HISTORICAL INFLUENCE OF MAN ON THE VEGETATION

Abstract

The Prasilske Lake is the glacial lake in the Bohemian Forest (Sumava Mts) located on theCzech side in the elevation of 1,079 m above sea level. The lake area is 4 ha, the maximal depth is 15.5 m.The lake catchment area is situated in the sub-alpine zone. The studied area has never been the object offorest or agricultural farming in the history because of its inaccessibility. The sediment dating was carriedout by means of lead isotope 210Pb. The oldest layer established by this isotope in the Prasilske Lakewas in the depth of 0.47 m. This dating was used for the deepest layer of sediment and its age was datedto the year of 1843 (depth 0.11 m) and a base of this profile to the medieval age (depth 0.47 m), whichcorresponds to about the 12th-13th century A.D. The analysed profile (0-0.47 m) can be divided into thelocal pollen assemblage zones PRI-1 (depth 0.37-0.47 m), PRI-2 (depth 0.25-0.37 m), PRI-3 (depth 0.12-0.25 m), PRI-4 (depth 0.06-0.12 m), PRI-5 (depth 0.02-0.06 m), PRI-6 (depth 0-0.02 m). On the basis ofdating by the 210Pb method the age of sediment (0-0.11 m) is established into the range of 1843 to 1994.It is noticeable in the pollen spectrum that it concerns a locality situated already above the forest border,the pollen curves of stratigraphical important taxons (mainly woody species) do not change markedly. Therich woody component is formed mainly by pollen grains of Picea and Fagus. The herbaceous component(NAP) is very diverse; however, in a general way the pollen grains of woody species (AP) predominate dueto the above mentioned deciduous forests. A representation of the herbaceous component (NAP) is veryvaried as far as species are concerned, human influence is very visible here (e.g. occurrence of cerealsCerealia, Zea mays, Fagopyrum-type, weed: Centaurea cyanus, Agrostemma githago etc.). The dating ofthis part also corresponds to the results of the pollen analysis. Of the plants producing spores the findingsof lesser clubmoss (Selaginella-type cf. Selaginella selaginoides) and water plant quillwort (Isoetes), whosenearest contemporary place of the finding in our territory is in the Cerne and Plesne Lake and Wielki Staw(the Giant Mts), were quite interesting. The most of spores were recorded at the family Polypodiaceae andgreen alga Botryococcus, which indicate cold and humid conditions of the occurrence.