Wild boar (Sus scrofa L.) populations have steadily increased in Switzerland during the past two decades. As a consequence, reports of wild boar grubbing damage in forests and agricultural fields have become much more frequent as these omnivore animals obtain a large portion of their diet by rooting or grubbing in the soil. While the economical damage of these events has been discussed intensively, considerably less attention has been given to how wild boar grubbing affects forest ecosystem processes. Wild boar grubbing involves disrupting the understory vegetation and impacts the top 15 cm to 70 cm of the organic and mineral soil. This has a strong effect on forest soil physical, hydrological, chemical and biological properties. Although several studies have shown how grubbing alters some of these properties, we are not aware of any comprehensive study that has investigated the impacts of grubbing on soil carbon (C) and nitrogen (N) pools at the ecosystem level. Thus, the objective of our study was to assess how grubbing affects soil C and nitrogen (N) pools in different forest ecosystems of Switzerland. We collected forest floor (all surface organic layers combined) and mineral soil samples (0 to 30 cm) on paired plots (freshly grubbed, non-grubbed) in mixed hardwood stands growing on both alkaline (6 stands) and acidic parent material (6 stands) at low elevations (400 to 700 m) as well as in mixed conifer stands on acidic parent material (4 stands) at high-elevation (1200 to 2000 m). Samples were analyzed for C and N (LECO induction furnace; LECO Corp., St. Joseph, MI) and soil C and N pools calculated.

Results/Conclusions

Preliminary data indicate that grubbing by boars significantly reduces the thickness of the forest floor and therefore reduces forest floor C and N pools. In contrast, our preliminary analyses showed that mineral soil C and N pools of the top 0 to 15 cm were higher on grubbed compared to the non-grubbed plots, while the pool of the 15 to 30 cm mineral soil layer remained unchanged. Thus, our results significantly improve our knowledge of how a natural disturbance (wild boars) might alter soil C and N pools in forested ecosystems and will be of great importance for predicting how ecosystem characteristics and forest processes might be altered when the abundance or spatial distribution of wild boars change in Switzerland.