Holocene Vegetation History from the Salym-Yugan Mire Area, West Siberia
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1 1 The Holocene 12,2 (2002) pp. 177–186 2 3124567891011121318192526 27 Holocene vegetation history from the 28 Salym-Yugan Mire Area, West Siberia 1 2,3 2 29 Aki Pitka¨nen, * Jukka Turunen, Teemu Tahvanainen and 2 30 Kimmo Tolonen 1 31 ( Karelian Institute, Section of Ecology, University of Joensuu, PO Box 111, 2 32 FIN-80101 Joensuu, Finland; Department of Biology, University of Joensuu, 3 33 PO Box 111, FIN-80101 Joensuu, Finland; Department of Geography and the 34 Centre for Climate and Global Change Research, McGill University, 805 35 Sherbrooke Street West, Montreal, Quebec, H3A 2K6, Canada) 36 Received 21 November 2000; revised manuscript accepted 25 July 2001 37 Abstract: The pollen stratigraphy of an ombrotrophic patterned ridge-hollow raised bog in the Salym-Yugan Mire Area in boreal West Siberia (60°10ЈN, 72°50ЈE) covers the entire Holocene period. Pollen data from three parallel peat cores suggest that, contrary to previous assumptions, Betula forests did not spread into tundra until the Boreal period (9000–10000 cal. BP). After 9000 cal. BP, Pinus sylvestris and Picea abies forests displaced Betula forests in the area and dominated until 4100–4300 cal. BP, when Picea decreased considerably due to a climatic change and Pinus sylvestris became the most abundant tree species. Average pollen influx estimates during the wooded period, from about 9000 cal. BP onwards, were 5600–6350 grains cm–2 yr–1, similar to pollen-trap estimates from boreal coniferous forests. Key words: Paleoecology, palaeoclimate, vegetation history, boreal region, raised bog, mire, West Siberia, 38 Holocene. 49 50 51 Introduction part of West Siberia, Russia (Figure 1). Salym-Yugan Mire is part 71 of the Great Vasyugan Mire, which covers an area of 5.4 million 72 52 West Siberia refers to the area between the Ural mountains and hectares (Botch and Masing, 1983). The climate is continental, 73 53 the Yenisey river, largely occupied by the Ob-Irtysh basin, lying with mean January and July temperatures of –22°C and +16°C. 74 54 25–95 m above sea level. Mires of the West Siberian lowland The mean annual temperature is –3.2°C and the annual precipi- 75 55 cover 50–75% of the land (Romanova, 1967) and provide about tation 400–500 mm (Russia’s Weather Server, 1999). The study 76 56 60% of all the peat deposits of the former Soviet Union and 40% area is situated about 200 km south of the permafrost limit (Baulin 77 57 of the global peat deposits (Walter, 1977). Knowledge of the veg- and Danilova, 1984). 78 58 etation history of this vast West Siberian area is important for a The study area is covered with wooded or open mires with 79 59 better understanding of climatic changes in the Northern Hemi- islands of dry uplands. The wooded islands and dry soils on river 80 60 sphere during the Holocene. Present knowledge is based mostly banks comprise about 20% of the land area. The landscape is 81 61 on data collected from sites along the Ob and Irtysh rivers almost flat, and the absolute heights in the area range between 58 82 62 (Khotinskiy, 1984), and the palaeoclimatic reconstructions are and 65 m a.s.l. Latin names of the tree species are according to 83 63 based on only a few dated pollen diagrams (Velichko et al., 1997; Ha¨met-Ahti et al. (1998). The wooded mires are dominated 84 64 Peteet et al., 1998; Khotinskiy, 1984; Blyakharchuk and Sulerzhit- mainly by Scots pine (Pinus sylvestris L.) with scattered Siberian 85 65 sky, 1999). Our aim is to reconstruct the Holocene vegetation pines (Pinus cembra L. ssp. sibirica (Du Tour) Krylov). The for- 86 66 history in the middle boreal vegetation belt from peat cores from ests on dry uplands consist of pure young Pinus sylvestris stands. 87 67 the Salym-Yugan Mire. Birch (Betula pubescens Ehrh.) forests and a few large Siberian 88 pines are found along riverbanks. Siberian fir (Abies sibirica 89 Ledeb) larch (Larix sibirica Ledeb) and spruce (Picea abies L. 90 68 Study area Karst. ssp. obovata (Ledeb) Hulten) are completely absent on the 91 69 The study area is situated in the Khanty-Mansi Autonomous Dis- dry uplands in the study area. However, Picea abies and Abies 92 70 trict of the Tyumen Region (60°10ЈN, 72°50ЈE), in the central sibirica are relatively abundant about 10–20 km north of the study 93 area, where dry uplands are more prevalent in the landscape. 94 17 *Author for correspondence (e-mail: aki.pitkanenȰjoensuu.fi) Paludification has been a strong process since the end of the last 95 12 Arnold 2002 10.1191/0959683602hl533rp 1 1 1 178 The Holocene 12 (2002) 2 534 1312 14 15 Figure 2 Aerial view of the study site and the coring points (A, B and 16 6 7 C). The point studied by Liss and Berezina (1981) is indicated by L. 17 8 Figure 1 Location of the study area (indicated with an asterisk). Sites (Photograph provided by D.L. Varlyguin.) 18 9 referred to in text indicated by crosses (x). (1) Pur-Taz site. (2) Niznevar- 10 tovsk site. (3) Bugristoye bog. (4) Sverdrup island. all identified pollen taxa and unidentified pollen (Varia). Spores 125 were excluded from the total pollen sum. Spore values were based 126 96 glaciation (Walter, 1977). However, the mire has expanded on the sum of spores (excluding Sphagnum) and total pollen. 127 97 slightly during recent millennia and was nearly to its present width Sphagnum values were calculated from the sum of Sphagnum 128 98 7000–8000 years ago (Turunen et al., 2001). spores and total pollen. For absolute pollen values, the volume of 129 99 According to Grosswald (1980; 1998), the study area was pollen samples was based on the volume-mass samples of the peat 130 100 covered during the last glaciation by an ice-dammed lake, which cores (Turunen et al., 2001). Pollen influx values were calculated 131 101 was formed by an ice sheet centred in the Kara Sea area. The according to the formula (C*L)/T, in which C = average pollen 132 –3 102 latest studies (Mangerud et al., 1999; Svendsen et al., 1999) indi- concentration of samples (pollen grains cm ) between two 133 103 cate that the maximum extent of the Eurasian ice sheet in the Kara radiocarbon datings, L = length (cm) of the sequence between 134 104 Sea region during the Late Weichselian has been overestimated datings, and T = time period (cal. BP yr) in the peat sequence. 135 105 and that the great rivers of West Siberia had free outlets to the The treeless vegetation phase is evident in the pollen assem- 136 106 Kara Sea. However, the existence of ice-dammed lakes during blages. However, the long-distance transport of arboreal pollen 137 107 earlier phases of Weichselian glaciation is possible. (AP) and the weak pollen production of non-arboreal pollen 138 (NAP) may obscure the interpretation of the data (Birks and Birks, 139 1980). Studies from tundra areas indicate that about 60–25% of 140 108 Material and methods the pollen consists of NAP taxa (including Cyperaceae and 141 Poaceae as major taxa), reflecting a treeless vegetation (Aario, 142 109 Three peat cores were taken from the central plateau along a tran- 1940; 1943; Ritchie, 1974; Ritchie and Lichti-Federovich, 1967; 143 110 sect at 800 m intervals in September 1998 with a Russian side- Lichti-Federovich and Ritchie, 1968). In forest tundra areas, 144 111 cutting peat sampler 50 × 500 mm (Jowsey, 1966). Two peat cores which are open wooded landscapes, the proportion of NAP is 145 112 (4.54 and 5 m long) with radiocarbon datings from several depths lower (18–12%) (Ritchie, 1974; 1977; Lichti-Federovich and Rit- 146 113 were chosen for pollen analyses (cores A and B). In addition, chie, 1968). In this study, AP values less than 25% of the total 147 114 pollen samples were analysed from the basal peat of core C, which pollen are interpreted to indicate treeless vegetation. 148 14 115 had the oldest radiocarbon age (Figure 2). Peat subsamples of 1 Peat samples taken for C dating (Table 1) were analysed at 149 3 116 cm were taken from the basal 10 cm at continuous 1 cm intervals, the University of Helsinki Dating Laboratory. All results were 150 13 117 at 2 cm intervals between 10 and 20 cm from the base and at 10 corrected for isotopic fractionation based on the C values given 151 118 cm intervals for the rest of the cores. The pollen samples were in Table 1. Radiocarbon ages were converted to calendar years 152 119 weighed and treated according to procedures described by Ber- using CALIB 3.0.3 (Stuiver and Reimer, 1993). Two additional 153 120 glund and Ralska-Jasiewiczowa (1986), excluding sieving of datings (Table 1) from the marker level of an abrupt increase of 154 121 samples. A minimum of 200 arboreal pollen grains were counted, pine and birch pollen in the study area were made by Liss and 155 122 but in a few samples poor in pollen the minimum number of tree Berezina (1981). 156 123 pollen counted was 50 pollen grains. The relative pollen values The names of chronozones and their ages (converted to cali- 157 124 of trees and herbs were based upon the total pollen sum including brated radiocarbon years) used in this paper follow Mangerud 158 1 1 1 Aki Pitka¨nen et al.: Holocene vegetation history from a mire in West Siberia 179 2 74373 75 Table 1 Peat radiocarbon datings from the studied points.