FIRE IN SEMIARID, MALLEE SHRUBLANDS - SIZE OF FLAMES FROM DISCRETE FUEL ARRAYS AND THEIR ROLE IN THE SPREAD OF FIRE

Aspects of flammability of the major fuel arrays in a mallee shrubland community, and the basis for fire-spread in these discrete fuels, are examined and discussed. Relationships between plant size and weight o f litter (shrubs and mallee eucalypts) or grass hummocks (Triodia irri tans) were studied. Hummock mass was a function of hummock diameter an d height. On ignition, maximum flame length was related to hummock hei ght and diameter. For mallee eucalypts the mass of litter beneath indi vidual plants was related to the diameter of the litter bed. Flame len gth was also related to litter bed diameter. In other species of shrub s, fires were not sustained independently. We hypothesize that T. irri tans will play a major role in fire spread in communities because flam es from hummocks will have the greatest ability to bridge gaps between fuel arrays (flames longer than in eucalypts). Size of hummocks will have an important bearing on propagation of fire across fuel-gaps. By contrast, the main role of eucalypts in fire-spread may be as a source of burning brands which initiate spot fires. There is scope to unders tand fire-spread in these communities on the basis of flame lengths (i n conjunction with plant size) in relation to wind.