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.
