Soil disturbance by native animals maintains key ecosystem processes in an arid Australian woodland

Background/Question/Methods

Animal reintroductions have become increasingly popular in order to increase dwindling populations of threatened species. An unexpected benefit of animal reintroductions is their potential to contribute positively to the maintenance and restoration of degraded ecosystems. Recent initiatives therefore have attempted to couple research on animal reintroduction with studies of their effects on soil and ecological processes. We compared the effects of the reintroduction of two locally-extinct Australian vertebrates (Burrowing bettong, Greater bilby) with that of two extant native vertebrates (Short-beaked echidna, Gould’s sand goanna) and an exotic soil-disturbing vertebrate (European rabbit) on soil and plant processes in markedly different environments in an arid Australian woodland. We describe the effects on soil and water processes, how their disturbances affect patches, and how this influences soil nutrient concentrations and ultimately, landscape function. We do this by considering four propositions linking the foraging pits of animals to the maintenance and recovery of critical ecosystem processes: We propose that animal disturbances 1) increase soil formation rates, 2) concentrate litter and water, 3) contribute to soil nutrient stores, and 4) maintain a diversity of niches for plants and microbes.

Results/Conclusions

Echidnas and goannas moved substantial quantities of soil, up to 3 t ha^-1 yr^-1. Bilbies moved considerably more (up to 6 t ha^-1 yr^-1). Soil disturbance was highly patchy, and concentrated under shrub and tree canopies and coarse woody debris. Foraging pits tended to accumulate more litter, and pit soils had greater soil moisture and higher levels of total and labile carbon, and total nitrogen than adjacent surfaces. Compared with the surface, decomposition of the soluble components of pit-resident litter was greater in the foraging pits where bilbies had been reintroduced. On degraded pastoral sites, however, decomposition was lower in pits of feral rabbits than at the surface. Pits of native animals supported a richer plant community than those of rabbits, and the richness of the pit-resident soil microbial community was greater than non-pit soils. Overall our results indicate that animal foraging is an important geomorphic mechanism capable of mobilizing substantial volumes of soil in arid and semi-arid environments and with potential effects on soil function. The results give us valuable insights into how arid systems functioned prior to species losses, and provide renewed impetus for the reintroduction of soil-disturbing animals to restore degraded systems.