Vegetationsgeschichtliche Untersuchungen im Küstenbereich von Istrien (Jugoslawien)

Abstract

Sediments of the brackish water containing Lake Palu, situated in a sink hole nearby the co as of the Adriatic Sea and about 10 km S of Rovinj (Istria, Yugoslavia) were studied for pollen and macrofossils. The pollen diagram can be divided into 5 pollen zones. The first pollen zone starts with the lowermost pollen-containing sediments dating back to the 5th millenium BP and ends with the beginning of Roman times in Istria. During that time, the vegetation of Western Istria consisted of deciduous submediterranean oak forests and a belt of evergreen trees mainly with Quercus ilex, probably not wider than 20–30 m, following the shore of the Adriatic Sea. This vegetational zonation can be considered to be the natural one not yet influenced by human activity. The first definite hints for human activities, which caused changes in the vegetation, are due to the beginning of Roman colonization in Istria during the first two centuries BC (beginning of zone 2). As in Dalmatia, one can successfully use the beginning of the curves of Juglans and Castanea for dating. With the beginning of zone 3, an increase of the amount of plants indicating farming activity and an increase of the percentages of mediterranean evergreen woody plants – mainly Phillyrea – indicate the development of the Roman colonies in Istria. The forest clearance, which was necessary to enlarge the cultivated area, must have taken place mainly in the area of deciduous oak forests. Subsequently the evergreen tree species could form a wider belt than it was possible under undisturbed conditions. Most probably the evergreen plants rather formed a maquis than a forest in the newly occupied area. The maquis mainly consisted of Phillyrea and Quercus ilex. From the end of Roman times in Istria to early Middle Ages, the indicators in the pollen diagram for human activity remain without changes. This corresponds very well with the history of Istria saying that all invasions of foreign people between the 5th and the 8th century AD did not influence very much population and agriculture especially in southern Istria. Most probably during late Middle Ages, e.g. under Venetian government, there was a strong development of juniper heaths, which must have been due to increased forest clearance and grazing (zone 4). In zone 5, juniper heaths were replaced to a certain degree by a Phillyrea maquis. Today, the maquis belt near the coast is about 200 m wide. – The fossil record of water plants clearly shows that till the end of zone 2, Palu was a freshwater lake. Afterwards water from the Adriatic Sea came in through gaps in the limestone rocks and, subsequently, freshwater plants like Nymphaea, Myriophyllum and Ceratophyllum were abruptly replaced by Ruppia and other water plants indicating a brackish environment. In addition 3 profiles with marine sediments were studied with the aim to find out the differences between marine and non-marine pollen sequences of nearby situated localities. The marine material investigated comprises 2 cores from the Limski Kanal, one core from the shelf bottom off Poreč and some samples from different parts of the Gulf of Piran. The Limski Kanal is situated 14 km N of Palu and the cored sediments cover more or less the same period as found at Palu. In spite of the activity of burrowing benthic organisms, it was easy to divide the pollen diagrams into those pollen zones already known from Palu. Nevertheless, several differences can be found, especially when comparing the amount of conifer pollen. The oldest sediments so far cored at the shelf bottom off Porec are to be dated to Boreal or early Atlantic times. The uppermost sediments which are covered only by a thin shill lager, were dated by radiocarbon to 6640 ± 120 BP. Therefore, sedimentation must have ended here about 6000 years ago, and consequently it could be demonstrated that the pollen sequence does not overlap those obtained at Palu and the Limski Kanal. In the pollen diagram, the Corylus curve starts with high values and shows a decrease to amounts still higher than the very small ones found in Palu and in the Limski Kanal. The lowermost samples contain among others pollen grains of Myriophyllum and ostracods typical for brackish water. So at that time, the northern border of the Adriatic Sea was approaching the latitude of Poreč. From the northernmost part of the Adriatic Sea, two samples were studied consisting of a peaty material overlain by a thin layer of sand which forms the surface of the bottom. The pollen content of both samples indicates a Pleistocene age. Pollen grains of Menyanthes and freshwater plants indicate that this area was situated outside the northern border of the Adriatic Sea when the peaty material was formed.