Evaluation of a car-based method for mapping the invasive Lupinus polyphyllus Lindl in road infrastructure

Growing recognition of the negative impacts of invasive alien plants on native species diversity and ecosystem function has led to greater focus on effective management strategies. Monitoring is crucial for both prevention of establishment and planning of eradication of established IAPs. However, monitoring is often constrained by resource limitations, and less time-consuming methods risk providing too low levels of detection. Lupinus polyphyllus is a highly problematic non-native plant species in Europe. We evaluated the accuracy of a car-based survey method for mapping L. polyphyllus in road verges and how the physical characteristics of the stands influenced their detection from the car. At the 200 m scale the accuracy of the survey by car was 85%, while at the scale of individual stands the accuracy was lower (72%). Results indicated that detection probability was influenced by stand density and position in the road verge. Dense stands had the highest detection probability, while single plants were less likely to be detected. Stands present in side and back slopes were more likely to be detected than those only in one slope, with the side slope stands having the lowest detection probability. Our study shows that the car-based survey is a reliable method for mapping the presence and abundance of L. polyphyllys in road verges. Such information is useful for designing management strategies to hinder seed production and dispersal of the invasive. Since the accuracy of detection of single plants was lower, more detailed surveys at local scales are recommended for early eradication.