A world review of mild fire and forest decline

This report is a world review of forest decline in relation to inadequate regular mild fire and consequent changes in soils, nutrients, mycorrhizae and other soil factors. Released by John O’Donnell on 5 January 2025.

The role of mild fire and forest decline

Published research work by a number of experienced researchers clearly shows that a large amount of research has been completed in relation to forest decline across the world, including eucalypt decline, and decline in forest health associated with changed fire and grazing regimes.
The author considers that exclusion of frequent low intensity mild fire as a primary cause of forest decline in native forests across the world. Based on considerable evidence, the author believes that changed soil processes are the hidden drivers of forest decline. Exclusion of regular mild fire destabilises nutrient cycles, alters soil physics and chemistry, and undermines the root–mycorrhizal foundation of forest health. Above ground symptoms (crown thinning, pest outbreaks) are consequences of these below ground changes.

The full review is included here.

The full review has pulled together 82 key references in relation to inadequate regular mild fire and consequent changes in soils, nutrients, mycorrhizae and other soil factors.

Lack of regular mild fire, ecosystem change and forest health

Research across Australia and globally shows that exclusion or lack of regular mild fire has profoundly altered forest ecosystems, driving forest decline in forests and fire-adapted species. Authors such as Jurskis, Burrows, and Forestry Corporation of NSW highlight that reduced low-intensity burning leads to soil nutrient imbalances (particularly nitrogen accumulation), dense understories, weakened tree physiology, and heightened susceptibility to pests, parasites, and arbivory. These changes increase fuel loads, making forests more vulnerable to severe, less controllable wildfires.

Evidence from long-term experiments and case studies demonstrates that human management decisions, including fire suppression, grazing exclusion, fertiliser use, and conservation policies, are the primary drivers of forest decline. Research highlighted above underscores that frequent, low-intensity fire is essential for sustaining nutrient cycles, structural diversity, and long-term forest health, and that its absence has led to widespread decline and heightened ecological imbalance.

Research across multiple regions demonstrates that the absence of regular low-intensity fire is a major driver of forest decline, balanced ecosystems and forest health. Overall, the evidence converges on the importance of mild fire and soil processes in maintaining forest resilience, biodiversity, and long-term health.

Lack of regular mild fire and changes in soils, nutrients, mycorrhizae and other factors

Research demonstrates that exclusion of regular mild fire alters soil moisture, nutrient status, and microbial communities, driving chronic forest decline. Collectively, research studies highlighted above reveal that soil changes from fire exclusion destabilise root physiology, water relations, and stress signalling, making forests increasingly vulnerable to compounding climate and biotic pressures.

Research consistently shows that exclusion of regular mild fire disrupts soil chemistry and physical properties, driving chronic forest decline. Research findings support the conclusion that mild fire is essential for maintaining soil equilibrium, root function, and long-term forest health, with Australian research leading in demonstrating these links.

Research shows that exclusion of regular mild fire profoundly alters fungal communities through changes in soils, driving forest decline. The evidence supports that fire regimes and mycorrhizal dynamics jointly underpin forest health, with disruption of either leading to decline.

Collectively, these findings support the conclusion that regular mild fire and adaptive management are essential to maintain soil equilibrium, root physiology, and long-term forest health and resilience.

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Source & image credit: John O’Donnell