Scott O’Keeffe, ecologist, The Nimbin GoodTimes
Around 15 years ago, people living in the Maleny area of Southeast Queensland noticed a decline in the health of some large mature bunya pines (Araucaria bidwillii). The crowns of the trees began turning brown, quickly followed by foliage well below the crown.
Within a short time, all foliage would be shed, branches cast, and the affected tree would be dead. At the time nobody reported the problem.
Years passed and more trees died until the deaths became too obvious to ignore. Concerns grew about how the disease might affect the region’s National Parks where ancient Araucarian forests of bunya and hoop pines (Araucaria cunninghamii) still exist, as well as the closely related Australian kauri pines (Agathis robusta).
An investigation took place after the realisation that the condition might threaten the native softwood forestry industry: 40,000 hectares of commercial hoop and bunya pine plantations are managed by the Queensland state with smaller areas in NSW.
The investigation showed that dead and dying bunya pines in the Bunya Mountains near Dalby are infected with a water mould, Phytopyhora multivora, a pathogen that attacks the feeder roots of trees, making it impossible for them to transport water and nutrients.
Hoop and bunya pines in the Maleny and Landsborough areas showed symptoms of infection from the closely related Phytopthora cinnamomii. This organism also affects the extremely rare Wollemi pine (Wollemia nobilis) in the Blue Mountains, New Zealand kauri pines (Agathis australis) and a variety of other plants including avocados.
Araucarian Dieback (AD) is on the move. The pathogens can be spread by flowing water, or the movement of infected soil and plant material. Forestry operations, mountain bikes, bushwalkers, feral pigs – all of these are known vectors of the fatal disease. Aerial surveys in 2019 showed that AD had spread throughout the Bunya Mountains.
Sanitising stations at the entrance to national parks where Araucarians are found were among the preventative measures taken to prevent spread of AD. Visitors are required to step through a tray of disinfectant to kill any pathogens on their footware. But people, this didn’t work. As a result, authorities decided to keep the location of the Wollemi pine a secret from the public, but bushwalkers managed to find the conservation area, bringing Phytopthera with them.
Containing the pathogen has been beneficial and has bought time while research is done to find treatments for AD. One treatment shows promise. Phosphite injected into the tree’s trunk can boost its immune response. Healthy trees can be protected and those in the early stages of infection can recover. This is good news, but can we afford to inject all at-risk trees with phosphite?
In the Bunya Mountains where the landscape has had minimal human impacts, the pattern of infection differs from that in highly modified environments such as Maleny and Landsborough. Dieback is always fatal but in the Bunya Mountains not all trees are affected. In Landsborough and Maleny all trees in the affected areas die. In heavily modified environments soils lose their structure and condition and become less able to support healthy plant growth. Now there is the added stress of changes to climate.
Since more than one Araucarian species is associated with ‘Araucarian dieback’ is it really a specific disease? Dr. Louise Shoey, a plant pathologist and leading researcher into AD suggests that although the cause of dieback is phytopthora organisms, the condition is analogous to coral bleaching.
In other words, AD is a syndrome rather than a specific disease, which explains why two pathogens are associated with Araucarian dieback in Australia, New Zealand, South and Central America. Therefore, we may need to address AD’s pathogens as well as land degradation.
Although progress has been made to find treatments, this takes time, and we also need to take serious preventative action to protect healthy populations of Araucarians. Recognising the presence of the condition is necessary if you want to slow its spread. We also need to make biosecurity as high a priority as halting logging in native forests. The CSIRO points out that, among the many threats to biodiversity, invasive organisms are probably the greatest.
The Northern Rivers region supports important areas of largely intact Araucarian forest, remnant patches of hoop pine regrowth, and planted hoop, bunya and other Araucarian pines.
Over recent years, I have seen an increase in the number of trees in the modified landscape that show symptoms of decline like those in trees affected by AD. I do not want to see a repeat of the mistake that was made in Queensland. It would be foolish to ignore that what I am seeing is nothing out of the ordinary. Hoop pines are dying, and we should be finding out why. It may not be AD, but we might find it’s a problem we can solve.
I’ve reported what I’ve seen to the appropriate authority, the Department of Primary Industries (DPI). Their first response was not encouraging. From the desktop they declared that there was a low risk of dieback affecting local Araucarians.
As a former biosecurity officer who has worked on containing the spread of myrtle rust, yellow crazy ants, and fire ants among other things, I pointed out how easily the die-back organisms are spread, especially when there are so many potential vectors.
Risks include equipment carrying infected soil moved between Queensland and New South Wales. The same thing could happen with livestock. Visitors to the Northern Rivers travelling from infected areas in Queensland could bring the organism with them when they visit the world Heritage areas on the border where we have substantial Araucaria forests.
After I expressed these concerns, I was pleased when the DPI got back to me to arrange a visit to the Northern Rivers in the new year. An investigation into the apparent decline in our local Araucaria trees will be made. That does not just mean hoop pines. I have also seen symptoms in Norfolk Island pines and bunya pines that have been planted in the region.
I hope that this investigation will be directed at finding out what is causing this problem rather than just trying to disprove the theory that the dead trees are affected by the same condition that is killing trees in Queensland. Something out of the ordinary seems to be happening.
We should try to find the cause and fix the problem whatever its origin. Expect good news, but prepare for more preaching…
This article appeared in The Nimbin GoodTimes, December 2024.