西欧地中海地区中新世以来的植被演化和现代地中海植被的形成

FLORA EVOLUTION OF NORTHWESTERN MEDITERRANEAN AREA SINCE THE MIOCENE AND THE APPEARANCE OF MEDITERRANEAN VEGETATION

从距今2500万年的中新世初到更新世,欧洲地中海沿岸地区的植被是从东亚型的热带——亚热带常绿阔叶林逐渐过渡为旱生性的蒿——藜草原。古热带和亚洲、北美成份从晚中新世起逐渐消失,少数一直延续到中更新世。孢粉分析表明,地中海成分从中上新世起有明显增加,地中海常绿硬叶林的发展与北极冰盖的形成密切相关。

The transition between Miocene and Pleistocene climates of Mediterranean area is characterized by a graduel cooling trend from a tropi-subtropical type to a cold and dry one, which is punctuated by some more or less important climate fluctuations. The megatherm elements of Miocene flora come to disappear since Late Miocene and the Asia-American elements decrease evidently in Middle Pliocene.Palynological studies from the Pliocene sediments show that two stages of climate deterioration can be dissociated. They are respectively -3.2 Ma., marked by the decline of eastern Asia climate rhythm (estival rain), and-2.3 Ma. corresponding to the first glaciation in north Europe.A number of sites of palynological investigation make possible to restore the Nepgene environment. It makes in evidence that the Mediterranean vegetation is of Middle Pliocene origen, which is more and more developing during the Quaternary.During Pleistocene glaciations, the pollen flora in northwestern Mediterranean region alternate mainly between steppe (Artemisia and Chenopodiaceae) and caducous oak and pine forest.