Palaeoenvironmental significance of plant macrofossils from the Piànico Formation, Middle Pleistocene of Lombardy, North Italy

Compressed leaves and carpological assemblages from the Piànico Formation, which was deposited into the Piànico-Sèllere palaeolake, are newly studied, and the early 20th century leaf collection by Rytz is preliminarily revised. Despite the occurrence of two tephra layers, the dating of this Formation is still controversial: a long temperate period (Piànico-Sèllere Interglacial), corresponding to its lower BVC (“Banco Varvato Carbonatico”) member, would either correlate to OIS 11 or to OIS 19. The macrofloral record of the BVC member includes the locally extinct species Acer cappadocicum Gleditsch sensu lato, Pinus peuce Griseb., Prunus lusitanica L., Pyracantha coccinea M.J. Roemer, and Rhododendron ponticum L. var. sebinense (Sordelli) Sordelli. A number of other locally extinct species (Picea omorika (Pancic) Purkine, Rhamnus alaternus L., Tilia caucasica Rupr.) have not been figured and described in detail by the reporting authors, thus they should be confirmed by better documentation. From the biostratigraphic point of view the Piànico fossil flora does not display taxa typical for the Early Pleistocene (e.g. Carya, Liquidambar, and Eucommia), and a single fruit remain may putatively be assigned to the extinct species Potamogeton marginatus Dorofeev, which occurs from the Holsteinian to the Weichselian in Eastern Europe. Re-examination of the plant macrofossil record confirms that aquatic plants are absent from the leaf assemblages of the Piànico Formation and only very rarely occur as carpological remains (Najas marina L. and Potamogeton). The presence of lake-margin species suggests that patches of sedge and reed marshes bordered the lake at the beginning of BVC deposition, and later decreased or disappeared. On the low mountain slopes, steeply dipping into the lake, closed and prevalently deciduous woody vegetation was growing during the BVC deposition. Evergreen shrubs to small trees might well have grown as understorey in the deciduous woodlands (Buxus, Ilex) or in more open, drier rocky places (especially Pyracantha). The macrofossil evidence suggests that, unlike Picea abies (L.) Karsten, P. peuce and Abies cf. alba were not restricted to higher altitudinal belts. The occurrence of P. abies cones in the basal layers of the MLP (“Membro di La Palazzina”) member most probably indicates the settlement of spruce close to the lake-shore. This would be in agreement with the cooling-related contraction of broadleaved forests and the expansion of cool-adapted vegetation types to lower elevations, as indicated by palynological data of the upper part of the Piànico Formation.