IAWA Journal, Vol. 21 (2), 2000: 181–196

THE DENDROCHRONOLOGICAL POTENTIAL OF TEN SPECIES IN

THE THREE GORGES RESERVOIR REGION OF byby Limin Xiong1, Naoki Okada & Takeshi Fujiwara Wood Quality Laboratory, and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan

SUMMARY

About 250 , representing 10 species, were collected from the Chi- nese Three Gorges Reservoir region as part of a study to use rings as indicators of environmental change in this area. Five species do not show distinct ring boundaries or cannot be cross-dated with each other. The dendrochronological potential of the remaining five species, two and three hardwoods, are assessed in this paper. These five species, Cathaya argyrophylla, Cinnamomum camphora, Gordonia acu- minata, Pinus massoniana, and Schefflera delavayi, have distinct an- nual growth rings and little occurrence of double or missing rings. Tree- ring width and maximum latewood density chronologies from the five species range in length from 38 to 138 years. These relatively short chronologies are just long enough to conduct a preliminary dendro- climatic evaluation. Preliminary climate modeling demonstrates some significant relationships between tree-ring data and temperature, pre- cipitation, and river flow. Key words: Tree-ring width, maximum latewood density, dendro- chronological evaluation, Chinese Three Gorges Reservoir, Cathya argyrophylla, Cinnamomum camphora, Gordonia acuminata, Pinus massoniana, Schefflera delavayi.

INTRODUCTION

The building of the Three Gorges Dam in the middle reaches of the Changjiang (Yang- tze) River has great social, economic and ecological significance. Periods of flood and drought associated with the Chinese Three Gorges Reservoir region affect mil- lions of people. Future climatic variation in this area will also affect the structure and management of the dam. Currently our understanding of extreme events is insufficient for developing models useful for long-term prediction. This problem is due in part to our incomplete knowledge of how often these events have occurred in the past. Records of instrumental climate data in the Three Gorges Reservoir region only extend back about 70 years and this is obviously too short to detect the full range of natural vari-

1) Current address: New Zealand Tree-Ring Laboratory, Soil, and Ecological Sciences Division, P.O. Box 84, Lincoln University, New Zealand. E-mail: [email protected]

Downloaded from Brill.com09/26/2021 10:07:05AM via free access 182 IAWA Journal, Vol. 21 (2), 2000 ability likely to be present. While a considerable number of historical documents exist in this area, very little quantitative data exist which are needed to understand the present limits of climate variability and to develop regional climatic models. Tree rings are widely used to detect environmental changes (e.g., Fritts 1976; Hughes et al. 1982; Cook & Kairiukstis 1990). Events like fires, flooding, river-flow changes, extreme weather conditions, landslides and volcanic eruptions can be traced in tree-ring sequences (Schweingruber 1988). Many authors have used tree rings to study river flows, flooding histories and to extend existing short river-flow records with considerable success. Stockton (1971) showed that dendrochronology can play a useful role in hydrological analysis. Jones et al. (1984) illustrated that changes in river runoff can be reconstructed using English oak tree-ring data. Holmes et al. (1979) succeeded in the calibration and reconstruction of annual run-off for two Argentine rivers using the ring widths of two species of Araucaria and Austrocedrus. Analysis of tree-ring data by Stockton and Jacoby (1976) showed that the average annual amount of water assumed to be available in the Colorado River had been incorrectly esti- mated. Dendrochronological studies in China have been focused on the northeastern part, north-central China, the Tibetan Plateau, Hengduan Mountains and northwest China. Wu (1992) reviewed the statues of dendrochronology in China. By 1992, a total of 39 tree-ring width chronologies had been developed from 10 species of 6 genera (Abies, Cypressus, Picea, Larix, Sabina, and Pinus). After that, Bräuning (1994) developed 24 tree-ring width chronologies of various Picea, Abies, Larix and Juniperus species from eastern Tibet. About the same time, tree-ring width and density chronologies were developed from Pinus armandii at Huashan in north-central China (Shao & Wu 1994; Wu & Shao 1994) and a 389-year rainfall record was reconstructed from these chronologies (Hughes et al. 1994). More recently, Shao and Wu (1997) reported a temperature reconstruction from five chronologies which were developed from three Larix, Picea and Pinus species at Changbai Mountain, northeast China. A 360-year river runoff was reconstructed from nine Picea chronologies in the Urumqi River Basin, northwest China (Li et al. 1997). However, only a few tree-ring related studies in the middle reaches of the Changjiang River have been published. Dong et al. (1995) studied Pb and Zn contents in tree rings of two Pinus species. Sun and Zhong (1997) did a study on the tree-ring power spectrum analysis of Gordonia acuminata. Fur- thermore, dendrochronological potential is great in the Three Gorges Reservoir area. For example, of the 3,012 species in this region, 53 tree species reach old growth form. Several of these tree species attain estimated ages around 300 to 500 years in this area (Chen et al. 1994). In addition to the living trees, there are thousands of archaeological sites that will be submerged in the damʼs reservoir after its com- pletion in 2009. Of the 121 most important sites, 15 are sites of AD 1900 to AD 1400, 46 are sites of AD 1400 to 200 BC, 33 are sites of 200 BC to 2000 BC and 27 are sites before 2000 BC (Zich 1997). Quite a number of these archaeological sites are built of timber. The dating of archaeological samples using dendrochronology has been car- ried out in many areas of the world (Baillie 1982, 1995; Nash 1999). The relocation of old buildings in the Three Gorges Reservoir region provides an excellent opportu-

Downloaded from Brill.com09/26/2021 10:07:05AM via free access Xiong, Okada & Fujiwara — Dendrochronological potential in Chinese trees 183 nity to collect archaeological samples. They will offer a great chance to develop a chronology beyond a thousand years. Furthermore, the reconstruction from tree rings could be compared with seasonal climate records derived from ancient documents. This region, having the potential for excellent tree-ring based climate reconstruction, as well as extensive documentary records, presents an opportunity for comparing and linking these two types of proxy environmental records. The initial survey in this study was made to determine which species might be most suitable for dendro- chronological study in the Three Gorges Reservoir region. The questions we are try- ing to answer are: 1) Is it possible to develop a cross-dated tree-ring chronology from the Three Gorges Reservoir region? 2) Did tree-ring parameters respond significantly to environmental forcing? 3) Which environmental factor did affect tree growth most in this area?

MATERIAL AND METHODS Field sampling Evergreen broad-leaved forest dominated by Fagaceae, Lauraceae, Magnoliaceae and Theaceae is the main forest type in the Three Gorges Reservoir region. Forests here belong to the hygrophilous evergreen forest type which requires mesic condi- tions, a monsoon climate and occurs on the east coast of the subtropical Asian conti- nent. Conifers are a component of these forests and are widely dispersed over almost all areas where evergreen broad-leaved forest occurs (Zhong 1997). Both and hardwood species native to this area were sampled for the assessment of dendro- chronological potential. The selection of species was based on the following criteria: potential old trees exist or were widely used in old buildings; wide distribution in the area; and the possibility of obtaining sampling permission. Tree-ring samples were collected in September 1997 and July 1998. We sampled about 250 living trees of 10 species and some archaeological samples from an old building (under restoration). The sampling locations are indicated in Figure 1 and the sites, species, and number of trees sampled are listed in Table 1. Core samples were taken from living trees using increment borers, and cross sections were cut from fallen trees and archaeological samples.

Cross-dating, chronology development and correlation analysis The cores were extracted with ethanol and benzene following Schweingruber et al. (1978), then the cores were mounted and sliced to 2.0 mm for X-ray radiographing. The Skeleton Plot method was applied to the sliced cores (sanded with appropriate sanding papers) for cross-dating (Stokes & Smiley 1968). Tree-ring parameters were measured from X-ray film, using the Dendro 2003 Tree-Ring-Workstation (Walesch Electronic, Switzerland). The image loaded with Dendro 2003 was visually verified against the Skeleton Plot. After obtaining tree-ring measurements, a check was made for cross-dating quality between trees using the computer program COFECHA (Holmes 1983; Holmes et al. 1986; Grissino-Mayer et al. 1997). Examinations were made of 10 species, and dated chronologies prepared using only five of these: 2 conifers and 3 hardwood species. This selection is based on the fact that the tree-ring boundaries

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Fig. 1. The locations of the hydrological, meteorological stations and sampled tree-ring sites.  : Tree-ring sites, BM = Baima Mt. forest station, Wulong; GL = Gele Mt., Chongqing; HZ = Hezui, Shizhu; JY = Jinyun Mt., Beibei; NS = Nan Mt., Chongqing; WS = Wushan; YT = Yangtigou, Shizhu. / Cuntan hydrological station. $ Temperature series locations. - Gridded precipitation locations (the centre of the gridbox), A (30.00° N, 105.00° E) is not on the map. of some species were not clear and that some species were difficult to cross-date. The standardization method applied in this study was a double detrending method using ARSTAN (Cook 1985; Grissino-Mayer et al. 1997). Firstly, a linear-exponential or linear regression or a horizontal detrending was applied which is supposed to remove the ageing growth trend. Secondly, a spline curve was applied which fitted to 2/3 of the length of each tree-ring series to filter out some non-climatic signals. A quantitative evaluation of the relationship between various climatic parameters and tree growth can be studied using the simple correlation function (CF) and the more complex response function (RF). Here, in the preliminary study, only the simple correlation function was applied to the tree-ring data. The analysis was performed for each of the pre-whitened residual chronologies of ring width and maximum latewood density chronologies, using the regional climate data averaged throughout the region. The correlation function was applied with the following climate parameters: mean monthly temperature; total monthly rainfall; average monthly maximum tempera- ture; average monthly minimum temperature; and river-flow records. Temperature data were downloaded from the NOAA (National Oceanic and Atmospheric Adminis- tration) website (Peterson 1997). The temperature series is the average of five climate stations that have all passed quality control and homogeneity adjustment. These five

Downloaded from Brill.com09/26/2021 10:07:05AM via free access Xiong, Okada & Fujiwara — Dendrochronological potential in Chinese trees 185 (m) 1430 1360 1430 1405 520 720 720 795 690 685 750 750 510 510 271 530 650 Elevation

' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '

(E) 107º 33 107º 33 107º 33 107º 33 106º 26 108º 23 108º 23 106º 22 106º 22 106º 22 106º 22 106º 22 106º 37 106º 37 109º 53 109º 57 108º 24 Longitude

' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '

(N) 29° 16 29º 16 29º 16 29º 16 29º 34 30º 31 30º 31 29º 50 29º 50 29º 50 29º 50 29º 50 29º 34 29º 34 31º 05 31º 08 30º 02 Latitude

sublanceolata

var. Species Lithocarpus polystachya Pinus massoniana delavayi Schefflera Cathaya argryophylla Pinus massoniana funebris Cupressus Liquidambar formosana Pinus massoniana Pinus massoniana funebris Cupressus acuminata Gordonia Pinus massoniana Cinnamomum camphora Pinus massoniana Ficus virens Pinus massoniana Ginkgo biloba

8 / 15 20 / 40 10 / 20 9 / 20 20 / 40 / 22 11 9 / 18 20 / 40 20 / 40 26 / 55 15 / 30 25 / 50 10 / 20 20 / 40 10 / 20 10 / 20 / 22 11 Number of trees / cores

Table 1. The Chinese Three Gorges Reservoir region tree-ring collections. Three Gorges The Chinese 1. Table

Site name Baima Mt. Forest Station, Wulong Wulong Baima Mt. Forest Station, Wulong Baima Mt. Forest Station, Wulong Baima Mt. Forest Station, Wulong Baima Mt. Forest Station, Gele Mt., Chongqing Hezui, Shizhu County Hezui, Shizhu County South Side, Jinyun Mt., Beibei North Side, Jinyun Mt., Beibei Jinyun Mt., Beibei Jinyun Mt., Beibei Jinyun Mt., Beibei Nan Mt., Chongqing Nan Mt., Chongqing County Wushan of Town The County Wushan Liaping, Shizhu County Yangtigou,

1, 2 1

1 2 1 1 1 1 1 2 1 1 1, 2 2, 3 1 2 2 Collected in September 1997. Collected in July 1998. Includes living trees and archaeological samples.

Chronology Code BMF BMP BMS BMY GLP HZC HZL JLP JSP JYC JYG JYP NSC NSP WSF WSP YTG 1) 2) 3)

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I ; D: ;

Liquidambar formosana H ; I: Gordonia acuminata Gordonia ; C: ;

G Ginkgo biloba ; H:

F Cathaya argyrophylla Cathaya sublanceolata ; B: ; var. var.

E Ficus virens Schefflera delavayi Schefflera

; G: D

C Cupressus Cupressus funebris ; F:

. — Scale bar (under A) for all the graphs = 10 mm. . — Scale bar (under B

A Cinnamomum camphora

Fig. 2. Radiographs of the sampled ten species. — A: — species. ten sampled the of Radiographs 2. Fig. E: carpus polystachya

Downloaded from Brill.com09/26/2021 10:07:05AM via free access Xiong, Okada & Fujiwara — Dendrochronological potential in Chinese trees 187 stations are Chongqing [29.52° N, 106.48° E, 351 m a.s.l. (above sea level)], Jinfo Shan (28.88° N, 107.45° E, 2,040 m a.s.l.), Liangping (30.68° N, 107.80° E, 455 m a.s.l.), Pengsui (29.30° N, 108.17° E, 311 m a.s.l.) and Youyang (28.83° N, 108.77° E, 665 m a.s.l.) (Fig. 1). Precipitation data sets were obtained from the homepage of the Climatic Research Unit, University of East Anglia, UK (Hulme 1997). The pre- cipitation series used here is the average of two gridded series (A: 30.00° N, 105.00° E, 377 m a.s.l.; B: 30.00° N, 108.75° E, 423 m a.s.l.). River-flow records are from the Cuntan Hydrological Station, 9 km downstream from the Chongqing City, on the mainstream of the Changjiang River. The common period of the climate data series is from 1925 to 1990. The relationship between climate and tree growth was examined for the common period of climate data and tree-ring data. The common time span of the chronology data sets was only from 1960 to 1987, due to the shortness of chronol- ogy NSC (see Table 1 for details of the abbreviations); the time span of river flow is from 1958 to 1985 (1960 to 1985 used for NSC). This span of 28 years (26 years for NSC), while very short for statistical comparison, was all that was available for use in this preliminary study. In order to simplify the procedure, a twelve-month dendro- climatic year was used for analysis, extending from previous October to current Sep- tember. A correlation function in the program PRECONK (Fritts 1996) was used for screening the climate sensitivity of the tree rings.

RESULTS Tree-ring structure of different species The radiography of the ten species is shown in Figure 2. The ring widths of all ten species show some variation. These variations could reflect past environmental fluc- tuations. Ring boundaries are very clear for the first five species (Fig. 2A–E). The ring boundaries of Cupressus funebris (Fig. 2F) are clear but the species could not be cross-dated. After reviewing the disks we obtained from an old building, we found there are many wedging rings in Cupressus funebris. Ficus virens (Fig. 2G) has many false rings and it is questionable whether the rings are annual. Ginkgo biloba (Fig. 2H) has clear ring boundaries but we could not cross-date the materials we obtained. This may be because the Ginkgo samples were taken from a village and human distur- bance (e.g. taking and fruits) was too strong. The last two species, Liquidambar formosana and Lithocarpus polystachya (Fig. 2 I & J), have indistinct ring bounda- ries. It was difficult to conduct any tree-ring analysis on these two species. Therefore, the following presentation will only focus on the first five species (A to E in Figure 2). The ring structure of the five species was microscopically examined (Fig. 3). Schefflera delavayi is a ring-porous species, the earlywood vessels are distinctly larger than those of the latewood and it is very easy to recognize the zone of earlywood and latewood (Fig. 3A). Gordonia acuminata (Fig. 3C) is a semi-ring-porous species in which the earlywood is marked by a zone of occasional large vessels. Cinnamomum camphora (Fig. 3E) is a diffuse-porous species in which the vessels are fairly uni- form and distributed throughout the growth ring (Kaennel & Schweingruber 1995). Thick-walled fiber bands in the latewood mark the ring boundaries of these three spe-

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A

B

C

Fig. 3. Ring structure of the five cross-dated species.

A: Schefflera delavayi. Scale bar = 0.3 mm. D B: Cathaya argyrophylla. Scale bar = 0.1 mm.

C: Gordonia acuminata. Scale bar = 0.3 mm.

D: Pinus massoniana. Scale bar = 0.25 mm.

E: Cinnamomum camphora. E Scale bar = 0.9 mm.

Downloaded from Brill.com09/26/2021 10:07:05AM via free access Xiong, Okada & Fujiwara — Dendrochronological potential in Chinese trees 189 cies. The two conifer species, Cathaya argyrophylla and Pinus massoniana (Fig. 3B & D), had clear ring boundaries. The transition from earlywood to latewood is con- tinuous in these two species. Tree ring width index Tree

Tree Tree ring maximum density index

Year Fig. 4. Residual chronologies of tree ring width and latewood maximum density of the five cross-dated species. Site code is the same as in Table 1. The species are: BMS, Schefflera delavayi; BMY, Cathaya argyrophylla; JYG, Gordonia acuminata; JYP, Pinus massoniana; NSC, Cinnamomum camphora.

Downloaded from Brill.com09/26/2021 10:07:05AM via free access 190 IAWA Journal, Vol. 21 (2), 2000 3 0.95 0.32 0.56 0.71 0.54 0.48 0.27 0.43 1.13 0.67 SNR

2 0.49 0.24 0.36 0.42 0.35 0.32 0.22 0.30 0.53 0.40 APC

0.22 0.22 0.28 0.40 0.33 0.10 0.06 0.05 0.09 0.08 Mean . sensitivity

tion 0.76 0.79 0.70 0.70 0.81 0.654 0.713 0.703 0.479 0.216 Auto- correla-

87 83 49 58 50 0.96 0.35 1.49 2.00 3.24 Standard deviation

820 790 610 820 9.98 4.50 1210 Max. 10.32 14.89 21.42 measure

510 810 570 470 590 1.89 0.87 2.99 2.74 4.72 Mean measure

tion 0.46 0.41 0.48 0.38 0.43 0.35 0.33 0.40 0.41 0.39 Inter- correla-

1

0 0 0 0 0.21 0 0 0 0 0.20 (%) ABS

millimeter and the annual measurement of density is in kilogram per cubic meter 8 / 11 9 / 13 9 / 13 7 / 12 7 / 10 8 / 14 10 / 19 18 / 31 10 / 19 22 / 35 Number of trees / cores

Period 1868–1996 1812–1997 1925–1996 1921–1996 1959–1996 1868–1996 1815–1997 1944–1996 1921–1996 1958–1996

Table 2. General statistics of different tree-ring chronologies for the five cross-dated species. The annual measurement of ring width is in tree-ring chronologies for the five cross-dated species. 2. General statistics of different Table

ABS (%): percentage of absent (missing) rings. APC: agreement with population chronology. SNR: signal to noise ratio.

Code tree-ring width Total BMS BMY JYG JYP NSC Maximum tree-ring density BMS BMY JYG JYP NSC 1) 2) 3)

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Tree-ring width and maximum density chronologies The ten chronologies developed in this study are shown in Figure 4. These include five tree-ring width chronologies and five latewood maximum density chronologies developed from the five species. A summary of the statistics for these chronologies is presented in Table 2. The number of trees included in the chronologies is usually less than the total number collected, since suppression, competition, or other problems render some sampled trees unusable for cross-dating. The inter-correlation is a statis- tical measure of the agreement of all the tree-ring series included in a site; values above 0.328 exceed 99% confidence limits based on the studentʼs t-test with 50 ob- servations. The three hardwood species (BMS, JYG, NSC in Table 2) have higher inter-correlations than those of the conifers in the tree-ring width chronologies. How- ever, the two chronologies from Jinyun Mt. (JYG, JYP in Table 2) have higher inter- correlations in maximum wood density than those of other locations. NSC had the highest average annual ring-growth rate (mean measurement of ring width, see Table 2) and BMY had the lowest. Standard deviations for individual ring indices, first-order autocorrelation (a measure of how similar a tree ring is to the preceding yearʼs growth), and mean sensitivity (a measure of the relative difference in tree-ring parameters from one ring to the next) are calculated for each chronology. Mean sen- sitivity values are higher in width chronologies than those of density chronologies. Within width chronologies, mean sensitivity and standard deviation are higher in JYP and NSC. The relatively large value of auto-correlation and low value of mean sensi- tivity indicates the presence of more low frequency variance in the series. This is more obvious in density series than in width series. The auto-correlation can be re- moved by auto-regression modeling in the program ARSTAN (Cook 1985), i.e., to obtain residual chronologies. APC (agreement with population chronology) and SNR (signal to noise ratio) are produced from residual chronologies. APC indicates the common variance due to common forcing factors over a site. This may be the com- mon climatic effect experienced by all trees over a wide area of the site. SNR values indicate the applicability of the tree-ring series in dendro-ecological analysis. In gen- eral, higher APC and SNR indicate a greater climatic influence on tree growth (Cook & Kairiukstis 1990). BMS and JYP have higher APC and SNR in ring-width chro- nologies, whereas JYP and NSC have higher values in density chronologies, com- pared with the others.

Climate correlation analysis Table 3 shows that there are 40 significant coefficients in the correlation functions, 20 for ring width and 20 for ring density. More than half (24) of the coefficients show significant correlations with current growth months of June to September in all corre- lation functions. Examining species by species, there are 15 significant coefficients which appeared in NSC, 8 in JYP, 7 in BMS, 6 in JYG and 4 in BMY. For the different climate parameters, total monthly rainfall has 10 significant coefficients in both width and density. Each of the three temperature parameters has 8 significant coefficients, and river-flow accounts for 6 significant coefficients. In all the 10 groups of correla-

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Table 3. Summary of the significant correlation function coefficientsρ ( < 0.05). A twelve-month span is shown back to the previous October. The current growth season is from May to September. Chronologies without any significant correlation coefficients are not included in the table. Months: Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Ring width vs average monthly temperature BMS – JYG – JYP + NSC – Ring width vs total monthly rainfall BMS + + BMY – JYP – NSC + + Ring width vs river flow JYG + JYP + NSC + Ring width vs average monthly maximum temperature BMS – JYG – NSC – Ring width vs average monthly minimum temperature JYG – JYP + NSC + – Maximum ring density vs average monthly temperature BMS + JYP – NSC + + Maximum ring density vs total monthly rainfall BMS – BMY + JYP – NSC + Maximum ring density vs river flow JYG + + JYP + Maximum ring density vs average monthly maximum temperature BMS + JYP – NSC + – + Maximum ring density vs average monthly minimum temperature BMY – – NSC + +

Downloaded from Brill.com09/26/2021 10:07:05AM via free access Xiong, Okada & Fujiwara — Dendrochronological potential in Chinese trees 193 tion functions, the pair of ring width and total monthly rainfall had the highest number of significant coefficients (6 coefficients) and the second was the pair of ring density with mean monthly maximum temperature (5 coefficients).

DISCUSSION

The dendrochronological potential of five species from the Three Gorges Reservoir region has been presented here. The chronologies exhibit significant inter-correlation between series and moderate values of mean sensitivity. These indicate usefulness of the chronologies in dendrochronological studies. One application of dendrochronology that has aroused worldwide interest is paleoclimatic reconstruction. Information can be obtained on a year-to-year resolu- tion and low frequency fluctuations of the order of decades to centuries can also be determined. Such data can be useful in determining statistical probabilities of various climatic events, such as droughts and floods in this area, as well as revealing the presence of long-term trends or cycles that may be useful in climate predictions. This will require relatively long chronologies. The five chronologies presented here are only ranged from 38 years (site NSC) to 186 years (site BMY). The time series cre- ated now are obviously too short for interpreting long-term trends. However, old trees or old archaeological samples from these five species exist in this area. For example, Chen et al. (1994) recorded several old Cinnamomum camphora trees in Wuxi County, with diameters over 170 cm and ages estimated to be 900 years. This species is also widely used for artefacts and furniture. This species offers the greatest possibility to extend chronologies back more than a few hundred or beyond a thousand years. Simple correlation analysis showed very positive results. The five species ana- lysed are sensitive to environmental conditions. The tree-ring width data significantly correlated with current summer rainfall in BMS and NSC; and summer river flow is significantly correlated with both ring width and ring density in JYG and JYP. This means that these four species could be used for the reconstruction of past summer rainfall and river-flow records. It is during the summer period that most droughts and floods occur in this area. A long-term rainfall and river-flow reconstruction produced from tree rings then could be used to build a model to predict future floods that will benefit the management of the Three Gorges Dam in the future. Dendrochronological techniques may be effectively applied in various types of ecological studies in the Three Gorges Reservoir region. By employing cross-dating methods, accurate determinations can be made of tree ages and growth rates. Dendrochronological methods are particularly suitable for use in studies of popula- tion dynamics and the dating of successional histories. Past events at a site, such as logging history and insect attacks, can be accurately dated from marked changes in growth rates (Norton & Ogden 1990). We are currently conducting research to deter- mine the accurate timing and causes of growth decline of Pinus massoniana in this area. Although detailed data are not yet available, comparisons of several Pinus chro- nologies and sulphur isotope analysis of tree rings suggest that the abrupt growth decline since the 1970s may be caused by acid rain. Landslides have been another

Downloaded from Brill.com09/26/2021 10:07:05AM via free access 194 IAWA Journal, Vol. 21 (2), 2000 serious concern in the Three Gorges Reservoir region. Landslides in this area have resulted in many human deaths in recent years. Landslides may be dated either by dating trees growing on the new surface, or by dating scars and reaction wood in trees deformed by the event (Schweingruber 1988). This can be applied for studying land- slide impacts in the Three Gorges Reservoir region. In conclusion, tree-ring materials from the Three Gorges Reservoir region could be successfully cross-dated. Both ring width and maximum latewood density param- eters of the five cross-dated species showed some significant correlations with cli- mate factors. This study, as the first part of dendroecological studies in this area, would be improved with more information on site conditions, tree physiology studies and environmental records. Future efforts should be made to use more environmental parameters and expand the chronology beyond a few hundred or a thousand years using modern and archaeological samples.

ACKNOWLEDGEMENTS

This project was supported by a Japanese STA Postdoctoral Fellowship to the first author. The Spring Sunshine Program of the Ministry of Education of China and the New Zealand Vice- Chancellors Committee partially funded travelling costs. The Forestry Bureau of Chongqing kindly gave permission to sample the trees. Li Xuguang, Pan Jie, Deng Hongping and Yang Chengwen assisted with sampling in the field. Zhong Xianghao and Liu Shuzhen provided river- flow data. K. Yasue gave some suggestions on the early stage of this study. Y. Hirakawa and K. Yamashita helped in various aspects of the experiment. Louise Cullen and Stephen Urlich have read the revised manuscript.

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