Despite it being an introduced species, the Norfolk Island Pine (Araucaria heterophylla) is an iconic feature that lines the beaches of the Gold Coast, with their distinctive silhouettes standing tall against the skyline.
However, recent research led by Griffith University shows some of these towering trees are facing an increasing threat, with many showing signs of decline due to a combination of environmental stresses such as climate change and harmful pathogens.
In the first half of the 20th century, the first Norfolk Island Pines were planted by early settlers that set up their new lives on Gold Coast. The trees planted at Burleigh Heads in Justins Park by the Justins brothers in 1934 are arguably the most iconic on the coastline.
PhD Candidate Anna Petrova from Griffith's Green Infrastructure Research Labs (GIRLS), who led the study with the City of Gold Coast and Heritage Tree Care, investigated the tree decline in eight sites along the Gold Coast stretch.
Petrova's research sought to understand the cause of this decline and analyse the existing solutions to protect these trees.
Among the preliminary findings was the presence of pathogens from the Botryosphaeriaceae family that attack trees weakened by the droughts. Greenmount's trees on the southern Gold Coast were also found to have the shortest branchlets and generally a different pattern of decline.
"Our initial findings suggest that while pathogens play a significant role, it is the combination of unsuitable climatic conditions and urban stresses that makes the trees susceptible to these diseases," Petrova said.
"Losing mature trees like Norfolk Island Pines is not only an environmental and cultural loss but also an economic one.
"Replacing trees is expensive, and it takes decades for new trees to mature. That's why it's critical to improve soil management, tree selection, and ongoing monitoring to ensure the health of our urban forests."
The increasing number of extreme weather events, including prolonged droughts, exacerbated these stresses, which resulted in weakening Norfolk Island Pines along the coastline and left them vulnerable to pathogens like those from the Botryosphaeriaceae family.
The most recent decline in Norfolk Island Pines was observed following the 2018-2019 drought, with symptoms such as browning tips, defoliation, and shortened foliage.
Soils in urban areas also often offered a hostile environment – often compacted, dry, and nutrient-poor – putting immense pressure on tree species.
Petrova's findings would assist the City of Gold Coast Council and Heritage Tree Care to assist in their assessment of proactive measures to protect these trees.
Soil decompaction and injections of micronutrients were being used to improve root health and water retention with Petrova's team testing the effectiveness.
These treatments, combined with the use of compost and biochar, were aimed at enhancing soil health and tree resilience.
"Urban soil management needs to be more proactive," Petrova said.
"We need to monitor tree health regularly and ensure that we're selecting species that are resilient to the unique challenges posed by urban environments and local pathogens."
Petrova added that further research into tree species that were more suitable for the changing climate and a deeper understanding of existing pathogens was essential for preserving the Gold Coast's urban canopy.
With a commitment to soil management and ongoing research, Petrova said the goal was to mitigate the decline of Norfolk Island Pines and other important urban trees.
"But ultimately, we need to consider two options: to continue planting the pines and invest more into their management, or accept that the climate will be changing and start thinking about gradually replacing some of them with more drought and pathogen tolerant species."
PhD Candidate Anna Petrova
