Version 1.3 17 September 2014

A tool to estimate and manage vegetative fuel loads on your property

Residents’ Vegetative Fuel Load Guide

The main purpose of this guide is to help residents estimate the vegetative fuel load on their property and suggest ways to manage or reduce the fuel load. It also gives a brief explanation of Building Protection Zones (BPZ).The sample methods and tables used in this guide are specifically tailored for the Northern Jarrah Forest, the most common vegetation type in the Shire of Mundaring. It does not represent other possible types of vegetative fuel.

Fuel typesForest fuels can be divided into four different layers: • Canopy; • Bark;• Elevated fuel (shrubs up to 2m); and • Surface litter (leaf litter). Surface litter and elevated fuel are the types that contribute most to the overall fuel hazard. Tree canopy, bark and coarser fuels (thicker than a pencil) will affect fire behaviour, but their impact is less significant and as such they are not considered in this guide. Large logs are not readily flammable and provide good habitat for fauna. Regular fuel load assessments are encouraged to maintain fuel loads at an appropriate level.

Users of this guide must understand that the fuel measuring method used in this booklet only gives an indicative fuel load. To establish a complete and accurate fuel load requires extensive knowledge and experience, and is beyond the scope of this guide.

About this guide

How to use this guide

VEGETATIVE FUEL LOADS

Why are fuel loads a major concern?Three major factors influence fire intensity: temperature, wind and fuel load. Of these factors, fuel load is the only one we can influence in order to reduce bushfire risk.

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How to measure fuel loads

Divide your property into different sections (cells) based on the vegetation variation across the site. The fuel load in each cell is measured with a minimum of three samples to establish an average fuel load for the cell.

Measuring surface fuel load

Surface fuel loads are determined by measuring leaf litter depth using a simple depth gauge. The gauge can be made at home using a circular Ø15cm cardboard disk with a ruler slotted through its centre (McCarthy et al, 1999). The guages are also available from the Shire.

Clear a small hole in the leaf litter and remove any coarse material. Place the end of the ruler on the soil surface (as shown in the figure above). Gently press down on the disk (enough to hold a tennis ball under water). Read the litter depth, adjusting for any ‘dead’ length on the end of the ruler (if any). Use this measurement to establish litter weight per hectare from table A.

Measuring scrub fuel loadScrub fuel loads are determined by assessing the average height and density of the vegetation and classifying it as ‘Sparse’ (easy to pick any path through), ‘Medium’ (can pick a path through), or Dense’ (difficult to walk through). Refer to table B to establish the scrub base weight. Refer to table C to determine the most appropriate Scrub Flammability Factor. Scrub weight per hectare is calculated by multiplying the Scrub Base Weight by the Scrub Flammability Factor.

Figure 1. Leaf litter depth gauge.

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Calculating total indicative fuel load

The Total Indicative Fuel Load (TIFL) is calculated as:

TIFL = Litter weight + (Scrub Weight x Scrub Flammability Factor)For example, with a leaf litter depth of 10mm (5.3 t/ha from table A), dense scrub with an average height of 0.9m (3.0t/ha from table B) and consisting of no more than 20% dead materials (giving a scrub flammability factor of 2 from table C):

TIFL = 5.3t/ha + (3.0t/ha x 2) = 11.3t/ha

Any cell with a fuel load above that set out in the Shire’s Fire and Burning Information Book (included annually with rate notices) needs to have its fuel load reduced.

Fuel load tables

REDUCING FUEL LOADS

Excessive fuel loads pose a direct threat to life and properties. It is the owner and/or occupier’s responsibility to manage fuel loads in accordance with the Shire’s Firebreak Notice. In most cases this means maintaining fuel load in natural bush areas to 8 tonnes/ha and implementing a building protection zone around habitable dwellings (refer to page 6).

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Hazard reduction burning

The objective of a fuel reduction burn is to reduce, but not totally remove, the amount of surface litter and elevated fuels. For larger lots, this is best achieved by a low intensity burn, i.e. burn in the cooler part of the day, mid-afternoon and onwards, when the dew level is increasing.

Before conducting a fuel reduction burn, consider how the fuel load distribution, topography (fire travels uphill) and weather will affect the fire behaviour. Inappropriate burning can endanger lives, property and the environment. If conducting a fuel reduction burn, it is important to ensure that the surface litter and elevated fuels are dry, and weather conditions are appropriate to ensure minimal smoke is produced so it does not create a nuisance for neighbours.

All burning must abide by the conditions stipulated in the Shire of Mundaring’s Fire & Burning Information Book. Alternatively, you can contact your local volunteer fire brigade or a commercial operator to undertake the burn for you for a fee.

For smaller lots in residential zoned areas, it is often safer and more practical to rake up the material and take it to one of the transfer stations or conduct a pile burn.

If conducting a pile burn, it is important to ensure that it does not create a smoke nuisance to the local community. This can be achieved by having a hot, clean burn that produces minimal smoke. Do not burn recently cut green waste or wet fuel due to recent rain. A smouldering fire is the result of incomplete combustion and will create excessive smoke.

Figure 2. Fuel reduction burn with minimal smoke

Figure 3. Pile burn with minimal smoke.

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Though burning is a natural part of our bush, it is not always the best option to reduce fuel loads. Burning too frequently encourages weeds to grow, which can cause an increased fire risk. Modifying the vegetation is often a more economical and environmentally sustainable option. This includes, but is not limited to:• Rake and remove fallen leaves, twigs and bark on a regular basis.• Remove weeds by slashing, spraying or cutting.• Selectively prune and manage scrub so there is not a continuous fuel

load for the fire to travel through.• Remove low hanging branches (under 2m)

Contact the Shire’s Environmental Services on 9290 6651 for more information. Be clear before you clear.

Note: The Shire’s waste transfer stations accept green waste from residents for free.

Vegetation modification

A Building Protection Zone (BPZ) is a low fuel area immediately surrounding a habitable dwelling (20m or more, depending on slope), and is designed to minimise the likelihood of flames contacting your house. The list below suggests how to establish a BPZ. Full BPZ requirements are in the Shire’s Firebreak Notice.• Reduce the fuel load and maintain to 2t/ha.• Create a clear separation between adjoining or nearby tree crowns

(i.e. the outer branches). A small group of trees close together may be treated as one crown.

• Ensure there are no tree branches hanging over habitable dwellings.• Ensure no trees or shrubs are within 2m of building.• Prune tree branches that hang within 2m of the ground to create a

clear separation between the ground fuel and canopy fuel.• Maintain all grass to 5cm or less.

BUILDING PROTECTION ZONES

Figure 4. Example of a BPZ.

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ENVIRONMENTAL CONSIDERATIONS

When considering fuel load reduction measures, it is important to consider the protection and conservation of plants and animals. Although fire is a natural part of the Jarrah Forest, with some species being dependant on fire for their existence, others are susceptible to the impact of poor fire management. They can be protected by considering the following points:

• Protect biodiversity by selecting a fuel load reduction technique that has minimal impact on plants, animals and the land.

• If you burn, consider developing a seven year burn plan for your property by dividing it into sections (burn cells). Burn the cells at different intensities and at different seasons. This will give a mosaic fuel load pattern across the property and offer a refuge for animals, provide for different species requirements and opportunities for plants to regenerate.

• Consider post-fire weed management, as recently burnt areas are susceptible to weed invasion or infestation.

• Protect and retain significant habitat for animal refuge (e.g. logs, tree hollows) and retain all habitat trees suitable for protected species, such as black cockatoos. Habitat trees are protected and require federal government approval to be removed.

• Ensure the retention and protection of any Declared Rare Flora (DRF) that is protected under the Wildlife Conservation Act (1950). Contact Department of Parks and Wildlife to find out if DRF exists on your property.

• Watercourses and their associated vegetation are considered as an Environmentally Sensitive Areas (ESA) and are vulnerable to the impacts of poor management. Contact the Shire before undertaking any work on these areas.

• Consider post-fire erosion risk. Water will move faster across newly burnt land due to a lack of vegetative ground cover.

For more information refer to the Shire’s Fire and Burning Information Booklet or contact the Shire on 9290 6666.

Figure 5. A local Western Bearded Dragon.

Figure 4. Example of a BPZ.

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7000 Great Eastern Highway Mundaring WA 6073

9290 6666www.mundaring.wa.gov.au

Fire enquiries - 9290 6696Environmental enquiries - 9290 6651