Bioturbation on a south-east Australian hillslope: estimating contributions to soil flux

The contribution of bioturbation to downslope soil transport is significant in many situations, particularly in the context of soil formation, erosion and creep. This study explored the direct flux of soil caused by Aphaenogaster ant mounding, vertebrate scraping and tree-throw on a wildfire-affected hillslope in south-east Australia. This included the development of methods previously applied to Californian gopher bioturbation, and an evaluation of methods for estimating the volume of soil displaced by tree-throw events. All three bioturbation types resulted in a net downslope flux, but any influence of hillslope angle on flux rates appeared to be overshadowed by environmental controls over the spatial extent of bioturbation. As a result, the highest flux rates occurred on the footslope and lower slope. The overall contribution of vertebrate scraping (57.0 +/- 89.4 g m(-1) yr(-1)) exceeded that of ant mounding (36.4 +/- 66.0 g m(-1) yr(-1)), although mean rates were subject to considerable uncertainty. Tree-throw events, which individually cause major disturbance, were limited in their importance by their scarcity relative to faunalturbation. However, tree-throw might be the dominant mechanism of biotic soil flux on the mid-slope provided that it occurs at a frequency of at least 2-3 events ha(-1) yr(-1). Although direct biotic soil flux appears to be geomorphologically significant on this hillslope, such transport processes are probably subordinate to other impacts of bioturbation at this site such as the enhancement of infiltration following wildfire.