Ecosystem changes induced by Robinia pseudoacacia: results from invaded landscapes in the Veneto Region

Invasive alien species are one of main threats to biodiversity conservation worldwide. Indeed, widely spread species can become an important feature of a landscape and can have strong impacts over large areas. Investigating the role and impact of invasive alien species is fundamental to tackle this issue through appropriate landscape management and planning. Here we present results from a number of studies investigating the potential ecosystem changes induced by the presence of black locust (Robinia pseudoacacia L.) in forest habitats, as well as the potential influence of forest management on these dynamics at the landscape scale. Black locust, a N-fixing tree, is the most widely spread alien woody species in Europe and has an impact on many natural and semi-natural habitats. We selected several forest sites in hilly and riparian landscapes in the Veneto region (northern Italy) within and outside the Natura 2000 European network of protected sites. We considered the effects of this species on ecosystems after its invasion of fields and other abandoned areas, but also in managed coppice and high forests. We surveyed vascular plant species and soil features in nearby paired plots dominated by black locust, invaded, and by native tree specie, non-invaded. Results show that plant diversity is not influenced by the alien tree species. Invaded plots are rich in nitrophilous and alien species. Black locust showed compositionally heterogeneous plant communities, but species composition clearly differed between invaded and non-invaded plots. Furthermore, the effects on functional plant trait composition were substantial and can be linked to differences in soil conditions with native stands. Further research will investigate the presence of nitrogen fixing archaea in invaded and non-invaded forest soils. Management and conservation decisions should consider these impacts, the landscape context and specific environmental features in which black locust forests develop.