Phytomass and carbon storage during the Eemian optimum, late Weichselian maximum and Holocene optimum in Eastern Europe

Global and Planetary Change 16–17 Ž1998. 181–195

Phytomass and carbon storage during the Eemian optimum, late Weichselian maximum and Holocene optimum in Eastern Europe E.M. Zelikson ) , O.K. Borisova, C.V. Kremenetsky, A.A. Velichko Laboratory of EÕolutionary Geography, Institute of Geography, Russian Academy of Sciences, Staromonetny lane 29, 109017 Moscow, Russian Federation Received 19 February 1996; accepted 1 October 1997

Abstract The phytomass stored in terrestrial vegetation at 5.5, 18 and 125 Ka BP, representing the environmental extremes of the Late Quaternary, was estimated for the Russian Plain, excluding the northern coast and adjacent piedmont. The estimates are based on paleovegetation maps by Grichuk wGrichuk, V.P., 1982. Rastitel ‘nost’ Evropy v pozdnem pleistotsene. In: Gerasimov, I.P., Velichko, A.A. ŽEds.., Paleogeografiya Evropy za Posledniye sto Tysyach Let. Nauka, Moscow, pp. 92–109, Žin Russian..x for Eemian optimum, by Velichko and Isayeva wWorld Atlas of Resources and Environment, 1996. Lionty, H.A. ŽEd... Institute of Geography of RAS, Moscow, Vienna.x for the Late Glacial Maximum, and by Khotinskiy wKhotinskiy, N.A., 1984. Holocene vegetational history. In: Velichko, A.A. ŽEd.., Late Quaternary Environments of the Soviet Union. Univ. of Minnesota Press, Minneapolis, pp. 179–200.x for the Late Atlantic, together with analysis of the ecological–coenotic connections of plants and their modern areas. Vegetation on the East-European Plain at 125, 18 and 5.5 Ka BP contained 81.0, 3.1 and 61.4 million kilotons of phytomass, which represents 36.5, 1.4 and 27.6 Gt of carbon. The phytomass of terrestrial plants thus represents an important sink of carbon. Its marked changes make it an important part of the carbon balance during the Pleistocene and the Holocene. q 1998 Elsevier Science B.V. All rights reserved. Keywords: phytomass; Eemian optimum; Russian Plain

1. Introduction Vegetation is one of the most important factors of the terrestrial carbon storage because phytomass is a major sink of carbon. Carbon makes up about one half of the phytomass by weight, which is why data on the phytomass stored in past vegetation is necessary to estimate the changes in the carbon balance. The generally accepted conversion factor from phy)

Corresponding author. Tel.: q7-095-2380298. Fax: q7-0959590033. E-mail: [email protected]

tomass to carbon is 0.45 ŽAjtay et al., 1979.. Carbon storage during the environmental extremes is of special interest. From this point of view, the key intervals of the last 125–130 thousand years are the Last Interglacial ŽEemian–Mikulino. optimum 125 Ka BP, when mean global temperature deviated from modern values by ; q28C., Last Glacial Maximum at 18 Ka BP, and the Holocene optimum 5.5 Ka BP, when the mean global temperature deviated from the modern values by ; q18. This problem now attracts the attention of many scientists whose estimates of the phytomass storage

0921-8181r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 9 2 1 - 8 1 8 1 Ž 9 8 . 0 0 0 3 1 - 9

182

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

are mainly made by means of modeling. Another way is to use as a source of information the reconstructions of spatial distribution of terrestrial biomes of the high taxonomic level for different time slices of the Quaternary ŽAdams et al., 1990.. The specific values of phytomass storage for the past vegetation types are generally considered to be equal to those of their modern vegetation analogues. Our approach is based on the reconstruction of the vegetation, taking into account all available paleobotanical Žincluding palynological. data, as well as the data on the coenotic connections of the plants. The information basis for the estimation of the phytomass and carbon storage 5.5 ka, 18 ka, and 125 ka BP was provided by a set of paleogeographical reconstructions for the territory of Europe, the former USSR and the Northern Hemisphere, that were worked out in the Laboratory of the Evolutionary Geography of the Moscow Institute of Geography of RAS ŽAtlas of paleoclimates and paleoenvironments of the Northern Hemisphere, 1992; Velichko, 1984; Velichko et al., 1982, 1983, 1984, 1991.. The vegetation map of the Eemian Interglacial optimum was compiled by Grichuk Ž1984. on the basis of palynological and paleofloristic data from more than 70 sites within the polygon. It should be mentioned that Grichuk used several methods to map paleovegetation. Along with the pollen spectra interpretation, he used paleofloristic data to reconstruct the composition and distribution of the plant communities of the past. The vegetation map for Late Atlantic time by Khotinskiy Ž1984. used data from more than 120 sites, including 40 sections with radiocarbon dates. The number of sections which include the deposits of Late Glacial Maximum with paleobotanical data is lower; there are 41 sites within the polygon and some of them, mainly in the south, have no radiocarbon dates. The variation of insolation and the spatial distribution of temperatures and precipitation between above-mentioned key intervals, caused substantial differences in the composition and area of each vegetation units. As the result, the phytomass and carbon storage changed substantially from one epoch to another and it differed substantially from the modern situation. These changes affected considerably the carbon balance during the Late Pleistocene and Holocene climatic shifts. The main objective of this paper is to work out a

method to estimate the phytomass storage in paleovegetation on the basis of properties of plant communities, such as height and density of vegetation, and the number of layers, etc., which strongly influence the net phytomass storage. These qualities can be defined by means of analysis of plant behaviour in coenoses, which requires information on paleofloras. Paleofloristic analysis enables us to find the closest possible analogue of paleovegetation among the modern communities. We use the net phytomass storage in such analogous plant communities for our calculations, rather than the mean values of phytomass storage in the biomes of high taxonomic level.

1.1. Methods A very important methodological question is the estimation of the specific values of the phytomass storage in the plant communities of the past. The only source of information is modern plant communities which can be considered their present-day analogues. There is a broad range of variation in specific values for one and the same plant community, and especially for the communities formed by the same dominant plantŽs. in different climatic and environment conditions ŽTable 1.. For instance, the mean specific values of phytomass storage for steppes are from 1.9–2.2 ktrkm2 in grass-herb steppes and meadow steppes to 1.3–1.4 ktrkm2 in dry steppes, and only 0.5–0.6 ktrkm2 for steppe communities on slightly saline soils ŽBazilevich, 1993.. These variations depend on the floristic composition of the communities and on their structure, meaning such features as plant density, coverage, the number of layers, etc. These features, in turn, depend on the composition of the coenosis-forming species, the degree of their development, and the climatic and soil conditions. Some of the plant species are closely connected with the communities of a definite type Žindicative plants.. For example, the plants Eurotia ceratoides, Ephedra, and Kochia prostrata, which are connected with the continental arid climate of dry steppes, semideserts and deserts, as well as in the high mountains ŽPamir up to 4000 m above sea level and Altai., and which were very typical for the

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

183

Table 1 Examples of the specific values of the phytomass storage in different zones Ž10 3 trkm2 . after Bazilevich Ž1993. (1) Tundra Typical tundra South tundra Mountain tundra

1.108 2.693 3.866 2.316 0.519 1.581

Taimyr peninsula, upper parts of watersheds Taimyr peninsula, slopes of watersheds Taimyr peninsula, slopes of watersheds Yamal peninsula, slopes of watersheds Koryakskoye Upland, 550 m altitude Mountains of the N–E Asia, 1200–1700 m altitude

22.197 32.530 39.500

Russian Plain, Oka-Don interfluve Byelorussia, Pripyat’ and Middle Dnieper basin Moldavia, Dniester-Dunai interfluve

East European Plain 1.274 1.749 1.270 1.312 0.650

West Siberia 1.676 2.255 1.630 1.479

(2) Broad-leaÕed forests

(3) Steppes Meadow steppes Typical steppes Dry steppes Dry steppes on saline grounds

periglacial steppes, always form communities with low coverage and simple structure. As we cannot avoid using the modern specific values of the phytomass storage for the calculation of the phytomass of the past vegetation, the main question is how to choose the correct estimations. The quantitative correlation of components of pollen spectra reflects the type of vegetation that existed during the time interval under study and the composition of its dominant Žat the taxonomic level of genera, or even families, for grass and herb.. If we have sufficiently complete paleofloristic data, we can use the method of modern concentration area of the plant species of the fossil flora worked out by Grichuk Ž1984. whereby we assume that the modern vegetation of the area, where all plants of the fossil flora Žor most of them. presently grow, is a modern analogue of the past vegetation. For example, the modern concentration areas for the fossil floras of the Mikulino ŽEemian. climatic optimum in the Kama and Vyatka basins, on the territory, which was then occupied by the broadleaved forests with spruce, are located in the drainage basin of Nieman ŽIvanova, 1973.. Therefore, it is possible to use the estimation of the phytomass storage in the modern forests in the basin of Nieman

as a specific value for the spruce–broad-leaved forests of the Mikulino climatic optimum. The modern analogues for the periglacial steppes and forest-steppes, which occupied the East-European Plain during the LGM of the Valdai ŽWeichsel. glaciation are the present-day formations of the Altai, which now exist in areas with a cold and continental climate, such as Chuiskaya basin. We therefore use their specific values of the phytomass storage which, in steppes, reach only about 0.5–0.6 ktrkm2 ŽKuminova, 1960.. If the paleofloristic information available is not sufficient to apply the method of the modern concentration area of the plants determined in the fossil flora, we should choose the modern analogues according to specific features of the past vegetation and which are indicated by the presence of certain characteristic plants. For example the periglacial steppes were connected with soils low in humus and generally saline because of the climatic aridity. They included plant species Žalso growing now on such soils. which formed communities characterized by low density and an absence of distinct layers. So we cannot apply the estimations of the phytomass storage in the modern meadow and grass–herb steppes as specific values of the phytomass storage for the

184

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

Fig. 1. Vertical projections of the steppe communities ŽAlekhin, 1951.: Ža. meadow steppe in the Kursk district, Žb. dry steppe, Askania Nova reservation.

periglacial steppe because these two northern types of steppe vegetation are distinguished by high density and by plant communities of several layers, the first of them formed by high plants ŽFig. 1a.. At the same time, the properties of southern dry steppes were very close to those of the periglacial steppes ŽFig. 1b.. Many indicative plants, typical for the periglacial steppes Ž E. ceratoides, K. prostrata, Ephedra distachya, and others., presently grow in dry steppes, so there is a clear resemblance in the floristic composition between these two vegetation types. The specific values of the phytomass storage of the southern dry steppes are very close to the values of the Altai mountain steppe, the closest modern analogues of the periglacial steppe vegetation. So we can suppose that the specific values of

the periglacial steppe communities were close or at least not higher than those of southern dry steppes. 2. Comparison of the phytomass storage in the key intervals of the Late Pleistocene and Holocene on the key region (‘polygon’) of the East European Plain Methodical approaches to the phytomass estimation for three key intervals of the Late Pleistocene and Holocene Ž125, 18 and 5.5 Ka BP. were worked out using the data for the East-European Plain, the environmental and vegetation history of this region being thoroughly studied. The territory of the EastEuropean Plain between 25–308 and 558E, 468 and 658N was chosen as a key region Ž‘polygon’.. It is

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

big enough to reveal all the landscape features and the vegetation zonal structure. Not taken into consideration were the northern coast of the East European Plain, as well as the peripheral piedmont areas adja-

185

cent to it. The equal-area projections used for the maps of vegetation allow us to make comparable area measurements of each vegetation unit. Carbon storage in the paleosoils was estimated for

Fig. 2. Ža. Present Žpotential. vegetation in the East-European Plain Žin the borders of the key region.. According to Rastitel‘nost’ Evropeiskoi chasti SSSR Ž1980., simplified. Ž1. northern taiga, Ž2. middle taiga, Ž3. south taiga, Ž4. coniferous-broad-leaved forests, Ž5. broad-leaved forests, Ž6. forest-steppe, Ž7. grass and grass-herb steppes, Ž8. dry steppe, Ž9. semidesert, Ž10. desert. Lakes and sea are not hatched. Žb. Vegetation on the East-European Plain during the Holocene optimum, 5.5 Ka BP. According to Khotinskiy Ž1984. simplified. Ž1. pine forests, Ž2. south taiga, Ž3. coniferous-broad-leaved forests, Ž4. broad-leaved forests, Ž5. forest-steppe, Ž6. mesophilous grass-herb steppe, Ž7. semidesert, Ž8. desert. Lakes and sea are not hatched. Circles: sites; shaded circles: sites with radiocarbon datings. Žc. Vegetation on the East-European Plain during the Valdai ŽWeichselian. maximum 18 Ka BP. According to Velichko and Isayeva ŽWorld Atlas of Resources and Environment, 1996, simplified.. Ž1. ice sheet, Ž2. periglacial forest-steppe with tundra elements, Ž3. periglacial steppe, Ž4. dry steppe and semidesert. Lakes and sea are not hatched. Shaded circles-sites. Žd. Vegetation on the East-European Plain during the Mikulino ŽEemian. optimum. According to Grichuk Ž1982., simplified. Ž1. dark coniferous forests, Ž2. coniferous-broad-leaved forests, Ž3. broad-leaved forests with hornbeam, Ž4. forest-steppe, Ž5. dry steppes and semidesert. Lakes and sea are not hatched. Shaded circles: sites.

186

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

Fig. 2 Žcontinued..

the same territory and for the same time intervals by Morozova et al. Ž1998. Žthis volume., so their results are used for the comparison of the data of the paleopedological and paleobotanical investigation. 3. The present-day vegetation A map of the potential Žpre-agricultural. vegetation, which corresponds to present-day environmental conditions, was used for the calculations of the phytomass storage in the modern natural vegetation.

Certainly, the modern plant cover on the territory under investigation, especially in its central and southern parts, is strongly disturbed by anthropogenic activities and only small patches of the natural plant communities persist. Thus, the real phytomass storage differs very much from the estimated values. The phytomass storage in modern natural vegetation is determined by anthropogenic factors, rather than by natural factors, and does not correspond to the present-day climatic and soil conditions.

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

187

Fig. 2 Žcontinued..

The simplified present-day vegetation map ŽFig. 2a. is based on the map worked out by the group of authors from the Botanical Institute of RAS ŽRastitel‘nost’ Evropeiskoi chasti SSSR, 1980.. In the North of the area under consideration, coniferous northern taiga forests are spread, Siberian spruce Ž Picea oboÕata. being their main dominant. European spruce Ž Picea abies . grows only in the south and southwest parts of the area. The climatic conditions in the territory of northern taiga are characterized by low summer and winter temperatures caused not only by high latitudes, but also by summer invasions of cold Arctic air and by cool and moist

Atlantic air masses. This territory is mainly swampy and permafrost is present in its eastern part. Because of the unfavorable climatic conditions, the northern taiga forests are characterized by simple structure of plant communities Žlow tree and shrub layers are usually absent., low density of the canopy, and low quality of stands. Consequently, specific values of phytomass storage are low ŽTable 2.. The middle taiga coniferous forest covers the territory south of the northern taiga subzone and is composed mainly of European spruce, and partly by Siberian spruce, as well by their hybrids. The temperate continental climate of its area is characterized

188

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

Fig. 2 Žcontinued..

by rather warm and moist summers and cold winters. The structure of these forests is also rather simple; only one tree layer is usually present and the shrub layer, if present, is poorly developed. The canopy density is quite high Ž0.7–0.8., as is the stand quality and tree height. The phytomass storage specific values for these forests are higher than for the northern taiga communities Žabout 19.7 ktrkm2 .. The southern taiga forests are spread in the central part of the East European Plain. This area features favorable climatic conditions with a comparatively

long growing season. These forests are composed mainly of European spruce, plus pine Ž Pinus sylÕestris ., birch and aspen; the latter two tree species also form secondary forests. The nemoral Žbroadleaved. tree species, such as Quercus robur, Tilia cordata, and Ulmus laeÕis, grow in the southern part of the south taiga zone, but do not play a noticeable coenotic role there. The tree layer includes usually 2–3 sublayers, the stand quality reaches the second or even the first class. The phytomass storage specific values for the forests of the south taiga subzone

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

are the highest within the European taiga Ž26.6 ktrkm2 . and close to the values of the coniferousbroad-leaved forests. Two southern subzones of the forest belt in the East-European Plain, the coniferous-broad-leaved and broad-leaved forests, occupy the most favorable regions of the territory under consideration, and the natural vegetation there is disturbed to a greater degree because of the anthropogenic activity. The zonal forest communities in the coniferous-broadleaved subzone are formed by the European spruce and nemoral tree species, such as oak Ž Q. robur . and lime ŽTilia cordata.. Such trees as elm, ash, maple also take part in these communities. West European tree species Ž Quercus petraea, Quercus pubescens, Tilia platyphyllos, Carpinus betulus . grow only in the western part of the broad-leaved forest and forest-steppe subzones Žto the West of the Dnieper River..The broad-leaved and coniferous-broad-leaved forest communities usually include several tree and shrub layers, tree stands are of high quality Ž1–2 classes. and the phytomass storage specific values are high, especially in the broad-leaved zone.

Table 2 The modern Žpotential. phytomass storage on the East European plain Žin the limits of the test area. Vegetation

Northern taiga coniferous forests Middle taiga coniferous forests Southern taiga coniferous forests Coniferous-broad -leaved forests Broad-leaved forests Forest-steppe Grass steppe Dry steppe Semidesert Desert Sea, lakes

Area Ž10 3 km2 .

Phytomass storage Specific Total Ž10 6 t. values Ž10 3 trkm2 .

187.0

13.9

2599.3

435.0

19.7

8569.5

390.4

26.6

10 384.6

478.0

26.3

12 571.4

467.0

32.5

15 177.5

252.0 445.6 219.6 133.0 119.8 72.6

13.0 1.3 1.0 0.8 1.0 y

3276.0 579.3 219.6 106.4 119.8 53 603.4

189

The forest communities of the forest-steppe subzone are formed by Q. robur with the addition of other nemoral trees and various shrubs. The steppe communities Žof meadow steppe type. are characterized by the rich floristic composition and the complex structure, thus explaining their comparatively high specific values of phytomass storage. In the southern types of steppes, especially in dry steppes, the structure of the communities is simpler and their coverage is significantly lower, as well as the specific values of the phytomass storage. These parameters are still lower in semidesert communities ŽTable 2.. The specific values of the phytomass storage in the modern zonal plant communities, presented in Table 2, were calculated for each vegetation type as a mean quantity of all values, quoted by Bazilevich Ž1993. for this plant community on the territory under investigation. For the forest-steppe it was supposed that about 50% of the territory was covered by forests. They occupied 50% of the territory in the East European forest-steppe before the development of agriculture ŽRastitel‘nost’ Evropeiskoi chasti SSSR, 1980.. Overall, the phytomass storage in the potential vegetation on the East European Plain Žin the borders of the above mentioned key region. reached more than 53 Gt, and the carbon storage about 23.7 Gt.

4. Holocene optimum, ; 5.5 Ka BP The vegetation units on the East European Plain during the Holocene optimum were close to their modern analogues by their properties but, due to the warmer climate, there were certain differences in their ranges and especially in the position of their northern borders ŽKhotinskiy, 1984 and Fig. 2b.. The northern part of the territory under consideration, where northern and middle taiga communities are now spread, was occupied by southern taiga 5.5–6 Ka BP. It was replaced to the south by coniferous-broad-leaved forests, their southern limit being close to the modern border between middle and southern taiga in the western part of the EastEuropean Plain and to the modern border between

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

190

Table 3 The phytomass storage on the East European plain during the Holocene optimum, 5.5 Ka B.P. Žin the limits of the test area. Vegetation

Pine forests Southern taiga coniferous forests Coniferous-broad -leaved forests Broad-leaved forests Forest-steppe Steppe Semidesert Desert Sea, lakes

Area Ž10 3 km2 .

Phytomass storage Specific Total Ž10 6 t. values Ž10 3 trkm2 .

43.2 465.0

18.8 26.6

812.2 12 369.0

341.7

26.3

8986.7

1121.3

32.0

35 881.6

179.3 624.9 220.8 75.4 128.4

13.0 1.3 0.8 1.0 y

2330.9 812.4 176.6 75.4 61 444.8

115% of the modern Žpotential. total phytomass storage.

the southern taiga and coniferous-broad-leaved forests in its eastern part. The southern borders of the broad-leaved forest subzone and forest-steppe were close to their modern positions. On the whole, the area occupied by nemoral broad-leaved forests during the Holocene optimum was greater than now, and that of the forest-steppe smaller than now. The border between the semi-desert and desert was generally close to its modern position. The specific values of the phytomass storage for the zonal plant communities are considered to be equal to their modern parameters because of the close similarity of the middle Holocene and modern communities. One of the proofs of this fact is the position of the modern concentration areas of the middle Holocene fossil floras. For example, the area determined by Ivanova Ž1973. for the flora from the section on the Sit’ma River Ža tributary of Vyatka in the south of the southern taiga subzone. is situated in the Upper Volga region which is to the west of the site, but within the same vegetation subzone. The calculation shows, that the phytomass storage on the territory under consideration reached about 61.4 Gt in the Holocene optimum 5.5 Ka BP, that is, about 115% of the modern values ŽTable 3., and the carbon storage was about 27.6 Gt. Such a small

deviation from the modern estimation is to be expected; one of the reasons being the fact, that in the central regions of the East-European Plain there were areas with smaller annual sum of precipita-tion during the Holocene optimum than at present.

5. Last Glacial Maximum, ; 18 Ka BP During the last glaciation most of the ice-free area in the East-European Plain was occupied by the periglacial zone. Flora and vegetation at that time existed in a severely cold and arid climate Žthe deviation of the mean January temperature from modern values was not less than y108. and inevitably could have little in common with the modern flora and vegetation of the East European Plain. Of course, there were such plant species as Betula alba and some herbs which are still growing there, but the main part of the glacial flora, as well as the plant communities of that time, were alien to the modern East European flora. Now we can find only more or less close analogues of the periglacial vegetation within the mountain regions of the continental areas in southern Siberia, mainly in the Altai Mountains. The vegetation cover on the East European Plain had a relatively simple structure during the maxi-

Table 4 The phytomass storage on the East European Plain during the Late Valdai ŽWeichselian. maximum, 18 Ka B.P. Žin the limits of the test area. Vegetation

Periglacial forest-steppe Periglacial steppe Dry steppe and semidesert Ice sheet Sea, lakes

Area Ž10 3 km2 .

Phytomass storage Specific Total Ž10 6 t. values Ž10 3 trkm2 .

971.4

2.2

2137.1

1084.9

0.7

759.4

218.7

1.0

218.7

581.7 343.3 3115.2

6% of the modern Žpotential. total phytomass storage.

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

mum of the Valdai ŽWeichsel. glaciation ŽFig. 2c. according to Velichko and Isayeva ŽWorld Atlas of Resources and Environment, 1996.. The main part of the ice-free territory was occupied by periglacial forest-steppe with tundra elements in the north and by the periglacial steppe in its central and southern parts. As palynological data show, the communities of dwarf birch and willow were a constant element of both vegetation types. A rather narrow belt of the dry steppe and semidesert was situated in the SouthEast along the coast of the Caspian Sea. The specific values for the periglacial steppe communities were calculated on the basis of modern estimations of phytomass storage in Altai dry steppes and in the dry steppes on slightly saline soils. The estimations of the phytomass storage in the shrub tundra Ždwarf birch and Salix communities. were also taken into consideration. For the periglacial forest-steppe the specific values of the phytomass storage were calculated on the basis of the estimations for the periglacial steppe communities and the modern values for the birch and pine woodlands. It was supposed that open woodlands occupied about 40% of the whole area of the periglacial forest-steppe and the shrub tundra communities about 10%. The rest of the territory was covered by the periglacial steppe communities. During the Last Glacial Maximum the phytomass storage reached only 6%, about 3.1 Gt, of the modern one and the carbon storage about 1.4 Gt ŽTable 4..

6. Last Interglacial Optimum, ; 125 Ka BP

Numerous sites of the Eemian ŽMikulino. Interglacial are known on the territory of the ‘polygon’ ŽFig. 2d.. Lacustrine and peat sediments of this age are very rich in pollen and spores. In eastern Europe, as well as in western Europe, palynological data provide a reliable means to determine their stratigraphic position because of the specific character and sequence of pollen zones. Their Eemian age was confirmed by ThrU dates of mollusc shells obtained from several sites beyond the polygon. The specific values of the phytomass storage characteristic for the interglacial vegetation units were estimated by the parameters of their modern analogues in the present-day concentration areas of fossil floras or those analogues which were chosen on the basis of structural and floristic resemblance with the modern communities. The latter method was applied where the modern values are not acceptable and where the concentration areas could not be determined because of the scarce paleofloristic data. For example, the closest modern analogue of broadleaved forests with Q. robur and C. betulus as main dominants is the present-day communities that occupy the lowland habitats in the basin of upper Elba River. For a long time the area was used for agriculture and such forests have been largely destroyed; those that do remain are disturbed. That is why the modern floristically rich forests of the same compo-

Table 5 The phytomass storage on the East European Plain during the Mikulino ŽEemian. Interglacial, 125 Ka B.P. Žin the limits of the test area. Vegetation

We cannot consider those communities that existed on the East-European Plain during the Mikulino ŽEemian. optimum as identical to the modern plant communities. The Last Interglacial was separated from the present time by a glacial epoch when there was no possibility for the thermophilous flora and vegetation to survive in eastern Europe. During the Holocene warming, the immigrating thermophilous plants formed their communities in accordance with their ecological and coenotic properties, but this process caused only a distinct resemblance between the interglacial and newly formed Holocene communities. There was no direct inheritance.

191

Coniferous forests with birch Coniferous-broad -leaved forests Broad-leaved forests with hornbeam Forest-steppe Steppe Sea, lakes

Area Ž10 3 km2 .

Phytomass storage Specific Total Ž10 6 t. values Ž10 3 trkm2 .

263.2

21.0

5527.2

547.0

34.0

18 598.0

1394.9

35.0

48 821.5

606.1 146.8 242.0

13.0 1.3

7879.3 190.8 81 016.8

150% of the modern Žpotential. total phytomass storage.

192

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

sitions and structure of the communities in the western regions of the East-European Plain and in the Caucasus were chosen as analogous plant communities and their specific values were used for the assessment of the phytomass storage in Mikulino interglacial broad-leaved forests Žthe hornbeam, which grows in the Caucasus, is included in the C. betulus .. During the optimum of the Mikulino ŽEemian. interglacial the main part of the East European Plain was covered by forests ŽFig. 2d.. The dark coniferous forests with birch and broad-leaved tree species, such as Q. robur, T. cordata, Ulmus sp. sp., existed in the northeast of the territory, the role of the broad-leaved species increased to the south. These

forests differed from modern communities of the same type by the presence of birch in the non-disturbed, primary forests. Farther to the south the coniferous-broad-leaved forests were spread, and south of them the broadleaved forests which occupied the main part of the forest zone. They differed from the modern East European broad-leaved forest by their floristic composition. Such West European tree species as C. betulus, Q. petraea, Q. pubescens, T. platyphyllos were among the dominants of Eemian forests in the East European Plain. Their southern boundary went farther to the south compared to its present-day position-close to the boundary between forest-steppe and steppe on the main part of the territory and close

Fig. 3. The phytomass storage in the East European Plain Žwithin the ‘polygon’. for the key intervals of the Late Quaternary and its correlation with the present-day one Ž%.. Ž1. north taiga, Ž2. middle taiga, Ž3. pine forest, Ž4. south taiga, Ž5. coniferous forest with birch, Ž6. coniferous-broad-leaved forest, Ž7. broad-leaved forest, Ž8. forest-steppe, Ž9. steppe, Ž10. grass steppe, Ž11. dry steppe, Ž12. semidesert, Ž13. desert, Ž14. periglacial forest-steppe, Ž15. periglacial steppe, Ž16. dry steppe and semidesert.

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

to the modern boundary between grass-herb and dry steppes in its eastern part. The forest-steppe extended to the Black Sea coast during the Mikulino ŽEemian. interglacial, and only near the Caspian Sea was a narrow belt of the dry steppe that was transitional to a semidesert. The total phytomass storage on the territory under study during the Mikulino ŽEemian. optimum reached up to 81.0 Gt, or 150% of the modern one ŽTable 5., and the carbon storage about 36.5 Gt.

7. Discussion The main features of the phytomass storage distribution among the vegetation zones for the key intervals of the Late Pleistocene and the Holocene and their general correlation for the area of the East European ‘polygon’ are summarized by the diagram ŽFig. 3.. The percentage correlation shown on it reflects both the phytomass storage and the carbon storage variations in the area under consideration during the Late Quaternary key time intervals 5.5, 18 and 125 Ka BP. They reveal large-scale oscillations between the warm and cold epochs Žinterglacial optimums, the Holocene optimum included, and the Late glacial maximum., as well as between warm epochs with different character Žthe Holocene and Mikulino–Eemian optimums.. It is clear that such oscillations exerted an influence upon the carbon balance during the Quaternary. The comparison of the presented values of the phytomass and carbon storage on the East-European Plain with the parameters obtained for the territory of the North Eurasia in the borders of the former USSR show that the correlation of the phytomass storage during the Mikulino optimum and present time is similar for both regions; the first value reaches about 150% of the second one. During the Holocene the phytomass storage on the whole territory of the former USSR was somewhat higher than in the East-European Plain, about 120% of the present-day one ŽVelichko et al., 1991.. However, in Siberia, according to Monserud et al. Ž1995. it reached also about 120% of the modern phytomass storage in the potential vegetation Ž105 Gt and 85.9 Gt, respectively.. During the Last Glacial Maximum the phytomass storage was about 20% of the modern

193

one on the territory of the former USSR, which is higher than in the East-European Plain because the degradation of the forest and woodland, as well as of the steppe vegetation in the continental areas of the Asian part of the country, was less expressed than in eastern Europe ŽVelichko et al., 1991.. The degradation of the vegetation during the Last Glacial Maximum was still less marked in the tropical and subtropical regions. That is why the present-day global carbon storage amounts only to 110–140% of the Late Glacial estimation Žaccording to Adams et al., 1990.. The estimations of the biomass storage in Europe during the last 22 Ka obtained by A.-K. Gliemeroth Ž1995. are quite comparable with the above-cited values. The biomass storage during the Holocene optimum for 7 Ka BP made up about 116% of the present-day potential biomass storage in Europe. During the Pleniglacial 22 Ka BP the biomass storage made up only 4.8% of the presentday real biomass. The similarity of the parameters given by Gliemeroth to our estimations for eastern Europe is informative, but its significance should not be overestimated because the time intervals considered by authors are not quite the same and the phytomass storage is not equal to the biomass storage, although it makes up the main part of the latter one. Phytomass storage estimations obtained from modelling based on pollen spectra can be considerably different from the above values which are derived from the reconstruction of paleovegetation. Thus, Peng et al. Ž1994. reached the conclusion that the carbon storage in phytomass in Europe has not changed since 6000 BP.

8. Conclusions The specific values of the phytomass storage in present-day plant communities, which represent more or less close analogues of the vegetation units that existed during the Late Quaternary, give the only possible source of the information about such values of the Late Quaternary plant communities. In choosing the modern analogues it is necessary to take into account the type of the vegetation Žforest, steppe, desert, etc.. and the floristic and structural properties of the paleocommunity, as well as those of the

194

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195

modern one. This is especially important for the vegetation of the glacial epoch, because the environment, and consequently the biota which existed then have no close present-day analogues. The estimation of the phytomass storage in the vegetation on the continents during the key time intervals of the Late Pleistocene and the Holocene Ž5.5, 18 and 125 Ka BP. was carried out for rather a limited area of eastern Europe, but is nonetheless in good agreement with the data for other territories, obtained not only by these authors, but by other scientists as well. Hence we can conclude that the estimation of the terrestrial phytomass storage in the Late Quaternary vegetation on the basis of the paleobotanical data and the above discussed methodical approach is quite possible and reliable. Vegetation on the East European Plain during the key intervals of the Late Quaternary 125, 18 and 5.5 Ka BP accumulated 81.0, 3.1 and 61.4 Gt of phytomass, respectively, which corresponds to 36.5, 1.4 and 27.6 Gt of the carbon. It is evident that the phytomass of terrestrial plants represents an important sink of carbon and the carbon storage in vegetation cover was subjected to substantial change, with a minimum at around the Last Glacial Maximum. Therefore it constituted an important influence on terrestrial the carbon balance during the Pleistocene and the Holocene.

Acknowledgements The authors are very grateful to Prof. Hugues Faure for stimulating research and providing support. They are very thankful to Prof. V.P. Grichuk for valuable advices and consultations, and to two anonymous referees for correcting and improving written English of this paper. Liliane Faure organizational skills were much appreciated. This work is part of the Project ‘Dynamics of the terrestrial biota’ supported by the European Community ŽINTAS No. 93-2037., and by the French CNRS and Russian Academy of Sciences Cooperative Exchange Programme Ž1994–1997.. It is a contribution to the INQUA Commission on Terrestrial Carbon and IGCP Project No. 404 Žjoint programme of IUGS and UNESCO..

References Adams, J.M., Faure, H., Faure-Denard, L., McGlade, J.M., Woodward, F.I., 1990. Increases in terrestrial carbon storage from the Last Glacial Maximum to the present. Nature 348, 711– 714. Ajtay, G.L., Ketner, P., Duvigneaud, P., 1979. Terrestrial primary production and phytomass. In: Bolin, B., Degens, E.T., Kempe, S., Ketner, P. ŽEds.., The Global Carbon Cycle, SCOPE 13. Wiley, Chichester, pp. 123–181. Alekhin, V.V., 1951. Rastitel ‘nost’ SSSR. Sovetskaya nauka, Moscow, 512 pp. Žin Russian.. Atlas of Paleoclimates and Paleoenvironments of the Northern Hemisphere ŽLate Pleistocene– Holocene., 1992. Frenzel, B., Pesci, M., Velichko, A.A. ŽEds... Stuttgardt, Budapest, 149 maps, 146 pp. Bazilevich, N.I., 1993. Biologicheskaya Productivnost’ Ecosistem Severnoi Evrazii. Nauka, Moscow, 293 pp. Žin Russian.. Gliemeroth A.-K., 1995. Palaookologische Untersuchungen uber Die Letzten 22000 Jahre in Europa. Gustav Fischer Verlag, Stuttgart, 252 pp. Grichuk, V.P., 1982. Rastitel ‘nost’ Evropy v pozdnem pleistotsene. In: Gerasimov, I.P., Velichko, A.A. ŽEds.., Paleogeografiya Evropy za Posledniye Sto Tysyach Let. Nauka, Moscow, Nauka, pp. 92–109 Žin Russian.. Grichuk, V.P., 1984. Late Pleistocene vegetational history. In: Velichko, A.A. ŽEd.., Late Quaternary Environments of the Soviet Union. Univ. of Minnesota Press, Minneapolis, pp. 155–178. Ivanova, N.G., 1973. Experience with the dating of alluvial deposits of the Vyatka river and vegetation reconstruction on the basis of paleofloristic evidence. In: Grichuk, V.P. ŽEd.., Palynology of Pleistocene and Pliocene. Proceedings of the III International Palynological Conference. Nauka, Moscow, pp. 64–69 Žin Russian, with English abstract.. Khotinskiy, N.A., 1984. Holocene vegetational history. In: Velichko, A.A. ŽEd.., Late Quaternary Environments of the Soviet Union. Univ. of Minnesota Press, Minneapolis, pp. 179–200. ` pokrov Altaya. Izdatel’stvo Kuminova, A.V., 1960. RastitelInyi AN SSSR, Sibirskoye Otdeleniye. Novosibirsk, 450 pp. Žin Russian.. Monserud, R.A., Denissenko, O.V., Kolchugina, T.P., Tchebakova, N.M., 1995. Global Biogeochem. Cycles 9 Ž2., 213–226. Morozova, T.D., Velichko, A.A., Dlussky, K.G., 1998. Organic carbon content in the Late Pleistocene and Holocene fossil soils Žreconstruction for Eastern Europe.. Global Planet. Change 16–17, 129–150. Peng, C.H., Guiot, E., Van Campo, E., Cheddadi, R., 1994. The vegetation carbon storage variation in Europe since 6000 BP: reconstruction from pollen. J. Biogeogr. 21, 19–31. Rastitel‘nost’ Evropeiskoi chasti SSSR, 1980. Gribov, S.A., Isachenko, T.I. Lavrenko, E.M. ŽEds.., Nauka, Leningradskoye Otdeleniye, Leningrad, 429 pp. Žin Russian.. Velichko, A.A., 1984. Late Pleistocene spatial paleoclimatic reconstructions. In: Velichko, A.A. ŽEd.., Late Quaternary envi-

E.M. Zelikson et al.r Global and Planetary Change 16–17 (1998) 181–195 ronments of the Soviet Union. Univ. of Minnesota Press, Minneapolis, pp. 261–285. Velichko, A.A., Grichuk, V.P., Gurtovaya, Y.Y., Zelikson, E.M., Borisova, O.K., 1982. Paleoklimaticheskiye rekonstruktsii dlya optimuma mikulinskogo mezhlednikov’ya na territorii Evropy. Izvestiya AN SSSR, seriya geograficheskaya 1, 15–19, Žin Russian.. Velichko, A.A., Grichuk, V.P., Gurtovaya, Y.Y., Zelikson, E.M., 1983. Paleoklimat territorii SSSR v optimum mikulinskogo mezhlednikov’ya. Izvestiya AN SSSR, seriya geograficheskaya 6, 30–39, Žin Russian..

195

Velichko, A.A., Barash, M.S., Grichuk, V.P., Gurtovaya, Y.Y., Zelikson, E.M., 1984. Klimat Severnogo polushariya v epokhu poslednego, mikulinskogo mezhlednikov’ya. Izvestiya AN SSSR, seriya geograficheskaya 1, 5–18, Žin Russian.. Velichko, A.A., Borisova, O.K., Gurtovaya, Y.Y., Zelikson, E.M., 1991. Climatic rhythm of the Last Interglacial in the Northern Eurasia. Quaternary Int. 10–12, 191–213. World Atlas of Resources and Environment, 1996. Lionty, H.A. ŽEd.., Institute of Geography of RAS. Moscow, Vienna.