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Journal of Geographical Sciences >

2019 , Vol. 29 >Issue 2: 180 - 196

DOI: https://doi.org/10.1007/s11442-019-1591-4

Research Articles

Spatio-temporal distribution and transformation of cropland in geomorphologic regions of China during 1990-2015

  • GAO Xiaoyu , 1, 2 ,
  • CHENG Weiming , 1, 2, 3 ,
  • WANG Nan 1, 2 ,
  • LIU Qiangyi 1, 2 ,
  • MA Ting 1 ,
  • CHEN Yinjun 4 ,
  • ZHOU Chenghu 1
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  • 1. State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • 2. University of Chinese Academy of Sciences, Beijing 100049, China
  • 3. Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China
  • 4. Institute of Agricultural Resources and Regional Planning of CAAS, Beijing 100081, China
* Corresponding author: Cheng Weiming (1973-), PhD and Professor, specialized in digital geomorphology and GIS. E-mail:

Author: Gao Xiaoyu (1994-), Master, specialized in cropland use and agricultural resources management. E-mail:

Received date: 2018-09-06

  Accepted date: 2018-11-07

  Online published: 2019-02-25

Supported by

National Natural Science Foundation of China, No.41421001, No.41590845, No.41571388

National Key Basic Research Program, No.2015CB954101

Copyright

Journal of Geographical Sciences, All Rights Reserved
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Abstract

Landforms are an important factor determining the spatial pattern of cropland through allocation of surface water and heat. Therefore, it is of great importance to study the change in cropland distribution from the perspective of geomorphologic divisions. Based on China’s multi-year land cover data (1990, 1995, 2000, 2005, 2010 and 2015) and geomorphologic regionalization data, we analyzed the change in cropland area and its distribution pattern in six geomorphologic regions of China over the period of 1990-2015 with the aid of GIS techniques. Our results showed that the total cropland area increased from 177.1 to 178.5 million ha with an average increase rate of 0.03%. Cropland area decreased in southern China and increased in northern China. Region I (Eastern hilly plains) had the highest cropland increase rate, while the cropland dynamic degree of Region IV (Northwestern middle and high mountains, basins and plateaus) was significantly higher than that of other regions. The barycenter of China’s cropland shifted from northern China to the northwest over the 25-year period. Regions IV and I were the two regions with the greatest increase of cropland. Region II (Southeastern low and middle mountains) and Region V (Southwestern middle and low mountains, plateaus and basins) were the main decreasing cropland regions. The area of cropland remained almost unchanged in Region III (Northern China and Inner Mongolia eastern-central mountains and plateaus) and Region VI (Tibetan Plateau). The loss of cropland occurred mostly in Regions I and II as a result of growing industrialization and urbanization, while the increase of cropland occurred mainly in Region IV because of reclamation of grassland and other wasteland. These analyzing results would provide fundamental information for further studies of urban planning, ecosystem management, and natural resources conservation in China.

Key words： spatio-temporal distribution; transformation of cropland; geomorphologic regions; China

Cite this article

GAO Xiaoyu , CHENG Weiming , WANG Nan , LIU Qiangyi , MA Ting , CHEN Yinjun , ZHOU Chenghu . Spatio-temporal distribution and transformation of cropland in geomorphologic regions of China during 1990-2015[J]. Journal of Geographical Sciences, 2019 , 29(2) : 180 -196 . DOI: 10.1007/s11442-019-1591-4

1 Introduction

Land use and land cover change (LUCC) is an essential part of global environment changes and plays an important role in maintaining the structure and production of ecosystems (Restrepo et al., 2017). LUCC can influence material circulation and organism processes in the terrestrial system over time and space, including water circulation, greenhouse gas emissions, resources sustainable utilization and biodiversity (Hao and Ren, 2009; Liu et al., 2014; Tian et al., 2015). Moreover, LUCC is influenced by factors such as the global economy, national policies and climate change. Since 1995, the International Geosphere and Biosphere Program (IGBP) and International Human Dimensions Program (IHDP) have developed and implemented the Land Use and Cover Change Science Research Program taking land use/cover as the core content in the research of global change. The Global Land Project (GLP) commenced in 2005 and emphasized not only the integration and simulation of the coupled human-environment system but also the effect of different management practices and policy decisions on LUCC (Turner et al., 2007; Yan et al., 2016). The dynamic monitoring and study of LUCC has become one of the most important aspects of researching global climate and environmental change.
Agricultural land is one of the most active land-use forms by human beings, which covers one third of the global surface (Yao et al., 2017; Ye et al., 2009) and plays a crucial role on regulating global climate change and ensuring food security (Ren et al., 2012). China is a large agricultural country, feeding one fifth of the world population with less than 7% of the cropland worldwide (Tian et al., 2016). The development of Chinese agriculture has been faced with resource shortages, environmental depredation and the demands of the huge population, while it is also restricted by poor agricultural production conditions (Chen, 2001). In recent years, increasing numbers of scholars have started to study topics such as regional ecological system health (Peng et al., 2017; Yang et al., 2017) and the comprehensive improvement of “empty village” phenomenon (Liu et al., 2013; Li and Wu, 2017) rather than a simple evaluation of quantity and quality in rural land use. Since the early 1990s, the process of urbanization and industrialization has been continually increasing in China. Cropland has been increasingly converted to urban land uses and has thus decreased rapidly. In response, the Central Rural Work Conference proposed the 1.2 billion ha of prime farmland as a “red line” to ensure China’s food security in 2003. Furthermore, China has promulgated a series of policies and regulations to protect farmland, including returning farmland to forestland and grassland, and maintaining a dynamic balance of total arable land. However, there remains a phenomenon of providing low-quality cropland to offset losses of high-quality cropland, and thus the quality and productivity of cropland has decreased seriously. Therefore, the spatio-temporal distribution of cropland has become an important research topic in the field of LUCC. Many scholars have monitored and analyzed the change in cropland in different spatial scales and regions with the help of remote-sensing data (for example, Landsat TM/ETM+ and China-Brazil Earth Resources Satellite) (Liu et al., 2005; Liu et al., 2010; Kotoky et al., 2012; Kraemer et al., 2015; Restrepo et al., 2017; Yao et al., 2017).
The type of land use can alter the modes and extents of exogenic force, influencing the formation, development and evolution of landform and geomorphology. Furthermore, topography and geomorphology are some of the most basic components of the ecological environment, restricting the form and effect of land use by allocating surface water and energy (Song and Chen, 1993; Zhou et al., 2009; Cheng et al., 2011; He et al., 2016). Cropland is one of the most sensitive LUCC types (Liu et al., 2001), thus geomorphologic factors play a vital role in influencing the spatio-temporal distribution and transformation of cropland. Altitude and slope affect climate factors, such as temperature and precipitation, but also restrict the difficulties in reclaiming cropland. Therefore, topography and geomorphology determine the spatio-temporal distribution of cropland and strongly influence cropland quantity and quality (Liu et al., 2001; Cheng et al., 2012; Wang et al., 2018). Extracting three typical kinds of geomorphologic types in Chongqing, Tian et al. (2010) concluded that topography and geomorphology have significant influences on the status of land use and land development. The amount of newly reclaimed cropland in deep hills is apparently higher than that in shallow hills. Cheng et al. (2012) showed that there are observably spatial differences of the cropland in diversity genetic types regions in Xinjiang based on water resource regionalization and geomorphologic characteristics. Taking Chengcheng County located in complex topography regions of Loess Plateau as an example, Fu et al. (2011) analyzed the effect on farmland productivity by loess landforms. They found that the high-quality farmland mainly distributed on the Loess Plateau with flat terrain, better irrigation and higher fertility.
At present, research about changes in cropland area influenced by topography and geomorphology are concentrated at the scale of city, county or watershed and relatively little research has been conducted at national or provincial scale (Cheng et al., 2012; He et al., 2016). Some researches relied solely on unique geomorphologic features in their study areas, and therefore, it was difficult to explore deeply the effect of topography and geomorphology on cropland in multiple geomorphologic regions (Tian et al., 2010; Fu et al., 2011; Stevens et al., 2014). Because the same climate conditions are typically found across a single geomorphologic region, it is of great importance to study the spatio-temporal distribution of China’s cropland from the perspective of several first-class geomorphologic divisions. According to the topographical and geomorphologic conditions, we divided China’s cropland into six regions. We then quantified and described the spatio-temporal distribution of cropland in China during 1990-2015 based on the national land use and land cover database interpreted by remote sensing images. Our study can provide basic information for further study of urban landscape planning, ecosystem management and protection. Moreover, data related to the conversions between cropland and other land-use types at spatio-temporal scales can be used as reference for utilization and management of agricultural resources, natural disasters, diseases and food security.

2 Data and methods

2.1 Data sources

In this research, geomorphologic regionalization data and cropland data from 1990 to 2015 were used for analyzing spatio-temporal distribution and transformation of cropland in China.
2.1.1 Geomorphologic regionalization data
Geomorphologic regionalization data were acquired from China’s State Key Laboratory of Resources and Environmental Information Systems (LREIS). Based on the regional differentiation and genesis of essential geomorphologic types, we divided the entire country into six major geomorphologic regions (Li et al., 2013; Zhao et al., 2017), including Region I (Eastern hilly plains), Region II (Southeastern low and middle mountains), Region III (Northern China and Inner Mongolia eastern-central mountains and plateaus), Region IV (Northwestern middle and high mountains, basins and plateaus), Region V (Southwestern middle and low mountains, plateaus and basins) and Region VI (Tibetan Plateau) (Figure 1).
2.1.2 Cropland data in China
Based on the national land use and land cover database of Resource and Environment Data Center of Chinese Academy of Sciences (CAS), we acquired cropland data for 1990, 1995, 2000, 2005, 2010 and 2015. The database was supported by the National Science and Technology Supporting Plan and the Innovative Program of the CAS, covering the multi-temporal land-use status of national land area at 1:100,000 scale (Zhao et al., 2015; Liu et al., 2010; Ning et al., 2018). The database was constructed using remote-sensing images, such as Landsat TM and ETM, as the main data source based on a rapid-extraction human-computer interaction method via a high-resolution remote sensing-unmanned aerial vehicle (UAV) ground survey observation system. The land-use types include six classes, such as cropland, woodland, grassland, water body, built-up land and unused land. Through investigating and recording field data, the accuracy of the six land-use classes was above 94.3%, meeting the requirement of users’ mapping accuracy at 1:100,000 scale (Liu et al., 2010). Then we rasterized the land-use data at 100-m resolution for convenience. The aim of our study was to extract cropland data and analyze its spatio-temporal distribution based on geomorphologic regionalization during 1990-2015.

2.2 Methods

With the aid of GIS techniques, we extracted the cropland data from the national land use and land cover database for 1990, 1995, 2000, 2005, 2010 and 2015. We then analyzed the change in cropland area and its distribution pattern by overlaying analyses with data from different geomorphologic regions (Figure 1). Finally, we obtained the characteristics of cropland and other land-use types based on the transformation attribute table of croplands.
Figure 1 Distribution of China’s cropland in different years
Notes: The geomorphologic regions supplemented and modified based on Li et al., 2013.
2.2.1 Dynamic degree of cropland (DDC)
The dynamic degree can reflect the changing ratio of the land use in different regions. The index of land-use dynamic degree proposed by Liu et al. (2005), which can comprehensively express characteristics of the distribution of land use patterns (Liu et al., 2010; Zhao et al., 2015; Ning et al., 2018). The dynamic degree of cropland (DDC) was calculated for 1990-2015 as follows:
$DDC=\frac{\Delta {{S}_{i-j}}+\Delta {{S}_{j-i}}}{{{S}_{i}}}\times \frac{1}{t}\times 100%$ (1)
where Si is the total cropland area at the start of monitoring (ha), Δsi‒j is the lost cropland area during the time period (the total area of the cropland converted to others) (ha), Δsj‒i is the newly reclaimed cropland area during the time period (the total area of the others converted to cropland) (ha), and t is the period of time with a unit of year. DDC value reflects the annual change rate of cropland within the regions during the period of t.
2.2.2 Barycenter model of newly reclaimed cropland
The barycenter model is an important tool to study the temporal and spatial variation of spatial elements during the process of regional development, which is extensively applied in the fields of urban planning and LUCC (Yin et al., 2017). The changing cropland’s spatial state determines its barycenter distribution (Li et al., 2017). The barycenter of the newly reclaimed cropland was calculated for 1995-2015 using the following equations:
${{X}_{T+1}}=\frac{\sum\limits_{i=1}^{n}{{{M}_{i}}{{X}_{i,T}}}}{\sum\limits_{i=1}^{n}{{{M}_{i}}}}$ (2)
${{Y}_{T+1}}=\frac{\sum\limits_{i=1}^{n}{{{M}_{i}}{{Y}_{i,T}}}}{\sum\limits_{i=1}^{n}{{{M}_{i}}}}$ (3)
where XT+1 and YT+1 represent the barycenter (longtitude and latitude) at the end year, Mi is the percentage of the newly reclaimed cropland area to the cropland area at the start of monitoring in the region i, Xi,T and Yi,T represent the barycenter (longtitude and latitude) at the start year in region i, and n is the count of geomorphologic regions.
However, the above equations were not applied to calculate the barycenter for 1990 because 1990 was the start of monitoring. The equations for calculating the barycenter of 1990 were as follows:
$\overline{X}=\frac{\sum\limits_{i=1}^{n}{{{A}_{i}}{{X}_{i}}}}{\sum\limits_{i=1}^{n}{{{A}_{i}}}}$ (4)
$\overline{Y}=\frac{\sum\limits_{i=1}^{n}{{{A}_{i}}{{Y}_{i}}}}{\sum\limits_{i=1}^{n}{{{A}_{i}}}}$ (5)
where $\overline{X}$ and $\overline{Y}$ represent the barycenter (longtitude and latitude) of national cropland in 1990, Ai is the cropland area of the ith geomorphologic region, and Xi and Yi are the barycenters (longtitude and latitude) in region i, respectively.

3 Results

3.1 Spatio-temporal distribution and transformation of cropland in China

There was little change in the total cropland area in China (177.1 to 178.5 million ha) during the period of 1990-2015, representing an average increase of just 0.03% per year. The cropland was distributed mainly in the second and the third gradient terrain of central and eastern China (Figure 2). Splitting the data into two sections around 2000, the cropland area increased 2.8 million ha during 1990-2000, whereas it decreased 1.4 million ha during 2000-2015. The newly reclaimed cropland was mainly found in the northeastern and northwestern regions, with the woodland and grassland conversion to cropland. A large amount of cropland was lost in southeast coastal areas of China because of rapid urbanization.
Figure 2 Distribution of the reclaimed and lost cropland in China during 1990-2015
The newly reclaimed cropland primarily came from grassland and woodland during 1990-2000, whereas it was converted from grassland and unused land during 2000-2015 (Figure 3). The area of cropland converted from built-up land was very small compared with the area from other land uses.
Figure 3 Land use and land cover change of reclaimed and lost cropland in China during 1990-2015
The lost cropland was mainly caused by the large expansion of built-up land, grassland and woodland. The cropland was rapidly converted to built-up land during 2000-2015, and especially the cropland area converted to built-up land accounted for 84% of all lost cropland area from 2010 to 2015. This was because of the exceptionally rapid economic growth and the expansion of urbanization. Finally, the area of high-quality cropland was severely reduced because of construction of new buildings.
From the perspective of geomorphologic regionalization, the newly reclaimed and lost cropland was concentrated on low terrain and large plain areas (58.6% and 60.9% respectively), followed by platforms and hills (Figure 4). The cropland decreased gradually with the increased relief amplitude (difference between the highest altitude and the lowest altitude). Plains, hills and platforms were generally preferred to be reclaimed and occupied because of the small relief amplitude (<200 m). In contrast, it is difficult to exploit and utilize the cropland scattered on high-relief mountains, so the limited amount of cropland available was gradually abandoned. There was small change in cropland area in high mountainous areas, and there was little cropland scattered on extremely high-relief mountains.
Figure 4 Change of cropland area in different geomorphologic regions in China during 1990-2015

3.2 Dynamic degree of geomorphologic regions

The DDC values of different geomorphologic regions are presented in Table 1 and Figure 5. The change ranges are the total absolute areas of newly reclaimed and lost cropland. Except for Region IV, there was a slight change in cropland areas of other geomorphologic regions in the period of 1990-2015, with small average DDC values (<1%).
Table 1 Dynamic degree of cropland (DDC) in different geomorphologic regions
Region I Region II Region III
Change ranges (ha) DDC (%) Change ranges (ha) DDC (%) Change ranges (ha) DDC (%)
1990-1995 5,125,436 1.40 940,063 0.56 1,733,440 1.29
1995-2000 1,981,791 0.53 692,366 0.42 840,587 0.62
2000-2005 1,345,601 0.36 671,039 0.40 815,059 0.59
2005-2010 797,084 0.21 246,073 0.15 196,102 0.14
2010-2015 914,676 0.24 427,295 0.26 325,892 0.24
Region IV Region V Region VI
Change ranges (ha) DDC (%) Change ranges (ha) DDC (%) Change ranges (ha) DDC (%)
1990-1995 1,380,978 4.06 423,537 0.25 64,006 0.61
1995-2000 720,985 2.15 215,656 0.13 54,301 0.51
2000-2005 930,895 2.62 373,304 0.22 41,949 0.39
2005-2010 335,846 0.85 276,716 0.16 18,363 0.17
2010-2015 1,065,573 2.61 324,831 0.19 17,915 0.17
Figure 5 Change in dynamic degree of cropland (DDC) in different geomorphologic regions during 1990-2015
The cropland area increased in Region IV, with an average increase of 8.9´104 ha per year. Moreover, the cropland areas fluctuated greatly with DDC values far exceeding those of other regions. The DDC values were 4.06%, 2.62% and 2.61% during 1990-1995, 2000-2005 and 2010-2015, respectively. The newly reclaimed cropland mainly stemmed from reclaiming grassland in Tarim Basin, the Ili River Valley and Junggar Basin, owing to the mass production of cash crops, the great progress of agricultural technology and the vigorous generalization of agricultural policies.
The barycenter of China’s land cultivation shifted from northern China to the northwest over the 25-year period, parts of which began in Region IV and moved northwest continuously during the period of 1995-2015 (Figure 2).
The cropland areas of Regions I and II initially increased before 2000 and then decreased after 2000. The cropland area of Region I increased 5.489´104 ha annually, while that of Region III decreased 1.5´103 ha annually. The cropland areas of Regions II and V showed a decreasing trend with reducing area of 5.9´104 ha and 2.8´104 ha, respectively. However, there was little cropland and little change in Region VI, which was covered by glaciers throughout the year because of the high terrain and altitude.

3.3 Spatio-temporal distribution of geomorphologic regions

The spatio-temporal distribution of cropland in the six regions is shown in Table 2. Region I had the biggest area (7.49´107 ha on average), which was twice or three times greater than that of other regions. There was a large amount of high quality croplands in Region I because of the low terrain and the excellent hydrothermal conditions. Inversely, the cropland areas of Regions IV and VI only accounted for 10% and 3% of that of Region I because of the poor hydrothermal conditions. The spatial structure and distribution of cropland were mainly influenced by the natural environment, thus area of cropland varied with the geographical conditions.
3.3.1 Geomorphologic Region I (Eastern hilly plains)
The cropland area in Region I increased by 1.35´106 ha with an annual amount of 5.4´104 ha. The increase rate of cropland during 1990-2000 was more rapid than that during 2000-2015 (Figure 6). The newly reclaimed cropland area was the largest during 1990-1995, which was twice to sixteen times greater than that of other study periods. Woodland, grassland and unused land were the main source types of the newly reclaimed cropland in Songnen Plain, Liaohe Plain, Sanjiang Plain and other parts of northeast China. However, there was little cropland in eastern coastal areas. The newly reclaimed cropland concentrated on Liaohe Plain by the conversion of grassland during 1990-1995 and Songnen Plain by the conversion of woodland during 1995-2000.
Figure 6 Change in reclaimed and lost cropland in Geomorphologic Region I during 1990-2015
Notes: (a)-(e) are local enlarged drawings of Geomorphologic Region I.
The lost cropland was mainly in the vicinity of northeastern provincial capital cities and eastern coastal areas. The ratio between newly built-up land and lost cropland continued to increase; making up 37% of the total newly reclaimed cropland area during 1990-1995 to 91% of that during 2010-2015. Along with the rapid economic development, urban expansion accelerated continuously and the traffic network continued to improve. Large built-up areas replaced cropland with an increasing rate in northeastern provincial capital cities, the Beijing-Tianjin-Hebei region and eastern coastal areas (especially the Yangtze River Delta). Because of the low terrain and easily exploited land in Region I, high productivity and high-quality cropland became the best choice for urban expansion. The change from built-up land to cropland continued to accelerate. However, the newly supplied cropland was mainly made up of woodland, grassland and unused land. As a result, there was a serious decline in cropland quality in this region.
3.3.2 Geomorphologic Region II (Southeastern low and middle mountains)
Over the whole study period, the cropland in Region II decreased continuously from 3.35´107 ha to 3.30´107 ha, with an annual amount of 5.9 ´ 104 ha (Figure 7).
Figure 7 Change in reclaimed and lost cropland in Geomorphologic Region II during 1990-2015
Notes: (a)-(e) are local enlarged drawings of Geomorphologic Region II.
A small increase in cropland mainly took place in 1990-2005. Specifically, it concentrated on southern Guangxi by the conversion of woodland (47.4%), water bodies and grassland during 1990-1995, Dongting Lake and Poyang Lake by the conversion from water body during 1995-2005. These results showed that a serious reclamation of cropland from lakes took place during this period.
Table 2 Temporal and spatial change characteristics of cropland in different geomorphologic regions
Geomorphological regions Changes in cropland area (104 ha/a) Characteristics of newly
reclaimed cropland		 Characteristics of lost cropland
Region I
(Eastern hilly plains)		 +5.40 It was mainly converted from grassland and unused land, concentrating on Songnen Plain, Liaohe Plain, and Sanjiang Plain It was mainly reclaimed to built-up land, and occurred in the vicinity of northeastern provincial capital cities and eastern coastal areas (especially Yangtze River Delta). The proportion of converting built-up land to cropland continued to increase.
Region II
(Southeastern low middle mountains)		 -5.92 The increased reclaimed cropland occurred mainly during 1990-2000. And it concentrated on southern Guangxi by the conversion of woodland, Dongting Lake and Poyang Lake by the conversion of water body. Its area was far more than the reclaimed cropland. Most of the decreased cropland was changed to woodland (low-middle mountains, hills and valleys of Zhejiang and Fujian provinces) and built-up land (the Pearl River Delta and southeastern coastal areas) during 1990-2000.
Region III
(Northern China and Inner Mongolia eastern-central mountains and plateaus)		 -0.15 It mainly occurred in 1990-2005, with grassland reclamation in domination. It was primarily distributed in upland plains of northeastern Inner Mongolia, Hetao Plain and western Loess Plateau. And the proportion of grassland to reclaimed cropland was gradually reducing. Most serious loss occurred in 1990-2005, with the conversion from cropland to grassland, especially in 1990-1995. The effect of returning farmland to forests and pastures was significant in the central part of the Hetao Plain and at bend of the Yellow River.
Region IV
(Northwestern middle and high mountains, basins and plateaus)		 +8.93 The reclaimed cropland mostly came from the conversion of grassland, scattering on oasis areas with better conditions of water and land resources, including northern Tarim Basin (Aksu and Korla), Junggar Basin and so on. The cropland loss was not apparent in Region IV with most serious loss occurring in 1990-1995, and 67.2% of them converted to grassland. This happened mainly on the fringes of cropland or peripheries of cities and towns because of serious cropland abandonment.
Region V
(Southwestern middle and low mountains, plateaus and basins)		 -2.83 The change of cropland was much smaller than regions I and IV. The reclaimed cropland emerged in 1990-2000, by the conversion from woodland and grassland (above 88.2%). There were plenty of forests and shrub lands to be re-cultivated in hills, mountains valleys of Hubei, Guizhou, and Yunnan provinces. With the accelerated industrialization and urbanization, a great deal of cropland was exploited to built-up land, and the proportion of cropland converted to built-up land was gradually increasing.
Region VI
(Tibetan Plateau)		 +0.06 Almost unchanged. Almost unchanged.
Most of the decreased cropland was changed to woodland and built-up land during 1990-2000. The newly reclaimed woodland was mainly distributed in low-middle mountains, hills and valleys of Zhejiang and Fujian provinces, where afforestation was visible on the cold bare sloping land. Most of the decreased cropland was turned to built-up land during 2000-2015. The major periods of converting cropland to built-up land were 2000-2005 and 2010-2015, with areas of 3.95´105 ha and 3.64´105 ha, respectively. The newly reclaimed built-up land was concentrated on the Pearl River Delta and southeastern coastal areas during 2000-2010. It was widely distributed in southeastern cities until 2015 with the extension of urbanization scale.
3.3.3 Geomorphologic Region III (Northern China and Inner Mongolia eastern-central mountains and plateaus)
In this region, the cropland decreased slightly by 3.8´104 ha over the whole period, with an average loss of 1.5´103 ha per year (Figure 8). Grassland was the main source of the newly reclaimed cropland, making up 80%, 69% and 75% of the total cropland area in the periods of 1990-1995, 1995-2000 and 2000-2005, respectively. The change mainly occurred in upland plains of northeastern Inner Mongolia, Hetao Plain and the western Loess Plateau. The rate of grassland conversion to cropland reduced gradually over time.
Figure 8 Change in reclaimed and lost cropland in Geomorphologic Region III during 1990-2015
Notes: (a)-(e) are local enlarged drawings of Geomorphologic Region III.
Cropland loss mainly took place in 1990-2005, particularly with the conversion from cropland to grassland in 1990-1995 (5.27´105 ha). The change of cropland to woodland and grassland mainly occurred in the whole Hetao Plain during 1990-1995, in the northern Hetao Plain during 1995-2000, and in central part of the Loess Plateau during 2000-2005.
Compared with the spatial distribution of cropland change in 1990-2005, the newly reclaimed and lost cropland were both concentrated on Hetao Plain and the Loess Plateau. This change reflected that the effect of returning farmland to forests and pastures was evident on the one hand while on the other hand new cropland should be added at the same time.
Lots of cropland was converted to built-up land during 2010-2015, particularly in the central parts of both Shaanxi and Gansu provinces.
3.3.4 Geomorphologic Region IV (Northwestern middle and high mountains, basins and plateaus)
Region IV witnessed an increase in cropland area of 2.23´106 ha with an annual average of 8.9´104 ha during 1990-2015, and its newly reclaimed cropland area was the largest of the six geomorphologic regions. The main changes in land-use types in this region were between cropland and grassland (Figure 9).
Figure 9 Change in reclaimed and lost cropland in Region IV during 1990-2015
Notes: (a)-(e) are local enlarged drawings of Geomorphologic Region IV.
The newly reclaimed cropland mostly came from the conversion of grassland, scattered in oasis areas with better conditions of water and land resources, including northern Tarim Basin (Aksu and Korla) and Junggar Basin. In order to encourage farmers to reclaim cropland, many preferential policies and facilitation measures were proposed and carried out by the central government and Xinjiang local government, including grain production subsides and agricultural tax exemption. In particular, the speed and quantity of cropland exploration peaked during 2000-2005.
Cropland losses were not apparent in Region IV during 1995-2015. The lost area of cropland reached 7.3´105 ha only in the period of 1990-1995, and 67.2% of the lost cropland was converted to grassland. The lost cropland was spread on the fringes of cropland or peripheries of cities and towns. Cropland loss was particularly serious in the Kashi area because of widespread cropland abandonment during this period.
3.3.5 Geomorphologic Region V (Southwestern middle and low mountains, plateaus and basins)
Over the whole study period, the cropland in Region V continuously decreased by 7.1´105 ha in total, with an annual area of 2.8´104 ha. The change in cropland was much smaller than in Regions I and IV. The newly reclaimed cropland emerged in 1990-2000, mostly from conversion from woodland and grassland (above 88.2%). There were plenty of forests and shrub lands available for cultivation in the hills and mountains valleys of Hubei, Guizhou and Yunnan provinces. However, the area of newly reclaimed cropland was small during 2000-2005 in this region (Figure 10).
Figure 10 Change of reclaimed and lost cropland in Geomorphologic Region V during 1990-2015
Notes: (a)-(e) are local enlarged drawings of Geomorphologic Region V.
With the accelerated industrialization and urbanization, a great deal of cropland was exploited as built-up land and the proportion of cropland converted to built-up land was gradually increasing. The conversion of cropland to built-up land was mainly concentrated in provincial capitals or large cities.
3.3.6 Geomorphologic Region VI (Tibetan Plateau)
Because of the complicated topographical conditions, small resident population and underdeveloped economy, the cropland area changed very little in Region VI and only increased by 60 ha annually (Figure 11). Newly reclaimed cropland was converted from grassland. The lost cropland was very small and was mainly converted to grassland and built-up land.
Figure 11 Change in the reclaimed and lost cropland in Geomorphologic Region VI during 1990-2015

4 Discussion and conclusions

Cropland is one of the most sensitive and fragile land-use types. With the accelerated industrialization and urbanization, both the quantity and quality of cropland is faced with severe challenges and many problems. With the aid of the GIS technique, we extracted cropland data, analyzed the spatial structure and distribution of China’s cropland, and discussed the relationship between cropland and other land-use types in the period of 1990-2015.
There was little change in the total cropland area in China during 1990-2015. The cropland was distributed mainly on the second and the third topographical steps of central and eastern China. The barycenter of China’s cropland shifted from northern China to the northwest. The rapid urbanization and the occupation of high-quality cropland were the critical factors influencing the spatio-temporal distribution of cropland in China.
There was a large number of high-quality cropland in Region I because of the low terrain and abundant water resources. Region I has the largest cropland area, covering an average area of 7.49 ´ 107 ha. Inversely, the cropland areas of Regions IV and VI accounted for less than 10% of that of Region I because of the complicated geographical conditions and the extensively distributed mountains, plateaus and basins.
Owing to the large area of the geomorphologic regions, the DDC values were relatively small. In region IV, the cropland areas fluctuated greatly with DDC values far exceeding those of other regions, having an annual average increasing amount of 8.9 ´ 104 ha. The DDC values in Region IV were 4.06%, 2.62% and 2.61% during 1990-1995, 2000-2005 and 2010-2015, respectively. The newly reclaimed croplands were mainly from the exploitation of grassland areas distributed across the northern Tarim Basin (Aksu and Korla) and Junggar Basin. However, the DDC values in other regions were less than 1%.
From the perspective of land-use types, the newly reclaimed cropland primarily came from grassland, woodland and unused land, especially during 1990-2000. The lost cropland was mainly converted to built-up land, woodland and grassland during 1990-2015. The principal reason for cropland losses was that a large amount of high-quality cropland was indiscriminately occupied by built-up land. From the perspective of geomorphologic regions, the newly reclaimed and lost cropland was concentrated on vast plains (58.6% and 60.9%, respectively), followed by platforms and hills. The larger the relief amplitude, the smaller the cropland area.
The newly reclaimed cropland mainly occurred in Regions I and IV, and the lost cropland mainly occurred in Regions II and V. There was no change in cropland area in Regions III and VI.
However, we only analyzed spatio-temporal distribution of cropland in China during 1990-2015 based on geomorphologic regionalization. The main drivers of cropland change need to be explored deeply in different geomorphologic regions. Cropland serves as an essential base and guarantee for human survival and development. Cropland protection is related to food security, sustainable development and social stability. Further research is therefore needed focusing on reasonable utilization and risk assessment of China’s cropland based on geomorphologic regionalization.

Acknowledgements

We thank Alex Boon, PhD, from Liwen Bianji, Edanz Editing China (www.liwenbianji. cn/ac), for editing the English text of a draft of this manuscript. We also thank Professor Liu Yongbo in the University of Guelph for checking and revising the language, and the editor and anonymous reviewers for their labor and precious time for improving our manuscript.

The authors have declared that no competing interests exist.

References

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[16]
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[17]
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[18]
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[19]
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[20]
Ren W, Tian H, Tao B et al., 2012. China’s crop productivity and soil carbon storage as influenced by multifactor global change.Global Change Biology, 18(9): 2945-2957.Much concern has been raised about how multifactor global change has affected food security and carbon sequestration capacity in China. By using a process-based ecosystem model, the Dynamic Land Ecosystem Model (DLEM), in conjunction with the newly developed driving information on multiple environmental factors (climate, atmospheric CO2, tropospheric ozone, nitrogen deposition, and land cover/land use change), we quantified spatial and temporal patterns of net primary production (NPP) and soil organic carbon storage (SOC) across China's croplands during 1980–2005 and investigated the underlying mechanisms. Simulated results showed that both crop NPP and SOC increased from 1980 to 2005, and the highest annual NPP occurred in the Southeast (SE) region (0.32 Pg C yr611, 35.4% of the total NPP) whereas the largest annual SOC (2.29 Pg C yr611, 35.4% of the total SOC) was found in the Northeast (NE) region. Land management practices, particularly nitrogen fertilizer application, appear to be the most important factor in stimulating increase in NPP and SOC. However, tropospheric ozone pollution and climate change led to NPP reduction and SOC loss. Our results suggest that China's crop productivity and soil carbon storage could be enhanced through minimizing tropospheric ozone pollution and improving nitrogen fertilizer use efficiency.

DOI PMID

[21]
Restrepo A M C, Yang Y R, Hamm N A S et al., 2017. Land cover change during a period of extensive landscape restoration in Ningxia Hui Autonomous Region, China.Science of the Total Environment, 598: 669-679.Abstract Environmental change has been a topic of great interest over the last century due to its potential impact on ecosystem services that are fundamental for sustainable development and human well-being. Here, we assess and quantify the spatial and temporal variation in land cover in Ningxia Hui Autonomous Region (NHAR), China. With high-resolution (30m) imagery from Landsat 4/5-TM and 8-OLI for the entire region, land cover maps of the region were created to explore local land cover changes in a spatially explicit way. The results suggest that land cover changes observed in NHAR from 1991 to 2015 reflect the main goals of a national policy implemented there to recover degraded landscapes. Forest, herbaceous vegetation and cultivated land increased by approximately 410,200ha, 708,600ha and 164,300ha, respectively. The largest relative land cover change over the entire study period was the increase in forestland. Forest growth resulted mainly from the conversion of herbaceous vegetation (53.8%) and cultivated land (30.8%). Accurate information on the local patterns of land cover in NHAR may contribute to the future establishment of better landscape policies for ecosystem management and protection. Spatially explicit information on land cover change may also help decision makers to understand and respond appropriately to emerging environmental risks for the local population. Copyright 2017 Elsevier B.V. All rights reserved.

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[22]
Song N P, Chen Z X, 1993. A study on the relationship of landform and landuse.Journal of Ningxia University (Natural Science Edition), 14(3): 27-31. (in Chinese)

[23]
Stevens F, Bogaert P, Van O K et al., 2014. Regional-scale characterization of the geomorphic control of the spatial distribution of soil organic carbon in cropland.European Journal of Soil Science, 65(4): 539-552.The heterogeneity of the spatial distribution of soil organic (SOC) at the landscape scale is generally not considered in regional or national SOC dynamics models. In cropland this heterogeneity is controlled largely by topography, which influences the distribution of , energy and sediments, and thus the SOC dynamics. Sediment redistribution rates have increased strongly since the mechanization of agriculture. The over implification of landscape processes in regional models of C dynamics may add to the uncertainty in C balances. Therefore, a better characterization of the importance of landscape cale effects on the SOC distribution throughout a region is needed. This study characterized the relative importance of geomorphology in the SOC horizontal and vertical variability across croplands in the Belgian loess belt region. A large legacy dataset of soil horizons was exploited together with 147 recently sampled profiles. Mean SOC depth profiles for different soil types were compared. Various topographic attributes were computed from a digital elevation model, and their influence on SOC was quantified through simple linear models. Finally, SOC content was mapped at three depth layers through multiple linear models, and results were cross alidated. The legacy dataset allowed identification of significant differences in the mean SOC profile according to texture, drainage or profile development classes. A clear relationship between SOC content and topographic attributes was demonstrated, but only for the recently sampled profiles. This may be explained by a substantial error in the location of the profiles of the legacy dataset. This study thus shows evidence that the major control of the vertical distribution of SOC is related to topography in a region where observed heterogeneities for other commonly involved factors are limited. However, the large amount of unexplained variability still limits the usefulness of the spatial prediction of SOC content, and suggests the importance of additional influencing factors.

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[24]
Tian H Q, Chen G S, Lu C Q et al., 2015. Global methane and nitrous oxide emissions from terrestrial ecosystems due to multiple environmental changes.Ecosystem Health & Sustainability, 1(1): 1-20.Abstract Greenhouse gas (GHG)-induced climate change is among the most pressing sustainability challenges facing humanity today, posing serious risks for ecosystem health. Methane (CH4) and nitrous oxide (N2O) are the two most important GHGs after carbon dioxide (CO2), but their regional and global budgets are not well known. In this study, we applied a process-based coupled biogeochemical model to concurrently estimate the magnitude and spatial and temporal patterns of CH4 and N2O fluxes as driven by multiple environmental changes, including climate variability, rising atmospheric CO2, increasing nitrogen deposition, tropospheric ozone pollution, land use change, and nitrogen fertilizer use. The estimated CH4 and N2O emissions from global land ecosystems during 1981–2010 were 144.39 ± 12.90 Tg C/yr (mean ± 2 SE; 1 Tg = 1012 g) and 12.52 ± 0.74 Tg N/yr, respectively. Our simulations indicated a significant ( P 4</sub> (0.43 ± 0.06 Tg C/yr) and N2O (0.14 ± 0.02 Tg N/yr) in the study period. CH4 and N2O emissions increased significantly in most climatic zones and continents, especially in the tropical regions and Asia. The most rapid increase in CH4 emission was found in natural wetlands and rice fields due to increased rice cultivation area and climate warming. N2O emission increased substantially in all the biome types and the largest increase occurred in upland crops due to increasing air temperature and nitrogen fertilizer use. Clearly, the three major GHGs (CH4, N2O, and CO2) should be simultaneously considered when evaluating if a policy is effective to mitigate climate change.

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[25]
Tian H Q, Ren W, Tao B et al., 2016. Climate extremes and ozone pollution: A growing threat to China’s food security.Ecosystem Health & Sustainability, 2(1): 1-10.Abstract Ensuring global food security requires a sound understanding of climate and environmental controls on crop productivity. The majority of existing assessments have focused on physical climate variables (i.e., mean temperature and precipitation), but less on the increasing climate extremes (e.g., drought) and their interactions with increasing levels of tropospheric ozone (O3). Here we quantify the combined impacts of drought and O3 on China's crop yield using a comprehensive, process-based agricultural ecosystem model in conjunction with observational data. Our results indicate that climate change/variability and O3 together led to an annual mean reduction of crop yield by 10.0% or 55 million tons per year at the national level during 1981 2010. Crop yield shows a growing threat from severe episodic droughts and increasing O3 concentrations since 2000, with the largest crop yield losses occurring in northern China, causing serious concerns in food supply security in China. Our results imply that reducing tropospheric O3 levels is critical for securing crop production in coping with increasing frequency and severity of extreme climate events such as droughts. Improving air quality should be a core component of climate adaptation strategies.

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[26]
Tian M, Gao M, Bao J X et al., 2010. The effect of topography and geomorphology on the amount of newly-increased cultivated land.Journal of Southwest University (Natural Science Edition), 32(11): 98-103. (in Chinese)Using the land-use map with a scale of 1 2 000,the topographic map and the data of the first detailed land survey,the effects of topography and geomorphology on the amount of newly-increased cultivated land in Chongqing were studied with three kinds of typical physiognomy of shallow hill,deep hill and middle-low mountain as the study objects,with 2 sampling sites for each kind.The results showed a significant difference in the amount of newly-increased cultivated land of land consolidation under different physiognomical conditions.Before the implementation of land consolidation,the major land use type was paddy field in shallow hill regions,with a relatively high net cultivated land coefficient,but the major land use type was dryland in deep hill and middle-low mountain regions,with a lower net cultivated land coefficient.The rate of increase in cultivated land of shallow hill was 4.98% and 5.02% and that of deep hill and middle-low mountain regions was 10.95% and 5.47% and 16.07% and 10.15%,respectively,after the implementation of land consolidation.It is thus concluded that topography and geomorphology have significant influences on the status of land use and the potential of newly-increased farmland and on the newly-increased farmland as well.

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[27]
Turner B L, Lambin Eric F, Reenberg Anette, 2007. The emergence of land change science for global environmental change and sustainability.Proceedings of the National Academy of Sciences of the United States of America, 104(52): 20666.

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[28]
Wang J, Zhang Z, Liu Y, 2018. Spatial shifts in grain production increases in China and implications for food security.Land Use Policy, 74: 204-213.China’s food security remains a worldwide concern due to its huge population and rapid urbanization. As demonstrated by statistics, China’s total grain output has been continuously increasing since 2003. Meanwhile, the grain production growth has shown various spatial disparities across the country. This paper explores the spatial shifts in grain production increase and their potential impacts at county-level in China. The results show that the barycenter of grain production has moved northward obviously and crossed the Yellow River, which served as the main irrigation water source for agriculture in North China. Both absolute grain output growth and relative growth patterns demonstrate that North China, especially the region of north bank of the Yellow River, has been the significant area contributing to grain production. China has shifted grain production to the marginal regions with lower land productivity and higher natural risk. Although China’s grain output has increased continuously, the grain output system is now more vulnerable and unstable than before. In the final part, the paper discusses the three main factors influencing the spatial shifts in grain output, which are farmland protection system, farmer-protecting grain subsidy policies and the dramatic improvement in agricultural infrastructure, and gives some suggestions on the improvement of farmland protection system and agricultural support policy.

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[29]
Yan F Q, Zhang S W, Kuang W H et al., 2016. Comparison of cultivated landscape changes under different management modes: A case study in Sanjiang Plain.Sustainability, 8(10): 1071. doi: 10.3390/su8101071.

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[30]
Yang R H, Yang Q Y, Zeng L et al., 2017. Evaluation on ecological security and analysis of influence factors of rural land based on BP-ANN model.Research of Soil and Water Conservation, 24(3): 206-213. (in Chinese)

[31]
Yao Z Y, Zhang L J, Tang S H et al., 2017. The basic characteristics and spatial patterns of global cultivated land change since the 1980s.Journal of Geographical Sciences, 27(7): 771-785.In this paper, we analyzed the spatial patterns of cultivated land change between 1982 and 2011 using global vector-based land use/land cover data.(1) Our analysis showed that the total global cultivated land area increased by 528.768×104 km~2 with a rate of 7.920×104 km~2/a, although this increasing trend was not significant. The global cultivated land increased fastest in the 1980 s. Since the 1980 s, the cultivated land area in North America, South America and Oceania increased by 170.854×104 km~2, 107.890×104 km~2, and 186.492×104 km~2, respectively. In contrast, that in Asia, Europe and Africa decreased by 23.769×104 km~2, 4.035×104 km~2 and 86.76×104 km~2, respectively. Furthermore, the cultivated land area in North America, South America and Oceania exhibited significant increasing trends of 7.236× 104 km~2/a, 2.780×104 km~2/a and 3.758×104 km~2/a, respectively. On the other hand, that of Asia, Europe and Africa exhibited decreasing trend rates of –5.641×104 km~2/a, –0.831×104 km~2/a and –0.595×104 km~2/a, respectively. Moreover, the decreasing trend in Asia was significant.(2) Since the 1980 s, the increase in global cultivated lands was mainly due to converted grasslands and woodlands, which accounted for 53.536% and 26.148% of the total increase, respectively. The increase was found in southern and central Africa, eastern and northern Australia, southeastern South America, central US and Alaska, central Canada, western Russia, northern Finland and northern Mongolia. Among them, Botswana in southern Africa experienced an 80%–90% increase, making it the country with the highest increase worldwide.(3) Since the 1980 s, the total area of cultivated lands converted to other types of land was 1071.946×104 km~2. The reduction was mainly converted to grasslands and woodlands, which accounted for 57.482% and 36.000%, respectively. The reduction occurred mainly in southern Sudan in central Africa, southern and central US, southern Russia, and southern European countries including Bulgaria, Romania, Serbia and Hungary. The greatest reduction occurred in southern Africa with a 60% reduction.(4) The cultivated lands in all the continents analyzed exhibited a trend of expansion to high latitudes. Additionally, most countries displayed an expansion of newly increased cultivated lands and the reduction of the original cultivated lands.

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[32]
Ye Y, Fang X Q, Ren Y Y et al., 2009. Cropland cover change in Northeast China during the past 300 years.Science in China Series D Earth Sciences, 52(8): 1172-1182.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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[33]
Yin G, Liu L, Jiang X, 2017. The sustainable arable land use pattern under the tradeoff of agricultural production, economic development, and ecological protection: An analysis of Dongting Lake basin, China.Environmental Science & Pollution Research, 24(32): 1-17.To find a solution regarding sustainable arable land use pattern in the important grain-producing area during the rapid urbanization process, this study combined agricultural production, locational co

DOI PMID

[34]
Zhao G S, Liu J Y, Kuang W H et al., 2015. Disturbance impacts of land use change on biodiversity conservation priority areas across China: 1990-2010.Journal of Geographical Sciences, 25(5): 515-529.Land use change is one of the main drivers of biodiversity loss. In the last 20 years, China's land use pattern has undergone profound changes. This study constructs an Ecosystem Comprehensive Anthropogenic Disturbance Index(ECADI) to assess disturbance impacts of land use change between 1990 and 2010 on biodiversity conservation priority areas at national and regional scales. Four levels of biodiversity conservation areas were categorized: generally important areas, moderately important areas, important areas, and very important areas. The results indicated a higher ECADI value in 2010 in Central and Eastern China than in Western China, and the values of the moderately important, important and very important regions were lower than the average value of the whole country at all levels. Notably, in recent 20 years, the change extent of ECADI values in Central and Eastern China were much greater compared with that in Western China, and ECADI values in the moderately important, important and very important biodiversity conservation areas all showed increasing trends, with the increasing extent lower than that of whole China at all levels. Due to human activities such as urbanization in Eastern China and cropland reclamation in Northeast China and Xinjiang, ECADI values showed a medium increase trend(the change rate was about 1%–5% in 10 years), which indicated the need for more conservation efforts in those regions. However, ECADI values in the Loess Plateau presented a low decline trend(the change rate was about –1% to –0.1% in 10 years) after 2000 because of the obvious effectiveness of Green for Grain Project. Furthermore, the variation was negligible in the Tibetan Plateau.

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[35]
Zhao M, Cheng W M, Zhou C H et al., 2017. Spatial differentiation and morphologic characteristics of China’s urban core zones based on geomorphologic partition.Journal of Applied Remote Sensing, 11(1): 016041. doi: 10.1117/1.JRS.11.016041.Based on a previous study that used the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light images to partition different types of night-lit areas within individual cities, 456 urban core zones in China, representing highly developed areas in 2012, were extracted. Then, several morphologic indices were selected for characterizing for each urban core zone, and the spatial differentiation and morphologic characteristics of urban core zones located within different geomorphologic regions in China were quantitatively analyzed. The results showed that urban core zones were most widely distributed in the eastern region comprising hilly plains, with a decreasing distribution trend from northeast to southwest, and the least distribution was in the Tibetan Plateau. The contours of most of these zones appeared to be relatively simple and compact, and evidenced seven shapes. Regions at lower altitudes with flat terrains were more likely to demonstrate a wide range of urban core zones, especially those with complex shapes. This study represents a preliminary effort toward the construction of an interactive coupling mechanism for urban and geomorphologic environments (e.g., altitude, relief of land surface, geomorphologic types, geomorphologic region). Its findings contribute to enhancing understanding of the spatial morphologic characteristics of highly developed areas in China.

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[36]
Zhou C H, Cheng W M, Qian J K et al., 2009. Research on the classification system of digital land geomorphology of 1:1000000 in China.Journal of Geo-Information Science, 11(6): 707-724. (in Chinese)Geomorphologic classification system is essential to geomorphologic research and mapping.Using the compiling methodology and standard of geomorphologic maps with a scale of 1 1 000 000 in 1980's in China,based on the summarization of geomorphology,classification research at home and abroad,and the technology such as remote sensing image,digital elevation model(DEM) and computer automated cartography and so on,this research concludes and summarizes the principles followed in the classification process of digital geomorphology;analyzes the mutual relations hips among them;discusses various indexes of digital land geomorphologic classification: including morphology,genesis,material composition,age etc.The classification system puts forward numerical classification methodology of 3 classes,6 grades and 7 layers of digital Land geomorphology in China;presents data organization method of digital geomorphology,that is: morphology and genesis types represented by polygon map spot,morphology and structure type represented by point,line and polygon map spot together.Moreover,the article specifically presents the geomorphologic types of different layer and different level of various genesis types.The research of classification system of digital geomorphology provides a basis for the interpretation and cartography of Land geomorphology based on multi-source data such as remote sensing etc.

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