Paleoenvironmental reconstructions for the south Valdai Hills as paleo-analogues of possible regional vegetation changes under global warming.

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Central Forest State Reserve

The boundary of the Valdai Ice sheet (after Velichko et.al. 2004)

Location of study area

Late Pleistocene

Late Pleistocene vegetation and climate dynamics were reconstructed by pollen and plant macrofossil records of the buried organic sediments of the CFSNBR.Pollen profile indicates the broad-leaved forest dominated by oak and elm, with participation of lime, maple and ash in the first half of the Interglacial and hornbeam at the optimum phase. There have been determined nuts of Carpinus betulus (it is absent in the modern flora of the territory) and numerous water plant remains characteristic for Mikulino climatic optimum (Brasenia holsatica, Trapa natans, Salvinia natans). During the second half of warm period, the gradual cooling and increasing humidity of climate brought about a development of dark-coniferous communities. The end of the Interglacial (so-called “pine zone” - biosone E7 by Menke & Tynni, 1984, or M8 by Grichuk, 1982) was characterized by unstable environments. A number of short-term phases of pine-birch forests with spruce alternating with birch woodlands were identified.

According to data available, the first post-Eemian cooling was divided into two stages by a short climatic amelioration. This minor warming is indicated by an increase in arboreal pollen percentages and concentration. In this phase, birch open woodlands spread over the area, while the proportion of grassland was slightly reduced. Probably, the climate of the initial part of the glacial epoch was characterized by inner instability resulting in the sequence of second-, and even third-order climatic oscillations expressed against the background of the overall trend towards cooling.

In the optimum of the interglacial the January temperature exceeds present temperature by 5-8°Ñ, and for July – by 2-4°Ñ. During the second half of warm period, the gradual cooling and moistening of climate resulted in development of dark-coniferous forest communities.

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This work was supported by RFBR grant ¹ 05-05-64479

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HoloceneHolocene vegetation dynamics were reconstructed on the

base of pollen and plant macrofossil records of peat profile Staroselsky moch in the Reserve.Since 8000 14C years BP the area of the CFSNBR is characterised by a rapid expansion of mixed coniferous broadleaf forest with oak, lime, ash and elm. In the middle Holocene the environment conditions were the most favorable for warm-demanding tree species, the role of elm reached 30-40% and part of lime was about 10%. The proportion of spruce didn't exceed 10% in the middle Atlantic (6000-5500 14C yr. BP) and increased to 20-40% in the latest phase (4500-5500 14C yr. PB). The Holocene optimum was followed by a gradual cooling and moistening of climate resulting in a greater abundance of spruce (up to 60-80% in forest stands) (Novenko et al. 2009).

The climatic reconstructions based on pollen records suggest significant temperature fluctuation in the Late Glacial and the Early Holocene (in time interval 12000-8000 14C years BP). Several warming periods in the second part of the Holocene have been identified: Late Atlantic (4500-4800 14C years BP), the Middle Subboreal (at c. 3500 14C years BP), Early Subatlantic (at 2500 14C years BP) and the Mediaeval Warm Period (MWP, IX-XII centuries). The curve of the January temperature shows the clear pronounced cooling of the Little Ice Age (XV-XVII centuries).

The climate of warm periods is characterized mainly by an increase in winter temperatures of 1-4C above modern values. The mean annual and summer temperatures exceeded their present values by 1C. Precipitation amounts were 600-800 mm per year (close to modern climate). Pollen data indicate that during the Middle Subboreal and the Early Subatlantic warm phases the role of the spruce was significantly reduced by 40-50%, while broadleaf trees and birch become more abundant. The MWP was characterized mainly by spreading of secondary birch forests, probably induced by human impact.

Methods

The paleoenvironmental reconstructions in the CFSNBR are based on pollen, plant macrofossil and radiocarbon data from several profiles of both buried organic sediments and modern raised bogs (Novenko et al. 2008, 2009). Polynological studies of 40 surface samples in the different plant communities of the CFSNBR have shown that percentage composition of the main components of pollen assemblages is well able to describe the amount of spruce, lime and elm in the forest stands while the amount of pine and birch there was strongly overrepresented. The data allowed the estimation of coefficients of a linear model determining the parts of spruce and some broadleaf species in forest stands.

The quantitative characteristics of the Holocene climate (temperature of warmest and coldest months, mean annual temperature and precipitation) were calculated using the information-statistical method developed by Klimanov (1984). This approach is based on multi-dimensional regression models which describe every pollen assemblage as a function of climatic variables. The close relation between the percent proportion of pollen assemblages and climatic characteristics (temperature and humidity) allowed developing this model. 317 pollen diagrams (2414 pollen assemblages) for radiocarbon-dated sections have been analysed. Besides, the percentages of arboreal plants were included in the model taking into account the correcting factors which depend on informative value of taxa. The mean statistical errors for the reconstructions are +\-1°C for the mean annual and July and January temperature, and +\-100 mm for annual precipitation.

The summer and winter temperatures of the last Interglacial were reconstructed on the base of V.P. Grichuk's method of climagrams (Grichuk, 1985). Climagrams are special graphs showing the present climatic fields of different plants. To create these graphs, meteorological data from a large number of sites within the modern range of considered species have been collected. This method comprises adding together climagrams of

IntroductionAn assessment of reaction of south taiga forest ecosystems on global climatic changes,

appearing mainly as temperature growth and changes in precipitation regime, is one of very important scientific problems demanding multy-proxy paleoenvironmental investigations. Reconstructions of climatic changes in the Holocene and past Interglacial will allow us to find paleo-analogues for possible landscape dynamics at the regional level of the south of Valdai Hills (Central European Russia).

The Central Forest State Natural Biosphere Reserve (CFSNBR) in the south Valdai Hills has been chosen as a key region for this study. The landscape of CFSNBR is most typical for south taiga zone and represented mainly by mature spruce forests. It is situated in area between continental area of central Russia and maritime areas of Western Europe. Mean annual air temperature of the area is close to the south limit of taiga zone; therefore flora and vegetation of CFSNBR should be very sensitive even to relatively small climatic and environmental changes.

To describe possible dynamics of the vegetation cover, paleoclimatic and paleoenvironmental reconstructions of the past epochs are used as analogies for future predictions. Nowadays many global and regional paleoclimatic reconstructions have been compiled for various warming and cooling periods of the Late Pleictocene and Holocene (Velichko 2002). Taking into account expected growth of the global temperature due to climatic changes in these studies, two situations assuming increases of global temperature by 1?C and 2?C are generally considered. According to data of paleogeographic investigations, the thermal maximum of the Holocene (about 6-5.5 ka BP) corresponds well to the first situation; the optimum of the last Interglacial (Mikulino-Eemian-Sangamon, stage 5e of the deep-sea oxygen curve, about 125 ka BP) period that could be considered as a paleoanalogue for the second one (Velichko et al. 2004).

Pollen diagram of Holocene peat profile “Staroselsky moch”.

Temperature reconstruction for the Last Interglacial

Canopy species composition (upper graphs) and temperature of coldest and warmest months (lower graphs) in the Holocene

1 2 3 1.E.Yu. Novenko , A.V. Olchev , K.V. Krasnorutskaya I.S. Zuganova

1.- Institut of Geography RAS, Staromonetny 29, 119017 Moscow, Russia, e-mail: lenanov@maile.ru; 2 - Institute of Ecology and Evolution RAS,

3 - Southern Scientific Centre of RAS, Rostov-on-Don, Russia .