Native trees like the paperbark are central to the culture of the traditional owners of K’Gari (Fraser Island).
“These species are living stories,” says Matilda Davis, who works with the Butchulla Aboriginal Corporation as a biosecurity and climate change officer on the World Heritage-listed island.
Apart from many being edible or medicinal, these trees have ancestral and spiritual connections, and are key to the health of Butchulla country, she says.
For example, the paperbark (Melaleuca quinquenervia)—called “deebing“ by the Butchulla people — can let them know when it’s safe to sustainably harvest certain foods.
“When the deebing flowers, it’s a seasonal indicator for particular kinds of seafood,” Ms Davis says.
Paperbark and other tea-trees belong to a large family known as Myrtaceae, which also include eucalypts, lilly pillies, bottlebrushes and guavas.
But a pandemic of an invasive fungal disease is making it harder for some Myrtaceae species to bounce back after intense bushfires.
Myrtle rust (Austropuccinia psidii), which can appear as a bloom of golden spots on leaves, can suck the life out of new growth.
The disease, which was first detected on K’gari in 2013, is a real worry for the Butchulla, Ms Davis says.
“Myrtle rust is threatening our ability to practice culture.”
The ‘other pandemic’: the spread of myrtle rust
Myrtle rust originally comes from South America, where the native Myrtaceae species have co-evolved a natural resistance to it.
But, the plant fungus has jumped from the wild — not unlike the virus that causes COVID-19 — and become a “pandemic strain”, causing disease across the globe.
Its tiny spores have hitched a ride on the wind or on people’s clothes, with globalization playing a key role in the spread.
The disease has proven devastating to many “naïve” species of Myrtaceae that did not evolve with fungus.
Since it landed in Australia in 2010, it has infected forests in New South Wales, Queensland, Victoria, the Northern Territory, Tasmania and most recently Western Australia.
Fungus targets growing tips of plant
When the fungus lands on species susceptible to infection it can rob the plant’s cells of nutrients, and kills off the growing tips — the new leaves, stems, flowers and fruit.
The plant is forced to put more energy into new growth, but if the plant cannot fight off the fungus, it becomes re-infected.
“So you get this repeated cycle of growth and dieback and eventually the plant runs out of reserves and declines,” says forest pathologist Geoff Pegg of the Queensland Department of Agriculture and Fisheries.
Dr Pegg has been working to document the impacts of myrtle rust on trees impacted by fire, including on K’Gari where he is collaborating with Ms Davis and the Butchulla Aboriginal Corporation.
A shrub called midyim berry (Austromyrtus dulcis) is among the Myrtaceae species affected on K’Gari.
The plant is important for the health of the country, Ms Davis says.
She says many animals depend on the berry, which is “sweet with a distinct aftertaste.”
But myrtle rust affects the formation of the flowers and tasty berries in plants growing in areas recovering from bushfire.
‘Unprecedented’ extinction event of rainforest species likely
A recent survey of rainforests in Eastern Australia predicted a “plant extinction event of unprecedented magnitude” due to myrtle rust.
“Sixteen species are doomed with extinction within a generation,” says co-author of the survey, Rod Fensham, a plant ecologist from the University of Queensland.
Among the most at risk were the thready-bark myrtle (Gossia inophloia) and native guava (Rhodomyrtus psidioides).
And a further 20 species could be at risk.
“It’s an extraordinary example of a disease phenomenon,” he says.
“It’s a pretty profound event.”
Dr Pegg has also seen the devastating effects of myrtle rust on the east coast, and not just in rainforests.
“There are thousands of dead trees in some sites that we’ve looked at.”
He points to one forest at Tullebudgera not far from the Gold Coast, where there were 3,400 dead trees per hectare.
When he started the study in 2014, the high-rainfall forest was dominated by Myrtaceae species such as eucalypts and silky myrtle (Decaspermum humile).
Now most of seedlings that are surviving are non-Myrtaceae natives, and weeds like lantana and camphor laurel.
fire and rust
While Dr Fensham doesn’t count paperbarks among the worst affected trees, others like Dr Pegg emphasize they are still at risk, especially after bushfires.
“We’ve seen quite significant impacts in some sites,” Dr Pegg says.
Bob Makinson of the Australian Network for Plant Conservation is also worried about paperbarks from a biodiversity perspective.
Even without sending paperbarks extinct, he says, the impact of myrtle rust on such species could have broader implications for the ecology.
“The paperbark is such an important tree for wetlands and riverbanks where there are not many other trees that can tolerate the water-logging conditions there,” Mr Makinson, a conservation botanist, says.
“This species is important for providing shade on the water, for reducing erosion and for keeping freshwater wetlands running.”
And, he adds, insects, birds and flying foxes rely on the paperbark’s flowers.
“We don’t know what the knock-on effects will be of reduced flowering in those populations that are severely affected by myrtle rust,” Mr Makinson says.
Some individual trees in a species are more resistant to myrtle rust — just as some of us appear to be naturally more resistant to COVID-19.
But Dr Pegg says only 15 to 35 per cent of paperbark seedlings in New South Wales study sites have shown natural resistance to the fungus.
What about eucalypts?
During the 1970s, myrtle rust decimated eucalypts in Brazil, where they were planted as an exotic tree.
Thankfully, testing so far has shown eucalypts growing natively in Australia have promising levels of resistance, although there is some concern about a few eucalypt species.
And just as we’ve had to worry about the rise of more infectious strains of COVID-19, new strains of myrtle rust may be on the way.
In fact, last year, Brazilian scientists reported the evolution of a new “highly aggressive” fungus that was attacking eucalypt plantations in that country, which had been bred to be resistant.
“An introduction of a new strain like that to Australia could actually increase the risk to our eucalypts,” Dr Pegg says.
Stopping the spread to save species
To stop the spread of the disease to new areas, quarantine is essential – as is monitoring.
When the fungus reached the Northern Territory in 2018, this kicked off a monitoring program which subsequently picked up myrtle rust in the Kimberley region of Western Australia.
Symptoms of myrtle rust can appear variable and are sometimes hard to identify the disease unless the plants are dripping with what some have described as a “yellow sludge” of spores.
Botanic gardens and others are using every tool in the book to identify plants with natural resistance to myrtle rust.
The idea is to preserve seed or other biological material which could be crucial in saving species.
And, it wouldn’t be a pandemic without a vaccine in the wings — Australian scientists hope to use RNA-interference vaccines to get the fungus to self-destruct.
But you can also help by washing your clothes (including hat!) if you’ve been in the bush in affected states, and by following quarantine rules.
And think about planting threatened species in your backyard.
Dr Fensham suggests that native guavas can make a nice addition to the home garden.
“We need more people committed to growing these things and trying to get them to reproduce,” he says.
Avoiding ‘upside-down country’
Meanwhile, back on K’Gari, Ms Davis hopes to collect seeds from paperbarks and other affected trees in an effort to conserve genetic diversity, which will be key to their survival.
And she wants to see a shift away from “bad fires” with high flames that leads to a reverse in the color scheme of forests—resulting in brown burnt treetops and green new growth below.
“That is a good indicator for us that that country is stressed,” she says.
“We call it upside-down country.”
She says evidence links cooler, less-intense fires with lower impacts from myrtle rust infection.
So she’d like to see a move towards traditional “Galangoor gira” — or “good fire” — practices, something Dr Pegg agrees could be explored in the future.
Ms Davis says the “positive and respectful” partnership with scientists like Dr Pegg is allowing for a two-way learning, placing traditional custodians of the land at the center of the response to ecological problems like myrtle rust
“I do believe the answers are in our old people’s ways.” she says.
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