Although there are many advantages to prescribed burning, it has in its package an amount of disadvantages. The affect on animals can be quite severe. Ground logs in a forest or woodland develop hollows which can be suitable for small animals such as the chuditch or numbat. The hollows in trees, such as the jarrah and marri, provide excellent refuge sites for brushtail possums and phascogales. Hot fires can wipe out much of these and leave very little shelter for animals. A prescribed burning always produces smoke, however due to the intensity levels the amount produced is usually lower than summer wildfires. The difficulty caused is that the safest condition under which to light prescribed fires in WA is with south- easterly and south-westerly winds. These wind directions bring smoke straight from the forest into the city. Therefore any "pollution problem" associated with bushfire smoke in Perth is more related to prescribed burning than to wildfires. There are relatively few days each year when conditions suit both the prescribed burning objectives and air quality objectives; this makes it very difficult for a successful burn to be carried out objectively.
Bushfire smoke is a contributor to air pollution.
Photo - Lachlan McCaw, Autumn 1993 Landscope
While in some areas fire can be advantageous (such as Kings Park, WA), it causes many damages to other environments. This can be observed by looking at the desert environment of the Great Sandy Desert. Fire is a natural component of the desert ecosystem, being started naturally by lightening strikes and for many years been a traditional practise of the Aborigines. Desert plants have evolved a wide range of adaptations to survive and regenerate, however after a fire the land itself is very prone. Much of the sand planes and dune fields of the desert is covered in spinifex, which is very flammable. This makes the desert a very fire-prone environment. The spinifex is important for reducing wind erosion by trapping wind-borne sand and seed. However, after a fire the land is temporarily denuded of vegetation, which leaves the soil vulnerable to erosion. After a fire the thousands of tonnes of ash and thousands of seeds which have accumulated beneath spinifex hummocks are redistributed by wind, whereas there is virtually no soil or seed movement on unburnt areas.
In cases such as these the decision to use a planned burning program is a lot more difficult. While the spinifex is an essential component to keeping soil erosion to a minimum, it is also very fire-prone. A wildfire out of control could cause severe damage, whereas a planned burn kept until strict control may not have the same degree of impact. Conversely, a fire of any sort will have negative results on the land erosion.
Spinifex is essential in keeping soil erosion to a minimum.
Photo - Marie Lochman, Winter 1994 Landscope