Under Ministry of Education, Lanzhou University, Lanzhou 730000, China; ... and Environment Sciences, Northwest Normal University, Lanzhou 730070, China).
Journal of Integrative Plant Biology 2007, 49 (2): 150−156
Hydrological Response of Populus euphratica Olve. Radial Growth in Ejinaa Banner, Inner Mongolia Pu-Xing Liu1, 2*, Jian-Feng Peng1 and Fa-Hu Chen1 (1Center for Arid Environment and Paleoclimate Research, Key Laboratory of Western China’s Environmental System Under Ministry of Education, Lanzhou University, Lanzhou 730000, China; 2
College of Geography and Environment Sciences, Northwest Normal University, Lanzhou 730070, China)
Abstract Populus euphratica Olve. is a dominant tree species in Ejinaa Oasis of the lower reaches of the Heihe River, Inner Mongolia, China. In recent years, the population of this species has shown signs of degradation that are suggested to be probably associated with the decrease of surface water. In this study, the history of river runoff in this region was examined with a dendrochronological study of P. euphratica from four sites. It is found that tree-ring widths in the all sites have negative correlation with runoffs of all months at the Zhengyixia hydrological station. Principal component (PC) analysis of the tree-ring chronologies shows that the first PC (PC1) accounts for 49.98% of the total variances. The first PC is found to have a significantly negative correlation with runoffs in March and April (– 0.52 and – 0.43, respectively, P < 0.05). This negative correlation might be related to variations in the depth of underground water. Key words: dendrohydrology; lower reaches of Heihe River; Populus euphratica; Principal Component Analysis; radial growth; response model. Liu PX, Peng JF, Chen FH (2007). Hydrological response of Populus euphratica Olve. radial growth in Ejinaa Banner, Inner Mongolia. J. Integr. Plant Biol. 49(2), 150−156.
Available online at www.blackwell-synergy.com/links/toc/jipb, www.jipb.net
Tree growth is sensitive to climate variability in semi-arid and arid regions. Research on this sensitivity has indicated that trees respond to variations of water availability (soil moisture) by producing variations in the widths of the growth rings (BritoCastillo et al. 2003). In regions where moisture limits tree growth, tree rings have been found to be a useful proxy of past hydrologic variations (Stockton and Jacoby 1976; Meko and Graybill 1995). Annual or seasonal runoff has been successfully reconstructed from tree rings in the middle and western regions of America (Smith and Stockton 1981; Meko et al. 2001;
Received 1 Sept. 2006
Accepted 28 Nov. 2006
Supported by the National Natural Science Foundation of China (40371009 and 40421101) and China International Collaboration Project (2002CB714004). *Author for correspondence. Tel: +86 (0)931 891 2793; Fax: +86 (0)931 891 2330; E-mail: . © 2007 Institute of Botany, the Chinese Academy of Sciences doi: 10.1111/j.1672-9072.2007.00425.x
Woodhouse 2001; Jain et al. 2002). Stahle et al. (1999) found that the growth of African Pterocarpus angolensis DC. tree reflects the total precipitation variation of the wet season in Zimbabwe. Pederson et al. (2001) found that ring-width chronologies of Scots pine (Pinus sylvestris L.) and Siberian larch (Larix sibirica Ledebour) trees in northeastern Mongolia are highly correlated with annual runoff. In China, since the beginning of the 1980s, researches on dendrohydrology along Tarim River (Li 1989; Li et al. 2000) have indicated that ring-width of P. euphratica, a widely distribution tree in the desert area in western China, positively relates to annual runoff. It would be important to test whether the same tree species responds to the hydrological environment in the same way in different climatic regions. P. euphratica of Ejinaa Banner in the lower reaches of the Heihe River, Inner Mongolia, China, is one of the most widespread woody species in desert region of Middle Asia. In Ejinaa Banner it is not only a dominant species of the oasis vegetation and an indicator of eco-environmental degradation, but also has the major function of fixing sand and maintaining ecological services. It contributes to maintaining the existence of 80% of
Hydrological Response of Tree-Ring Radial Growth in Ejinaa 151
the local total population and 70% of the local livestock (Gao et al. 2000). It has vital influences on the regional economy and social development of the oasis in the region. In recent years, P. euphratica has largely degenerated and attracted much more public attention. Scholars have studied the causes of the degradation and protective measures of P. euphratica from the perspectives of ecology, tree physiology and geology (Wei 1990; Liu et al. 2002; Zhang and Shi 2002; Su et al. 2003; Luo and Cui 2004; Zhang et al. 2004a, 2004b; Zhou et al. 2004; Gao et al. 2000, 2005). The relationships between the growth of P. euphratica trees and hydrological variation, however, have still not been clear by now. It is an open question as to whether or not the decrease of water resources would result in population decline of P. euphratica. Tree-ring research in the region is a potential way to solve the problem (Liu et al. 2005). In this study, we used the methods of dendrochronology to: (1) develop regional chronologies of P. euphratica in Ejinaa Banner; (2) analyze the relationship between radial growth of P. euphratica and river runoff; and (3) discuss the causes of P. euphratica degradation and measures of restoring the regional eco-environment.
to the other and involved a linear combination of the four site chronologies (Zhang and Hebda 2004). The series of PC scores over the chronology length represent growth variation common to the four sites. The weight associated with each chronology conveyed information about the growth relationship between a specific site and the PC: the higher the weight is, the closer the relationship is (Legendre and Legendre 1998). For the first PC, the weights of the four site chronologies are all positive (0.553, 0.463, 0.522 and 0.456, respectively), indicating that the growth variations at all sites are positively correlated with the first PC. Therefore, the first PC reflected a common growth response throughout the four sites and a largest contribution of variance. Relationships between tree-ring width and temperature, precipitation and runoff are tested in this study. It is found that the best correlation is between tree-ring width and runoff. Relationships between tree-ring growth and runoff were evaluated using the first PC chronology and the chronologies for each of the four sites. The runoff data is the observed data at
Results Ring-width chronologies of P. euphratica trees were developed for the four sites in the study area (Figure 1). Mean correlation coefficients among individual series range from 0.519 to 0.597 (Table 1), indicating that annual variation in tree-ring growth is largely controlled by a common environmental factor. The tree rings are sensitive to environmental variation as seen from the values of mean sensitivity (0.338–0.393). The firstorder autocorrelation of the tree-ring series ranges from 0.556–0.779 (Table 1), indicating a lag effect of the preceding year’s condition on tree rings of the growth year. The lowest value of EPS in the four chronologies is 0.858, indicating that these chronologies contain useful regional signals (Cook and Kairiukstis 1990). The PC results of the four chronologies for the common interval 1916–2002 (Table 2) indicate that the first and second eigenvectors accounted for 49.98% and 20.39% of the total variances, respectively. Each PC was orthogonal (unrelated)
Figure 1. Tree ring-width chronologies of Populus euphratica at four sites (CG, Chaganshaha; LX, Langxinshan; UPB, Jianguoyingbei; SHNR, Saihannaoer) in Ejinaa Oasis.
Table 1. Statistics of tree-ring chronologies of Populus euphratica in Ejinaa Banner, Inner Mongolia Site
Sample
Earliest
Mean measurement
Standard
Mean
Mean
code
size
year
(mm)
deviation
correlation
sensitivity
EPS
First-order autocorrelation
SHNR
31
1917
2.84
2.224
0.579
0.338
0.901
0.779
UPB
49
1903
2.09
1.555
0.597
0.338
0.929
0.659
CG
37
1869
2.07
1.730
0.519
0.384
0.858
0.749
Lx
34
1848
2.63
1.196
0.589
0.393
0.878
0.556
CG, Chaganshaha; LX, Langxinshan; UPB, Jianguoyingbei; SHNR, Saihannaoer; EPS, agreement with population chronology.
152
Journal of Integrative Plant Biology
Vol. 49
No. 2
2007
Table 2. Results of principal component analysis of Populus euphratica chronologies for the common interval 1916–2002 at four sites in Ejinaa Banner, Inner Mongolia Principal
Eigenvalue
component
Variance
Cumulative
(%)
(%)
1
1.999
49.98
49.98
2
0.816
20.39
70.37
3
0.698
17.44
87.81
4
0.488
12.19
100.00
the Zhengyixia hydrological station for the period of 1954– 1999. We calculated the correlation coefficients between treering chronologies and the runoffs of months from previous October to October of the growth year, and also for intervals of combined months to reflect seasonal influences (Table 3). It is shown that the tree-ring width index for four sites at all most all months has negative correlation with runoffs except the top site in June and July (Table 3). The negative correlation is even clear if the first PC is used to calculate the correlation coefficient. Especially, the tree-ring growth had a most significant value of correlation coefficient with the runoff in March and April (−0.52 and −0.43, respectively, and −0.52 for combined February to April).
controls changes in the depth of the groundwater. The growth of P. euphratica trees in the study area is considered to need daily mean temperature higher than 5 °C (Wei 1990). The first and last day of mean daily temperature higher or equal to 5 °C occurs on April 5–6 and on October 18–20, respectively, in Ejinaa Banner (edited by Ejinaa 1998). Therefore, the mean growth period of the tree is from early April to mid-October. The hibernation period should be from the previous mid-October to current March. The growth of P. euphratica in the area mainly depends on groundwater. The best suitable groundwater depth for the tree growth is between 2 m and 4 m with becoming shallow in spring. The depth of groundwater in April−October ranges from 1.49 m to 3.85 m in the study area, which can meet the water demands of P. euphratica. More groundwater, therefore, could be harmful to tree growth in this region. Extra more water induces activation
Discussion The negative relationship between tree growth and runoff observed in this study is different from that in Tarim basin of Xinjiang where the tree-ring width of Populus euphratica had a positive correlation with runoff (Li 1989). The growth of P. euphratica mainly relies on groundwater (Li 1989). At present, the depth of groundwater is very shallow along the river in Ejinaa Banner. Changes in the depth of groundwater are closely related to Zhengyixia runoff, and the seepage of runoff also
Figure 2. Comparison of the first PC of Populus euphratica tree-ring chronologies and Zhengyixia runoff from 1954–2001.
Table 3. Correlation coefficients between tree-ring chronologies and runoff from October of the previous year to October of the growth year and for combined months in Ejinaa Banner, Inner Mongolia (numbers in black indicate confidence above 95% level) PC1
SHNR
UPB
CG
LX
Months
PC1
SHNR
UPB
CG
Pf 10
Months
− 0.37
− 0.42
− 0.25
− 0.05
− 0.14
f7
− 0.04
− 0.22
− 0.15
− 0.11
LX 0.39
Pf 11
− 0.19
− 0.16
− 0.22
− 0.03
0.01
f8
0.01
− 0.13
− 0.09
− 0.07
0.27
Pf 12
− 0.11
− 0.00
− 0.22
− 0.04
0.08
f9
− 0.29
− 0.27
− 0.14
− 0.25
− 0.12
f1
− 0.26
− 0.05
− 0.29
− 0.08
− 0.14
f10
− 0.35
− 0.55
− 0.28
0.12
− 0.11
f2
− 0.19
− 0.07
− 0.20
− 0.06
− 0.11
f2–3
− 0.50
− 0.48
− 0.43
− 0.11
− 0.39
f3
− 0.52
− 0.52
− 0.42
0.02
− 0.26
f3–4
− 0.50
− 0.64
− 0.38
− 0.05
− 0.34
f4
− 0.43
− 0.59
− 0.32
0.06
− 0.16
F2–4
− 0.52
− 0.61
− 0.41
− 0.07
− 0.37
f5
− 0.17
− 0.38
− 0.06
0.00
0.01
F4–10
− 0.28
− 0.48
− 0.28
− 0.27
− 0.20
f6
− 0.16
− 0.19
− 0.27
− 0.25
0.26
Pf10–3
− 0.43
− 0.41
− 0.37
− 0.15
− 0.27
CG, LX, UPB, and SHNR are the same as in Table 1. f, runoff of the current year; PC1, the first principal component; Pf, runoff of the previous year.
Hydrological Response of Tree-Ring Radial Growth in Ejinaa 153
of anaerobic bacteria in the rhizosphere and accumulation of poisonous matters such as sulfured hydrogen, firedamp, and ferrous hydrogen, which is disadvantageous for absorption of nourishments and the breath of roots. The root system under such conditions will be easily poisoned and vulnerable to decay (Li et al. 1989). To prevent roots from rotting in hibernation period when the evaporation is relatively weak, the growth of P. euphratica needs fewer water supplies. However, the runoff of Zhengyixia Station occupies 56.54% of the total annual flow in the period. The time of leakage of the runoff centralizes in winter half year, which differs from other regions such as Tarim basin for the supply of the groundwater. Because the temperature
normally is 10–15 °C below zero, the water supply to underground in winter half year could make soil freeze and frequent freezing-melting cycle happens during spring when temperature rises (Zhang and Shi 2002). The damage to roots by freezing and melting affects the growth of P. euphratica in the following year. This also partly contributes to the negative correlation between the chronologies and the runoff in autumn and winter of the previous year and February–March of the current year. The negative correlation of the tree-ring width and runoff is clearly shown to compare the first PC and runoff changes over the past 50 years (Figure 2). The mean score of the first PC was 1.057 and mean variance was 1.467 when the runoff decreased sharply to a mean value of 8.113×108 m3 in years
Figure 3. Geography map shown the lower reaches of Heihe Rive and Ejinaa Banner, the area circled by the light dash line. The four sampling sites (CG, Chaganshaha; LX, Langxinshan; SHNR, Saihannaoer; UPB, Jianguoyingbei), hydrological and meteorological stations are also marked.
154
Journal of Integrative Plant Biology
Vol. 49
No. 2
2007
1989–2001 (Figure 2). In contrast, the mean score of the first PC was 0.694 with a mean variance of 0.767 when the runoff increased to a mean value of 10.842×108 m3 in years 1954– 1988. The growth–runoff relationship has implications in management of regional water resources and growth of P. euphratica population. Tree ring-width chronologies are developed at four sites along the banks of the west branch of the Heihe River in Ejinaa Banner. These data contain useful information about past changes in hydrological situation. Correlation analyses showed that treering growth was significantly negatively correlated with runoff
in March and April. The runoff might affect the growth of P. euphratica trees by manipulating changes in the depth of groundwater. The tree rings were wide in 1989–2001 when the runoff sharply decreased, while the tree rings were narrow in 1954–1988 when the runoff was high. This differs from that in Tarim basin. It is necessary that we strengthen the monitoring and investigation of groundwater variation and take this into account when making policies concerning sustainable management of the Ejinaa Oasis.
Materials and Methods
Figure 4. Hydroclimate regimes for the period of 1960–2001 at Zhengyixia hydrological station and Ejinaa weather station. (A) Month mean precipitation and temperature. (B) Variations of the annual temperature and annual precipitation (the dash lines show the trend). (C) Month runoff.
Ejinaa Banner, a stockbreeding region where people from different minorities live, is located in the lower reaches of the Heihe River (also called Ejinaa River), Inner Mongolia, China (Figure 3). The total area is 11.41×10 4 km 2, of which Ejinaa oasis only takes up 2.84%. The total population is 16.5 thousand, of which 71.2% live in Ejinaa oasis, which is fertile and is the foundation for the existence and development of the region (Liu et al. 2002). The Heihe River is the only water source. The topography of the Ejinaa Banner is flat with an elevation ranging from 900 to 1 100 m.a.s.l. The climate is continental with mean annual temperature and annual precipitation of 8.7 °C and 35.8 mm, respectively. High temperature coincides with high precipitation in summer. The trends of the precipitation and the temperature from 1960–2001 indicate that mean annual temperature increases slightly whereas the annual precipitation decreases (Figure 4). Besides the dominant tree species P. euphratica, which grows mainly along riverside, other plant species in the Ejinaa Oasis include Elaeagnus angustifolia L., Tamarix ramosissima Ledeb, Achnatherum splendens (Trin.) Neuski, Sophara alopecuroides L. and Phragmites australia (Cav.) Trin. ex Steud. The main soil type is forest-shrub meadow soil that alternates with fixed and semi-fixed wind-sand soil (Gao et al. 2005). We selected four sites and sampled 188 increment cores of P. euphratica along the west branch of Ejinaa River (Figure 3). At each site, increment cores were collected from at least 20 living trees that were usually sparsely distributed. The runoff of the Heihe River seeping through the surface is the main supplementary source of the groundwater in Ejinaa Banner. Mean annual runoff of Zhengyixia hydrological station from the lower reaches of the Heihe River is approximately 10.10 × 108 m3. The runoff is high from December to next March and low from April to June (Figure 4). The depth of groundwater does not exceed 4 m in the study area at present. Increment core samples were mounted and sanded to make the rings clearly visible. The tree rings were then cross-dated and measured using a Velmex sliding linear encoding device and the software MesureJ2x. The computer program COFECHA was used to check the quality of cross dating (Holmes 1983).
Hydrological Response of Tree-Ring Radial Growth in Ejinaa 155
Those samples that did not have clearly visible rings were removed from chronology building. COFECHA also provides a calculation of mean sensitivity of the chronologies, a measure of relative year to year differences in ring-widths (Fritts 1976). Growth trends and other non-climatic effects were removed from measured and dated series (Stokes and Smiley 1968; Fritts 1976; Cook and Kairiukstis 1990; Woodhouse 2001). The raw ring-width measurements were standardized using the program ARSTAN. The program offers several commonly used methods of standardization (Cook and Holmes 1986). For this study, raw measurements were initially fitted with a negative exponential curve for chronology development at four sites. Principal component (PC) analysis (D’Arrigo et al. 2000; Shao et al. 2004; Zhang and Hebda 2004) was used to summarize the regional variation in radial growth patterns carried by the chronologies at four sites with the software PCA (GrissinoMayer et al. 1996). To understand the relationship between P. euphratica radial growth and hydrologic variability, we used the first PC to analyze its correlation with hydrological factors, and to determine the best correlated months and period. In this study, we selected monthly runoff of 46 years from Zhengyixia hydrological station spanning 1954–1999. Because trees often show some delay in transmitting climatic conditions into growth (Fritts 1976; Meko and Graybill 1995), we conducted correlation analysis between the first PC of tree-ring chronologies and the runoff from the previous October to the current October.
and reconstructions of Northern Hemisphere temperature. Holocene 10, 669–672. Ejinaa Chorography Compilation Committee (1998). Ejinaa County Annals. Local Chronicles Press, Beijing (in Chinese). Fritts HC (1976). Tree Rings and Climate. Academic Press, London. Grissino-Mayer HD, Holmes RL, Fritts HC (1996). The International Tree-Ring Data Bank Program Library Version 2.0. User’s Manual. The International Tree-Ring Data Bank, Tucson, Arizona. Gao RH, Dong Z, Zhang H, Li JQ (2005). Study on regeneration process and biodiversity characteristic of Populus euphratica community in the Ejinaa Natural Reserve, Inner Mongolia of China. Acta Ecol. Sin. 5, 1019–1025 (in Chinese with an English abstract). Gao RH, Zhan GW, Guo XH (2000). Discuss Populus euphratica forest of Ejinaa ecological effectiveness and protect countermeasure. J. Arid Land Resour. Environ. 14 (Supp1.), 74–77 (in Chinese with an English abstract). Holmes RL (1983). Computer assisted quality control in tree-ring dating and measurement. Tree-Ring Bull. 43, 69–75. Jain S, Woodhouse CA, Hoerling MP (2002). Multidecadal streamflow regimes in the interior western United States: Implications for the vulnerability of water resources. Geophys. Res. Lett. 29, 321–324. Legendre P, Legendre L (1998). Numerical Ecology. Elsevier Science BV, Amsterdam, Holand. Li JF (1989). Research on Dendroclimate and Dendrohydrology in Xinjiang. Meteorology Press, Beijing (in Chinese). Li JF, Yuan YJ, You XY (2000). Dendrohydrology and Application.
Acknowledgements
Science Press, Beijing (in Chinese). Liu PX, Chen FH, Gou XH, Huang XZ, Peng JF (2005). Establish-
We would like to thank Dr Edward R. Cook from the LamontDoherty Earth Observatory of Columbia University and Dr Connie A. Woodhouse from the National Oceanic and Atmospheric Administration Paleoclimatology Program for supplying references.
ment of tree-ring chronology and response analysis in past 100 years for Ejinaa Banner, Inner Mongolia. J. Desert Res. 25, 764–768 (in Chinese with an English abstract). Liu ZL, Zhu GY, Hao DY (2002). The mountain-basin complex of the Heihe River and resource-environment safety of oasis zone in the lower reaches. J. Nat. Resour. 17, 286–293 (in Chinese with an English abstract).
References
Luo XY, Cui CY (2004). Reason for the degradation of Populus euphratica in Ejinaa area, Inner Mongolia: A case study in
Brito-Castillo L, Díaz-Castro S, Salinas-Zavala CA, Douglas AV (2003). Reconstruction of long-term winter streamflow in the Gulf of California continental watershed. J. Hydrol. 278, 39– 50.
‘‘strange forest’’. Geo. Sci. Technol. Inf. 23, 81–84 (in Chinese with an English abstract). Meko DM, Graybill DA (1995). Tree-ring reconstruction of Upper Gila River discharge. Water Resour. Bull. 31, 605–616.
Cook ER, Holmes RL (1986). Users Manual for ARSTAN. Labora-
Meko DM, Therrell MD, Baisan CH, Hughes MK (2001). Sacra-
tory of Tree-ring Research, University of Arizona, Tucson,
mento River flow reconstructed to A.D.869 from tree rings. J. Am.
American.
Water Resour. Assoc. 37, 1029–1040.
Cook ER, Kairiukstis LA (1990). Methods of Dendrochrology Appli-
Pederson N, Jacoby GC, D’Arrigo R, Buckley B, Bugarjav C,
cations in the Environmental Sciences. Kluwer Academic
Mijiddorj R (2001). Hydrometeorological Reconstructions for
Publishers, Dordrecht, Netherlands.
Northeastern Mongolia Derived from Tree Rings: AD 1651–1995.
D’Arrigo RD, Jacoby GC, Pederson N, Frank D, Buckley B, Nachin B et al. (2000). Mongolian tree-rings, temperature sensitivity
J. Climate 14, 872–881. Shao XM, Huang L, Liu HB, Liang EY, Fang XQ, Wang LL (2004).
156
Journal of Integrative Plant Biology
Vol. 49
No. 2
2007
Millenary precipitation variation from tree-ring records in Delingha area, Qinghai. Sci. China Ser. D 34, 145–153 (in Chinese with an English abstract). Stokes MA, Smiley TL (1968). An Introduction to Tree Ring Dating. University of Chicago Press, Chicago. Smith LP, Stockton CW (1981). Reconstructed stream flow for the salt and Verde Rivers from tree-ring data. Water Resour. Bull. 17, 939–947. Stahle DW, Mushove PT, Cleaveland MK, Foig F, Haynes GA (1999). Management implications of annual growth rings in Pterocarpus angolensis from Zimbabwe. For. Ecol. Manage. 124, 217–229. Stockton CW, Jacoby GC (1976). Long-term surface-water supply and streamflow trends in the Upper Colorado River basin based
China Forestry Publishing House, Beijing (in Chinese). Woodhouse CA (2001). A tree-ring reconstruction of streamflow for the Colorado Front Range. J. Am. Water Resour. Assoc. 37, 561–570. Zhang L, Dong ZC, Huang XL (2004a). Modeling on relation between major plants growth and groundwater depth in arid area. J. Desert Res. 24, 110–113 (in Chinese with an English abstract). Zhang QB, Hebda RJ (2004). Variation in radial growth patterns of Pseudotsuga menziesii on the central coast of British Columbia, Canada. Can. J. For. Res. 34, 1946–1954. Zhang WW, Shi SS (2002). Study on the relation between groundwater dynamics and vegetation degeneration in Erjina Oasis. J. Glaciol. Geocryol. 24, 421–425 (in Chinese with an English abstract).
on tree-ring analyses. Lake Powell. Res. Project Bull. 18, 1–70.
Zhang XY, Gong JD, Zhou MX, Si JH (2004b). Spatial and tempo-
Su PX, Zhang LX, Du MW, Bi YR, Zhao AF, Liu XM (2003). Photo-
ral characteristics of stem sap flow of Populus euphratica. J.
synthetic character and water use efficiency of different leaf
Desert Res. 24, 489–492 (in Chinese with an English abstract).
shapes of Populus euphratica and their response to CO 2
Zhou MX, Xiao HL, Luo F, Li SZ, Song YX, Xiao SC (2004). Ground-
enrichment. Acta Phytoecol. Sin. 27, 34–40. (in Chinese with
water salinity characters and its relationship with vegetation
an English abstract).
growth in Ejinaa Delta. J. Desert Res. 24, 432–436 (in Chinese
Wei QJ (1990). Diversiform-Leaved Poplar (Populus euphratica).
with an English abstract).
(Handling editor: Jin-Zhong Cui)
