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 of litter (shrubs and mallee eucalypts) or grass hummocks (Triodia irritans) were studied. Hummock mass was a function of hummock diameter and height. On ignition, maximum flame length was related to hummock height and diameter. For mallee eucalypts the mass of litter beneath individual plants was related to the diameter of the litter bed. Flame length was also related to litter bed diameter. In other species of shrubs, fires were not sustained independently. We hypothesize that T. irritans will play a major role in fire spread in communities because flames 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 understand fire-spread in these communities on the basis of flame lengths (in conjunction with plant size) in relation to wind.