| Summary: | Hopen, a small island in the Barents Sea, is situated within the polar desert region. Altogether 26 vascular plants have been noted in four inventories conducted between 1873 and 1982. The temperature climate following the Little Ice Age has fluctuated considerably but with a clear warming after 1920. New areas have become available to the plants since permanent snowfields have melted. The number of species has increased from 17 in 1873 to 19 in 1982, but the turnover has been relatively large. Hopen does not show island biogeography equilibrium. Instead, the July mean temperature is probably the determining factor for the number of species. Mainly seed-dispersed species have colonized Hopen during this period. The origin of the vascular flora and the migration mechanisms are difficult to interpret if it is considered that the entire Svalbard Archipelago was simultaneously under ice during the Weichsel glaciation.Key words: vascular flora, polar desert region, climatic fluctuations, dispersal, island biogeography Mots clés: flore vasculaire, région désertique polaire, variations climatiques, dispersion, biogéographie insulaire
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