10. Fire and its impacts

10.1 Background

Bushfires and controlled burns

Fires are a natural part of the Australian landscape. Many native plants burn readily, and fire is vital for the health of numerous native species and ecosystems. The ACT landscape has evolved with fire. Aboriginal people developed a sophisticated understanding and use of fire to manage land and resources and reduce bushfire risk (see Ngunnawal Country section).

Cultural burning on Country – this type of controlled burn can improve the health of native ecosystems such as grasslands. Photo: ACT Parks and Conservation Service.

A bushfire is an unplanned fire that burns in grass, bush or woodland and can have devastating impacts on people, property, plants and the environment. Fires can harm water quality in rivers, catchments and water storages. The smoke from bushfires and controlled burns increases air pollution, especially airborne particles and summer smog. These pollutants can affect people, especially those with asthma and breathing problems.

The ACT has a high risk of bushfires. There are large areas of forest in the Namadgi National Park, Tidbinbilla Reserve and the Lower Cotter Catchment. Canberra suburbs are also at risk of fire due to bordering bushland, grassland and forests of the Canberra Nature Park.

Bushfires need fuel, oxygen and an ignition source to start and spread. The fire intensity and speed of spread depends on air temperature, the amount of fuel (such as fallen bark, leaf litter and small branches) and the moisture in it, wind speed and slope angle. The higher the air temperature, the more likely it is that a fire will start or continue to burn.

Managing fire risk and ecosystem health

Reducing undergrowth can help manage bushfire severity. The ACT Parks and Conservation Service do this through controlled burns, also called prescribed or hazard reduction burns. Experienced fire managers carefully light fires in planned areas when weather conditions are suitable, usually in spring and autumn. Controlled burns help protect homes, buildings and farms, and Canberra’s water supply. They also create fire breaks that help prevent bushfires spreading.

But it is vital to ensure ecosystem and biodiversity outcomes are considered before conducting fuel reduction burns so that ecologically appropriate burning is undertaken. That’s because if plants are burnt too frequently, they cannot grow to maturity and develop the seeds for future generations. But some plants need fire to grow their seeds and so too little fire can also be a problem.

Banksia life cycle

Banksia are plants with distinctive flower spikes and fruiting cones and heads. There are over 100 Banksia species. All but one occur naturally only in Australia. Woody capsules protect Banksia seeds from fire. Once the fire has passed, the plant releases seeds to the forest floor, which is full of nutrients.

Research on the life-cycle of one of these plants, Banksia spinulosavar cunninghamii (Hairpin Banksia), is helping fire managers preserve plant diversity in forests when doing controlled burns.

This species takes a long time to produce seed, so it suffers if burnt too often. There must be enough time between fires for plants to mature and produce sufficient seed, and for enough seedlings to survive. Fire intervals of at least 15 years allow Hairpin Banksia populations to maintain an adequate seed source.

Silver Banksia (Banksia marginate) is the only naturally occurring banksia in the Canberra region. Photo: Australian National Botanic Gardens.

Saving lizards

Controlled burns can improve the health of ecosystems and biodiversity that depend on fire for regeneration and regrowth. The Grassland Earless Dragon is a small species of dragon lizard thought to be extinct until its rediscovery in the early 1990s. The endangered animals live in patches of natural grassland in the ACT, and just across the NSW border in Queanbeyan. They use burrows for shelter, temperature regulation, and to lay their eggs in spring.

A Grassland Earless Dragon. The green mark is used to track individual dragons during the monitoring period. Photo: ACT parks and Conservation Service.

There was a decline in the number of dragon lizards after above-average rainfall from 2013 to 2015 changed their grassland habitat. To improve the habitat, the ACT Government ran a large-scale ecological burning program over more than 50 hectares of the grasslands. These burns opened up the vegetation, and the dragon lizards soon re-colonised the areas that had been burnt.

Small-scale burns undertaken at Jerrabomberra West in an area where Grassland Earless Dragons used to live. Photo: ACT parks and Conservation Service.

Fire danger ratings

Every day during the bushfire season, fire services throughout Australia produce a fire danger rating. The rating shows how a fire is likely to behave if it started on that day. The fire danger rating is represented by different colours. Green, for example, represents low to moderate fire danger risk. Red represents extreme fire danger risk.

Fire services determine the fire danger rating from a fire danger index, which assesses the potential severity of bushfire given the predicted conditions. The index is a measure of how difficult it would be to contain the fire, as well as the risk to community, property and landscape.

The Bureau of Meteorology calculates the fire danger index from forecast air temperature, relative humidity and wind speed, along with drought conditions and soil moisture levels.

A fire danger index of 1 means a very low risk of fire occurring, and that it will be easy to control. A fire danger index of 100 means that fires may be so severe that control will be virtually impossible.

Elevated fire danger conditions (severe, extreme or catastrophic) occur when the fire danger index is greater than 50. Elevated fire danger conditions are uncommon in the ACT, averaging fewer than three days a year, usually in January. However, in the future, climate change is expected to increase both the average and severe fire danger index.