Das Trockenelement in der jungtertiären Flora Mitteleuropas

Zusammenfassung

Im Jungtertiär Ungarns sind einzelne Floren wie im Alttertiär durch das massenhafte Vorkommen mikro- und stenophyller Holzarten ausgezeichnet. Sie verdanken ihre Entstehung, wie im Alttertiär, einem im nordatlantischen Raum Eurasiens gelegenen Entwicklungszentrum und einem Halbtrockenklima. Dieses Klima entsprach dem heutigen Klima in höherem Mass als das Klima desselben Raumes im Alttertiär. Ein Teil der jungtertiären Trockenarten sind aus dem Alttertiär zurückgebliebene Elemente. Sie überlebten die feuchteren Zeiten an günstigsten Stellen. Unter ihnen sind die meisten mit rezenten Arten abgelegener Gebiete, so des öfteren der südlichen Hemisphäre, verwandt. Nur wenige (z.B. Arbutus unedo L.) sind heute mediterran. Die im Jungtertiär entstandenen Trockenarten sind mehrheitlich mit mediterranen Arten verwandt. Die Hartlaubgehölze mediterraner Verwandtschaft kamen im Karpatenbecken in grösster Zahl im ersten Abschnitt des unteren Sarmats vor und beherrschten zu dieser Zeit die Trockenwälder.

Die Umweltverhältnisse des oberen Tortons waren jenen von Makaronesien ähnlich. Im unteren Sarmat entwickelte sich ein Klima von echt mediterranem Charakter. Etwas später milderte sich indessen die sommerliche Aridität und die Niederschläge nahmen zu. Die Trockenwälder wurden durch mesophile Waldungen verdrängt. Die Entwicklung der Strauchschicht verspätete sich aber gegenüber der Kronschicht und mediterrane Straucharten erschienen in grösster Anzahl unter einer Kronschicht, die zur Hauptsache aus mesophilen Arten bestand. Eine überaus reiche Entwicklung von xerophilen Quercus-Arten charakterisiert den stark geschichteten xero-mesophilen Mischwald von Balaton-Déllö.

Summary

By analizing the Late Tertiary floras of Hungary the writer found that from Middle Miocene time the number of the leaves of xerophytic character increases. According to his opinion these xerophytic types were — like those of the Early Tertiary — formed in a plant evolution center situated in the North Atlantic region in the latitude of the Spanish and Moroccan “meseta” or a little more northward. This dry element called “xero-atlantic” element appears as third besides the temperate Turgayan and the warmer evergreen Poltawa-element.

In Hungary the climate changed in the Tortonean to a subtropical one with a hot and dry summer and a mild and moist winter approaching the recent climate of the Mediterranean region. This climate was favourable to the hard-leaved arborescent vegetation.

In the German text a list of the dry elements hitherto observed is given with their leaf character, their living equivalent and its geographical distribution. Then the origin of these species is discussed especially whether they are descendants of the Poltawan or Turgayan flora. At the beginning of the dry period of the Late Tertiary, during the Late Tortonean and Early Sarmatian, some dry elements of the Austral type (Proteacea, Myrsinaceae, Callistemophyllum) are yet found. Then the forms of Mediterranean type become dominant. A special attention is paid to the dry oakes. The majority of the hard-leaved oaks is Mediterranean but some of them (e.g. Quercus pseudoilex Kov.) have their equivalence in the Gulf region of North America. The typical hard-leaved oaks of the Pacific region are in no connection with the species of Mediterranean relationship and according to Axelrod (1958) they had their center of evolution in the Sierra Madre region. Besides the hard-leaved forms there are deciduous and semideciduous oaks and one of the laurel type. The latter has his equivalence in southern Atlantic North America.

The climate from the Tortonean to the Early Pliocene is fairly well known. During the Tortonian it was similar to the recent climate of the Canary Islands with a rainless summer and a mild winter. The aridity of the summer was nevertheless moderated by the equalized temperature and the high air moisture. At the beginning of the Sarmatian the climate changed to a more extreme one, the summer became hot and dry. In the younger Sarmatian the precipitations increased and the summer aridity decreased.

The changes in the vegetation followed the changes of climate. The greatest evolution of the arid and semiarid plant forms took place during the early Sarmatian. But no treeless formations, steppes, or desert vegetation can be supposed. The Tortonean forests were dominated by the Lauraceae. In consequence to the increasing aridity the Lauraceae disappeared from the tree level but remained as shrubs. In the Early Sarmatian especially in the flora of Erdöbénye, the hard-leaved forest was the dominant plant formation consisting of hard-leaved, half-evergreen oaks and other deciduous trees with xeromorphic foliage (Acer decipiens A.Br. etc). The majority of the dry elements were of Mediterranean type. The evolution in the undergrowth of the forest was a little late and the hard-leaved shrubs reached their highest evolution at a time in the Sarmatian when the hard-leaved forest changed gradually into a mesophilous one.