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

The highlands and mountains of Iceland are one of the largest remaining wilderness areas in Europe. This study aimed to provide comprehensive and up-to-date data on non-native plant species in these areas and 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 the immigration of alien species to Iceland differ between highland and lowland areas? (3) Does the incidence of alien species in the disturbed and undisturbed areas within Icelandic highlands differ? (4) Does the spread of non-native species in Iceland proceed from lowlands to highlands? and (5) Can we detect hot-spots in the distribution of non-native taxa within the 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 highland and lowland areas are similar, but it is clear that the process of colonization of highland areas is still in its initial phase. Non-native plants tended to occur close to man-made infrastructure and buildings including huts, shelters, roads 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 identified using the Getis-Ord Gi* statistic and these were linked to human disturbance. This research suggests that human-mediated dispersal is the main driving force increasing the risk of invasion in Iceland's highlands and mountain areas.