Wild boar impact on forest regeneration in the northern Apennines (Italy)

- A new methods to exclude only wild boars was implemented and tested.
- The wild boar impact on the forest regeneration was estimated.
- The grid-exclosure method was effective in reducing wild boar activity impact.
- Wild boars foraged preferentially bigger fruits of Turkey oak.
- Wild boar activity reduced seedling survival, in particular of subordinate species.

The foraging activities of wild boar (Sus scrofa L.) have been suggested to impact biodiversity and ecological processes in a wide array of ecosystems. Data indicate that wild boar affects forest vegetation by feeding on above- and belowground plant parts, as well as by soil disturbance causing plant mortality and influencing seedling recruitment. In this paper, we investigated wild boar impacts on forest regeneration within three different types of mixed deciduous woodlands, respectively dominated by chestnut (Castanea sativa), Turkey oak (Quercus cerris) and beech (Fagus sylvatica) occurring in the northern Apennines (Italy), a mountain area where wild boar numbers have increased rapidly in recent decades. The goal of our study was to present a robust procedure targeted towards estimating wild boar impact on fruits predation and seedling survival of tree species. We evaluated the impact comparing wild boar excluding plots with completely access free ones. Differently from the majority of other experiments, we used replicated exclosure plots (by means of an electro-welded iron grid) excluding wild boars without excluding all other large ungulates such as deer and native small vertebrates. This method, tested with camera trapping surveys, was effective in reducing time spent by wild boar on experimental plots in comparison with other animals. Nevertheless, the number of fruit was similar in the exclosure plots and completely access free plots. Our study demonstrated, however, that wild boar feeds preferentially with the bigger fruits that are visually more attractive and have higher energetic potentialities too. The proportion of seedlings survived at the end of the period studied was significantly higher in wild boar excluding plots compared to those completely access free. Moreover, the dominant species were not equally influenced by the exclosure method, with chestnut and beech more markedly affected with respect to Turkey oak. Finally, the seedling survival of subordinate tree species, compared to the one of dominant plants, was reduced by the activity of wild boars in all the woodlands studied. This impact could lead to reduced tree species richness of the woodlands under study with negative effects on the biodiversity of plants and animals within these ecosystems.