The history of the land use of many developed countries shows that the courses of industrialization of economy and urbanization of population are usually accompanied by marginalization of agricultural land use.China is now in a developing stage with rapid industrialization and urbanization,and changes such as "the more rapid non-agriculturalization of agricultural land,the continuous loss of farmland,abandonment of arable land,the substantial loss of labor force sources from rural areas,the shrinkage of agriculture in the eastern littoral,etc." has occurred in the process of agricultural land use in recent years.Many scholars have studied these changes and their driving forces,mostly adopting a correlation analysis in statistics.These researches encountered a lot of criticism,deeper analyses of the mechanism are called,but little progress has been made.So seeking a new synthetical research approach is especially important. This paper firstly defined the essence of the marginalisation of arable land and its criterion to diagnose.Then,based on the cost-income data of three kinds of grain crops such as paddy,wheat and maize during the period 1980-2002, this paper diagnosed the marginalisation phenomena of cultivated land use in China.The results show that there were once suspicious marginalisation evidence and two times obvious marginalisation phenomena of the cultivated land utilization in the last two decades in China.The suspicious evidence only had a faint trace in 1987,and the first and the second ones were in evidence in 1991 and 1996,but the second one was wider and more serious.The marked decline of the degree of intensity of the cultivated land use,the notable shrinkage of the sown area of the grain crops and the severe abandonment of the cultivated land had causal relations with the action of the margilisation of arable land.Theory of the marginalisation of arable land use is useful to explain the changes of arable land use in China.

Based on data sources (e.g., SPOT-5 images, 1:1 million topographic maps, distribution maps of returning farmland to forest and Chongqing forest project, social and economic statistics information, etc.) this paper identified the characteristics and influencing factors of farmland marginalization. The results indicated that: (1) During the last 10 years (2002-2012), the rate of farmland marginalization was 16.18% in the study area. This phenomenon was mainly found in high mountainous areas of northern Qiyao mountain and middle mountain areas of southern Qiyao mountain. Moreover, farmland marginalization, to a great extent, will increase, associated with non-agriculturalization of rural labors and aging of remaining labors. (2) Elevation, relative distribution radius from village and road connection degree had a greater influence on farmland marginalization in the study area. Farmland marginalization rate showed an increasing trend with the increase of elevation, and 60.88% of the total farmland marginalization area is found at an altitude above 1000 m asl. The marginalization trend for slope and distribution radium was similar with altitude. (3) Farmland area per labor and average age of farm labor were major driving factors of farmland marginalization. Farmland transfer and small agricultural machinery sets affected the farmland marginalization in the aspects of management and productivity efficiency. (4) Farmland with "comparative disadvantage dominated marginalization" accounted for 55.32% of the total farmland marginalization area, followed by "location dominated marginalization"(33.80% ). (5) According to the specific real situation, different policies are suggested to mitigate the marginalization as follows: "continuous marginalization" policy will further exert the impact of returning farmland to forest on "terrain dominated marginalization"; "anti-marginalization" policy is suggested from arranging new rural residence and improving rural road system for "location dominated marginalization"; while "anti-marginalization" policy is planned from improving management and micro-mechanization point of view for "comparative disadvantage dominated marginalization". A new idea was promoted by integrating high resolution remote sensing and statistical data as well as survey information to identify land marginalization and driving forces in mountainous areas, and hence solved the scale problem on patches and villages.

利用SPOT-5 影像、1：1 万地形图、退耕还林和森林工程图、社会经济统计等数据，分析了重庆市石柱县耕地边际化的特征和发生原因。结果发现：① 10 年间研究区耕地边际化率16.18%，主要分布于七曜山的北部高山区和南部中山区，而且伴随农村劳动力的非农化和留守劳动力的老龄化，边际化在很大程度上还会加剧。② 海拔、地块相对村庄的分布半径和道路连接度对耕地边际化的发生影响较大。边际化率随海拔升高而增加，特别是≥1000 m集中边际化的60.88%，在坡度和地块相对村庄的分布半径上也有类似规律。③ 劳均耕地面积和务农劳均年龄是影响耕地边际化的主要因素，耕地流转和微型农机台数是从适度规模经营、提高劳动生产率上影响耕地边际化。④“比较劣势主导边际化”分布最广，占总边际化的55.32%，其次是“区位主导边际化”，占33.80%。⑤“地形主导边际化”实施类似退耕还林继续扩大的“顺边际化”政策，“区位主导边际化”从合理安排新居点、完善农村道路体系上实施“反边际化”，“比较劣势主导边际化”从提高适度规模经营、微型机械化程度上开展“反边际化”。

Changes of rice production in Southern China are crucial to national food security. This study employed Landsat images to map the distributions of paddy rice cropping systems in Southern China in 1990 and 2015, and then explored the impact of rice multiple cropping index changes on grain production capacity. The results indicated that: (1) From 1990 to 2015, the multiple cropping index of rice decreased from 148.3% to 129.3%, and the loss area due to conversion of double cropping rice to single cropping rice ("double to single") was 253. 16×104 hm2. The area with most dramatic changes was located in the Middle-Lower Yangtze Plain. The rice cropping systems in Southern China showed a change pattern of "double cropping rice shrinkage and single cropping rice expansion" from north to south. (2) From 1990 to 2015, "double to single" led to a reduction of 6.1% and 2.6% in rice production and grain production, respectively. Hunan and Jiangxi, located in the main rice producing areas, as well as Zhejiang with better economic development, had a large reduction in rice production due to "double to single", all exceeding 13%. (3) The grain production capacity of "double to single" paddy field is equivalent to that of 223.3×104 hm2 of newly reclaimed cultivated land. The equivalent newly reclaimed cultivated land is 54% of the total newly reclaimed cultivated land through the land consolidation project during 2001-2015, as well as 1.7 times the target of the newly cultivated land goal for the national land consolidation plan (2016-2020). Making full use of the "double to single" paddy field can save approximately 167.44 billion yuan newly reclaimed cultivated land costs. Therefore, instead of pursuing low-quality "new" arable land, it is better to make full use of the existing high-quality "old" arable land. The government should change the assessment method of cultivated land balance, and incorporate the sown area increased by improving multiple cropping index into the cultivated land compensation indicator.

中国南方地区水稻生产的变化对国家粮食安全具有重要影响。本文利用Landsat数据提取1990-2015年南方地区水稻种植制度分布及变化,并分析其对粮食产能的影响。结果表明：① 1990-2015年,水稻复种指数从148.3%下降到129.3%,双季稻改种单季稻（“双改单”）损失的播种面积为253.16万hm²,区域上以长江中下游地区变化最为突出。南方地区水稻种植制度整体呈现由北向南“双退单进”的变化格局;② 1990-2015年,“双改单”导致全国水稻产量减少6.1%,粮食产量减少2.6%。水稻主产区湖南省和江西省以及经济发展较好的浙江省因“双改单”水稻减产幅度较大,均超过13%;③ 充分利用“双改单”稻田的粮食产能相当于新增耕地223.3万hm²,为2001-2015年通过土地整治项目新增耕地总量的54%,是2016-2020年全国新增耕地规划目标的1.7倍,可节省约1674.4亿元新增耕地开垦费用。因此,与其追求低质量的“新”耕地,不如充分利用已有的高质量“旧”耕地,政府应转变耕地占补平衡的考核方式,将因提高复种指数增加的播种面积纳入补充指标。

<p>More and more farmland has been abandoned in many developed countries since the 1950s, and then the abandoned land further evolved into a global land use phenomenon, which deeply changed the landscape in vast rural areas. "Land use change-driving mechanism-impacts & consequences-policy response" in global farmland abandonment were reviewed and the results indicated that: (1) Farmland abandonments mainly occurred in developed countries of Europe and North America, but the extent to which varied distinctly. (2) Socio-economic factors were the primary driving forces for the farmland abandonment. And land marginalization was the root cause of land abandonment, which was due to the drastic increase of farming opportunity cost, while the direct factor of abandonment was the decline of agricultural labor forces. (3) Whether to abandon, to what extent and its spatial distributions were finally dependent on combined effect from the physical conditions, labor characteristics, farming and regional socio-economic conditions at village, household and parcel scales. Farmland abandonment was more likely to occur in mountainous and hilly areas except for Eastern Europe due the unfavorable farming conditions. (4) Ecological and environmental effects should be the focus on the study of farmland abandonment, while which is positive or negative are still in dispute. (5) The increase of agricultural subsidies indeed will be conductive to slow down the farmland abandonment, but it is not the only and reasonable method.</p> <p>Due to rapid urbanization in China, there will be a high probability of abandonment expansion in the near future. However, few researches focused on this rapid land-use trend in China, leading to inadequate understandings of dynamic mechanism and consequences of this phenomenon. Thus, in the end of the paper, some directions of future research in China were presented: regional and national monitoring of abandonment dynamics, trend and risk assessment, social-economic effects assessment and informed policymaking.</p>

20世纪后半叶以来许多发达国家发生明显的耕地撂荒现象,并逐渐演变为全球性土地利用现象,深刻地改变了广大农村地区土地景观.本文以"土地利用变化--驱动机制--环境效应--政策响应"的框架系统梳理耕地撂荒主要研究进展.研究表明:① 全球耕地撂荒仍主要发生在欧美发达国家,但发展程度的区域差异很大;② 社会经济要素变化是耕地撂荒最主要驱动力,务农机会成本上升等原因引起的耕地边际化是撂荒发生的根本原因,而劳动力析出是造成耕地撂荒的直接原因;③ 耕地撂荒与否,撂荒程度以及撂荒地空间分布受村镇,农户,地块三个尺度的自然条件,劳动力特征,农业生产条件和区域社会经济条件等多方面因素的综合影响;④ 生态环境效应是当前撂荒效应研究的焦点,但该效应是以积极还是消极为主仍存争议;⑤ 增加农业补贴是当前减缓耕地撂荒的主要措施,但并非唯一和最合理的措施.未来,快速城镇化进程将促使中国耕地撂荒现象愈演愈烈,所以当前研究有待加强,本文认为应加强大范围耕地撂荒信息提取和监测,撂荒趋势预测和风险评估,社会经济效应评估及政策设计等方面研究.

Cropland abandonment is spreading from developed countries to developing countries such as China. Cropland abandonment in China commonly occurs in mountainous areas due to their specific natural and geographical conditions. However, due to the lack of dependable monitoring methods via medium-high-resolution remote sensing images, the scale of abandoned cropland in many mountainous areas of China is unclear, and the mechanisms driving cropland abandonment have not been clearly identified. To overcome these limitations, we took Zhong County of Chongqing in China as an example, and used Landsat 8 OLI_TIRS remote sensing image data to develop a method for mapping abandoned cropland in mountainous areas based on annual land use change monitoring. At the same time, the ridge regression method was adopted to analyze the factors influencing cropland abandonment. These analyses showed that the cropland abandonment rate in Zhong County of Chongqing was as high as 7.86%, while the overall accuracy of identifying abandoned cropland was as high as 90.82%. Among the social and economic factors that affect cropland abandonment, the rural population, economic development, and livestock husbandry development were the most important ones. At the land parcel scale, large-scale cropland abandonment occurred in areas at elevations above 650 m or with slopes of more than 15°.

This paper aims to examine the plot quality characteristics of abandoned terraces in the mountainous areas of Southwest China and explore the key influencing factors that trigger the abandonment of the terraces. To further clarify the driving mechanism of the abandonment of terraced fields in mountainous areas and find ways to sustainable use of terraced fields, this paper takes Baidu Village, Jianhe County, Guizhou Province as the research area. Based on the survey data of farmers and the high-resolution UAV image data, we have an in-depth exploration of the scale of abandonment of terraced fields in mountainous areas, the spatial distribution of abandoned terraces, and the quality characteristics of plots. Then, through the construction of a binary Logistic regression model, quantitative analysis is carried out on the effect of the quality factors of each area on the abandonment of terraces. The results show that: (1) The sample terraces of Baidu Village are mostly concentrated in areas with relatively large cultivated height differences, steep slopes, and relatively long tillage distances, and the area of terraces contracted by the sample farmers is 62.518 hm2. The abandoned terraces cover an area of 21.354 hm2, and the abandonment rate is 34.16%. (2) The dominant factor affecting the abandonment of terraces among the quality characteristics of terraces is the perfection of irrigation facilities; the second factor is the use of mechanical power; the third factor is the degree of ridge collapse; the fourth factor is the cultivated area; the fifth factor is the comprehensive topographical conditions. Among them, the perfection of irrigation facilities, the use of mechanical power, the size of farming area and the abandonment of terraced fields are all negatively correlated, and the degree of ridge collapse and comprehensive topographical conditions are positively correlated with the abandonment of terraced fields. The research results have important theoretical and practical significance for promoting the sustainable use and management of terraced fields in the mountainous areas of southwest China.

为分析西南山区梯田撂荒地块质量特征及影响因素,厘清山区梯田撂荒与可持续利用机制,本文以贵州省剑河县白都村为例,综合运用农户调查数据与无人机高分辨率影像数据探讨梯田的撂荒规模、空间分布情况及地块质量特征;构建二元Logistic回归模型,对影响梯田撂荒的各地块质量因素作用大小进行定量分析。结果表明：① 白都村样本农户的梯田面积为62.518 hm²,多集中分布于耕作高差、坡度和耕作距离较大区域,其撂荒面积为21.354 hm²,撂荒率为34.16%。② 梯田的地块质量因素对其撂荒的贡献程度表现为：灌溉条件>动力使用状况>田埂坍塌状况>耕作面积>综合地形条件,其中灌溉条件、动力使用状况、耕作面积与梯田撂荒均呈负相关,田埂坍塌状况和综合地形条件与梯田撂荒呈正相关。研究结果对于推进西南山区梯田的可持续利用与管理具有重要的理论及实践意义。

Faced with a crisis of growing food demand, the Chinese government has taken drastic steps to safeguard the nation’s farmland and promote intensive land-use. However, China's rapid urbanization and high economic growth have caused significant negative effects on agricultural production. Farmland abandonment has become a general phenomenon in China directly impacting total agricultural production. Here, we analyzed spatial and temporal variation of farmland abandonment in China from 2002 to 2013 with data from the Chinese Household Income Survey (CHIP). Logit modeling was used to capture the main factors that led to this phenomenon. We found that during this period, the ratio of farmland abandonment rises from 0.32%~5.72% in China. Farmland shrinkage caused by “Forest transition” is unavoidable in China. At a regional level, farmland abandonment rates in middle, eastern and western China are 0.81%, 6.91% and 7.65% respectively. The health condition of the householder, total farmland area of the household and agricultural income of the household are the most crucial impact factors determining farmland abandonment. Bad health and large farmland area will induce farmers to idle their farmland and increasing agricultural income will prompt them to take full advantage of farmland. The farmland transfer in plain areas is effective for facilitating farmland use and preventing farmland abandonment, but is not significant in mountain areas. The policy implication here is establishing an intermediary platform for farmland transfer at the grass-roots level to impel farmland transfer in plain areas and agricultural scale management at a national level.

耕地闲置已经成为中国的普遍现象,这与中国政府耕地集约利用的主张相违背,也直接影响到农业产量。本文利用中国家庭收入调查（CHIP）数据分析了2002&#x02014;2013年中国闲置耕地的时空变化特征,采用Tobit模型探讨了影响耕地闲置的主要因素。结果表明：①2002&#x02014;2013年间,中国闲置耕地比例从0.32%上升到5.72%,可能无法避免&#x0201c;森林转型&#x0201d;引致的耕地在空间上收缩现象,从区域上看,东中西部闲置耕地占耕地总面积的比例分别为0.81%、6.91%与7.65%;②全国层面上,户主的健康状况、家庭耕地总面积、家庭农业收入成为农户耕地闲置与否的最关键因素。户主健康恶化与较多的耕地面积均会促使农户闲置耕地,而家庭农业总收入的增加能起到促进农户充分利用耕地的作用;③平原地区的土地流转能有效利用耕地资源,防止土地闲置,而在山区土地流转对耕地闲置的影响不明显。建议积极建立基层的土地流转中介平台,以推动平原地区的土地流转与全国层面的农业规模经营。

Cropland abandonment is the main land-use change in mountainous areas globally. It has profoundly altered rural land-use structure,agricultural landscapes,and farmer livelihoods in mountainous areas and has huge environmental and socioeconomic impacts. Since 2000,with the rapid rise in labor costs and the exodus of the rural labor force,croplands in China’s mountainous areas have been facing a greater risk of abandonment due to rough terrain and slow development of agricultural mechanization. Case studies and reports have increasingly demonstrated that cropland abandonment in these areas is severe. Considering that sloping croplands account for about 25% of total croplands in China,cropland abandonment is not only related to informed policy-making regarding land use and sustainable rural development in mountainous areas,but possibly has a significant negative impact on food security. Quantitative analyses of cropland abandonment at a national level in China have not been performed. Hence,in this study,a large-scale survey was carried out to estimate the extent of cropland abandonment in mountainous counties to offer a scientific basis for relevant policy-making and further study of cropland marginalization. The results show that 78.3% of 235 surveyed villages have experienced cropland abandonment to some extent. During 2014-2015,the abandonment rate of croplands in mountainous counties was 14.32%,showing a distribution pattern of “south-high and north-low” at the provincial level. The abandonment rate for the Yangtze River Basin was the highest,while that for the northeastern mountainous area was the lowest.

耕地撂荒是当前全球山区主要的土地利用变化现象,它深刻地改变了山区农村土地利用结构、农业景观和农户生计,并带来了巨大的生态环境和社会经济效应。2000年以来,随着中国劳动力成本的快速上升和农村劳动力的大量析出,中国山区农业因地形限制,机械化发展受阻,耕地面临着较大的撂荒风险。越来越多的案例研究和报道表明中国山区耕地撂荒现象越演越烈。中国山区面积广、坡耕地比重大,耕地撂荒不仅关系到山区农地的合理利用政策和山区可持续发展政策的制定,并可能引起粮食安全问题,但目前仍缺少全国层面的定量化评估研究。因此,本研究通过开展大范围的抽样调查对中国山区县撂荒规模进行了推算,以期为相关政策制定以及耕地边际化进一步研究提供参考。研究结果表明,在235个调查村庄中,78.3%的村庄出现耕地撂荒现象;基于县样本统计的2014-2015年全国山区县耕地撂荒率为14.32%;山区耕地撂荒率在省级尺度上呈现出南高北低的空间格局,其中,长江流域一带的山区耕地撂荒率最高,东北的长白山区最低。

At present, China’s food security situation is grim because cultivated land is the basis of food security, but abandoned cultivated land has become a common phenomenon of land use change. This study used the panel data of household survey in China to analyze the change of cultivated land use behavior and influencing factors of farming households that contracted cultivated land from 2010 to 2016, and examined the probability change and regional difference from the perspectives of explicit abandonment and implicit abandonment. The results show that: First, cultivated land contracted by farmers experienced both explicit and implicit abandonments. Implicit abandonment is relatively large, but the phenomenon of abandonment in the future will gradually decrease. Second, in terms of consistency, investment in seeds, pesticides, and fertilizers, and the implementation of agricultural subsidy policies have significant inhibitory effects on land abandonment, but their marginal effects will be reduced. Land expropriation will prompt farmers to choose land abandonment, which has a negative long-term effect. Third, the influencing factors of explicit and implicit abandonments are different. Explicit abandonment is significant in hilly areas. The scale of cultivated land and the strategy of returning the grain plots to forestry and grass can reduce the probability of implicit abandonment for farmers. Natural hazards will cause explicit and implicit land abandonment, the marginal effect of natural hazards on explicit abandonment will be reduced, but the marginal effect on implicit abandonment will increase. Last, in terms of spatial differences, it is still possible that the cultivated land in the economically developed areas will experience an explicit abandonment, and the main grain-producing areas may continue to experience an implicit abandonment. In the future, it is necessary to formulate and improve relevant land and agricultural policies, continue to increase agricultural investment, carry out large-scale land transfers, and so on in order to solve the problem of farmland abandonment.

现阶段中国的粮食安全问题严峻,耕地是保障粮食安全的基础,耕地撂荒已成为影响粮食安全的土地利用变化现象。本文采用中国家庭追踪调查数据,分析2010—2016年承包耕地的农户耕地利用行为的变化影响因素,着重从显性撂荒和隐性撂荒两个角度研究其概率变化及区域差异。研究发现：①农户承包的耕地同时存在显性和隐性撂荒现象,隐性撂荒比例较大,但未来撂荒的现象均将逐渐减少;②一致性方面,种子农药化肥投入、农业补贴政策等对撂荒的抑制作用显著,但其边际效应都将减小;土地征用会促使农户选择撂荒,存在负面的长程作用;③显性和隐性撂荒的影响因素有差异,丘陵地貌区显性撂荒显著,耕地规模化和退耕还林还草补贴能减少农户隐性撂荒的概率;自然灾害发生将会导致显性和隐性撂荒,但自然灾害对显性撂荒影响的边际效用减少,对隐性撂荒影响的边际效应却增加;④在空间差异上,经济发达区域的耕地发生显性撂荒的概率仍较大,粮食主产区继续发生隐性撂荒的概率较大。未来应制定和完善相关土地制度和农业政策,继续加大农业投资和大规模开展土地流转等解决耕地撂荒难题。

Cropland abandonment has increasingly occurred in China, which potentially affects national food and ecological security. This study collected existing publications focusing on cropland abandonment. Then, we extracted the key characteristics of cropland abandonment events, including time, location, magnitude, and driving force. The meta-analysis was carried out on these items to disclose the spatio-temporal pattern and main drivers of cropland abandonment in China in the last three decades. We found that there were a total of 163 counties in which cropland abandonment occurred according to the existing literature. These counties were mostly located in southern China and, in particular, exhibited a pattern of a T-shape on 90 degree anticlockwise rotation. The vertical axis exhibited a north-south belt across southeastern Gansu Province, eastern Sichuan Province, Chongqing, western Guizhou Province, and northern Yunnan Province. The horizontal axis exhibited a west-east belt along the middle to lower reaches of the Yangtze River across southern Hubei Province, northern Hunan Province,w and central to southern Anhui Province. In the provinces of Hunan, Sichuan, and Anhui, cropland abandonment can be found in 24, 23, and 21 counties, respectively; in Hubei, Chongqing, Fujian, Gansu, and Yunnan provincial-level areas, there are more than 10 counties with cropland abandonment. The formation of the “T” structure underwent two stages. Before 2010, there were 102 counties with cropland abandonment that mainly existed along the middle to lower reaches of the Yangtze River, where the horizontal axis occurred. Since 2010, there have been 63 counties with cropland abandonment, mostly existing in the north-south belt from southeastern Gansu to northern Guizhou, where the vertical axis occurred. The spatio-temporal patterns of cropland abandonment events matched well with the labor emigration from agriculture in the context of regional economic development and industrial restructuring. The low economic efficiency of agriculture and the shortage of agricultural labor are two common drivers leading to cropland abandonment in 86% and 78% of counties, respectively.

当前耕地撂荒已成为一种日益普遍的土地利用变化现象,对粮食安全和生态环境具有重要影响。为揭示1992-2017年中国耕地撂荒的时空特征及驱动机制,采用集成分析的思路,对县（市）域尺度撂荒的研究成果进行了汇总梳理,从中提取撂荒时间、位置、规模（程度）、成因等信息,并进行了荟萃分析。结果发现：1992-2017年全国范围内有撂荒记录的县（市）共165个,主要分布于南方,集中分布区呈逆时针旋转90°的“T”字型,纵轴自北至南贯穿甘肃东南部、四川东部、重庆境内,直至贵州西部和云南北部;横轴位于长江中下游地区,自西向东贯穿湖北、湖南、安徽、江西。其中,湖南、四川、安徽有撂荒记录的县（市）数量较多,分别为24个、23个、21个,其次是湖北、重庆、福建、甘肃、云南,均超过10个。“T”字型结构的形成经历两个阶段,大致以2010年为界,此前有撂荒记录的县（市）为102个,集中分布于沿长江中下游的东西向带状区域,形成横轴;此后新增63个县（市）,集中分布于自甘肃东南部至贵州西部和云南北部地区的南北向带状区域,形成纵轴。撂荒格局的形成过程与区域经济发展和产业结构调整背景下的农业劳动力析出基本同步。农业收益低和劳动力不足分别是86%和78%的县（市）撂荒形成的共性因素。

China is one of the most populous countries in the world. Like other developing countries, huge population and its rapid growth are intensifying food insecurity. Cropland intensification driven by the government and rural households plays a key role in food production and provision at national level. However, since the implementation of reform and opening up, more and more rural workers have shifted to non-agricultural industries. Meanwhile, the wage increase rate of the ordinary labor in China is much higher than that of the prices of farm produce and also faster that of agricultural means of production. The increasing off-farm migration and rising wage make the shares of farm income in the total family income decline even further. So farmers' pursuance has turned from maximizing the output of land to maximizing the income of labor force with the development of market economy. The wage rise and the change of farmers' goal have exerted a great effect on agricultural land use in some parts of China, especially in the developed provinces of eastern China, which is mainly embodied in two aspects: decreases of multi-cropping index and labor input. Meanwhile, due to the high labor productivity, the agricultural restructuring with more vegetables, tea and fruit trees has been very apparent. And the spatial-temporal expansion of this trend will continue for a long time. To ensure grain production, the national grain subsidy programme introduced in 2004 has achieved initial targets, so future work and potential development in this field should be done to encourage scale management of farmland.

Terracing, developed in those large mountainous areas with high pressure of dense population, is believed as one of the most effective land use approaches. Based on the geographical and climatic differences, the various types of terraces are widely distributed and highly evaluated in terms of ecological and cultural values around the world. Since ancient times, humans have used terracing practices for intensive agricultural production. The main objective of terracing is for mitigating water erosion, stabilizing hill slopes, improving site conditions and crop productivity. During the last decades, agricultural land use in the world has changed considerably. Terraces in many regions were abandoned and had resulted in increasing soil erosion, slope collapse and land degradation along with the socioeconomic development. In this study, through summarizing the origin, history and distribution of terraces in different geographical regions and environmental conditions around the world, we discussed how the different historical and environmental contexts such as climate change, public policy, demographic migration and economic change affected the cycles of terracing construction, usage and abandonment. Aiming at maintaining the sustainable use and mana-gement of terraced fields, further studies regarding water management and terrace maintenance needed to be enhanced.

梯田是在大面积多山地形和较高人口密度条件下产生的山区土地高效利用方式,广泛分布于世界各地,并且在不同的地理气候条件下产生了不同的类型,具有重要的生态价值和文化价值.梯田作为陡坡耕作区古老的土壤保持措施,有利于农业集约化,一般而言,梯田建设的目的是为了保持水土,减少产流产沙,改善立地环境,便于农业生产.在当前社会经济发展的背景下,大面积的梯田遭到荒废,不仅浪费了土地资源,还易导致严重的土壤侵蚀、坡面坍塌和土地退化.本文综述全球不同地理区域和自然环境条件下梯田的起源、发展以及分布特征,主要选择亚洲、欧洲、美洲和非洲四大重点区域进行系统介绍,并针对每一大洲内的典型国家做了案例剖析.在此基础上,深入探讨梯田建设、利用和荒废过程与气候变化、国家政策、人口变迁等因素的关系,最后针对目前梯田区存在的水资源紧张和梯田荒废退化两个严重问题,提出了尚需开展的研究工作,以期为梯田的可持续利用与管理提供参考依据.

With the rapid development of urbanization and the continuous loss of the rural labor force, large areas of farmland have been abandoned in some regions of China. Remote sensing technology can indirectly help to detect the size and quantity of abandoned farmland, which is of great significance for the protection of farmland and food security. Using Qingyun and Wudi counties of Shandong Province as the study area, and based on the Landsat data and HJ-1A data, this paper uses the CART decision tree classification method to develop land use maps from 1990 to 2017, set down rules to identify abandoned farmland, and explore the spatial distribution, duration, and reclamation area of abandoned farmland. The results showed that the accuracy of the CART decision tree classification was higher than 85% from 1990 to 2017. The maximum abandoned farmland area was 5503.86 hm2 from 1992 to 2017, and the maximum abandonment rate was 5.37%. The rate of farmland abandonment reached the peak from 1996 to 1998, and the overall trend of abandonment has decreased year by year after 2006. The maximum duration of abandonment was 15 years during the period of 1992 to 2017. Most of the durations were within four years and a few durations were more than ten years. From 1993 to 2017, the maximum reclamation area of abandoned farmland was 2022.3 hm2, and the minimum reclamation area was about 20 hm2. The maximum reclamation rate was 67.44% and the annual average reclamation rate was 31.83%. The results from this paper not only help analyze the driving forces of farmland abandonment in the study area, but also provide references for the identification of abandoned farmland in other areas.

由于城镇化的快速发展和农村劳动力不断流失,中国部分地区出现大面积的撂荒现象。利用遥感技术可以间接提取撂荒耕地的规模和数量,对耕地的保护和粮食安全有重要意义。以山东省庆云县和无棣县为研究区,基于Landsat数据和HJ1A数据,采用CART决策树分类方法,制作了1990-2017年的土地利用图,制定了撂荒地的识别规则,在此基础之上提取了研究区的撂荒地空间分布、持续撂荒时间分布和撂荒地复垦区域。结果显示：1990-2017年基准期影像的CART决策树分类精度高于85%;1992-2017年间,研究区撂荒地面积最大值为5503.86 hm²,最大撂荒率为5.37%,其中1996-1998年撂荒率最高,2006-2017年撂荒地面积的整体趋势逐年降低;1992-2017年间最大持续撂荒时间为15年,大部分耕地持续撂荒时间在4年之内,少数耕地持续撂荒时间超过10年;1993-2017年撂荒耕地复垦面积最大为2022.3 hm²,最小复垦面积约为20 hm²,复垦率最大值为67.44%,年均复垦率为31.83%。研究结果不仅能够为研究区撂荒驱动因素分析提供数据支撑,而且也可以为其他地区的撂荒耕地识别提供参考。

Farmland marginalization has become the main trend of land-use change in the mountainous areas of China. Using annual survey data of major agricultural production costs and earnings at national and provincial levels in China, this study aims to analyze the reasons and mechanism behind farmland marginalization in mountainous areas. We find that farmers on plains are able to reduce their per mu labor input effectively through intensive use of agricultural machinery, which has minimized the impact of the increase in labor price. However, it is extremely challenging for farmers in mountainous areas to use the same method owing to the rough terrain. Thus, per laborer farming area in these areas has increased relatively slowly, causing a widening gap in agricultural labor productivity between the two regions. With the rapid rise in labor costs since 2003, the marginalization of cultivated land in mountainous areas is evident. In 2013, the net profit of agricultural production in mountainous China fell below zero. Since 2000, the land-use and land-cover change in these areas was characterized by the reduction of farmland area, reforestation, and the enhancement of the NDVI value. The high correlation between the NDVI change rate and the ratio of change in farmland (r = -0.70) and forest (r = 0.91) in mountainous areas at provincial level further attests to the trend of farmland marginalization there. Finally, we summarize the mechanism of such marginalization against the backdrop of the rapid increase in the opportunity cost of farming and the rapid fall of agricultural labor forces in mountainous areas. This study contributes to a deep understanding of the development process of farmland marginalization and abandonment as well as forest transition in Chinese mountainous areas.