A new study in the journal Austral Ecology provides the most comprehensive analysis ever performed of the fire history of forests in the Australian Alps. This is a significant piece of work because it says that unburnt forests are less fire prone than those that have been recently burnt.

This has implications for how we manage these forests and woodlands. The current widely held assumption is that by reducing fuel loads, fire reduces the flammability of most eucalypt-based forests.

The study, by Dr. Philip Zylstra of the University of Wollongong (and available here) via the Australian Alps says:

‘The study provides an evidence base for fire management in the Alps that is based on observed reality rather than theoretical concepts.

‘Throughout the period for which fires have been consistently mapped across the Australian Alps National Parks, they have been smaller and less severe in long unburnt forests’. This is consistent across the five broad forest formations that cover the Alps’ (these forest types are Tall Wet Forest, Open Forest, Subalpine Forest and Woodland, Dry Open Forest and Low, Dry Open Forest).

‘It is widely assumed that more frequent fire makes forests less flammable. This study demonstrates that the opposite is true for the Alps. Whether through climate change or direct action, more fire makes the Alps more likely to burn, potentially locking them into a landscape trap, where fires accelerate in frequency until vulnerable ecosystems collapse.’

The study looked at fires in five key forest types in the Alps and assessed how fire frequency changed over time. To take the example of snow gum woodlands, after a fire passes through, they are unlikely to burn for 6 years after fire, then more flammable until 25 years old. However, ‘forests older than this are 2.3 times less likely to burn than younger forest’. A similar pattern can be observed in the other forest and woodland types.

The take home message seems to be that if we can reduce the frequency of fire in these ecosystems through the juvenile ‘danger’ period when there is a lot of vigorous re-growth, they become less fire prone after a period of 14 to 28 years (depending on the forest type). This means that older forests should be left alone rather than burnt to reduce fuel load, and younger forests should be encouraged to mature rather than being treated with fire to keep them permanently in a juvenile/ more flammable stage in their growth.

With the onset of human induced climate change, it is – sadly – clear that we will require more intense human management of vegetation in the Alps if we are to protect vulnerable ecosystems (for instance, see this story on the impacts of more frequent fires on alpine ash forests in the Upper Kiewa catchment which has led to the need to manually reseed these forests). David Bowman from the University of Tasmania has pointed out that changing fire regimes may require us to take a more interventionist approach in the future, and ‘that we will probably need greater human intervention if we are to protect ecological values’.

This study looks at the impacts of fire frequency on forest flammability. There is also a conversation to be had about what this would mean in the real world in terms of whether vegetation types would shift over time if they were managed to exclude fire wherever possible. This study does not address the ecological impacts of changing fuel reduction management practises.