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O R I G I N A L A R T I C L E

The changes of vegetation cover in Ejina Oasis based on waterresources redistribution in Heihe River

Wang Yaobin Feng Qi Si Jianhua

Su Yonghong Chang Zongqiang Xi Haiyang

Received: 19 March 2010/ Accepted: 9 March 2011/ Published online: 23 March 2011

Springer-Verlag 2011

Abstract The Ejina Oasis (EO), located in arid northwest

China, is a typical arid area in the world. The ecosystem inthe oasis has become worse since the 1990s. However, it

began to improve after the Chinese government took the

mandatory measure to redistribute the water in Heihe in

2000. To understand this change, the remote sensing ima-

ges in 1990, 2000 and 2006 were selected, and exertion

related Land Use/Cover Change (LUCC) model was

employed. Results showed that: (1) non-vegetation cover

was the main body of the vegetation cover in oasis,

showing a trend of increase at the beginning and diminu-

tion later, while low, medium and high vegetation cover

was the other way around; (2) the area of low, medium and

high vegetation cover in 2006 was less than that in 1990;

the status and trend index Ptof oasis vegetation cover was

0.62 in 19902000, which means that the oasis ecosystem

of Ejina was getting worse and was under an unbalanced

status; Pt was 0.27 in 20002006 indicating that the oasis

ecosystem was restored obviously and the whole system

tended to be balanced; (3) all of these changes should be

attributed to the water resources redistribution in Heihe

River, which played a leading role, as well as the measures

and relevant policies taken by the local government, which

promoted the rapid recovery of the medium and high

vegetation.

Keywords Ejina Oasis Vegetation cover LUCC

Water resources redistribution in Heihe River Northwest China

Introduction

In arid areas, vegetation acting as an important ecological

indicator can reflect the status of environment directly

(Li1999), and the vegetation cover changes can represent

evolvement and variance of the environment. Researches

on vegetation cover changes have become an important

instrument to bring about the changes of environment and

their laws in arid areas (Wu and Wang1980). In arid inland

river basins, the central role of vegetation in the ecological

environment cannot be ignored (Wang et al. 2002). The

vegetation cover and its growth are one of the important

indicators reflecting the status of regional eco-environment,

while changes in the perennial vegetation cover are a

mirror that can reflect the changes of the environment

district in a variety of time (Jia et al. 2007). There is no

other substitution for the vegetation cover in maintaining

the stability of ecological environment in the lower reaches

of the Heihe River (Zhao and Cheng2001). Therefore, it is

of great significance to study vegetation cover changes in

the lower reaches of the Heihe River.

The Normal Difference Vegetation Index (NDVI) is

currently the most extensively applied one for representa-

tion of vegetation cover status (Tucker 1979). In the field

of vegetation study, foreign scholars mainly use NDVI to

analyze trends of vegetation cover changes and their rela-

tionships with climate (Cihiar et al. 1991; Eklundh1998;

Nicholson and Farrar1994). In recent years, the results of

some studies suggest that the growth of vegetation is

affected by global warming (Myneni et al. 1997, 1998).

W. Yaobin (&) F. Qi S. Jianhua S. Yonghong C. Zongqiang X. HaiyangCold and Arid Regions Environmental and Engineering

Research Institute, Chinese Academy of Sciences,

Donggang West Road 320, Lanzhou 730000, Gansu, China

e-mail: [email protected]

W. Yaobin

The Lab and Department of Equipment Management,

Northwest Normal University, Lanzhou 730000, China

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Environ Earth Sci (2011) 64:19651973

DOI 10.1007/s12665-011-1013-0


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The role of vegetation cover in high-latitude area of the

northern hemisphere is increasingly remarkable (Myneni

et al. 1997; Keeling et al. 1996; Zhou et al. 2003). Some

researches associate the activity of human beings with the

changes in vegetation cover (Vicente-Serrano et al. 2005),

and consider the tropical rain forest region in Brazil, the

arid and semi-arid desert area in Africa and Central Asia as

hot spots in this research (Tucker and Nicholson 1999;Beurs and Henebry 2004; Barbosa et al. 2006). Many

domestic scholars also have done a lot of studies in this

field. Some researches indicate that the vegetation cover in

western and northwestern areas of China was enhanced at

large (Zhang et al. 2006a). In the past 20 years, the vege-

tation cover activity of China is increasingly remarkable

(Fang et al.2003). There is an obvious spatial difference in

the climatic factor influence on NDVI of the vegetation

cover (Chen et al. 2001; Li et al. 2002). NDVI is highly

relevant to the temperature, the change of climate and

rainfall (Sun et al. 1998; Li and Tao 2000; Gong et al.

2002; Tang and Chen2003). Rainfall is the root reason forthe constraint on the growth of vegetation in the northern

desert, and the changes in vegetation cover has clearly a

hysteretic effect (Li and Shi2000).

Many scholars have also done a lot of fruitful researches

on the vegetation cover changes of EO, namely researches

on the relationship between: vegetation cover change and

run-off and groundwater (Zhong et al. 2002a; Zhang et al.

2002; Xi et al. 2007; Jin et al.2008; Cao et al. 2004; Feng

et al.2009); vegetation cover change and soil water and salt

balance (Feng et al. 2009; Zhang et al. 2006a; Li et al.

2003); vegetation cover change and climate change (Cao

et al. 2003; Huang 2003; Zhang et al. 2003); vegetation

cover change and human activities (Li et al.2004; Zhong

et al.2002b; Su et al.2004), etc. All of these studies provide

a scientific basis for the reconstruction of vegetation and

ecology. However, few studies proceed with the general

trend of vegetation cover area change and analysis on this

trend of vegetation cover change. To make up for this and to

contribute to the protection and recovery of the vulnerable

ecosystem in EO, this paper, adopting Landsat thematic

mapper (TM)/Landsat Enhanced TM (ETM) remote sens-

ing images of EO and the related LUCC model, makes a

detailed analysis of the general trend of the vegetation cover

changes of the oasis and compares each vegetation cover

grades and related parameters in the two periods of time.

Materials and methods

Study area

EO is a typical representative of oases in arid areas. It is

located in the extreme arid climate zone in China with a

total population of about 16,200 and an area of 3.288 km2.

Though located in the eastern and western sides of the

Ejina River with an annual average temperature of 8.3C

and yearly average rainfall of 5070 mm only, the yearly

average evaporation is over 3,000 mm. The surface water

is so poor that the run-off and groundwater become the

main water resource in EO (Gong et al. 1998; Wang and

Chen1998). The scope of this research (Fig. 1) covers theEO totally with an area of about 16,100 km2, based on the

remote-sensing image of satellite orbit No.P133/33.

Data and methods

To ensure feasibility and reliability of the results, this paper

chose its base data sources from the images of Landsat-

5TM and Landsat-7ETM? (1990 and 2006 with TM, 2000

with ETM?), selecting the remote-sensing image in July

2000 as the division when the water redistribution measure

in Heihe was enforced. The remote-sensing image of

September 1990 was selected as the representative for thepre-redistribution period (when the oasis was getting

worse) and the remote-sensing image of September 2006 as

the post-redistribution period (when the situation in the

oasis was getting better).The reason for selecting July 2000

was that the next month, August 2000, was the time at

which the measure of water redistribution would be carried

out in the Heihe River. September 1990 and September

2006 were selected because it is generally accepted that

Fig. 1 Location map of the study area

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September is the best time of the year for the vegetation

cover in the area and the remote-sensing image is of best

quality because the sky is free of cloud at that time. First,

the geometric and atmospheric corrections, radiometric

rectification and image cropping were carried out on ima-

ges with ENVI 3.5, and color composites were generated

by displaying the bands 4, 3 and 2 (R, G, B), respectively.

Geometric correction was carried out on a 1:50,000 topo-graphic map using the second-order polynomial transform

method by selecting 25 control points with average distri-

bution of less than 0.5 pixel root mean square error

(RMSE).The radiometric rectification was carried out by

means of image regression method, with which the image

reflection of the ETM? in July 2000 was calculated. Based

on the previous calculation, the atmospheric radiation on

the image of 1990 and 2006 was calculated. Second, the

three periods of vegetation coverage was calculated based

on NDVI and two components sub-pixel model. The veg-

etation cover grade was classified based on the particularity

of the oasis and the vegetation coverage (Table 1). Third,spatial superposition operation was conducted to study the

vegetation cover grades map in different periods to obtain

the corresponding transfer matrix of vegetation cover

grade. Last, the trend of vegetation cover was evaluated by

the related LUCC model.

Related LUCC models

The research approach to vegetation cover change included

mainly the following: vegetation index, regression analy-

sis, decision tree, artificial neural network, sub-pixel

analysis, etc. All these methods can reveal the changes in

the vegetation cover well. On the other hand, they are

unable to analyze the various types of vegetation cover

transformations. This paper combines vegetation index

with the LUCC model, which can reveal the changes of

vegetation cover in the study area and reflect various types

of vegetation cover transformations. The related LUCC

models are listed below (Shi et al. 2000).

Change rate Rd is used to reflect the changes of total

amount of different land cover types:

Rd Ub Ua=Ua 100% 1

Single type trend degree Rs shows the change speed in

amount of a certain LUCC type at a certain period of time

in the region:

Rs Ub Ua=Ua=T 100% DUin DUout=Ua=T 100% 2

Single type trend degree Rss expresses the dimensional

change of a certain LUCC type at a certain period of time

in the region:

Rss DUin DUout=Ua=T 100% 3

Ps is an index to reflect the trend of changes and the

status of LUCC type, when 0 B Ps B 1, the trend of

changes is upward, when 0[Ps C 1, it is fall.

Ps Rs=Rss DUin DUout=DUin DUout 1 Ps 1

4

Pt Xni1

DUouti DUinij j.Xn

i1

DUouti DUinij j

0 Pt 1

5Pt is an index to show the overall trend of changes and

the status of regional LUCC, when 0 B Pt\ 1/4, it is in

balance; when 1/4B Pt\ 1/2, in quasi balance; when

1/2 B Pt\ 3/4, in unbalance; when 3/4 B Pt B 1, in

extreme unbalance.

Ub and Ua are a certain type area at the beginning and

ending period of research; T is the study period; DUoutiis

the sum of the area of a certain type converting into the

other type at period t, while DUiniis the sum of the area of

a certain type transforming from the other type.

Results

Changes of the vegetation cover area in the oasis

With the help of statistical functions of ArcGIS and the

grade (Table1), vegetation cover areas in the oasis in

1990, 2000 and 2006 were classified and collected to

analyze the characteristics of vegetation cover area changes

in EO (Table 2). It can be seen from the table that the main

Table 1 The description of vegetation cover grade

Section Grade Code Description

\5% Non-vegetation

cover

N Equivalent to bare land,

sand and Gobi

530% Low vegetation

cover

L Equivalent to semi-

mobile sandy land,

low-yield grassland

and uncultivated

farmland

3060% Medium vegetation

cover

M Equivalent to shrub

woodland, medium

and low-yielding

grassland, fixed sandy

land and overflow land

[60% High vegetation

cover

H Equivalent to dense

shrub land, forests and

high-quality arable

land

Environ Earth Sci (2011) 64:19651973 1967

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part of the area was non-vegetation, among which the

cover area in 2000 was the biggest with a value of

11183.76 km2, accounting for 69.41% of the total. The area

of 659.09 km2 was more than that in 1990. In 2006, the

area decreased by 306.62 km2 compared with 2000 and

increased by 352.47 km2 compared with 1990. However,

the low, medium and high vegetation cover areas in 2000

were the smallest with reductions of 497.06, 148.78 and

13.17 km2, respectively, compared with that in 1990. In

2006, the corresponding areas increased by 240.79, 57.14and 8.49 km2, respectively, compared with that in 2000

and decreased by 256.27, 91.64 and 4.68 km2 compared

with that in 1990, respectively.

Dynamic changes of vegetation cover in the oasis

between 1990 and 2000

With the help of ArcInfo software, Map Algebra Method

(Shi et al.2000) and the related LUCC models, Table 3,4

and 5 were obtained to analyze dynamic changes of the

vegetation cover in EO. It can be seen from the tables that

during 19902000, there were mainly four types of vege-tation cover changes: LN, MN, NL and ML. These

four types made up over 87% changes of the total areas in

the oasis. It concretely showed that the non-vegetation

cover increased while the low and medium vegetation

covers decreased. Among them, the increase in the non-

vegetation mainly came from the low and medium vege-

tation. The low vegetation accounted for 76.58% of the

increase of the non-vegetation area, while the medium was

21.06%. The increase of the low vegetation was mainly

from the non-vegetation and medium vegetation with 58.55

and 36.77%, respectively. The increase of the medium

vegetation was from the low vegetation and non-vegetationwith 47.11 and 45.49% respectively. The increase of the

high vegetation was from the non-vegetation, the low

vegetation and the medium vegetation, accounting for

36.01, 19.86 and 44.14%, respectively. On the whole, the

non-vegetation area increased in this period in the oasis,

while the low, medium and high vegetation decreased. The

decrease in the medium and high vegetation areas was

particularly remarkable and the corresponding Rd were

-37.49 and -32.34, respectively; Rs were -3.75 and

-3.23, respectively. Only the non-vegetation cover

increased, and the corresponding Rd was 6.26 and Rs was

0.63. The index of the status and trend of the entire oasis Ptwas 0.62, indicating that transfer of types in the area

showed a two-way tendency and was under an unbalanced

status.

Dynamic changes of vegetation cover in the oasis

between 2000 and 2006

Similarly, it can be seen from Table 6,7 and 8 that during

20002006, there were mainly five types of vegetation

cover changes: NL, LN, LM, MN and NM. These

Table 2 The changes in the vegetation cover area in Ejina Oasis (km2, %)

Code 1990 2000 2006 19902000 20002006 19902006

Area % Area % Area % Variation Variation Variation

N 10524.67 65.32 11183.76 69.41 10877.14 67.51 659.09 -306.6 352.47

L 5150.69 31.97 4653.63 28.88 4894.42 30.28 -497.06 240.79 -256.3

M 396.83 2.46 248.05 1.54 305.19 1.89 -148.78 57.14 -91.64

H 40.72 0.252 7.55 0.17 36.04 0.22 -13.17 8.49 -4.68

Table 3 The transfer matrix of vegetation cover changes in Ejina

Oasis between 1990 and 2000 (km2, %)

2000

N L M H Total

(occupancy %)

1990

N 93.96 36.01 6.51 136.48(13.55)

B 68.85 26.38 4.77

C 58.55 45.49 36.01

L 573.75 37.29 3.59 614.63

(61.04)

B 93.35 6.07 0.58

C 76.58 47.11 19.86

M 157.79 59.00 7.98 224.77

(22.32)

B 70.20 26.25 3.55

C 21.06 36.77 44.14

H 17.65 7.51 5.86 31.02

(3.08)

B 56.90 24.21 18.89

C 2.36 4.68 7.40

Total 749.19 160.47 79.16 18.08 1006.90

(Occupy %) (74.41) (15.94) (7.86) (1.80)

B is a proportion that the i vegetation cover grade in 1990 converted

into j in 2000

C is a proportion that the j vegetation cover grade in 2000 transformed

from i in 1990


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five types accounted for over 91% of the changes in the

total areas of the oasis, which clearly shows that the low

and medium vegetation cover increased and the non-

vegetation cover decreased. Among them the increase of

the low vegetation area was mainly from the non-vegeta-

tion, making up 89.61% of the increase of the low vege-

tation. The increase of the medium vegetation was mainly

from the low vegetation and the non-vegetation covers

occupying 67.65 and 29.78%, respectively. The increase in

the non-vegetation was mainly from the low and medium

vegetation covers with 73.66 and 24.44%, respectively.

The increase in the high vegetation was from the medium,low and the non-vegetation areas, accounting for 53.54,

20.59 and 25.87%, respectively. In light of the general

trend, only the non-vegetation cover was decreased during

this period, showing a trend of fall; and the low, middle

and high vegetation cover areas all increased, showing a

trend of upward. Among them the medium and high

vegetation covers had an apparent tendency to increase,

and the corresponding Rd were 23.04 and 30.82, respec-

tively, while Rswere 3.84 and 5.14, respectively. The non-

vegetation cover showed a decreasing trend; its Rd was

-2.74 and Rswas -0.46. The index of the status and trend

of the whole oasis Pt was 0.27, indicating that transfer oftypes in the area was under a kind of quasi-balance status.

Comparison of changes of vegetation covers

in the oasis between 19902000 and 20002006

It can be concluded from Figs.2 and 3, which are com-

parison of the types of vegetation cover changes in the oasis

based on Table4 and Table7 that the type of vegetation

cover changes showed consistency in the two periods.

Table 4 The kind of vegetation cover change type in Ejina Oasis between 19902000 (km2, %)

Encode Change type Unit area Total rate Encode Change type Unit area Total rate

21 LN 573.75 56.98 41 HN 17.65 1.75

31 MN 157.79 15.67 34 MH 7.98 0.79

12 NL 93.96 9.33 42 HL 7.51 0.75

22 ML 59.00 5.86 14 NH 6.51 0.65

23 LM 37.29 3.70 43 HM 5.86 0.58

13 NM 36.01 3.58 24 LH 3.59 0.36

Table 5 The LUCC model analysis of vegetation cover changes in Ejina Oasis between 1990 and 2000 (km2, %)

Code U1990 U19902000 DUin DUout Rd Rs Rss Ps

Area Area Area % Area %

N 10524.67 10388.19 749.19 7.12 136.48 1.30 6.26 0.63 8.42 7.48

L 5150.69 4536.06 160.47 3.12 614.63 11.93 -9.65 -0.97 15.05 -6.45

M 396.83 172.06 79.16 19.95 224.77 56.64 -37.49 -3.75 76.59 -4.90

H 40.72 9.70 18.08 44.40 31.02 76.18 -32.34 -3.23 120.58 -2.68

Pt = 0.62

U19902000is the area of the type of vegetation cover that did not change; DUoutis the sum of the area of a certain type that was converted into the

other type between 1990 and 2000; DUinis the sum of the area of a certain type transformed from the other type between 1990 and 2000

Table 6 The transfer matrix of vegetation cover changes in Ejina

Oasis between 2000 and 2006 (km2, %)

2006

N L M H Total

(occupancy %)

2000

N 566.48 64.03 7.49 638.00

(51.90)B 88.79 10.04 1.17

C 89.61 29.78 25.87

L 260.16 145.44 5.96 411.56

(33.48)

B 63.21 35.34 1.45

C 73.66 67.65 20.59

M 86.31 57.44 15.50 159.25

(12.96)

B 54.20 36.07 9.73

C 24.44 9.09 53.54

H 6.70 8.23 5.51 20.44

(1.66)

B 32.78 40.26 26.96

C 1.90 1.30 2.56

Total 353.17 632.15 214.98 28.95 1229.25

(Occupy %) (28.73) (51.43) (17.49) (2.36)


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Table 7 The sort of vegetation cover change type in Ejina Oasis between 2000 and 2006 (km2, %)

Encode Change type Unit area Total rate Encode Change type Unit area Total rate

12 NL 566.48 46.08 34 MH 15.50 1.26

21 LN 260.16 21.16 42 HL 8.23 0.67

23 LM 145.44 11.83 14 NH 7.49 0.61

31 MN 86.31 7.02 41 HN 6.70 0.55

13 NM 64.03 5.21 24 LH 5.96 0.48

32 ML 57.44 4.67 43 HM 5.51 0.45

Table 8 The LUCC model analysis of vegetation cover changes in Ejina Oasis between 2000 and 2006 (km2, %)

Code U2000 U20002006 DUin DUout Rd Rs Rss Ps

Area Area Area % Area %

N 11183.76 10545.76 353.17 3.16 638.00 5.70 -2.74 -0.46 8.86 -5.19

L 4653.63 4242.07 632.15 13.58 411.56 8.84 5.17 0.86 22.43 3.83

M 248.05 88.80 214.98 86.67 159.25 64.20 23.04 3.84 150.87 2.55

H 27.55 7.11 28.95 105.08 20.44 74.19 30.82 5.14 179.27 2.87

Pt = 0.27

Fig. 2 The comparison of vegetation cover changes type in

19902000 and 20002006 in the Ejina Oasis

Fig. 3 The comparison of area of vegetation cover changes type in


Fig. 4 The comparison of DUin of vegetation cover changes in


Fig. 5 The comparison of DUout of vegetation cover changes in



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During 19902000, LN type was the most obvious one

with a value of 573.75 km2; during 20002006, NL was

the most obvious one with a value of 566.48 km2. These six

NL, LN, LM, MN, NM and ML change types in

vegetation cover were all relatively prominent in the two

periods. NL type had the greatest difference in its area with

a value of 472.52 km2, followed by LN and LM types,

while other types were opposite but not so obvious.From Figs.4and5, based on Tables 5 and 8, it can be

seen that in the two periods, DUin(the total area of a certain

type of transform from the other type) of the non-vegeta-

tion cover in 20002006 was smaller than that in

19902000; the other of the low, medium and high vege-

tation cover were all larger than that in 19902000. By

contrast, DUout (the total area of a certain type that was

converted into the other type) of the non-vegetation cover

in 20002006 was larger than that in 19902000; and that

of the other low, medium and high vegetation cover were

all smaller than that in 19902000. At the same time, the

biggest difference ofDUin was in the low vegetation coverwith an area of 471.68 km2. The biggest difference of

DUout was in the non- vegetation cover with an area of

501.52 km2.

In the same way, Figs. 6 and 7 are used to analyze Rsand Ps. It can be seen from Fig. 7 that in the two periods,

the trends of vegetation cover changes Ps were opposite.

During 19902000, the non-vegetation cover showed a

trend of upward, and the other low, medium and high

vegetation cover showed a fall. On the contrary, during20002006, the non-vegetation cover showed a trend of

fall, while the others were upward. It can be seen

from Fig.6 that during 19902000, the transformation

speed (Rs) of the medium vegetation cover was the fastest,

followed by the high vegetation, while the transformation

speed of the high vegetation cover was the fastest, followed

by the medium vegetation during 20002006. The other

low and non-vegetation cover had no obvious difference in

transformation speed.

Discussions and conclusions

During 19902000, EO the ecosystem had degenerated.

The area of transformation of non-vegetation was higher

than that in 20002006, and its area was increasing,

reflecting an upward trend. At the same time, transfor-

mation of other areas of low, medium and high vegetation

was lower than that in 20002006, and their areas were

decreasing, indicating a trend of fall. In contrast, during

20002006, the ecological restoration in EO was obviously

effective. The area of transformation of non-vegetation

cover was higher than that in 19902000, and its area

reduced, showing a trend of fall. At the same time, the

transformation of the other areas of low, medium and high

vegetation cover was lower than that in 19902000

respectively, and their areas increased, indicating an

upward trend. During the whole study period, consid-

ering many factors which affected the change in the veg-

etation cover in EO, the increase in the average annual

temperature was greater, the change in rainfall was not

obvious or in decreasing trend (Wang and Zhang 2007;

Wang and Meng 2008; Wulan and Dang 2005), the pop-

ulation increment was steady and the livestock had a

slightly decreasing trend (Su et al. 2004,2005). The water

volume from the run-off and the depth of reserved under-

ground water mainly affected the changes in the vegetation

cover of the oasis (Feng et al.2009; Li et al.2004; Su et al.

2004). Before 2000, cultivation of a large number of

farmland and construction of large and medium reservoirs

in the middle and upper reaches of Heihe River led to sharp

reduction in the volume of downstream water and decline

of groundwater levels. Meanwhile, EO was placed in a

kind of passive state. All of these caused deterioration in

the woods, grass and vegetation. The shallow-root plants

Fig. 6 The comparison of Rs of vegetation cover changes in


Fig. 7 The comparison ofPsvegetation cover changes in 19902000

and 20002006 in the Ejina Oasis


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were replaced gradually by xeric and ultra-xeric plant death

(Zhang et al.2003). However, the Chinese government has

taken a mandatory measure to redistribute the water in

Heihe since 2000, which increased the water volume and

groundwater levels in the lower reaches and recovery of

certain populous emphatic, shrubs and desert vegetation.

The ecological environment of the vegetation in EO was

obviously improved (Si et al. 2005). However, the oasisvegetation cover in 2006 was lower than that in 1990,

indicating that there was still a long way to go in terms of

oasis restoration.

Different types of vegetation cover changes were seen

consistently in the two periods. During 19902000, the

most obvious one was the LN type while it was NL

during 20002006. This is mainly because the oasis veg-

etation cover was mainly composed of the low and the non-

vegetation covers during the study periods, which

accounted for more than 97%. During 19902000, the oasis

was in a kind of passive state and the ecosystem had

degenerated, so that the change of the LN type was themost obvious. Since the Heihe River redistribution was

implemented in 2000, the vegetation ecology had begun to

be restored. Therefore, the change of the NL type was the

most visible during 20002006.

During 19902000, the transformation of the medium

vegetation cover was the fastest and was followed by the

high vegetation cover, whereas it was the high and the

medium vegetation during 20002006. It is mainly due to

excessive cultivation of farmlands, excavation, mining and

deforestation by people who were driven by economic

interests during 19902000, which led to a widespread

destruction of grassland and death of shrubs. Improper or

excessive grazing patterns resulted in excessive use of

excellent pasture and serious pasture degradation. During

20002006, some effective measures were taken by the

local government, like fencing, stable breeding, ecological

migrants and retreating farmland to pasture, forests and

grasslands, culture of the artificial repairs to sow saxoal in

stockade area, transplant of liquorices and large-scale

irrigation of natural grassland and etc. All of these mea-

sures have helped the vegetation cover of EO to recover

rapidly (Si et al. 2005).

Acknowledgments This research was supported by the NationalScience Fund for Distinguished Young Scholars of China

(No.40725001) and National Science Fund of China (No.91025024).

The authors are grateful to the anonymous reviewers for their reading

of the manuscript, suggestions and critical comments.

References

Barbosa HA, Huete AR, Baethgen WE (2006) A 20-year study of

NDVI variability over the northeast region of Brazil. J Arid

Environ 37(2):288307

Beurs KM, Henebry GM (2004) Trend analysis of the pathfinder

AVHRR Land (PAL) NDVI data for the deserts of central Asia.

IEEE Geosci Rem Sens Lett 1(4):282286

Cao L, Dou YX, Zhang DY (2003) Effect of climate change on

ecological environment of Heihe field. Arid Meteorol 21(4):

4549 (in Chinese)

Cao WB, Wan L, Zhou X, Hu FS, Chen JS (2004) Effects of variation

in water environment on ecosystem in the lower reaches of the

Heihe Watershed. Hydrogeol Eng Geol 31(5):2125 (in Chinese)

Chen YH, Li XB, Shi PJ (2001) Variation in NDVI driven by climate

factors across China, 19831992. Acta Phytoecologica Sinica

25(6):716720 (in Chinese)

Cihiar J, Laurent ST, Dyer JA (1991) Relation between the NDVI and

ecological variables. Rem Sens Environ 35(3):279298

Eklundh L (1998) Estimating relations between AVHRR NDVI and

rainfall in east Africa at 102 day and monthly time scales. Int J

Remote Sens 19(3):563568

Fang JY, Piao SL, He JS (2003) The vegetation activity enhanced in

the last 20 years in China. Sci China (Series C) 33(6):554565

(in Chinese)

Feng Q, Si JH, Xi HY (2009) Hydrothermal process and ecological

recovery technology of the desert oasis (in Chinese). Science

Press, Beijin

Gong JD, Dong GR, Li S, Gao SY, Xiao HL, Shen JY (1998)

Degeneration of physical environment and its control in EO at

the lower reaches of Heihe River. J Desert Res 18(1):4450

(in Chinese)

Gong DY, Shi PJ, He XZ (2002) Spatial features of the coupling

between spring NDVI and temperature over northern hemi-

sphere. Acta Geographica Sinica 57(5):505514 (in Chinese)

Huang CY (2003) A diagnostic analysis for the impact of climate

change on ecolo-environment and natural vegetation in the

Heihe River Valley. Clim Environ Res 8(1):8490 (in Chinese)

Jia YH, Zhao CY, Nan ZR (2007) Review of study on vegetation

cover change in the lower reaches of Heihe River in Northwest

arid area. Prog Geogr 26(4):6474 (in Chinese)

Jin XM, Hu GC, Li WM (2008) Hysteresis effect of runoff of the

Heihe River on vegetation cover in the Ejian Oasis in

northwestern China. Earth Sci Front 15(4):198203

Keeling CD, Chin JFS, Whorf TP (1996) Increasing activity of

northern vegetation inferred from atmospheric CO2 measure-

ment. Nature 382:146149

Li XZ (1999) Assessment of land use change using GIS: a case study

in the Uanos de Orinoco. Wagemigen University Press,

Netherlands

Li XB, Shi PJ (2000) Sensitivity analysis of variation in NDVI-

temperature and precipitation in typical vegetation types across

China. J Plant Ecol 24(3):379382 (in Chinese)

Li BG, Tao S (2000) Correlation between AVHRR NDVI and climate

factors. Acta Ecologica Sinica 20(5):898902 (in Chinese)

Li XB, Chen YH, Zhang YX (2002) Impact of climate change on

Desert Steppe in northern China. Adv Earth Sci 17(2):254261

(in Chinese)

Li ZJ, Ni H, Tang ML, Zhou AG (2003) Analysis on the correlationbetween distribution of water-salinity-organic material-bearing

in soil and growth of vegetation along the lower reaches area of

Heihe River. Volcanol Miner Resour 24(2):143150 (in Chinese)

Li S, Li F, Sun W, Li BS (2004) Modern desertification process in

Ejina Oasis and its dynamic mechanism. Scientia Geographica

Sinica 24(1):6167 (in Chinese)

Myneni RB, Keeling CD, Tucker CJ, Asrar G, Nemani RR (1997)

Increased plant growth in the northern high latitudes from

19811999. Nature 386:698702

Myneni RB, Tucker CJ, Asrar G, Keeling CD (1998) Interannual

variations in satellite-sensed vegetation index data from 1981 to

1991. J Geophys Res 103(6):61456160


1 3


9/9

Nicholson SE, Farrar TJ (1994) The influence of soil type on the

relationship between NDVI, rainfall and soil moisture in

semiarid Botswana. Rem Sens Environ 50(2):107120

Shi PJ, Gong P, Li XB (2000) Methods and practice in LUCC

Research (in Chinese). Science Press, Beijin

Si JH, Feng Q, Zhang XY, Su YH, Zhang YW (2005) Vegetation

changes in the lower reaches of the Heihe River after its water

import. Acta Botanica Boreali-Occidentalia Sinica 25(4):

631640 (in Chinese)

Su YH, Feng Q, Lv SH, Zhang YW, Si JH (2004) The degradation of

ecological environment in Ejinaqi and its cause analysis. Plateau

Meteorolog 23(2):264270 (in Chinese)

Sun HY, Wang CY, Niu Z, Buhe A, Li B (1998) Analysis of the

vegetation cover change and the relationship between NDVI and

environment factors by using NOAA time series data. J Rem

Sens 2(3):204210 (in Chinese)

Tang HP, Chen YF (2003) Intra-annual variability of NDVI and its

relation to climate in northeast China Transect. Quat Sci

23(3):318325 (in Chinese)

Tucker CJ (1979) Red and photographic infrared linear combinations

for monitoring vegetation. Rem Sens Environ 8(2):127150

Tucker CJ, Nicholson SE (1999) Variations in the Size of the Sahara

Desert from 1980 to 1997. Ambio 28(7):587591

Vicente-Serrano SM, Lasanta T, Alfredo Romo (2005) Analysis of

spatial and temporal evolution of vegetation cover in the Spanish

Central Pyrenees: role of human management. Environ Manag

34(6):802818

Wang GX, Chen GD (1998) Changes of hydrology and ecological

environment during late 50 years in Heihe River Basin. J Desert

Res 18(3):233238 (in Chinese)

Wang J, Meng JJ (2008) Characteristics and tendencies of annual

runoff variations in the Heihe River Basin during the past

60 years. Scientia Geographica Sinica 28(1):8387 (in Chinese)

Wang HQ, Zhang B (2007) The driving force of environmental

change during the last 40 years in the Heihe River Basin. J Arid

Land Resour Environ 21(10):4347 (in Chinese)

Wang GX, Cheng GD, Shen YP (2002) Dynamic tendency of arid

oasis under the influence of water resources decrease: a case

study of Ejina Oasis in Heihe River Basin. Chinese J Appl Ecol

13(5):564568 (in Chinese)

Wu ZY, Wang XP (1980) The vegetation of China (in Chinese).

Science Press, Beijin

Wulan TY, Dang B (2005) Analysis of the climate changes and its

possible infulunce on Ejina banner in recent 50 year. J Inner

Mongolia Normal Univ 34(4):498501 (in Chinese)

Xi HY, Feng Q, Si JH (2007) Influence of water transport project on

groundwater level at lower reaches of the Heihe River. Arid

Land Geograph 30(4):487495 (in Chinese)

Zhang L, Dong ZC, Xu JX (2002) Natural stand and its water

requirement in lower reach of Heihe River. Irrig Drain

21(4):1620 (in Chinese)

Zhang MT, Shi SS, Zhang W, Na YF (2003) Ecological environment

changes and causes analysis in Ejina Oasis. Sci Soil Water

Conserv 1(4):5660 (in Chinese)

Zhang B, Meng B, Hao X, Ding WH (2006a) Heterogeneity of soil

moisture and salt contents and its eco-environmental effects in

oasisdesert belt in arid zone-taking Zhangye Oasis in the

middle reaches of Heihe River as a case study. J Desert Res

26(1):8184 (in Chinese)

Zhang J, Zhang Q, Yang LH, Li DL (2006b) Seasonal characters of

regional vegetation activity in response to climate change in west

China in recent 20 years. J Geograph Sci 16(1):7886

Zhao WZ, Cheng GD (2001) A number of issues about eco-

hydrological processes in arid reviewed. Chin Sci Bull

46(22):18511857 (in Chinese)

Zhong HP, Liu H, Wang Y, Tuo Y, Geng LH, Yan ZJ (2002a) Water

resource and eco-environment protection in Ejian Oasis in

northwest arid region of China. Adv Sci Technol Water Resour

22(4):911 (in Chinese)

Zhong HP, Liu H, Wang YI (2002b) Relationship between Ejina

Oasis and water resources in the lower Heihe River Basin. Adv

Water Sci 13(2):223228 (in Chinese)

Zhou L, Kaufmann RK, Tian Y, Myneni RB, Tucker CJ (2003)

Relation between interannual variations in satellite measures of

northern forest greenness and climate between 1982 and 1999.

J Geophys Res 108(1):10292002


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