Changes in the flora of some Aegean islets 1968–2000

Abstract.

The flora of 17 islets was studied during the period 1968–2000, with thorough inventories from 1971. At each visit the species present and their population sizes were noted. The flora of the smallest islets of hard rock consisted mainly of perennials, and remained unchanged in terms of species present throughout the period of study. In the larger and more complex islets the major part of the flora consisted of islet-specialised taxa staying for long periods of time. To them are added some other mostly casual species from the close large islands, introduced by human influence, birds or winds and standing for most of the turnover in the islets’ flora. Few changes were observed in the plant communities of rock crevices, the spray zone of the shores and other constant habitats. The dominant perennial species forming layer of shrubs or subshrubs also mostly remained the same. Most of the changes concerned soil spaces opened by animals or erosion. Most annual species were found to survive by an extreme seed bank strategy. Many taxa common on the neighbouring islands were lacking or casual on the islets. Some others reached dominance or high frequencies that have not been observed on islands or in mainland areas. The conditions for the flora on the Aegean islets are considered to differ fundamentally from that on large isolated islands because they are situated comparatively close among each other and to islands and mainland areas. They are also vulnerable towards catastrophic events and therefore frequently presenting opened targets for invasions. The islet-specialised taxa are found to retain good ability for dispersal over moderately long distances. The grazing of the islets is stated to be an important factor for the evolution of islet adapted and specialised taxa.