Zarys historii rozwoju flory Holarktydy

Władysław Szafer

Abstract


Outline of the development of the Holarctic Flora

This is a short description of the changes in the development of the flora of Holarctis from the Cretaceous Period to the present time. It is based upon ca. 250 original scientific works of 122 authors cited in the text. Some of them were inaccesible to the author at the time of the war, especially those from the U. S. A. and Eastern Asia. After a short characterization of the Cretaceous floras of Greenland, newly investigated by Seward and Convay (1935), the author accepts the point of view emphasized especially by E. W. Berry (1937 and 1938) and Holicki (1930 and 1936), that although the Cretaceous center of origin of the Angiospermes was probably in Greenland, that group of plants spread through the whole world as early as the Eocene. 1 The Changes in the Holarctic flora in the older Tertiary Period were chiefly influenced by the great geological transformations of land and sea and especially by the changeable history of the Thetys-sea. At the time of the Middle Tertiary the rise of many mountain ranges created new possibility for the differentiation of the flora. On the other hand one must accept that the climatic zones were clearly developed already at the time of the Miocene and that these zones underlay the process of shifting which happened to be the main factor responsible for the geographical changes in the flora of the whole of Holarctis. The results obtained by E. Oliver (1034) concerning the history of the Sequoja — forests in North America are the best proof of the soundness of this assumption. Similar facts were recorded also from Europe and Asia. For the explanation of the floristical connection between Middle Europe and East in the Tertiary Period of greatest value are the ideas of A. Krischtafo wi tsch (1935), who introduced in science the clear distinction of two types of flora (Turgaja and Poitawa), which had quite different sources of origin and a quite different history in the Tertiary. In the upper Tertiary Period (Pliocene) there occurred the most characteristic changes in the flora of Holarctis which in the first place were responsible for the renovation of the Middle European flora. The North American and East Asiatic sectors were comparatively less influenced. This subject is treated by the author in three separate chapters. Some new conceptions given there are supported by the exceptionally rich fossile flora of Krościenko in Poland, which was the object of the author’s investigations since 1938 (printed 1946, as preliminary note 1938). The Pleistocene is the space of time, which caused the most important changes in the composition and geographical distribution of the flora. The author treated this chapter with special attention. After discussing the problems connected with the shifting of the North - Pole, he describes first the changeable history of the North American flora in the Pleistocene then the analogical history of the flora of Europe and Asia. Almost all the problems of diluvial paleogeography are mentioned and critically discussed. The most important among them are: 1. the localization of refugial regions 2. the history of the Mediterranean area, 3. the relation between the glacial and interglacial periods, 4. the migrations of mountain plants during the glacial episodes of the pleistocene and the movements of the polar timber line, 5. the peculiarities of the glacial „tundra“, 6. the history of the steppe formations in Europe. After a description of the late glacial Period in Europe, the treatise is closed by a short glance at the problem of postglacjal changes in the flora of Holarctis.

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