Modelling the risk of coastal habitat invasion by the aquatic plant Iris pseudacorus to inform monitoring and management efforts

Effective management of invasive species often relies upon early detection and rapid implementation of management actions. Unfortunately, early detection can be hampered in coastal regions where sites may be challenging to access and survey or resources are limited. Conventionally considered a freshwater plant with a near-global invaded range, yellow flag iris ( Iris pseudacorus ) is sufficiently tolerant of salinity to disperse through seawater and successfully invade coastal habitats. Clarifying the characteristics that influence coastal habitat suitability for I. pseudacorus and identifying locations at risk of invasion is critical for monitoring and control efforts. We developed a Maxent species distribution model to inform the risk of coastal invasion by I. pseudacorus in southern British Columbia (Canada). Among the variables assessed, precipitation during the driest quarter was the most important contributor in predicting I. pseudacorus’ s coastal habitat suitability (40.6% variable contribution [VC]). Urban areas (24.9% VC), south-facing aspects (6.2% VC) and locations at elevations (7.9% VC) at or above the mean high tide extent were also considered suitable for establishment. Though proximity to perennial freshwater sources (7% VC) was also predicted to provide suitable habitat, close distance to these features was not found to be essential. Regionally, invasion hotspots were predicted in coastal habitats around Tofino/Ucluelet (western Vancouver Island), the Fraser River delta (metro Vancouver), and among the southern Gulf Islands and southern Vancouver Island (capital region). Land managers can use these variables of interest and geographic locations to inform early detection monitoring efforts that help attenuate the emerging threat of I. pseudacorus in coastal ecosystems.