The smell of smoke in the autumn and spring air is an increasingly familiar one to many Australians. It signifies that time of year when land management agencies in southern Australia feverishly try to meet their burning targets.
But what are the consequences for biodiversity of setting such targets in Australia’s ecosystems? In recent research conducted in south-eastern Australia’s Murray Mallee region, our team (the Mallee Fire and Biodiversity Team) found that such policies can set in motion changes that persist for over 100 years.
Today it has been announced this research is one of three projects nominated for the Eureka Science Prize for Environmental Science, sponsored by the NSW Office of Environment and Heritage. The winners will be announced on September 10.
Fire over the long term
We found that fire dramatically changes the abundance of resources critical to animals in semi-arid ecosystems, such as spinifex hummocks and tree hollows. This doesn’t just occur in the immediate aftermath of a fire; the impacts continue for a century after burning.
To put this in perspective, a fire in 1914 at the beginning of World War I would still be affecting where particular animal species occur today. Similarly, a fire lit today will influence the mallee ecosystem through to the year 2114 and beyond.
But Australian ecosystems love fire, right?
These long-term effects of fire were surprising, but equally fascinating was the post-fire preferences of the native fauna.
It often is assumed that plants and animal species in Australian environments generally benefit from fire. This view arises from the logic that if fires occur frequently within a region, then the species must have adapted to cope with frequent fire.
However, although large wildfires do occur frequently somewhere within the Murray Mallee region (typically every 10 to 20 years), substantial areas can avoid wildfire for long periods (50, 80 or even more than 100 years).
We found that these older stands of mallee vegetation are critical to many animal species. A number of species of reptiles, small mammals and particularly birds had clear preferences for sites of 30-100 years post-fire.
For instance, the Murray striped skink (Ctenotus brachyonyx) and the yellow-plumed honeyeater (Lichenostomus ornatus) are both most common in sites that have not burned for 60-100 years.
Species dependent on spinifex grass, such as the mallee emu-wren (Stipiturus mallee), mallee ningaui (Ningaui yvonneae) and southern legless lizard (Delma australis), reach their greatest abundance at 20-50 years post-fire when large amounts of spinifex cover occur.
A mismatch between ecology, policy, and management
If long-unburnt mallee vegetation is so valuable for wildlife, then it is important that this is recognised in fire management and policy.
But in Victoria, there is a blanket state-wide target of undertaking planned burning of 5% of public land annually.
Assuming no areas are burned twice within 20 years (a fairly safe assumption for the mallee), meeting this target would essentially result in all mallee vegetation in the region being less than 20 years post-fire within 20 years. If this is realised, the consequences for many species will be disastrous.
Why the mismatch?
The target for burning 5% of public land annually was recommended by the Victorian Bushfires Royal Commission into the Black Saturday fires of 2009. These devastating fires swept through Victoria with tragic results: 173 people lost their lives and scores more their livelihoods.
The 5% target was proposed as a means to minimise the risk of another tragedy like Black Saturday. Planned fires can reduce fuel loads and therefore the logic is that this will reduce the risk of large wildfires.
While few would debate the need to minimise risk to human life and property from wildfire, there is a legitimate debate around how burning large tracts of land in remote regions such as the Murray Mallee will achieve this aim.
Scientists from the Department of Environment and Primary Industries have estimated that less than 3% of the statewide risk to life and property is located in the Murray Mallee region. Yet 16.9% of the planned burning by area in 2012-2013 occurred there. Conversely, although the more populated areas closer to Melbourne accounted for 31% of risk, only around 1.6% of planned burning took place in that region.
If, and when, the next tragic loss of life occurs as a consequence of bushfires, the question will be where we burned to minimise risk, not just how much.
If we don’t change our policies, we risk doing ecological harm, while at the same time making humans little safer.
We would welcome an alternative approach that identifies areas to burn on the basis of where the greatest reduction in risk to life and property can be achieved, while also minimising the risk to biodiversity.
Further reading: Explainer: backburning and fuel reduction