Limited impacts of simulated soil disturbance by rewilded vertebrates on above- and below-ground biodiversity

Rewilding with locally extinct terrestrial vertebrates has been a popular conservation initiative over the past few decades. Among the animals used for rewilding are the small- to medium-sized vertebrates that forage in the soil and that have been lost from many ecosystems due to habitat destruction or predation by exotic species. Soil foraging by these animals creates surface depressions that generate resource-rich patches and novel niches. Thus, their reintroduction can have beneficial effects on both the biodiversity and functioning of the ecosystems they inhabit. An important knowledge gap, however, is the extent to which soil foraging by these animals might compromise ecosystem functioning if they reach extremely high densities in the absence of natural predators, such as occurs with the extensive soil disturbance by feral pigs. We performed a field experiment to test the effects of increasing soil disturbance and herbivory, and their interaction, on ecosystem functioning and the diversity of multiple taxa in a dry subhumid grassy woodland. Of the 106 possible attribute x treatment combinations assessed, we found only eight effects (three declines and five herbivory effects that varied depending on disturbance or community) in response to increasing levels of soil surface disturbance or herbivory. System-based modelling revealed that the greatest overall effects on our organisms were due to plants (plant richness, plant biomass, litter depth), with generally positive effects of plants on surface-active arthropods, negative effects on the whole metazoan community, and a negative litter effect, but only on microbes. Levels of disturbance (0–60%) and herbivory (0–100%) imposed in our treatments were greater than those observed under natural conditions. Our results suggest therefore that there are unlikely to be substantial negative impacts of reintroducing soil-foraging animals on biodiversity or ecosystem functioning in our target dry woodlands, even under potentially large levels of disturbance and herbivory.