Distribution, drivers and management implications of riparian invasive alien plant species in the Ballisodare catchment.

Invasive alien species (IAS) are an ever-increasing threat to biodiversity and a substantial economic burden, costing Ireland approximately €2.1 billion in 2021. Despite this, repeated failures to manage IAS led the European Commission to refer Ireland to the EU Court of Justice in December 2023 for non-compliance with Regulation (EU) 1143/2014. Many invasive alien plant species (IAPS) spread across riparian zones as waterbodies act as vectors for propagule dispersal, causing negative ecological consequences. Flooding events are recognised as a major source of riparian IAPS (RIAPS) spread and are becoming more frequent under climate change. However, local information of the spatial extent and distribution of RIAPS is limited. As a member state of the European Union, Ireland is legally obligated under Regulation (EU) 1143/2014 to monitor, manage, and where possible, eradicate IAPS. This project provides the first dedicated IAPS assessment of the Ballisodare catchment, Co. Sligo through desk analysis and a field study of the Ballisodare and Unshin rivers to map the previous and current IAPS distribution in ArcGIS Pro. Desk-based analysis found 278 previous records of 14 IAPS and indicated strong associations with urban areas, likely reflecting effort biases. Field mapping 16 km of riparian corridor identified nine RIAPS covering 169,914 m². Rhododendron ponticum was spatially dominant (35% of area) followed by Heracleum mantegazzianum (20%) while Reynoutria japonica only represented 0.7%, despite comprising 66% of desk records. Invaded areas were associated with woodlands and historic estates, with forestry being disproportionately invaded. These findings highlight the need for further RIAPS monitoring and effective upstream management strategies of RIAPS in the Ballisodare catchment.