are seeking to plant a few of them this year.”
While working in Mt Barker in January, Mr Johnson spotted another example. “Their friendly neighbourhood arborist, Courageous Chris Lawry, has been planting trees on roundabouts for a while now… He’s proved it is possible and his sky hasn’t fallen in yet, nor the road.”
Johnson is aware of more than 500 Moreton Bay figs in the care of councils around Greater Adelaide, plus over 650 Hills figs (Ficus microcarpa var. hillii) and a number of other fig species.
The evergreen fig will drop leaves as a coping strategy during extreme heat. The longer the heatwave, the more leaves are lost.
They can take a battering from strong winds and coastal trees fare the worst, never reaching their height potential.
But despite the challenges, Johnson feels the Moreton Bay fig “is one tree that should remain resilient in the changing climate”, relaying the tale of a Darwin tree that lost all its leaves in Cyclone Tracy and yet survived.
“They handle 46 degrees in Adelaide summers in the middle of the city and in northern suburbs, they grow on the escarpment on the southern side of Kings Park in Perth, their roots are great for holding the soil in place on the steep grade,” Johnson says.
“Often getting heat tolerant long-lived trees established can be a problem in cooler areas – as arborists aim to do, to provide resilient urban forest canopy for the future – but the large mature Moreton Bay figs in Hobart prove, they can handle cooler temperatures too.”
Johnson says he’d like to see them planted with stormwater soakage systems, because “they’d save us a fortune in drainage costs and the extra transpiration would help keep the city cooler”. “Nature-based solutions are the way to go in solving many of our urban – and human – problems, and big, resilient, long-lived, self-mulching, habitat providing, fun-to-climb-and-hide-in trees like the Moreton Bay fig are prime candidates.”
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Originally published by Cosmos as The massive trees you grew up with are under threat
Clare Peddie joined Cosmos in 2022 after 15 years as Science and Environment Writer at The Advertiser in Adelaide. She previously worked at CSIRO Land and Water, UniSA, and the Cooperative Research Centre for Vaccine Technology. A passionate science communicator with an extensive and ever-expanding network of contacts, she thrives on exploring new ideas with talented people. Follow @ClarePeddie