Much of Australia differs from anywhere else in the world in that it combines a hot, dry Mediterranean climate with tall forests, producing large quantities of combustibles. These conditions make Australia particularly prone to wildfires, which threaten human life, property, and the environment. The study of bushfires must take into account weather, sources of ignition and fuel. Fuel is the only factor which can be managed. Planned burns are WA’s first method of defeating wildfire. The second method is a fast response by well- trained fire fighters. The first method - reducing the fire’s energy source - makes the second effective.
While some people believe that regular planned burns encourage additional forest fuels,
decades of research show that fuels are always lighter after a fire, although with time will
accumulate. The rate of accumulation varies considerably between environments - in a dense
forest it builds rapidly whereas in drier forests it may take many years.
In Australia fire is a natural abiotic factor and many species depend upon the occurrence of
fire to survive. Although some species are favoured by long periods without fire, they can
still recover from it. Other species flourish due to the presence of fire, while yet others are
unaffected by low intensity fire but are killed by high intensity fire whereas some will not
regenerate except after high intensity fire.
Often the effects of a wildfire are overall damaging to the environment, while the effects of a planned burn are in the long term beneficial. Compared with a wildfire, the visual impact of a planned burn is small. A severe wildfire can leave tree trunks blackened and leaves scorched. A low intensity burn blackens only the understorey, and many areas are left unburnt. The visual effects of a low intensity planned burn, unlike those of a severe wildfire, disappear within a year due to regeneration after a fire (see Kings Park study below).
Kings Park, WA, is an excellent example of the regeneration of the environment after a fire. In 1989 an extremely hot fire swept through a large area of Kings Park, burning the understorey shrubs, foliage and small branches of trees. The visual impacts were large, but as regeneration progressed what was to occur was an extraordinary wildflower season.
The zamia palm (left) and Parakeelya (right) regenerate well after a fire.
The native flora is well adapted to occasional bushfire, and many plants need fire to regenerate. Many of the larger trees in Kings Park have thick, protective bark which resists all but the most severe fires. After a fire scorches the crown, epicormic buds (special leaf- buds just under the bark of the trunk and branches) shoot out from under the bark as clumps of foliage. This is so the tree can continue to carry out essential functions. Grasstrees are very resilient to fire as the trunk is made of dense matting of burnt leaf-bases that protect leaf- buds. CSIRO research scientist Malcolm Gill has shown that the flowering of grasstrees is stimulated by fire. Many species of native plants have massive rootstocks or tubers beneath the soil which, after a fire, burst into new shoots. The fruits of many trees are hard, woody and highly fire-resistant whereas with others only the heat from a fire will split the fruits casing and release the seeds inside them.
These are all adaptations which assist in protection during and regeneration after a fire. How quickly an area regenerates depends upon the species present. By looking at the Kings Park regeneration, the varying degrees of regeneration can be observed and also seen is the amount of impact of the fire.
Approximately one month after the fire, zamia palm leaves and grasstrees began to unfurl, and new growth began to shoot from trunks of banksias, eucalypts and sheoaks. The lignotubers of resprouting shrubs such as blueboy and pixie mops helped new growth as they were protected by the soil. Many orchids, milkmaids and rhizomes (such as flax lily) began growing, with the help of their stored food reserves in tubers. Once the winter rains began, open areas began to fill with parrotbush, Halcea prostrate and kangaroo paw seedlings. The open conditions and extra nutrients from the ashbeds allowed temporary plants to take advantage, and plants such as the parakeelya, slender lobelia and button creeper began to occupy the area.
Many species, such as the kangaroo paw and swan river myrtle, flowered in profusion because of the removal of surrounding competition. Others, such as the red ink sundew, several species of orchid, and grasstrees, were stimulated into flowering due to the production of ethylene gas during the fire. The absence of dense scrub also makes the diminutive species such as flying duck and hare orchids easier to spot. Finally, at the beginning of spring, hare orchids, white bunny, and banded greenhood contained ripe seed capsules, while cowslip orchids, red beaks, pansey donkeys, pink fairies, king spiders and blue ladies were blooming with flower.
The fire in Kings Park did cause problems. Many perennial weed species (such as the veld green and weeping lovegrass) were able to grow in areas they previously could not occupy. Dead leaves can increase the chance of another fire, and the cost of controlling the wildfire was enormous. This is why a planned burn caters for the positive effects of a fire - such as aiding growth and regeneration - but reduces the severity of damaging impacts that an uncontrolled fire can cause.