A tale of heavy metals, railways, plants and pollinators: the promise of phytoremediation in urban areas

An ecological approach to the restoration of cities’ polluted areas is fundamental for the preservation of urban biodiversity. Within the National Biodiversity Future Center (NBFC), this research aims at addressing the impact of urbanisation on biodiversity by evaluating the effects of highly degraded landscapes on the ecosystem services quality. These knowledge advancements will constitute a baseline to design optimal restoration strategies. The study focuses on polluted areas in Milan (Italy): three dismissed railway sites contaminated by heavy metals and organic pollutants. Monitoring activities contributed to assessing the ecological value of these sites from both a floristic and pollinator perspective in response to a phytoremediation approach implemented through the planting of different species, trees, and shrubs mainly. During the spring and summer of 2023, floristic surveys were conducted, resulting in the identification of over 150 species, with a significant portion being non-native. The vegetation cover featured mixed woodlands, shrublands, and dry grassland patches. Simultaneously, entomological samplings were carried out, targeting wild bees, wasps and hoverflies. The results showed the collection of 390 wild bee specimens from 14 genera, with Halictus and Anthidium being prominent. Additionally, 134 hoverflies and other flower visitors were recorded. This study shows how sites such as railway yards, degraded from a landscape and aesthetic perspective, instead play an important ecological role in supporting plants and pollinator communities in urban areas. Ecological regeneration efficiency will be assessed by post-operation biological samplings to provide useful indications on how to improve contaminated sites, accounting as well for wild plants and pollinators.