Non-native species in the vascular flora of highlands and mountains of Iceland

The highlands and mountains of Iceland, defined here as areas located above 400 m above sea level (m.a.s.l.) are one of the largest remaining wilderness areas in Europe. The present study was aimed to provide the first comprehensive and up-to-date data on non-native plant species from this region. The study was aimed to answer the following questions: (1) How many non-native vascular plant species inhabit highland and mountainous environments in Iceland? (2) Do temporal trends in alien species immigration to Iceland and highland areas differ? (3) Do human disturbed and undisturbed areas within Icelandic highlands differ in terms of alien species occurrence? (4) Is spread within the highland areas a second step in alien plant colonization? and (5) Can we point out hot-spots in the distribution of non native taxa within highlands? Overall, 16 non-native vascular plant species were detected, including 11 casuals and 5 naturalized taxa (1 invasive). Results showed that temporal trends in alien species immigration to Iceland and to highland areas are similar, but it is clear that the process of colonization of highland areas is still in its initial phase. It was evidenced that non-native plants tend to occur close to man-made infrastructure and buildings including huts, shelters, road network etc. Analysis of spatio-temporal patterns showed that the spread within highland areas is a second step in non-native plant colonization in Iceland. Several statically significant hot spots of alien plant occurrences were be identified using Getis-Ord Gi* statistic and linked to human disturbance. This research suggests that human-mediated dispersal is the main driving force increasing the risk of invasion in Icelandic highlands and mountain areas.