Impact of Prunus serotina Ehrh. invasion on heathland vegetation: a case of study in North-Western Italy

Prunus serotina is one of the worst invasive alien plants throughout Europe, able to rapidly replace autochthonous vegetation and form monospecific stands both in open lands and forested areas. Invasion by shrubs and trees due to abandonment of traditional management practices, is one of the major threats to the conservation of “European dry heaths”, a priority habitat included in the Council Directive 92/43/EEC. The aim of this study was to assess the effects of P. serotina invasion on heathland vegetation in terms of species composition and cover, with special regards to the dominant Calluna vulgaris and Molinia arundinacea, in an area of North-Western Italy subjected to massive invasion by this alien species. We collected data on the plant cover along an invasion gradient in 10 linear transects running from P. serotina invaded stands towards non invaded ones. P. serotina differently affected the heathland vegetation. In particular, the cover of C. vulgaris and other typical heathland species such as Cytisus scoparius sharply decreased at P. serotina cover increasing. On the contrary, positive or no effect of P. serotina cover was found on M. arundinacea. Our results showed that shaded conditions created by the alien tree disfavored light demanding C. vulgaris and C. scoparius, enabling fast grower M. arundinacea to outcompete and replace them. This study emphasizes the urgency to develop management strategies to effectively control P. serotina spread in the area and to restore typical heathland species.