Veget Hist Archaeobot (2006) 15: 357–371DOI 10.1007/s00334-006-0055-9

ORIGINAL ARTICLE

Cesare Ravazzi · Marta Donegana · Elisa Vescovi ·Enrico Arpenti · Marco Caccianiga ·Petra Kaltenrieder · Laurent Londeix ·Stefano Marabini · Stefano Mariani · Roberta Pini ·Gian Battista Vai · Lucia Wick

A new Late-glacial site with Picea abies in the northern Apenninefoothills: an exception to the model of glacial refugia of trees

Received: 23 April 2005 / Accepted: 22 February 2006 / Published online: 27 July 2006C© Springer-Verlag 2006

Abstract We describe a new palaeobotanical site atBubano quarry on the easternmost Po plain, northern Italy.Pollen and macrofossils from river and marsh sedimentsdemonstrate the occurrence of Picea in a Pinus sylvestrisforest growing in a radius of some tens of kilometres southof the sedimentation place, at the beginning of the Late-glacial interstadial. The Late-glacial and Holocene his-tory of Picea in the northern Apennines is reconstructedon the basis of the palaeobotanical record. The sharp cli-matic continentality increase eastwards across the northernApennines from the Tyrrhenian to the Adriatic coast isconsidered significant for the survival of Picea during theLate-glacial. The most critical phase of survival is relatedto the moisture changes and consequent Abies competitionassociated with the last glacial-interglacial transition andthe early Holocene. The residual spruce populations ex-panded during the middle Holocene. The history of Piceain the northern Apennines is a case of ineffective inter-glacial spread of tree populations from pre-existing standsof LGM (Last Glacial Maximum) and Late-glacial age.

Communicated by Pim van der Knaap

C. Ravazzi (�) · M. Donegana · E. Vescovi · E. ArpentiC.N.R. – Istituto per la Dinamica dei Processi Ambientali,via Pasubio 5,24044 Dalmine, Italye-mail: cesare.ravazzi@idpa.cnr.it

E. Vescovi · P. KaltenriederInstitute of Plant Sciences, University of Bern,Altenbergrain 21,CH 3013 Bern, Switzerland

M. CaccianigaDip. Scienze Biologiche, Sezione di Botanica Sistematica eGeobotanica, Universita di Milano,Via Celoria 26,20133 Milano, Italy

L. LondeixDepartement de Geologie et Oceanographie,UMR CNRS 5805, Universite Bordeaux 1,

Avenue des Facultes,F 33405 Talence cedex, France

S. Marabini · S. Mariani · G. B. VaiDip. Scienze della Terra e Geologico-Ambientali,Universita di Bologna,Via Zamboni 67,40126 Bologna, Italy

R. PiniC.N.R. – IDPA at Dip. Scienze Geologiche e Geotecnologie,Universita di Milano Bicocca,Piazza della Scienza 4,20126 Milano, Italy

L. WickInstitute of Prehistory and Archaeological Science,University of Basel,Spalenring 145,CH 4055 Basel, Switzerland

Keywords Plant migration . Quaternary refugia .Apennines . Late-glacial . Picea abies

Introduction

Several questions of palaeoecology and plant geogra-phy related to the history of trees since the Last GlacialMaximum (LGM) have been intensively discussed in re-cent years. One of the major problems is the reliabilityof palaeobotanical methods in detecting small tree popula-tions. Combining pollen and plant macrofossil data makes itpossible to integrate the regional information on vegetationprovided by pollen with the advantages of plant macrofos-sils, to obtain a rich documentation of local vegetation, hightaxonomic detail, and the potential for radiocarbon dat-ing (Birks and Birks 2000). In the Mediterranean regions,however, the available macro- and mega-fossil record is atpresent very sparse and does not allow any detailed recon-struction of past tree migration. Whereas the mechanisms

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Fig. 1 Location of the Italian sites mentioned in the present paper.The solid line shows the present distribution limit of Picea abies at thesouthern Alpine border. Two isolated spruce spots known in the north-ern Apennines (Chiarugi 1936, 1958) are marked A (massif of Alpedelle Tre Potenze – Monte Cimone) and B (Passo del Cerreto, close tothe massif of Monte Cusna). The broken line shows the present coast.A sea level of − 85 m has been adopted (from Lambeck et al. 2004) toshow the Adriatic depression dried up and the coast of the TyrrhenianSea at about 14,500 cal b.p. Site information (name, geographic dis-trict, site type, altitude a.s.l., reference): [Alps] Lago Basso, centralAlps, lake, 2250 m (Wick 1994); Pian di Gembro, central Alps, peatbog, 1350 m (Pini 2002); Palu di Sonico, central Alps, peat bog, 660 m(Gehrig 1997 as Palu di Edolo); Passo del Tonale, central Alps, peatbog, 1883 m (Gehrig 1997); Lago di Lavarone, eastern Italian pre-Alps, lake, 1115 m (Arpenti unpublished); Modolo, peat bog, easternItalian pre-Alps, 434 m (Bertoldi 2000); Palughetto, eastern Italian

pre-Alps, peat bog, 1040 m (Avigliano et al. 2000); Azzano Dec-imo, Friulian foreland, fluvial deposits, 10 m (Pini 2005); [Po valleyfoothills] Lago di Fimon, Berici foothills, lake, 26 m (Wick unpub-lished); Lago della Costa, Euganei foothills, lake, 7 m (Kaltenrieder,unpublished); [northern Apennines] Berceto, Apennines of Parma,lake and peat bog, 815 m (Bertoldi et al. 2004); Lagdei, Apennines ofParma, peat bog, 1255 m (Bertoldi 1981); Prato Spilla, Apennines ofParma, peat bog, 1350 m (Lowe 1992); Lama Lite, Apennines of Reg-gio Emilia, buried archaeological site, 1760 m (Castelletti et al. 1976;Ravazzi 1989); Lago del Greppo, Tuscan side of the northern Apen-nines, lake, 1445 m (Vescovi unpublished); Chioggiola near Pavullo,Apennines of Modena, peat bog, 710 m (Bertolani Marchetti et al.1977); Bubano, Romagna plain, fluvial deposits, 12 m (this paper);Forlı, Romagna plain, fluvial deposits, 30 m (Firbas and Zangheri1934, 1954)

of Holocene Picea expansion can be shown using pollen ac-cumulation rates (Giesecke 2005), the detection of small,scattered populations and the interpretation of their dy-namics with palaeoecological techniques is a difficult task,and conflicting evidence can be obtained from pollen andmacrofossils at different places, such as the question ofglacial survival of boreal trees in southwest Norway (Kull-man 2002; Giesecke and Bennett 2004; Birks et al. 2005).

A recent synthesis of the late Quaternary history of Piceaabies in southern Europe suggests that the maximum con-traction of Picea populations in southern Europe occurredduring the Late-glacial dry phases (Ravazzi 2002). Theimproving climate at the beginning of the Late-glacial in-terstadial about 14,500 years ago favoured the expansion of

spruce in the Alps, whereas in the Apennines Picea failedto spread from residual populations, and expanded onlyseveral thousand years later during the middle Holocene(Chiarugi 1936; Ravazzi 2002). This delay has been re-lated to the influence of oceanic air masses on upper forestbelts (Ravazzi and Pini 2002). An important time lag be-tween immigration and expansion of conifers has also beenproposed in the western Alps (Wick and Tinner 1997), theBalkans (Willis 1994), and the Pirin mountains in Bulgaria(Blyakharchuk et al. 2001).

In this paper, we discuss problems related to the Late-glacial and Holocene tree spread versus survival, immigra-tion and expansion of small populations of Picea in theregion between the northern Apennines and the Po plain in

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Fig. 2 Geological setting ofthe region of Imola, includingthe plain, Apennine foothillsand Romagna Apennines(catchments of rivers Santernoand Sillaro); 2b: Stratigraphiccolumns of the Sillaro andSanterno river catchments

northern Italy. We present a new Late-glacial site yieldingmacroremains of Picea abies in the south-eastern Po plainabout 10 km from the edge of the Apennine foothills (Figs. 1and 2), a crucial region where no palaeobotanical siteshave been dated so far to the Late-glacial. Sites are scarcebecause the relevant deposits are hidden under a thickHolocene alluvial cover which has been deposited since thetime when the Adriatic coastal line reached its maximumtransgression about 7000 cal b.p. (Amorosi et al. 1999) andwith the contribution of strong subsidence rates (Carminatiet al. 2003). The excellent deposits studied here allowed forboth micro- and macrofossil investigations. We consider thedifferent components of the past ecosystems of this allu-vial plain, the dynamics of the plain, and the importance ofazonal habitats for the survival of tree populations, even ofreduced size. The comparison with other palaeobotanicalrecords from the Apennines provides further evidence forthe delay or ineffectiveness of the interglacial spread ofPicea populations from presumed refugia occupied duringcold periods in the Apennines. This exception to the usualmodel of glacial refugia is a major issue to be dealt with inthe mountain chains of the Mediterranean region.

The Bubano site: location and geological setting

The Bubano site (44◦ 25′ 40′′ N; 11◦ 47′ 20′′ E; 12.5 ma.s.l.; town of Mordano, province of Bologna) consists ofa large silty-clay quarry providing raw material for a brickfactory. It is located 10 km north of the town of Imola at thenorthern edge of the Romagna high to middle plain whichis part of the south-easternmost Po plain (Figs. 1 and 2)comprising the rivers Santerno and Sillaro. The region ofImola includes three major physiographical and geologicalregions (Fig. 2):

(i) The Romagna Apennines (Apennino Romagnolo),composed of marine and brackish sediments, show dif-ferent stratigraphies in the Santerno (Miocene to earlyPleistocene) and Sillaro (Cretaceous to early Pleis-tocene) catchments (Fig. 2, top left).

(ii) The northern Apennine Plio-Pleistocene foothills(Gonze Formation and Sabbie Gialle in Fig. 2).

(iii) The plain close to the Apennine fringe, composed oflate Pleistocene to Holocene mainly alluvial plain de-posits (full patterns in Fig. 2). The Bubano area belongsto this region. A succession of three main composite

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Fig. 3 Stratigraphy and correlation of the sections BRUwest andBRUest-A, and the core BRUest-B in the Bubano quarry. SMP =San Martino Palaeosol

intra-valley terraced alluvial systems has been recog-nized from the top of the middle Pleistocene to theHolocene (Fig. 2, top left). At the northern foothilledge, the terraced deposits are replaced by their dis-tal equivalents buried under recurrent overlaps of theplain sediments during periods of high sea-level. Twosettings are distinguished: (a) running down from theedge of the valleys, the uppermost deposits of the plainconsist of a gravelly unit (coarse alluvial fan) of lastpleniglacial age overlain by a finer unit of Late-glacialto Holocene age. The latter sediments are exposed atthe Bubano quarry. (b) in the morphological highs be-

tween the incised streams, the Olmatello Formation isdirectly overlain by a loamy unit with thin palaeosolsrich in Mn pisolites and frequent evidence of plas-tic deformation after discontinuous permafrost condi-tions (Vai 1989). This unit contains late Palaeolithiccherty tools suggesting a last pleniglacial age, and isin turn overlapped by Holocene fine-grained alluvialdeposits with intercalated humic palaeosol horizons,one of which, the S. Martino Palaeosol (SMP in Fig.3), is traced through the entire Faenza and Imola plainsand which has locally yielded Neolithic pottery (4000to 3000 b.c.) (Marabini et al. 1987).

The lower portion of the Romagna plain is a place wheresubsidence continued at a mean rate of about 1.5 mm/yrduring the late Quaternary (Carminati et al. 2003; Anto-nioli and Vai 2004). A coring and mapping campaign bythe Regione Emilia-Romagna has improved our knowledgeof the last two glacio-eustatic cycles (Amorosi et al. 2004,2005). The late Pleistocene cycle consists of shallow ma-rine deposits about 20–40 m thick, followed by an alluvialplain succession more than 70 m thick, topped by an impor-tant erosional unconformity. The second (Holocene) cycleis formed by 20–30 m of thick marine to transitional de-posits related to the last sea-level rise and maximum level.During the maximum Holocene transgression, the coastwas located eight km east of Bubano (Antonioli and Vai2004).

Stratigraphic setting of the Bubano quarry

The 14 m thick succession exposed in the large Bubanoquarry (acronym BRU, Figs. 3 and 4) consists of fine-grained, flat-lying, laterally continuous alluvial plain de-posits. The sedimentation spans from the Late-glacial tothe late Holocene and was interrupted at times by phases ofsoil formation. Several vertisols developed during the Late-glacial, the upper three named Ringhiera III-II-I palaeosols(Fig. 3). The well-developed S. Martino Palaeosol (SMPin Fig. 3) has been identified in the Holocene succession,and it is cross-cut by a meandering sandy channel dividing

Fig. 4 The exposure BRUestin the Bubano quarry (16 Dec.2004)

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the western (BRUwest) from the eastern (BRUest) quarryareas. The lower filling of this channel is dated by woodfragments to 7.8 cal ka b.p. (Fig. 3). A second minor loamychannel filling contains Iron Age to Roman pottery andbrick remains.

The fine-grained succession exposed in the quarry is un-derlain at about 20 m depth by gravels of last pleniglacialage (Marabini and Vai, unpublished data). The mainchronostratigraphic analogues of this succession are theperiglacial detrital sediments at over 800 m a.s.l. in thehigh Santerno valley near Firenzuola (A in Fig. 2) and thealluvial terrace of Pedagna south of Imola (B in Fig. 2).

Material and methods

The sections exposed in the quarry near the village ofBubano during the year 2002 were measured as depths inthe field, described, and periodically monitored to collectfossil remains in 2002–2005.

The palaeobotanical investigation was concentrated onthe lowermost, eastern, part of the Bubano quarry area(BRUest), with special emphasis on the layers yieldingconifer remains.

Pollen analysis was carried out on a section on the frontof BRUest (BRUest-A; 11 samples) and on a core takenwith a modified Livingstone piston corer at 100 m dis-tance (BRUest-B; 16 samples). The two sites were easilycorrelated using lithostratigraphic features seen on the ex-posed quarry face (Fig. 4), although some lateral variationin thickness and grain size occurs, as expected in allu-vial plain environments. Pollen preparation followed stan-dard chemical treatments (Moore et al. 1991), excludingheavy liquids. Pollen nomenclature follows the ALPAD-ABA (Alpine Palynological Database) list of pollen types(version 2000; housed at the Institute of Plant Sciences,University of Bern). Pollen slides from BRUest 12.55 mwere analysed for identification of dinocysts.

From the layers BRUest-A 12.75 m and 12.7–12.8 m,about 200 g of sediment was sieved on 0.5–0.8 and 2 mmmeshes. A qualitative study of macrofossil types was car-ried out on the complete sieved fractions, whereas percent-ages of the most common types were determined by count-

ing 200 items in a subsample. Macrofossil identificationwas based on Bertsch (1941), Berggren (1969), Schochet al. (1988) and a modern reference collection. Conifercones were found during visual inspection of the quarryoutcrop, so they originate from a large volume (>1 m3) ofsand and silty sand belonging to the sandy layer BRUest-A11.6 to 12.65 m depth, naturally washed by rain (Fig. 3).This is the only layer of the entire BRUest exposure that hasyielded macrofossils. The needle fraction from BRUest-A12.55 m was separated, washed with distilled water, dried,and submitted for AMS radiocarbon dating. Five needles ofPicea and Pinus were dehydrated in an increasing alcoholconcentration, included in paraffin wax, and cut with a mi-crotome. The thin sections were rehydrated and observedwith a light microscope.

In order to compare the site of Bubano with other recordsrelevant to the regional dynamics of Picea during the Late-glacial, some well-dated lacustrine sites were selected andpollen accumulation rates of Picea (influx in grains/cm2

and year) were calculated.

Results

Chronology of the Late-glacial sediments and soils

Four radiocarbon dates were obtained from the organic richlayers exposed on the face of the Bubano BRUwest quarryarea (Table 1). The clear organic rich layers were easily cor-related to BRUest following the horizontal, laterally con-tinuous layers. The Ringhiera I-II-III vertisols containedorganic matter within the clayey aggregates. Sieving didnot reveal any macroscopic organic debris useful for dat-ing. Bulk sediment can provide ages either too old or tooyoung, owing to reservoir or contamination effects. Also,the age of the humic portion of a soil may be older oryounger than the real sample (Olsson 1986). This is thecase for BRUwest 10.2 m, the age of which may be tooyoung compared to BRUwest 8.7 m (charcoal fragment).Organic debris occurs in the coarser layer BRUest 12.55 mfrom which a fraction of Pinus and Picea needles has beenseparated and dated by AMS. This age can be regarded ashighly reliable, and fits the correlation with the BRUwest

Table 1 Radiocarbon datesfrom the Bubano quarry

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Fig. 5 Pollen diagrams from the section BRUest-A (left) and the core BRUest-B (right). Lithological patterns as in Fig. 3

ages. We conclude that the basal portion of the Bubanosuccession includes the upper part of the Late-glacial, start-ing earlier than the Bølling-Allerød (Late-glacial intersta-dial) (16–14 m depth of the exposures). The Ringhiera IIIpalaeosol burying event is very close to the onset of theinterstadial, whereas the Ringhiera II and I palaeosols wereformed during the interstadial.

The palynological record

The record of the two sequences studied is shown in sep-arate pollen diagrams which have been correlated on thebasis of lithostratigraphy (Fig. 5). General features com-mon to both sections are: (1) the dominance of Pinussylvestris/mugo, except in some intervals which are rich inherbs and also in reworked pollen grains (>14 m and 11.5–10.8 m depth); (2) the absence or sporadic pollen grains ofthermophilous trees; (3) the very poor pollen representationof trees of oceanic climate (Abies, Fagus); (4) the nearlycontinuous curve of Picea, and its expansion above theRinghiera III palaeosol; (5) the expansion of Betula abovethe Ringhiera III palaeosol; and (6) the variable content ofxerophytes as well as terrestrial herbs, wetland and marshherbs, and aquatic plants (Potamogeton) reflecting the suc-cession of organic-rich and detrital layers. The fungal sporeGlomus, an endomycorrhizal fungus occurring on the rootsof a variety of host plants, is abundant in the organic-richlayers. It suggests aerobic conditions and active decompo-sition of organic matter. Among the group of xerophyticplants, Hippophae is remarkably abundant. Rare types ofinterest for the palaeoecological reconstruction are Rumex

acetosella, Menyanthes, Limonium humile type, includingseveral species today living in Italy (Turner and Blackmore1984), Papaver argemone type (including P. argemone L.;Kalis 1980), and Lythrum portula (including L. portula (L.)D.A.Webb; Booi et al. 2003).

The comparison of the pollen records within the litho-stratigraphically correlated interval (13.3–12.8 m depth)reveals significant differences in pollen percentage values,such as chenopods, although the general features of thepollen records are similar in the two studied sites, with dom-inance of Pinus and low occurrence of Picea and Betulawith continuous curves and peaks of wetland and aquaticplants. As the sites are only 100 m apart, this observationis taken as an evidence of rapid lateral changes in tapho-nomic and environmental conditions, as is usual in alluvialsystems.

Reworked pollen and dinocysts

The category of reworked pollen grains, with an abradedwall surface, consists of early Pleistocene types such asTsuga. Also included here are a few pollen grains ofPinus and Picea with lower reflectivity of the pollen wallcompared with fresh grains. By combined observation ofcorrosion and wall reflectivity, reworked pollen grains areclearly distinguishable from normal, well preserved grains.The reworked component also includes dinoflagellatecysts, which occur in variable abundances all along therecord. A sample from BRUest 12.55 m was analysed indetail. The dinocysts were badly preserved and often wrin-kled. The following types were recognized: Spiniferites

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Fig. 6 Cone fragments ofPicea (A) and Pinus sylvestris(B, D), detail of scale andapophysis (shield at the outerend of the cone scales) of Pinussylvestris (B1), and badlypreserved, small cones of Pinussp. (C)

ramosus, S. bulloideus, Achomosphaera ramosasimilis,Nematosphaeropsis cf. lemniscata, Systematophoraplacacantha, Reticulatosphaera actinocoronata, andCleistosphaeridium?/Impletosphaeridium?. Spiniferitesspp. were relatively the most abundant. Systematophoraplacacantha is an extinct species which lived from theYpresian to Messinian periods, with its greatest occur-rence from the Rupelian to Serravallian. Reticulatosphaeraactinocoronata is also extinct (Priabonian to Piacenzian,with its greatest occurrence during the Oligocene andMiocene). Nematosphaeropsis lemniscata (Ypresian torecent, but also present since the Chattian) lives in marinewater and cannot be considered as autochthonous here.Other genera have both a relatively wide stratigraphicaland ecological range. These dinocysts cannot have grownin Late-glacial ephemeral lakes or alluvial plains. Wetherefore conclude that they are reworked, mostly fromOligo-Miocene sediments, such as the sandstone belong-ing to the Marnoso-Arenacea Formation, outcroppingextensively in the upper Santerno catchment (Fig. 2).

The macrofossil record

Only the samples BRUest 12.75 m (peaty vertisol) andBRUest 12.55 m (sands) contained a component of macro-scopic organic debris. The macrofossil spectrum BRUest12.75 m was composed of herbaceous stems and leaves,among which were in situ rhizomes and fruits of Cyper-aceae including Cladium, Scirpus and Carex, Lycopus, andanimal remains. Conifer parts were absent. This spectrumis referable to the autochthonous flora growing in the wet-land (Ringhiera III palaeosol) before the alluvial depositionof conifer-rich silty sands. In BRUest 12.55 m, the organicfraction of the sand was dominated by small-sized frag-ments of needles, wood, and sporadic and mostly abradedcones outside the sample size analysed (Figs. 6 and 7).Eight Pinus cones have been collected and analysed. Theshape of the apophysis (Fig. 6B, B1 and D) is specificfor Pinus sylvestris. A few fragmentary cones and severalcone-scales of Picea have also been collected. Even themost complete cones of Picea (Fig. 6A) are poorly pre-

Fig. 7 Needles of Picea (1–4) and 2-needle short shoot of Pinus(5–6). From BRUest 12.55 m, dated 12080 ± 60 b.p. Scale: 1 cm

served, but identification at genus level is possible becausethe cone scales are much larger and lack a distinct apoph-ysis. Charred remains were not present. The cross sectionsof the Pinus needles display two vascular bundles (Fig. 8),typical of Pinus subgenus Diploxylon. The absence of resinducts in the parenchyma allows to exclude the Pinus nigragroup and points to P. sylvestris or P. mugo (Krussmann1986). Although P. mugo is not represented by cones sofar, we cannot exclude its occurrence, because most of thePinus cones are strongly abraded and unidentifiable (Fig.6C). Betula bracts and seeds were not abundant. They areall identified as B. alba. Alnus sp. is represented by onecone bract only (less than 1%).

Discussion

Dispersal, sedimentation, and preservation of plantparts: pollen versus macroremains

The main quantitative differences between pollen andmacrofossil abundance of conifer parts can be examined

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Fig. 8 Cross section andscheme of related anatomicalstructure of a needle of Picea(a, a′) and Pinus subgen.Diploxylon (b, b′), from sampleBRUest-A 12.55 m dated to12,080 ± 60 b.p. ep: epidermis;hy: hypodermis; st: stoma; vb:vascular bundle; vbs: vascularbundle sheath; tf: transfusiontissue

in sample BRUest 12.55 m. The representation of Piceaneedles (14 and 9% in different size fractions) is slightlylower than that of pines (14 and 20%). However, Picea is20 times less represented in pollen percentages than Pinussylvestris/mugo. These differences are due to differentproduction, dispersal and preservation characteristicseither of the vegetative or the reproductive organs ofthese genera. Pinus sylvestris and P. mugo are consideredto be pollen super-producers, with a production of oneorder greater than Picea (Jackson and Lyford 1999). Thesedimentation rate of the pollen of Picea and Pinus in airis 5.5 and 4.2 cm/sec respectively (Jackson and Lyford1999), and their respective buoyancy on the water surfaceis not much different (Bernard and Pons 1985; Heusser1988). On the other hand, the number of needles dispersedby Picea is higher than by Pinus (Kozlowski 1973). Pineneedles are less suited to floating in water as they fall apartinto small pieces.

The proportion between bisaccate conifer tree pollen andthe pollen of smaller broad-leaved trees such as Betulaand Alnus may be taphonomically increased by differentbuoyancy (Heusser 1988). A possible hydraulic selectionaccording to sediment size (Brown and Pasternack 2004)and different decantation in water according to pollen size(Borgatti et al., in press) are difficult to judge from theBubano record because of further post-depositional biasdue to variable pollen preservation. Indeed, the basal weath-ered clay (16–14 m) shows deteriorated pollen grains, lowpollen concentration, and abundance of Cichorioideae. Theoverlying peaty vertisol (Ringhiera III) displays a similarconcentration of Cichorioideae, but their percentage valuesare much lower. This suggests that the assemblage of thelower part was affected by selective deterioration of pollengrains in partially oxygenated sediments, thus producingan over-representation of Cichorioideae. On the other hand,the abundance of Aster type is related to levels rich in or-

ganic matter and may represent wetland plants colonizingseasonal ponds. The increasing trend of Betula pollen, ir-respective of these lithological changes, can be related toregional dynamics rather than to local sedimentary changes.

The provenance of conifer remains

The assemblage rich in conifer remains is probablyallochthonous, as shown by the following evidence: (a)the conifer macrofossils mainly occur in coarse-grainedlayers. They sometimes represent the selected finer fractionof litter, floated and deposited during alluvial events; (b)conifer macrofossils do not occur in the clayey and peatyvertisol, which bears evidence of only herbaceous plantsgrowing in situ.

We now raise the question of provenance. The palaeogeo-graphic setting of the Romagna plain during the LGM andLate-glacial (Antonioli and Vai 2004) points to a small rivercatchment of Apennine origin (river Sillaro or Santerno, seeFig. 2), excluding the river Po and the other major water-courses. Given that the Sillaro and Santerno catchmentsare quite similar in petrography, the only reliable methodto distinguish between them is the presence of reworkedmicrofossils common in Apennine marine bedrock of Cre-taceous and Cenozoic age (Ravazzi et al. 2004). BRUest12.55 m contains reworked dinocysts of Oligo-Mioceneage, which favours the river Santerno (Sect. 4.3.) as the ori-gin. Reworked pollen may instead originate from middleor late Pleistocene deposits, outcropping as terraced unitsin the foothills of the Imola region (Fig. 2).

In conclusion, the conifer remains may originate fromany distance within the Santerno catchment, either in theplain close to the sedimentation site, or in the foothills 10-15 km to the southwest, or even in the mountain sector upto 45 km southwest of Bubano.

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Table 2 Macrofossil spectra (% values) of samples BRUest-A 12.7-12.8 m and BRUest-A 12.55 m (basal part of section BRUest-A)

+ : presence <1%. Lithology: BRUest 12.7–12.8 m laminated siltyclay with woody fragments; BRUest 12.55 m: alternating centimetrethick layers of coarse and silty sands, with dispersed plant macrore-mains in the coarser sands

Reconstruction of the sedimentary environmentand vegetation patterns

The investigated deposits show a phase of active aggra-dation of the Santerno alluvial plain during the upperpart of the Late-glacial. Individual coarse-grained layersof laminated sands and silty sands, including BRUest12.55 m, represent levee episodes, whereas imbeddedthin-grained clay, usually rich in organic matter, wasformed in marshy environments. Typical marsh herbs suchas Cladium, Scirpus, Carex and Lycopus are associatedwith these deposits (Table 2). The marshy depositsdisplay slickensides and pedoturbations representing theeffects of mud-cracks and root activities during phases of

desiccation. Calcareous concretions occur in the deeperpart of the vertisol profiles, especially in Ringhiera IIand in the organic-rich soil BRUest-B 14.0–14.2 m. Suchpedogenic processes (vertisol features) are common in theLate-glacial and Post-glacial evolution of the lowermostPo plain, where frequent seasonal alluvial phases led tothe formation of extensive marshes, periodically affectedby decreased river discharge and prolonged desiccation.The development of a calcium-rich horizon in the deeperpart of the profile, with frequent carbonate nodulesfilling pedotubules, suggests lateral movement of groundwater.

The sediment evidence also suggests dry sand barswhich would have been covered by pioneer vegetationof ephemeral grasslands dominated by therophytes andhemicryptophytes, indicated by pollen of Papaver arge-mone, Lythrum portula, Chenopodiaceae, Polygonum spp.,Compositae, Rumex acetosella, and Limonium humile type.Papaver argemone is today considered an archaeophyte,growing as a weed in cereal fields (in the community ofsyntaxonomic order: Centauretalia cyani Tx. 50; Pignatti1982; Scholz 1996; Preston et al. 2004). Taxa with similarpollen morphologies do not occur in the modern Europeanflora, except in Greece (Layka 1976). The finding of thischaracteristic pollen in BRUest 12.86 and 12.94 m suggeststhat one of the primary habitats of this plant, before the agri-cultural revolution, was related to ephemeral grasslands onalluvial deposits.

The absence of trunks, stems, and large wood alongthe studied succession and over the entire large pit ofBubano rules out the possibility that the site was woodedbefore and during the Late-glacial interstadial. This is sup-ported by the detection of only small root structures withinthe palaeosols. However, the considerable pollen repre-sentation of Juniperus and Hippophae suggests that scrubvegetation formations could have developed on the allu-vial plain, as a serial stage towards the development ofsteppe woods formed of Pinus sylvestris, Betula alba, Al-nus glutinosa, and, eventually, Picea abies on stable soils.The pedological and palaeoecological setting discussedabove suggests that the edaphic conditions were extremelydry, and unfavourable for the spread of broad-leaved ther-mophilous trees, the pollen of which does occur, but onlysporadically.

The pollen record does not show clear evidence of theimpact of the Late-glacial interstadial climate improvementon the development of vegetation, apart from a possibletrigger on Betula and Picea expansion observed betweenthe levels dated to 12,680 and 12,060 b.p.

The Late-glacial history of Picea in the northernApennines

The present distribution of Picea abies in the Apenninesis restricted to two small areas near the divide betweenParma and Tuscany (Toscana) (Fig. 1A and B). One smallpopulation grows above the Abies belt at Alpe Tre Potenze,above the Abetone pass, between 1450 m altitude and the

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Fig. 9 Short pollen diagrams from sites recently investigated in the eastern part of northern Italy, showing selected pollen percentage curvesand influx (site information in Fig. 1)

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divide at 1850 m (Fig. 1A). The main question addressedhere is whether these high-altitudinal spruce stands havea phylogeographical linkage with the Late-glacial popu-lation located in the foothills of the northern Apenninesor at the border with the Po plain documented in this pa-per. The latter is the only candidate so far available, butthe palaeobotanical evidence is incomplete and controver-sial (Fig. 9). We discuss first the survival of Picea duringthe Late-glacial and the relevant ecological and climaticfactors.

The Bubano record shows that Picea was a minor com-ponent in the Pinus sylvestris – Betula woodlands whichbecame established in the Apennine foothills or the highestpart of the plain before and during the Late-glacial inter-stadial. Other evidence of LGM and Late-glacial Piceais scattered along the northern side of the Apennines andthe border with the Po plain. The “glacial” finds of Piceafrom Forlı (Firbas and Zangheri 1934, 1954), though un-dated, are currently believed to belong to the LGM or tothe Late-glacial because of their lithostratigraphic position.To the west, the records from Lagdei and Berceto in theApennines of Parma (Fig. 1) also have a continuous Piceapollen curve, but only before the Late-glacial interstadial(Fig. 10; Bertoldi 1981; Lowe 1992; Watson 1996; Ravazzi2002; Bertoldi et al. 2004). This earlier Picea disappear-ance in the western northern Apennines has its counterpartin the opposite behaviour of Abies. In the Parma Apennines,Abies expanded at the beginning of the Late-glacial inter-stadial and very soon reached the watershed (Lowe 1992;Ravazzi 2002). At Lago del Greppo, the Abies expansionis delayed to the early Holocene (Fig. 9F). We propose thatthis delay was triggered by regional climatic differences,and that the opposite behaviour is the consequence of com-petition between Abies and Picea under different climaticregimes. Today, the Tyrrhenian side of the northern Apen-nines is affected by strong rains, with averages between1400 and 2500 mm/year (Fig. 11). This pattern is producedby orographically forced upslope precipitation in autumnand winter (Frei and Schar 1998), related to cyclogene-sis centred on the Tyrrhenian Sea during the cold season(Mennella 1967; Borghi and Giuliacci 1982). In contrast,the eastern, Adriatic, side is drier. Furthermore, 14,500years ago the sea level was 85–90 m lower than at present(Lambeck et al. 2004), and consequently the Adriatic de-pression was still part of the Po plain (Fig. 1). This greatercontinentality on the Adriatic side of the Apennines wasaccompanied by loess deposition during the LGM (Cre-maschi 1990), and these effects persisted at least until theBølling-Allerød (Late-glacial interstadial), as proven by theLate-glacial micromammal sequence preserved in caves(Torre et al. 1996). The dry climate on the Adriatic sidemay have prevented the expansion of Abies, a moisture de-manding species. The delayed Abies expansion at the onsetof the Holocene may be related to increased moisture, atthe same time as the early Holocene sea ingression over thenorthern Adriatic depression (Correggiari et al. 1996). Thistime lag, in turn, may have reduced competition and thusfavoured the survival of Picea on the north-eastern slope ofthe Apennines during the Late-glacial.

Early Holocene local spruce extinctions and middleHolocene expansion

The autochthony (native status) of the modern Picea standsgrowing in the northern Apennines was demonstrated byChiarugi (1936) through a pollen record at Lago del Greppo(Alpe Tre Potenze). This site is being investigated in moredetail by one of us (E.V.). Selected pollen curves and therelevant radiocarbon chronology (Fig. 9F) clearly show theexpansion of Picea from 6600 b.p. (7470–7500 cal b.p.)after a long period of small records, compatible with theoccurrence of small populations, between the Late-glacialand the expansion event. This expansion is marked by astrong increase of Picea pollen influx and a related decreaseof the main competitor Abies. Similar trends of oppositePicea and Abies behaviours can be observed in the moun-tain belt of the central and eastern Alps, at sites where Abiesand Picea were co-dominant in the woods. Here, the polleninflux of Picea is suppressed by an expansion of Abies (forexample, Pian di Gembro, Fig. 9A, level 560 cm; Lago diLavarone, Fig. 9B, decreasing trend starting at 405 cm).The importance of Abies as the main competitor of Piceais shown in the western Alps, too (de Beaulieu et al. 1993),whereas it is not evident in the record from the Po plainand the northern foothills at the Po plain border. Neithertree was part of the Late-glacial – Holocene vegetation onthe plain around Venice, thus a migration through the plainfrom the Alps towards the Apennines, as hypothesised onthe base of molecular data (Scotti et al. 2000), is unlikely(Figs. 9C, D and 10).

The dynamics observed at Lago del Greppo has no par-allel in the northern Apennines. Picea pollen is generallyabsent or only scattered during the early Holocene (PratoSpilla, Fig. 10), and disappears later (Prato Spilla andother records shown in Cruise 1990; Lowe 1992; Loweand Watson 1993; Watson et al. 1994; Watson 1996). Apeculiar history is documented at Lama Lite, 1760 m a.s.l.,Monte Cusna (Fig. 1). A Mesolithic camp dated to thevery beginning of the Holocene (Castelletti et al. 1976)is associated with a buried soil containing Picea pollen,covered by colluvial deposits and cambic soils containingAbies and Fagus pollen only (Ravazzi 1989). Interestingly,this site is located only 12 km east of Passo del Cerreto,the second small modern site of Picea in the northernApennines (B in Fig. 1). A late Holocene pollen recordhere displays a continuous curve of Picea, though with lowvalues (Chiarugi 1958). These data suggest a phylogeo-graphical link between the Mesolithic Picea populationand the modern one in the region of the Cusna mountainrange. A report of large peaks of Picea pollen in the lowermountain belt of the Romagnan Apennines (AppenninoRomagnolo) (palude della Chioggiola near Pavullo, 700 ma.s.l., Fig. 1; Bertolani Marchetti et al. 1977) has not beenconfirmed by a recent re-investigation. Actually, at thissite Picea occurs with low pollen values (0.5–2%) duringthe middle Holocene (Vescovi, in preparation).

In synthesis, the still very fragmentary record from thenorthern Apennines suggests that a few Picea populationssurvived the Late-glacial to Holocene transition, and that

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Fig. 10 Picea pollen percentage curves from selected sites in the Alps, the Apennines and the plain plotted against calendar age. Siteinformation in Fig. 1; Sagistalsee from Wick et al. (2003)

Fig. 11 Average annual precipitation (mm/year) of the northernApennines and the central Alps, trentennial series 1961–1990 (fromDesiato et al. 2005; Frei and Schar 1998)

they survived until now only on two mountain ranges,whereas elsewhere they became extinct during the earlyHolocene. The residual Picea populations that survived thecompetition with Abies expanded during the mid Holocene.The following physical information about the position ofthe modern spruce stand at Alpe Tre Potenze may help us tounderstand how spruce could have survived there for manymillennia. Although the site of Lago del Greppo (1440 ma.s.l.) lay within the Abies belt since 8900 b.p. (Fig. 9F),the uphill ridges of Alpe Tre Potenze and Monte Cimone

reach an altitude of 1750–2165 m, which is the maximumelevation of the northern Apennines, and above the upperlimit of Abies. Factors that favour Picea over Abies are acool microclimate on the northern slope because of the pre-vailing northwest-southeast orientation of the divide, andthe sandstone bedrock which is acidic and tends to formcoarse loose material. The mountain summits of the north-ern Apennines divide are on average much lower (about1600 m) than those of the ranges of Alpe Tre Potenze –Monte Cimone (1940–2165 m) and Cusna (2120 m), so theformer were reached by the Abies belt at the very begin-ning of the Holocene (Lowe 1992; Watson 1996), whichmay have hindered the Holocene migration of Picea.

Conclusions

The new palaeobotanical site of Bubano helps to reducethe knowledge gap about vegetation and climate history ofthe southern part of the Po plain and the northern Apen-nine foothills in northern Italy during the final stages ofthe Pleistocene. Pollen and macrofossils contained in riverand marsh sediments demonstrate the occurrence of Piceain Pinus sylvestris woodland vegetation growing not farfrom the sedimentation place at the beginning of the Late-glacial interstadial (roughly correlated to Interstadial G1in the GRIP stratigraphy). According to sedimentologicalevidence, this conifer woodland covered the plain or thefoothills in a radius of 15–45 km south of the Bubanoquarry. At that time this part of the Romagna plain wastreeless and subject to active aggradation of fine sediments

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with pioneer vegetation of ephemeral grasslands rich intherophytes (short lived, annual plants). The absence ofAbies and broad-leaved thermophilous trees together withthe occurrence of shrubs and herbs adapted to dry sitesand pedogenic features characteristic of a very dry sea-son point to a continental climate locally marked by dryedaphic conditions, which would have been unfavourablefor the establishment of broad-leaved thermophilous trees.

The occurrence of Picea during the Late-glacial atBubano provides the opportunity to trace the origin of therestricted Picea stands which grow at present in the re-gion of the Alpe Tre Potenze and Monte Cusna mountainranges. During the LGM and at the onset of the Late-glacial,several records in the northern Apennines demonstrate theoccurrence of native Apennine populations. In the west-ern ranges of the Parma Apennines, the Picea record endsbefore the Late-glacial interstadial, at the time of Abiesexpansion. Eastwards, in the Romagna Apennines, Abiesexpansion was delayed until the early Holocene and sev-eral Picea records extend into the Holocene. This oppositebehaviour between Picea and Abies has been related to theeffects of competition between the two taxa under differentclimatic regimes. The sedimentary and palaeobiologicalrecords provide evidence that the climate of the Adriaticdepression was much more continental than on the Tuscanyside, which was exposed to moist winds from the Tyrrhe-nian Sea. Delayed expansion of Abies in the easternmostsectors of the northern Apennines may have favoured thesurvival of Picea there during the Late-glacial.

Further Abies expansion in the Adriatic region at the onsetof the Holocene was related to the moisture increase con-nected with the early Holocene sea transgression over thenorthern Adriatic depression. During the early Holocene,competition with Abies is considered to have been signif-icant for the extinction of parts of the residual Picea pop-ulations, which only survive until now at two high altitudemountain ranges. These two residual Picea populations thatsurvived the competition with Abies expanded during themid-Holocene.

The Late-glacial and Holocene history of Picea in thenorthern Apennines is a case of delayed or ineffective inter-glacial spread of tree populations from presumed survivalareas that existed during cold periods. Similar develop-ments are also shown in other Mediterranean regions, suchas in the Balkans (Stefanova and Ammann 2003). The fac-tors responsible for failing migration in our study regionare partially geographical, namely the low altitude of themain divide in the northern Apennines, and partially eco-logical, including the early and effective competition byother trees during the Late-glacial, a time when the Piceapopulation in the area was already much reduced. There-fore, although there is no doubt that climatic change wasthe driver for this history, the cold-extreme phase of theglacial-interglacial cycle, that is the LGM interval between19 and 30 ka ago (Lambeck et al. 2002), was not respon-sible for extreme reduction or even extinction. This is con-trary to the general assumption concerning glacial refugiaof trees, that the coldest stages of the last glaciation werethe most critical periods for the survival of trees (Bennett

et al. 1991). Instead, the dramatic changes associated withthe last glacial-interglacial transition and the overall largemoisture changes may explain the Late-glacial collapse ofPicea populations in Mediterranean mountains and the de-layed expansion during the middle or late Holocene.

Acknowledgements We are pleased to dedicate this paper toBrigitta Ammann, who first highlighted situations of delayed coniferexpansion in the Balkans, recalling the problems discussed in thepresent paper. The results of this study have been achieved thanksto her steady support, and within the project SNSF 3100AO-101218“Long term population dynamics of major forest trees under stronglyand weakly changing climates”, which is currently in progress underher coordination. This is also a contribution to the PalaeoclimatologyResearch Line of the C.N.R. – Istituto per la Dinamica dei ProcessiAmbientali, Section of Milano.

The core BRUest-B was obtained with the help of the IPS, Univer-sity of Bern, thanks to the power of W. Tanner and the helpfulnessof W. Tinner and D. Colombaroli. We thank the Museo Tridentino diScienze Naturali for the permission to use the pollen record from theLavarone lake, a part of the OLOAMBIENT project coordinated bythis Museum and funded by Provincia Autonoma di Trento, ServizioUniversita e Ricerca Scientifica. We are indebted to Federica Quagliaand Laura Lattuada, who skilfully prepared the thin section of fossilneedles under the direction of G. Vailati (Department of Biology ofthe University of Milan). The advice of Pim van der Knaap (Uni-versity of Bern), as well as the accurate revision by T. Giesecke(University of Uppsala) and an anonymous reviewer, were greatlyappreciated.

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