Planning for prescribed burning

Details: Last Updated on Friday, 09 November 2012 12:01

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Effectiveness of prescribed burning and wildfire control

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Experience over a wide range of weather conditions and vegetation types has shown that the direct attack on wildfires that have flame heights of more than three meters or where fires are moving faster than approximately 200 metres per hour (in forest) is not likely to succeed. Fire behaviour is directly affected by the quantity of available fuel, and there is a good chance that direct attack on the flanks of a fire will succeed where fires run into recently burnt areas.

The very large fire of 9 - 11 of January 2003 south of Perth near Mt Cooke that affected unique rocky outcrop communities and threatened farms to the east, would have far more extensive if prescribed burns undertaken in the previous five years had not been present at strategic locations in this fire prone area.

Strategic prescribed burns that aided in suppression of Mt Cooke wildfire

Planning for prescribed burning

Prescribed fire is a very deliberative process. Careful planning is undertaking to determine why, when and how a prescribed burn will be undertaken. Planning for prescribed fire is undertaken for lands the Department of Environment and Conservation (DEC) manages across the entire State. DEC uses prescribed fire across the State to achieve land management objectives involving:

The conservation of biodiversity,
The management of wildfire risk,
The management of vegetation and
The development of new knowledge.

Planning for prescribed fire considers the history and variety of past fire events over the landscape to determine the most appropriate place and time to apply fire to achieve these land management objectives.

Planning to apply prescribed fire must consider many issues before determining the location, extent, timing and prescription parameters for any particular burn. When fire planning involves issues associated with the management of dieback disease, fauna species habitat, rare flora, mining rehabilitation or using fire as a silvicultural treatment, five to eight year lead times may be required to ensure all preparation and pre-burn planning steps are completed.

DEC prepares a plan for its burning program that identifies the areas that are to be subject to prescribed fire, the scheduling of these burns in the coming year and an indication of the schedule of burning for three years into the future. The process used to develop these plans is called the Master Burn Plan (MBP) process.

Each of the department's Regions prepares a MBP. In the Regions of the southwest, annual burn plans and three year indicative burn plans are prepared. In the other Regions only an annual burn plan is prepared. These regions are very large and contain extensive areas of arid and remote country.

Each year many wildfires occur in these Regions and the occurrence of irregular rainfall events that significantly affect fuel loads and flammability across the regions make longer term planning difficult.

Prescribed burning required to meet the needs of biodiversity conservation are identified first. Prescribed burning that is required for vegetation management, such as post timber harvesting for forest regeneration, is added to the program. This program is then assessed using the Wildfire Threat Analysis approach to determine if the requirements for the strategic protection from wildfire have been met. If they have not, amendments are made to the program to ensure strategic protection is achieved.

At the completion of each burning season (spring and autumn in the southwest and the wet and dry in the north) the progress of the prescribed burning program is reviewed, the occurrence of any wildfires that have occurred are considered and the MBP is reviewed and re-scheduled to take account of these fire activities.In preparing the MBP each year, stakeholders from the community are provided with opportunities to consult and contribute to the development of the MBP.

Each prescribed burn that is scheduled has a Prescribed Fire Plan (PFP) prepared for it. This plan identifies all the preliminary work that need to be undertaken to prepare the burn for ignition. These works include numerous tasks and checks to ensure the burn can be undertaken safely and effectively and achieve the desired outcome. Some of these tasks are checking for rare flora, determining the fauna species that are likely to be present, undertaking fuel sampling to determine fuel loads, maintaining access around the burn boundaries, preparing plans to deal with dieback disease of weed infestations, notifying neighbours and users of the area such as beekeepers and tourism operators and preparing maps and documentation to assist personnel undertaking the burn.

The PFP also identifies the weather conditions and fuel conditions that are required to achieve the stated purpose objectives of the burn. A ‘prescription’ is prepared that sets limits and conditions of when and how the burn is to ignited.

The PFP also identifies any monitoring work that needs to be undertaken after the burn to monitor and record the burn outcomes and assess how well the burn outcomes met the burn objectives.

Low intensity, patch burn designed to provide protection to natural and community assets are usually conducted in Spring and Autumn when weather is mild and fire behaviour is moderate and easier to manage.

In southern parts of Western Australia Spring burning is undertaken when fuels are still reasonably moist from winter rains. The moisture content of the fuels affects fire behaviour resulting in mild, slow moving fire with low flame height and low fire intensities. Flames are usually extinguished over night when the air gets cooler and the moisture in the air (relative humidity) increases. Burning under these conditions results in a patchy burn with some areas within the burn area left unburnt. These areas act as refuges for flora and fauna and provide reservoirs for recolinisation into the burnt areas. As the Spring progresses and the effect of sun and wind continue to dry the fuels it makes them more flammable, and the opportunity to undertake safe burns decreases.

proposedburnprogram

Autumn burning is undertaken when ground fuels are beginning to wet up as a result of rains associated with the break of the season. The moisture content of the dry fuels from summer continue to increase with each rainfall event. The relatively dry fuels affect fire behaviour resulting in moderate intensity fire with low to moderate flame height. Bark and dead woody material above ground can catch alight and scorching of tree canopies is common. Larger fuels such as limbs and logs can catch fire and continue to smoulder for days. Burning under these conditions results in a more uniform burn with larger areas within the burn area being burnt and fewer, smaller areas remaining unburnt. These burns tend to result in regeneration and resprouting of vegetation, a release of nutrients and a reinvigoration of local habitats. As the autumn progresses, temperatures decrease and rainfall continues to wet the fuels making them less flammable. The opportunity to undertake effective burns decreases.

The Master Burn Planning process has been completed for planned burns during the next three years in the south-west forest region WA. An indicative prescribed burn program has now been developed for the spring 2012 period and the six seasons for spring 2012 to autumn 2015. The proposed burns are designed to meet either a primary purpose, or a combination of purposes that include:

Biodiversity conservation through application of scientifically based fire regimes to maintain and protect native flora and fauna communities and/or habitats;
Community protection-protection of human life, property, public assets, parks, water catchments, timber values and plantations;
and silvicultural burns for regeneration of native forests following timber harvesting.

The extent of the indicative burn programs for the south-west regions for the six seasons for spring 2012 to autumn 2015 is shown on the maps below. These areas are based on coarse block boundaries only and are certain to be changed following internal consultation and field inspections and further input from the community engagement processes.

Maps of the intended burn program for all regions for spring 2012 (ten region/district maps, one forest regions map) are available for download below. Also available for download are the maps for the six seasons - spring 2012 to autumn 2015 (three region maps).