Landscaping Directory International

Landscaping For Fire Safety

The principles of landscaping for bush fire protection aim to:

• Prevent flame impingement on the dwelling

• Provide a defendable space for property protection

• Reduce fire spread

• Deflect and filter embers

• Provide shelter from radiant heat

• Reduce wind speed.

Vegetation choices

There is no such thing as a plant that will not burn. Some species may be regarded as ‘fire retardant' but if there is enough heat and wind, all plants will burn. However, fire retardant plants can reduce the impact of fire and help provide a defensible space around your home.

With this in mind, careful attention must be paid to species selection, their location relative to their flammability, avoidance of continuity of vegetation (horizontally and vertically), and ongoing maintenance to readily remove flammable fuels (leaf litter, twigs and debris).

Major attributes of vegetation which affect bush fire attack:

• Moisture content of leaves

• Volatile oil content of leaves

• Mineral content of leaves

• Leaf fineness

• Density of foliage

• Continuity of plant form

• Height of lowest foliage above ground

• Size of plant

• Dead foliage on the plant

• Bark texture

• Quantity of ground fuels including garden mulch

• Fineness of ground fuels

• Compaction ability of ground fuels

• Mineral content of ground fuel.

The higher moisture content of leaves the less bark that will be available and the lower the leaf drop, all of which will assist with maintenance of the understorey and reducing bush fire attack.

Scented leaves indicate a high oil content and oil is a volitile fuel.  Among the most flammable are Eucalypts, but there are many others including most pines (a very few are far less flammable, like Ponderosa) and cypresses,
casaurinas, cistus, citrus, and lavender. Any plant, like wattles, where the sap oozes out and dries in thick globules should be avoided. Dry saps burns beautifully and can explode. Trees with sap like this will also explode in a hot fire. Wattles and acacias are probably the best example of this.

Avoid any plant with lots of dead or dry material like jasmine, potato vines, Chinese jasmine, kiwi fruit, persimmon, giant rambling roses and many others accumulate dead wood as they grow larger, and even though the live plant may not be particularly flammable, the dead wood, especially by the house, can add enormously to the intensity of the fire.

Avoid any plant with rough, thick or flaking bark, that will burn even on the living tree.

When choosing plants, be sure not to introduce weed species into an area. Fire events may provide the opportunity for weed species to spread and
may contribute fuel to an area of otherwise lower fuel loads.

It's best to contact local authorities, plant nurseries and plant societies to determine suitable species for your area but here are some suggestions of plants that have low resin content and low to moderate fuel volumes at maturity:

Australia

Angophora costata
Hymenosporum flavum
Magnolia grandiflora
Photonia glabra
Banksia marginata
Grevillea victoriae 'Murray Queen'
Myoporum parvifolium
Hakea salicifolia
Pelargonium peltatum
Verbena peruviana


California

Trees
Maple (Acer sp.)
Strawberry Tree (Arbutus unedo)
Incense cedar (Calocedrus decurren)
Pittosporum (Pittosporum spp.)
Cotton wood (Populus spp)
Quaking aspen (Populus tremuloides)
Pomegranate (Punica granatum)
Coast live oak (Quercus agrifolia)
Blue Oak (Quercus douglasii)
California black oak (Quercus kellogii)
Valley Oak (Quercus lobata)

Shrubs or low growers
Manzanita (Arctostaphylos spp.)
Rockrose (Cistus spp.)
Bush Morning Glory (Convolvulus cneorum)
Myoporum (Myoporum spp.)
Oleander (Nerium oleander)
Italian buckthorn (Rhamnus alaternus)
Cape Honeysuckle (Tecomaria capensis)
California Bay Laurel (Umbellularia californica)


Ground Covers
Prostrate coyote bush (Caccharis pilularis)
Creeping Coposma (Coprosma kirkii)
Trailing African Daisy (Osteospermum fruiticosum)
Trailing Gazania (Gazania rigens leucolana)
Lavender Cotton (Santolina spp.)
Vinca (Vinca spp.)

Trees as Windbreaks

The use of trees as windbreaks is a common practice but trees also provide a useful function, trapping embers and flying debris, which would otherwise reach the house. The tree crown will rarely carry fire unless there is a significant fuel loading on the ground.

By reducing the wind speed, a row of trees also slows the rate of spread of a bush fire and a dense foliage traps radiant heat, lowering bush fire radiant heat.

Because of the effect of turbulence, a balance has to be struck between a high density of trees (thatmaximises the trapping of embers and radiant heat but also maximises turbulence) and a lower density (that allows more embers and radiant heat to pass through but minimises turbulence). A windbreak that allows 30–60% of the wind to pass through is ideal as less than this becomes too solid with ember laden winds being carried over the top of the break.

To be effective a windbreak must:

• be located on the side of the lot from which fire weather normally approaches;

• be of sufficient length (generally 100 metres minimum length);

• be located at a distance of one to three times the height of fully grown trees

• use smooth barked eucalypts, rainforest trees or deciduous trees;

• make sure there are no breaks of sufficient size to allow winds to funnel through; and

• be separated by sufficient distance from the hazard so as not to be consumed and become a hazard itself.

Vegetation Management

Priority should be given to not allowing fine debris to accumulate close to the building. Secondly, removal of understorey fuels aids in the reduction of flame heights and likely canopy fire, thereby reducing overall radiant heat. Removal of loose bark and fine fuels reduces both heat output and ember generation, while the retention of taller trees with canopies will also assist in filtering out embers.

To maintain a garden that does not contribute to the spread of bush fires the following tips are essential:

• maintaining a clear area of low cut lawn or pavement adjacent to the house

• keeping areas under fences, fence posts and gates and trees raked and cleared of fuel

• utilising non-combustible fencing and retaining walls (rock is best)

• breaking up the canopy of trees and shrubs with defined garden beds

• organic mulch should not be used in bush fireprone areas and non flammable material should be used as ground cover, eg. pebbles, recycled crushed bricks

• planting trees and shrubs such that the branches will not overhang the roof; the tree canopy is not continuous; and there is a windbreak in the direction from which fires are likely to approach

Maintenance of Property

Sensible arrangements for landscaping and maintenance of the property are critical in the prevention of losses.

The following items should be implemented in advance of the bush fire season:

• removal of material such as litter from the roof and gutters

• ensure painted surfaces are in good condition with decaying timbers being given particular attention to prevent the lodging of embers within gaps

• check pumps and water supplies are available and in working order

• driveways are in good condition with trees not being too close and forming an obstacle during smoky conditions

• check tiles and roof lines for broken tiles or dislodged roofing materials

• screens on windows and doors are in good condition without breaks or holes in flyscreen material and frames are well fitting into sills and window frames

• drenching or spray systems are regularly tested before the commencement of the fire season

• hoses and hose reels are not perished and fittings are tight and in good order

• doors are fitted with draught seals and well maintained

• mats are of non combustible material or in areas of low potential exposure

• woodpiles, garden sheds and other combustible materials are located downslope and well away from the house

• trees and other vegetation in the vicinity of power lines and tower lines should be managed and trimmed

Photo credit to USBC Geography Department

Thank you to the Rural Fire Service of New South Wales