Review of eucalypt decline and dieback in relation to
lack of low intensity fire management across Australia

John O’Donnell, June 2023

This review has been designed to tease out the key issues in relation to eucalypt decline with key researcher text available to assist readers in understanding important information, issues and key references.   This approach allows integration of key information in one place to better assist readers in understanding the key issues and references.

There are a considerable number of research papers and authors who have identified exclusion of low intensity mild fire as the major cause of eucalypt decline across a number of Australian native forests and woodlands outlined in the references used list. 

Key research authors in relation to establishing root cause of eucalypt decline relating to soil changes associated with inadequate low intensity fire include Turner, Lambert, Jurskis, Horton, Landsberg and Ellis.  Other useful contributions have been made by Ishaq, Jones, Davidson, Close, Dijkstra and Adams. Howitt also identified eucalypt decline as linked to a reduction in burning in his legendary 1890 paper. There are 66 papers identified in the “key references used for this review” list and an additional 39 other references in the Section 7 list. 

Jurskis (2016) makes critical observations in relation to chronic decline:

… chronic decline involving a wide range of arbivores has affected a wide range of eucalypts across Australia since European settlement, and is currently rampant in many areas of forest and woodland. Pasture improvement and/or exclusion of fire and grazing are the major causes of chronically declining health of eucalypts.

Lack of low intensity fire, eucalypt decline and the link to soil factors is explored in great depth in Section 4.  Key soil factors relating to eucalypt decline include pH, Aluminium, nitrogen, phosphorus availability, N:P ratio, C:N ratio, organic matter, soil wetness, mycorrhizae and other soil microbiota in some cases.

Jurskis (2005 a) got to the root of the decline issue “It appears that chronic abiotic stress causes tree decline when the function of roots is impaired by changes in soils”.  As noted in this review, feeder roots and mycorrhizae degenerate before the onset of above-ground symptoms.  Horton (2011) and Horton et (2013) undertook important research in relation to ectomycorrhizal (ECM) fungal communities. Horton et (2013) note “ altered soil chemistry associated with eucalypt forest decline mediates changes in the ECM fungal community”.

The author considers that exclusion of frequent low intensity mild fire is the primary cause of eucalypt decline in Australian native forests and woodlands and this has been inadequately recognised in many studies, research papers, articles, reviews, management plans, legislation, policies and reports on land and fire management. This lack of recognition is in itself a major environmental issue and ignores up to 60,000 years of Aboriginal burning practices across the landscape.

There is rapid expansion of eucalypt decline across Australia as detailed in the review.

There are extensive negative consequences of lack of fire and resultant eucalypt decline and these consequences have been identified in Section 9 of the review.   These consequences highlight the need for urgent on the ground action and adaptive management.

A lot of effort has been undertaken in relation to research on forest decline and diebacks, with little adaptive management responses, at least in Australia.  There has also been confusion between the different described diebacks.  Researching symptoms of decline rather than primary factors has resulted in a lot of lost funding, time and lost opportunities for adaptive management. 

There is often evidence in the landscape of the impacts of changed fire regimes with contrasts in forest health/ decline due to different fire regimes that are often visible.  There are opportunities to observe this by assessing opposite sides of tenure boundaries; the top and bottom sides of roads; between drainage lines and spurs and between reserves and general management zones in areas where decline has commenced.  The case studies in Section 8 highlight case study examples.

The key US federal legislation commitment in place reducing fuel loads, increasing prescribed burning, improving forest health and expanding community mitigation work under the Bipartisan Infrastructure bill and other legislation provides a useful adaptive management role model for Australian forests suffering decline or likely to suffer decline.  A good example of a forest health strategic plan, this being 20-Year  Forest Health  Strategic Plan for Eastern Washington, is provided.

Getting to the root of the decline issue is time critical, inaction in relation to this issue results in continuation of eucalypt decline across Australia and is resulting in increasing areas of eucalypt decline, more open eucalypt crowns and forests with dense understoreys and increased bushfire risks and impacts. 

About John O’Donnell

John is a retired district forester and environmental manager for hydro-electric construction and major highway construction projects. His main interests are mild maintenance burning of forests, addressing the culture of massive fuel loads in our forests setting up large bushfires, forest health, establishing safe/ healthy and resilient landscapes, adaptive forest management, fire fighter safety, as well as town and city bushfire safety.