Climate Stress Accelerates Tree Loss Across Australia’s Forests, Says Report

Tree loss is accelerating across Australia’s forests as a result of chronic stress due to a warming climate, according to the study published in the journal Nature Plants.

The research analysed records spanning 83 years from more than 2,700 forest plots across four major forest biomes: Tropical savanna, tropical rainforest, warm temperate forest and cool temperate forest.

Regardless of location or vegetation structure, the study discovered that tree deaths have steadily increased over the past few decades in all types of forests.

Researchers reported that mortality rates rose most sharply in hot, dry regions and in dense forests where trees compete more intensely for water and light. “This temporal trend persisted after accounting for stand structure and was exacerbated in forests with low moisture index or a high competition index,” the authors wrote in the paper.

Average mortality was higher in species with characteristics linked to rapid growth, such as low wood density, high specific leaf area, and shorter maximum height. Nonetheless, the rate at which mortality rose was generally comparable across various functional groups, indicating a general climatic driver as opposed to species-specific factors.

The results are consistent with similar patterns seen in boreal forests in Canada, temperate forests in the western United States and Europe, and tropical rainforests in the Amazon. The ability of forests to absorb and store carbon, a crucial buffer against climate change, is threatened by this overall rise in tree mortality, according to the scientists.

The study centred around “background tree mortality”, deliberately excluding deaths caused by logging, land clearance or major fire events. This allowed them to assess what changed over the decades and impacted the forests.

Since the pre-industrial era, the world has warmed by an average of roughly 1.2 degrees Celsius annually, according to the authors, who concluded that rising temperatures were the most likely reason for the rise in tree deaths.

Australia's forests are under more stress due to the warming trajectory, increasing atmospheric aridity, and more frequent droughts, which compromise their long-term resilience.

Climate Stress Signals

The findings reflect warnings from the IPCC Sixth Assessment Report, which associates rising temperatures and drought frequency to increasing forest mortality globally. Climate change is also raising the risk of forest fires and the spread of forest pests, particularly in mountain, dryland and coastal forests.

The Food and Agriculture Organisation of the United Nations (FAO) has also reported that climate stress is weakening forest carbon sinks. According to the FAO’s Global Forest Resources Assessment 2020 report, the world’s total growing stock of trees slightly declined from 560 bn cubic metres in 1990 to 557 bn cubic metres in 2020, reflecting a net loss in forest area. However, growing stock and biomass per unit area have increased globally, with tropical forests in South America, Central America, and Africa holding the highest density.

Supporting these trends, NASA data indicate declining vegetation productivity in warming and drying regions, including Australia.