DEER, TREE FERNS, AND THE RETURN OF THE BROWSERS

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Landscape-Scale Impacts of Deer on Tree Ferns in South-Eastern Australia

In 2025, a team of ecologists led by Ami Bennett published a study in Austral Ecology exploring how wild deer interact with one of Australia’s most iconic plant groups: the tree ferns. The research surveyed more than 4,500 tree ferns across over 200 wet forest sites in Victoria, documenting patterns of browsing and the likely influence of deer, particularly sambar.

The results sparked plenty of discussion. Tree ferns under a metre tall were regularly browsed, while larger individuals, especially those over two metres, were rarely touched. No preference was detected between the main species— Dicksonia antarctica and Cyathea australis—and the less common Todea barbara appeared similarly affected, though in too small numbers for firm conclusions.

To some, the findings highlight a looming ecological threat. To others, they provide evidence that deer are performing an ecological role that has been missing from Australia since the extinction of its megafauna. This review examines the study’s findings and considers the broader context of deer as large herbivores that shape landscapes in subtle ways.

Tree ferns: ancient survivors of the forest

Tree ferns are among the most recognisable plants in Australia’s cool temperate and wet forests. With lifespans exceeding 200 years and growth rates measured in millimetres per year, they form towering, palm-like trunks topped by crowns of fronds that provide shade, moisture, and structure to the understorey. They host epiphytes, shelter invertebrates, and even regulate stream temperatures. In short, they are keystone plants whose influence extends far beyond their own biomass.

Because of their slow growth, tree ferns are often seen as vulnerable to disturbance. A frond stripped by a browser can be replaced, but repeated removal might slow growth or prevent small individuals from ever reaching safe heights. This makes them a natural focal point for research into herbivory in Australia’s wet forests.

What the study found

Bennett and colleagues combined two approaches. At the landscape scale, they examined vegetation surveys across the Greater Melbourne region. At the local scale, they conducted detailed assessments of tree ferns in the Yarra Ranges National Park. In both cases, browsing impacts were strongly related to plant height.

This height-limited pattern is consistent with the reach of deer, especially sambar, which are abundant in Victoria’s forests. Camera traps occasionally captured sambar feeding on ferns, confirming the link. In the Yarra Ranges, where only sambar occur, browsing was widespread; in other areas, fallow and red deer may also have contributed.

Importantly, tree ferns were not disappearing. Despite browsing, they remained abundant across all surveyed sites. The impacts, while visible, were partial and did not extend to mature plants towering above browsing height.

Deer as ecological actors

Australia has lost its giant kangaroos, browsing diprotodonts, and other megafauna, which once shaped forests and woodlands, stripping foliage, opening gaps, and recycling nutrients. Their extinction left a missing ecological role that smaller macropods and possums never entirely replaced.

Deer may be stepping into that gap. Their browsing on tree ferns, shrubs, and understorey plants is not random destruction, but rather part of the same ecological process observed in forests worldwide. In Europe, North America, and Asia, deer influence plant growth patterns, regulate forest structure, and maintain mosaics of open and closed understorey.

The Australian data suggest a similar pattern: tree ferns grow through a ‘window of vulnerability’, being heavily browsed while small, but becoming safe once they reach a certain height. This is the classic herbivore–plant dynamic, where browsing pressure shapes survival curves and influences forest composition.

A balanced perspective

Of course, herbivory has its consequences. If browsing pressure is too high, recruitment of young ferns could slow, potentially altering forest structure in the long term. But it is equally important to recognise that browsing does not equate to loss. Tree ferns evolved in the presence of browsers, and many show resilience through continuous frond replacement.

The Bennett study did not find local extinctions or collapsed populations. Instead, it documented contemporary coexistence: browsing was common, but tree ferns were still present in healthy numbers across the landscape. That balance is a vital nuance in discussions often dominated by alarm.

Deer and the niche of lost megafauna

The idea that introduced deer might function as ‘ecological surrogates’ for extinct megafauna is controversial but worth considering. Australia’s ecosystems developed with large browsers, and the loss of those species almost certainly altered forest dynamics. With deer now established, some of those lost processes may be returning.

Sambar and fallow deer, for example, open up dense understorey in gullies and riparian zones, potentially increasing habitat heterogeneity. By consuming foliage within their browsing range, they may reduce competition for taller plants while creating microhabitats used by birds and small mammals.

This does not mean all impacts are positive, nor that deer perfectly replicate extinct species. But it suggests their role is more complex than simply ‘pests damaging vegetation’. They are, for better or worse, part of the ecological story of modern Australia.

Knowledge gaps and future directions

The Bennett study also highlights areas where more research is needed:

Answering these questions will help determine whether browsing pressure is within a natural, sustainable range or if management needs to reduce densities in sensitive habitats.

Living with deer

Whatever the answers, deer are here to stay in many parts of south-eastern Australia. Eradication is unrealistic; management will focus on achieving balance. That balance requires acknowledging both sides of the ledger: the risks to slow-growing plants like tree ferns, as well as the ecological functions that deer now provide.

Bennett and colleagues have given us a good picture of how deer and tree ferns interact. The story is not one of imminent floral collapse, but of an evolving relationship between introduced herbivores and native plants. Tree ferns are still thriving in the shadow of browsing pressure, and deer are fulfilling a role as the large browsers our forests have lacked for millennia.

Conclusion

The debate around deer often polarises into two camps: destructive invaders or valuable game animals. The reality, as this study shows, is more nuanced. Deer browse tree ferns widely, yet the plants endure. Impacts are real, but they are also bounded, shaped by plant height and resilience.

Seen through the broader lens of ecology, deer may be restoring a missing dimension of herbivory to Australian forests. They are not ghosts of the past, nor perfect replacements for extinct megafauna, but they are active players in the ecosystems they now inhabit. Recognising this complexity—neither demonising nor romanticising—is the key to moving forward with thoughtful management and open-minded science.