PALYNOSTRATIGRAPHY OF THE LAST GLACIAL PERIOD IN THE VOLCANIC REGION OF CENTRAL ITALY

PII: S1040 –6182(97)00065–7

Quaternary International, Vol. 47/48, pp. 3 —20, 1998. Q 1998 INQUA/Elsevier Science Ltd All rights reserved. Printed in Great Britain. 1040— 6182/98 $19.00

PALYNOSTRATIGRAPHY OF THE LAST GLACIAL PERIOD IN THE VOLCANIC REGION OF CENTRAL ITALY M. Follieri, M. Giardini, D. Magri and L. Sadori Dipartimento di Biologia Vegetale, Universita% degli Studi di Roma **La Sapienza++, P.le Aldo Moro 5, I-00185 Roma, Italy The summarized pollen records from the crater lakes of Valle di Castiglione, Lagaccione, Lago di Vico and Stracciacappa, in the Lazio region, are presented and correlated with each other. They outline the history of the vegetation during the last glacial period. The local name ‘Lazio Complex’ is used to describe seven main fluctuations of trees during the Pleniglacial. The succession of the main forest and non-forest periods of the last climatic cycle is generally similar to what is known in central and northern Europe, but the floristic composition and the vegetational configurations seem much more complex and sensitive to climatic changes. The history of Zelkova, Abies, Picea, Corylus, ºlmus, Carpinus betulus, ¹ilia and Fagus in central Italy is outlined. Q 1998 INQUA/Elsevier Science Ltd. All rights reserved

of its geomorphology. Lazio lies between the Tyrrhenian Sea to the west and the Apennines chain to the east, its elevations range from 0 to over 2000 m above sea level, its coasts are extensive, and its lakes and rivers numerous. Along the coasts, flat areas with PlioQuaternary marine and continental deposits extend inland towards the Meso-Cenozoic limestone mountains, which face the sea in the southern part of the region. But Lazio is also characterized by a considerable extension of volcanic rocks, covering approximately 30% of its area (Accordi and Carbone, 1988). Hydromagmatic explosions, generating maar craters, occurred in most of the districts of the ‘Roman comagmatic province’ (860 to 40 ka; Fornaseri, 1985), particularly at the end of their activity (Accordi and Carbone, 1988). The lakes considered in this paper (from north to south: Lagaccione, Lago di Vico, Stracciacappa and Valle di Castiglione) belong to the four different volcanic districts of this province, the Vulsini, Vico-Cimini, Sabatini and Colli Albani volcanic districts, respectively (Fig. 1). The climate of the region is particularly complex because of the geographic position: on one side there is the mild influence of the Tyrrhenian Sea (the mean annual temperature reaches 16°C at some coastal weather stations), and on the other there are the Apennines which bar the way to westerly air streams and cause high rainfall (the average annual precipitation exceeds 1600 mm at some mountain stations). A wide range of local modifications is superimposed on this general trend, producing a remarkable variability of climatic and ecological conditions; so, for example, the number of months with summer aridity varies from 0 to 4. In a recent work, Blasi (1994) defines 15 different phytoclimatic units in Lazio, described also in floristic, physiognomic and syntaxonomic terms. Lazio, located at the border between the Temperate Region and the Mediterranean Region, shows a marked transitional character; the existence of weather stations with some summer aridity in the temperate sector on the one

INTRODUCTION The geomorphology of the mid-Tyrrhenian side of Italy is strongly influenced by the activity of Quaternary volcanism, which variously modelled the surfaces of a wide region and determined favourable situations for the formation of crater lakes. The sediments from volcanic lakes are particularly suitable for palaeoenvironmental investigations: when collected from the deepest part of the basins, they generally provide continuous sequences, showing relatively undisturbed sedimentation when significant inflows are absent. In the Lazio region, where volcanic activity ended long before the Holocene began, and where the lacustrine sedimentation was not interrupted by ice cover, it is possible to find long sequences enabling the history of vegetation during the last tens, and sometimes hundreds, of thousands of years to be studied with continuity (Follieri et al., 1993). Lazio, in the heart of the Mediterranean basin, is a particularly suitable region for biostratigraphical studies on the last glacial period. In fact, besides having long continuous records from crater lakes, it has a vegetation very sensitive to climatic changes, and certainly had sites favourable for the survival of mesophilous and thermophilous trees also during periods when they had disappeared from other regions, either too cold or too dry. The pollen records from four crater lakes enable a tentative assessment of the history of the vegetation in the region during the last glacial period, based on the works published at the time of the submission of the present paper (July 1994).

STUDY SITES The Lazio region is characterized by a remarkable variety of natural environments, mainly because of its particular geographic position in the centre of the peninsula, the diversity of its lithology and the complexity 3

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M. Follieri et al. TABLE 1. Location and a brief description of the investigated sites (VdC: Valle di Castiglione; Lgc: Lagaccione; V.I: Lago di Vico, core I; Stra: Stracciacappa)

Site

VdC

Lgc

V.I

Stra

Latitude E Altitude (m.a.s.l.) Max. elevation catchment area (m) Catchment area (km2) Distance from the sea (km) Volcanic district Present situation Lake diameter (km) Mean annual temperature (°C) Mean annual precipitation (mm) Geoelectrical investigations Length of core (m) Estimated age (yrs) Analysed pollen samples

41°53@ 44 768 60 36 Albani Dried out 1 15 ca. 800 Yes 88.25 '250,000 380

42° 34@ 355 481 2 35 Vulsini Dried out 0.9 14 950 Yes 49.50 ca. 100,000 191

42°19@ 510 965 38 38 Vico-Cimini Extant ca. 5 13 '1500 No 15.20 ca. 90,000 257

42°10@ 220 358 (2 29 Sabatini Dried out 1 14 1050 No 32.60 ca. 60,000 147

hand, and of stations with fairly high rainfall in the coastal belt on the other, induced Blasi (1994) to propose two phytoclimatic regions of transition (Temperate Transition Region and Mediterranean Transition Region). This complex climatic situation also explains the presence of elements belonging to the Mediterranean flora inland in the region, and, on the contrary, of elements of temperate flora (Eurosiberian) along the coast. On the whole, about 3000 species of vascular plants have been assessed (Anzalone, 1984), taking into account also the further complication of a chorological connection, peculiar to Lazio, with southern and eastern floras, as already shown by Montelucci (1976—77). »alle di Castiglione The Valle di Castiglione crater (Fig. 1) is an eccentric explosive centre, located on the northern flank of the Colli Albani volcanic district, about 20 km east of the centre of Rome (Table 1). The lacustrine sediments which filled the original depression have been drilled continuously in a borehole, 88 m deep. The lithostratigraphy of this core has been described by Narcisi et al. (1992), while pollen analysis has been carried out by Follieri et al. (1988, 1989); palynological and lithostratigraphical data have been compared both at the scale of the entire sequence (Follieri et al., 1990) and at the scale of annual laminations (Magri and Narcisi, 1992). The chronological framework has been tackled using various methods: 21 14C dates (Table 2) for the uppermost 10 m of the core (Alessio et al., 1986), a count of the annual laminations (Magri and Narcisi, 1992), comparison with oxygen isotope stratigraphy and synchronization with the variation of the astronomic parameters (Magri, 1989a; Narcisi et al., 1992). The entire sequence is estimated to span more than 250 ka. The record from Valle di Castiglione can be regarded as a key sequence for the understanding of the Quater-

FIG. 1. Location map of the study sites in the volcanic region of Lazio (dotted area). (1) Lagaccione; (2) Lago di Vico; (3) Stracciacappa; (4) Valle di Castiglione.

nary environmental changes in central Italy, as it contains two complete interglacial-glacial cycles, clearly highlighted by both pollen and sedimentological data. A summary pollen diagram spanning the last 130 ka is reported in Fig. 2. At the end of the Eemian (estimated age: 129—115 ka; Follieri et al., 1989), during which the greatest expansions of evergreen Mediterranean vegetation and Zelkova occurred, a drastic and sudden drop of the total pollen concentration and of the arboreal pollen percentage is found (Magri and Follieri, 1992). Steppe and grassland dominated the landscape. The arboreal

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TABLE 2. Uncalibrated 14C ages of lacustrine sediments from Valle di Castiglione (VdC), Lagaccione (Lgc), Lago di Vico (core V.I) and Stracciacappa (Stra) for the last glacial period

Site

Lab. code

Depth (m)

14C age (yr BP)

VdC VdC VdC VdC VdC VdC VdC VdC VdC VdC VdC Lgcl Lgcl Lgcl Lgcl Lgcl Lgc2 V.I V.I V.I V.I V.I V.I V.I V.I V.I V.I Stra2 Stral Stral Stral Stral Stral

R-1331 S2/E R-1332 S2/FS1 R-1547 S2/1 R-1548 S2/2 R-1549 Sl/3 R-1550 Sl/4 R-1551 Sl/5 R-1552 Sl/6 R-1553 Sl/7 R-1554 Sl/8 R-1555 Sl/9 GX-18019 GX-18020 GX-18021 Ua-3862, AMS Ua-3863, AMS Ua-3864, AMS Ua-3856, AMS Ua-3372, AMS Ua-3857, AMS Ua-3858, AMS Ua-3373, AMS Ua-3859, AMS Ua-3374, AMS Ua-3375, AMS Ua-3860, AMS Ua-3861, AMS Ua-3866, AMS GX-18016 GX-18017 Ua-3867, AMS GX-18018 Ua-3868, AMS

4.30—4.50 5.13—5.50 7.17—7.30 7.30—7.50 9.85—10.00 10.00—10.10 10.10—10.25 15.10—15.20 15.20—15.40 15.40—15.60 17.00—17.10 9.90—10.05 12.90—13.05 16.15—16.30 19.30—19.35 23.80—23.85 26.15—26.20 1.21 1.36 1.52 2.10 2.64 3.68 4.90 6.44 7.23 8.41 3.65 4.15—4.30 5.55—5.70 7.19—7.22 8.65—8.80 9.19—9.22

14,220$145 20,300$700 24,900$370 25,800$600 31,300$900 27,200$1500 32,900$1600 '34,000 '43,000 41,000$4700 '43,000 16,080$550 20,615$940 22,750$1230 29,090$680 28,750$650 '38,000 10,255$90 11,295$165 14,385$140 20,500$230 21,950$345 25,210$420 32,985#1195/—1040 34,875#1500/—1265 '38,000 '38,000 12,060$130 19,745$820 22,150$1140 30,540$800 33,430$1190 36,330$1630

vegetation was mainly constituted by Pinus and Juniperus; deciduous oaks were the only angiosperm trees. During the following forest period, correlated with the St Germain I, Fagus and deciduous oaks were the main components of a dense vegetation. At the end of this phase, Abies reached the highest values of the sequence. A recession of the forest, named Montaigu at La Grande Pile and recognized in many other European sites (Reille et al., 1992), is clearly visible at Valle di Castiglione (zone VdC-12b, see Follieri et al., 1988). In the following, non-wooded zone (30.40—28.00 m), Chenopodiaceae dominate. Juniperus and Pinus show appreciable values. The steppe is replaced by a forest in the succeeding zone, correlated with the St Germain II period, characterized by high AP percentage values (about 80%). The arboreal vegetation was mainly constituted by Pinus, ºlmus, Abies, Zelkova, and Carpinus betulus. The last part of the forest expansion of the St Germain II is probably missing at Valle di Castiglione,

as well as the beginning of the following zone; in fact, the sediments, including also a paleosol, do not contain pollen. Then the last pleniglacial period is found, dominated by grassland and steppe formations, but also with several weak expansions of angiosperm trees. There is a general trend, from the base of the zone to the top, from an open woodland through a woodland-steppe to harsh steppe conditions. At the beginning of the zone two main arboreal peaks, in which Pinus, Fagus, deciduous and evergreen oaks are the dominant trees, followed by several minor fluctuations, all these are recorded. Throughout the zone there is a complete lack of Carpinus orientalis/Ostrya, Olea, Phillyrea, Rhamnus and »itis. During this period the last occurrence of Zelkova is recorded (Follieri et al., 1986a). After about 30 ka BP the angiosperm trees were even more sporadic: trees like Carpinus betulus and ¹ilia never appeared.

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FIG. 2. Tentative correlation of the summary pollen diagrams from Valle di Castiglione, Lagaccione, Lago di Vico and Stracciacappa. AP: arboreal pollen Pinus and Juniperus excluded; NAP: non-arboreal pollen. Roman numerals indicate the events of the Lazio Complex described in the text. The standard deviations of the radiocarbon dates are listed in Table 2.

The new immigration of trees at around 4 m (estimated age 14,000 years BP; Follieri et al., 1986b), preluding to the postglacial reafforestation, is not discussed in this paper.

¸agaccione The Lagaccione di Capodimonte maar, 2 km apart from Lago di Bolsena, (Fig. 1) is a hydromagmatic crater formed during the last period of development of the Vulsini volcanic district (Metzeltin and Vezzoli, 1983). Further data are listed in Table 1. The modern vegetation around Lagaccione is mainly represented by deciduous oak-forests dominated by Quercus pubescens Willd., with Q. cerris L., Q. robur L. and Q. petraea (Mattuschka) Liebl. The abundance of Castanea sativa Mill. shows the man-induced alteration of natural vegetation. Near Lago di Bolsena the vegetation is characterized by the presence of evergreen oak woods on rocky slopes. A summary pollen diagram, combining the results of two cores (0.0—5.5 m and 6.0—42.0 m), is reported in

Fig. 2. Preliminary pollen analyses have been published by Magri (1989b, 1993); a detailed paper on the whole sequence is in preparation. A lithostratigraphical study of the core has been carried out by Narcisi and Anselmi (this volume). The pollen record is characterized by alternating forest and non-forest phases. Three periods are found with arboreal pollen values higher than 80%, corresponding to the stretches of core with high organic matter content (Narcisi and Anselmi, this volume). The zone between 42.00 and 39.20 m is a very marked forest period, with peaks of total pollen concentration higher than 1,000,000 grains g~1 of dry sediment. The dominant taxa are Abies and Fagus, accompanied by deciduous Quercus, Pinus, Betula, Carpinus betulus, and low percentages of Juniperus, Picea, Acer, Buxus, Fraxinus, ¹ilia, »iscum, Hedera, ºlmus, Corylus, Quercus ilex type, Zelkova, Ericaceae, Alnus. This zone is correlated with the St Germain I forest period. The zone between 37.70 and 35.50 m includes three different expansions of trees: the earliest, with high AP percentages and concentrations, is dominated by

Palynostratigraphy of the Last Glacial Period

7

Fagus, Carpinus betulus, Abies and deciduous Quercus; the second displays percentages of Fagus of over 60% and an appreciable diffusion of deciduous Quercus, Pinus, Abies, Carpinus betulus, Corylus, ºlmus; the third peak of AP, not very pronounced, is characterized by deciduous Quercus and Pinus, with very low values of almost all other arboreal plants. This zone is correlated with St Germain II s.l. The zone between 5.5 and 0.5 m, corresponding to the Postglacial, displays a very rich flora and a significant diffusion of Mediterranean taxa. Only preliminary data are available for this period. Except for the three forest periods, the pollen diagram from Lagaccione is dominated by steppe elements, mainly Gramineae, Artemisia and Chenopodiaceae. Between 32.60 and 19.15 m the steppe formations are interrupted by several oscillations of tree pollen curves (Magri and Giardini, 1992). Pinus was the dominant arboreal taxon. Deciduous oaks were the most frequent angiosperm trees accompanied by Fagus, Betula, Corylus, ¹ilia, ºlmus and sporadic occurrences of Acer, Alnus, Ericaceae and Quercus ilex type. The palynostratigraphic features of the record suggest for the base of the sequence an age of about 100 ka.

ized by deciduous oaks. This fluctuating forest period is correlated with the St Germain II s.l., on the basis of (a) a close similarity with the pollen diagram from Lagaccione (Fig. 2) containing both the St Germain I and the St Germain II interstadials, the latter characterized by two main forest oscillations followed by a weak spread of oaks, as in the diagram from Lago di Vico, (b) the age of the Monte Venere scoria cone ascribed to the final activity of the Vico volcano, for which two K-Ar dates (95$9 ka: Laurenzi and Villa, 1985; 85$4 ka BP: Palacin, 1985) are available, and (c) the occurrence at Lagaccione of a tephra layer at the bases of the St Germain II (37.95 m), related by Narcisi and Anselmi (this volume) to the last period of activity of the Vico volcano. Then a prolonged period, in which grassland and steppe formations were dominant, is recorded; this is interrupted by many minor fluctuations of the values of angiosperm trees, mainly deciduous Quercus, Betula, Corylus and ºlmus. A new reafforestation began in correspondence with the radiocarbon date 11,295$165 yr BP, although a real forest, with tree percentages of over 80% and with a sudden increase of angiosperm trees, is recorded only after the radiocarbon date 10,255$90 yr BP.

¸ago di »ico

Stracciacappa

The Vico volcano (Fig. 1) activity started before 0.4 Ma and ended around 0.09 Ma (Bertagnini and Sbrana, 1986). Further data are listed in Table 1. The lake significantly influences the climate inside the caldera, inducing persistently wet conditions in the environment, both in the soils and in the vegetation (Lulli et al., 1990). The typical vegetation of the caldera of Vico is a forest composed of Fagus sylvatica L., Quercus cerris L. and Castanea sativa Mill. accompanied by euroasiatic elements. Extrazonal populations of Quercus ilex L. and other taxa of Mediterranean sclerophyllous vegetation are found on rocky slopes (Scoppola et al., 1989). Previous palynological studies have been carried out on the lacustrine sediments of Lago di Vico, always on cores collected at the lake margin (Frank, 1969; Leroy, 1992; Francus et al., 1993). The pollen diagram in Fig. 2 is from a core 15 m long, drilled at a water-depth of 22.60 m (Magri and Sadori, 1993). Seventeen radiocarbon dates are available from the core, ten of which are older than 10,000 years (Table 2). The pollen record apparently does not include the Eemian, as the floristic and vegetational characters of the forest phases do not show the typical features of the last interglacial, as it is known for central Italy. At the base of the sequence two periods of forest expansions are found, separated by a period with increased non-arboreal pollen values. The forests were formed by deciduous oaks, Fagus, Pinus and Abies, and by many other mesophilous trees in low quantities. A third weaker arboreal oscillation is mainly character-

The Stracciacappa crater (Fig. 1), active during the last explosive phase of the Sabatini volcanic district between 80 and 40 ka (De Rita and Zanetti, 1986a, b), is located about 35 km north of Roma (Table 1). The modern vegetation of the area consists of deciduous forests with Quercus cerris L., Q. frainetto Ten., Fraxinus ornus L., Carpinus betulus L., Cornus mas L., Acer campestre L., while in the open areas Rubus ulmifolius Schott, Crataegus monogyna Jacq., Acer monspessulanum L., Prunus spinosa L. are found (Blasi et al., 1981). A continuous borehole was drilled in the centre of the lake bed to a depth of 32.60 m, reaching the volcanic basement at around 29 m. The available radiocarbon dates from the Stracciacappa core relative to the last glacial period are listed in Table 2. A summary pollen diagram is reported in Fig. 2. A preliminary work has been carried out by Giardini (1993). A detailed paper is in preparation. The pollen record from Stracciacappa begins in Pleniglacial sediments, as it does not include any major forest phase before the Holocene. The Stracciacappa record confirms and improves the results obtained at Valle di Castiglione, Lagaccione and Lago di Vico, indicating that during the last pleniglacial several weak expansions of angiosperm trees took place in the region, interrupting the succession of steppe and grassland formations dominated by Artemisia, Gramineae and Chenopodiaceae (Magri and Giardini, 1992). During the pleniglacial, the highest values of tree pollen exceed 60%; angiosperm trees alone account for 30%

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M. Follieri et al.

of total pollen. A considerable number of arboreal taxa were present, the most important being Pinus, deciduous Quercus, Corylus, Betula, Fagus, ºlmus, and Carpinus betulus. The beginning of the Postglacial is recorded at about 3.5 m depth. Although the results shown in Fig. 2 for the Holocene are still preliminary, the spread and development of the arboreal vegetation seems to generally agree with the history of the vegetation outlined in the other pollen diagrams from central Italy.

BIOSTRATIGRAPHICAL CORRELATIONS OF THE FOUR SEQUENCES In Fig. 2 the summary pollen diagrams from the four sites of Lazio are ordered from oldest to youngest, and a correlation is suggested for the recorded vegetational phases. Although the sites are relatively close to each other, correlation of the pollen sequences are not always easy, partly because of the variety of local situations, and partly from the methodological difficulty of objectively evaluating the relative importance of similarities and dissimilarities.

The Eemian is found only at Valle di Castiglione, where it is recognized on the basis of the widespread diffusion of thermophilous and Mediterranean vegetation (Follieri et al., 1988, 1989). At Lagaccione, Lago di Vico and Stracciacappa high percentages of Quercus ilex type are found only during the Postglacial (Fig. 3), and so the possibility that these sequences include the Eemian is excluded. The St Germain I forest phase is recorded in two sequences: Valle di Castiglione and Lagaccione (Fig. 2). In the latter, however, the diagram starts after pollen zone VdC-12b of Valle di Castiglione (see Follieri et al., 1988), correlated with the Montaigu event, found in many European sequences (Reille et al., 1992). The St Germain I period is a well-developed forest episode, characterized at both sites by the expansion of Fagus and Abies (Figs 4 and 5) together with many other deciduous trees. The steppe period after St Germain I is clearly recognized both at Valle di Castiglione and at Lagaccione: except for Pinus, trees disappeared almost completely. It is in this period that the chenopods at both sites reach the highest values of the last interglacial-glacial cycle. The St Germain II forest period is recorded completely at Lagaccione and at Lago di Vico, while at

FIG. 3. Quercus ilex type: pollen percentage diagrams of the four study sites.

Palynostratigraphy of the Last Glacial Period

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FIG. 4. Fagus: pollen percentage diagrams of the four study sites.

Valle di Castiglione it seems to be interrupted towards the end, where the sediments do not contain pollen. This period is characterized by two main expansions of trees, the first with higher pollen concentration values, and by a minor third oscillation. At all sites Abies (Fig. 5), ºlmus (Fig. 6) and Carpinus betulus (Fig. 7) appear as the distinctive taxa: in the whole sequence of Valle di Castiglione (spanning more than 250,000 years) they are found contemporaneously with high percentages only at this time. Besides, towards the end of the forest phase there is an appreciable, though slight, increase of Picea (Fig. 8). Local differences of vegetation composition can be pointed out: at Valle di Castiglione Zelkova (Fig. 9), at Lagaccione Fagus (Fig. 4) and at Lago di Vico deciduous oaks (Fig. 10) show important expansions. The period between the St Germain II and the Lateglacial is characterized by Artemisia, Gramineae, and Chenopodiaceae alternately dominant; however the succession of steppe and grassland formations is often interrupted by several weak tree expansions. Pinus and Juniperus (Fig. 2) were the most frequent arboreal taxa. Considering all trees together, at the four sites the arboreal pollen peaks at 60%. In some cases, pollen values of the angiosperm trees alone exceed

35%. It seems convenient to use the local name ‘Lazio Complex’ for this series of more or less pronounced oscillations. Some episodes, recognized in at least three records out of four, have been tentatively singled out (Roman numerals) and palynologically correlated among sequences, also taking into consideration radiocarbon dates where available. The beginning of the Pleniglacial is recorded at Lagaccione and Lago di Vico; Pinus, the only tree worth mentioning, displays at both sites the highest percentage values of the sequences and a significantly similar trend (Fig. 2). At Valle di Castiglione the presence of a paleosol at 24 m suggests a drying out of the basin without lacustrine sedimentation (Narcisi et al., 1992). This might be the reason why the first oscillation of arboreal pollen of the Lazio Complex (episode I) visible at Lagaccione, Lago di Vico and Stracciacappa (Fig. 2) is not recorded at Valle di Castiglione. The following two important expansions of trees (II and III), the trend of which is easily recognized at Valle di Castiglione, Lagaccione and Stracciacappa, can be used as reference points for correlating the diagrams: for this reason the basis of episode II is shown in Figs 2—12. The following weak oscillation of episode IV is also evident at Valle di Castiglione, Lagaccione and

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M. Follieri et al.

FIG. 5. Abies: pollen percentage diagrams of the four study sites.

Stracciacappa. At Lago di Vico the general trend of vegetational fluctuations is more confused, only one important oscillation being distinct. The next peak of angiosperm trees (V) is dated by radiocarbon around 35 ka at Lago di Vico and Stracciacappa; it may easily be recognized also at Valle di Castiglione, while at Lagaccione a possible attribution of the spread of trees at 23 m to episode V contrasts with the 14C date 28,750$650 years BP, which might not be correct. An oscillation of trees (VI) is radiometrically dated at Stracciacappa, Lago di Vico and Valle di Castiglione at around 33 ka BP, while an arboreal peak at around 30 ka (VII) is visible at Lagaccione, Lago di Vico and Stracciacappa. The end of episode VII has been represented in Figs 2—12, as a useful marker for correlation, in that it concludes the succession of fluctuations of the Lazio Complex and delimits the beginning of a period poorer in arboreal taxa. From the floristic point of view, in episodes I—VII a relatively high number of taxa is recorded, with numerous appreciable expansions of angiosperm trees: deciduous Quercus (Fig. 10) and Corylus (Fig. 11) are the most important, together with Betula, Fagus, ¹ilia, ºlmus, Carpinus betulus, and Picea. Fagus (Fig. 4) is

more abundant at Valle di Castiglione and Lagaccione. Picea (Fig. 8) exceeds 5% at Stracciacappa and Lagaccione. Zelkova (Fig. 9) shows during the Pleniglacial oscillations its last appearances at all sites. Its extinction is recognized before episode VII, in agreement with previous observations (Follieri et al., 1986a). Between around 30 ka BP (episode VII) and the beginning of the reafforestation preluding the welldeveloped arboreal vegetation of the Postglacial, there is a period with very low values of angiosperm tree pollen: ¹ilia (Fig. 12) and Carpinus betulus (Fig. 7) are completely absent. An event with particularly low arboreal pollen percentage and concentration values is dated by 14C at Lago di Vico at 21,950$345 yr BP and is found at Valle di Castiglione, Lagaccione and Stracciacappa at similarly estimated ages. The only, very weak, spread of trees (mainly oaks and Picea) is found at Valle di Catiglione, Lago di Vico and Stracciacappa around 20 ka BP (Fig. 2). The events of the Lateglacial and Postglacial are beyond the scope of this paper. The fact that the fluctuations of the Lazio Complex are recognized in different sequences indicates that these are not occasional oscillations. It is when particular situations are found only in one sequence that local

Palynostratigraphy of the Last Glacial Period

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FIG. 6. ºlmus: pollen percentage diagrams of the four study sites.

conditions are relevant. For example, the appreciable diffusion of angiosperm trees of episode VI (ca. 33 ka BP) at Lago di Vico compared to the other sites (Fig. 2), and the spread of Fagus during episodes II and III at Valle di Castiglione and Lagaccione (Fig. 4) are most likely the results of locally diversified vegetation patterns. In other cases, anomalies in the pollen records may be ascribed to sedimentary processes. For example, the break of lacustrine sedimentation at Valle di Castiglione, documented by the formation of a paleosol at 24 m, explains the lack of episode I in the pollen record. In general, excluding the very small fluctuations, the four sequences from Lazio correlate satisfactorily well with one another, which should indicate that they reflect climatic changes, at least at a regional scale.

VEGETATIONAL FEATURES OF THE LAZIO COMPLEX The general trends of expansion of arboreal taxa found at the four Lazio sites during the last glacial period are by and large similar. As to the individual taxa, some of them are not living any more in the

region, others have spread only in a number of periods, while still others show local differences of diffusion. The history of Zelkova (Fig. 9) deserves to be mentioned first. This arboreal taxon, belonging to the family Ulmaceae, is at present extinct on the Italian peninsula; Zelkova sicula Di Pasquale, Garfi and Quezel still lives in Sicily (Quezel et al., 1993); Zelkova abelicea (Lam.) Boiss. occurs on the Island of Crete (Jalas and Suominen, 1976; Sarlis, 1987). Zelkova characterizes the Eemian interglacial at Valle di Castiglione. Continuously found during the St Germain I forest period, it expanded anew during the St Germain II (observed also at Lagaccione and Lago di Vico) and was rare during the Lazio Complex until somewhat before 30 ka BP, when it disappeared. Outside Italy, Quaternary pollen of Zelkova has been recorded separately from ºlmus only in Greece, in levels older than the Upper Pleistocene (van der Hammen et al., 1971; Tzedakis, 1991, 1994). Abies alba Mill., the only fir occurring in the Italian peninsula, is not native in the Lazio region at present, but is found in the Alps, in the southern Apennines, and at a few isolated sites in the central and northern Apennines (Giacobbe, 1950; Quezel, 1980). The four pollen diagrams throw light on the history of Abies and

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FIG. 7. Carpinus betulus: pollen percentage diagrams of the four study sites.

its disjunct areas of distribution: very rare during the Eemian (Fig. 5), Abies characterizes both the St Germain forest periods; in particular, during the St Germain II s.l. it shows two successive expansion phases. After this time it was only sporadically present. It is difficult to state whether the single pollen grains found in the sediments up to the present underwent long-distance transport or were produced by single trees or small stands of this species in the landscape, and so it is impossible to establish the exact age of its extinction in the region. Though Abies is considered as under-represented in the pollen rain (Reille, 1990), very low percentages of fir, certainly transported from long distances, are recorded in recent sediments at the four sites. This might suggest that, in a similar way, the sporadic findings of the Pleniglacial may have been of distant origin, and that the present-day distribution may be the result of a disjunction which occurred during the last glacial period. At that time, in fact, Abies is abundantly represented in pollen diagrams both from southern Italy, at Laghi di Monticchio in Basilicata (Watts, 1985), at Canolo Nuovo in Calabria (Gru¨ger, 1977), and in a marine core from the Tyrrhenian Sea (Rossignol-Strick and Planchais, 1989),

and from northern Italy in the Apennines (Bertoldi, 1980). The arboreal taxon which is probably the most characteristic for the glacial period is Picea (Fig. 8). It reaches appreciable frequencies at Stracciacappa ('7%) and at Lagaccione ('5%). According to Huntley and Birks (1983) pollen values greater than 5% represent local presence. At Valle di Castiglione the values of Picea are lower (max. 2.7%), but they are the highest values throughout the whole 250,000-year core. At Lago di Vico spruce has even lower percentages, but the trend of its oscillations parallels the other sequences. The history of Picea, as outlined in the four diagrams, starts with a spread at the end of the St Germain II forest phase; a second increase took place during episodes II—IV of the Lazio Complex. Interestingly, a small peak of spruce is recorded around 20 ka BP at Lago di Vico and Stracciacappa. The presence of pollen of Picea in central Italy, even if in low percentages, is very remarkable, as its present-day geographical distribution is very northern: in Italy Picea abies (L.) Karsten lives only in the Alps and at a very few relict stations in the northern Apennines (Pignatti, 1982; Jalas and Suominen, 1973). The sites studied in Lazio

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FIG. 8. Picea: pollen percentage diagrams of the four study sites.

provide evidence that, from about 80 ka to about 20 ka, the geographical distribution of spruce was definitely more southern than at present. Together with deciduous Quercus (Fig. 10), representing the bulk of angiosperm trees throughout the glacial period, Corylus pollen (Fig. 11) was always present in all arboreal fluctuations of the Lazio Complex, when it generally reached higher values than during the St Germain I and II forest phases. The maximum expansion of Corylus is recorded at all sites during the Holocene. At Valle di Castiglione the percentages of hazel during the Postglacial are the highest of the entire 250,000-year sequence. ºlmus (Fig. 6) is commonly found during all forest oscillations. However, it was particularly abundant during the St Germain II, when it characterized the period together with Abies at high percentages, and during the Postglacial, when it mostly expanded together with Corylus. As already noted, a parallel behaviour of Carpinus betulus (Fig. 7) and ¹ilia (Fig. 12) may be observed after 30 ka, when both are completely absent in all sequences until the Postglacial reafforestation. However small populations could have been living in the region, as indicated, for example, by the considerable spread of

¹ilia early in the Holocene at all sites (to almost 8% at Valle di Castiglione). A taxon showing significant differences from one site to the other is Fagus, probably in relation to its climatic and edaphic requirements. In particular, the spread of beech is very diversified during the St Germain II, when it shows two high peaks at Lagaccione, one important and one minor expansion at Lago di Vico, and only low percentages at Valle di Castiglione. However, it is at Valle di Castiglione that Fagus reaches its highest values for the Lazio Complex. On the basis of these observations it is clear that the history of vegetation in the region shows a considerable dynamism, even during those periods when at higher latitudes in Europe there are no appreciable vegetational changes. This confirms that the Italian peninsula was a privileged area for the survival of mesophilous and thermophilous trees during the glacial periods (Bennett et al., 1991; Zagwijn, 1992). Considering the floristic composition and the vegetational configurations recorded in the diagrams it seems possible to differentiate the most important biostratigraphical units of the last climatic cycle: St Germain I, St Germain II, Pleniglacial interstadials (Lazio Complex) and Postglacial. The individual oscillations of the

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FIG. 9. Zelkova: pollen percentage diagrams of the four study sites.

Lazio Complex cannot be easily distinguished from each other by their vegetational features: they are very similar to one another and can only be differentiated by considering their general trends within continuous records or, in the case of the most recent fluctuations, when they can be radiometrically dated.

CORRELATIONS WITH OTHER CONTINUOUS POLLEN RECORDS The four sites studied in central Italy show that even in the same region, where the vegetational features and the biostratigraphical units should be comparable, it is difficult to correlate all the very slight oscillations. It clearly appears that, albeit crater lakes are very suitable for palaeoecological research, differences in the sediment deposition and in the local climatic conditions may complicate the correlations even at a regional scale. When comparisons are to be made at a much wider scale, difficulties increase proportionally and much caution is necessary. For this reason, long continuous records are preferable and probably indispensable for supraregional comparisons.

The characteristics of past flora and vegetation in the Lazio records are generally very different from those of other long European pollen sequences, so that any detailed comparison between the biostratigraphical units of the Italian sites and the contemporary ones of the other localities is very problematic. Comparisons with other sequences and the chronostratigraphical framework are therefore mainly based on (a) identification of vegetational phases acting as biostratigraphical markers, such as the Eemian and the Holocene, (b) definition of the patterns of succession and the importance of the various expansions of trees, and (c) radiometric dates. Considering the sequence of the main forest and steppe phases, the Valle di Castiglione, Lagaccione, Lago di Vico and Stracciacappa pollen records seem to fit satisfactorily into the framework of the European biostratigraphy for the last interglacial/glacial cycle, as it has been gradually outlined in the last few years. This is particularly true for the most important forest phases, namely Eemian, St Germain I (Bro¨rup) and St Germain II (Odderade), but is less evident for the minor fluctuations of trees (Lazio Complex). In fact, for its geographical position central Italy may be

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FIG. 10. Quercus deciduous: pollen percentage diagrams of the four study sites.

considered as a region very sensitive to climatic changes, and which, therefore, experienced many more fluctuations of vegetation in the past than other European regions at higher latitudes. A clear example of this sensitivity is the development of forest vegetation during the St Germain II. In the central and north European sequences, for example La Grande Pile (Woillard, 1978; de Beaulieu and Reille, 1992), Les Echets (de Beaulieu and Reille, 1984a, 1984b), Lac du Bouchet (Reille and de Beaulieu, 1990), Gondiswil (Wegmu¨ller, 1992), Samerberg (Gru¨ger, 1979a, b), Basin of Wurzach (Gru¨ger and Schreiner, 1993), and Oerel (Behre and Lade, 1986; Behre, 1989), the St Germain II (Odderade) appears as a well-developed forest phase, with no important fluctuations in it. The north/south vegetation gradient in Europe was considerably steeper than today (de Beaulieu and Reille, 1984a, b). So, whereas in northern Germany, in the Netherlands and in Denmark the Odderade shows only traces of temperate forests, at La Grande Pile there is a major expansion of Quercus and Corylus, accompanied at Les Echets also by a high peak of Carpinus. On the contrary, in the Bavarian Alps (Gru¨ger, 1979a, b), in the Basin of Wurzach (Gru¨ger and Schreiner, 1993) and on the Swiss Plateau

(Wegmu¨ller, 1992) there were thick Picea stands. Three sites from Lazio (Fig. 2) record this period, characterized by Abies, ºlmus and Carpinus, accompanied by many other deciduous trees like Quercus, Fagus and Zelkova. Two major forest oscillations, the first with much higher pollen concentration values, are clear at Lagaccione and Lago di Vico. During the intervening episode, when herbs increase, deciduous trees, present with most taxa, maintain values of around 10—20% (Fig. 2): for this reason both fluctuations are ascribed to the St Germain II s.l. In fact, in the steppe episode recorded at Valle di Castiglione and Lagaccione between St Germain I/and St Germain II, the decrease of tree percentages is much more drastic and evident. A correlation seems possible between these two peaks of trees and the two arboreal fluctuations recorded in Greece at Tenaghi Philippon (Wijmstra, 1969) during the Elevtheroupolis (Odderade), and perhaps also with the fluctuations of oaks in Spain at Padul (Pons and Reille, 1988) during pollen zone i, correlated with the St Germain II. Instead, any detailed correlation of the following third smaller peak, mainly composed of oaks, with either Ognon I of the French sites (Woillard, 1978; de Beaulieu and Reille, 1992) or the third interstadial of the German and Swiss sites

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FIG. 11. Corylus: pollen percentage diagrams of the four study sites.

(cf. Wegmu¨ller, 1992; Gru¨ger and Schreiner, 1993) or with the Oerel interstadial in northern Germany (Behre, 1989) would be hazardous. On the whole, as noted before, it seems that the sequences from southern Europe show a greater number of events than those from more northern countries, and among these the Italian records have a more considerable vegetational complexity. This is particularly true for the numerous small oscillations of the Pleniglacial, which in northern Europe have been seldom found together in the same sequence. The biostratigraphy of the last glacial period in central-northern and north-western Europe has been recently reviewed by Behre (1989) and Ran (1990). In NW Germany Behre and Lade (1986) have described, subsequent to the Odderade, and from within the context of a continuous series, two clearly delimited interstadials, the Oerel and the Glinde, dated at 58—54 ka and 51—48 ka BP, respectively (Behre and van der Plicht, 1992). For the middle part of the last Pleniglacial, several authors (cf. review in Ran, 1990) have described interstadials with a more or less closed tundra vegetation in north-west Europe. The proposed ages (Ran and van Huissteden, 1990) are 49—41 ka BP for the Moershoofd complex, 38—36 ka for the Hengelo

interstadial and 32—26 ka for the Denekamp interstadial complex. In France the Pleniglacial is recorded in a few long sequences. The clearest weak spread of trees, mainly Betula and Pinus, is dated around 31—29 ka at La Grande Pile (Grand Bois interstadial; Woillard, 1978; Woillard and Mook, 1982) and around 35—30 ka at Lac du Bouchet (Reille and de Beaulieu, 1990, Creer et al., 1990). A spread of Quercus, Alnus and Corylus is dated 29,500$1200 yr BP at Biscaye (Mardones and Jalut, 1983). Older oscillations recognized at La Grande Pile are dated (Woillard and Mook, 1982) around 40 ka BP (Charbon interstadial) and around 50 ka BP (Pile interstadial). A slight positive fluctuation of trees at Biscaye (Mardones and Jalut, 1983) is correlated with the last two mentioned interstadials. The sporadic appearances of deciduous trees at Les Echets (de Beaulieu and Reille, 1984a, b) and at Lac du Bouchet (Reille and de Beaulieu, 1990) are interpreted as having only local biostratigraphical significance, in relation to the location and importance of refuge areas inherited from a regional past. The same interpretation is given for the pollen zones of the last Pleniglacial at Padul, Spain, for which the relation with climatic episodes is not certain (Pons and Reille, 1988), although

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FIG. 12. ¹ilia: pollen percentage diagrams of the four study sites.

oaks attain 10%. Of course the possibility of finding reworked pollen must be considered, especially in sediments of glacial periods: this — in addition to perhaps problematic dates by 14C — would complicate any correlation based on minor changes in the pollen diagrams. The arboreal fluctuations recorded in Greece at Tenaghi Philippon during the Pleniglacial (Wijmstra, 1969), having been correlated by the author with the north-west European biostratigraphy, are considered as induced by general climatic phenomena. In another Greek sequence, at Ioannina (Tzedakis, 1993, 1994), a prominent feature is the continuous presence of arboreal pollen during the open vegetation periods, suggesting the local occurrence of tree populations; however, the succession of vegetational phases during the last Pleniglacial has not been discussed in detail. A close correlation of the Italian sequences with either the continuous long records from the French sites where it was not possible to establish a detailed Pleniglacial palynostratigraphy, or with the north-west European sequences which are very numerous and framed in a chronostratigraphy, but always discontinuous, appears very problematic. It suffices to quote the simplest case, that is the events of 35—33 ka. At Valle di

Castiglione, Lago di Vico and Stracciacappa two distinct episodes are visible around 35 ka (V), and 33 ka (VI). Although some uncertainty remains about the exact ages of these episodes, that have dates with standard deviations of 1000—1500 yr (Table 2), it is unquestionable that they are distinct, being observed in continuous records. The question however remains whether episodes V and VI of the Lazio Complex are to be correlated with the Hengelo interstadial at 38—36 ka and with the Denekamp complex between 32 and 26 ka, both periods dated with much lower standard deviations (cf. Zagwijn, 1974) than the Italian sequences. It is clear that a close correlation of the vegetational events during the last Pleniglacial in central Italy with other European pollen sequences is impossible, also because of the vegetational complexity and the wealth of fluctuations documented in the Italian sites. It is also clear that a correlation of the episodes of the Lazio Complex with the succession of oscillations described in the oxygen isotope stratigraphy (cf. Martinson et al. 1987) or in the ice-core records (cf. Dansgaard et al., 1993), cannot at present be more than outlined (see suggestions of West, 1984). The temptation remains to reconcile the individual events of the Lazio Complex with the small fluctuations shown in stages

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4 and 3 of the isotope curve: the coincidence is impressive. However, knowledge on this period is still too scanty. At the moment, on the basis of the general trend of the oscillations, it seems reasonable to advance only the hypothesis that the boundary between stages 4 and 3 can be put at the beginning of episode II of the Lazio Complex, the most pronounced of the Pleniglacial, even if the synchronism of these events has still to be proved. CONCLUSIONS The four long pollen records from Lazio make a substantial contribution to our knowledge of the last glacial period. Several fluctuations of vegetational cover, recognized during the last Pleniglacial, have been framed into a new regional biostratigraphical unit, named the ‘‘Lazio Complex’’. In general, excluding the minor fluctuations, the four sequences can be satisfactorily correlated. This suggests that the recorded vegetational oscillations are not occasional, but reflect climate changes of at least regional scale. The pollen records from Valle di Castiglione, Lagaccione, Lago di Vico and Stracciacappa outline a history of vegetation which, for the general patterns of the most important events, agrees with what is known from central and northern Europe. However, compared with the other sequences, the Italian records show a greater number of events and a remarkable vegetational complexity. This may be due to the fact that the geographical situation of the Italian peninsula makes its vegetation very sensitive to climatic changes, favouring a considerable dynamism of vegetation even in those periods when at higher latitudes in Europe there were no appreciable changes. So, during the last glacial period, it has been possible to follow the history of some taxa no longer living in central Italy and of other taxa expanding only in a number of periods, or showing local differences of diffusion. This vegetational and floristic diversity is of particular interest from the biostratigraphical point of view, making it possible to differentiate the most important events of the last climatic cycle: Eemian, St Germain I, St Germain II, Pleniglacial interstadials (Lazio Complex) and Postglacial. Even so, it has not been possible to distinguish the individual events of the Lazio Complex, which can be differentiated only when their trends are considered within continuous records. ACKNOWLEDGEMENTS This research was supported by the EC project EUROMAARS (contr. SCI-0295C) and by the EC Programme Environment (project EV5V-0027). We are grateful to Prof. Dr. E. Gru¨ger and to Prof. Dr. W.H. Zagwijn for comments and suggestions.

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