Scientists warn that the wrong fire patterns could see more losses of threatened species across the country.
Grant Williamson, University of Tasmania, Brett Murphy, University of Melbourne, and David Bowman, University of Tasmania
The scale and impact, both economic and ecological, of recent bushfire disasters demands a rethink of fire management strategies. A controversial approach receiving more attention internationally is the use of large grazing animals to reduce fuel loads.
But research we published this week shows cattle grazing does little to reduce Australia’s most destructive bushfires.
There are few specific examples of this management intervention being used in Australia. The exception is cattle grazing in the Victorian High Country, part of the Australian Alps. This has been controversial, pitting pastoralists against environmentalists, and scientists against scientists.
It raises questions about acceptable and unacceptable land uses in national parks. And it raises the issue of Australian cultural heritage, including the perpetuation of an iconic “Man from Snowy River” cultural tradition of summer pasturing of cattle in the Australian Alps.
Proponents of grazing within the Alpine National Park claim “grazing reduces blazing”. The clear public message is that the severe fires seen in Australia’s alpine forests in recent years can be reduced in extent, intensity, and ultimately damaging effects by the continuation of cattle grazing.
But environmentalists point to the degradation cattle cause to alpine ecosystems by spreading weeds, triggering erosion, trampling bogs and fouling streams.
This debate involves an unusual intersection of scientific, environmental, legal and political dimensions. The Victorian Labor Government banned grazing in the Alpine National Park in 2005 because of environmental concerns. When the Coalition came to power in Victoria in 2010, they proposed resolving this issue with a grazing trial of 400 head of cattle per year to investigate hypothesised fire mitigation.
This trial was then blocked by the then Labor Federal Environment Minister on the grounds it would have an unacceptable impact on endangered species under the Environment Protection and Biodiversity Conservation Act.
A Federal Court case brought by the Victorian government subsequently found the Federal Environment Minister acted appropriately. Grazing is still banned within the Park.
In this context, we tried a “natural experiment” to discover whether cattle grazing can reduce blazing. We surveyed over 11,400 km2 of the Victorian Alps by analysing satellite images of the area. We looked at vegetation maps, looked back in time using historical satellite pictures, and took advantage of the cessation of grazing this decade and the extensive area burnt by fires over this period.
To implement our study as a classical experiment – for example by manipulating grazing pressure and imposing experimental fires – would be completely impractical, and prohibitively expensive given the same geographical scale and the risks of application of extensive high-severity fires. It would also be unethical given the potential threats to biodiversity, and under current legislation, unlawful.
We overlaid maps of crown scorch derived from satellite imagery following large bushfires in 2002/03 and 2006/07 with the location of pastoral leases. Crown scorch is a measure of fire intensity, based on the degree to which flames have reached a height which enables them to burn the forest canopy. This crown scorch can be detected in satellite images.
Using geospatial statistics we found that cattle grazing had no effect on the likelihood of crown scorch in eucalypt forests and woodlands.
This result is biologically plausible given that cattle are grazing animals, not browsing animals – they do not extensively feed on woody vegetation focusing on grasses instead. Our study is also consistent with previous ground-based studies that have demonstrated the cattle prefer to graze in grassy areas.
Fires in eucalypt forests are important to study, because to their extreme intensity. Fires in these forests are driven by high fuel loads on the forest floor and dense forest structure. Eucalypt forests have the added capacity for fast-moving fires to occur in the upper canopy, carried by the highly flammable leaves. Such fires are nearly impossible for fire fighters to control.
In comparison, fire intensity in grasslands is much lower, fires are easier to control, and grasslands recover rapidly after fires.
Our study does not rule out the use of cattle to manage grassy fuels – this approach may be crucial in tropical savannas, especially where invasive grasses fuel fires that compromise the ecological integrity of native vegetation.
Brett Murphy, University of Melbourne
Fire and biodiversity have a complex relationship in northern Australia. Tim Flannery and others blame the current northern biodiversity crisis, at least in part, on changed fire regimes. Improving fire management is critical to conserving savanna landscapes – but who pays for it? A new funding model, tapping into the carbon economy, has emerged in the far north and is rapidly transforming fire management and biodiversity conservation.
A new funding model for fire management
The idea that land management could be funded by carbon credits emerged from Aboriginal-owned Arnhem Land in the Northern Territory. By the 1990s it was clear that the region’s enormous biodiversity values were being eroded by frequent, intense late dry season fires.
To address this problem, a trailblazing group of Western scientists and land managers, and Aboriginal Traditional Owners developed a program of prescribed burning early in the dry season to pre-empt large, intense wildfires late in the dry season.
The most innovative part of their work was to link improvements in fire management to reductions in greenhouse gas emissions. They also realised that this emissions reduction (or abatement) could be used to secure resources for land management.
The abatement occurs because early dry season fires tend to be patchier and less intense than late season fires, and therefore burn less fuel. Because less fuel is burnt, fewer emissions are produced.
The project that resulted from this early work – the 28,000 km² West Arnhem Land Fire Abatement project – has operated since 2005 and is funded by one of the world’s largest energy companies, ConocoPhillips. They provide $1 million annually in return for an abatement of greenhouse gases equivalent to 100,000 t of CO₂.
It is clear that fire management in western Arnhem Land has shifted the fire regime from one dominated by late dry season fires (decreasing from 29 to 13% of the landscape annually), to one dominated by early dry season fires (increasing from 9 to 17% of the landscape annually).
There is abundant evidence that an early-dominant fire regime favours many declining components of the biota, including endemic sandstone heaths (now federally listed as endangered), rainforests, and the northern cypress pine.
Extending the Arnhem Land model across the north
The viability of these projects was given a substantial boost in 2012 when the Commonwealth government approved the use of savanna fire management to generate carbon credits. This approach to funding fire management is now being adopted across northern Australia, on a range of land tenures, including conservation areas.
For example, Fish River Station is a new 1,781 km² reserve recently acquired jointly by the Commonwealth government, Indigenous Land Corporation and private conservation organisations. It has recently been given approval to operate a carbon offset project based on fire management.
Other, larger carbon–fire projects are being developed on Aboriginal lands in central Arnhem Land, the Kimberley, south of the Gulf of Carpentaria, and Cape York Peninsula. Private conservation organisations such as the Australian Wildlife Conservancy are also developing carbon projects on their savanna properties.
The potential for biosequestration
Under the existing accounting methodology, savanna fire projects generate carbon credits by reducing the emissions of two potent greenhouse gases – methane and nitrous oxide (with potencies 25 and 298 times that of CO₂, respectively). However, the effect of fire on the storage – or sequestration – of carbon by savanna systems is effectively ignored.
Several colleagues and myself analysed data from an array of long-term vegetation monitoring plots throughout savannas of the Top End, and found that even modest reductions in the frequency of intense fires cause a large increase in the amount of carbon stored as tree biomass.
Our “back of the envelope” calculations suggest that the recent improvements in fire management in Arnhem Land would increase tree biomass by an amount equivalent to around .22 t of CO₂ per hectare per year. This is about five times the methane and nitrous oxide abatement that underpins existing fire projects.
We are now working on a more rigorous approach to modelling biosequestration across northern Australia. It seems likely that biosequestration can be worked into a carbon offset system and, once approved by the Commonwealth, the viability of carbon–fire projects will increase dramatically.
There is little doubt that the new carbon economy is transforming fire and biodiversity management across northern Australia. Many areas managed for biodiversity conservation can now generate a substantial income beyond the public purse. This will surely allow the further privatisation of biodiversity conservation, at a time when non-government organisations are already playing an increasingly central, and indeed successful, role in conservation in northern Australia.
Implementing biodiversity-friendly fire regimes remains an enormous management challenge in the north. Although the carbon economy is unlikely to be a panacea, it certainly provides a much-needed income stream for sustainable land management, especially for the vast lands outside of the traditional conservation estate.
Brett Murphy, University of Melbourne; Clay Trauernicht, University of Tasmania, and David Bowman, University of Tasmania
Conservationists should take heart that Australia is finally waking up to the biodiversity crisis in Australia’s north. It is an urgent problem: right now, a diverse assortment of our small mammals – bandicoots, tree-rats, possums – are rapidly vanishing from northern Australia’s most iconic biodiversity strongholds.
Work in Kakadu National Park has shown that between 1996 and 2009 mammal populations crashed, with species richness and total abundance decreasing by 65% and 75% respectively.
Most alarming is that scientists can’t tell us why this is happening, let alone how to stop it.
Prominent conservationist Tim Flannery recently drew attention to the plight of northern Australian mammals in his Quarterly Essay and accompanying article in The Conversation (as have others writing in The Conversation and other media). Though valuable, these articles tend to oversimplify the complex and unresolved ecological questions that must underpin an appropriate management response.
Flannery asserts that “the main driver appears to be changes in fire regime, compounded by the presence of feral cats”. This overstates our current understanding.
Unlike most other conservation issues in Australia, the most immediate obstacle is lack of knowledge. We simply don’t know why mammals are declining or what management interventions could halt the decline.
Frequent fire hazards
There is widespread agreement that the mammal decline has something to do with fire. However, scientists have failed to answer the critical question – with a large budget, what type of fire regime should (and could) land managers implement to benefit small mammals?
The managers of Kakadu – the epicentre of the northern mammal decline – have been roundly criticised by conservation scientists for their excessive use of prescribed burning to prevent high-intensity wildfires. However, these same scientists have been remarkably silent on alternative management approaches.
There is evidence that high fire frequencies are detrimental to small mammals, demonstrated most significantly in the work by John Woinarski and colleagues. They found that in Kakadu, sites that had been most frequently burnt experienced the greatest small mammal declines over the period 1996-2009.
The challenge is understanding exactly what it is about fire regimes that has changed. The breakdown of traditional Aboriginal fire management – and possible increase in the size and intensity of fires – is often suggested as a trigger. However, in places like Kakadu this occurred many decades before mammal populations crashed.
A tinderbox landscape
There is a widely held view that there is too much fire in parks like Kakadu. However, calls for widespread reductions in fire frequency in the north tend to overlook the fundamental ecology of fire.
Fire is so prevalent in this region not because of people, but because of the intense monsoon climate. A reliable wet season promotes rapid grass growth, and a long dry season promotes drying of grassy fuels.
Abundant lightning at the end of the dry season ensures high fire activity. The effect of humans is to merely “jump start” the fire season, providing an ignition source earlier in the year.
It is inevitable that a large proportion of the landscape burns each year. For Kakadu, this figure is remarkably constant at around 45%.
The only “lever” available to land managers is whether burning occurs predominantly in the early (April–July) or late (August–November) dry season.
This fact has driven the prevailing approach to fire management in northern Australia – that of extensive early dry season burning to pre-empt intense late dry season fires.
Fighting fire with fire
It is well known that many fire-sensitive plants (such as the northern cypress pine, and to a lesser extent sandstone heaths) benefit from an earlier fire regime. There is also evidence that this applies to small mammals too.
Based on satellite-derived fire mapping since 1980, we know that the proportion of Kakadu that burns each year has not changed over the last 32 years. However, it is clear that there has been a dramatic switch from late dry season to early dry season fires. Although such a shift in fire season is thought to be good for biodiversity, including mammals, there may be more insidious changes that have taken place.
For example, retired Kakadu ranger Greg Miles has suggested that a vicious grass–fire cycle is now firmly established in Kakadu. The theory is that highly flammable speargrass (Sorghum species) increased in abundance following the breakdown of Aboriginal fire management, and now fuels fires of much greater intensity.
Even in the early dry season, speargrass fires tend to be of high intensity and low patchiness. Hence, abundant speargrass effectively negates the advantages of early dry season prescribed burning.
It is noteworthy that the introduced swamp buffalo was virtually eradicated from Kakadu in the 1980s, after more than a century in the park. Some suggest that this may have further promoted an increase in speargrass abundance and fire intensity. The only major change to have immediately preceded the mammal collapse in Kakadu was the eradication of the buffalo.
Whether a grass-fire cycle can be reversed is not clear. One option put forward is to burn heavily infested areas in the wet season, before the speargrass can produce seed. Another option that warrants objective consideration is grazing by exotic herbivores, especially as highly-flammable exotic grasses overtake the park.
We need a better understanding of how fire regimes have changed over the last century. Despite Kakadu having the best-described fire regimes in northern Australia, the available fire records are still relatively short (from 1980 on). These satellite-derived records are also limited to fire frequency, size and season. Recent changes in a broader spectrum of fire regime attributes, such as intensity and fine-scale patchiness, are highly uncertain.
Testing the critics’ claims
Vague calls for “less fire” are unhelpful. Instead, we need to specifically identify what kinds of fire management work best for mammals at landscape scales. This means considering the intervals between fires, fire intensity, size and patchiness.
We also need to determine whether areas of long, unburnt vegetation are important for small mammals’ survival, and how different species are affected by “mosaic” burning practices, in which fires of varying intensities, scales and times are burnt to create a patchwork or mosaic effect in the landscape.
Some researchers suggest that Aboriginal fire management would have resulted in such a mosaic, and the loss of this mosaic has triggered biodiversity declines. Although intuitively appealing, there is remarkably little direct evidence to support this hypothesis, especially in relation to small mammals.
The greatest challenge will be to translate these research findings into explicit management actions.
For example, Alan Andersen and colleagues described an approach to increasing the abundance of long unburnt areas, without actually decreasing the proportion of the landscape burnt each year. The trick is to decrease the randomness of burning, by concentrating prescribed burning on recently burnt areas, avoiding long unburnt areas.
If the current model of extensive early dry season burning is so obviously failing, then there is an onus on its critics to propose something new.
Unlocking answers from the land
Land managers need to do their bit too by facilitating collaborative research in conservation areas.
Sadly, national parks can be difficult places to conduct research in northern Australia, hindered by slow-moving bureaucracies and priorities other than biodiversity conservation.
The quantity and quality of research coming out of Australian Wildlife Conservancy properties in the Kimberley demonstrates how much easier it can be to conduct conservation research on private land.
Close collaboration between scientists and land managers is essential, ideally within an adaptive management framework. This is where new management interventions can be repeatedly tried, evaluated, improved or potentially abandoned.
Most importantly, unorthodox management interventions need to be objectively evaluated. These might range from grazing by large exotic herbivores (such as buffalo and cattle) to reduce fuel loads, to wet season burning of annual grasses.
As Tim Flannery points out, “things are now so dire that we cannot afford to persist with business as usual”.
26 April 2012
Trauernicht C, Murphy BP, Portner T, Bowman DMJS (2012) Tree cover–fire interactions promote the persistence of a fire-sensitive conifer in a highly flammable savanna. Journal of Ecology 100, 958-968.
TIME for a retrial? It seems that humans were not responsible for the extinction of a large flightless bird within 10,000 years of setting foot in Australia, as was suggested in 2005. We had an alibi: the bird was already on the way out when humans turned up 55,000 years ago.
Murphy BP, Williamson GJ, Bowman DMJS (2012) Did central Australian megafaunal extinction coincide with abrupt ecosystem collapse or gradual climate change? Global Ecology and Biogeography 21, 142-151.
ABC Radio, 8 July 2003