Fire maintains an Acacia aneura shrubland— Triodia grassland mosaic in central Australia

Abstract

Patches of fire-sensitive, closed-canopy Acacia aneura shrubland occur within a matrix of highly flammable Triodia grasslands in central Australia (<400 mm mean annual precipitation). We used digitised repeat aerial photography to chart the dynamics of these mosaics over 52 years (1950–2002). During this period, traditional Aboriginal fire management had largely ceased. The spatial extent of A. aneura shrubland patches varied over the 52-year study period but the aggregated change was small (an increase of 3.1% from 1950 to 2002, with the largest excursion a 13.1% decrease between 1950 and 1983). This change was restricted to within 50 m of boundaries between the shrublands and grasslands. Statistical modelling for the period for which landscape fire activity was available (1980–2002) showed that the dynamism of the boundaries was associated with burning. Fire effects on boundaries were mediated by the size of A. aneura patches, with small patches most likely to contract, explaining the dynamic spatial arrangement of small patches in the landscape. We conclude that a series of reinforcing fire, soil and vegetation feedbacks maintain the mosaic of shrubland patches. However these feedbacks might eventually be overwhelmed by large and sustained changes to fire regimes, leading to the landscape-wide dominance of Triodia grasslands.