Distinctiveness of wildfire effects on soil erosion in south-east Australian eucalypt forests assessed in a global context

The premise of this paper is that continued improvement in the understanding of wildfire impacts on soil erosion and better prediction of resulting hazards can be best achieved by adopting a concept of global regional variants and endemic factors that distinguish some regions in terms of post-fire erosion characteristics. The need for such an approach is exemplified here based on the fire-prone eucalypt forests in south-east Australia. Wildfire effects on vegetation, fauna, soil erodibility and erosion in this environment are evaluated and placed in the context of the global state-of-the-art for forest environments. In addition to expected variation resulting from, for example, geology, topography and climate of the area, it is argued that a distinctive post-fire behaviour is caused in these eucalypt forests by the interaction between specific characteristics of the vegetation, litter, soil properties, faunal activity and micro-scale surface features. Soil erosion limited only by post-fire rainfall intensity and quantity, or until bedrock is exposed, might be expected after wildfire on steep slopes in these forests given the non-cohesive character of the often sandy soils and their universally water repellent character. That this scenario is not realised, except possibly under extreme rainfall conditions, which rarely occur during the vulnerable post-fire period, can be attributed to a unique suite of features that disrupt or provide sinks for overland flow, bind the loose in situ soil and trap mobilised sediment. These include mats of fine roots, litter dam–microterrace complexes and faunal activity by small mammals and ants. In combination, these characteristics reduce post-fire hillslope-channel sediment transfer, at least under light to moderate intensity rainfall typical of post-fire periods following recent wildfires. Evidence is discussed suggesting that the long-term geomorphological role of wildfires in south-east Australia may be of relatively minor importance and confined largely to enhanced weathering of exposed outcrops and redistribution of soil across existing erosional and depositional landforms. The soil fertility and downstream water quality implications of widespread transfer of topsoil to watercourses resulting from frequent, often severe wildfires are nevertheless significant.