Can garden plant selection significantly reduce the effect of bushfire damage?
There is no doubt that it can. By thinking about the species that you plant and where you plant them - how close to structures such as houses and fences - you can reduce the damage the fire causes. Your decisions will impact on how the fire moves, what actually burns and how much debris will be flying around and this all helps to determine how much damage is done to the property. The topic of how readily hedges burn is very pertinent in Melbourne at the moment with the recent spate of arson attacks on hedges. Many conifers contain large amounts of resin and they go up like torches. In older gardens, you often see large Cupressus macrocarpa (Cypress) hedges up close to houses, even wooden houses, which poses a great risk. Eucalypts often produce oils that vaporise in the heat and they burn with great heat but very quickly. They are a hazard but only for a short time. Some plants are damaged by fire but don’t carry fire well eg some acacias (wattles) and Myoporum (Boobialla) species. These plants will slow up a fire. There are good lists of fire resistant plants in the textbooks. (A short list appear below.)
What other procedures can help reduce bushfire damage to gardens?
Mulch is something else that needs to be considered. You need to think about what kind of mulch you use, how deep it is and how flammable it is. In the Ash Wednesday fires we saw a number of splendid trees that actually survived the fire, but were effectively ringbarked by the ground fire in the mulch.
If you are able to water and keep the mulch moist the flammability is fairly low but a well-aerated mulch consisting of particles of mixed size (eg garden litter and wood chips) that has not been kept watered is very flammable. Unfortunately, bushfire danger is at its worst in times of drought and keeping mulch wet may be impossible. Removing mulch which conserves soil moisture is horticulturally undesirable especially in times of drought, but you need to have thought it through and have some kind of system in place. An option is to use non-organic mulch such as scoria or pebbles, though these may not be desirable from a horticultural or aesthetic point of view. You do need to consider what are the most valuable plants in the garden and take steps to protect those.
The most valuable plants will be the mature trees. These form the basic structure of the garden and will take decades to replace. Mulch should be scraped away from the base of the most vital trees and shrubs. Remember that grafted trees need special protection, because if the tops are severely damaged you may end up with just the rootstock. On the other hand some plants such as acacias regenerate rapidly after a fire and may be sacrificed more readily.
You should also consider what kind of watering system you have and whether it will survive extreme heat. Plastic fittings may melt as the fire approaches, so that the watering system becomes useless. Metal risers and brass fittings may allow you to keep watering your property and reduce damage in the event of a fire.
Other strategies to employ include good old-fashioned garden maintenance - keeping the garden neat and tidy and removing unwanted garden litter that can fuel a fire. Where possible the cutting of a fire-break 3-4 metres wide around the property will also help to slow down an advancing fire.
What immediate post-fire procedures are best to save plants damaged by fire and to encourage regeneration?
The first task is to find out what plants have been irreparably damaged and which are savable. The key to this is knowing your species and their ecology. Tree ferns, for instance, look terrible after a fire because all their fronds are burnt off, but the crowns will recover quite quickly and send out new foliage. Smooth-barked eucalypts are often badly damaged and may not be salvageable, but rough-barked eucalypts often survive. They look awful initially but they have epicormic buds and lignotubers and have evolved to survive bushfires. After the fires at Mount Macedon we came across some giant Redwoods (Sequoia) about to be felled in the clean up. Luckily we knew that these trees are fire resistant and we were able to save them. They recovered and stand out like beacons in the landscape now. We were also able to intervene to save some large rhododendrons which were badly scorched but not burnt. Within twelve weeks of the fire they came into leaf and recovered. It would have taken many years to grow new plants to this size.
Having said all this, it is also important that once trees are identified as being unable to be salvaged, they should be removed immediately while the equipment and help is at hand. Clinging on to hope that dead trees will recover may mean that in 6 months’ time you may be faced with a huge bill to remove the trees at your own expense. If they are very large trees, the bill could be in the tens of thousands of dollars.
Once the salvageable plants have been identified, then the dead bits need to be removed and any questionable bits left until the following spring, when it will become clear whether the branches are still living or not.
It is very important to seek professional help to identify what can be saved in a garden. Burnley graduates are trained to do this. When you consider that the gardens are what often draws people to live in beautiful but fire prone areas, they continue to have great value, even if the house has been destroyed. Quality advice is worth seeking, because it means that valuable plants may be able to be saved.
Profile: Dr Greg Moore is Principal of Burnley College, University of Melbourne. Apart from a general interest in horticultural plant science and ecology, Greg has a specific interest in all aspects of arboriculture. He was the inaugural president of the International Society of Arboriculture, Australian Chapter and continues to serve on the Chapter’s executive committee. He has been a member of the National Trust of Victoria’s Register of Significant Trees since 1988 and has chaired the committee since 1996.
Fire Retardant Plants:Acacia howittiiAcacia iteaphyllaAcacia pravissimaAngophora costataHymenosporum flavumMagnolia grandifloraPhotonia glabraBanksia marginataGrevillea victoriae 'Murray Queen'Myoporum parvifoliumHakea salicifoliaPelargonium peltatum Verbena peruviana
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