- Unlike destructive bushfires, tree health is often treated as a niche or technical issue, but its implications pose equally important questions about ecological resilience and public health, a new op-ed argues.
- Threats to Australian tree species are multiplying like an invisible bushfire via a proliferation of introduced insects and pathogens, the authors suggest, ahead of his country’s first national forum on the topic later this month, Safeguarding Australia’s Tree Health, in Brisbane.
- “We recognize bushfires as a national crisis because their impacts are visible and immediate, but some ecological crises arrive more quietly. If we fail to notice them early, the damage can become harder to reverse for forests, for biodiversity, and for the communities that depend on them,” they write.
- This article is a commentary. The views expressed are those of the authors, not necessarily of Mongabay.
Some of the most serious threats to our forests do not arrive with smoke or headlines. They move quietly, through bark and new growth, weakening ecosystems long before we notice. Without sustained attention, our unique flora and fauna remain vulnerable. Tree health is often treated as a niche technical issue, but it is also a question of ecological resilience, public health, and how well communities adapt to a hotter, more disturbed world.
Devastating bushfires are reshaping Australia’s landscapes and ecosystems, and climate change is accelerating species loss. But there is a quieter threat with ecological, economic and human consequences. Alongside fire and drought, microscopic pests and pathogens are spreading through forests and urban canopies, thinning tree cover, weakening ecosystems, and leaving them more vulnerable to the next shock.
Most of us appreciate the comfort of a shady tree on a hot day, and we’ve heard that the Amazon rainforests are the lungs of the planet. Yet many people underestimate the importance of healthy tree populations and how closely they are tied to our physical and mental health.
In his new book Nature and the Mind, Marc Berman, professor of psychology at the University of Chicago and director of the Environmental Neuroscience Lab, draws together evidence on how nature supports cognitive, physical and social well-being.
One of the starkest “natural experiments” he draws on comes from North America’s invasion by the emerald ash borer (Agrilus planipennis). Research has linked large-scale ash tree loss to human outcomes, including higher mortality from cardiovascular disease and higher rates of lower respiratory disease, with these relationships strengthening the longer the pest has been present.
The logic is grimly straightforward. When tree canopy goes, you lose multiple protective buffers at once, including shade and cooling, air-quality benefits, and the social cohesion that comes from people spending time outdoors in livable public spaces. Tree loss is not only an environmental issue. It is a public health issue.
While this example is particular to North America, here in Australia, we are not immune to similar biological incursions.
Polyphagous shot-hole borer
Polyphagous shot-hole borer (Euwallacea fornicates, or PSHB) is native to Southeast Asia and was detected in East Fremantle, Western Australia, in August 2021. Although capable of attacking a wide range of tree species, it shows a clear preference for certain susceptible hosts that support heavy infestation and reproduction. Females bore into trees, creating tiny “shot holes” and then introduce a fungus that blocks water transport and feeds their larvae. Although a symbiotic relationship for these two species, it’s a double hit for trees that leads to dieback and often death.
Despite being only the size of a sesame seed, this duo’s impacts are far-reaching. For example, Perth’s urban tree canopy is not just cosmetic, rather, it is “livability infrastructure” that provides essential cooling in Australia’s warmest state capital. But the list of PSHB host trees includes many commonly planted and native species that line parks and streets, both there and across Australia. Despite aggressive biosecurity control efforts, Perth’s priority has now shifted from eradication to long-term impact management after determining it was no longer technically feasible to eradicate PSHB from Western Australia.
That transition is a hard moment, as it forces a shift from “stop it” to “limit spread, reduce harm, and live with it.” If PSHB establishes in Queensland, modeling suggests Moreton Bay figs and plane trees, both highly reproductive hosts, would be among the most vulnerable. More broadly, it is a reminder that once invasive pests become established in tree systems, the challenge quickly becomes one of long-term adaptation, rather than simple removal.
Myrtle rust
Myrtle rust is caused by an exotic rust fungus (genus Austropuccinia) first detected in Australia on the New South Wales Central Coast in 2010. It threatens the Myrtaceae family (eucalypts, paperbarks, tea trees and bottlebrush), plants that shape ecosystems, catchments, wildlife habitat, and the character of our gardens.
The death of tens of thousands of trees has gone by unnoticed, and close to 20 species of Australian native plants are on the verge of disappearing. Plant communities have changed and waterways in these wet tropics are scarred with dead and dying watergums that once protected them from erosion while providing shade and habitat to a myriad of juvenile fish and crustaceans. The health of these waterways is also crucial to the Great Barrier Reef.
Extreme weather patterns have also seen fire and cyclones impacting a range of native ecosystems: a worrisome dynamic is how rust and fire can compound each other. Myrtle rust mainly infects new growth, so post-fire regeneration is susceptible, including seedlings and resprouts. Forest pathologist Geoff Pegg described regeneration as “perfect conditions for rust,” with new reshoots and seedlings repeatedly infected on a range of Myrtaceae, with disease incidence and severity increasing rapidly under ideal conditions.
On K’gari, fires in 2020 impacted more than 80, 000 hectares (nearly 200,000 acres) of the island’s vegetation. Subsequent assessment by Traditional Owners working alongside forest pathologists recorded myrtle rust symptoms in regenerating vegetation, including culturally and ecologically significant species like paperbark and satinay.
Similarly, recovery of vegetation in fire-impacted areas of Bundjalung National Park, New South Wales, was impacted by myrtle rust, with seedlings and reshoots of paperbark species (prickly melaleuca, broad-leaved paperbark) as well as eucalypts among the affected plants.
These are not isolated biological events. They are examples of how climate pressures and invasive pathogens interact, amplifying one another. They also show why tree decline should not be treated as a narrow pathology issue when its effects spill into waterways, biodiversity, cultural landscapes and community well-being.
Lessons for us all
There are lessons here about tree health, plant pathology, biosecurity, individual well-being and collective action. These threats cannot be ignored and there are no simple solutions, particularly when managing the impacts in native ecosystems from pests and pathogens that have extensive host ranges. Invasive pests and plant diseases are often framed as technical challenges, yet when trees decline, the effects ripple far beyond ecology, into public health, livability and economic resilience.
We are more dependent on trees than we like to admit, economically and ecologically, but also for human health and community well-being.
Biosecurity is a shared challenge that depends on what communities see, value and are empowered to act on. Trees and forests underpin ecosystems, communities, and economies. They hold cultural and spiritual meaning, and not surprisingly, there is mounting evidence of tangible health benefits.
A serious response must start with the basics. Constant vigilance, early detection, raising awareness, and working with those closest to the landscape to identify outbreak risks and track impacts over time.
We need sustained collective action that is locally grounded and brings together expertise across disciplines and practical local knowledge, not only scientific and technical fields. The broader lesson is simple: protecting tree health means protecting the ecological systems that support both nature and people.
We recognize bushfires as a national crisis because their impacts are visible and immediate, but some ecological crises arrive more quietly. If we fail to notice them early, the damage can become harder to reverse for forests, for biodiversity, and for the communities that depend on them.
Michael Reid is chief plant health manager for the state of Queensland, where his work focuses on plant health, biosecurity preparedness and response, and the broader social and ecological challenges posed by invasive pests and diseases. Ted Alter is founding partner of Creative Insight Community Development.
Banner image: A controlled burn in northeastern Victoria to reduce fuel load before summer fire season. Image courtesy of Michael Reid.
Related audio from Mongabay’s podcast: News of Australia’s “humpback comeback” has made waves recently and wildlife scientist and whale expert Vanessa Pirotta discusses this inspiring conservation achievement, listen here:
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Citation:
Donovan, G. H., Butry, D. T., Michael, Y. L., Prestemon, J. P., Liebhold, A. M., Gatziolis, D., & Mao, M. Y. (2013). The relationship between trees and human health: evidence from the spread of the emerald ash borer. American Journal of Preventive
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