Soil disturbance by animals at varying spatial scales in a semi-arid Australian woodland

Abstract

We studied soil disturbance by rabbits, echidnas, goannas, ants and termites at three different spatial scales across four vegetation communities (dense woodland, open woodland, shrubland, grassland) in semi-arid rangeland in western NSW. For analyses, bare and litter-covered surfaces (micro-scale) were nested within canopy and open patches (intermediate scale), which were nested within vegetation communities (landscape scale). Landscape-scale disturbances (rabbit warrens) were six and three times more abundant in open woodlands and shrublands, respectively, than in dense woodlands. Although individual warrens had a similar mass of excavated soil across all vegetation communities, in total, more soil was excavated in the grasslands than in the dense woodlands or shrublands. There were four times as many intermediate-sized disturbances (foraging pits and resting sites) under canopies than out in the open, and this was consistent across all vegetation communities. Echidna foraging pits and kangaroo resting sites dominated the canopy patches. Intermediate-sized disturbances scaled up to the landscape scale were marginally more abundant in the dense and open woodlands than in grasslands and shrublands. However, total mass of soil moved by all species did not differ among vegetation communities. The density of small-scale disturbances (ant nests, termite foraging galleries) did not differ at the landscape-, intermediate- or micro-scales. Our study documents the extent of animal activity in the semi-arid woodlands, and reinforces the notion that, as soil disturbance is scale-dependent, differences among species, habitats and communities will depend on the scale at which disturbances are examined.