Interest in soil carbon (C) storage and release has increased greatly in recent years. In addition to factors such as climate/land-use change, foraging activity by animals can have a considerable impact on soil C dynamics. To date, most research has considered livestock, while the impact of non-domestic large herbivores and omnivores on soil C processes has rarely been considered. Our goal was to determine how the European wild boar (Sus scrofa L.), a large omnivorous animal that consumes soil-inhabiting animals and belowground plant parts by grubbing in the soil, affects soil C dynamics. We measured soil respiration (CO₂), temperature, moisture, fine root and microbial biomass on paired grubbed and non-grubbed plots in six hardwood forest stands for a two-year period. We also measured disturbance frequency and used this information together with hunting statistics and forest cover data to model the total amount of CO₂ released from Swiss forest soils due to grubbing.
Results/Conclusions

Soil respiration was significantly higher on grubbed compared to non-grubbed plots during the two years. On average 23.1% more CO₂ was released from grubbed compared to non-grubbed plots, which we associated with potential alterations in diffusion rates of CO₂ as well as higher fine root and microbial biomass detected on the grubbed plots. Thus, wild boars considerably increased the small-scale heterogeneity of soil properties. Roughly 1% of Switzerland's surface area is similar to our sites (boar density/forest cover). Given a range in disturbance frequency of 27-54% at our sites, the model predicts that an additional 58507 to 115829 t CO₂ year-1 would be released due to boar activity. These numbers are small compared to the total soil respiration estimated for hardwood/mixed hardwood forests of Switzerland and suggest that boars have little effect on large-scale CO₂ emissions unless their numbers will increase and their range expand dramatically.