Topography not tenure controls extent of wildfire within Mountain Ash forests

Abstract

Two high intensity wildfire events, 70 years apart, burnt large areas of Mountain Ash forests in the Central Highlands, Victoria, Australia. Both resulted in Royal Commissions (the strongest form of judicial inquiry in Australia) as to their cause(s) owing to large losses of life and property. Here we tested the hypothesis that site 'wetness' – determined using a Topographic Wetness Index – is a major determinant of the extent of fire (% of sample points that burnt) within high intensity wildfire events and across tenures. We show that wetness dominated the extent of fire in these forests in both the 1939 and 2009 wildfire events. Mountain Ash forests are now strongly skewed in their distribution, with wetter and older forests favoured by protected tenures (e.g. National Parks) designed to meet needs for water and conservation. In 2009, the extent of fire at the stand scale in water catchments and conservation tenures was twice that in 1939. In land tenures with multiple uses (e.g. State Forests), the extent of fire was one-third less in 2009 than it was in 1939. Topographic controls on water availability, and major droughts, will likely continue to dominate the extent and likelihood of fire in these forests.