Environmental change in Crete: a 9000-year record of Holocene vegetation history and the effect of the Santorini eruption

Abstract

Palynological investigations were carried out in the coastal lowland of northwestern Crete, in the area of Lake Kournas. Results comprise the longest continuous vegetation record (9000 radiocarbon years) for Crete. From about 8500 to 7500 BP, open deciduous-oak forest occurred and appears to reflect the driest conditions of the Holocene. After 7500 BP, tree-pollen numbers increase. Some of these tree species are thought to be autochthonous, but for at least six species this is doubted and the presence of their pollen is ascribed to long-distance transport. Up to 6000 BP, the local vegetation included deciduous and evergreen oaks, Pistacia, Phillyrea and a variety of herbs. Only after 7000 BP, some species, e.g., Mercurialis annua, Cynocrambe and spores of Pteridium, might indicate the effects of Neolithic habitation. Towards 6000 BP, plane tree and Styrax (storax) appear; from about 6000 BP, olive is present and human activity becomes more evident. Slowly, pollen types indicative of the exploitation of present-day Mediterranean vegetation, e.g., Poterium and Ericaceae, appear and the presence of the alga Gloeotrichia indicates a rise in phosphate. A striking aspect of the sediment core nearest to the sea is a pumice layer originating from the Theran (Santorini) eruption. From the manner of its deposition it is concluded that no tsunami met the Cretan beach. Influence of the eruption from Thera on the vegetation is hardly visible. Decrease of economically important cultivated plants, e.g., olive, already took place decades, up to about a century, before the volcanic eruption. Around the time of the eruption, the values of some pollen types hardly changed, others increased and another group decreased. This pollen behaviour appears to be explained rather by socio-economic changes, such as withdrawing of the inhabitants to the interior for reasons other than volcanic effects. It is concluded from the pollen cores that no major climatic changes affected northwestern Crete during the Holocene but the first two millennia of the Holocene tended to be drier than the following period when there was an increase in moisture-demanding trees. It is difficult to assign changes in the Cretan vegetation to climatic effects in a period when human impact was gathering strength.