Prescribed Fire in Mallee Rangelands and the Potential Role of Aerial Ignition.

Abstract

Details are presented of prescribed fires imposed over several mallee areas ranging from 120 to 10,660 hectares. Particular attention is directed towards seven of these burns designed to assess the potential usefulness of aerial ignition for prescribed burning of large mallee paddocks. This ignition procedure is highly discriminating, enabling areas carrying sufficient fuel to be safely, and rapidly, burnt by numerous small fires resulting from aerial incendiaries released on a predetermined grid pattern. Fuel in the largest paddock burnt was ignited in two hours after releasing 13,000 spherical (3 cm diameter) incendiaries. In addition to overcoming problems of discontinuous fuel restricting spread of fire when using ground ignition procedures, this aerial technique also enables fuel to be ignited over large areas during narrow 'time windows' when optimal temperature and humidity conditions apply. On one mallee property, a prescribed fire programme based on autumn burning by aerial ignition in 1980, 1982 and 1985 resulted in substantial improvements in sheep productivity and husbandry. Lamb weaning increased by 30% and overall stocking rate was doubled, resulting in a gross margin increase from $2.31 to $5.88 per hectare. Such economic benefits following a reduction in mallee density will only accrue in open mallee communities where speargrass is the major herb and a multiple fire regime can be imposed. In mallee dunefields, where porcupine grass is the dominant understorey species, infrequent (every 15-20 years) single fires are the norm due to the time required for this perennial grass to regenerate. More frequent burning is generally precluded because the light textured soils of the dunes cannot produce sufficient ephemeral herbage, especially speargrass, to carry a fire.