Invasive alien plant species, riverbank instability and hydraulic risk: what do we know about Amorpha fruticosa, Arundo donax and Reynoutria japonica?

The spread of invasive alien plant species (IAPs) poses a serious threat to the biodiversity and effectiveness of rivers and drainage canals. Nevertheless, the reasons for the implications of increasing presence of IAPs on the stability and effectiveness of flood defences are still unclear. To point out the current knowledge on the topic, a systematic review was performed focusing on three of the key riparian IAPs: Amorpha fruticosa, Arundo donax and Reynoutria japonica. We searched for articles in the Scopus database, focused on the links between the three target species and hydrology and geomorphological processes. Only 7 papers were found containing what we were looking for. All the three target species are true «engineer plants», significantly regulating the edaphic and functional peculiarities of colonised environments, which correspond in the present case to river embankments. A. fruticosa slows down the water flow speed, increasing the flood risk. The extremely superficial A. donax root systems weaken bank stability, whereas R. japonica promotes soil erosion due to its peculiar roots’ morphology and extremely rapid biological cycles. This work shows that, despite clear evidence of the significant negative impacts mediated by the three IAPs of concern, the available levels of knowledge are wholly insufficient. In order to develop effective management strategies for riparian contexts globally, further investigations are needed urgently. Future research should focus on the structural/functional impacts of IAPs in riparian environments, not forgetting the additional effects of global changes and human impact on rivers and their functions.