Fire in the Arid Zone
Fire is generally not associated with desert landscapes but, fire can occur on a regular basis and is an important driving force in the ecology of arid areas in Australia. It is therefore critical that land managers plan for the use of fire and be ready to manage its impact.
 Satellite image of fire scar |
Current Fire Regimes
Climate is the driving force that determines the occurrence of fires in central Australia. During the last century periods of above average rainfall have occurred on cycles of 25 to 30 years. Historical accounts of extensive wildfire seasons show a direct correlation with these wetter years rather than periods of drought. However fires do occur at other times when local conditions contribute to the accumulation of fuel and enable ignitions to spread and develop into major fires.
Historically, the patterns of fire activity are associated with three distinct components of the landscape, with links to broad vegetation communities. 'Spinifex communities' are most regularly and extensively impacted upon by fire. 'Non-spinifex vegetation communities' have the least frequent incidence of fires. 'Mountain range areas', with a mix of spinifex and non-spinifex vegetation, have their own unique fire management issues. Interestingly, the separation roughly equates to areas of Aboriginal land, pastoral land, and conservation land respectively but during periods of above-average rainfall each landscape component can be severely affected by wildfires.
'Spinifex communities' occur on the extensive areas of sandplains and dunefields, typical of desert regions. Spinifex is a very flammable plant and fuel loads steadily accumulate as the spinifex hummocks increase with time. The rate of accumulation is variable in association with rainfall, and the interval between fires, limited by the accumulation of fuel, can be as long as 20 years.
The 'non-spinifex communities' are a diverse range of vegetation communities. They include grasslands on cracking clay soils, open woodlands with a mix of grasses and Acacias, and some areas of Acacia woodlands with minimal understoreys. Fuel loads in these areas respond more rapidly to rainfall relative to the spinifex areas, but cattle and other grazing animals, including termites, readily consume the grass. Therefore fuel loads only build to high levels across the landscape after extended periods of widespread rain when growth can far exceed consumption.
The 'mountain ranges' are complex areas, with non-spinifex communities dominating the flatter portions of the landscape and spinifex dominating the hills and ridges. Within the ranges are innumerable gorges and gullies, which are both important scenic locations for parks and tourism as well as refuges for animals and fire sensitive plant species.
Our knowledge of fire regimes is based on the use of satellite images to detect fires and to map their spatial extent. A series of satellite images over time allows us to build up a fire history for large areas and increases our knowledge of the time since fire, and the frequency of previous fires, for any specific location.
 Hot fires in buffel grass communities along drainage lines threaten the survival of long-lived River Red Gum trees. |
Threats
Large wildfires are undesirable for most plants and animals, especially if there are no unburnt island refuges within the burnt area. This includes both domestic stock and native animals. The time of the fire in relation to soil moisture and rainfall can also increase the impact of fires. Hot fires in dry times mean the post-fire recovery of vegetation and associated food resources is very slow. Uncontrolled ignitions in times of widespread fuel loads, especially during the past 3 years from 2000 to 2002 have caused large wildfires. The fires have damaged infrastructure and fences, destroyed pasture for grazing animals, and have directly killed cattle and other animals.
The fires can also reduce the extent of fire sensitive vegetation communities, such as mulga. The fires kill the mature mulga plants and increase the opportunity for spinifex to invade the mulga community.
A relative new feature of the fire regimes of central Australia is buffel grass (Cenchrus ciliaris). It was introduced as a pasture grass, but has taken over most alluvial areas and is continuing to spread into other habitats. Buffel grass can recover quickly from a fire and will out compete other plants to become dominant. The rapid build-up of buffel grass fuel has increased the fire frequency in many areas and long-lived woody species, such as river red gums (Eucalyptus camaldulensis), corkwoods (Hakea species) and beefwoods (Grevillea striata), are suffering from the frequent fires.
There are many areas in central Australia where it is desirable to exclude fire. These include sheltered gullies in range country, and long-lived fire sensitive communities such as mulga and lancewood. Protecting these areas from fire is a very difficult task.
 Active fire management programs, with the assistance of the Bushfires Council NT, can reduce the impact of wildfires. |
What We Can Do!
Land managers need to plan for fire, both for its use and its risk. Fire may not be a regular feature within any specific part of the landscape, but it is important to be prepared. Active fire management is required, as is the appropriate use and timing of fire.
The easiest job is to monitor spinifex areas and burn patches to create a mosaic of fire ages. It is also important to manage fuel loads in high-risk areas, especially along main travel routes where uncontrolled ignitions are most likely. It is possible to use fire as well as grading, slashing and grazing programs to reduce fuel loads.
It is more difficult to be prepared for seasons of above-average rainfall and widespread fuel loads. However it is important to plan to use of fire, for habitat management or control of woody thickening, and be ready to respond when season and rainfall conditions combine to create an opportunity to burn.
Further Reading
The book "Bushfires and Bushtucker" gives a description of the central Australian environment and the role of fire, and includes a comprehensive description of individual plant species and their response to fire. The book "Flammable Australia" discusses fire issues across all of Australia, and includes chapters on fire in spinfiex landscapes and other vegetation communities relevant to central Australia.
The full details are:
Latz PK (1995) Bushfires and Bushtucker, Aboriginal Plant Use in Central Australia. IAD Press, Alice Springs.
Bradstock RA, Williams JE, Gill AM (2002) Flammable Australia, The Fire Regimes and Biodiversity of a Continent. Cambridge Uinversity Press, Cambridge.