On Monday 1 November 2017, about 30 members and friends met for a talk on burning off in private bush blocks by Mike Wouters, senior fire ecologist for DENR.
Under recent changes to Native Vegetation Regulations, Regional CFS Officers have been delegated authority to approve clearing (including burning) for fuel management purposes.
- Fuel can be removed from within 20 metres of a building (house, school, nursing home, etc – essentially buildings where people live/work/congregate) without any approval.
- Fuel can be removed from within 5 metres of a structure (shed, pump house, out building, etc – essentially non-residential structures) without any approval.
- Vegetation modification (fuel removal) for other areas greater then this requires approval of the relevant CFS Regional Prevention Officer (Mt Barker or Gawler).
- To reduce fuel strategically (away from assets), a fire plan is needed to be approved by a sub-committee of the Native Vegetation Council. Burning for ecological outcomes requires approval by a sub-committee of the Native Vegetation Council, and it prefers to work with groups of landholders over several years.
- Blocks which are Heritage-listed need to include the intention to burn in the Fire Management Plan as part of the agreement.
Further details about exemptions and approvals are available on the CFS web site, www.cfs.sa.gov.au (follow links: community information > prepare > preparing your property for bushfire > native vegetation management) or the NVC website www.nvc.sa.gov.au.
Fuel Reduction is not necessarily burning. Raking, mulching and mowing are alternatives. (See CFS website.) This summer the greatest threat is from cropped land and pasture, especially if not grazed and if it includes phalaris, and infestations of gorse, broom, boneseed and blackberry. Fire intensity is lower in areas which have been slashed. Make use of windbreaks; they reduce wind speed and deflect sparks, making it easier to save a house.
Mike then discussed the nature of the vegetation that is the fuel for fires. He referred to the booklet “Overall Fuel Hazard Guide for SA” (available at www.environment.sa.gov.au/fire).
The overall fuel hazard is the sum of the various individual component hazards from bark, elevated fuel (shrubs and understorey plants up to 2m in height) and fine fuel on the surface. He stressed that stringy bark and the fine fuels matter most – essentially the dead leaves, twigs smaller than 6mm in diameter and live grasses/leaves less than 2mm in diameter. Fallen logs, standing trees and the leaf canopy contribute little to the spread of bushfires.
Elevated dead fine fuel cause more spread than the same fuel lying flat on the ground. Stringy bark is particularly bad as burning pieces break off and travel large distances with the wind as embers, like flying sparks. Larger ribbons of bark can also form embers travelling many kilometres.
He presented a graph that illustrated the pattern of build up of these fine fuels over time. In the mallee and open woodland, the fuel builds up linearly with time over about ten years to a loading of 20 tonnes per hectare (t/ha). After ten years the fuel load levels off at 20t/ha as the leaf matter decomposes at the same rate as fresh material is being deposited. In the wet forests of Victoria and Tasmania, the fuel builds up over a longer period of twenty years before stabilising at 30t/ha. Annual variations in climate are unimportant.
Mike then introduced a table showing reduction in fuel hazard following burning of various vegetation forms:
|Persistence of the effects of fire, years
|Forest, mallee, short shrubs, gum bark
|Forest, tall shrubs, stringy bark
How often to burn an area depends on the species concerned and the rainfall. Fire regime (fire interval, frequency, season, extent/patchiness) has a more significant impact on vegetation and fauna habitat than the impact of a single fire. These factors need to be considered when planning ecological burning. The minimum time between burns varies according to the vegetation type:
|Minimum time, years
|Euc. woodland with grassy under-story
|Euc. woodland with shrubby under-story
|Euc. forest with grassy under-story
|Euc. forest with shrubby under-story
However other elements of fire regime need to be considered as well – these are estimated in Ecological Fire Management Guidelines in preparation (early draft available at www.environment.sa.gov.au/fire). Many native plants respond positively after fire. The heat and smoke promote seed germination and there is less competition for light, water and nutrients.
When to burn an area depends on the species concerned. For example, an area containing many orchids and lilies is best burnt after flowering in November. They will respond to the reduced competition with brilliant displays in following years. Some orchids especially like open areas. However, spring burning may interrupt the flowering and breeding of other species – there are no simple answers. In planning ecological burning it is important to consider the longer term survival of populations rather than individuals of a species.
Mike made the important point that although fire often promotes the germination of weed seeds that have lain dormant in the ground, it provides the ideal opportunity to remove these weeds by spaying, slashing etc. that ultimately reduces the weed seed bank. Fire alone will not reduce weed problems, but integrated with other weed management, it can be a very useful tool.
It is interesting to put the carbon dioxide (CO2) emissions from fires into context. Australia as a whole emits approximately 330 million tonnes of CO2 annually. Large bushfires in Victoria emitted 105 million tonnes both in 2003 and 2006/07. On Black Saturday (7 February 2009) in Victoria 8.5 million tonnes of CO2 was estimated to have been released. Burning off savannah woodland in northern Australia emits 11.8 million tonnes of CO2 annually, while prescribed burning in the southern states of Victoria and WA emits 2 million tonnes of CO2 annually.
The worst offender is NT, with 20-30% of the whole territory burnt each year, mostly from annual grass fires on properties not requiring permission. There are no incentives to stop until Emissions Trading is introduced. Currently the government is trying to educate pastoralists to burn earlier, at the end of the wet, as carbon content is lower then.
Slashing and burning have similar effects on fuel in that they both reduce standing vegetation. Slashing leaves it on the ground where it adds to the ground fuel but reduces the flammability as it is on the ground rather than standing.
Fire is an integral part of the ecology of our landscape. Fire does not kill everything. Vegetation grows back – often stronger. It provides opportunity for some species. Animals survive low intensity fire, some by hiding in hollow logs, others by climbing higher into trees or by hopping away. Nomadic birds are attracted to burnt out areas but unfortunately birds that like thick undergrowth disappear.
Fire behaviour science is good for temperate forest/woodland fuel types and we are continually learning about other types. However the basic knowledge is robust and well understood (like the effects of fuel type, topography, climate, wind, of humidity, dryness of fuel, regeneration of species after fire etc.) Research has been going on since the 1960s with one of the earliest scientific studies in SA on the recovery of native vegetation after fire in the Mount Bold reservoir area. Studies have grown, particularly since the 1980s. We are definitely not flying by the seat of our pants.
Prescribed burning is a task that needs to be carefully planned and implemented to achieve the desired results and minimise the risks of escape. Unfortunately many landowners do not have either the skills or resources to conduct burning safely. This is one of the reasons that large scale burning of private lands was not recommended by the Victorian Commissioners into the bushfires of February 2009. Nevertheless we should not shy away from discussing the possibilities, as it will doubtless be a requirement in the future.
Legislation does not prevent landowners burning, with permits being required only for burning during the Fire Danger Season. Be well aware that if you light a fire on your property and it gets out of control, you can be legally liable for any impacts.
Fire prevention, management and biodiversity conservation is a community issue – there are biological and physical aspects, but it is the impacts people have on nature and the impacts bushfires have on people that causes the conflicts. Together landowners, community groups and agencies can manage fire for the best outcomes.