Abstract
In recent decades, the European populations of wild boar have grown substantially, as has the impact of this species, owing above all to its rooting activity. Our aim was to investigate the relationships between vascular plant understorey and wild boar rooting intensity. The questions we addressed are: does rooting intensity influence understorey species composition and diversity? Which functional traits are associated with different levels of rooting? We performed a comparative analysis of plant communities in areas with contrasting levels of rooting intensity within a Mediterranean deciduous lowland forest in central Italy. Besides comparing species composition and diversity, we tested the association between species traits and rooting levels through fourth-corner analysis. We found that contrasting levels of rooting were associated to different understorey species composition and evenness, while we observed no significant difference in species richness. In contrast with our expectations, sites with lower rooting returned i) lower evenness values and ii) a higher proportion of species characterized by traits related to resistance or response to herbivory, i.e., spinescence, clonality, endozoochory, underground storage organs, and low height values. Our findings suggest that current vegetation patterns partly depend on the legacy effect of past rooting disturbance, since the areas currently subjected to low rooting intensity were likely to be intensely rooted in the past. These areas may have developed a marked dominance of clonal thorny species that, in turn, inhibited further feeding activities by wild boar.
Highlights
IntroductionEuropean populations of wild boar (Sus scrofa L.) have grown substantially in recent decades (Saezroyuela and Telleria 1986, Wirthner et al 2012) owing both to the ability of this species to adapt to different environments (Schley et al 2008), and to a combination of reintroduction for hunting purposes (Champagnon et al 2012), increasing tree mast frequency (Bieber and Ruf 2005), insufficient hunting pressure, and lack of predators (Barrios-Garcia and Ballari 2012)
This study shows that wild boar rooting activity alters understorey composition causing modifications in species dominance through the selective predation or avoidance of species with different functional traits
The drastic recent increase in the density of wild boar likely caused severe shifts in understorey composition that in turn hampered the ability of wild boar to feed in the previously impacted areas, i.e., the areas in which we measured low rooting intensity are those in which such activity is limited by the occurrence of a dense thicket of Ruscus aculeatus
Summary
European populations of wild boar (Sus scrofa L.) have grown substantially in recent decades (Saezroyuela and Telleria 1986, Wirthner et al 2012) owing both to the ability of this species to adapt to different environments (Schley et al 2008), and to a combination of reintroduction for hunting purposes (Champagnon et al 2012), increasing tree mast frequency (Bieber and Ruf 2005), insufficient hunting pressure, and lack of predators (Barrios-Garcia and Ballari 2012). Wild boar is a natural component of forest ecosystems, when the population is over-abundant it may have a profound impact on several ecosystem components since the effects of large herbivores are positively related to their density, often in a nonlinear way (Nuttle et al 2014). Such impact acts through several mechanisms ranging from the modification of habitat structure to the alteration of disturbance regime and food webs (Valenzuela et al 2014). Rooting may affect some key ecosystem components such as soil, overstorey regeneration and the herb-layer, in areas that range from a few square decimetres to hundreds of hectares (Welander 2000, Li et al 2013)
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