Cesare Ravazzi

Late Quaternary history of spruce in southern Europe

The late Quaternary history of fossil spruces in southern Europe (Picea abies (L.) Karsten and Picea omorika (Pancic) Purkyne) is based on 163 selected pollen, charcoal and macrofossil records. The timing of immigration of P. abies is estimated from data where the Picea curve passed the threshold value of 4%. P. abies occupied the southern European mountain ranges – excluding the Pyrenees – during the middle part of the last interglacial. Spruce reached its late Quaternary maximum expansion during the early Weichselian, after which it retired from central Europe and expanded in southern Europe during the middle Weichselian interstadials. A general decline in geographical distribution occurred during the last glacial maximum, and populations were most restricted during the Alpine deglaciation. The concept of ‘glacial refugia’ does not apply to residual populations because current climatic reconstructions relate periods of maximum spruce decline to maximum continental dryness during the growth season, rather than to full glacial conditions. Spruce took part in late glacial and early Holocene tree expansions in the eastern Alps and Carpathian, but failed to spread from residual populations in the Apennines and the Pirin–Rila–Rhodopes Mountains. These differences are explained by the influence of oceanic air masses on upper forest belts with relation to geographic location and maximum elevation of mountain ranges. Late glacial spruce expansion in the Alps coincides with the abrupt warming at 14 700–14 500 yr cal BP. High migration rates were reached in the upper forest belts (e.g. 1500–2300 masl) during the early Holocene, and decreased since about 6 kyr cal BP, as a result of climatic cooling during the Neoglaciation (treeline depression), ecological competition with other tree species (Abies alba), climatic and physical setting of the highest ranges in western Alps, and human impact. The long late Quaternary fossil history of presently isolated spruce stands from the Apennines accounts for their state of genetic differentiation, which could not be fully understood from the shorter time interval of postglacial events.

Vegetation change in a climatic cycle of Early Pleistocene age in the Leffe Basin (Northern Italy)

Abstract The Plio-Pleistocene deposits of the Leffe Basin in the Lombardian Pre-Alps in Italy, first investigated in quarry and lignite mine shafts by Lona in 1950, were recently cored. The pollen record of part of this core reveals a sequence of four climatic cycles. One of them, which is about −1.6 Ma old and particularly characteristic, is discussed here. A long interglacial stage can be identified by the dominance of pollen of deciduous trees of temperate climate. It clearly shows a forest succession of a mixed oak forest of dry-temperate climate, followed by a strong development of a Juglandaceae assemblage rich in Arcto-Tertiary elements, some of them indicating a wet climate. In particular, the Carya peaks appear to be linked to a warm-temperate (14–16°C mean annual temperature), humid, maritime climate with a long growth season, if we compare them with modern and fossil analogs. This stage is followed by a cooling leading to a long phase of wet coniferous forest. This forest succession is subsequently interrupted by a brief period of open vegetation, indicating a drier and colder, continental climate, followed by a new vegetational cycle. The climate evolution is discussed in comparison with other recent pollen successions of uppermost Pliocene age in the Mediterranean area. The cycle described is estimated to have lasted about 30 ka. The entire Leffe lacustrine succession records eight climatic cycles of moderate amplitude. We suggest that this cyclicity has been induced by obliquity forcing. Correlation of the cold phases with the major glacial events of the Southern Alps, as proposed by Venzo (1950) and Lona (1950), is excluded.

K–Ar dating of an early Middle Pleistocene distal tephra in the interglacial varved succession of Piànico-Sèllere (Southern Alps, Italy)

Abstract A distal tephra has been discovered in the varved lacustrine succession of Pianico-Sellere, one of the best-preserved interglacial sedimentary assemblages, south to the Italian Alps. The K–Ar dating of the juvenile glass fraction gives an age of 779±13 ka. This age is supported by the observation of a reverse paleomagnetic direction, probably recorded before the Matuyama–Brunhes transition dated at 780 ka. The tephra belongs to the shoshonite series and the volcanic source is likely located in Southern Italy. The age of 779±13 ka is much older than that of the ‘Riss–Wurm’ interglacial, which was previously suggested on the basis of geological setting and macroflora studies. The Pianico tephra represents the first stratigraphical marker of an interglacial so far unsettled in the Southern Alps.

A new late glacial to early Holocene palaeobotanical and archaeological record in the Eastern Pre-Alps: the Palughetto basin (Cansiglio Plateau, Italy)

A late glacial to early Holocene lacustrine and peat succession, rich in conifer remains and including some palaeolithic flint artefacts, has been investigated in the Palughetto intermorainic basin (Venetian Pre-Alps). The geomorphological and stratigraphical relationships, 14C dates and pollen analyses allow a reconstruction of the environmental history of the basin and provide significant insights into the reforestation and peopling of the Pre-Alps. The onset of peat accumulation is dated to 14.4–14.1 kyr cal. BP, coinciding with reforestation at middle altitudes that immediately post-dates the immigration of Larix decidua and Picea abies subsp. europaea. Plant macrofossils point to the expansion of spruce about 14.3 kyr cal. BP, so far one of the earliest directly dated in the late glacial period of southern Europe. The previous hypothesis of an early Holocene spruce immigration in the Southern Alps from Slovenia needs reconsideration. Organic sedimentation stopped at the end of the Younger Dryas and was followed by the evolution of hydromorphic soils containing lithic artefacts, anthropic structures and wood charcoal. The typological features of the flint implements refer human occupation of the site to the end of the recent Epigravettian. Charcoals yielded dates either consistent with, or younger than, the archaeological chronology, in the early and middle Holocene. Copyright

Interglacial‐glacial cycles in the early Pleistocene of the Leffe basin (Northern Italy): Preliminary report

Palynological studies of the Leffe Basin lacustrine deposits (Lombard Pre‐Alps, Italy) reveal a succession of deciduous mesophytic arboreal communities, coniferous forests and brief phases of withdrawal of arboreal taxa. The pollen record can be easily correlated with a previous pollen diagram by Lona (1950). However, contrary to his interpretation, we believe that the cyclicity shown by vegetation dynamics cannot be correlated with the major glacial events that occurred in the Southern Alps, but perhaps with interglacial‐glacial cycles of moderate amplitude.

Polline fossile di Aesculus aff. hippocastanum L. nel Bacino di Leffe (Pleistocene inferiore). Posizione sistematica e significato paleoecologico

Abstract Fossil pollen of Aesculus aff. hippocastanum L. in the Leffe Basin (Early Pleistocene). Systematic position and palaeocology. A new pollen analysis has been undertaken in the lacustrine and palustrine deposits of Leffe (Northern Italy), in order to re-evaluate the flora, the vegetation dynamics and the climatic change at the southern margin of the Alps during the lowermost Pleistocene. The present paper deals with the systematic position and the ecology of a fossil taxon of Aesculus discovered in the Leffe sediments. The taxonomical approach is based on a comparative investigation on the pollen morphology of all the present-living species and the fossil taxon from Leffe. Some diagnostic features of the apertures and the exine ornamentation allowed to distinguish some groups, almost coincident with the sections in which the genus is presently subdivided. The pollen morphology of the taxa which belong to the sections living in temperate regions and in the subtropical-tropical SE-Asia (section Calot...

Il sito gravettiano di Piovesello sullo spartiacque dell’Appennino settentrionale. Risultati da un’indagine geoarcheologica, archeobotanica, palinologica e archeologica.

Gli insediamenti gravettiani dell’Europa sono tradizionalmente considerati come l’espressione della capacita di adattamento a condizioni climatiche rigide e talvolta estreme (Bocquet-Appel et al., 2005). Nell’Europa meridionale, climi piu miti hanno tuttavia permesso di mantenere il popolamento di vaste regioni e di creare le condizioni per una sostenibilita della frequentazione antropica di aree marginali (Willis et al., 2000), come il margine della pianura padana settentrionale e lo spartiacque appenninico. L’influenza del clima mediterraneo ha quindi favorito la resilienza dei gruppi di cacciatori-raccoglitori e permesso loro di mantenere reti di scambio su lunga distanza. Il settore piu settentrionale degli Appennini, ritenuto un’area priva di ritrovamenti, e stato la cornice di una recente indagine effettuata sul sito Gravettiano antico del Piovesello, localizzato a 870 m di quota sullo spartiacque ligure-emiliano (Peresani et al ., 2016). Ricognizioni di superficie e attivita di scavo programmato hanno permesso di indagare una paleosuperficie con manufatti litici in posizione primaria sigillati da una serie di colluvi limosi. L’integrazione di date radiocarbonio, analisi palinologiche e antracologiche ha concorso a ricostruire il paleoambiente dell’area circostante, dimostrando che il sito doveva trovarsi al di sopra del limite della foresta, in un ambiente semidesertico con vegetazione petrofitica, in prossimita delle fronti glaciali in corso di culminazione durante il GS5 (Peresani et al., in stampa). Le tracce della frequentazione umana si rivelano piuttosto effimere e sono legate all’utilizzo di strutture di combustione e alla produzione di manufatti litici, realizzati anche su materie prime provenienti dalla Francia meridionale. Nel loro insieme, le evidenze del Piovesello permettono di approfondire le conoscenze sulkle strategie messe in opera dai gruppi gravettiani nel quadro del popolamento umano durante la glaciazione. Sul piano paleoecologico, i risultati di questo studio assumono anche nuove implicazioni per la storia della biogeografia delle piante petrofile e dei loro relitti nell’Appennino settentrionale.

Fire on ice and frozen trees? Inappropriate radiocarbon dating leads to unrealistic reconstructions

Comment on Carcaillet & Blarquez (2017) ‘Fireecology of a tree glacial refugium on a nunatak with aview on Alpine glaciers’.