Ecological changes in the Palaearctic Region since the Pliocene.



The climatic sequence during and since the Pleistocene is summarized. For Europe, four glaciations are accepted, separated by interglacials during which the climate was more genial than the present. Moreover, each glacial and interglacial was divided into phases. Eastwards these vicissitudes diminished: only two glaciations. are discernible over most of Siberia and eastern Siberia has witnessed altogether less climatic change since the Pliocene than any other part of the Palaearctic.

The changes in the level of the oceans owing to the alternate locking-up and melting of masses of water in the ice-caps produced fluctuations of much local importance in the coast-lines during the Pleistocene.

The vegetation of Europe during the best documented glacial phase, namely Phase 2 of the Last Glaciation, is discussed on the basis of recent maps. The most important feature is that trees were practically eliminated from Europe north of a line through the Pyrenees, the southern foot of the Alps and the Carpathians, except for a strip of wooded tundra and wooded steppe across central Russia. Deciduous species were confined to the southern end of the Iberian, Italian and Balkan peninsulas, and the coasts of Barbary and Asia Minor. These (Phase 2) conditions are dated about 70,000 years ago; they recurred to a considerable extent in Phase 3, about 25,000 years ago. Moreover, after the first post-glacial (Allerød) advance of the trees to as far north as the Baltic, the “Younger Dryas” cold snap, only some 10,000 years ago, again eliminated most of the trees from north of the Alps.

By contrast with the foregoing, at the height of the interglacials deciduous and coniferous forest respectively extended several degrees further north than at present; at least in Europe, if not in Asia, treeless tundra was probably eliminated from the arctic lowlands.

At the maximum glaciation (the Third), the tree-growth was probably not much more strictly limited in western and central Europe than it was in Phase 2 of the Last Glaciation but in European Russia tundra and cold treeless steppe extended south right to the Black Sea and the Caspian.

In Palaearctic Asia the vegetational conditions during the glaciations are more obscure than in Europe; but during the Last Glaciation trees appear to have existed at least sparsely all across Siberia.

Finally, Dr. Brooks, Dr. Dimbleby, Dr. D. Lack and Professor Zeuner have all been good enough to criticize this review in draft. Its final errors and omissions are of course my own responsibility.