Alien or native? Examining a case of Melampyrum pratense in Iceland

In 2016, a single, large population of Melampyrum pratense (Orobanchaceae) was discovered in Vaglaskógur forest in NE Iceland. This population can be considered as extremely disjunct as the closest population of this myrmecochorous, slowly dispersing, hemiparasitic plant species is known from the Shetland Islands located ca. 1000 km south-east from Vaglaskógur. Our research was aimed at elucidating whether the species is a recent anthropogenic addition to the Icelandic flora or if its presence should be attributed to a natural long-distance dispersal event. In order to answer this question, we employed a diversified methodological approach consisting of a traditional vegetation survey, faunistic study and two mathematical modelling techniques. Our work showed that M. pratense inhabits an almost undisturbed birch forest, and the formation of the population of this size would take more than 3000 years given the absence of main dispersal vectors. Using the distribution modelling approach, we also determined that climatic conditions facilitating the establishment of the population were in place since at least mid-Holocene.