UDC 630.561.1.24+903

V. S. Myglan 1, O. C. Oidupaa 2, A. V. Kirdyanov 3, E. A. Vaganov 1

1 Siberian Federal University

79 Svobodny Ave., Krasnoyarsk, 660041, Russia

E-mail: vladimir@forest.akadem.ru

2 Tuva State University

36 Lenin St., Kyzyl, 667000, Republic of Tyva, Russia

3 Sukachev Institute of Forest SB RAS

Akademgorodok 50, p. 28, 660036, Russia

1929-YEAR TREE-RING CHRONOLOGY FOR THE ALTAI-SAYAN REGION (WESTERN TUVA)*

A new 1929-year tree-ring chronology for the Altai-Sayan region (Western Tuva) is presented and analyzed. The material for its construction was the wood of living trees and the remains of Siberian larch (Larix sibirica Ldb) trunks at the upper forest boundary (2400 m above sea level). The analysis of the correlation of tree growth indices with weather station data indicates the predominant influence of temperature in June-July on the variability of radial growth, which allows us to use the chronology to reconstruct the change in early summer temperature in the Altai-Sayan region. As applied to archeology, creating a chronology of this duration opens up opportunities for dating archaeological wood, i.e. determining the calendar time of construction of archaeological objects located on this territory for the entire period presented.

Introduction

Reconstruction of regional climate changes and analysis of the contribution of natural and anthropogenic factors to them are important for understanding current climate changes [Giorgi et al., 2001; Kondratiev. 2002]. However, for the territory of Siberia, the number of series of direct instrumental observations is small and their duration often does not exceed the last 50-70 years. In this regard, within the framework of the international research programs PAGES (global climate change in the past), great attention is paid to the research of natural "archives". Of particular interest is the use of such an indicator of changes in environmental conditions as annual tree rings. This makes it possible to obtain reliable information (with a resolution of a year, a growing season) about changes in the main climatic parameters in the past (Fritts, 1976; Cook and Kairiukstis, 1990; Vaganov, Shiyatov, Mazepa, 1996; et al.).

Dendrochronological studies are of considerable value for the continental regions of Eurasia, since components of mountain ecosystems at the border of their ranges, such as larch at the upper limit of growth (Adamenko, 1978; Oidupaa, Vaganov, and Naurzbayev, 2004), are sensitive to environmental changes. The variability of plant growth contains a strong climatic signal due to the short duration of vegeta-

* The work was carried out within the framework of the RFBR projects " Creation of an ultra-long tree-ring chronology for dating archaeological sites and reconstructing the climate of the Altai-Sayan region over the last two millennia "(N 08 - 06 - 00253-a) and "Comparative analysis of the response of radial tree growth in Central and East Asia to current climate change" (N 07 - 04 - 92108-GFEN_a).

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Figure 1. Location of sample collection sites for constructing long-term tree-ring chronologies (a) and weather stations, the data of which were used in the work (b).

M-T - Mongun-Taiga, XX-Khalzan Hamar, SD-Solongotun Dawa.

Shiyatov, 1986; Ovchinnikov and Vaganov, 1999]. At the same time, in contrast to the Subarctic, for which there is a significant number of long-term paleoclimatic reconstructions [Vaganov and Shiyatov, 1999; Naurzbaev, Vaganov, and Sidorova, 2003; Hantemirov and Shiyatov, 2002; Sidorova and Naurzbaev, 2002; et al.], the number of such reconstructions is clearly insufficient for the Altai-Sayan region. Only a few continuous tree-ring chronologies (DCS) with a length of more than a thousand years have been created: according to the Siberian larch (Larix sibirica Ldb) for the Gorny Altai (1093 years) [Ovchinnikov, Panyushkina, Adamenko, 2002] and according to the Siberian pine (Pinus sibirica Tour) for the territory of Northern Mongolia (1728 years) [D'Arrigo, Jacoby, Pederson et al., 2001]. In this paper, for the first time, we construct and analyze a 1929-year DCS for Siberian larch in the Mongun-Taiga region (Western Tuva).

Material and methods

The research area is the western (mountainous) regions of the Republic of Tuva. The sharply continental climate, remoteness from major cities and industrial centers, the presence of tree remains on the upper border of the forest, and a significant number of archaeological sites make this region very promising for dendrochronological work. The main material for the study was Siberian larch wood (Larix sibirica Ldb), which has a high sensitivity of growth to changes in environmental conditions and a wide ecological growth amplitude (it is present in almost all forest-vegetation belts on the upper border of the forest).

During the 2007 expedition work in the Mongun-Taiga area (Fig. 1), three plots were laid at the upper border of the forest (2000 - 2100 m above sea level) at a distance of 10 km from each other. Cores were taken from living trees (Fig. 2, a), and cuttings were taken from the remains of tree trunks preserved higher up the slope (Fig. 2, b).

Measurements of the width of annual rings were performed on a semi-automatic LINTAB unit (with an accuracy of 0.01 mm). The series were dated using a combination of graphical cross-dating [Douglass, 1919] and cross-correlation analysis (DPL [Holmes, 1983] and TSAP V3.5 [Rinn, 1996] in the package of specialized programs for dendrochronological studies). In order to maximize the preservation of long-term climatic changes in the indexed series, the age trend was removed in the classical way [Fritts, 1976] using negative exponential and linear regression in the ARSTAN program [Cook, Krusic, 2008].

The quality of the constructed chronology was evaluated on the basis of traditional dendrochronological methods-

2. Sample collection sites, a - present upper forest boundary (June 2007); b-tree trunk remains on the day surface.

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zateley. The standard deviation characterizes the amplitude of the partial variability of growth, EPS is the sensitivity of DCS to changes in external factors (it depends on the number of samples analyzed and shows how a particular limited sample reflects the signal of the population or general population), RBAR is the average value of the correlation coefficient between individual series [Wigley, Briffa, Jones, 1984; Cook, Kairiukstis, 1990].

To compare the growth indices with climate data, we used a series of monthly observations of surface air temperature and precipitation from the meteorological stations closest to the study area (see Fig. 1): Ak-Kem (49° 58 'N, 86° 42' E, 2050 m above sea level) for the period 1961-1995, Kyzyl (51° 45 'N, 94° 25' E, 634 m above sea level) from 1944 to 1986, Ulang (49° 48' N, 92° 05' E, 934 m above sea level) for 1943-1983, Uygha (48° 58' N, 89° 58' E, 1,715 m above sea level).) from 1959 to 1991 and calculated for a geographical coordinate grid of 0.5° x 0.5° from 1901 to 2002. We used data for the square 88° 00 '- 90° 50 'n., 50° 00' - 51° 00' V. D. [Mitchell and Jones, 2005]. Standardized tree-ring chronologies for Northern Mongolia (Khalzan Khamar, Solongotun Dawa) (Jacoby et al., 2008) and Gorny Altai (Ovchinnikov, Panyushkina, Adamenko, 2002) were used to compare the variability of growth indices in the Altai-Sayan region.

Results and discussion

The total number of dated models was 98, including 20 for living trees and 78 for dead ones, which made it possible to construct a tree-ring chronology lasting 1929 years (from 78 to 2006) (Fig. 3).

The average age of the samples is 365 years, and the maximum age is 804 years. This suggests that DCS reflects not only intra-centennial, but also secular climatic fluctuations. The percentage of" dropped " rings is small (0.5%). The distribution of model trees on the calendar scale is uneven and tends to decrease in their number as we move into the past, with the smallest number observed in the interval from 450 to 600 years.

The analysis of EPS and RBAR indicators (Figure 4) shows that, with the exception of the period 450-600 years. (when the EPS value falls below the significance criterion-0.85), the constructed DCS is suitable for climate reconstructions. The decrease in EPS and RBAR values in the period from 450 to 600 is due to the low availability of samples from this period, probably due to the death of trees due to a sharp cold snap that occurred after the "536 event", as well as the destruction of part of the peripheral rings of trees that have lain on the daytime surface for more than 1000 years. According to historical evidence, 536 and a number of subsequent years are characterized by cold summers with heavy fog, low yields, famine, epidemics, and the death of plant and animal populations (Baillie, 1994; Stothers, 1999). According to the results of earlier dendrochronological studies, a decrease in the radial growth of trees was observed for a period lasting from 10 to 24 years after this event in England [Bailie, 1994], Mongolia [D'Arrigo, Frank, Jacoby, Pederson, 2001], in the east of Taimyr and the North Caucasus.-

3. Tree-ring chronology of the Mongun Taiga from 78 to 2006 (gray curve - typical fluctuations in growth indices, black-smoothed out by a 42-year low-pass filter, horizontal line - arithmetic mean) (a), the distribution of trees used for its construction relative to the time of their growth beginning (b) and the number of trees that fell for each analyzed interval (c).

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4. Values of EPS and REAR indicators for the tree-ring chronology of the Mongun Taiga.

5. Variability of radial tree growth according to tree-ring chronologies for the Altai-Sayan region.

- a Gorny Altai; b-Mongun Taiga; c-Khalzan Khamar; d-Solongotun Dava (the short length of this series is explained by the fact that only the last 520 years of the 1738-year standardized chronology are publicly available). The gray curve shows typical fluctuations in growth indices, while the black curve shows smoothed 11-year moving averages.

in the north-east of Yakutia (Sidorova, Naurzbaev, Vaganov, 2005), which indicates the global nature of this phenomenon. 3, a) shows that, in addition to the middle of the VI century ("event of 536"), a significant decrease in growth was observed in the first half of the IX century, the first half of the X century, at the end of the XII - beginning of the XIII century, the first half of the XIV century, and in the XVII century. - XIX centuries - "small ice age". High growth is characterized by the III-IV centuries, the beginning of the VI, the middle of the VII-end of the VIII, the end of the X-middle of the XII, the first half of the XV, the middle of the XVI century. and the present time (starting from the second half of the XX century).

To clarify the question to what extent the tree-ring chronology constructed by us is consistent with other long-term DCS for the Altai-Sayan region, we compared the growth indices (Fig. 5) and calculated the correlation coefficients for both individual pairs of chronologies and the general one (Table 1). The results of the analysis indicate a high synchronicity and consistency in the data obtained in the Altai-Sayan region. changes in the growth rate. The obtained values of the correlation coefficients between DCS for Western Tuva and Gorny Altai (Table 1) show that a signal for a common limiting factor is recorded in both of them. This makes it possible to combine the data of the series into one and use the tree-ring chronology for the Mongun Taiga to date wood from the archaeological sites of Gorny Altai.

To estimate the climate signal contained in the DCS, response functions were calculated from available instrumental and calculated climate data (Table 2). As expected, the main effect on the variability of radial tree growth is exerted by temperatures

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Table 1. Correlation coefficients of tree-ring chronology growth indices for Mongun Taiga (M-T) with DCS for Northern Mongolia (Khalzan Khamar (XX), Solongotun Dawa (SD)) and Gorny Altai (HA)

Timeline

M-T

N, years

M-T

N, years

GA (Larix sibirica Ldb)

0,62

759 - 1999

0,63

1475 - 1994

XX (Larix sibirica Ldb)

0,47

1326 - 1998

0,56

"

SD (Pinus sibirica TourJ

0,35

1475 - 1994

0,35

"

Note. Significant correlation coefficients at p < 0.05 are shown in bold; N is the sample size.

Correlation coefficients of the average monthly temperature in June-July according to weather stations with growth indices Table 2.*

Weather Station

June

N

July

N

June-July

N

Ak-Kem

0,62

35

0,37

35

0,69

35

Kyzyl

0,53

43

0,31

43

0,56

43

Ulaanbaatar

0,54

40

0,23

40

0,54

40

Uyghi

0,50

41

0,38

43

0,57

37

Based on estimated data**

0,44

102

0,30

102

0,50

102

* See note. go to Table 1.

** For a square of 88° 00 '- 90° 50 'N., 50° 00' - 51° 00' V. D.

June-July (the relationship with the temperature of other months is insignificant) with the prevailing influence of June. The results obtained are in good agreement with the data of other researchers in the Altai-Sayan region (D'Arrigo, Jacoby, Pederson et al., 2001; Ovchinnikov, Panyushkina, and Adamenko, 2002).

The correlation coefficients presented in Table 2 indicate the presence of a strong climate signal in the constructed DCS. For example, a comparison of growth indices with data from the Ak-Kem weather station can explain up to 47% of the total temperature variability in June-July. The presence of a stable and significant relationship between the growth indices and data from weather stations located at a distance of 300-400 km from the sample collection point shows that the variability of tree growth reflects changes in summer temperature, at least on a regional scale.

The analysis of the constructed tree-ring chronology (Figure 5) is of some interest in relation to issues related to the Kyoto Protocol, "global warming", and the increase in surface air temperature due to the anthropogenic component (Kondratyev, 2002). The variability of housing and communal services growth indices for the Mongun Taiga shows that, despite a relatively long positive trend (since the early 1900s), the current warming cannot be attributed to extraordinary ones, since it does not go beyond the natural variability. This conclusion is confirmed when comparing the modern and paleogranitsa distribution of woody vegetation, because, despite the pronounced expansion of larch undergrowth in the study area, the difference between the upper border of the forest at the present time and in the past is approximately 250 m. Since the average temperature changes by 0.6°C for every 100 m of altitude difference [Glaciation..., 2006], it can be argued that in certain periods the early summer temperature exceeded the modern one by about 1.5°C. Similar results were obtained based on the analysis of 293-year tree-ring chronologies for Siberian larch (Larix sibirica Ldb) constructed for the Altai-Sayan region: the dynamics of summer temperatures indicates that no significant warming was observed in the XX century [Oidupaa, Vaganov, and Naurzbayev, 2004].

No less important is the analysis of the intra-centennial variability of growth (and hence temperature) recorded in the Mongun-Taiga housing and communal services in historical terms. Climate fluctuations of this duration (along with other factors) have a significant impact not only on the functioning of mountain ecosystems [Shiyatov and Mazepa, 2007], but also on social processes related to the economic activity of the population [Myglan et al., 2007], which often affect the functioning of mountain ecosystems.-

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share in the role of a kind of their "catalyst". The following examples can be cited: a sharp cold snap at the end of the XII-beginning of the XIII century and the unstoppable onslaught of the Mongols on China and the West, the emergence of the Genghis Khan empire; a cold snap at the end of the XVI-beginning of the XVII century (according to European sources, at this time there were cold years "without summer" [Borisenko, Pasetsky, 1988; Barrash, 1989]) and Turmoil in Russia, colonization of vast territories of Siberia in the shortest possible time. It can be suggested that it is the sharp change of warm climatic periods to cold ones that destabilizes the economic activity of the population and initiates the development of migration processes.

Conclusion

The results presented in this paper can be called preliminary, since the work on the ultra-long tree-ring chronology continues. To date, there are two main tasks: increasing the replication of samples, especially for the period from 400 to 600 years, and the duration of DCS to obtain better climate reconstructions. If the chronology is extended to the third and second centuries BC, it will open up significant prospects associated with the use of archaeological material, and it will be possible to date "floating" tree-ring chronologies built on the remains of wooden structures from monuments of the first millennium BC (for example, for the Ulandryk River Valley [Slusarenko et al., 2002; Slusarenko et al., 2001]). In order to solve these problems, it is planned to conduct joint expedition work by employees of the Siberian Federal University, the Institute of Archeology and Ethnography of the Siberian Branch of the Russian Academy of Sciences, Tuva State University and the Institute of Forest of the Siberian Branch of the Russian Academy of Sciences to collect wood samples at the upper border of the forest and from archaeological sites.

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