Soil Disturbance by Invertebrates in a Semi-arid Eucalypt Woodland: Effects of Grazing Exclusion, Faunal Reintroductions, Landscape and Patch Characteristics

Abstract

Soil disturbing invertebrates are common elements of arid and semi-arid landscapes. Disturbances such as burrows, nest entrances, emergence holes and mounds of ejecta soil have large, but often poorly understood, effects on ecosystem properties and processes as broad as pedogenesis, soil movement and water infiltration. We examined disturbances created by a range of invertebrates in a semi-arid eucalypt woodland in eastern Australia in relation to three levels of disturbance varying from areas currently grazed by domestic herbivores to those where domestic herbivores have been removed, with and without the reintroduction of locally-extinct omnivorous native mammals. Overall, the tunnels and ejecta soil from ant nests comprised 80% of all invertebrate disturbances across all sites and treatments. There were significantly more invertebrate disturbances at sites where domestic herbivores had been excluded, more disturbances on dunes and in the swales than on plains, and more under shrubs than under trees. The cover of disturbances by invertebrates tended to increase with increasing cover of disturbance by native vertebrates, but only under exclosure where no locally-extinct native mammals had been reintroduced. Our results indicate that invertebrate-created disturbances are a common feature of semi-arid woodland soils, and that management activities, such as grazing and the reintroduction of locally-extinct vertebrates, will affect their density, potentially influencing a range of ecosystem processes.