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Journal of Geographical Sciences >

2017 , Vol. 27 >Issue 2: 223 - 239

DOI: https://doi.org/10.1007/s11442-017-1373-9

Research Articles

An analysis of oasis evolution based on land use and land cover change: A case study in the Sangong River Basin on the northern slope of the Tianshan Mountains

  • ZHANG Qi , 1, 2 ,
  • LUO Geping , 1 ,
  • LI Longhui 1 ,
  • ZHANG Miao 1, 2 ,
  • LV Nana 1, 3 ,
  • WANG Xinxin 1, 2
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  • 1. State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, CAS, Urumqi 830011, China
  • 2. University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. College of Resources and Environmental Sciences, Xinjiang University, Urumqi 830046, China

Author: Zhang Qi (1991-), specialized in land use and land cover change, remote sensing and GIS application. E-mail:

*Corresponding author: Luo Geping (1968-), PhD and Professor, specialized in the remote sensing of natural resources and the environment, land use and cover change (LUCC) and ecological effects. E-mail:

Received date: 2016-07-08

  Accepted date: 2016-08-06

  Online published: 2017-04-10

Supported by

National Natural Science Foundation of China, No.U1303382

The National Basic Research Program of China, No.2014CB460603

The Project of State Key Laboratory of Desert and Oasis Ecology, No.Y471163

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

This study investigated oasis evolution and the changes of peripheral desert in the Sangong River Basin since the 1950s by rebuilding seven land cover maps derived from black-and-white aerial photographs (1958, 1968, and 1978), a color-infrared aerial photograph (1987), Landsat Thematic Mapper (TM) imagery (1998), Satellite Pour l’Observation de la Terre (SPOT) imagery (2004), and Landsat Operational Land Imager (OLI) imagery (2014). The results showed that: (1) Since 1950, the oasis consecutively expanded more than four times from an alluvial fan to an alluvial plain, causing the shrinkage of desert landscapes that were dominated by a Haloxylon ammodendron Bunge community (HBC) and a Tamarix chinensis Lour community (TLC). Furthermore, the primary (1958-1968) and final (2004- 2014) stages were the most important periods, during which agricultural land experienced the most rapid expansion during the period 1958-1968, and the built-up area showed the most rapid expansion after the 2000s. (2) Two basic management modes, a “local mode” formed by the local governments and a “farm management mode” developed by Xinjiang Production and Construction Corps, together promoted oasis evolution under various land-use and land- cover (LULC) stages. (3) The evolution of the modern oasis during the 1950s-2004 showed the general features of an arid oasis, while during the period of 2004-2014 it was characterized by a large-scale inter-basin water diversion or the import of new water sources. (4) The oasis expanded at the expense of desert vegetation, resulting in distinct variation in the structure of the desert plant community, which will make it more difficult to protect the desert ecosystem.

Key words： oasis evolution; land-use and land-cover change; desert plant community; land management; Sangong River Basin

Cite this article

ZHANG Qi , LUO Geping , LI Longhui , ZHANG Miao , LV Nana , WANG Xinxin . An analysis of oasis evolution based on land use and land cover change: A case study in the Sangong River Basin on the northern slope of the Tianshan Mountains[J]. Journal of Geographical Sciences, 2017 , 27(2) : 223 -239 . DOI: 10.1007/s11442-017-1373-9

1 Introduction

As one of the most important components of global change, land-use and cover change (LUCC) has received worldwide attention (Turner II, 1994; Pascual, 2003; Foley, 2005; Gao, 2015). However, the evaluation of LUCC in arid regions was scarcely quantified before the 1980s due to the unavailability of satellite data (Liu, 2009; Ma, 2013; Yang, 2013; Huang, 2015; Luo, 2015). There were many uncertainties in previous studies caused by the use of low-resolution images, short data series, and scattered historical data, resulting in a lack of knowledge regarding the effects of LUCC on climate change and the carbon/water cycle (Ge, 2008; Ye, 2009; Li, 2010; Liu, 2011).
LUCCs in China, especially in the arid areas of northwest China, including Xinjiang, have been significant since the 1950s. Due to massive exploitation at the watershed level from troops stationed in Xinjiang from the 1950s to the 1960s (Chen, 2008; Chen, 2008; Liu, 2014), land-use and land-cover (LULC) in arid watersheds has changed remarkably, with a transfer from desert to artificial oasis, and a replacement of river runoff by reservoirs and irrigation canals. However, LULC information is scarce, and some is based only on qualitative descriptions, and it is therefore difficult to assess the impact of human activity on the desert ecosystem. The northern slope of the Tianshan Mountains is an area of Xinjiang that has been heavily exploited. Studies of LUCC and its drivers have been conducted based on remote sensing images, mainly after the 1970s (Luo, 2006; Tang, 2006; Luo, 2008). We acquired aerial photographs of the Sangong River Basin for 1958 and 1968, which enabled an LUCC analysis to be conducted. As a typical case study at the watershed scale, the reconstruction of the LUCC process during the 1950s and 1960s enabled an evaluation of oasis evolution in Xinjiang.
The continuous expansion of the oasis occurred through the shrinkage of peripheral desert landscapes or a desert-oasis transition zone that was constantly transferred into artificial oasis. In previous studies, the shrinking of peripheral desert landscapes has been generally described as a change between desert and artificial oasis (agricultural land), with a lack of detailed information about how oasis expansion impacts on desert ecology (Cheng, 2005; Tang et al., 2006), and especially on desert plant communities. Nevertheless, vegetation plays a crucial role in desert landscapes, especially in energy transformation and material circulation. Hence, it is necessary to analyze the variation of vegetation in oasis-desert ecosystems to comprehensively understand the ecological response.
Therefore, this study analyzed oasis evolution based on LUCC, as a case study in the Sangong River Basin. Our major objectives were as follows. (1) To rebuild an LULC dataset from the 1950s based on black-and-white aerial photographs (1958, 1968, and 1978), a color-infrared aerial photograph (1987), Landsat Thematic Mapping (TM) imagery (1998), Satellite Pour l’Observation de la Terre (SPOT) imagery (2004), and Landsat Operational Land Imager (OLI) imagery (2014). (2) To analyze variation in LULC in an oasis and plant communities in a desert based on a statistical model. (3) To reveal the extent of the socioeconomic background and different land management regimes as drivers of change, and conduct a preliminary discussion on the ecological effects of oasis expansion.

2 Materials and methods

2.1 Study area and environmental conditions

The Sangong River drains from the Tianshan Mountains and flows northward into the southern Junggar Basin in Xinjiang (Figure 1). The basin is lower lying in the south than in the north, and is a typical mountain-oasis-desert ecosystem. The study area was the plain in the Sangong River Basin, which consists of two physiographical units: an oasis in the middle and a peripheral desert (Figure 1). The oasis in this study was specified as an artificial oasis, and developed from natural land-cover into a highly artificial ecosystem due to human development and management activities (Chen et al., 2008). The oasis evolution started in 1949, which marked the peaceful liberation of Xinjiang. Due to different modes of zonal management, the study area could be divided into a “farm management mode (FMM)” developed by the Xinjiang Production and Construction Corps (XPCC) and composed of the Fubei and Liuyunhu farms, and a “local mode (LM)” formed by the local governments and composed of Fukang city and bearby towns including Jiuyunjie.
Figure 1 Location of the Sangong River Basin on the northern slope of the Tianshan Mountains

2.2 Data source

Several data sources were used in this study. (1) Black-and-white aerial photographs (1958, 1968, and 1978), a color-infrared aerial photograph (1987), Landsat TM imagery (1998), SPOT5 imagery (2004), and Landsat OLI imagery (2014) that were used to obtain LUCC data (Table 1). (2) High-resolution Google Earth images for 2002, 2006, and 2014 that were used to validate the LULC types. (3) The Annals of Fukang County and the survey data and interviews, which were used by a researcher to verify LUCC. (4) LULC and plant community distribution data obtained by a field investigation in 2014, which determined the LULC in 2014. (5) Documented data that validated LULC in 1978, 1987, and 1998, and desert plant communities in 2004. (6) Topographical maps and a digital elevation model (DEM), to determine the boundary of the study area.
Table 1 Remote sensing images used in the study
Year Data type Image acquisition date Resolution or scale
1958 Black-and-white aerial photographs 1958 1:35,000
1968 Black-and-white aerial photographs 1968 1:35,000
1978 Black-and-white aerial photographs August 1978 1:35,000
1987 Color-infrared aerial photograph June 1987 1:70,000
1998 Landsat TM imagery August 1998 30 m
2004 SPOT5 imagery June 2004 10 m
2014 Landsat OLI imagery August 2014 15 m
Aerial photogrammetry professionals processed two digital orthophoto maps from aerial photographs taken in 1958 and 1968. All remote sensing images were converted into the World-Geodetic-System-84 (WGS-84) geographical coordinate system and Universal Transverse Mercator (UTM) (45°N) projection coordinate system and then geometrically corrected. Aerial photographs taken in 1978 and color infrared photographs taken in 1987 were geometrically corrected based on topographic maps from the 1980s. SPOT5 imagery from 2004 and Landsat OLI imagery from 2014 were geometrically corrected by Google Earth imagery in 2004 and 2014, with the root mean square error (RMSE) within 0.5 pixels. All images were cross corrected to conduct the LUCC analysis.
The LULC classification referred to the national standards of land-use classification (GB/T21010-2007) (MLR, 2007), oasis LULC classifications, and plant community classifications used in previous studies (Luo, 2003; Lv, 2007; Chen, 2008; Luo et al., 2015). Plant communities were named after the dominant species, based on the principles of plant community classification, and their spatial distribution was classified by combining the survey data with remote sensing images. LULC classification was divided into three levels. The first grade contained oasis, desert, and mountain; the second grade included agricultural land, built-up area, water, soil-desert, and sandy-desert; and the third grade was a finer classification of soil-desert and sandy-desert (Table 2). Some linear features, such as rural roads, ditches, and shelterbelts, which could not be classified for technical reasons, were regarded as agricultural land, built-up areas, or other classifications and were not listed separately.
A natural oasis was situated in the alluvial plain before 1949, but did not develop further due to the lack of water facilities. Based on this knowledge, we referred to The Annals of Fukang County and socioeconomic statistics (1949-1992) to roughly determine the scope of the oasis in 1949. In addition, due to the relatively low levels of human activity from 1949 to the 1960s, the LULC in the oasis remained unchanged between 1949 and 1958, with the LULC and plant community distribution of 1949 remaining largely intact.
LULC classification was evaluated by the overall accuracy and Kappa coefficient (Giles, 2002) (Table 3). Overall accuracy represents the degree of consistency in LULC between random samples and the actual land cover type. Kappa coefficients represent the consistency of two images (between classification maps and Google Earth images, field data, or credible classification maps), determined by not only the proportion of correct classifications, but also the errors in classification (Donker, 1993). It is generally accepted that the Kappa coefficient represents the classification accuracy. When the Kappa coefficient is greater than 0.75, it is considered that there is good consistency between two images.
Table 2 Classification of land use and land cover (LULC)
Grade I Grade II Grade III (abbreviation)
Oasis Agricultural land: includes irrigated lands, and other cultivated lands equipped with irrigation facilities
Built-up area: includes cities (Fukang City and the South Junggar oil-based towns), land used for townships and settlements, and industrial and mining land (rural villages, industrial enterprises, mining areas, stone pits, and brickyard fields).
Water: includes reservoirs and ponds.
Desert Soil-desert Haloxylon ammodendron Bunge Community (HBC),
Tamarix chinensis Lour Community (TLC),
Reaumuria songarica (Pall.) Maxim Community (RMC),
Tamarix chinensis Lour - Reaumuria songarica Maxim Community (TL-RMC),
Grass (G)
Sandy-desert Haloxylon ammodendron Bunge Community (HBC),
Reaumuria songarica Maxim Community (RMC)
Mountain Mountain (only low mountains and hills existed in the study area)
LULC in 2014 was assessed using random samples of Google Earth high-resolution satellite images from July 14, 2014 and survey data collected on August 9, 2014. LULC in 2004 was validated by random samples of Google Earth high-resolution satellite imagery data from June 16, 2004, and plant community distribution data (Lv et al., 2007). LULC in 1998, 1987, and 1978 was validated by stratified random sampling with reference to the LULC map of the oasis (agricultural land, built-up, water, etc.) (Luo et al., 2003; Luo et al., 2008), with each layer containing 30 random points (Table 3).
Table 3 Accuracy assessments of classifications of land use and land cover (LULC) in the oasis
Year Method Validation data Overall
accuracy (%)		 Kappa
coefficient
1978 Stratified random sampling LULC in oasis (Luo et al., 2003; Luo et al., 2008) 87.50 0.84
1987 Stratified random sampling LULC in oasis (Luo et al., 2003; Luo et al., 2008) 90.00 0.88
1998 Stratified random sampling LULC in oasis (Luo et al., 2003; Luo et al., 2008) 92.00 0.89
2004 Random sampling Google images with high-resolution and plant community distribution (Lv et al., 2007) 90.67 0.89
2014 Random sampling and field investigation Google images with high-resolution survey data 87.97 0.86
Due to the insufficient amount of data for sampling, the classification accuracy of LULC in 1958 and 1968 could not be verified. However, because the aerial photographs in 1958 and 1968 had a scale of 1:35000, higher than the other images, the LULC accuracy in the oasis would be similar to or even higher than for 1978. There was no obvious variation in desert plant communities, except for the area influenced by human activities. In addition, desert plant communities in 1958 and 1968 were interpreted by the same researchers who participated in the field investigation of vegetation communities; thus, the interpretation accuracy of desert plant communities was similar to that in 2014. Moreover, auxiliary information such as crop area and yield data from The Annals of Fukang County and socioeconomic statistics were used to verify the oasis area in 1950. The classification accuracy in different periods satisfied the requirements of LUCC research (Janssen, 1994).

2.3 Methods

LUCC processes can be described by variations in LULC (Luo et al., 2003; Pontius, 2004; Luo et al., 2008; Feng, 2011), which directly reflect the changing extent of each land type during a given period. Quantitative parameters based on variations in the area of land type include the net change (ΔU), the relative change (ΔS), the status and trend of individual land types (Ps), and the total status and trend of the whole area (Pt) (Table 4).
Table 4 Statistical models for the quantitative analysis of land use and cover change (LUCC)
Parameter Meaning Expression
Individual land types Net change (ΔU) The areal change of a land type over a period △U=(Ub-Ua)/Ua╳100%
Relative change (ΔS) Sum of the loss and gain (i.e., the overall change) of a land type over a period △S=(△Ua-△Ub)/Ua╳100%
Status and trend (Ps) Describes the strength of a contraction or expansion in a land type, and describes whether or not a particular LULC type is in a stable state \(P_S=\frac{\Delta U_{in}-\Delta U_{out}}{\Delta U_{in}+\Delta U_{out}}\)-1≤PS≤1 and △Uin+△Uout≠0
Whole area Total status and trend (Pt) Describes the state of LUCC in the whole study area \(P_t=\frac{\sum^n_{i-1}|\Delta U_{in}-\Delta U_{out}|}{\sum^n_{i-1}\Delta U_{in}+\Delta U_{out}},\)0≤Pt≤1

Notes: Ua represents the area of a LULC type at the beginning of a period; Ub represents the area of a land type at the end of a period; ΔUout (≥0) represents the area of a land type lost or converted to other land types over a period; ΔUin (≥0) denotes the total area gained by or converted from other land types. Ps (> 0) reflects the expansion of a land type, Ps (< 0) reflects the contraction of a land type, and Ps (= 0) indicates that losses and gains for a land type are balanced. Pt is the total status and trend of the whole area. To better determine the influence of LUCC on Pt, it can be divided into four levels: (1) Balanced status (0-0.25), where there is equality between the losses and gains of a particular land type in a given area; (2) Quasi-balanced status (0.25-0.50), where there is a slight inequality between losses and gains; (3) Unbalanced status (0.50-0.75), where there is a significant difference between losses and gains; (4) Extremely unbalanced status (0.75-1), which indicates an extremely significant difference between the losses and the gains.

3 Results and discussion

3.1 The process of oasis evolution based on LUCC

Figure 2 shows the position of the oasis in the Sangong River Basin in eight years (1949, 1958, 1968, 1978, 1987, 1998, 2004, and 2014). Although the scale and status of oasis expansion were significantly different during these periods (Figures 2 and 3, Tables 5 and 6), expansion was the main feature throughout its evolution. Based on the size and status of the oasis, the expansion process could be divided into four stages: (1) expansion along a river (from 1949 to 1968), (2) abandonment (from 1968 to 1978), (3) intensive conversion and extensive expansion (from 1978 to 2004), and (4) urbanization (from 2004 to 2014) (Figure 3).
The oasis in 1950 was located in the alluvial fan and its edge in Sangong River, extending northward to the groundwater overflow zone (Figure 2a), where abundant water resources, a deep soil layer, and fertile soil were present. This location was ideal for the development of traditional agriculture, and therefore the location of the oasis remained relatively stable (Luo et al. 2004). The plain beyond the groundwater overflow zone mainly consisted of desert landscape, which was unused by the local people who were unable to develop an artificial oasis, resulting from constraints in production techniques and water availability before 1950. After the peaceful liberation of Xinjiang in 1949, troops collectively undertook an oasis development project in 1954, forming the XPCC. The XPCC performed the historical mission of “reclaiming land and guarding the border areas”, which led to the large-scale exploitation of land, and began the massive expansion of the oasis. This period was the early stage of the modern oasis evolution (1949-1958), with the main task being the expansion of the old oasis along with a simple diversion of groundwater along the river (Figure 2b). Compared with 1949, the oasis area in the Sangong River Basin had increased by 29.06 km2 (i.e., a 30% increase) by 1958.
Figure 2 The spatial patterns of land-use and land-cover (LULC) in the Sangong River Basin from 1949 to 2014. (HBC, TLC, RMC, and TL-RMC are abbreviations of Haloxylon ammodendron Bunge Community, Tamarix chinensis Lour Community, Reaumuria songarica Maxim Community, and Tamarix chinensis Lour-Reaumuria songarica Maxim Community, respectively.)
From 1958 to 1968, water reservoirs were built in the Sangong River Basin, and a large- scale expansion of the oasis occurred, with a significant transformation from soil-desert to oasis (Figure 2b-c and Figure 3a-b). Fubei and Liuyunhu farms were established by the XPCC in the Sangong River Basin in 1959, and the plain reservoir was built in the groundwater overflow zone for flood storage. This resulted in a massive reclamation in the soil- desert and the establishment of agricultural irrigation and forest protection (Figure 2b-c and Figure 3a-b). At the same time, as water moved from the piedmont and productivity improved, the oasis in the alluvial fan expanded upstream; thus, this period of oasis expansion is also referred to as “tracing and migrating towards the origin”. During this period, the oasis expanded significantly, experiencing its fastest rate of expansion over the whole period of the evolution of the modern oasis. The oasis area increased by 123.48% from 1958 to 1968, and the extent of agricultural land and the built-up area increased by 115% and 502%, respectively, based on the analysis of ΔU and ΔS (Table 6).
During the period of 1968-1978, the LUCC of the oasis in the Sangong River Basin was in a balanced state (Pt = 0.34) with the outward expansion of agricultural land gradually slowing (Figure 2c-d and Figure 3c-d). Compared with the previous period, only 10% of the increased extent of the oasis was influenced by the Cultural Revolution in China. The Cultural Revolution was a special period in Chinese history, during which there was falling productivity and a stagnant economy, resulting in a relatively slower expansion of the oasis. In addition, there had been a massive exploitation of land in the previous period, with a limited awareness of oasis development and poor drainage in the new oasis. This resulted in secondary salinization of the soil and a dereliction of irrigation land in the oasis that was not suitable for cultivation.
From 1978 to 2004, LULC was mutually transformed in the oasis and expanded outward in a relatively unstable state (Figure 2d-g), i.e., from a quasi-balanced to unbalanced state (the oasis Pt values were 0.45, 0.75, and 0.69 in the three periods from 1978 to 1987, 1987 to 1998, and 1998 to 2004, respectively). And unstable state is a normal state in oasis evolution. In total, the extent of agricultural land and the built-up area increased by 120.26 and 37 km2, respectively, during this period. The built-up area was 2.5 times larger than in 1978, with most of the increase occurring from 1987 to 1998. Most of the LUCC occurred through the “household contract responsibility system” after the “reform and opening-up” period.
From 2004 to 2014, many water reservoirs was established (the area was three times larger than before) and the drip irrigation technique became popular, improving agricultural water use efficiency and contributing to a further large-scale expansion of the oasis (Figure 2g-h and Figure 3g-h). Peripheral desert was further developed into agricultural land and the built-up area increased significantly, and thus LUCC was significant and remained in an unbalanced stage during this period. The oasis also experienced a fast rate of urbanization during this period, with the built-up area expanding by 48.38 km2. LUCC in the whole study area was still in an unbalanced state (Pt = 0.83), with a similar extent of change to that in 1958 and 1968. During this period, the LUCC features of the oasis were similar to other oases in which water facilities had been improved (inter-basin water transfer and drip irrigation).
Figure 3 Maps showing the land-use and land-cover change (LUCC) in the Sangong River Basin in the period 1958-2014
Table 5 The areal structure of land-use and land-cover (LULC) in the Sangong River Basin in the period 1958-2014
Year Parameter Oasis Desert
Water Agricultural land Built-up area Total Sandy-desert Soil-desert Total
1958 Area (km2) 0.00 127.50 1.73 129.23 380.46 828.56 1209.02
Proportion of Grade I land 0.00 0.99 0.01 1 0.31 0.69 1
Proportion of study area 0.00 0.08 0.00 0.09 0.25 0.55 0.80
1968 Area (km2) 4.49 273.89 10.42 288.81 376.08 672.67 1048.75
Proportion of Grade I land 0.02 0.95 0.04 1 0.36 0.64 1
Proportion of study area 0.00 0.18 0.01 0.19 0.25 0.45 0.70
1978 Area (km2) 7.09 298.43 15.64 321.16 374.81 646.11 1020.93
Proportion of Grade I land 0.02 0.93 0.05 1 0.37 0.63 1
Proportion of study area 0.00 0.20 0.01 0.21 0.25 0.43 0.68
1987 Area (km2) 6.45 305.81 26.07 338.34 374.11 635.07 1009.18
Proportion of Grade I land 0.02 0.90 0.08 1 0.37 0.63 1
Proportion of study area 0.00 0.20 0.02 0.22 0.25 0.42 0.67
1998 Area (km2) 8.11 356.69 43.45 408.25 373.54 565.83 939.37
Proportion of Grade I land 0.02 0.87 0.24 1 0.40 0.60 1
Proportion of study area 0.01 0.24 0.03 0.27 0.25 0.38 0.62
2004 Area (km2) 10.70 418.68 52.56 481.94 372.39 494.05 866.44
Proportion of Grade I land 0.02 0.87 0.11 1 0.43 0.57 1
Proportion of study area 0.01 0.28 0.03 0.32 0.25 0.33 0.58
2014 Area (km2) 42.95 500.97 100.94 644.86 370.68 333.14 703.82
Proportion of Grade I land 0.07 0.78 0.16 1 0.53 0.47 1
Proportion of study area 0.03 0.33 0.07 0.43 0.25 0.22 0.47
Although there have been significant differences in the speed, size, and status of the various stages of oasis expansion under different socioeconomic conditions, the oasis has clearly expanded over time. The area of oasis in the Sangong River Basin has increased by 544.7 km2, which is 4.44 times larger than in 1949. By considering the uncertainties in the 1949 boundary described in The Annals of Fukang County, historical documents, and LULC types in 1958, the current oasis area was more accurately compared with that of 1958, and was found to have increased 3.99-fold. The primary (1958-1968) and final (2004-2014) stages were the most remarkable periods of oasis expansion, and were the most important stages in the development of the modern oasis. The oasis evolution in the Sangong River Basin during the period 1950-2004 was similar to the oasis development reported in the Manas River and Heihe River basins (Cheng et al., 2005; Liao, 2012), both of which show the general features of oasis evolution in arid areas. During the period 2004-2014, LUCC was the result of large-scale inter-basin water diversion or the development of new water sources.
Table 6 Land-use and cover (LUCC) change in the oasis-desert system of the Sangong River Basin in the period 1958-2014
Period Parameter Oasis Desert Whole area
Agricultural land Built-up area Water Total Soil-desert Sandy-desert Total
1958-1968 ΔU (%) 114.82 501.75 - 123.48 -17.96 -1.15 -12.43
ΔS (%) 134.44 501.75 - 24.62 1.15
Ps 0.85 1 1 -0.83 -1
Pt 0.86 0.84 0.85
1968-1978 ΔU (%) 8.96 50.13 57.9 11.20 -3 0.19 -1.81
ΔS (%) 31.57 53.92 60.42 11.35 1.27
Ps 0.28 0.93 0.96 -0.21 0.15
Pt 0.34 0.52 0.43
1978-1987 ΔU (%) 2.47 66.65 -8.99 5.35 -1.52 0.08 -0.91
ΔS (%) 9.43 76.01 13.12 12.53 1.65
Ps 0.26 0.88 -0.69 -0.01 0.05
Pt 0.45 0.45 0.45
1987-1998 ΔU (%) 16.64 66.67 0.45 20.66 -11.19 0.11 -6.86
ΔS (%) 23.92 68.28 36.08 27.7 0.7
Ps 0.7 0.98 0.71 -0.37 0.16
Pt 0.75 0.59 0.65
1998-2004 ΔU (%) 17.38 20.97 31.87 18.05 -13.13 -0.3 -7.85
ΔS (%) 25.82 22.49 54.65 36.35 0.99
Ps 0.67 0.93 0.58 -0.37 -0.31
Pt 0.69 0.83 0.78
2004-2014 ΔU (%) 19.65 92.03 301.54 33.80 -29.53 -0.85 -16.76
ΔS (%) 26.28 92.45 350.70 37.82 1.90
Ps 0.75 1 0.86 -0.8 -0.45
Pt 0.83 0.79 0.81
1958-2014 ΔU (%) 292.92 5728.99 - 399.00 -57.39 -1.91 -39.14
ΔS (%) 334.45 5728.99 - 71.44 1.99
Ps 0.88 1 1 -0.81 -0.96
Pt 0.91 0.84 0.88

Notes: ΔU: the net change; ΔS: the relative change; Ps: the status and trend of individual land types; Pt: and total status and trend of the whole area

At the regional level, LUCC differed in the two zones of LM (formed by the local governments) and FMM (developed by the XPCC).
During the period of 1958-1968, the oasis area increased 9.48-fold, with the majority of the expansion occurring in the FMM. The area of increase was only 0.46 times in the LM (Table 7). During the “Great Leap Forward” phase of Chinese economic development and the early period of the Cultural Revolution, poor productivity and a lack of understanding of oasis evolution, together with the extensive and rapid land reclamation resulted in ecological degradation. Poor drainage in the new oasis area, a falling underground water level, and soil salinization resulted in the abandonment of the oasis. In the process of developing the new oasis, much of the TL-RMC communities disappeared, and peripheral HBC, RMC, and other natural vegetation was cut for firewood. The vegetation in the area suffered unprecedented levels of damage.
Table 7 Comparisons of land-use and cover change (LUCC) between the farm management mode (FMM) and the local mode (LM) in the oasis in the Sangong River Basin in the period of 1958-2014
Period Parameter FMM LM
Agricultural land Built-up area Total Agricultural land Built-up area Total
1958-1968 ΔU (%) 945.49 - 9.48 42.32 376.33 0.46
ΔS (%) 950.01 - 63.27 376.34
Ps 1.00 1.00 0.67 1.00
Pt 1.00 0.70
1968-1978 ΔU (%) -5.64 0.57 -0.05 18.31 37.12 0.19
ΔS (%) 28.01 99.52 33.99 41.91
Ps -0.20 1.00 0.54 0.89
Pt 0.26 0.56
1978-1987 ΔU (%) 0.35 0.33 0.00 3.56 70.69 0.03
ΔS (%) 6.80 56.87 10.80 83.35
Ps 0.05 0.99 0.33 0.85
Pt 0.30 0.49
1987-1998 ΔU (%) 24.14 0.12 0.24 12.92 78.53 0.13
ΔS (%) 26.18 33.34 22.81 80.53
Ps 0.92 0.98 0.57 0.98
Pt 0.93 0.67
1998-2004 ΔU (%) 28.64 0.13 0.29 11.25 23.32 0.12
ΔS (%) 33.67 11.96 21.55 25.23
Ps 0.85 1.00 0.52 0.92
Pt 0.85 0.58
2004-2014 ΔU (%) 18.18 1.00 0.18 20.58 110.73 0.32
ΔS (%) 18.97 13.03 30.94 111.29
Ps 0.96 1.00 0.67 0.99
Pt 0.96 0.79
1958-2014 ΔU (%) 1768.29 - 17.77 164.15 5072.49 2.00
ΔS (%) 1779.61 111.08 208.33 74.90
Ps 0.99 1.00 0.79 1.00
Pt 0.99 0.84

Notes: ΔU: the net change; ΔS: the relative change; Ps: the status and trend of individual land types; Pt: total status and trend of the whole area

In addition, some of the LUCC in the LM and FMM regions also resulted from the differences in land management, especially after 1978 due to the Chinese reform and opening-up policy. Land-management differences resulted in zonal LUCC discrepancies. During the initial stage of reform and opening-up (from 1978 to 1987), the LM experienced a conversion from a “collective ownership land system” to the “household contract responsibility system”, separating ownership and usage rights of farmers and requiring family units to undertake irrigation. This reformation led to remarkable changes in LULC types in the LM, especially in agricultural land. Nevertheless, agricultural land expanded little (only by 0.35%) in the FMM. During the later stage of reform and opening-up (from 1987 to 2004), the booming productivity resulted in the irrigation of abandoned farmland in the inner oasis area in the FMM. This occurred under a new policy that promoted uniform sowing and fertilizer application, as well as more efficient irrigation methods, which benefited both the economy and the local ecology. LULC conversion inside and outside the oasis was significant in the FMM and was much greater than in the LM during this period (Table 7).
Throughout the entire process of oasis evolution, the different land management regimes in the FMM and LM resulted in increasing discrepancies of LUCC. The land in the FMM was “state-owned”, while it was “collectively-owned” in the LM. The two completely different models of land ownership resulted in significant differences in the land management modes throughout the various historical stages of development, with their different economic systems, causing LUCC to take different forms in the different areas during these periods. For example, after the reform and opening-up period, the LM was uniformly sowed and irrigated by small family units, while the FMM was uniformly sowed and fertilized, with more efficient irrigation methods applied, resulting in differences in land reclamation, fertilization, irrigation management, prevention of soil salinization and desertification, defense against natural disasters, agricultural development, and even socioeconomic benefits. This contributed to huge diversities in LUCC between the LM and FMM during the evolution of the modern oasis (Table 7). The entire process of the evolution of the modern oasis has been promoted by practices in the LM and FMM, together with the various LUCC stages.

3.2 The variation of peripheral desert plant communities during oasis expansion

Consecutive expansion was a characteristic of the oasis evolution, which resulted in deforestation and the destruction of desert vegetation. RMC, TL-RMC, HBC, and other natural plant communities in the area where the oasis developed were degraded or even disappeared, which resulted in a significant variation of the area and structure of plant communities as the oasis expanded (Table 8 and Figure 2).
At the beginning of oasis evolution, the area of soil-desert was larger than the area of sandy-desert. However, as the oasis expanded, the area of soil-desert decreased, becoming smaller than the area of sandy-desert in the final stage of oasis expansion (Table 8). The oasis expansion in the soil-desert was accompanied by a decline in the plant communities in the same areas. The most significant decrease was for HMC, with a reduction in area of 192.06 km2 over the 65-year study period, followed by TLC, with a decrease of 154.47 km2. The area of sandy-desert decreased only by 9.78 km2, and was less influenced by the distance to water than soil-desert. The area of HBC declined only by 7.28 km2. Although much of the HBC in soil-desert was destroyed in the early period of oasis evolution, the native HMC was not visible (Sun, 2010). Only the secondary HMC was apparent, having benefited from protection and enclosure, as well as the increase in precipitation after 1980 (Liu, 2005). The increase in precipitation led to a trend for desert vegetation cover to increase, with the shallow roots of shrubs and herbs being more sensitive to precipitation (Wang, 2011).
Table 8 The land use and cover change (LUCC) in deserts in the Sangong River Basin in the period of 1958- 2014
Year Parameter Soil-desert Sandy-desert Total
TL-RMC RMC TLC HBC G Total RMC HBC Total
1958 S 324.07 221.24 193.78 36.85 52.62 828.56 22.62 357.84 380.46 1209.02
Pct1 0.39 0.27 0.23 0.04 0.06 0.06 0.94
Pct2 0.27 0.18 0.16 0.03 0.04 0.69 0.02 0.30 0.31
1968 S 265.57 196.03 119.79 36.81 54.46 672.67 22.62 353.46 376.08 1048.75
Pct1 0.39 0.29 0.18 0.05 0.08 0.06 0.94
Pct2 0.25 0.19 0.11 0.04 0.05 0.64 0.02 0.34 0.36
1978 S 264.22 170.18 129.21 36.76 45.75 646.11 21.69 353.13 374.81 1020.93
Pct1 0.41 0.26 0.20 0.06 0.07 0.06 0.94
Pct2 0.26 0.17 0.13 0.04 0.04 0.63 0.02 0.35 0.37
1987 S 259.37 174.21 115.62 36.23 49.64 635.07 21.60 352.51 374.11 1009.18
Pct1 0.41 0.27 0.18 0.06 0.08 0.06 0.94
Pct2 0.26 0.17 0.11 0.04 0.05 0.63 0.02 0.35 0.37
1998 S 247.26 157.62 103.07 36.02 21.86 565.83 21.34 352.20 373.54 939.37
Pct1 0.44 0.28 0.18 0.06 0.04 0.06 0.94
Pct2 0.26 0.17 0.11 0.04 0.02 0.60 0.02 0.37 0.40
2004 S 203.86 135.09 97.07 35.05 22.97 494.05 20.60 351.79 372.39 866.44
Pct1 0.41 0.27 0.20 0.07 0.05 0.06 0.94
Pct2 0.24 0.16 0.11 0.04 0.03 0.57 0.02 0.41 0.43
2014 S 132.01 120.57 39.31 35.05 6.20 333.14 20.12 350.56 370.68 703.82
Pct1 0.40 0.36 0.12 0.11 0.02 0.05 0.05
Pct2 0.19 0.17 0.06 0.05 0.01 0.47 0.03 0.50 0.53

Notes: S: area (km2); Pct1: proportion of Grade II land; Pct2: proportion of desert land. (HBC, TCL, RMC, TL-RMC, and G are abbreviations of Haloxylon ammodendron Bunge Community, Tamarix chinensis Lour Community, Reaumuria songarica Maxim Community, Tamarix chinensis Lour - Reaumuria songarica Maxim Community, and Grass, respectively.)

3.3 Analysis of the ecological effects of oasis evolution

There is a lack of inter-basin water transfer, although annual runoff (water) from mountainous area is relatively stable. The more it was consumed in the oasis, the less it was available for desert ecosystems. It is apparent from the oasis evolution in the Sangong River Basin that the continuous expansion of an oasis in an arid area leads to a continuous increase in water demand in the oasis (Yan, 2006). Oasis expansion causes a series of social disputes and ecological problems (such as intensified competition for limited and precious water resources in arid areas, the drying up of rivers, lake shrinkage or disappearance, reduction of biodiversity, desertification, and sandstorms), resulting in the protection of the ecosystem in the oasis periphery becoming more difficult (Saiko, 2000; Liu, 2014). With intensive oasis expansion and urbanization in arid areas, more studies are needed to fully reveal the oasis evolution process, its ecological response mechanism, and its environmental effects, which will then contribute to ecological protection, sustainable development, and socioeconomic stability.
In the later stage of development of the modern oasis, booming productivity resulted in the full utilization of various resources in the surrounding arid area. Some resources have been overexploited. The most notable example is water resources, which is the most fundamental aspect of oasis development. With the establishment of an anti-seepage water conservancy, and the promotion and popularity of advanced drip irrigation under mulch, both the consumption of water resources and water use efficiency in the oasis have been increasing. This has resulted in the reduction of groundwater recharge and lowering of groundwater levels in the desert area (Yan, 2005; Wang, 2015). Faced with the decline of groundwater levels, desert vegetation relying on groundwater can acquire water by increasing root length or depth, by allocating assimilation products to the roots as much as possible. Once the root is unable to obtain the water needed for survival, vegetation will degrade (Zhao, 2006).
In these later stages of oasis development, little irrigation water is available to infiltrate and recharge groundwater, because most of it is consumed by evapotranspiration, following the popularization of drip irrigation technology and improvements in water use efficiency. Thus, salt carried by the irrigation water was readily accumulated in the soil, especially in the root layer, negatively affecting crop yield (Su, 2011; Luo, 2014). Hence, irrigation water not only meets the demand of crop consumption, but also provides water to remove salt from the root layer soil (Sun, 2012; Sun, 2013). Consideration needs to be given to how sufficient water can be provided for this leaching process by making full use of winter fallow water for continuous irrigation. This is necessary for the long-term application of drip irrigation technology, and is also an objective of agricultural irrigation management in an oasis environment (Luo, 2014).

4 Conclusions

This study analyzed the evolution of the oasis in the Sangong River Basin by rebuilding a LUCC process using seven land cover maps derived from black-and-white aerial photographs (1958, 1968, and 1978), a color-infrared aerial photograph (1987), Landsat TM imagery (1998), SPOT imagery (2004), and Landsat OLI imagery (2014). This revealed the characteristics and ecological effects of the evolution of the modern oasis.
(1) During the period studied the oasis expanded overall, but there were significant differences in the speed, size, and status of the oasis expansion in the different stages of development and under different socioeconomic systems. The primary (1958-1968) and final (2004-2014) stages were the fastest and most important periods of oasis evolution. The oasis in the Sangong River Basin during the period of 1950-2004 displayed the general features of most arid oases, while during the period of 2004-2014 the area was characterized by large-scale inter-basin water diversions or new water sources.
(2) Two basic management modes were identified: the LM (formed by the local governments) and the FMM (developed by the XPCC). The formulation and development of these two modes resulted in significantly different land management regimes. The land under the FMM was “state-owned” while it was “collectively-owned” under the LM. Following the reform and opening-up period, the LM was irrigated by family units, while in the FMM there was uniform sowing and fertilizer application, with the use of more efficient irrigation methods, resulting in a diversity in irrigation management. This led to two different kinds of human-driven LUCC in each of the LM and FMM. The evolution of the modern oasis was driven by a combination of the LM and FMM across the whole area.
(3) Over the period studied the oasis expanded at the expense of desert vegetation. Natural communities of HBC and TLC were destroyed and cut down, resulting in a distinct variation in the structure of desert plant communities, which has made it more difficult to protect the ecosystem of the desert-oasis. Furthermore, the expansion of the arid area surrounding the oasis has led to a continuous increase in water consumption, resulting in a series of social disputes, as well as economic and ecological problems.

The authors have declared that no competing interests exist.

References

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Liu J, Jin T, Liu Get al., 2014. Analysis of land use /cover change from 2000 to 2010 and its driving forces in Manas River Basin, Xinjiang.Acta Ecologica Sinica, 34(12): 3211-3223.Based on Landsat TM /ETM( Thematic Mapper / Enhanced Thematic Mapper) image data from 2000 and 2010and some other survey and statistical data,this paper first analyzed the characteristics of land use /cover change in the Manas River Basin of Xinjiang. We used numerical computation methods and index models,including land use /cover structural changes,the single land use /cover dynamic index,the land-use transfer matrix and the land use degree index,to determine the features of land use /cover change both temporally and spatially. Subsequently,the main drivers of land use /cover change and the interaction between different factors were analyzed based on a comprehensive consideration of natural factors and human factors. The findings of this study may be summarized here.( 1) The land use /cover structure of this basin was dominated by unused land in both 2000 and 2010,followed by cultivated land and grassland,and lastly by water( the smallest area). The extent of land use in 2010 increased compared with that in 2000 across the whole basin. Thecultivated land and built-up land increased at an accelerated rate,especially in the middle region,which at the same time resulted in a significant expansion of artificial oasis and led to an evidently decreasing trend of woodland and unused land.In the upper reaches,the most obvious change of land use /cover was the areas of grassland,glaciers and snow-covered land-a clear sign of expansion.( 2) The cultivated land indicated a quite remarkable outward and inward expansion trend.According to our data for the conversion of land use /cover in 2010,the new cultivated land was mainly derived from desert shrubbery land,desert and saline-alkali land. Grassland was mostly concentrated in the upper reaches and experienced an obvious increasing trend second only to cultivated land. The increased area was mainly converted from bare rock on the mountain and piedmont desert. Built-up land also showed a noticeable increase because of the occupation of desert,cultivated land and woodland. According to our data for the change in destination of land use /cover in 2000,the reduced woodland primarily evolved to cultivated land and built-up land in the middle reaches,and to grassland and bare land in the upper reaches. Additionally,the reduced unused land was mainly transformed into artificial oasis land types. A greater proportion of bare land and sand,saline-alkali land and desert was converted into cultivated and built-up land.( 3) The climate of this basin was characterized by a warming and wet trend from 1959 to 2010. Climate change was the dominant factor of land use /cover change in the upper reaches. The increase in precipitation,especially short-term heavy rainfall,might be the primary cause of the advance of glaciers and snow-covered land. In the middle reaches,the most noticeable features were the increase in cultivated and built-up land and the degradation of desert vegetation. It could be speculated that this was mainly attributable to the intensified anthropogenic activities concomitant with economic growth and the increase in population. Moreover,the reduction in gross irrigation water uptake led to an even greater reduction in return water,which led to an even greater reduction in the water needed ecologically and a degradation of natural oasis land. The evident decline in terminal lakes and serious degradation of the associated vegetation in the lower reaches are directly attributable to the combined impact of climate change and human activities.

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[16]
Liu J, Kuang W, Zhang Zet al., 2014. Spatiotemporal characteristics, patterns and causes of land use changes in China since the late 1980s.Acta Geographica Sinica, 69(1): 1-11. (in Chinese)Land-use/land-cover changes (LUCCs) have links to both human and nature interactions. China’s Land-Use/cover Datasets (CLUDs) were updated regularly at 5-year intervals from the late 1980s to 2010, with standard procedures based on Landsat TMETM+ images. A land-use dynamic regionalization method was proposed to analyze major land-use conversions. The spatiotemporal characteristics, differences, and causes of land-use changes at a national scale were then examined. The main findings are summarized as follows.Land-use changes (LUCs) across China indicated a significant variation in spatial and temporal characteristics in the last 20 years (1990–2010). The area of cropland change decreased in the south and increased in the north, but the total area remained almost unchanged. The reclaimed cropland was shifted from the northeast to the northwest. The built-up lands expanded rapidly, were mainly distributed in the east, and gradually spread out to central and western China. Woodland decreased first, and then increased, but desert area was the opposite. Grassland continued decreasing. Different spatial patterns of LUC in China were found between the late 20th century and the early 21st century. The original 13 LUC zones were replaced by 15 units with changes of boundaries in some zones. The main spatial characteristics of these changes included (1) an accelerated expansion of built-up land in the Huang-Huai-Hai region, the southeastern coastal areas, the midstream area of the Yangtze River, and the Sichuan Basin; (2) shifted land reclamation in the north from northeast China and eastern Inner Mongolia to the oasis agricultural areas in northwest China; (3) continuous transformation from rain-fed farmlands in northeast China to paddy fields; and (4) effectiveness of the “Grain for Green” project in the southern agricultural-pastoral ecotones of Inner Mongolia, the Loess Plateau, and southwestern mountainous areas. In the last two decades, although climate change in the north affected the change in cropland, policy regulation and economic driving forces were still the primary causes of LUC across China. During the first decade of the 21st century, the anthropogenic factors that drove variations in land-use patterns have shifted the emphasis from one-way land development to both development and conservation.The “dynamic regionalization method” was used to analyze changes in the spatial patterns of zoning boundaries, the internal characteristics of zones, and the growth and decrease of units. The results revealed “the pattern of the change process,” namely the process of LUC and regional differences in characteristics at different stages. The growth and decrease of zones during this dynamic LUC zoning, variations in unit boundaries, and the characteristics of change intensities between the former and latter decades were examined. The patterns of alternative transformation between the “pattern” and “process” of land use and the causes for changes in different types and different regions of land use were explored.

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[17]
Liu J, Shao Q, Yan X et al., 2011. An overview of the progress and research framework on the effects of land use change upon global climate.Advances in Earth Science, 26(10): 1015-1022. (in Chinese)In this paper,the primary scientific issues about the impacts of land use and land cover change(LUCC) on global climate are analyzed,and its research progress is reviewed.LUCC-climate-ecosystem research system integrated with satellite and field observation is constructed,with the consideration of the intercross,integration and interpenetration among subjects to study the land use change effects on global climate.Furthermore,dynamic patterns and mechanisns of LUCC,research approaches about the mechanisms and effectiveness of LUCC impacts on ecosystem and climate,and then the technical routes for the application of integrated satellite-earth research system to land use change effects on global climate are discussed and analyzed.The following scientific objectives will be realized based on above research approaches and technical routes. ① to further study the basic regulation,driving forces and its climatic/ecological effects of LUCC in three spatial scales: typical regions,key nations and global;② to illustrate the mutual-feedback mechanisms among anthropogenic activities,climate change and LUCC processes,and to reveal the impact mechanisms of large scale LUCC processes on climate and terrestrial ecosystem;③ to construct integrated simulated platform on multiple scale LUCC and its climatic and ecological effectiveness,and to quantitatively simulate the different spatial and temporal scale of LUCC trends and its climatic/ecological effects in different scenarios,then to define the contribution rate of large scale LUCC impacts on climate change in two ways,that is through initiation of the budget change of greenhouse gases and through the change in land surface and atmosphere processes;④ to propose the strategy to responding to the impacts of LUCC on climate and ecosystem in the future,and to supply scientific basis for nations to respond to global change and to achieve sustainable development.

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[18]
Liu X, Yang J, Yang Q, 2005. Analysis on the variations characteristics of air temperature, precipitation in the Sangong River Basin in the past 40 years.Research of Soil and Water Conservation, 12(6): 54-57. (in Chinese)The basic features of annual air temperature,precipitation in the Sangong River basin in the past 40 years are analyzed,the main results are as follows.1.There are linear increase trends in the changes of the temperature and precipitation in Fukang and Tianchi,the climate is changing from warm-dry to warm-wet.2.The average temperature change range of Fukang and Tianchi is maximum in winter and minimum in summer every season;the precipitation is maximum in summer and minimum in winter.And the trend is increasing in temperature and precipitation.3.The temperature rising from the sixties,every decade increasing is more than 0.3鈩;precipitation change is not so obvious as the temperature,but the precipitation is increasing.4.The periods of temperature and precipitation of Fukang respectively have about 5.0 and 3.3 years;the temperature of Tianchi have about 2.7 years main period and 8 years hypo-period,and the precipitation have about 2.9 years main period and 4.4 years hypo-period.

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[19]
Luo G, Amuti T, Zhu Let al., 2015. Dynamics of landscape patterns in an inland river delta of Central Asia based on a cellular automata-Markov model.Regional Environmental Change, 15(2): 277-289.The analysis of landscape pattern changes is of significant importance for understanding spatial ecological dynamics and maintaining sustainable development, especially in wetland ecosystems, which are experiencing indirect human disturbances in arid Central Asia. This study attempted to examine the temporal and spatial dynamics of landscape patterns and to simulate their trends in the Ili River delta of Kazakhstan through quantitative analysis and a cellular automata (CA)-Markov model. This study also sought to examine the effectiveness of using the CA-Markov model for investigating the dynamics of the wetland landscape pattern. The total wetland area, including the river, lake, marsh, and floodplain areas, and the area of sandy land have remained steady, while that of desert grassland has decreased slightly, and shrublands have increased slightly from approximately 1978 to 2007. However, the wetland and shrubland areas exhibited a trend of increasing by 18.6 and 10.3聽%, respectively, from 1990 to 2007, while the desert grassland and sandy land areas presented the opposite trend, decreasing by 30.3 and 24.3聽%, respectively. The landscape patterns predicted for the year 2020 using probabilistic transfer matrixes for 1990鈥2007 (Scenario A) and 1990鈥1998 (Scenario B), respectively, indicated that the predicted landscape for 2020 tends to improve based on Scenario A, but tends to degrade based on Scenario B. However, the overall Kappa coefficient of 0.754 for the 2020 predicted landscapes based on Scenarios A and B indicates that the differences in the predicted landscapes are not distinct. This research indicates that the applied CA-Markov model is effective for the simulation and prediction of spatial patterns in natural or less disturbed landscapes and is valuable for developing land management strategies and reasonably exploiting the wetland resources of the Ili River delta.

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[20]
Luo G, Zhou C, Chen X, 2003. Process of land use/land cover change in the oasis of arid region.Acta Geographica Sinica, 58(1): 63-72. (in Chinese)Using remote sensing imagery data of 1978, 1987 and 1998, and tak in g the typical oasis in alluvial-diluvial fan/alluvial-plain type in Sango ng River basin as the study area, the process and trend of oasis LU CC are analyzed by applying the methods of remote sensing (RS), geograp hic information system (GIS) and statistics. The main results of oasis LUCC in Sangong River basin are as follows. (1) RS and GIS are powerful techniques and m ethods in capturing oasis LUCC data and analyzing its spatial change. ( 2) Establishing mathematical models in the range, speed, regional diffe rences and trend index of LUCC, especially the model of LUCC trend and s tate, the process and trend of oasis LUCC can be deeply studied, including bi-direction process, single-direction process, positive and negative proces s, rising and falling trend, etc. These models are applied to oasis of Sangong River basin and satisfactory effects have been obtained. (3) The LUCC in oasis has had a slow tendency since 1978 and obviously shows tempor al and spatial differences. In the period of 1978-1987, the index of oasis LUCC trend and state was 0.58, which indicates that oasis LUCC presented non-equilibrium state with the transitional process in single direction and evident regional differences: the state of LUCC was qua si-balanced in the upper part of oasis, but non-balanced in the middle a nd lower parts of oasis. In the period of 1987-1998, the index of oasis LUCC trend and state was 0.3, which indicates that the state of oasis LUCC was quasi-balanced with the transitional process in bi-direction and showed the different regional changes compared with the period during 1987-1 998: the state of LUCC was non-balanced in the upper and middle parts of oasis, but balanced in the lower part of oasis. (4) No matter how qua ntitative change or spatial change, the speed of LUCC in the middle pa rt of oasis is the biggest among its parts and more than that of LUCC of ent ire oasis; the next is the lower part and the smallest is the upper part, whose speeds are all less than that of LUCC of entire oasis.

[21]
Luo G, Zhou C, Chen X, 2006. Landscape plaque stability study in the oasis of arid region: A case study of Sangong River watershed.Chinese Science Bulletin, 51(SupplⅠ): 73-80.

[22]
Luo G, Zhou C, Chen Xet al., 2008. A methodology of characterizing status and trend of land changes in oases: A case study of Sangong River watershed, Xinjiang, China.Journal of Environment Management, 88(4): 775-783.Land change is often studied with Markov models to develop a probability transition matrix. The existing methods dependent on such matrixes cannot effectively characterize some important aspects associated with land change such as status, direction, trend and regional variations. This study presents mathematical models to quantify these elements, defining unbalanced, quasi-balanced and balanced status, one- and two-way transitions and the rising or falling trends. Using these models and remote-sensing imageries, the landscape was studied for a case area, the oasis of Sangong River in Xinjiang, Northwest China where typical arid conditions prevail. Land expansion and contraction among various land types and for the entire oasis were analyzed for the periods of 1978–1987, 1978–1998 and 1987–1998. The changes were closely related to a strong economic growth after the land-reform campaign and adoption of the market economy in China in the 1980s to early 1990s, a process not strictly Markovian that requires stationarity and randomness. Information on land-change status and trend is important for a better understanding of the underlying driving processes but also for land-use planning and decision-making.

DOI PMID

[23]
Luo Y, 2014. Long term effects of drip irrigation on soil salinization in arid area oasis.Science China: Earth Science, 44(8): 1679-1688. (in Chinese)

[24]
Lv G, Du X, Yang Jet al., 2007. Community stability of deserts vegetation at Fukang oasis-desert ecotone.Arid Land Geography, 30(5): 660-665. (in Chinese)The deserts vegetation at Fukang oasis-desert ecotone is studied in this paper.Based on the vegetation survey data for the sampling field, the method of stability measurement,which was discovered and applied to the ecology study in the industry manufacture by French ecologist M.Godron,is modified and introduced to study the spatial stability of community of vegetation.The result shows that the community is more stable when the percentage accumulation and accumulated relative cover degree trend to 20/80,which is the stability ratio of community.The result verified that the stability of different plant community is different in different deserts vegetation of oasis-desert ecotone from the space.The community stability of deserts vegetation of plant at Fukang oasis-desert ecotone is influeced by interspecific competition,environment pressure and disturbances,even the community stability with the same edificators appear bigger difference.

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[25]
Ma C, Ren Z, Li X, 2013. Land use change flow and its spatial agglomeration in the loess platform region.Acta Geographica Sinica, 68(2): 257-267. (in Chinese)The conception of land use change flow was put forward in this paper, and the dynamics of land use change in the loess platform region was analyzed with the models of land use change. In addition, the spatial agglomeration of land change flow was studied. The results are obtained as follows. The proportion of cultivated land is predominant in the study area, however, that of unused land is very low, which means that reserved cultivated land resource is scarce. The proportions of forest land, grassland and waters are low, indicating that the ecosystem is at risk. The land use change flows relationships of cultivated land and built-up land, cultivated land and grassland, cultivated land and forest land played key roles in the land use change of the loess platform region. The flow of cultivated land to built-up land was the main reason for the loss of cultivated land resources, and the flow of grassland to cultivated land was the main complement source of cultivated land. The land use change flow of cultivated land to built-up land was 26668.80 ha from 1985 to 2010, accounting for 40.75% of the total. The flow of grassland to cultivated land was 18923.90 ha, accounting for 28.91% of the total. The disturbed degree from high to low is water ecosystem, forest ecosystem, and grass ecosystem. Land system was relatively stable from 1985 to 1990, yet it changed significantly from 1990 to 2000. The spatial features of land use were different at different scales. The land use change rate around cities was higher than that of other regions at a 25-year scale, however, the region with a high land change rate changed from the central part of loess platform region to the marginal zone at a 5-year scale.

DOI

[26]
Ministry of Land and Resources of the People’s Republic of China (MLR, PRC). GB/T21010-2007 Classification of Land Use Status.(in Chinese)

[27]
Pascual J I, Lorente N, Song Zet al., 2003. Selectivity in vibrationally mediated single-molecule chemistry.Nature, 423(6939): 525-528.Abstract The selective excitation of molecular vibrations provides a means to directly influence the speed and outcome of chemical reactions. Such mode-selective chemistry has traditionally used laser pulses to prepare reactants in specific vibrational states to enhance reactivity or modify the distribution of product species. Inelastic tunnelling electrons may also excite molecular vibrations and have been used to that effect on adsorbed molecules, to cleave individual chemical bonds and induce molecular motion or dissociation. Here we demonstrate that inelastic tunnelling electrons can be tuned to induce selectively either the translation or desorption of individual ammonia molecules on a Cu(100) surface. We are able to select a particular reaction pathway by adjusting the electronic tunnelling current and energy during the reaction induction such that we activate either the stretching vibration of ammonia or the inversion of its pyramidal structure. Our results illustrate the ability of the scanning tunnelling microscope to probe single-molecule events in the limit of very low yield and very low power irradiation, which should allow the investigation of reaction pathways not readily amenable to study by more conventional approaches.

DOI PMID

[28]
Pontius R G, Shusas E, McEachern M, 2004. Detecting important categorical land changes while accounting for persistence.Agriculture, Ecosystems and Environment, 101(2/3): 251-268.The cross-tabulation matrix is a fundamental starting point in the analysis of land change, but many scientists fail to analyze the matrix according to its various components and thus fail to gain as much insight as possible concerning the potential processes that determine a pattern of land change. This paper examines the cross-tabulation matrix to assess the total change of land categories according to two pairs of components: net change and swap, as well as gross gains and gross losses. Analysis of these components can distinguish between a clearly systematic landscape transition and a seemingly random landscape transition. Multiple resolution analysis provides additional information concerning the distances over which land change occurs. An example of change among four land categories in central Massachusetts illustrates the methods. These methods enable scientists to focus on the strongest signals of systematic landscape transitions, which is necessary ultimately to link pattern to process.

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[29]
Saiko T A, Zonn I S, 2000. Irrigation expansion and dynamics of desertification in the circum-Aral region of Central Asia.Applied Geography, 20(4): 349-367.The aim of this paper is to examine the causes and dynamics of desertification in one of the world's worst disaster areas, the Aral Sea region. During the 1960s, a large-scale irrigation campaign aimed at achieving independence in cotton production was launched in Soviet Central Asia. From 1960, ever-increasing water withdrawal from the two inflowing rivers—the Amudarya and Syrdarya—has resulted in the dramatic decline of the level, area and volume of the sea. Desiccation was accompanied by the development and further acceleration of various desertification processes. The study reveals that, for different reasons, the predominant direction and trends of desertification have been changing during each of the four identified periods from 1961 to 1995. The main desertification processes recorded in the Circum-Aral region (‘Priaraliye’ in Russian) were a decline in the groundwater level, increased mineralization and chemical pollution of watercourses, soil salinization, the spread of xerophytic and halophytic vegetation, and deflation and aeolian accumulation, with the development of salt storms. Recent improvements in the situation are also discussed, along with their causes. Zonation of Priaraliye is carried out and an outlook for the future is given.

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[30]
Su L, Abudu S, Hudan Tet al., 2011. Effects of under-mulch drip irrigation on soil salinity distribution and cotton yield in an arid region.Acta Pedologica Sinica, 48(4): 708-714. (in Chinese)Soil salinization has become more and more severe in arid regions. Make an appropriate irrigation regimes to leaching soil salinity is a key scientific issue under drip irrigation in the silt loam soil in arid region. A 3-year field experiment was carried out to investigate the effects of different drip irrigation regimes on soil salinity distribution and cotton yield at Akesu agricultural ecosystem national scientific research station, Chinese Academy of Sciences. Throughout cotton growing season, the peak cure of soil salt under mulch moved downward with the increases of DIA (drip irrigation amount). The quantity of drip irrigation increased from 3 000 mhmto 4 800 mhm, peak value of soil salt moved downward from 35cm to 65cm. The results showed that the peak cure of soil salt under mulch decreased in the order 1.6 DIA>1.4 DIA>1.2 DIA>DIA after irrigation. At the same time, the peak cure of soil salt under mulch also moved downward with the increases of drip irrigation discharge rates for all treatments except 3.2 L htreatments because of the capability of infiltration of porosity of soil less than the drip irrigation discharge rate. The peak cure of soil salt under mulch decreased in the order 2.6 L h>2.2 L h>1.8 L h>3.2 L hafter irrigation. The soil salinity moved gradually from deep soil to surface soil and moved slowly from under mulch to inter-mulch simultaneously with elapse time. With the increasing of quantity of drip irrigation or drip irrigation discharge rates, seed yield presenting increased except 1.6 DIA and 3.2 L htreatment. Both water deficit and heavy irrigation will decrease the cotton yield, as well as the high and law drip irrigation discharge rate. Therefore, quantity of drip irrigation of 1.4 DIA and appropriate drip irrigation discharge rate of 2.6 L hwas the best drip irrigation regimes for the higher cotton yield in the silt loam soil in arid region.

[31]
Sun L, Luo Y, 2013. Study on the evolution trends of soil salinity in cotton field under long-term drip irrigation.Research of Soil and Water Conservation, 20(1): 186-192. (in Chinese)Drip Irrigation under film is a prevailing irrigation method in arid area of northwest China due to its outstanding efficiency of water saving and production increases.However,issue on rise of salt accumulation in crop field under long-term drip irrigation should been dealt with as soon as possible.In this paper,the Hydrus 2D model was calibrated and validated by using the observed data of dynamics progress of soil salt obtained from field experiment which was conducted in Manasi river irrigation district,Xinjiang Uygur Autonomous Region.The result showed that Hydrus 2D model was a useful tool to simulate soil salt distribution and accumulation under drip irrigation.Then soil salt accumulation in different quota brackish water under long-term drip irrigation was simulated and analyzed.We found that soil salt increased with the irrigating years,but it finally reached a stable equilibrium for its increasing speed got slower which was chiefly due to salt leaching increase while transpiration was suppressed by increased soil salt.The equilibrium times were 10,15,20 and 35 years,respectively,while then contents of irrigated water salinity were 4.8,3.2,1.6 and 0.8 g/L and with irrigation water rate of 420 mm,contents of soil salt at root zone were 4.8,3.2,1.6,0.8 mg/cm3,respectively,and corresponding guarantee rate of transpiration requirement were 72%,80%,85% and 91%,respectively.In order to maintain soil salt below the tolerance of crop,contents of irrigated water salinity were 4.8,3.2,1.6 and 0.8 g/L,rates of irrigation water should be more than 495,470,425 and 395 mm,respectively.

[32]
Sun L, Luo Y, Yang C Jet al., 2012. Salt Distribution and accumlation in soils different in rate of under-mulch drip irrigation with brackish water.Acta Pedologica Sinica, 49(3): 428-436. (in Chinese)Under-mulch drip irrigation is an important irrigation method in irrigation agriculture of Xinjiang.However,soil salt accumulation induced by its slow deep leaching and brackish irrigation water is an urgent problem in development of sustainable agriculture. To explore characteristics of the salt distribution and accumulation in soils as affected by rate of under-mulch drip irrigation with brackish water,a field experiment was carried out in the Water-saving Irrigation Experiment Station of the Shihezi University.The experiment was designed to have three irrigation rate treatments,Treatment Q36: 3 150 m3 hm-2,Q48: 4 200 m3 hm-2 and Q60: 5 250 m3 hm-2,and used water 3.32 g L-1 in salinity.Analysis of soil samples taken before and after the irrigation indicated that the soil salinity in the root area demonstrated a basical declining trend at the forming stage of a wetted soil volume,and accumulation at the redistribution phase of soil water,while that in the soil under the root displayed an opposite way,rising in the former phase and falling in the latter.Analysis of salt distribution and balance in the soil profiles after harvest show that in Treatments Q36 and Q48,the input of salt with the irrigation stayed mainly in the 0~120 cm soil layer column,while in Treatment Q60,soil salinity increased significantly in the soil below 120 cm.Irrigation contributed about 21 percent of the increase.It was found that after 36 hours of irrigation,the wet front got into 80,90 and 120 cm deep in Treatments Q36,Q48 and Q60,respectively.The water from the dripper infiltrated deep into the soil,bringing down salt into deep layers of the soil profile,which contributes positively to mitigating the problem of salt accumulation in the surface soil.

[33]
Sun P, Zhou H, Li Yet al., 2010. Trunk sap flow and water consumption of Haloxylon ammodedron growing in the Gurbantunggut Desert.Acta Ecologica Sinica, 30(24): 6901-6909. (in Chinese)Haloxylon ammodendron distributes widely in the west arid region of China.Studying its water consumption will be beneficial to quantifying ecological water requirement and re-vegetating the desertification region.In the current study,the heat pulse technique was applied to study the trunk sap flow of Haloxylon ammodendron in the Gurbantunggut Desert during the whole growing season.The results showed that the diurnal variation of sap flow of Haloxylon ammodendron was affected multiply by soil moisture,meteorological factors and plant physiological characters.However,the dominant factors that determined the variation of the trunk sap flow of Haloxylon ammodendron were different under different soil water conditions.When the Volumetric Soil Water Content(胃v) in the root zone was from 8.7% to 12.1%,the daily trunk sap flow of Haloxylon ammodendron had a very good correlation with soil water content.When the 胃v in the root zone was more than 12.1%,the diurnal variation of sap flow of Haloxylon ammodendron was mostly affected by meteorological factors.When 胃v was less than 8.7%,there was mostly affected for the daytime and nighttime sap flow.Under such conditions,there was no correlation between the sap flow and meteorological factors,and it was mostly determined by plant physiological characters.In April,the soil water content in the root zone was the most abundance for the whole year.The curve of the sap flow variability in daytime is a bimodal type and the accumulative process curve is "S" type.The sap flow during daytime was significantly higher than nighttime.The average diurnal trunk sap flow of Haloxylon ammodendron in April is about two times as much as it in other months.After May,with the soil water content decreases,there are no obvious difference in sap flow between daytime and nighttime,and the accumulative process curve is a linear type.The sap flux of Haloxylon ammodendron varied from 0.156L路cm-2路d-1 for the plant growing in the native Gurbantunggut Desert to 0.876 L路cm-2路d-1 for the plant growing under drip irrigated plantation in the Taklimakan Desert.However,all of the Haloxylon ammodendron plants were in the normal growth conditions,it means that the range of ecological water requirement of Haloxylon ammodendron is very wide.Comparing with other research result,the sap flux of Haloxylon ammodendron growing in the native Gurbantunggut Desert is lowest.The water consumption of Haloxylon ammodendron with trunk diameters of 7.8cm and 9.0cm was respectively 95mm and 117mm from April to September.In addition,the shapes of the diurnal curves of sap flow for Haloxylon ammodendron are similar among plants of different trunk diameters.The bigger diameter size means more water consumption.The low water consumption of Haloxylon ammodendron is very important for the region of desertification with annual mean precipitation at about 150mm,like Junggar Basin.As a result,it is possible to re-vegetate the region without irrigation.With Haloxylon ammodendron as a candidate plant for re-vegetating the region,the contradiction of water demand between the economic development and ecological restoration can be partially solved.

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[34]
Tang F, Chen X, Luo Get al., 2006. Two typical LUCC process and driving force analysis in the oasis of arid region: A case study of Sangong River watershed in north Tianshan Mountain.Science China: Earth Science, 36(Suppl. II): 58-67. (in Chinese)

[35]
Turner II B, 1994. Local faces, global flows: The role of land use and land cover in global environmental change.Land Degradation and Rehabilitation, 5(2): 71-78.The emergence of land-use and land-cover change (LUCC) as one of the major themes within the global environmental change research community poses a series of difficult but not insurmountable problems. LUCC takes place incrementally through the operation of sets of human and biophysical forces largely specific to the locale in question, but cumulatively LUCC contributes significantly to global environmental change. Linking LUCC to global change requires the cooperation of the natural and social sciences to bridge the local to global dynamics involved. The International Geosphere-Biosphere Programme and the Human Dimensions of Global Environmental Change Programme are undertaking the development of an international research project with such aims in mind. This project seeks to improve understanding of LUCC dynamics by balancing the need for a nuanced understanding at the local level with the need from improved regional and global LUCC models. The rudiments of this effort and some of problems confronting it are outlined here.

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[36]
Wang J, Bai J, Luo Get al., 2015. Growth and water consumption characteristics of cotton in Manas Basin during recent 34 years.Transactions of the Chinese Society for Agricultural Machinery, 46(8): 83-89. (in Chinese)Abstract Xinjiang is one of the three major cotton-producing areas in China, and provided 45% of the nation's production. Due to the intensive agricultural management, the cotton planting in Xinjiang go through three cropping periods in 1980-2013. The three cropping periods are as following: period of furrow irrigation with non-mulching (NF period, 1980-1993), period of furrow irrigation with mulching (MF period, 1994-2004) and period of drip irrigation with mulching (MD period, 2005-2013). Under the condition of sufficient irrigation, the seed yield of cotton was closely influenced by air temperature, and the evapotranspiration was more related to irrigation water amount. The seed yield reached the maximum value of 4 493.3 kg/hm2 in MD period, while ET had the peak value of 714 mm in NF period. In the recent 34 years, the seed yield and evapotranspiration of cotton were generally increased. The annual increasing rate of seed yield (83.97 kg/hm2) was greater than that of evapotranspiration (5.46 mm). Thus water use efficiency (WUE) and irrigation water use efficiency (IWUE) of cotton were also increased. WUE and IWUE reached the peak value of (0.7卤0.1) kg/m3 and (1.0卤0.3) kg/m3, respectively, which were close to the levels in humid regions. 漏, 2015, Chinese Society of Agricultural Machinery. All right reserved.

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[37]
Wang Z, Shi Q, Wang Tet al., 2011. Spatial-temporal characteristics of vegetation cover change in mountain- oasis-desert system of Xinjiang from 1982 to 2006.Journal of Natural Resources, 26(4): 609-618. (in Chinese)Dynamics of vegetation cover plays an important role in the coexistence and balance evolution mechanism of mountain-oasis-desert system(MODS) in Xinjiang.Based on the satellite-derived NDVI data,produced by GIMMS(Global Inventory Monitoring and Modeling Studies) group,derived from the NOAA/AVHRR(National Oceanic and Atmospheric Administration/the Advanced Very High Resolution Radiometer) land dataset,the fractional vegetation cover(fvc) was calculated at a spatial resolution of 8 km脳8 km and at a 15-day interval,for the period January 1982 to December 2006 and then the annual maximum fvc was obtained by the maximum value composites(MVC) method.Under the basic pattern of MODS in Xinjiang,the fvc spatial-temporal dynamics characteristics of trends,rate,amplitude,and variability of 25 years in Xinjiang were analyzed by dividing the whole region into four subregions in terms of regional differentiation,and mountain,oasis,desert system in every subregion by altitude and landuse.The results showed that the fvc dynamics increased significantly in general,but fluctuated remarkably in the period from 1982 to 1995 and relatively stable from 1996 to 2006,varied significantly with different subregions,and subsystems of mountain,oasis and desert,in which the vegetation cover of oasis increased mostly rapidly,but desert decreased most obviously.On the amplitude and variability,the eastern and southern subregions exceed the northern and Yili subregions,desertmountainoasis,and the lower fvc is larger than the higher fvc.The significant improved subregions are located in oasis,its surrounding areas and part of mountains,but the degenerated subregions are mostly situated in desert of eastern and southern Xinjiang.There are different change characteristics in different fvc subregions,that is,the vegetation degenerated in lower fvc subregions and improved in higher fvc subregions.

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[38]
Yan J, Chen X, Luo Get al., 2005. Response of the changes of shallow groundwater level and quality to LUCC driven by artificial factors: A case study in Sangong River Watershed in Xinjiang.Journal of Natural Resources, 20(2): 172-180. (in Chinese)以新疆三工河流域绿洲为例，应用遥感、地理信息系统、空间插值和统计分析的方法，初步分析干旱区绿洲土地利用／土地覆被变化对绿洲浅层地下水位水质变化的影响。研究数据包括1978、1987和1998年三期遥感数据和近25年8口常年观测井水位数据及。1987和1998年两期20口观测井水质数据。结果表明，绿洲随着城市、工矿用地为主的非农业用地和以耕地为主的农业用地的持续增加，浅层地下水水位与水质发生了显性的时空变化。冲洪积扇绿洲主要城镇聚居区地下水位以年均45cm的速率下降，冲积平原下部绿洲地下水位以年均7cm的速率呈现缓慢的上升趋势；绿洲地下水水质趋于恶化，矿化度总体呈现上升的态势，且冲积平原绿洲地下水矿化度上升的幅度普遍大于冲洪积扇绿洲，这与地形、水地质条件、土地资源开发、灌排强度、地表蒸发、化学肥料和农药的使用密切相关。

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[39]
Yan J, Chen X, Luo Get al., 2006. Ground water level temporal and spatial variation in response t o the change of land cover in arid oasis region.Chinese Science Bulletin, 51(Suppl I): 42-48. (in Chinese)

[40]
Yang Y, Zheng D, Zhang Xet al., 2013. The spatial coupling of land use changes and its environmental effects on Hotan oasis during 1980-2010.Acta Geographica Sinica, 68(6): 813-824. (in Chinese)Under the background of climate warming, implementation of China's Western Development Policy, and aids from 19 provinces and municipalities for economic development in Xinjiang since 2009, Hotan oasis has faced great challenges for demands of water and land resources. The visual interpretation method was used to process TM/ETM+ image on some field surveys in this region. Then the land use changes in Hotan oasis and their environmental effects were analyzed by using spatial coupling. Some conclusions can be drawn as follows. (1) There have been some obvious spatiotemporal changes in the land-use structure of Hotan oasis. The areas of cultivated land and urban-rural-land increased by 32.32% and 142.27%, respectively; while those of bushland and desert grassland reduced by 23.12% and 18.82%, respectively. The former came mainly from the grassland and forest and unused-land reclaimed during the period of 1980-2010. Because of the expansion of cultivated-land towards the northwest, the gravity center of cultivated-land shifted 4.96 km with a direction against the prevailing wind. (2) The spatial coupling, which is linked by water consumption, exists between middle and lower reaches, which show a rise and a fall of the integrated index, information entropy and balanced degree, as well as the oasis areas. For the excessive water consumption in middle reaches, there is less and less water in lower reaches, resulting in serious land degradation. (3) Expansion of cultivated land in oasis exploitation increased the comprehensive level of land use; while the information entropy also increased, which severely damaged the vegetation in transitional zone, resulting in ecosystem instability, then posed a threat to the ecological security of Tarim River. It is suggested that the agricultural restructuring should be carried out. To be specific, sown area of the high water consumption crops should be reduced. At the same time, the laws and regulations on water resource distribution in Tarim River Basin should be implemented to ensure water resource balance, eco-water resource increase, as well as to prohibit expansion of cultivated land and over-exploitation of groundwater.

[41]
Ye Y, Fang X, Ren Yet al., 2009. Cropland cover change in Northeast China during the past 300 years.Science China: Earth Science, 39(3): 340-350. (in Chinese)Land use/cover change induced by human activities has emerged as a “global” phenomenon with Earth system consequences. Northeast China is an area where the largest land cultivation activities by migrants have happened in China during the past 300 years. In this paper, methods including documentary data calibration and multi-sourced data conversion model are used to reconstruct historical cropland cover change in Northeast China during the past 300 years. It is concluded that human beings have remarkably changed the natural landscape of the region by land cultivation in the past 300 years. Cropland area has increased almost exponentially during the past 300 years, especially during the past 100 years when the ratio of cropland cover changed from 10% to 20%. Until the middle of the 19th century, the agricultural area was still mainly restricted in Liaoning Province. From the late 19th century to the early 20th century, dramatic changes took place when the northern boundary of cultivation had extended to the middle of Heilongjiang Province. During the 20th century, three agricultural regions with high ratio of cropland cover were formed after the two phases of spatial expansion of cropland area in 1900s–1930s and 1950s–1980s. Since 1930s–1940s, the expansion of new cultivated area have invaded the forest lands especially in Jilin and Heilongjiang Provinces.

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[42]
Zhao W, Liu H, 2006. Recent advances in desert vegetation response to groundwater table changes.Acta Ecologica Sinica, 26(8): 2702-2708. (in Chinese)The aim of this paper is to review studies to evaluate how desert vegetation (including xerophytes growing in dry habitats and mesophytes constituting desert riparian forest) response to groundwater table changes at different scales (i.e. individual scale, population scale, community scale and patch scale). Results collected in this study show that desert vegetation response to groundwater table changes in a significant nonlinear way as a result of plant adaptation to the environmental factors such as climate, soil, and groundwater. Based on the review, it is pointed out that: soil heterogeneity and plant plasticity on the basis of the balance between groundwater and plant, and the combination of long-term monitoring with controlled experiments should be taken into consideration in the future researches; applications of isotopic trace technology and Hyperspectral-Remote-sensing technology should be enhanced to promote related researches in the future; plant hydraulic lift at the individual, community and ecosystem level, phenotypic plasticity and adaptive value of plant responding to the changing water quality as well as to the groundwater table fluctuations deserve more scientific attention; the responses of desert vegetation to groundwater table at microcosmic scale (molecule scale) and mechanisms provoking this kind of responses should be further studied; and integrated research at landscape scale and ecosystem scale, which served to provide basis for inland river basin management, also should be furthered.

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