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In forests from Tasmania’s cloud‑draped slopes to the shimmering savannas of the Top End, trees are dying younger and faster than scientists had expected.1
The shift is subtle at first – thinning canopies, bare upper branches, a few more dead trunks on the ridge – but long‑term monitoring shows a steady, continent‑wide rise in tree mortality over recent decades.1
A major study led by Western Sydney University has linked this trend to Australia’s warming, drying climate, with mortality increasing most rapidly in hot, dry regions and dense stands where trees compete hard for water and light.1
In tropical rainforests, the annual chance of a tree dying has more than doubled since the 1960s, while warm temperate forests have seen mortality rates more than triple over similar periods.1
Even in cool temperate forests in southern Tasmania, where trees evolved with cold and wet conditions, death rates have climbed significantly since the mid‑20th century.1
Ecologists describe these changes as an emerging “canopy crisis” with far‑reaching implications for carbon storage, water, wildlife and people who depend on forests.3
The question now facing researchers, First Nations land stewards and forest managers is how to protect vulnerable ecosystems as climate‑driven stress accelerates and traditional management tools strain under the load.2
Rising mortality across the continent
The new analysis of long‑term plots across Australia, published in the journal Nature Plants, found that the probability of a tree dying each year has risen in every major forest type since the mid‑1900s.1
The researchers combined decades of measurements from more than 100,000 individually tagged trees with climate records, revealing a clear link between mortality and increasing temperatures as well as shifts in rainfall patterns.1
In tropical rainforests, annual mortality rose from about 0.5 per cent in the 1960s to around 1.3 per cent by 2020, effectively more than doubling the rate at which canopy trees die.1
In warm temperate forests, mortality increased from roughly 0.2 per cent in the 1940s to 0.7 per cent in the late 2010s, while cool temperate forests saw mortality climb from about 0.4 to 0.7 per cent over a similar period, indicating a broad, multi‑biome trend.1
Distinguished Professor Belinda Medlyn, a plant physiological ecologist who led the study, says the pattern is consistent with rising heat and evaporative demand pushing trees closer to their hydraulic limits, even in forests adapted to Australia’s famously tough climate.1
“We are seeing increased mortality not just after extreme events, but as a long‑term signal that tracks the warming and drying of the climate,” she explains, warning that the trend undermines assumptions that forests will reliably soak up carbon as emissions climb.1
Independent forest ecologist Professor David Lindenmayer from the Australian National University, who was not involved in the study, calls the findings a “serious warning” about the stability of forest ecosystems under climate change.12
He notes that accelerated mortality, layered on top of logging, land clearing and altered fire regimes, will have cascading effects on habitat structure, carbon stocks and catchment hydrology in already stressed landscapes.12
Heat, drought and hydraulic failure
While old age, competition and storm damage have always killed trees, researchers say climate‑driven heat and drought are increasingly tipping forests over physiological thresholds they once rarely reached.2
A series of studies on eucalypt dieback across eastern Australia has traced canopy loss to what plant physiologists call “hydraulic failure”, when trees can no longer maintain water columns from roots to leaves as soils dry and heat intensifies.2
During the 2019 drought, many regions of eastern Australia recorded their lowest rainfall and highest temperatures on record, and widespread eucalypt canopies browned or shed leaves in a desperate effort to conserve water.2
Researchers at Western Sydney University’s Hawkesbury Institute for the Environment found a close relationship between tree size, leaf loss and internal water stress, with prolonged drought creating embolisms – tiny air bubbles – that break the continuous columns of water inside the xylem, pushing trees closer to lethal thresholds.2
Associate Professor Brendan Choat, a tree physiologist involved in the work, describes eucalypt dieback as the visible tip of a deeper hydraulic crisis fuelled by drought, heatwaves, previous fire damage and insect attack acting together.2
“These forests evolved with variability, but the combination of hotter droughts and legacy stresses means trees are operating much closer to their safety margins, so relatively small additional shocks can trigger widespread canopy collapse,” he says, warning that larger, older trees are often most vulnerable because they need more water to sustain tall crowns.2
Different regions, different pressures
In the Top End and across northern savannas, climate change is stacking on top of changes in fire regimes to alter the balance between trees and grasses in ways that could reduce tree cover and carbon storage over time.4
Warmer temperatures and shifts in rainfall interact with late dry‑season fires, which burn hotter and more extensively than traditional patchy cool burns, killing young trees and hollowing old ones that once survived lower‑intensity fire.4
In the southwest of Western Australia, long‑term drying, heatwaves and emerging pests are placing jarrah and karri forests under increasing strain, contributing to episodes of canopy decline and dieback that threaten biodiversity and water supplies for Perth and regional towns.7
Forest managers in the region report more frequent tree stress during summer, with reduced streamflows and soil moisture shrinking the buffer that once carried trees through dry spells, especially in regrowth stands where density is high.7
Alpine and sub‑alpine forests in south‑eastern Australia face a different but equally worrying mix of threats, including rising temperatures, reduced snow cover, repeated fires and outbreaks of pests such as the native mountain pine beetle and exotic pathogens.8
Studies on snow gum and alpine ash show that more frequent fires are preventing stands from reaching maturity, while warming favours shrubs and grasses that alter fuel loads and water yield, increasing the risk of a shift from tall forest to more open, flammable vegetation types.8
Along the east coast, from Queensland’s rainforests through New South Wales tablelands to Victorian foothills, a patchwork of canopy dieback syndromes has emerged, including “bell miner associated dieback”, “koala dieback” and high‑altitude eucalypt decline, often involving interactions between drought, nutrient changes, insects and disease.9
A review for the NSW Natural Resources Commission concluded that crown dieback is now widespread across southern Australia and threatens the ecosystem services that eucalypt forests provide in rural and mixed‑use landscapes.9
Ecological, cultural and economic fallout
When canopies thin and large trees die, the impacts ripple through forest food webs, microclimates and water cycles, often in ways that are hard to reverse within human timescales.3
Large old trees provide hollows for gliders, parrots, bats and possums, and their loss can trigger sharp declines in hollow‑dependent species as well as shifts in understorey vegetation that favour more generalist and invasive plants.3
Forests currently absorb roughly one third of human carbon dioxide emissions globally, but rising mortality and more intense fires threaten to weaken or even reverse this sink, turning some forests into net sources of greenhouse gases.6
Recent research suggests that parts of Australia’s tropical forests may already be close to a tipping point where tree deaths and fires outpace growth, with implications for national emissions budgets and the credibility of land‑based offsets.6
For First Nations communities, canopy loss can sever cultural relationships with specific species and places, eroding songlines, bush food resources and the ability to practise cultural burning in the ways that ancestors did.10
Indigenous land stewards across northern and south‑eastern Australia describe the death of long‑lived trees as both ecological harm and cultural grief, especially where species such as river red gums, box eucalypts or bunya pines are central to ceremony and identity.10
Economically, accelerating tree mortality threatens industries from timber and tourism to agriculture that depends on forested catchments for reliable water and shade.3
Forest‑based tourism in regions like Tasmania’s tall eucalypt forests and Queensland’s rainforests relies on intact canopies and iconic big trees, while agriculture in many upland catchments depends on forest cover to regulate flows, reduce erosion and maintain cool microclimates along creeks and gullies.3
Lessons from Indigenous fire management
One of the most widely cited successes in climate‑era forest management comes from Indigenous‑led savanna burning programs in northern Australia, which use early dry‑season burns to reduce the intensity and extent of destructive late‑season wildfires.4
By creating fine‑grained mosaics of burnt and unburnt country, these programs lower fuel loads, protect older trees and fire‑sensitive habitats, and cut greenhouse gas emissions compared with business‑as‑usual fire regimes dominated by large late‑season burns.4
Research on Indigenous fire management and carbon markets has found that savanna burning projects across northern Australia generate millions of dollars in carbon credit income each year, alongside health, employment and cultural benefits for participating communities.4
An evaluation of the Savanna Fire Management Program reported that carbon revenue helps fund ranger jobs, vehicles and equipment, allowing Traditional Owners to spend more time on Country and strengthen local governance, language and law through active fire stewardship.11
Warddeken Land Management, the North Australian Indigenous Land and Sea Management Alliance and other groups have shown that embedding Indigenous knowledge in regional fire strategies can reduce greenhouse emissions, restore patchiness and protect fire‑sensitive rainforest pockets and stone country woodlands that were being scorched by late‑season wildfires.20
These experiences are now informing efforts to adapt cultural burning and Indigenous land management principles to southern and temperate forests, although ecologists caution that different fuel types, land tenures and social histories mean approaches cannot simply be transplanted without careful co‑design.4
Assisted regeneration, diversification and policy reform
As climate stress rises, scientists are testing forms of “assisted regeneration” and “assisted migration” – practices that use human intervention to help forests recover or transition towards compositions more likely to cope with future conditions.5
These include planting provenances or closely related species from warmer, drier regions, thinning dense regrowth to reduce competition for water, and actively re‑establishing key species after severe fires where natural regeneration is failing.5
In some harvested or fire‑affected eucalypt forests, managers are experimenting with mixed‑species plantings and structural diversity to spread risk, rather than recreating single‑age stands that may be more vulnerable to synchronous drought or pest outbreaks.5
A growing body of research suggests that forests with higher species and age diversity can be more resilient to climate extremes, although such interventions raise complex questions about which future ecosystems society is willing to accept and how to weigh carbon, biodiversity and cultural values.5
Policy reforms are also in play, as governments grapple with the gap between climate targets on paper and the realities of forests under stress.3
Reviews of native forest logging in several states, and debates over the integrity of land‑sector offsets, have sharpened scrutiny of whether current rules adequately protect large old trees, maintain habitat structure and account for heightened fire and mortality risks in carbon accounting frameworks.3
For many First Nations land councils, the priority is ensuring that adaptation strategies respect Indigenous rights and decision‑making, and that investments in restoration or carbon projects flow to communities with deep relationships to Country.10
Indigenous leaders argue that meaningful co‑governance of forests, beyond project‑by‑project partnerships, will be essential if adaptation is to strengthen rather than further erode cultural authority on land and waters already transformed by colonisation and climate change.10
Managing fire risk in a hotter world
The 2019‑20 Black Summer fires highlighted how extreme heat, drought and fuel loads can combine to overwhelm even well‑resourced fire services, scorching more than 24 million hectares and killing or displacing billions of animals.13
In tall eucalypt forests, the fires killed many large trees outright and set in train a wave of delayed mortality as drought‑stressed survivors succumbed to pests, disease or secondary stresses in the years that followed, prompting calls for a re‑assessment of fuel management and landscape planning under climate change.13
Fire scientists and Traditional Owners emphasise that fuel reduction burning alone cannot offset the effects of hotter, drier summers and more frequent fire weather extremes, particularly when burns are carried out at scales and intensities that damage soil, understorey structure and cultural values.14
Instead, they advocate a combination of culturally informed mosaic burning, strategic fuel breaks near settlements, careful treatment of flammable plantations and suburban interfaces, and strong emissions cuts to reduce the likelihood of Black Summer‑scale fire seasons becoming the norm.14
In alpine and montane forests, reducing repeated high‑severity fires will be crucial to preventing long‑term loss of obligate seeder species such as alpine ash, which can be wiped out if stands are burned again before young trees can reach reproductive age.8
Managers are exploring a mix of protection zones, rapid response to ignitions in sensitive areas and post‑fire planting to maintain these forests, though some scientists warn that even with active intervention, parts of the high country may transition to shrublands or grasslands under continued warming.8
This decade’s choices
Scientists are clear that there are hard limits to how much adaptation can achieve if global emissions continue on a high trajectory and Australia keeps warming beyond the thresholds forests evolved with.6
The long‑term monitoring of tree mortality suggests that without rapid, deep cuts to greenhouse gas emissions, more forests will cross tipping points where rising deaths, more frequent fires and altered species composition lock in new, more open and less carbon‑dense states.6
Medlyn and colleagues argue that maintaining forests as net carbon sinks will require stabilising global temperatures as close to 1.5 degrees Celsius above pre‑industrial levels as possible, combined with regional strategies to reduce non‑climate stresses such as logging, land clearing and poorly planned development in fire‑prone areas.1
Lindenmayer and other ecologists add that protecting large intact forest areas, particularly those that still contain high densities of big old trees, is a cost‑effective way to safeguard carbon, biodiversity and water yields against mounting climate risks.12
For Indigenous land stewards, the priority this decade is to scale up programs that support communities to live on and care for Country, combining ancestral knowledge and modern tools in fire management, weed control and restoration.4
They stress that whether forests retain their ecological and cultural functions under climate change will depend as much on whose knowledge is valued and resourced as on which technical interventions are chosen.10
Across research groups, agencies and communities, there is a shared recognition that the coming years are pivotal for Australia’s forests, not only because climate impacts are accelerating, but because trees dying today will shape canopy structure, species composition and carbon balance for decades to come.6
The decisions taken this decade – on emissions, land use, cultural governance and investment in adaptation – will determine whether the next generation inherits forests that can still shade, shelter and sustain life, or landscapes where the ghosts of lost canopies are written into bare ridgelines and empty hollows.6
References
- Trees in Australia’s forests are dying faster as the climate warms – Western Sydney University.
- Finding the drivers of Australia’s massive eucalypt dieback problem – Western Sydney University.
- Causes of large-scale eucalyptus tree dieback and mortality – NSW Natural Resources Commission / Murdoch University.
- Diffusion of Indigenous fire management and carbon-credit schemes – Frontiers in Forests and Global Change.
- Yes, forest trees die of old age. But the warming climate is killing them faster – The Conversation.
- Climate change accelerates tree deaths across Australian forests – Phys.org.
- Jarrah forest management in a drying climate – WA Department of Biodiversity, Conservation and Attractions.
- Managing fire regimes for Alpine Ash forests – NESP Threatened Species Recovery Hub.
- Review of eucalypt decline and dieback in relation to lack of resilience – Journal of Development / ARR.News.
- Caring for Country: Indigenous land management in a changing climate – Central Land Council.
- Savanna Fire Management Program: Annual report 2021 – Indigenous Land and Sea Corporation.
- Rising tree death rates in all types of Australian forest tied to climate change – ABC Science.
- Royal Commission into National Natural Disaster Arrangements – Final Report.
- Optimising prescribed burning for future climate – NESP Earth Systems and Climate Change Hub.
- Lessons from Top End Indigenous fire management – NESP Resilient Landscapes Hub.
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