Wild boar (Sus scrofa L.) populations steadily increased in Switzerland during the past two decades. Reports of wild boar grubbing damages in forests and agricultural fields therefore became much more frequent in the recent past, since these omnivore animals obtain large parts 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 on how wild boar grubbing affects ecosystem processes, in particular in forested ecosystems. However, grubbing incorporates the forest floor and often also parts of the mineral soil into deeper soil horizons and therefore affects forest soil physical, hydrological, chemical and biological properties. Although several studies showed how grubbing altered some of these properties, we are not aware of any comprehensive study that would have investigated grubbing effects on the ecosystem scale. In order to study possible impacts of wild boars on forested ecosystems, we will conduct several (small/intermediate scale) case studies comparing vegetation and soil parameters in grubbed and non-grubbed areas. We will put special emphasis on changes in C and nutrient contents and stocks as well as CO₂ emissions, which could be of rising interest with regard to the global warming discussions. We will also investigate the effect of grubbing on soil physical (soil density, texture) and hydrological properties, since they are important for forest soil fertility (and therefore tree growth) as well as for forest soil erosion. Additionally, we will study the effect of grubbing on the abundance and diversity of micro- and macro-invertebrate communities at the ecosystem level, which so far has mostly been neglected when studying the impact of wild boars on soil properties.

Further, we will survey wild boar grubbing frequencies and intensities at different locations in several Swiss cantons in order to establish a relationship between hunting bag and grubbing events. These findings, combined with the case studies results, will be extrapolated to assess large scale effects of wild boar grubbing on forest ecosystem processes in Switzerland. The outcome of this study should allow us to predict what will happen if wild boar populations continue to increase and spread in Switzerland.

Collaborators: USDA Forest Service, Moscow ID, USDA Forest Service Redding CA, Michigan Technological University Houghton MI, WSL (Rhizosphere processes)