Increased fire frequency

Fuel Reduction Burning (FRB) is currently a prescribed management technique for fire prone areas of Australia. Whilst it may be effective in the short-term, can it really be a sustainable practice and if it is used on a continual basis will it really reduce the frequency and intensity of ‘bush’ fires?

Australian flora and fauna have evolved to use fire as a tool for renewal. Many Australian plants need fire in order for their seed capsules to open and to enable their seeds to be dispersed. Many areas of Australia are dry throughout most of the year, so there is not enough moisture available to enable the decay of debris, fallen branches and leaves, to occur. As a result the amount of debris continues to accumulate on top of the soil and it takes a long time for it to break down without fire.

Areas where fire occurs frequently evolve to become dry sclerophyll forests. The predominant plant family in these forests is Myrtaceae, being mainly of the genus Eucalyptus, Melaleuca, and Leptospermum. These plants contain large amounts of oil, oil that is highly flammable. These are the kinds of areas where bush fires occur extremely frequently.

If these forests are not burnt for a long time, they begin to change. In areas that have not been burnt for 300 to 500 years, the forest type becomes an open rainforest. For an area to become a closed rainforest in Australia then the frequency of fire is around every 1000 years. Hence frequent burning in order to reduce fuel, FRB, will have an adverse effect by promoting the growth of dry sclerophyll forest, which is the kind of forest that requires fire in order to rejuvenate. That is FRB will lead to the evolution of even more dry-sclerophyll forests, which is not the kind of forest desired if one wishes to reduce the incidence or intensity of fire.

The other concern about frequent fuel reduction burning is one from a horticultural or soil science perspective. This kind of burning is designed to reduce the amount of debris, especially leaf matter, on the forest floor. Hence, this reduces the amount of humus in the soil. Humus is the organic matter that allows a soil to hold moisture, so a soil with greater humus content can hold more moisture. Soils that hold more moisture are cooler in summer and are not degraded easily. If soils are moister then there is more water available for evaporation and plant growth, especially for plants other than those from dry sclerophyll forests. More evaporation also means that there is more moisture going into the air and hence the temperature will be lower. It also means moisture is available to go into making clouds, which means that there is more likelihood of a higher rainfall.

Given that frequent burning promotes forest types that require fire for survival to evolve and that frequent burning reduces the amount of organic matter available to give soils better water-holding capacity, then this kind of burning in the long run will increase the frequency and intensity of bush fires. We need to rethink our use of FRB (fuel reduction burning) as a long term fire-management tool. In order to promote forest types that are not so dependent upon fire, as well as increasing the moisture content of Australian soils the frequency of burning has to be greatly reduced. Fuel reduction burning may prove not to be a solution for long term fire management.


About tonykennedy

I live in Canberra and am interested in keeping people informed about events important in Australia.
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