SOIL TEMPERATURES DURING EXPERIMENTAL BUSHFIRES IN RELATION TO FIRE INTENSITY - CONSEQUENCES FOR LEGUME GERMINATION AND FIRE MANAGEMENT IN SOUTH-EASTERN AUSTRALIA

1. Experimental fires were used to determine the influence of fire int ensity and subcomponents of intensity (fuel consumption and rate of sp read) on soil temperatures (at 0-10 cm depth) in shrub/woodland commun ities in the Sydney region of south-eastern Australia. 2. Temperatures >60 degrees C were achieved at depths of 0-3 cm. Such temperatures ar e sufficient to break seed dormancy in local legume species. 3. Maximu m change in soil temperature was not significantly affected by Byram f ire intensity. However, at 0-4 cm depth, maximum temperature change wa s significantly affected by the amount of fine fuel (particles <6 mm t hick) consumed on the ground (mainly litter, twigs and herbs). Fine fu el above the ground (shrub canopies), coarse fuel (6-25 mm thick) on t he ground and rate of spread did not significantly affect maximum chan ge in temperature in the top 4 cm of the soil. 4. The results indicate that 0.6-2.0 kg m(-2) of fine fuel burnt on the ground is likely to s timulate germination of buried seeds of local legumes (seed dormancy b roken at greater than or equal to 60 degrees C). 5. At the upper end o f this fuel consumption range, germination is predicted to occur down to 3-cm depth, while consumption at the lower end of the range will st imulate germination to a depth of 1 cm. Post-fire germination in Acaci a suaveolens was in accordance with these predictions. 6. These result s are discussed in relation to the use of prescribed fire for hazard r eduction. Prescribed fires with maximum potential for germination (max imum fuel consumption in the target range) will be close to, or in exc ess of, the limit for control unless the rate of spread is very low (< 0.10 ms(-1)), thereby imposing constraints on the use of prescribed fi re to achieve both protection and conservation objectives.