In this post Brett Murphy discusses his recent paper with colleagues Mark Cochrane and Jeremy Russell-Smith ‘Prescribed burning protects endangered tropical heathlands of the Arnhem Plateau, northern Australia’

In many fire-prone landscapes, wildfires threaten a range of societal and ecological values, including human life and property, crops and domestic livestock, as well as biodiversity and ecosystem services. One of the most important tools humans have to manipulate the occurrence of wildfire is prescribed burning – the deliberate application of landscape fire, typically under relatively mild fire-weather conditions.

I am a fire ecologist based in Darwin, Northern Territory, at the heart of Australia’s vast, fire-prone savanna landscapes. Much of my research focusses on how to best manage fire to conserve the unique biodiversity of this largely undeveloped region. I’m especially interested in the effectiveness of prescribed burning as a biodiversity conservation tool. Can it be used to modify fire regimes (the characteristic frequency, intensity and timing of fires in a landscape) to favour the persistence of biodiversity?

Prescribed burning being carried out using aerial incendiaries, fired from a helicopter, on the Arnhem Plateau in Kakadu National Park, northern Australia. (Photo: Clay Trauernicht)
Prescribed burning being carried out using aerial incendiaries, fired from a helicopter, on the Arnhem Plateau in Kakadu National Park, northern Australia. (Photo: Clay Trauernicht)

Conservation managers have typically used prescribed burning to reduce the intensity and size of subsequent wildfires, but whether prescribed burning can protect ecological communities vulnerable to repeated burning is controversial. In northern Australia, there is a widely held view among conservation biologists that too much prescribed burning takes place, driving excessively high fire frequencies, severely disadvantaging a range of plants and animals (most notably small mammals and birds).

The Arnhem Plateau’s fire problem

A place where fire is a critical conservation issue is northern Australia’s Arnhem Plateau – a stunningly beautiful, rugged and biodiverse landscape, home to many endemic plant and animal species. The region’s fire problems arose with the breakdown of traditional fire management, which had been practised for millennia by Indigenous Australians. Upheavals in Indigenous society following European colonisation of northern Australia, including forcible relocation to towns, meant that by the second half of the 20th Century few Indigenous people remained on the Plateau.

The rugged Arnhem Plateau in northern Australia. (Photo: Clay Trauernicht)
The rugged Arnhem Plateau in northern Australia. (Photo: Clay Trauernicht)

The loss of intensive fire management allowed the development of a ‘feral’ fire regime, characterised by frequent and very large wildfires, burning vast areas of the Plateau every few years. Such a fire regime is widely recognised as having severe impacts on a range of fire-sensitive plant communities. Most notable are the diverse Arnhem Plateau heathlands, formally listed as ‘endangered’ by the Australian Government, because of ongoing impacts of inappropriate contemporary fire regimes.

The heathlands contain a diverse range of shrubs, many with highly restricted ranges, and typically easily killed by even low-intensity fires. Fire-killed shrubs must recruit from soil- or canopy-stored seed following fire, and reach reproductive maturity before the next fire. Heathland shrubs typically require at least 5 years to mature – so if fires are more frequent than once every 5 years, local population declines occur.

In recent years, attempts have been made to bring the Plateau’s feral fire regime under control. The ground-breaking West Arnhem Land Fire Abatement (WALFA) project has brought together Indigenous landowners and Western scientists to rein in large wildfires using strategic prescribed burning, with considerable success. Similarly, Australia’s largest national park, Kakadu, which encompasses the western edge of the Arnhem Plateau, has been increasing its use of strategic prescribed burning on the Plateau since the 1990s.

Does prescribed burning help?

My recent research, with colleagues Mark Cochrane (South Dakota State University) and Jeremy Russell-Smith (Charles Darwin University), published in the Journal of Applied Ecology, shows that prescribed burning is moderating the detrimental fire regimes on the section of the Arnhem Plateau within Kakadu National Park.

We examined how a range of fire regime attributes changed over three decades (1980–2011), including:

  • annual burnt area;
  • proportion of fires occurring early in the dry season (under relatively mild fire conditions) versus late in the dry season (under relatively severe fire conditions);
  • the proportion of the landscape that was relatively long unburnt (at least 5 years since fire).

The last attribute is critically important for Arnhem Plateau heathlands, as many fire-sensitive shrubs of this community require long fire-free periods (5 years or more) to mature. Increasing the abundance of long unburnt habitat has also been strongly advocated for the conservation of small mammals, many of which are declining in the northern savannas.

Flowers of the fire-sensitive shrub Petraeomyrtus punicea, endemic to the Arnhem Plateau. (Photo: Clay Trauernicht)
Flowers of the fire-sensitive shrub Petraeomyrtus punicea, endemic to the Arnhem Plateau. (Photo: Clay Trauernicht)

Our research showed that, despite annual burnt area remaining constant over three decades, there was a clear trend of: (1) increasing dominance by early dry season fires (which tend to be relatively mild and patchy); and (2) increasing abundance of long unburnt habitat (almost doubling in area over three decades). These trends reflect the increasing effort to undertake strategic prescribed burning on the Plateau.

We were somewhat perplexed by the substantial increase in the abundance of long unburnt habitat, given little change in annual burnt area. There is an assumption amongst fire managers and conservation biologists alike that to increase the abundance of long unburnt habitat, annual area burnt must be reduced. Our work has shown that this is not necessarily the case.

We concluded that prescribed burning had decreased the ‘randomness’ of fire occurrence (i.e. all parts of the landscape having similar risk of fire), compared to an unmanaged fire regime. Under a regime of prescribed burning, certain areas would tend to be burnt more frequently (e.g. along natural ‘firebreaks’ such as river valleys, which tend to be targeted for burning by managers), while others would be burnt less frequently (e.g. areas far from natural firebreaks). The result is a more even distribution of fire frequency classes, with greater abundance of both frequently and infrequently burnt habitat.

Recently burnt Arnhem Plateau heathland, with fire-killed shrubs. (Photo: Brett Murphy)
Recently burnt Arnhem Plateau heathland, with fire-killed shrubs. (Photo: Brett Murphy)

Such a link between the randomness of burning and the abundance of long unburnt habitat has previously been proposed by Alan Andersen and colleagues.

The take-home message from our work is that prescribed burning is an effective tool to shift fire regimes to favour the persistence of flora and fauna sensitive to short fire intervals. In areas such as the Arnhem Plateau, prescribed burning should be prioritized as an ongoing management strategy. It is also likely that prescribed burning can be an effective conservation tool in other highly fire-prone landscapes.

You can read more about this research here http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.12455/full.

Guest post by Brett P. Murphy (brettpatrickmurphy@hotmail.com, www.brettmurphyresearch.wordpress.com, @brettpmurphy)

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