A. Kairiukstis (edd.), Methods of Dendrochronology, London 1990; E. Corona, Dendrochronology as a tool for the study of climatic variations, in AttiConvLinc, 95 (1992), pp. 113-28; F.H. Schweingruber, Baum und Holz in der Dendrochronologie, Zürich 1992; Id., Tree Ring and Environment Dendroecology, Bern 1996.
For a long time, the study of fossil pollen was applied only to sediments related to humid environments, such as lagoons, lakes, swamps and peat bogs, as they were thought to be the only ones to possess pollen content. Thanks to their peculiar characteristics (low energy, scarce free oxygen, acid pH), these basins are undoubtedly ideal for the deposition and conservation of pollen rains, so much so that they deserve the name of biological archives of vegetation. However, their geographical distribution is rather limited; in Europe, most of the humid environments are located in northern latitudes, in mountainous areas and in somewhat restricted coastal areas. Chronologically speaking, these sedimentary series are either very ancient (Pliocene – Lower Pleistocene) or recent (Late Glacial – Holocene). There are certainly some important exceptions that have made it possible to reconstruct the history of vegetation cover on a wider time scale. In this regard, we recall the site of Meikirch near Bern, the peat bogs of the Grande Pile in the Vosges and of Les Echets near Lyon, the deposits of the artificially dried up crater lake of Valle di Castiglione on the outskirts of Rome and the surveys of Tenaghi Phillipon in north of Greece. The palynological study of the sequences of deposits of this type has made it possible to draw up rich and complex diagrams (continuous pollen sequences) which, based on the type of floristic species present and the variations expressed as a percentage of their presence, reflect the different paleoenvironmental situations that occur. they took place during the Quaternary and are fundamental for reconstructing its history. The reconstruction of ancient landscapes becomes more complete and detailed if levels with vertebrate fossil faunas are contained in the sedimentary series. In addition to this applicative aspect, the continuous pollen sequences have an important biostratigraphic significance: it was in fact possible to highlight the succession of particular pollen associations (pollen biozones), corresponding to floristic coverings and peculiar climatic-environmental conditions, whose duration over time is underlined by the disappearance or by the diminished presence of some floristic elements which, due to changed conditions, have been forced to change their distribution area. Pollen biozonation is a particularly valid relative dating method in chronological terms and is also widely used for stratigraphic correlations; where it can be flanked by faunal biozonations, it greatly increases its potential. The palynological study of various ancient fluvio-lacustrine deposits in central-northern Italy (Bertoldi 1989), of which the biostratigraphic sequence of mammalian associations is also known, has allowed us to draw up a chronological and paleoecological picture of the Pliocene and the lower Pleistocene which highlights the vegetational phases that characterized the transition from the Tertiary to the Quaternary era. The continuous pollen sequences of northern Europe are undoubtedly those that provide the most complete and detailed picture of climatic variations and European floristic events starting from 2.5 million years ago and still constitute the most used reference model for biostratigraphic correlations. . Based on the pollen biozonation so far recognized in north-western Europe, the first phase of impoverishment of the Pliocene woods, called Pretigliano, corresponds to the first large and sensitive climatic cooling of the glacial type, dated in many places to about 2.3 million years ago. With this event, the series of fluctuations in average temperatures and rainfall began, which profoundly changed the environments and their floristic coverings until a few thousand years ago. The lower part of the Pleistocene (from 2.3-1.8 million up to 700.