Wild boar rooting impacts soil function differently in different plant community types

Abstract

While numerous studies focus on the ecosystem effects of invasive mammals, few explore the causal mechanisms of such effects. Wild boar is one of the most widely introduced invasive mammal species in the world. By overturning extensive areas of vegetation and soil to feed on belowground resources, wild boar alter the soil food web and thus many microbial-mediated soil processes. Here, we take advantage of a long-term, 8-year, wild boar exclosure experiment across three plant community types in Patagonia, Argentina to explore how wild boar impact soil communities and their potential function. Previous work in this experimental system found that wild boar significantly impacted litter decomposition in the field, but it remained unclear if this effect was mediated through changes in abiotic or biotic soil properties. To explore both the abiotic and biotic drivers of decomposition, we measured soil moisture, soil temperature, soil bulk density, and soil respiration as well as soil micro-arthropod richness and abundance, earthworm abundance, and microbial biomass inside and outside of 10 exclosures in each of three plant community types. To assess potential microbial activity, we measured potential decomposition rates, substrate-induced respiration, and soil microbial enzyme activity. Rooting decreased soil moisture by 18% across plant communities, and soil respiration by 30% in Nothofagus and Austrocedrus forests. Additionally, rooting decreased soil micro-arthropod richness and abundance by ~ 80% in shrublands. However, rooting had no effect on soil potential microbial activity. Together, our results suggest that changes in both abiotic and biotic soil factors likely mediate observed wild boar impact on decomposition rates. Overall, we show that wild boar rooting alters soil functioning, but the pathway of impact varies by plant community, suggesting that wild boar impacts on native ecosystems can be difficult to predict.