Environmental associations and effects of disturbances by common wombats in alpine Tasmania

The common wombat (Vombatus ursinus) is the largest extant fossorial mammal in Tasmania. Fossorial mammals have substantial edaphic and geomorphic effects, which, in turn can affect vegetation. We asked whether wombat disturbances were associated with particular environments in an alpine environment in Tasmania, and whether, and to what degree, they altered topography, soil or vegetation. Soil analyses, vegetation surveys and topographic transects were used to test for the effects of wombat activity. We contrasted toilets and controls. We compared adjacent burrows, mounds and paths. We also mapped burrows and animal trails. Wombat burrowing created distinct topography and was linked to feeding areas by path systems. There was no difference in bulk density, pH or phosphorus among burrow mounds, paths and undisturbed areas. Burrow mounds, usually used as toilets, were higher in nitrogen (mg L⁻¹) (9. 8 ± 6.3) than either paths (2.3 ± 2.0) or controls (1.08 mg L⁻¹ ± 1.5). Herbs were favoured by wombat disturbance, having a mean percentage cover of 27.8 ± 4.1 on burrow mounds compared to 14 ± 2.69 on controls, and a mean percentage cover of 51.6 ± 7.8 in toilets compared to 25.6 ± 4.8 in control plots. In contrast, shrubs have greater percentage cover in controls than on mounds (47.2 ± 12.0 cf. 12.7 ± 5.0) and toilets (37.3 ± 10 cf. 17.8 ± 6.5). Overall, wombat activity and modification of the alpine environment were concentrated in grassy vegetation above the winter water table, although paths, burrows and toilets extended into less grassy alpine communities. Our results imply that common wombats have a major role in engineering topography and soils with subsequent effects on vegetation, directly affecting at least 1.2% of the study area. Their reduction, or loss, is likely to lead to substantial changes in patterns of geodiversity and biodiversity.