Vlasta Jankovská

Indicative value ofPediastrum and other coccal green algae in palaeoecology

Sporopollenin layers in the cell wall of coccal green algae are responsible for the resistance of cell walls to destructive processes during fossilization as well as during chemical preparation of samples for pollen-analysis. Pollen slides of samples from limnic sediments thus also contain some algal cell walls. Although some pollen-analysts tried to stress this fact, the finds of algae in pollen slides have not been paid systematic attention yet, despite their potential use for a more accurate palaeoecological reconstruction.The article summarizes the results of palaeoecological studies showing how the algae can be used in palaeoecological reconstruction of past environments. The possibility of utilizing the indicative value of algal finds is demonstrated on examples of algal communities from fossil, subrecent and recent sediments from different longitudes, latitudes, and altitudes. The identification and indicative values of species and varieties ofPediastrum are included in a special review (Komárek & Jankovská, Biblioth. Phycol., in press). The contemporary knowledge of ecological requirements of the given taxa, completed by information from their fossil finds, makes possible the reconstruction of trophic and temperature conditions and of the purity of the water environment of the past water biotopes.

The European Modern Pollen Database (EMPD) project

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

Late Glacial and Holocene history of Plešné Lake and its surrounding landscape based on pollen and palaeoalgological analyses

Pollen analysis has been carried out on a 549 cm thick sediment profile from lake Plešné jezero (Plešné Lake) in the Bohemian Forest (Šumava, Czech Republic; 1090 m a.s.l.; 48°47′ N; 13°52′ E). Analyses of 67 samples characterise the development of the lake biotope and the surrounding landscape during the last ca. 14,000 years. The pollen diagram shows a very distinct transition between the Late Glacial and the Holocene biostratigraphic units at a depth of ca. 312 cm. In the surroundings of Plešné Lake the vegetation was treeless during the entire Late Glacial. The alpine tree limit, formed by Betula and Pinus with undergrowth of shrubs, might have been at ca. 500 m a.s.l. Pollen transported from long distances was significant due to the openness of the landscape, coming from southern Europe and even Africa, and including high numbers of Artemisia, Poaceae, Chenopodiaceae, and some other herbs and shrubs from steppe and forest-steppe areas in southern Europe or Africa (likely Ephedra, certainly Lygeum spartum). The expansion of shrubs, particularly Juniperus, preceded the expansion of trees near the end of the Late Glacial. Afforestation of the region by thin stands of Betula and Pinus occurred during the Preboreal. Significant warming in the Boreal resulted in the expansion of Corylus, Quercetum mixtum (QM) trees, and probably also Picea and Alnus. Picea as well as QM trees were further expanding during the Early Atlantic. Picea was the dominant tree during the Late Atlantic and Fagus started to spread towards its end. Abrupt expansion of Abies marks the Subboreal. A high degree of afforestation (Abies, Fagus, Picea) was characteristic for the Early Subatlantic. During Late Subatlantic, pollen of synanthropic plants appears. Phases of the lake biotope development were defined on the basis of coccal green algae and Isoëtes.

Holocene dynamics of the alpine timberline in the High Sudetes

The study focuses on the High Sudetes that represent the most distinctive islands of alpine forest-free area among hercynian mid-mountains of Central Europe. Based on data from newly taken cores and previously published pollen profiles, comparison of the development of the alpine timberline position is carried out. The first of the analysed pollen profiles — the Labský důl core in the Krkonoše Mts spans the whole period of the Holocene, the Keprník and Mezikotlí profiles in the Hrubý Jeseník Mts bring information from the Subboreal/older Subatlanticum turn to the present. An exceptional position of the Krkonoše Mts in terms of permanent presence of the alpine belt throughout the Holocene was confirmed. Three oscillations of the alpine timberline during the Lower Holocene were detected in the profile from the Labský důl site. In the Hrubý Jeseník Mts a temperature dependent forest-free area existed at least since Subboreal to the present.

Long-term vegetation dynamics and the infilling process of a former lake (Švarcenberk, Czech Republic)

Natural lakes are a rare phenomena within extraglacial areas of Central Europe. Almost all have been completely terrestrialized during the Holocene. This paper deals with one such former lake, located in southern Bohemia. Its extensive lacustrine and peat deposits were subjected to a multidisciplinary study that resulted in high-resolution pollen, macrofossil, algal and sediment-chemistry data interpreted in terms of past climate, geomorphology, soil, and regional vegetation development over the last 16,000 years. Against the background of these large-scale processes, local development took place, comprising the lake’s ontogeny from an arctic-type ecosystem hosting pioneer aquatic communities, through a highly diversified mosaic of eutrophic hydrosere habitats (shallow pools,Phragmites andCarex fen, alder carr), towards an oligotrophic mire that started to dome over the terrestrialized lake. At every individual development stage, specific processes characterized ecosystem function and composition: during the Late-Glacial with its rapid climatic changes, external forces induced the major stresses; while during the Holocene, autogenic changes of the wetland ecosystem played the most important role.

The relationships of modern pollen spectra to vegetation and climate along a steppe–forest–tundra transition in southern Siberia, explored by decision trees

We studied the relationships between surface pollen spectra, vegetation and selected climate characteristics along a strong gradient of climate continentality across the Western Sayan Mountains, southern Siberia. Representation of 111 pollen taxa in 81 surface samples from steppe, forest and tundra was related to the vegetation composition at various distances from the sampling point and to mean annual precipitation and mean July and January temperatures. These relationships were assessed by the decision tree models. The results show (1) which vegetation types are well distinguished by their pollen spectra; (2) which vegetation types are strongly similar in their pollen spectra and therefore their interpretation from fossil pollen spectra should be carefully considered; (3) tight relationship between surface pollen spectra and selected climate characteristics, which suggests that the past climatic conditions can be reasonably predicted from pollen spectra; and (4) an important role of weak pollen producers for assignment of pollen spectra to vegetation types or particular values of temperature and precipitation. We found the decision trees suitable for analysis of pollen/vegetation relationship because they (1) formally and precisely assign the pollen spectra to vegetation/landscape types or climatic variables by means of easy-to-interpret graphs; (2) identify pollen taxa that are best indicators of a particular vegetation type, landscape or climate characteristics; and (3) utilize the pollen signal of both strong and weak pollen producers. We compare the decision tree models with ordination and cluster analysis and suggest further applications.

Das Vorkommen einiger Chlorokokkalalgen in böhmischen Spätglazial und Postglazial

During the pollen analyses of Bohemian peat and limnic sediments numerous empty cell walls of some chlorococcal algae, particulary, of the genusPediastrum, were found. This material was taxonomically determined and the ecology of different taxa was reconstructed and compared with the present one. The greatest difference was found inPediastrum integrum andP. kauraiskyi occurring commonly in Central Europe in the lakes during the Late-Glacial and Postglaciíal Periods but very rarely at present. Our results were compared with some data given in the literature.

Using multi-proxy palaeoecology to test a relict status of refugial populations of calcareous-fen species in the Western Carpathians

The distribution pattern of relict and specialised species in calcareous fens was revealed to be non-stochastic, with ancient fens harbouring more of these species than younger ones. This phenomenon could be caused by long-lasting in situ survivals over millennia, but direct palaeoecological evidence is lacking. We addressed the question whether at least some ancient calcareous fens indeed retained open-fen patches throughout the Holocene, using a palaeoecological approach involving proxies with different taphonomies (pollen, vascular plants, bryophytes, molluscs). We identified three old fens in the Western Carpathians, where several postglacial relict species have recently been found, and we reconstructed their histories with respect to sedimentary processes, vegetation structure and dynamics of relict species. The development at all the sites started with a (semi)-open fen community dominated by sedges and brown mosses. The site with the highest recent number of relict species was reconstructed to harbour open patches continually since the late Glacial to the present, including the middle Holocene when open-fen patches were restricted. By contrast, at the site with the lowest recent number of relict species, a large sedimentary hiatus suggested peat mineralisation or erosion that prevented the survival of light-demanding species. At all the sites, characteristic snails of European Glacial periods occurred during fen initiation, but disappeared around the early/middle Holocene transition. The probability of a relict species being present in a modern fen community increases with fen age, but it also depends on the continual existence of open-fen patches and peat accumulation throughout the middle Holocene.

Ergebnisse der Pollen- und Grossrestanalyse des Moors «Velanská cesta» in Südböhmen

Die Abhandlung fasst die Ergebnisse der Pollen- und Grossrestanalyse aus dem Torflager «Velanská cesta» am südlichen Rand des Beckens Třeboňská pánev (Wittingauer Becken) in Südböhmen zusammen. Auf Grund dieser Resultate wurde eine Rekonstruktion der Vegetation des Moors selbst und auch der Vegetation seiner Umgebung ab Beginn der Sedimentation in jüngerer Dryaszeit bis heute vorgenommen.

Vegetationsverhältnisse und Naturumwelt des Beckens Jestřebská kotlina am Ende des Spätglazials und im Holozän (Doksy-Gebiet)

The method of pollen analysis was used to study a profile sample taken from the Jestřebské blato mire, the Doksy District (northern Bohemia). The aim of the palacobotanical analyses was to perform a reconstruction of vegetation and environment for geobotanical and archaeological research purposes. Sediments dating back to the end of the Late Glacial and to both the Early and Middle Holocene were pollenanalytically studied. The results of the pollen analyses recorded the development of vegetation during the end of the Late Glacial, Preboreal, Boreal and Atlantic Periods. Parkline pine stands of the end of the Late Glacial developed to closed pine forests, during the Preboreal. Even during the Boreal, the dominant pine formed forest communities were typical of the area under study, though trees with greater demands on temperature and moisture conditions continued to penetrate the existing communities. During the Lower and the first half of the Upper Atlantic Period, spruce forests and alder woods formed the dominant forest communities in mire. Nevertheless,Pinus was still dominant on extreme sites (both from the edaphic and geomorphological points of view). An early occurrence ofAlnus andPicea is another characteristic feature of the studied area. The conclusions drawn from pollenanalytical results were used for the reconstruction of the past environment of the Mesolithic and Neolithic Ages.