Trees across Australia’s forests are dying at increasing rates, with new research pointing to a long-term shift in forest health linked closely to a warming and drying climate.
The study, led by Western Sydney University and published in Nature Plants, analysed 83 years of data from more than 2,700 forest plots nationwide. It brings together records from tropical rainforests, savannas and temperate eucalypt forests to track background tree mortality, meaning tree deaths not caused by fire, clearing or logging.
The findings show that background mortality has risen steadily since the 1940s and that this pattern appears across all major forest types. Over the same period, tree growth has either stalled or slowed, suggesting the rise in deaths is not part of a natural cycle of renewal but reflects an imbalance between how fast trees grow and how quickly they are lost.
Researchers found that the trend closely follows Australia’s changing climate. Rising temperatures were identified as the dominant factor, with mortality increasing fastest in hotter, drier regions. Dense forests were also more vulnerable, as competition for water and light adds to environmental stress.
Professor Belinda Medlyn from the University’s Hawkesbury Institute for the Environment said the results point to mounting pressure on forest ecosystems.
“Australians rely on their forests for a wide range of ecosystem services, from cultural values and recreation to timber for houses. Increasing tree mortality in our unique forests will affect all of these. A particular worry is that the forests’ ability to store carbon will decline. This has significant implications for Australia’s net carbon balance,” she said.
‘Australians rely on their forests for a wide range of ecosystem services, from cultural values and recreation to timber for houses. Increasing tree mortality in our unique forests will affect all of these’
The research highlights broader consequences beyond Australia. Forests around the world absorb about one-third of human carbon dioxide emissions, acting as a buffer against climate change. If tree deaths continue to rise while growth remains weak, that buffering role will diminish.
“Forests worldwide absorb about one-third of human carbon dioxide emissions. If mortality continues to rise while growth stagnates, that buffering capacity will erode. Recent evidence from northern Australia’s tropical rainforests shows this process already unfolding, with the rainforests shifting from being net absorbers of carbon to net producers of carbon. This will weaken the planet’s ability to absorb emissions and amplify existing climate feedbacks, further narrowing the window for stabilising the global climate,” Professor Medlyn said.
The study describes the combined rise in mortality and lack of growth as a signal that forest resilience is under strain. While there are options to adapt forest management to reduce stress and protect long-term health, the researchers warn that current monitoring efforts are falling short.
Over the past 25 years, the number of forest plots being regularly monitored has dropped sharply, reducing the ability to detect slow but persistent changes across landscapes.
“Our results highlight the critical need for ongoing forest monitoring that is designed to detect long-term trends, in order to guide effective forest management for the future,” Professor Medlyn said.
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