Last year’s black summer – 18.6m hectares of land and 5900 buildings destroyed, most tragically of all, millions of animals and 34 people lost.
Yet, after one of the darkest moments in our history, we must now focus on seeing the light – in our increasingly hostile climate, arborists and landscape maintenance crews will find themselves more involved in the vital role of creating defendable space around aussie homes.
After a bushfire, two of the most immediate tasks are clearing of ash and burnt vegetation. Ash can be good, encouraging the germination of many native species.
Yet, very thick layers of ash make growing conditions too alkaline and may need to be reduced. Burnt soils can form water-repellent crusts or lose structure and wash away, while there is also a short-term impact on the soil’s micro-biology in the upper layer.
Soil remediation may involve the application of soil wetters to counter hydrophobic conditions. All burnt soils will benefit from the addition of 10cm of organic matter to improve water holding capacity while also attracting earthworms and soil microbes.
After a bushfire, clients may push for total removal of all trees. Yet, restrictions around vegetation clearance are contained within the planning schemes of local councils, so be safe! Usually it is acceptable to cull or lop vegetation within 10 metres of an existing building, plus some perimeter lopping under rules such as 10/30 and 10/50. In high bushfire risk areas, properties may need an even greater amount of clearance, which can be applied for through a planning permit.
Plants scorched through radiant heat rather than direct flame have a better chance of recovery. Consider saving selected trees, shrubs and orchards – they should be seen as assets that have had a lot of time and water invested in them.
Using a sharp knife progressively, scratch down burnt stems in search of a green, living cambium layer. Many Australian natives (for example, Banksia, Eucalyptus, Xanthorrhoea) will reshoot from protected buds at the base (lignotubers) or within trunks (epicormic growth).
With earthmoving equipment on site, you may be asked to assist with the general clean up. Again, be safe, issues can arise around asbestos as well as soil contamination from the burnt remains of treated timbers. If fire retardants were deployed, you’ll need to know how to manage the residues.
There are three ways in which properties are lost:
- Ember attack remains the most common way that a house catches fire with embers landing on flammable material (leaf litter) or on vulnerable parts of the house (eaves, timber decks)
- Radiant heat dries vegetation ahead of the fire and can also crack windows allowing embers to enter
- Direct flame contact occurs when vegetation is planted too close to the house or the high winds often associated with bushfires cause trees to fall onto the building
The Bushfire Attack Level rates the potential exposure of a building to bushfire – six ratings from BAL LOW, through to BAL FZ. Knowing the BAL rating of the property will give a guide to the amount and type of landscaping needed to create defendable space.
Yet, although appropriate landscaping is vital in fire-prone areas, it still needs to be part of an overall approach that also addresses water supply, access and building construction.
Removing flammable objects from around the house is essential to creating defendable space.
Mulching gardens in fire-prone areas can be problematic. Fine shredded and aerated organic mulches should be avoided because they ignite more easily. Coarse, compacted wood chip mulches are the better option.
Yet, it’s worth considering non-flammable alternatives such as pebble, gravel or crushed brick. Make sure you choose coarser grades of these materials that will allow leaves and debris to be raked or blown off the gardens without also losing the mulch.
“Plants are the primary source of fuel for a bushfire so it is vital to aim for the right plants in the right place.”
Locating landscape features with low flammability (lawns, swimming pools, vegetable gardens and orchards) between the house and the most likely direction of the bushfire will help to break up fuel continuity. However, even ‘fire history’ wasn’t always reliable in last year’s catastrophe.
At Cuddlee Creek in South Australia, fires usually came from the north or north west, but some properties had the fires approach three times from other directions!
Plants are the primary source of fuel for a bushfire so it is vital to aim for the right plants in the right place.
Last summer, many large rural properties surrounded by dry pasture were engulfed under relentless ember attack, while severe fires even moved beyond the rural fringe into the suburbs. Properties in the hills with exceptional growing conditions were devastated while fires also invaded coastal villages surrounded by highly flammable, low, wind-pruned bush. All of these scenarios require different plant selection responses so there can be no one-size-fits-all list of fire-resistant plants. Local councils and fire
authorities have compiled fire-wise plant lists for most locations across this great land.
Important aspects in selecting ‘fire-wise’ plants include:
- Avoid plants with high levels of oil, resin or wax (for example, paperbarks, tea trees, gums and pines)
- Stringy bark eucalypts and some paperbarks that shed bark should also be avoided as they can act as fuel ladders, carrying flame up into the canopy
- Select plants that produce minimal litter in summer (deciduous trees may be worth consideration)
- Choose plants with open and loose branching with leaves loosely spread unless creating a windbreak
- Consider plants that have wide, flat and thicker leaves as they have a higher moisture content relative to surface area
Considered and thoughtful placement of appropriate green life is also essential.
Using lawn areas to provide separation between garden beds will help to break up fuel continuity. Trees should be clumped to create at least two metres distance between canopies with few shrubs planted underneath to avoid the creation of fuel ladders. Shrubs should also be planted in clumps that are separated from each other.
Regular garden maintenance should be included as part of any Bushfire Survival Plan. Plants grow and will need to be maintained! On larger properties maintenance contractors need to be vigilant, maintaining tree canopy separation and density as well as eradicating any invasion by environmental weeds, which often create higher fuel loads.
Tree branches should be pruned to at least two metres above ground to increase vertical separation between ground level and the canopy. Ground level fuels, such as leaf litter and debris need to be collected on a regular basis. Irrigated and mown lawns help to break up fuel continuity but, remember, fires have also been started by ‘sparking a rock’ while slashing on hot, dry days.
The bushfire season has come around again and although it’s been said many times, it always bears repeating, on extreme bushfire days, leaving early still remains the safest option. Yet, hopefully, with a more holistic approach to bushfire preparation that includes appropriate landscaping and regular garden maintenance, our fantastic firies will be saving more properties and leaving more of the messages shown above.