Threat to grass trees

A serious threat to our iconic native grass trees

By Mary Bremner

The impact of the pathogen Phytophthora on our heathland and forest ecosystems is very real says Aireys Inlet resident and ecologist, Dr Mark Garkaklis.

We might call them grass trees, kangaroo tails, yaccas or by their scientific name Xanthorrhoea australis. Our grandparents may have referred to them as black boys. First inhabitants in other places named them bukkup, baggup, balgaor kawee. The local Wadawurrung people used the word djuwutj for the plant’s resin used in spear making and for patching up water containers. With their skirts of long, wiry, bluegreen foliage and dramatic flowering spikes, these plants are a highlight of our native bushland. They flower prolifically following a bushfire, providing a perch for the native birds that feast on their nectar. Notoriously difficult to establish in our gardens and very slow growing, they are thought to live up to 450 years in the wild. However, it is horrifying to find out that these iconic plants are under a very real threat of disappearing from our local heathlands. ‘Our grass trees are fighting what seems to be a losing battle, says Dr Mark Garkaklis.

Phytophthora plant killer

‘The enemy is the pathogen Phytophthora cinnamomi, commonly, but incorrectly, known as cinnamon fungus. It is actually more closely related to algae than fungi. Phytophthora draws its name from Greek words meaning “plant killer”. It is recognised as one of the 100 worst biosecurity threats on the planet.’ Mark was first involved in research into Phytophthora dieback in his home state of Western Australia. For his PhD, Mark studied the way ecosystems behave and what happens when you lose small elements from a system –how the ecosystem either stays resilient or transitions into something new. At the time, there was a lot of concern about the dieback of the jarrah forests, caused by Phytophthora. This destructive pathogen doesn’t only kill grass trees, but can also attack Victoria’s floral emblem, Epacrus impressa (pink heath), as well as Banksia marginata (silver banksia) and members of the Isopogon family. It can get into your garden, with roses and avocadoes also susceptible to its advances. It is the impact of the pathogen on our heathland and forest ecosystems that currently exercises Mark’s mind. Since 2000, Mark has been involved in relevant research

Dr Mark Garkaklis inspecting dieback infected grasstrees near the Great Ocean Road. with colleagues across Australia and New Zealand. Mark also teams up with his wife, Dr Barbara Wilson, to trap and study populations of endangered native mammals in the Otways region. Very few animals, and certainly no endangered mammals are found in areas impacted by Phytophthora dieback. By contrast, where there are healthy grass trees, there is a diversity of animal fauna. The impact of the destruction of their habitat is clear and very worrying for these passionate ecologists. An understanding of how the pathogen spreads is essential to its control. It seems most likely the disease – a water mould – was carried to Australia on the cuttings and plants brought in by the first European settlers, but it was not recognised as a threat until the 1970s. It is spread largely by our network of roads and tracks, formed with contaminated gravel. Vehicles and bikes that move along the roads can also spread the pathogen.

Where will you see the damage?

You can find evidence of this for yourself in the Anglesea Heath. Typically, the pathogen is carried very quickly downhill by water flowing from the road via a spoon drain. It infects the roots of plants in the path of the water – the roots and the vascular tissue that take water up to the plant degrade and it starts yellowing from the tips – it looks like it’s dying from drought. Eventually the plant succumbs. Once infection has taken hold, the pathogen can also progress laterally by root-to-root contact.

As grass trees die off, plants that are resistant to the dieback, such as sedges, repopulate the territory. To the untrained eye it might look like attractive native vegetation, unaware that 20 years earlier this might have been a grass tree grove. Mark is deeply concerned about the situation in the Eastern Otway Ranges where the disease has been let run and is now starting to take its toll. He cites, as an example, the area from Mt Ingoldsby Road to Gilbert Street, back around the Alcoa pit, along the Alcoa Boundary Track and up the Pipeline Track to Forest Road – all completely impacted by Phytophthora. Mark believes this has happened since the 1983 Ash Wednesday inferno – the fire-fighting activities and the subsequent regeneration work exacerbated the spread of the disease.

A glimmer of hope

As bad as all this seems, there is a glimmer of hope in the form of the chemical phosphite. It has been used for 20 years in Western Australia and found to be completely effective in protecting endangered plants, without any detrimental side effects. The chemical doesn’t kill the pathogen, but works by turning on the plant’s defence mechanisms. This prevents the pathogen from getting into the plant’s root systems and it is able to resist infection. Mark is excited at the prospect of this crucially important work. ‘We can’t afford just to write off all of our heathlands in Australia over the next 50 years,’ he said. In some areas in Western Australia, plants have regenerated in previously infected sites after treatment with phosphite. This has inspired Mark to start trials in the Anglesea Heath, working in conjunction with Deakin University, to see if they can successfully reestablish species sensitive to Phytophthora.

We must also do our bit

In the meantime, we can do our bit to avoid inadvertently contributing to the spread of the disease. Mark says quarantining pristine environments is the gold standard and swathes of Western Australian forest were protected in this way. However, as our recent experience with COVID has taught us, quarantining is not always practical or foolproof. If we want to be able to enjoy our beautiful bushlands now and into the future, Mark says we need to be mindful. ‘Never let your guard down,’ says Mark. ‘We need to be careful where we walk and be sure our boots and bike tyres are completely clean of mud, which may contain the pathogen. Where footbaths and brushes are provided we should use them. ‘If you’ve got a dirty mountain bike and you decide to make a new track through the bush, you’ll spread the disease,’ warns Mark. Fond of a military analogy when it comes to the battle being waged against Phytophthora, Mark says we all need to be ‘frosty’ – that is, stay sharp, aware and in focus. This doesn’t seem much to ask to help preserve our beautiful grass trees.