Not across the North Pole: plant migration in the Arctic.

• The vascular plant flora of 66 arctic islands was studied to determine whether the islands have been occupied by random long-distance dispersal (LDD) or in a highly structured northward migration pattern via intervening islands as stepping-stones. • A maximum parsimonious migration model minimizing dispersal distances of 1256 vascular plant taxa was calculated in the framework of network analysis. • Plant dispersal is not stochastic in the Arctic at the global scale. Inferred mean dispersal distances of the plants occurring on arctic islands are c. 580 km (median 460 km). A LDD across the North Pole could not be inferred in the model and species may be recruited mainly from the nearest mainland or islands. At smaller scales, among adjacent islands, dispersal of vascular plants may be incomplete. Arctic islands do not yet appearto be saturated with species. • The results suggest that changes in biodiversity in Arctic islands can be more easily predicted at the global scale than at the local scale. Because islands are not yet saturated with species, new colonizations may not necessarily be linked to climate change.