A 3585-Year Ring-Width Dating Chronology of Qilian Juniper from the Northeastern Qinghai-Tibetan Plateau

IAWA Journal, Vol. 30 (4), 2009: 379–394

A 3585-YEAR RING-WIDTH DATING CHRONOLOGY OF QILIAN JUNIPER FROM THE NORTHEASTERN QINGHAI-TIBETAN PLATEAU

Xuemei Shao1 *, Shuzhi Wang2, Haifeng Zhu1, Yan Xu1, Eryuan Liang3, Zhi-Yong Yin4, Xinguo Xu5 and Yongming Xiao5

SUMMARY This article documents the development of a precisely dated and well- replicated long regional tree-ring width dating chronology for Qilian juniper (Juniperus przewalskii Kom.) from the northeastern Qinghai- Tibetan Plateau. It involves specimens from 22 archeological sites, 24 living tree sites, and 5 standing snags sites in the eastern and northeastern Qaidam Basin, northwestern China. The specimens were cross-dated successfully among different groups of samples and among different sites. Based on a total of 1438 series from 713 trees, the chronology covers 3585 years and is the longest chronology by far in China. Comparisons with chronologies of the same tree species about 200 km apart suggest that this chronology can serve for dating purposes in a region larger than the study area. This study demonstrates the great potential of Qilian juniper for dendrochronological research. Key words: Northeastern Qinghai-Tibetan Plateau; Qilian juniper; dendrochronology; cross-dating; 3585-year chronology; archeological wood.

INTRODUCTION One of the aims of dendrochronology is to construct long-term chronologies covering hundreds to thousands of years. These chronologies have major applications to climatic interpretations, radiocarbon analysis, and dating of past events (Lara & Villalba 1993; Scuderi 1993; Hughes & Graumlich 1996; Stahle et al. 1998, 2007; Grudd et al. 2002; Helama et al. 2002; Naurzbaev et al. 2002; Friedrich et al. 2004; Bhattacharyya & Shah 2009; Fang et al. 2009; Guo et al. 2009; Liang et al. 2009; Park & Lee 2009; Sho et al. 2009; Tian et al. 2009; Zhang et al. 2009). Long chronologies have been established in many regions of the world (Ferguson 1968; Hantemirov & Shiyatov 2002; Eronen et al. 2002; Grudd et al. 2002). However, the development of long tree-ring chronologies in China has been limited by the lack of long-lived species and widespread land-use changes over the past few centuries due to rapid population growth.

1) Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, P.R. China. 2) Institute of Archaeology, Chinese Academy of Social Sciences, Beijing 100710, P.R. China. 3) Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, P.R. China. 4) Department of Marine Science and Environmental Studies, University of San Diego, 5998 Alcala Park, San Diego, CA 92110, U.S.A. 5) Qinghai Provincial Institute of Cultural Relics and Archaeology, Xining 810007, P.R. China. *) Corresponding author [E-mail: [email protected]].

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Recently, Qilian junipers (Juniperus przewalskii Kom., better known in China under its synonym Sabina przewalskii) growing in the northeastern part of the Qinghai-Tibetan Plateau have been reported to be several centuries to more than a millennium old (Liu et al. 2005; Liu et al. 2006; Gou et al. 2006; Zhang & Qiu 2007; Zhang et al. 2009). This species provides a unique opportunity to develop long tree-ring chronologies in China. The longest published chronology in China was developed using live and archeological wood of Qilian junipers from sites located near Dulan (Fig. 1) with a length of 2326 years (Zhang et al. 2003), hereafter named as the Dulan Chronology. Later it was extended to 515 BC by Sheppard et al. (2004). However, this chronology suffers from low sample depths before 100 BC and from AD 700 to 900. The availability of long-living trees and numerous logs excavated from the tombs of the Tang Dynasty (approximately AD 618–907) make the eastern Qaidam Basin an ideal region for developing long tree-ring chronologies. During recent investigations in the northeastern and eastern Qaidam Basin, we had the opportunity to develop a Qilian juniper chronology that is longer than the published chronology in China. This work serves two purposes: first, to provide a dating chronology specifically for the archeological wood in the study area, and secondly to examine the spatial extent over which good cross-dating can be expected for archeological dating chronologies and for living juniper chronologies.

97°E 98°E

37°N

37°N nghaı ke

36°N living trees dead trees archaeological wood 36°N 0 12.5 25 50 km km

97°E 98°E 99°E Figure 1. Locations of the 51 tree-ring sample sites in the study area (A). Site numbers are identified in Table 1. The two sites in the Qilian Mountains used for comparison are shown in the inset map of China (B).

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STUDY AREA The study area is located in the eastern part of Haixi Prefecture of Qinghai province, northwestern China (Fig. 1). It is situated in the Qaidam Basin that lies on the northeastern Qinghai-Tibetan Plateau, approximately one hundred km west of the Qinghai Lake, the largest inland lake in China. Branches of the Qilian Mountains are found in the north of the Qaidam Basin, and in the east and south are the Kulun Mountains. Ac- cording to meteorological records from the stations in the study area, the climate is arid and semi-arid and continental in nature. The annual mean temperatures range from -1 to 5°C, with mean January temperatures from -10 to -14°C and mean July temperatures from 10 to 17°C. The annual total precipitation is approximately 50–340 mm, declin- ing from east to west and from high to low elevation. Up to 84–89% of this total falls during May to September. Soils in the study area range from poorly developed loess of 20–50 cm thickness on gentle slopes to thin soils on steep slopes. Some sand dunes are also seen in places northeast of the study area. The study area is characterized by a desert steppe (Zheng 1996) with natural vegeta- tion consisting of various herbs and shrubs of desert species. Trees are almost exclusively conifers, composed of Qilian juniper and Qinghai spruce (Picea crassifolia). They are limited to the mountains between 3450 and 4230 m above sea level (a.s.l.). Due to the lack of meteorological measurements, we can only assume that the presence of the trees in this elevation zone indicates higher precipitation due to the orographic effect. Qilian juniper is an endemic species of northwestern China. As the name implies, the center of distribution is the Qilian Mountains, located to the east of our study area. It is a species with a wide ecological amplitude. Zongwulong Mountains in the study area has been thought as the westernmost limit of Qilian juniper’s natural range (Wang 1993). However, we observed Qilian junipers growing on the westernmost Buerhan- buda Mountains located in the south of Golmud city (94.29 °E) in 2006. The species has been found as far east as the west margin of the Loess Plateau and as far south as the Songfan area in Sichuan Province. This species is hardy and drought tolerant, mak- ing it the dominant species on dry sunny mountain slopes with thin rocky soils in arid and semi-arid regions. Junipers in the study area are widely spaced with tree heights ranging from 3 to 6 m and diameters at breast height from 30 to 50 cm. Occasionally, trees with diameters larger than 50 cm were seen in some stands. On steep slopes, severe soil erosion caused exposure of trees’ roots, while other trees simply grow in large rock fissures. We also observed a few trees with abrasion scars possibly caused by falling rocks and dead trees by lightning. Only at relatively wet sites in the east of the study area do they co-exist with Qinghai spruce, forming dense forests. Genetically similar juniper species include Sabina centrasiatica, S. vulgaris var. jarkendensis, and S. pseudosabina var. turkestanica, which are mostly found in northwestern China. Due to the harsh environment, Qilian juniper growth is extremely slow, forming wood with very narrow annual rings. Around local settlements, junipers have been used for the construction of houses and other structures. Known for its resistance to decay, juniper wood was considered as the top choice for coffin and tomb construction when burial ceremonies were popular. Local people reported that junipers were heavily logged along highways, railways and roads, for construction and heating/cooking purposes.

Downloaded from Brill.com10/07/2021 04:11:26PM via free access 382 IAWA Journal, Vol. 30 (4), 2009 0.5 MC 0.56 0.77 0.65 0.66 0.64 0.63 0.64 0.59 0.81 0.65 0.87 0.73 0.80 0.57 0.58 0.60 0.73 0.69 0.62 0.63 0.62 0.79 0.72 0.69 0.74 MS 0.26 0.37 0.42 0.50 0.38 0.36 0.26 0.30 0.55 0.50 0.59 0.57 0.50 0.31 0.22 0.31 0.38 0.30 0.30 0.28 0.31 0.37 0.35 0.24 0.38 0.28 % 0.0 0.00 1.22 1.71 1.84 1.37 1.04 0.30 0.49 3.12 3.36 3.03 4.06 3.33 0.47 0.03 0.26 1.30 0.64 0.82 0.42 0.53 1.32 1.18 1.24 0.14 PMR

yr ML 411.6 688.0 352.1 343.1 497.8 472.2 308.9 675.3 471.9 280.5 238.0 242.3 329.5 320.1 276.2 314.7 361.3 421.0 665.8 638.1 605.2 492.7 415.9 303.0 661.6 548.2 1468 BC-AD 105 AD 169-603 412 BC-AD 492 761 BC-AD 461 1580 BC-AD 756 874 BC-AD 793 AD 22-781 376 BC-AD 591 477 BC-28 BC 7 BC-AD 319 AD 80-413 331 BC-AD 408 AD 97-751 52 BC-AD 601 AD 151-653 146 BC-AD 789 157 BC-AD 783 484 BC-AD 784 381 BC-AD 782 BC-AD 789 511 33 BC-AD 743 31 BC-AD 655 246 BC-AD 589 209 BC-AD 644 AD 729-1794 AD 130-1568 Time span Time 3/4 4/7 9/17 4/5 42/82 55/106 2/4 8/15 2/4 3/5 2/3 9/17 8/14 12/21 5/10 16/35 46/96 16/35 20/27 16/31 6/10 2/6 5/11 4/12 8/16 15/29 Samples dated 8 11 4 46/77 55/110 2 11 5 3 9 8 15 5 16/35 46/96 16/35 22 17 9/18 2/6 6/13 4/12 20/40 21/42 Samples collected block block block block & core core block block block block block block block block core core core block block core core core core core core Specimen type tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb tomb dead tree dead tree Site type 3380 3060 3360 3190 3290 3245 3080 2877 3336 3544 3390 3556 3445 3280 3420 3440 3430 3440 3380 3450 3440 3440 4060 3960 Alt. m 97.21° 97.35º 97.25º 97.65º 97.79º 97.47º 97.35º 97.30º 96.83º 97.05º 97.98º 98.04º 98.04º 98.15º 97.99º 98.31º 98.30º 98.24º 98.24º 98.26º 98.30º 98.29º 98.05º 98.66º Long. E 37.42° 37.40º 37.43º 37.34º 37.42º 37.41º 37.41º 37.15º 37.54º 37.49º 37.40º 37.42º 37.37º 36.24º 35.86º 36.16º 36.18º 36.16º 36.26º 36.16º 36.18º 36.16º 37.46º 37.05º Lat. N Delingha Delingha Delingha Delingha Delingha Delingha Delingha Delingha Delingha Delingha Delingha Delingha Delingha Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Delingha Wulan County

1 BGT 2 BGX 3 NHT 4 XTT 5 MHG 6 AZG 7 SNC 8 BLE 9 AQTG 10 ZHG 11 BRT 12 GARG 13 ALST 14 ZGR 15 MKL 16 RSG 17 DXM 18 RXM 19 YCH 20 LSG 21 DLRS 22 DRX 23 DLH4S 24 WL2S Table 1. Sites and their tree-ring dating characteristics. Table Site Site no. code

Downloaded from Brill.com10/07/2021 04:11:26PM via free access Shao et al. — Tree-ring chronology of Qilian juniper 383 – 0.63 0.71 0.64 0.66 0.72 0.80 0.80 0.83 0.83 0.67 0.81 0.73 0.76 0.79 0.67 0.84 0.82 0.82 0.69 0.70 0.65 0.68 0.79 0.75 0.71 0.75 0.64 0.33 0.48 0.32 0.32 0.35 0.43 0.41 0.52 0.63 0.60 0.33 0.49 0.47 0.50 0.47 0.29 0.42 0.54 0.54 0.31 0.38 0.36 0.33 0.45 0.37 0.42 0.46 0.40 3.11 0.57 2.46 0.00 0.40 0.99 1.90 1.31 2.62 4.68 0.90 2.44 2.66 2.32 2.04 0.30 1.42 2.13 3.00 0.48 1.06 0.87 0.77 2.26 0.97 1.41 1.40 1.51 643.0 342.0 852.0 417.5 572.1 501.1 698.4 608.6 520.7 479.8 500.5 555.9 532.9 610.9 641.5 573.4 585.0 451.7 526.7 687.5 617.9 567.1 463.6 589.5 675.9 536.3 507.0 324.5 769 BC-AD 1689 AD 456-1693 AD 202 650 BC- AD 868-1736 AD 843-2001 AD 828-2001 AD 404-2002 AD 451-2002 AD 711-2003 AD 1237-2002 AD 943 -2002 AD 857 -2003 AD 845 -2002 AD 681 -2001 AD 900 -2001 AD 898 -2001 AD 969 -2001 AD 1077 -2002 AD 894 - 2004 AD 823 -2002 AD 539 -2002 AD 894 -2002 AD 847-2005 AD 877 -2001 AD 791 -2001 AD 798 -2002 AD 829 -2002 AD 718 -2002 13/28 8/18 1/1 9/16 31/59 34/73 79/168 67/144 67/146 29/67 29/58 20/40 44/91 43/99 50/103 32/65 27/55 33/80 40/73 28/59 40/89 19/39 46/92 34/75 38/80 22/44 28/56 21/45 21/42 23/50 20/40 31/61 34/73 79/168 67/144 67/146 29/67 29/58 21/42 44/91 43/99 50/103 32/65 27/55 33/80 40/80 28/59 40/89 21/42 46/92 34/75 38/80 22/44 28/58 26/53 core core core core core core core core core core core core core core core core core core core core core core core core core core core dead tree dead tree dead tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree living tree 4230 3686 3910 3730 3780 3920 3800 3700 3780 3500 3700 3700 3720 3700 3910 3830 3700 3820 3780 3850 3670 3850 3820 3840 3810 3800 3690 98.56º 97.00º 97.67º 97.24º 97.23º 97.54º 98.06º 97.78º 97.06º 98.29º 98.63º 98.66º 98.22º 98.42º 98.37º 98.38º 98.46º 98.20º 98.33º 98.56º 98.11º 98.19º 98.04º 98.16º 97.98º 97.67º 96.99º 36.19º 35.86º 35.92º 37.48º 37.47º 37.45º 37.44º 37.45º 37.51º 37.31º 37.01º 37.04º 36.74º 36.68º 36.35º 36.51º 36.47º 36.46º 36.28º 36.20º 35.99º 36.01º 35.96º 35.95º 35.82º 35.92º 35.86º Dulan Dulan Dulan Delingha Delingha Delingha Delingha Delingha Delingha Tianjun Wulan Wulan Wulan Wulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan Dulan

25 ERGS = mean length; PMR percentage of missing rings; MS sensitivity; MC correlation. ML 26 NMHS 27 KES 28 DLH1 29 DLH2 30 DLH3 31 DLH4 32 DLH5 33 DLH6 34 TJ1 35 WL1 36 WL2 37 WL3 38 WL4 39 XRH1 40 XRH2 41 XRH3 42 XRH4 43 KC 44 ERG 45 KXT 46 QSG 47 XRD1 48 XRD2 49 XRD3 50 KE 51 NMH

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MATERIAL AND SAMPLING

Qilian juniper trees that constitute the chronology presented here can be divided into three distinct groups: subfossil trees from archeological tombs, dead trees or snags on the hills, and living trees. Archeological wood was collected from the tombs located mainly on the alluvial fans at the foothills of mountains. In 1999, four tombs located in Dulan County were excavated by archeologists from Peking University, Beijing, China. These tombs are thought to be built in the time of the Tubo Kingdom based on the materials preserved inside (School of Archaeology and Museology 2005). There- after, a few other tombs, also located in Dulan County, were excavated by archeologists from the Qinghai Institute of Archaeology, and the chambers made of Qilian juniper logs in the tombs were preserved. In 2002, numerous juniper logs from two tombs in Xiatatu (XTT) of the town of Guolimu, 25 km east of Delingha, were collected by archeologists. These tombs are again dated to the time of the Tubo Kingdom based on the excavated materials (Cheng 2001; Xu 2001, 2002, 2005). In recent years, many tombs have been robbed and scattered juniper logs and blocks are sometimes seen on the ground. We collected wood discs and cores from such robbed tombs at 16 sites and from excavated tombs at six sites during the period of 2003 through 2007. A total of 22 archeological sites are included in this study (Table 1). Since 1998, tree-ring cores have been extracted from living junipers and standing snags at sites on the Zongwulong, Shalike, Qinghainan, Ela, and Buerhanbuda Moun- tains (Fig. 1). A total of 24 Qilian juniper sites distributed up to 200 km across have been sampled (Table 1). Except for two eastern sites (WL1 and WL2), where mixed forests of Qinghai spruce and Qilian juniper are present, Qilian juniper is the only dominant species at the other 22 sites. Since the percentage of missing rings is high for Qilian juniper growing in this arid region (Shao et al. 2003), we sampled many trees of different ages at some sites. We also selected stands from a variety of microenvironments, including hill slope hollows that can collect and preserve more runoff than ridgelines and top slopes, and the upper and lower limits of tree growth. Our sampling strategy facilitates the cross-dating of ring widths and reduces the chance that all collected specimens miss a ring for the same year at a site. To develop a chronology as long as possible for living trees, we have been going back to some sites several times to search for old trees in hard-to-reach locations. We also collected cores from standing snags at five sites, including three at the upper limit of tree growth (sites 23–25). Standing snags were collected to strengthen the sample depth for the earlier part of the period covered by the living trees, so that robust ring width estimations can be produced for the overlapping period between the archeological wood and living trees.

CROSS-DATING

The increment cores were air-dried and then glued to wooden mounts with the trans- verse surface facing up. The cores were sanded with increasingly fine grades of sand paper, to at least 600-grit so that all cellular details of the annual rings can be seen clearly under microscopes. We utilized the skeleton-plot technique (Stokes & Smiley

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1968; Fritts 1976) to cross-date the rings and the widths were measured A to the nearest 0.01 mm using a Uni- versity Model 4 system and a Lintab ring-width measurement system. To confirm that the rings in Qilian juniper in the study area are formed annually, we inspected the cellular characteristics of the rings microscopically and found that the boundary between the latewood of one ring and earlywood of the next was almost invariably sharp, with no B evidence of gradation in cell size or wall thickness in most cases (Fig. 2A). Further unambiguous evidence of annual rings came from the comparison of the samples taken in 2001 with those taken in 2004 from several sites. Three more rings corresponding to the number of years lapsed were observed in the 2004 samples than in 2001 samples by comparing the narrow-wide ring patterns. It could be concluded that the Qilian juniper in the study area formed C only one growth ring in each year under most environmental conditions. For Qilian juniper growing in the arid region, difficulties of cross-dating arise from missing rings associated with the extremely slow growth rates of this species. Therefore, cores from complacent and young trees were dated first since they contained fewer missing rings. The year-to-year variations in Figure 2. Samples of annual rings from Qilian ring widths from these trees composed juniper. A: normal narrow rings; B: rings that are a rough ring pattern to serve as the basis too narrow to date; C: a false ring indicated by for dating old trees. If there were inter- the arrow (magnified at× 40). vals in a core from an old tree in which many missing rings occurred or extremely low average growth rates had produced sequences of rings of only one or two cells in width (Fig. 2B), we would separate the core into two or more sections by discarding the problematic segments. A few false rings were identified by their un-sharp boundary between the latewood of one ring and earlywood of the next (Fig. 2C). To locate the missing rings rationally, a specimen with missing rings was verified by cross-dating its ring pattern with other cores in which

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NMS09B

EGS72B

MHG23B

MHG55B

BGT05A Ring width (mm)

XTT117A

XTT301A

XTT306B

BC Year

DLH329A

DLH437B

DLH441A

EG041F

EGS61A

EGS75A

NMS11D

Ring width (mm) WL2S09A

MHG32A

RXM02B

XT101B

ZGR01A

Year AD Figure 3. Patterns of ring-width variations. A: during the period of 850 BC to 600 BC for standing snags and archeological wood (separated by a dotted line), and B: during the period of AD 450 to AD 700 for living trees, standing snags, and archeological wood (separated by dotted lines); black dots show the location of missing rings.

Downloaded from Brill.com10/07/2021 04:11:26PM via free access Shao et al. — Tree-ring chronology of Qilian juniper 387 there were no missing rings present. Cores with ages younger than AD 1000 from the standing snags were not processed furthermore because the sample depth of the living trees was large enough for the later period. The accuracies of cross-dating and measurements were further checked using the COFECHA program with the default parameters (Holmes 1983). All segments of cores identified by the program as having unusual measurements or significant (p < 0.05) lag- ged correlation with the master chronology were visually rechecked. The calendar dates of the archeological wood were assigned by the COFECHA program using the cross- dated and undated tree-ring series function after deriving the master dating chronology of living trees and standing snags, and the floating dates of the archeological wood samples. The quality of cross-dating among the archeological sites themselves and between the archeological wood, standing snags, and living trees is illustrated in Figure 3, which indicates that the archeological wood, standing snags, and living tree specimens can be cross-dated accurately. In particular, the variation of ring widths in the period 732 BC to 726 BC (Fig. 3A) exhibits an excellent narrow-wide ring pattern for dating the wood of that period. The average 50-year segments intercorrelation from COFECHA is 0.61 for the period 750–701 BC and ranges from 0.59 to 0.67 for the period AD 450–700 (Fig. 3B). From these statistics we conclude that ring-width samples of Qilian juniper can be cross-dated very well in the study area regardless of samples from different groups of trees or from various tree growth limits, upper or lower.

Living trees Standing snags Archeological wood

-1600 -1200 -800 -400 0 400 800 Year Figure 4. Age profile of selected cross-dated tree-ring series.

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Figure 4 displays the age profile of selected cross-dated tree-ring series for the earlier part of the master chronology. The total time span for the archeological wood is 2373 years from 1580 BC to AD 793. The longest archeological sample covers 1627 years, from 1580 BC to AD 47 with only 20 missing rings (XTT301 in Fig. 4). The total time span of the standing snags is 2563 years covering 769 BC to AD 1794. The longest core of a dead tree covers 1605 years, from AD 58 to 1662 with 18 missing rings (EGS80 in Fig. 4). Some of the cores, such as EGS72, EGS61, and EGS80, form important links between the archeological samples and living trees. The living tree specimens are shortest in total time span, but the earliest ring of the living trees was dated to AD 404, lasting also 1599 years with only 19 missing rings (DLH329 in Fig. 4). The con- sistency in the time span of the longest series among the three types of samples seems to indicate that the maximum longevity of the species in the study area is longer than 1600 years. The maximum overlap is 1562 years between the archeological samples and the standing snags, and 390 years between the archeological samples and living trees. The excellent matching of the age profile of samples (Fig. 4) and strong cross- dating among the three types of specimens enable us to build a precisely dated and well-replicated regional master chronology for the study area.

CONSTRUCTION OF THE MASTER DATING CHRONOLOGY

To ensure the quality of the dating chronology, ring-width series with correlation coefficient less than 0.5 in the output of the COFECHA program (using the default parameters) and series with a percentage of missing rings larger than 2% were excluded in the final chronology development. A total of 1438 series from 713 trees were put together in the COFECHA program for the master dating chronology. The percentage of missing rings is 0.79% in this chronology. The mean length of the series is 555 years, the average mean sensitivity is 0.37, and the series inter-correlation is 0.67. Figure 5 shows the master dating chronology and the sample depth of the entire period. Sample size within the chronology is below ten series before 837 BC and is less than 3 trees before 1458 BC. Therefore, the first 740 years (from 1580 BC to 837 BC) of the chronology should be considered with caution. The sample size in 800 AD is 51 cores. Before AD 800, the maximum sample size is 313 cores around year AD 280; after AD 800, it is 864 cores around the year 1768. Earlier studies on Qilian juniper in Delingha and Dulan have found that the ring widths of the living trees in the study area responded mainly to drought (Zhang et al. 2003; Sheppard et al. 2004; Shao et al. 2005). Inferring from these results, the narrow rings in the dating chronology (Fig. 5) represent dry years. However, climatic inter- pretation of narrow rings before 1000 BC should be cautious due to low sample depth.

COMPARISON WITH QILIAN JUNIPER CHRONOLOGIES FROM NEARBY REGIONS

As mentioned in the previous sections, there are two versions of the Dulan chronology available in the study area. In a comparison between these two chronologies, Sheppard

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Figure 5. The dating chronology and its sample depth; marked years indicate narrow rings.

Downloaded from Brill.com10/07/2021 04:11:26PM via free access 390 IAWA Journal, Vol. 30 (4), 2009 et al. (2004) identified one ring located at AD 682 missing in the chronology developed by Zhang et al. (2003). When we compared the Zhang et al. chronology with the Delingha chronology, which is approximately 140 km north of the Dulan chronology and was developed using living trees in our earlier study (Shao et al. 2006), we verified that the Delingha chronology contains two more annual rings than the Zhanget al. Dulan chronology in the period between AD 650 and 900. A year-by-year comparison indicates that two rings dated at AD 711 and 875 are absent from the Zhang et al. Dulan chronology (Fig. 6) instead of one at AD 681. We compared the current dating chronology with the Dulan chronology and found that these two independently developed chronologies could be cross-dated perfectly after rings were added in AD 711 and 875 to the Dulan chronology. This suggests that dendrochronological techniques provide highly reproducible results for Qilian juniper, even though the species has a high percentage of missing rings in the study area. To investigate the spatial extent to which this dating chronology can be applied, we compared it with two other chronologies from the Qilian Mountains (Fig. 1B). One of these in the northern part of the Qilian Mountains is drought sensitive (Liang et al. 2006), while the other, located in the middle section of the Qilian Mountains contains temperature and precipitation signals (Liu et al. 2005). Figure 7 shows the two Qilian chronologies created by the COFECHA program and the dating chronology developed in this study for the period of AD 1800 onward. It is obvious that a number of narrow rings occurred simultaneously among the three chronologies. The narrow ring in 1824 was also present in Qilian juniper chronologies from Anyemaqen Mountains (Peng et al. 2007), which is approximately 250 km southeast of the center of the present study area.

660 680 700 720 740 760 780 800 820 840 860 880 900

Ring-width index 0

660 680 700 720 740 760 780 800 820 840 860 880 900 Year Figure 6. A year-to-year comparison of the Dulan chronology (Zhang et al. 2003) (thin line) with the Delingha chronology (thick line) during the period AD 650–900 for the original series (A) and the adjusted series (B); arrowheads indicate the location of the two missing rings added in the Dulan chronology, one at AD 711 and the other at AD 875.

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-2

-4 QF2

-2

-4 Ring-width index SDL

-2

-4 this study

1800 1850 1900 1950 2000 Year Figure 7. Comparison of the dating chronology (developed in this study) with two other Qilian juniper dating chronologies for the Qilian Mountain.

Severe and long-lasting drought events are most likely the result of regional atmospheric conditions. These events may have affected tree growth in a large region simultaneously. Therefore, the dating chronology developed in this study can be used in a region larger than the present study area in representing years with slow growth.

CONCLUSIONS

In this study, a precisely dated and well-replicated long regional tree-ring width dating chronology for Qilian juniper was developed using a total of 1438 series from 713 trees. The sampling effort covered 22 archeological sites, 24 living tree sites, and 5 standing snags sites in eastern and northeastern Qaidam Basin. Cross-dating was performed successfully among different groups of samples and among different sites scattered up to 200 km across. The dating chronology was developed using series with a high mean correlation coefficient (> 0.5) and a low percentage of missing rings (< 2%). The chronology is 3585 years long, which is 1065 years longer than the previous longest chronology in China. It correlates with the Dulan chronology developed by Zhang et al. (2003) after two missing rings were added to the Dulan chronology. Our results indicate that dendrochronological techniques provide highly reliable dating of past events using samples from Qilian juniper in the arid and semi-arid regions, although the samples should be treated with caution for missing rings and difficulties in measuring due to

Downloaded from Brill.com10/07/2021 04:11:26PM via free access 392 IAWA Journal, Vol. 30 (4), 2009 extremely harsh growth environments. In comparison with two other chronologies of the same species sampled approximately 200 km away, we found that narrow rings generally coincide in time, suggesting that some of the past climatic events may have had a widespread impact in the region that limited the tree growth. Therefore, the dating chronology developed in this study can be used beyond the study area, especially in representing severe drought conditions.

Acknowledgements

The authors would like to thank all colleagues and students who participated in the sampling field- work. Thanks are also due to Dr. Qibin Zhang for providing the Dulan chronology. This study was supported by grants from the Chinese National Natural Science Foundation (40671194 & 40371118), the National Basic Research Program of China (2005CB422002) and the program from the China Meteorological Administration (ccsf2007-28). Thanks also to the anonymous reviewer who provided valuable constructive suggestions.

References

Bhattacharyya, A. & S.K. Shah. 2009. Tree-ring studies in India – Past appraisal, present status and future prospects. IAWA J. 30: 361–370 (this issue). Cheng, Q.J. 2001. The key to Tuyuhun Kingdom. Study on Qaidam Exploitation: 71–74. Eronen, M., P. Zetterberg, K.R. Briffa, M. Lindholm, J. Merilainen & M. Timonen. 2002. The supra-long Scots pine tree-ring record for Finnish Lapland. Part 1, chronology construction and initial inferences. Holocene 12: 673–680. Fang, K., X. Gou, D.F. Levia, J. Li, F. Zhang, X. Liu, M. He, Y. Zhang & J. Peng. 2009. Varia- tion of radial growth patterns in trees along three altitudinal transects in north central China. IAWA J. 30: 443–457 (this issue). Ferguson, C.W. 1968. Bristlecone pine: science and esthetics: A 7100-year tree-ring chronology aids scientists; old trees draw visitors to California Mountains. Science 159: 839–846. Friedrich, M., S. Remmele, B. Kromer, J. Hofmann, M. Spurk, K.F. Kaiser, C. Orcel & M. Kuppers. 2004. The 12,460-year Hohenheim oak and pine tree-ring chronology from central Europe – A unique annual record for radiocarbon calibration and paleoenvironment recon- structions. Radiocarbon 46: 1111–1122. Fritts, H.C. 1976. Tree rings and climate. Academic Press, London. Gou, X.H., M.X. Yang, J.F. Peng, Y. Zhang, T. Chen & Z.D. Hou. 2006. Maximum temperature reconstruction for Anmaqing Mountains over the past 830 years based on tree-ring records. Quaternary Science 26: 991–998. Grudd, H., K.R. Briffa, W. Karlen, T.S. Bartholin, P.D. Jones & B. Kromer. 2002. A 7400-year tree-ring chronology in northern Swedish Lapland: natural climatic variability expressed on annual to millennial timescales. Holocene 12: 657–665. Guo, G., Z.-S. Li, Q.-B. Zhang, K.-P. Ma & C. Mu. 2009. Dendroclimatological studies of Picea likangensis and Tsuga dumosa in Lijiang, China. IAWA J. 30: 435–441 (this issue). Hantemirov, R.M. & S.G. Shiyatov. 2002. A continuous multimillennial ring-width chronology in Yamal, northwestern Siberia. Holocene 12: 717–726. Helama, S., M. Lindholm, M. Timonen, J. Merilainen & M. Eronen. 2002. The supra-long Scots pine tree-ring record for Finnish Lapland. Part 2, interannual to centennial variability in summer temperatures for 7500 years. Holocene 12: 681–687. Holmes, R.L. 1983. Computer-assisted quality control in tree-ring dating and measurement. Tree-Ring Bull. 43: 69–78.

Downloaded from Brill.com10/07/2021 04:11:26PM via free access Shao et al. — Tree-ring chronology of Qilian juniper 393

Hughes, M.K. & L.J. Graumlich. 1996. Multimillennial dendroclimatic studies from the western United States. In: P.D. Jones, R.S. Bradley & J. Jouzel (eds.), Climatic variations and forcing mechanisms of the last 2000 years: 109–124. Springer Verlag, Berlin, Heidelberg. Lara, A. & R. Villalba. 1993. A 3620-year temperature record from Fitzroya cupressoides tree rings in southern South-America. Science 260: 1104–1106. Liang, E., D. Eckstein & X. Shao. 2009. Seasonal cambial activity of relict Chinese pine at the northern limit of its natural distribution in North China – Exploratory results. IAWA J. 30: 371–378 (this issue). Liang, E.Y., X.H. Liu, Y.J. Yuan, N.S. Qin, X.Q. Fang, L. Huang, H.F. Zhu, L. Wang & X.M. Shao. 2006. The 1920s drought recorded by tree rings and historical documents in the semi- arid and arid areas of northern China. Climatic Change 79: 403–432. Liu, X.H., D.H. Qin, X.M. Shao, T. Chen & J.W. Ren. 2005. Temperature variations recovered from tree-rings in the middle Qilian Mountain over the last millennium. Science in China Series D-Earth Sciences 48: 521–529. Liu, Y., Z.S. An, H.Z. Ma, Q.F. Cai, Z.Y. Liu, J.K. Kutzbach, J.F. Shi, H.M. Song, J.Y. Sun, L. Yi, Q. Li, Y.K. Yang & L. Wang. 2006. Precipitation variation in the northeastern Tibetan Plateau recorded by the tree rings since 850 AD and its relevance to the Northern Hemisphere temperature. Science in China Series D-Earth Sciences 49: 408–420. Naurzbaev, M.M., E.A. Vaganov, O.V. Sidorova & F.H. Schweingruber. 2002. Summer temperatures in eastern Taimyr inferred from a 2427-year late-Holocene tree-ring chronology and earlier floating series. Holocene 12: 727–736. Park, W.-K. & K.-H. Lee. 2009. Tree-ring dating of coffin woods from Naeheung-dong in Gunsan, South Korea. IAWA J. 30: 459–468 (this issue). Peng, J.F., X.H. Gou, F.H. Chen, Y.X. Zhang, P.X. Liu, Y. Zhang & K.Y. Fang. 2007. Horizontal variations of climatic response of Qilian juniper (Juniperus przewalskii) in the Anyemaqen mountains. Acta Geographica Sinica 62: 742–752. School of Archaeology and Museology, Peking University & Qinghai Provincial Institute of Cultural Relics and Archaeology. 2005. Tibetan tombs at Dulan Qinghai. Science Press, Beijing. Scuderi, L.A. 1993. A 2000-year tree-ring record of annual temperatures in the Sierra-Nevada Mountains. Science 259: 1433–1436. Shao, X.M., X.Q. Fang, H.B. Liu & L. Huang. 2003. Dating the 1000-year old Qilian juniper from mountains of the eastern extreme of the Qaidam Basin. Acta Geographica Sinica 58: 90–100. Shao, X.M., L. Huang, H.B. Liu, E.Y. Liang, X.Q. Fang & L.L. Wang. 2005. Reconstruction of precipitation variation from tree rings in recent 1000 years in Delingha, Qinghai. Science in China Series D-Earth Sciences 48: 939–949. Shao, X.M., E.Y. Liang, L. Huang & L.L. Wang. 2006. A reconstructed precipitation series over the past millennium in the Northeastern Qaidam Basin. Advances in Climate Change Research 2: 122–126. Sheppard, P.R., P.E. Tarasov, L.J. Graumlich, K.U. Heussner, M. Wagner, H. Osterle & L.G. Thompson. 2004. Annual precipitation since 515 BC reconstructed from living and fossil juniper growth of northeastern Qinghai Province, China. Climate Dynamics 23: 869–881. Sho, K., H.A. Takahashi, H. Miyai, S. Ikebuchi & T. Nakamura. 2009. Tree-ring width and stable carbon isotopic composition of Japanese cypress in the Lake Biwa area, Central Japan, and their hydrologic and climatic implications. IAWA J. 30: 395–406 (this issue). Stahle, D.W., M.K. Cleaveland, D.B. Blanton, M.D. Therrell & D.A. Gay. 1998. The Lost Colony and Jamestown droughts. Science 280: 564–567. Stahle, D.W., F.K. Fye, E.R. Cook & R.D. Griffin. 2007. Tree-ring reconstructed megadroughts over North America since AD 1300. Climatic Change 83: 133–149.

Downloaded from Brill.com10/07/2021 04:11:26PM via free access 394 IAWA Journal, Vol. 30 (4), 2009

Stokes, M.A. & T.L. Smiley. 1968. An introduction to tree-ring dating. University of Chicago Press, Chicago. Tian, Q., X. Gou, Y. Zhang, Y. Wang & Z. Fan. 2009. May-June mean temperature reconstruction over the past 300 years based on tree rings on the Qilian Mountains of the northeastern Tibetan Plateau. IAWA J. 30: 421–434 (this issue). Wang, J. 1993. Qilian juniper. In: Editing Committee of Qinghai Forest (eds.), Qinghai Forest: 230–240. Chinese Forestry Publ. House, Beijing. Xu, X.G. 2001. Looking for lost Kingdom – discovery and excavation ancient tombs in Dulan. Study on Qaidam Exploitation 6: 66–70. Xu, X.G. 2002. Discovery, excavation and study of Tubo tombs in Dulan, Qinghai Province, China. Silk Roadology 14: 212–225. Xu, X.G. 2005. A study on coffin panel paintings of Tubo tombs in Guolimu. Chinese Tibetanist 1: 56–69. Zhang, Q.B., G.D. Cheng, T.D. Yao, X.C. Kang & J.G. Huang. 2003. A 2,326-year tree-ring record of climate variability on the northeastern Qinghai-Tibetan Plateau. Geophys. Res. Lett. 30: 1739–1741. Zhang, Q.B. & H.Y. Qiu. 2007. A millennium-long tree-ring chronology of Sabina przewalskii on northeastern Qinghai-Tibetan plateau. Dendrochronologia 24: 91–95. Zhang, Y., X. Gou, F. Chen, Q. Tian, M. Yang, J. Peng & K. Fang. 2009. A 1232-year tree-ring record of climate variability in the Qilian Mountains, northwestern China. IAWA J. 30: 407–420 (this issue). Zheng, D. 1996. The system of physico-geographical regions of the Qinghai-Xizang (Tibet) Pla- teau. Science in China Series D-Earth Sciences 39: 410–417.

Downloaded from Brill.com10/07/2021 04:11:26PM via free access