Vascular plant colonization and vegetation development on sea-born volcanic islands in the Aegean (Greece)

Inside the seawater-filled Santorini caldera (S Cyclades) the uninhabited islands Palea Kaimeni (PK) and Nea Kaimeni (NK) have been formed by submarine/subaerial activity. About 197 B.C. PK (0.54 km2) emerged, harbouring (in 1987) 178 vascular plant species, and covered by a mosaic of evergreen sclerophyllous and halophytic shrub communities and short-lived therophytic plant communities. NK, actually colonized by 156 vascular taxa, emerged ca 1570 A.D., its surface having enlarged to 3.44 km2 owing to four subsequent eruptive phases of the island’s volcano until 1950. At present, the most evolved vegetation type on NK is a steppe-like pioneer community rich in grasses and legumes apart from some Ficus carica trees which survived this century’s volcanic eruptions. The beginnings of shrub vegetation on NK, originating from PK’s consolidated woody canopy, are documented and evidence is shown of several ways of zoogenic and anthropogenic import of new vascular plants to the island. Comparative plant censuses demonstrate that permanent immigration of plants into NK overbalances by far the loss of species caused by the repeated destructions of the island’s plant cover. Cases of species turnover (verified extinctions and invasions), of pseudoturnover (due to sampling errors), of long distance dispersal and of successful stabilization of founder-populations are exemplified.