Fire in Australia's Tropical Savannas

A typical savanna fire burning through the grass beneath the trees.      Photo: Jean-Charles Perquin

When we think of “bushfires” many people think of the fierce wildfires that strike in the summer across southern Australia. It may come as a surprise, therefore, that the largest and most frequent fires in the continent occur in the southern winter and spring – and occur in northern Australia. In terms of sheer area, satellite images show that the vast majority of landscapes burnt over the last several years have been in northern Australia - as shown in the map below based on satellite imagery. Over 98% of large bushfires occur outside the more densely populated south-east and south-west of the country.

 

 

 

The northern savannas are primed for regular fire with vast grassy landscapes that flourish during the wet season and then, over months with very little rain, dry to a tinderbox. Although not nearly as intense as southern bushfires, the problems these fires are now creating for the people of the north are considerable, whether for managing cattle stations or protecting fire-sensitive plants and animals.

 

What types of fire occur in Australia's tropical savannas?

Regular, frequent fires in the far north

In the far north – the Kimberley, the Top End of the Northern Territory and Cape York Peninsula – large fires sweep across much of the landscape every year. The grasses that cover the ground in these areas can grow as high as 3 metres as they get plenty of sunshine and plenty of rain in the wet season – usually over 800mm. Then they dry out rapidly, and can carry fire throughout the dry season from shortly after the last rains. These dry grasses, supplemented by litter (leaves, twigs and bark) from the woodland trees, mostly Eucalyptus and Corymbia species, provide most of the fuel for savanna fires. They reach their most flammable state when the next wet season is about to begin around October - November.

 

Dense stands of spear grass - which re-grows every year - are common in the far north

These regular supplies of dry, grassy fuel for fire are one reason why north Australia has such frequent fire, particularly in the late dry season. The map below shows the frequency of fires over the last several years as measured by satellite sensors. More red patches equate to more frequent fires. Notice that the far north is very frequently burnt - particularly the north-west of the Northern Territory and the Kimberley and western Cape York Peninsula.

Fire frequencies in northern Australia 1997-2005 as detected by NOAA satellites (Landgate). The darker red areas show areas burnt in most of the 9 years, the lighter pink areas are burnt less frequently and the white areas unburnt by large fires.

Less regular fires in grazed country further south and east

Further inland, south and east in the tropical savannas, in the more open landscapes of places like the Queensland gulf, less rain falls in the wet season and there is often less grass as it is grazed by cattle. This reduces the fuel available for fires. Wildfires are often actively suppressed, and prescribed burning is generally excluded so that pasture can be used as livestock forage rather than as fuel for fire. In these landscapes fires are not as common - as shown in the fire frequency map above.

Intensive cattle grazing reduces the grass available to fuel fires

Extensive but not intense bushfires

If they are not burned, the grass and litter that fuel fires in north Australia will build up over 3-5 years - however they will not build up much further as it is continually being broken down by active tropical decomposers like termites, fungi and bacteria. This is in marked contrast to the situation in southern Australia's eucalypt forests where fuel can continue building up for several decades, preparing the ground for a massive conflagration.

As a result, even the most intense fires in the savannas are considerably less severe than a raging bushfire in the south. Crown fires in which the fire leaps from tree to tree, do not occur often in the north. Nevertheless, late dry season savanna wildfires are dangerous to people and property, and can cause severe damage to plants and animal populations and, as described below, there is evidence that these types of fire have increased in frequency in recent years. Preventing them is a key objective of fire management.

While they are not very intense, fires in the north can spread over vast areas with no roads or towns - across largely deserted landscapes covered in grass. While fires in the cooler, early dry season (April – June) are often small and patchy, once the high temperatures and stronger winds of the late dry season (October – December) combine with the now tinder-dry grasses a wildfire can result and can spread and spread. In 2004 a fire in the Tanami Desert covered around 60,000 square kilometres –almost the size of Tasmania!

For more information see the separate section on Fire Types , Fire Weather and Climate, Fuel for Fire and Fire Behaviour in the menu on the left. 

What are the main issues for managing fires in the north?

It appears that regular bushfire has long been a natural part of landscapes across north Australia – many of the plants and animals are adapted to some fires and evidence points to thousands of years of regular burning by Aboriginal people. With traditional practices, small patches of grassland were burned throughout the year as people moved through the country. In the Top End and northern Kimberley, many fires were lit in the early to mid-dry season - although fires were also lit throughout the year. These smaller and less intense fires of traditional practices maintain more diverse habitats than large, late fires.

So why worry about bushfires in northern Australia? Unfortunately there are increasing signs that the current patterns of fire we are seeing in north Australia are new patterns – and destructive ones.

For example, in the higher rainfall savanna woodlands of the far north as much as half of the area is now burnt either every year or every second year, typically late in the dry season (as shown in the red areas in the map below). As these late fires are generally intensely hot and extensive in area, they have the potential to devastate populations of fire-sensitive native plants and animals, to be costly and disruptive to pastoral operations, to pose a threat to communities and property, while having implications for greenhouse gas emissions.

Fire-affected areas as mapped by satellite in 1999 for northern Australia. Blue areas show fire scars mapped before July 31 and the red areas show those mapped from July 31 to the end of the year.  Source: WA Dept of Land Information

By contrast, in many of the intensively grazed regions further inland to the south and east, there is evidence that we are seeing new very low levels of burning which are thought to be contributing to the unchecked growth and increasing dominance of native trees and shrubs in once open grasslands and woodlands. These "woody weeds" are causing problems for beef cattle production and also degrade habitats for native plants and animals.

Why has there been a change in fire patterns?

There is no simple answer, but research points to a number of factors being involved in the change in fire patterns.

Wildfires in empty landscapes

A range of evidence indicates that for many thousands of years the landscapes of northern Australia were home to many scattered Aboriginal communities who used and manage fire for a number of purposes though much of the year. Aboriginal people would have used fire for hunting, for clearing country for walking through, for protecting important sites and food resources such as fruit trees and for many other reasons and consequently the country would have been subject to a range of different fires throughout the year. This landscape of patches of burnt and unburnt country made it difficult for any fire to spread too far before it encountered a fire break of previously burnt land.

Since European settlement, however, the landscapes of northern Australia have become increasingly emptied of people. Aboriginal people now live in larger communities and do not extensively occupy, or in many cases have access to, the landscapes they once managed. Cattle grazing operations are increasingly automated requiring fewer people on country. The end result is that much of the landscape is now empty and vast areas have little fire until late in the dry season when large amounts of fuel are primed for wildfire.

So are we seeing a more natural situation similar to what it would have been like before humans came to Australia with lightning driven fires? Not at all, despite the rather deserted landscapes, the evidence from fire agencies suggests that the overwhelming majority of bushfires across north Australia are still started by people. Common cases are where people light fires for fuel reduction burns, campfires or clearing up country, but often the fires get away from them. Added to this is the common observation that there now appear to be fewer people who are very knowledgeable about managing fires. Because so much land by the end of the dry season is covered with unburnt fuel, these situations in which a small fire is lit can easily become large wildfires that have nothing to stop them.

Reduced fire in cattle country

In the prime grazing lands, in places like the Mitchell grass downs of Queensland and the Barkly tablelands of the NT, grazing by cattle means there is less grass around to burn. Graziers are also understandably reluctant to light fires if they risk burning out the fodder they need to feed their cattle. The end result in these landscapes is less fire over the last century or so than there would have been during Aboriginal occupation – and this appears to be contributing to a “thickening” of woody shrubs and trees. This thickening of vegetation is seen in the pair of photos below which shows the area around Timber Creek in the grazing country of the NT. This thickening is mostly seen in the riverine plains - other parts of the landscape like the rocky escarpments are not thickening up.

Timber Creek, in the Victoria River District of the NT in 1950   (Mettam Collection)

The same view in 1996 showing denser vegetation next to the river and across the plain                     (Darrell Lewis)

Other factors

Various other factors have been linked to changing fire patterns in north Australia ranging from climate change to the spread of introduced grasses. Of particular concern in the Northern Territory is the spread of an introduced pasture grass, Andropogon gayanus or gamba grass. Gamba grass is a perennial species of African grass that is a useful pasture species and can be managed if it is grazed by cattle. However gamba grass is now invading savanna ecosystems throughout the Top End of the Northern Territory and when it is not grazed it grows vigorously in tall stands that provide fuel for intense fires. These fires in turn appear to be helping the spread of gamba grass which is adept at invading burnt areas.

A typically tall stand of gamba grass near Darwin.

 

What are the impacts of the new fire patterns on plants and animals?

Estimating the impact of the new fire patterns (also know as fire "regimes") draws on a number of different sources of knowledge: the traditional and observational knowledge of Aboriginal people, the experience and practical knowledge of other land managers and fire managers, and the knowledge that has come from scientific research into fire management.

Various lines of evidence indicate that a number of different species of plants and animals are declining in their numbers and distributions as a result of changed fire regimes. These include fire-sensitive plants such as cypress pine and groups such as the grain-eating birds. See our section on fire and biodiversity.

 

The Gouldian finch is a seed-eating bird that is thought to be threatened by, among other factors, changed fire patterns.

Two large-scale experiments, among many measuring the impact of fire on savanna woodlands, have been conducted in the NT. Among other findings these experiments have highlighted the importance that the frequency of fire has on plants and animals. It is important for the survival of some plant and animals species that their savanna habitat is burnt not more than once every few years - yet in many parts of the Top End of the NT, fire frequencies are greater than this. See our section on fire experiments.

Fore more information see the section on Fire Impacts on Biodiversity in the menu at the left.
 

What are the impacts of the new fire patterns on people and culture?

Frequent and intense late dry season fires affect many different aspects of the landscape, many of which are significant to Aboriginal people: for example the occurrence of bush tucker. Thus the new fire regimes can have a major impact on Aboriginal culture. See the section on Aboriginal fire management.

Fire also has an impact on the city dweller and on tourists. Smoke from fire drifts over towns and cities and can aggravate respiratory complaints and the blackened landscapes left by fires can often shock visitors to north Australia.

Northern fires can produce a great deal of smoke which can affect air quality over towns and cities particularly in the late dry season.

What are the impacts of the new fire patterns on agricultural production?

Other parts of north Australia have different fire management issues. Evidence from savanna cattle runs, particularly in north Queensland, suggests that a lack of burning in recent decades has contributed to widespread land degradation. One of the reasons for the absence of fire — in addition to a reluctance by many graziers to burn their land — is that increased stocking rates have reduced the availability of fuel. This has resulted in reduced fresh pasture growth, deteriorating pasture species composition, erosion, and a growing problem with woody weeds.

In most cases, fire is the only tool available to graziers for tackling these shrubs that are taking over their pastures. While much remains to be learnt about which fire regimes will be most effective, it seems that intense fires generally have the biggest impact. This raises difficult questions such as how to adjust stocking to allow the fuel build-up needed to carry hot fires and how to manage the fires safely.

In some situations, frequent low-intensity fires may be as effective as less frequent intense fires. Where the choice exists, this is likely to be the preferred alternative as it should be best for pasture rejuvenation, reducing the hazards of wildfire and the general health of the tropical savanna environment.

For more information see the sections on Fire and People, and Fire and Indigenous Culture in the menu at left. 

 

How can we better manage bushfires in north Australia?

People living in the savanna country have to recognise that managing the country, to a large extent, means managing fire. Wildfires can have devastating impacts on plants and animals as well as endangering lives and property. But, as part of the natural cycle in the savannas, fire also brings benefits. It promotes 'green pick' favoured by wildlife and stock, it regenerates food plants such as yams, and creates habitat for various native reptiles, mammals and birds.

A key part of managing fire will be using 'adaptive management', in which we learn from our mistakes in a constructive way.

A number of other initiatives are worth pursuing:

•  Developing better ways of monitoring fire so we can more easily learn using adaptive management. The North Australian Fire Information website is one monitoring tool.

• Developing better fire management techniques to tackle distinctive north Australian problems such as woody weed invasion and the need to protect large fire-sensitive areas like the sandstone escarpments from frequent fire.
  

• Supporting Aboriginal communities so they  can build on Indigenous Ecological Knowledge and put this into practice on their country along with tools from western scientific knowledge.

• Developing viable economic incentives for better fire management. The West Arnhem Fire Management Agreement addresses this issue and the building of Indigenous Ecological Knowledge.

• Provision of better education and other information resources on fire management in north Australia. For example see the Tropical Savanna CRC's Tropical Savanna Knowledge in Schools project.