SESS 2_16022011_TPR3.pub Il Quaternario Italian Journal of Quaternary Sciences 24, (Abstract AIQUA, Roma 02/2011), Congresso AIQUA Il Quaternario Italiano: conoscenze e prospettive Roma 24 e 25 febbraio 2011 A NEW LATE-GLACIAL POLLEN RECORD FROM VALLE DI CASTIGLIONE (ROME) Federico Di Rita1, Anna Paola Anzidei2 & Donatella Magri1 1 Dip. Biologia Ambientale, Sapienza Università di Roma 2 Soprintendenza Speciale per i Beni Archeologici di Roma, Roma Corresponding author: F. Di Rita ABSTRACT: Di Rita F., Anzidei A.P. & Magri D., A new late-glacial pollen record from Valle di Castiglione (Rome). (IT ISSN 0394-3356, 2011) New pollen data from Valle di Castiglione (Rome) highlight the vegetation development of the Roman area between 13,700 and 8000 cal BP. The late-glacial is characterized by a deforested landscape with a scanty presence of woody taxa during the interstadial. The postglacial development of forest vegetation is delayed by the local persistence of chenopods. Evergreen trees are continuously present throughout the pollen record. RIASSUNTO: Di Rita F., Anzidei A.P. & Magri D., Una nuova sequenza pollinica tardoglaciale a Valle di Castiglione (Roma). (IT ISSN 0394-3356, 2011) Nuovi dati pollinici da Valle di Castiglione (Roma) delineano lo sviluppo della vegetazione della Campagna Romana tra 13700 e 8000 anni dal presente. Il tardoglaciale è caratterizzato da un paesaggio deforestato, con un modesto aumen- to di alberi durante la fase interstadiale. La reforestazione postglaciale è posticipata a causa della persistenza, proba- bilmente locale, di chenopodiacee. La vegetazione sempreverde è sempre presente. Key words: pollen, late-glacial, central Italy, Mediterranean vegetation Parole chiave: polline, tardoglaciale, Italia centrale, vegetazione mediterranea an eccentric phreatomagmatic explosion crater of about 1 km in diameter belonging to the Alban Hills volcanic district. It is located at an elevation of 44 m a.s.l. approximately 20 km east of Rome. The area experienced a long history of human frequen- tation since the Neolithic, which certainly played an important role in the modification of the natural vegetational landscape of the site, whose potential vegetation is a mixed deciduous oak forest rich in Mediterranean elements (BLASI et al., 1995). 3. MATERIALS AND METHODS The analyzed sediments were collected down to 4 m depth in the central portion of the former Valle di Castiglione maar lake (core VdC09). Subsamples for pollen analysis were taken between 4 m and 1.35 m depth at 4 cm interval along the core. A total of 59 samples were chemically treated and analysed. The pollen sum does not include aquat- ics, hygrophytes, and spores. In the 20 samples with more than 50% AP (Arboreal Pollen) the mean count was 450 terrestrial pollen grains, while in the 39 samples with more than 50% NAP (Non Arboreal Pollen) an average of 340 terrestial pollen grains per sample were counted. Pollen preserva- tion was generally good, with an amount of indeter- minable (degraded, corroded and broken) grains never exceeding 10%. On the whole, 80 pollen taxa were identified. The results are represented on a summary pollen diagram plotted against the age of the sequence (Fig. 1). 1. INTRODUCTION This study presents new pollen data from the Valle di Castiglione maar lake, a site that provided one of the longest palynostratigraphical sequences of southern Europe (FOLLIERI et al., 1988). The new pollen record, studied within cooperation between the Laboratory of Palaeobotany of Sapienza Uni- versity and the Soprintendenza Speciale per i Beni Archeologici di Roma, is supported by six AMS dates and spans the time interval 13,700-8000 cal BP. It shows the vegetation development in the Roman area during the late-glacial and early Holo- cene. This represents a still poorly known time- period in the vegetation history of the Roman area, because of the scarcity of both pollen data and satisfactorily robust chronological settings in the existing records. The main objectives of the pre- sent work are: a) to reconstruct the vegetation re- sponses to the late-glacial climate fluctuations in the Roman area; b) to obtain new data on times and modes of the Holocene reafforestation in cen- tral Italy; c) to provide insights into the develop- ment of the evergreen Mediterranean vegetation during the transition from the late-glacial intersta- dial to the early Holocene. 2. STUDY AREA The site of Valle di Castiglione (41°53’30”N; 12° 45’35”E) is currently represented by the bed of an ancient lake, artificially dried out, which occupied 98 - 100 99 (7%) and a moderate but continuous record of ev- ergreen vegetation (<6%). On the whole, the AP percentages (<40%) point to a mostly open land- scape dominated by Chenopods-Artemisia steppes, less forested than other sites of the re- gion (LOWE et al., 1996; MAGRI, 1999; SADORI & MAGRI, 1999). Younger Dryas - The pollen record shows a new important development of xerophytic vegetation, mostly Artemisia, paralleling a slight decrease in deciduous and evergreen vegetation. Surprisingly, the diagram does not show a clear increase in conifers, differently from other records in the region (LOWE et al., 1996; MAGRI, 1999; SADORI & MAGRI, 1999). At Valle di Castiglione, during the interval 11,900-11,600 cal BP, conifers decrease, in corre- spondence with a cold shift in the GISP2 δ18O curve. During the Younger Dryas, the lake proba- bly experienced major hydrological changes, as suggested by a marked increase in aquatics. Early Holocene - Between 11,500 and 11,100 cal BP, the vegetation history is characterized by a remarkable peak of chenopods, possibly related to site-specific vegetation dynamics overshadowing a reafforestation process by deciduous taxa. In fact, the regional steppe vegetation dominated by Ar- temisia abruptly decreased at the Younger Dryas/ Holocene transition. Clear forest conditions (AP 70%), mostly determined by the development of The timescale was obtained by linear interpolation of six AMS dates from bulk sediment (Fig. 1), cali- brated using the IntCal09 calibration dataset (REIMER et al., 2009). 4. RESULTS AND DISCUSSION The vegetation development indicates that impor- tant changes in the vegetation structure and com- position occurred in the landscape between 13,700 and 8000 cal BP, consistently with the main cli- mate fluctuations recorded by the proxy GISP2 δ18O curve (Fig. 1). Late-glacial interstadial - The samples of the Valle di Castiglione diagram between 13,700 and 13,500 cal BP are characterized by high amounts of pollen of herbaceous taxa (NAP 90%) typical of the Pleis- tocene stadial stages in southern Europe (e.g. Ar- temisia, Chenopods and Poaceae). This pollen composition may be related to either a landscape almost completely dominated by xerophytes, or overrepresentation of local taxa due to selective pollen preservation. The latter hypothesis is sup- ported by the comparison with other pollen records of the Latium region, where NAP never reach such high values in this time interval (LOWE et al., 1996; MAGRI, 1999; SADORI & MAGRI, 1999). Between 13,500 and 12,700 cal BP there is a significant development of deciduous vegetation (30%) ac- companied by a fairly stable presence of conifers Fig. 1, Summary pollen percentage record from Valle di Castiglione (core VdC09) and the GISP2 δ18O record (available from http://www.ncdc.noaa.gov/paleo/icecore/greenland/summit/document/gispisot.htm) Diagramma pollinico percentuale sintetico di Valle di Castiglione (VdC09) e curva GISP2 δ18O (da http:// www.ncdc.noaa.gov/paleo/icecore/greenland/summit/document/gispisot.htm)  A new late-glacial pollen record from Valle ... 100 Ms. received: Testo ricevuto il trees corresponds to the attainment of high values in the GISP2 δ18O curve. REFERENCES BLASI C., DOWGIALLO G., FOLLIERI M., LUCCHESE F., MA- GRI D., PIGNATTI S. & SADORI L. (1995) - La vegetazio- ne naturale potenziale dell'area romana. Atti dei Con- vegni Lincei, 115, 423-457. FOLLIERI M., MAGRI D. & SADORI L. (1988) - 250,000-year pollen record from Valle di Castiglione (Roma). Pollen Spores, 30 (3-4), 329-356. LOWE J., ACCORSI C.A., BANDINI-MAZZANTI M., BISHOP A., VAN DER KAARS S., FORLANI L., MERCURI A.M., RIVA- LENTI C., TORRI P. & WATSON C. (1996) - Pollen strati- graphy of sediment sequences from lakes Albano and Nemi (near Rome) and from the central Adriatic, span- ning the interval from oxygen isotope stage 2 to the present day. Mem. Ist. It. Idrob., 55, 71-98. MAGRI D. (1999) - Late-Quaternary vegetation history at Lagaccione near Lago di Bolsena (central Italy). Rev. Palaeobot. Palynol., 106, 171-208. MAGRI D. & SADORI L. (1999) - Late Pleistocene and Holocene pollen stratigraphy at Lago di Vico (central Italy). Veg. Hist. Archaeobot., 8, 247-260. REIMER P.J., BAILLIE M.G.L., BARD E., BAYLISS A., BECK J.W., BLACKWELL P.G., BRONK-RAMSEY C., BUCK C.E., BURR G.S., EDWARDS R.L., FRIEDRICH M., GROOTES P.M., GUILDERSON T.P., HAJDAS I., HEATON T.J., HOGG A.G., HUGHEN K.A., KAISER K.F., KROMER B., MCCOR- MAC F.G., MANNING S.W., REIMER R.W., RICHARDS D.A., SOUTHON J.R., TALAMO S., TURNEY C.S.M., VAN DER PLICHT J. & WEYHENMEYER C.E. (2009) - IntCal09 and Marine09 radiocarbon age calibration curves, 0– 50,000 years cal BP. Radiocarbon, 51, 1111-1150. deciduous taxa, appear only around 11,100 cal BP. Conifers show a steady decline from 10,900 to 8000 cal BP. Evergreen vegetation experienced a slow increase from 11,300 to 10,200 cal BP, in agreement with the postglacial increase of the GISP2 δ18O values. Around 10,200 cal BP an abrupt rise of evergreen trees (20%), followed by fairly stable values (>10%) up to the top of the dia- gram, suggests that evergreen communities be- came important elements of the vegetational land- scape, approximately at the time when δ18O values from GISP2 reached a high and stable level. 5. CONCLUSIONS The new pollen analysis from Valle di Castiglione indicates that very diversified ecological situations have followed each other in the Roman area be- tween 13,700 and 8000 cal BP: • The late-glacial interstadial is characterized by a deforested landscape dominated by steppe vege- tation (Artemisia-Chenopods-Poaceae), with a modest increase of trees compared to the other pollen records of the region. • Although the prodromes of the Holocene reaffor- estation started around 11,500 cal BP, a clear for- est recovery appeared only at about 11,100 cal BP, probably because of a local marked persis- tence of herbaceous taxa. • Evergreen mediterranean trees show a continu- ous record, suggesting their constant presence in the vegetational landscape even during the late- glacial oscillations. A clear increase of evergreen January 13, 2011 13 gennaio 2011 F. Di Rita, A.P. Anzidei & D. Magri