Plant species selection and impact on tree resprouts by semi-free ranging pigs in a temperate deciduous forest

Silvopastoral systems with grazing pigs are mainly concentrated in Mediterranean regions, for instance in Iberian dehesas and montados . Conversely, in European deciduous forests, outdoor pig farming has almost disappeared, despite it could provide several environmental and socioeconomic benefits. For instance, pig grazing could be used for habitat restoration and conservation, while providing high quality meat products and promoting local breeds. In this study, we investigated (i) the plant species selection and (ii) the impact on tree resprouts (after a silvicultural cut) by semi-free ranging pigs in a degraded oak temperate forest in Northwestern Italy. We monitored pigs foraging behavior by direct observations and discriminated the plant species into three groups: preferred, indifferently consumed and avoided plants. The impact on the resprouts of six tree species was assessed by modeling the percentage of damaged shoots and their height through time using Generalized Linear and Additive Mixed Models. Swine expressed a selective foraging behavior, which was likely influenced by the forage quality and toxicity of plant species. The leaves and resprouts of Corylus avellana and Castanea sativa were highly consumed, whereas Acer and Quercus species and Fraxinus ornus were avoided. Mature leaves of Robinia pseudoacacia were highly preferred while its young resprouts were only slightly impacted, suggesting that pig grazing may not be effective to control this alien invasive species. Contrarily, pigs consumed Rubus sp. abundantly, suggesting they could be used to clear the understory in degraded forests.