Spatiotemporal dynamics of land cover and their impacts on potential dust source regions in the Tarim Basin,NW China

Human-driven dynamics of land cover types in the Tarim Basin are able to affect potential dust source regions and provide particles for dust storms. Analyses about dynamics of potential dust source regions are useful for understanding the effects of human activities on the fragile ecosystem in the extremely arid zone and also provide scientific evidence for the rational land development in the future. This paper therefore selected the Tarim Basin, NW China, as a representative study area to reveal spatiotemporal dynamics of land cover and their impacts on potential dust source regions. The results showed that farmland, desert and forest increased by 28.63, 0.64 and 29.27%, while grassland decreased by 10.29% during 1990–2010. The largest reclamation, grassland loss and desertification were 639.17 × 10³, 2350.42 × 10³ and 1605.86 × 10³ ha during 1995–2000. The relationship between reclamation and grassland loss was a positive correlation, while a highly positive correlation was 0.993 between the desertification and grassland loss at different stages. The most serious dust source region was the desertification during 1990–2010 (1614.58 thousand ha), and the serious region was stable desert (40,631.21 thousand ha). The area of the medium and low dust source region was 499.08 × 10³ and 2667.27 × 10³ ha. Dramatic reclamation resulted in the desertification by destroying natural vegetation and breaking the balance of water allocation in various regions.     

The myth of community and sustainable grassland management in China

Within national and international domestic academic circles, there are increasing calls for enhanced involvement of communities in formulating and implementing grassland management arrangements. In contrast to the current national policy of contracting grasslands to households, many scholars call for support for collective grassland use arrangements. Several reasons are given for increased recognition and support for community-based management of grasslands, including lower costs of exclusion and dispute resolution, economies of scale in herding and marketing, mitigation of environmental risk, and ensuring equitable access to grassland resources. One conclusion from this literature is that devolving authority for designing and implementing grassland management systems to communities would lead to more sustainable grassland use, a position that I term as the ‘myth of community.’ This paper presents the results of a study of grazing systems in two communities in Hongyuan County, Sichuan Province. Each community uses its grasslands collectively. However, the study found evidence of severe overgrazing, especially in winter pastures, suggesting that community-based management of grasslands is not necessarily sustainable. The paper discusses three potential policy innovations required to support sustainable grazing systems in China’s grassland areas: overcoming constraints in labor and land markets, and payments for environmental services that reward sustainable stocking levels.     

Effect of prohibiting grazing policy in northern China: a case study of Yanchi County

The prohibiting grazing policy (PGP) of the government “one size fits all” achieved certain effects, but also brought a series of issues. This article used a case study in the middle north of China to focus on the comparative study of three different degrees of illegal livestock grazing management patterns formed after PGP. The causes and characteristics of the illegal behavior and the impact to grassland ecosystem, social, and economic system were studied. The results showed that resource endowments and interest driven were the main causes for illegal grazing. The eco-economic analysis of “continuous grazing” pattern was poor, whereas the “breeding zone” and “barn feeding” pattern were relatively good. Grassland use still has great potential, and management patterns need to change.     

Rangeland management and climate hazards in drylands: dust storms,desertification and the overgrazing debate

This paper examines the theory and supporting evidence for links between desertification, drought and dust storms with a particular focus on studies undertaken in and around the Gobi Desert. Overgrazing of rangeland by pastoralists has been the most commonly cited cause of desertification in global drylands for more than 30 years, but the evidence supporting this link is not always convincing. Nonetheless, overgrazing, desertification and dust storms are frequently connected, regardless. Drought is another well-known and important driver of vegetation cover change. Distinguishing between vegetation cover adversely affected by drought and that reduced by grazing is imperative for policy makers because identifying the incorrect driver of vegetation change risks the development of inappropriate policy.     

近10年西藏高原土地沙漠化动态变化与发展态势

依据生态基准面的理论制定了西藏高原沙漠化土地分类分级体系。运用遥感、野外调查与 GIS等方法,对20世纪90年代沙漠化动态变化进行了研究,研究结果表明：西藏高原沙漠化扩大 2151．68km 2,升级率达 2．3％,动态度为 0．154％,沙漠化程度明显加重,形成沙漠化发展、稳定及逆转三种类型区。高原沙漠化发展演化的内在驱动力是以气候为主的自然因素,外在驱动力则是人为的"三滥"活动。预测到2005年、2010年沙漠化仍将缓慢发展。西藏高原是我国沙漠化正在发展-强烈发展的区域,发展态势严峻。高原沙漠化防治的基本策略应是全面保护、综合治理、适度开发、协调发展。     

吉林西部生态系统退化评价

吉林西部是一个典型的自然、经济和社会的复合系统,生态环境脆弱,土地沙化、碱化严重.在分析该区环境的基础上,提出了生态系统退化度的概念.以长岭县为例建立了生态系统退化度评价指标体系,包括土地背景质量、生态环境现状、经济发展水平、生态破坏速度诸要素15项指标.运用RS、GIS和数据库管理技术建立了生态系统退化度研究数据库.采用层次分析法,开展了以乡为单元的生态系统退化度评价,用MapInfo软件绘制了生态系统退化度数字化图,为研究区的生态建设提供了科学依据.     

2000-2010年鄂尔多斯地区沙漠化动态及其气候变化和人类活动驱动影响的辨识

以2000-2010年近10 a来鄂尔多斯地区沙漠化过程为研究对象, 在利用MODIS数据对沙漠化动态进行监测的基础上, 综合分析沙漠化逆转和发展地区气候变化和人类活动引起的NPP变化趋势, 定量评估近10 a来鄂尔多斯地区沙漠化动态及其与气候变化和人类活动间的关系. 结果表明: 2000-2010年间, 尽管鄂尔多斯地区沙漠化面积没有明显变化, 但是沙漠化程度呈现整体逆转的态势, 其中逆转的沙漠化土地面积达47 057 km²(占鄂尔多斯地区土地总面积的54.2%), 比发展的沙漠化土地面积高出近3倍. 气候变化是近10 a来鄂尔多斯地区沙漠化逆转的主导因素, 主要归因于2006年来降雨量的增加以及近10 a来春季风速的减小, 围封禁牧、 退耕还林(草)等政策的实施及其与有利气候条件的耦合进一步加快了区域沙漠化的逆转. 人类活动是导致近10 a来鄂尔多斯地区沙漠化发展的主要因素, 主要归因于部分地区生态保护政策的落实不力以及区域资源开发引起的环境破坏, 完全由人类活动引起的沙漠化发展主要分布鄂尔多斯的北部地区.     

生态建设政策交易成本及其结构的比较

将交易成本分析引入沙漠化地区生态建设政策分析过程, 确定交易成本由搜寻信息成本、签订合约成本、建设及营运成本、监督对方是否违约成本、违约后寻求赔偿成本共5部分构成. 每个部分根据研究区域生态政策实施的关键节点进行指标分解, 设计政策交易成本分析的21个指标. 为了将不同生态政策之间的绩效进行对比, 构造了交易成本结构指数, 它由内生交易成本占总交易成本的比重、农户投入占生态建设项目生产成本的比重、交易成本占生态建设项目交易成本与生产成本之和的比重共3个指标构成. 根据在宁夏盐池县的调研数据, 测算退耕还林政策和天然林保护政策的交易成本分别为640.87元·hm^-2·a^-1和41.49元·hm^-2·a^-1, 交易成本结构指数值分别为0.1242和0.2292, 实施效果分别是很好和较好;"三北"防护林政策的交易成本为806.08元·hm^-2·a^-1, 交易成本结构指数值为0.4149, 实施效果一般;草地禁牧政策的交易成本为530.45元·hm^-2·a^-1, 交易成本结构指数值为0.8575, 实施效果很差. 生态政策的交易成本及其结构分析, 将为不同生态建设政策的比较和绩效评价提供一个新的角度, 具有重要意义.     

The effect of desertification on carbon and nitrogen status in the northeastern margin of the Qinghai-Tibetan Plateau

Environmental degradation resulting from desertification often accelerates biodiversity loss and alters carbon (C) and nitrogen (N) stocks within grassland ecosystem. In order to evaluate the effect of desertification on plant diversity and carbon (C) and nitrogen (N) stocks, species compositions and C and N contents in plants and soil were investigated along five regions with different degrees of desertification in the northeastern margin of the Qinghai-Tibetan Plateau (control, light, moderate, severe and very severe stages). The study showed: (1) species composition and richness changed significantly with the development of grassland desertification; (2) the aboveground biomass C and N contents in the control were 101.60 and 4.03 g m^?2, respectively. Compared to the control, the aboveground tissue C and N contents significantly decreased from light, moderate, severe to very severe stages. (3) The root C and N contents in the control in 0–40 cm depth are 1,372.83 and 31.49 g m^?2, respectively, while the root C and N contents in 0–40 cm were also declining from the control, light, moderate, severe to very severe stages. (4) Compared to the plant, the soil made a greater contribution for C and N distribution, in which the soil organic C and total N contents in 0–40 cm depth in the control are 20,386.70 and 3,587.89 g m^?2, respectively. At the same time, soil organic C and N contents also decreased significantly from the control to very severe stages. These results suggest that grassland desertification not only alters species compositions and leads to the loss of plant diversity, but also results in greater loss of organic C and N in alpine meadow, in which there is a negative effect on reducing greenhouse gas emission.     

Eco-environmental degradation and causal analysis in the source region of the Yellow River

Based on three phases of satellite-image data and field investigation results collected between 1976 and 1996, climate changes and intensity of human activity were studied for the time period to investigate the causes responsible for the region's environmental changes. The results show that, compared with the data for the 1970s, the eco-environment in the source region of the Yellow River degraded markedly from the 1980s to the 1990s. Degradation was most prominent from the mid-1990s onward, with significant degradation of high-cold grassland and high-cold meadow vegetation, and also a rapid expansion of desertification. The area of degraded vegetation increased from 24.5% in the 1980s to 34.5% of total grassland and high-cold meadow in the 1990s. The rate of land desertification increased from 3.96% in the 1980s to 34.72% in the 1990s. The main reasons for these changes include the intensity of overgrazing (which was very high), and the climate in this region which is becoming drier and warmer, resulting in a gradual degradation of the permafrost.     

Changes in soil organic carbon and its active fractions in different desertification stages of alpine-cold grassland in the eastern Qinghai–Tibet Plateau

In recent years, the desertification of alpine-cold grasslands has become increasingly serious in the Qinghai–Tibet Plateau in China, but it has not received the same amount of attention as has desertification in (semi)arid areas. Little is thus known about the change in soil organic carbon (SOC) during alpine-cold grassland desertification. To quantify the impacts of desertification on vegetation, SOC and its active fractions in alpine-cold grasslands, areas of light desertified grassland, medium desertified grassland, heavy desertified grassland, serious desertified grassland, and nondesertified grassland were selected as experimental sites in the eastern Qinghai–Tibet Plateau in China. The species number, height and coverage of vegetation were surveyed, and the soil particle fractions, SOC and SOC active fractions (including dissolved organic carbon (DOC), microbial biomass carbon (MBC), and labile organic carbon (LOC) were measured to a depth of 0–100 cm. The results showed that alpine-cold grassland desertification resulted in a significant reduction in vegetation cover, plant biomass, fine soil particles, SOC, DOC, LOC and MBC. The decreases in DOC, LOC and MBC were more rapid and apparent than were those in SOC, and the decrease in MBC was the most obvious among them. The rates of reduction in SOC concentrations accelerated as desertification progressed; most of the SOC was lost in the middle and later desertification stages, with lower losses during early desertification. The results indicate that active SOC fractions, particularly MBC, are more sensitive to desertification and can be used as sensitive indicators of desertification. Efforts to limit desertification and reduce SOC loss in alpine-cold grasslands should focus on early desertification stages and adopt strategies to prevent overgrazing and control the erosion of soil by wind.     

Changes in soil physical and chemical properties during reversal of desertification in Yanchi County of Ningxia Hui autonomous region,China

Using field surveys and laboratory analysis, soil physical and chemical properties were studied at a site exhibiting the reversal of desertification in Yanchi County of China’s Ningxia Hui autonomous region. The dominant soil particle size changed from coarse-fine sand to a combination of very fine sand and silt + clay, and corresponding levels of each soil nutrient increased. The content of coarse-fine sand (2–0.1 mm) was significantly and negatively correlated with soil nutrient contents, whereas nutrient contents were significantly and positively correlated with the contents of very fine sand (0.1–0.05 mm) and silt + clay (<0.05 mm). The increasingly fine soil texture and the nutrient enrichment both facilitated rehabilitation of desertified land. The silt + clay content contributed the most to the increasing soil nutrient contents, and thus appears to be the key factor in reversal of desertification. Soil nutrient concentrations in the bulk soil increased with increasing content of soil nutrients with different particle fractions, and there were significant positive correlations between them. The nutrients in all particle size classes jointly decided the effect of soil nutrient contents on the reversal process. Principal-components analysis (PCA) revealed that the soil quality tended to increase during the reversal process, and that nutrient factors were more significant than particle size (i.e., were the dominant factor that influenced soil quality). Available nutrients and soil organic matter (SOM) were the most important nutrient factors. Silt + clay were the most important particle factors.     

Evaluation of changes in ecological security in China’s Qinghai Lake Basin from 2000 to 2013 and the relationship to land use and climate change

Ecological security evaluation is an important way to identify the need for improvement in a watershed and to assess the degree of regional sustainable development. Using a driver–pressure–state–exposure–response model, a comprehensive system of ecological security indicators was developed, and it was demonstrated in a case study of the main ecological problems facing the Qinghai Lake Basin. Indicators of the status of the natural ecological environment, socioeconomic pressure, and the degree of environmental damage were chosen to develop the model, and comprehensively evaluated the basin’s ecological security in 2000, 2004, 2009, and 2013 to reveal changes in the ecological security in response to changing climate and land use. The overall ecological security of the basin improved from 2000 to 2013, with considerable restoration and reconstruction of the ecosystem. From 2000 to 2004, environmental deterioration increased slightly as a result of pollution caused by human activities, excess land reclamation for agriculture, land desertification, and grassland degeneration. However, the obvious effect of ecological protection policies, such as conversion of farmland into grassland and stall feeding of livestock instead of grazing, led to improvement of the ecological environment from 2004 to 2013. Ecological security in the basin increased with increasing precipitation during the study period.     

Quantitative assessment of the contributions of climate change and human activities on global grassland degradation

Grassland degradation received considerable concern because of its adverse impact on agronomic productivity and its capacity to provide goods and service. Climate change and human activities are commonly recognized as the two broad underlying drivers that lead to grassland degradation. In this study, a comprehensive method based on net primary productivity (NPP) was introduced to assess quantitatively the relative roles of climate change and human perturbations on worldwide grassland degradation from 2000 to 2010. The results revealed that at a global scale, 49.25 % of grassland ecosystems experienced degradation. Nearly 5 % of these grasslands experienced strong to extreme significant degradation. Climate change was the dominant cause that resulted in 45.51 % of degradation compared with 32.53 % caused by human activities. On the contrary, 39.40 % of grassland restoration was induced by human interferences, and 30.6 % was driven by climate change. The largest area of degradation and restoration both occurred in Asia. NPP losses ranged between 1.40 Tg C year^?1 (in North America) and 13.61 Tg C year^?1 (in Oceania) because of grassland degradation. Maximum NPP increase caused by restoration was 17.57 Tg C year^?1 (in North America). Minimum NPP was estimated at 1.59 Tg C year^?1 (in Europe). The roles of climate change and human activities on degradation and restoration were not consistent at continental level. Grassland ecosystems in the southern hemisphere were more vulnerable and sensitive to climate change. Therefore, climate change issues should be gradually integrated into future policies and plans for domestic grassland management and administration.     

Exploring the potential of community-based grassland management in Yanchi County of Ningxia Hui Autonomous Region,China: an application of the SWOT-AHP method

The study analyzed the prospects and challenges of community-based grassland management (CBGM) in Yanchi County of Ningxia Hui Autonomous Region, China, using the strengths, weaknesses, opportunities, and threats approach combined with the analytic hierarchy process. Preference data were used from three stakeholder groups, namely, community, government, and academia, all of which are very familiar with Yanchi County. Representatives of local communities and academia perceive that the strengths and opportunities for CBGM outweigh its weaknesses and threats. However, representatives of government agencies hold an opposite view, as they anticipate that threats associated with the CBGM approach have the highest weight. We suggest the CBGM be implemented firstly in small villages, and then promoted in larger areas in the future.     

Comparative studies of the distribution characteristics of rocky desertification and land use/land cover classes in typical areas of Guizhou province, China

The Huajiang and Hongfenghu demonstration areas represent typical karst landforms and rocky desertification landscapes in Guizhou, China. These were selected for a comparison of rocky desertification and land use cover. Based mainly on 5 m resolution Spot 5, remote sensing images, topographic maps (1:10,000) and land use maps, the intensity and extent of rocky desertification, and slope characteristics of the two areas were interpreted. Spatial overlay analysis was used to compare the land use/land cover (LULC) and rocky desertification within each. The results were compared using the concepts of rocky desertification occurrence (RDO) among LULC classes and the structure value of desertification land (SVDL). The results demonstrated that (1) the landforms and extent of rocky desertification in the two areas are significantly different and the proportion of very steep slopes is one of the reasons leading to large areas of rocky desertification; (2) the RDO and SVDL show significant differences between the two areas; also rocky desertification intensity in various LULC classes cannot be measured in terms of RDO. High RDO may occur in low-intensity desertification land, and vice versa; (3) the structural characteristics of rocky desertification among various LULC are consistent among the woodland, “bare land” and “other grassland” land use classes in the two areas, but sequence slight > moderate > intense is not consistent between the areas. For the rocky desertification control, the present authors consider that the spatial distribution differences of rocky desertification and LULC among areas with different landform types area combined with the intensity of rocky desertification should be used in designing appropriate measures for control of desertification and rehabilitation of land.     

猫跳河流域土地覆被变化及其驱动力定量研究

应用RS、GIS以及GPS集成技术,以黔中喀斯特地区的猫跳河流域为对象,研究了这一地区从1973—2002年间土地利用／覆被的变化过程,并利用典型相关分析法研究了形成这种变化的驱动因素。研究表明,从1973—1990年,猫跳河流域耕地、建设用地、有林地、水域以及裸岩地呈增长趋势,而灌木林和灌草地趋于减少,流域生态环境质量下降。进入20世纪90年代后,有林地、灌草地、建设用地、水域持续增加,灌草地总量变化不大,耕地总量和裸岩地减少,流域生态环境质量趋于好转。定量分析表明,1990年以前,驱动建设用地变化的因素是总人口的变化,1990年以后则是农业产值;1990年以前驱动耕地变化的是农业人口的增长,1990年以后则和粮食产量的提高有关。      

吉林西部平原土地利用动态变化的RS-GIS集成研究

近20年来,吉林西部平原生态环境显著恶化,土地盐碱化、沙化、草地退化严重制约该区的可持续发展。以往人们很少从土地利用/覆盖（LUCC）变化的角度去分析研究生态环境问题。应用1989、2001年的TM卫星影像数据和RS-GIS集成技术进行土地利用/覆盖的动态监测,遥感影像解译,采用空间信息叠加的方法提取土地利用动态变化和土地利用类型相互转化的信息,揭示了土地利用类型两增（耕地、盐碱地）三减（草地、水体、湿地）的变化规律,讨论了驱使土地利用类型转化的原因,提出了保护利用土地资源的建议。     

Eco-environmental change detection by using remote sensing and GIS techniques: a case study Basrah province, south part of Iraq

This study examines the temporal and spatial dynamics of eco-environment degradation processes and change detection as evident from land use survey datasets (1990–2003) for the Basrah province, Iraq was taken as a case. Using a combination of techniques of RS, GIS, and GPS, the study identifies five prominent eco-environment degradation processes, namely: desertification, secondary salinization, urbanization, vegetation degradation, and loss of wetlands. Rates of conversion were calculated and distribution patterns were mapped with the aid of GIS. The results suggest that wind erosion was the dominant cause of eco-environment degradation in more than half of the study area. Coupled with this were increases in salinization processes, affecting 17.6% of the land area in 2003. Overall, severe eco-environment degradation was noticed to be the dominant eco-environment degradation grade (61.9% of total area), followed by moderate eco-environment degradation (18.9% of total area) in 2003. Incorporation of both natural and anthropogenic factors in the analysis provided realistic assessment of the risk of land degradation. The study area, in general, is exposed to a high-risk of eco-environment degradation.     

Extracting desertification from Landsat TM imagery based on spectral mixture analysis and Albedo-Vegetation feature space

Land desertification has been a worldwide environmental problem. Desertification monitoring and evaluation are very important content in desertification context. Scientific and accurate evaluation of desertification can provide scientific basis for decision making in mitigating desertification. Because of the advantage of large amount of information, short cycle and broad scope of data, less restrictions on the human and material resources and so on, remote sensing has become an important technology to monitor land desertification in the past 30 years. Desertification is the most typical and serious form of desertification in China, especially in the oasis zone distributed along inland rivers or in the lower reaches of inland rivers in northwestern China. Quantitative evaluation of the current desertification remote sensing methods used is mostly obtained through the vegetation index and vegetation cover, to gain information on the extent of desertification. As the arid and semiarid sparse vegetation cover, soil and soil moisture on the most common vegetation index have a greater effect. First, based on the spectral mixture analysis model, three kinds of endmember consisting of vegetation, water and bare soil were selected. The image dimensionality was reduced by the minimum noise fraction (MNF). The pixel purity index transformation was used to narrow the range of the endmember. On the scatter plot of MNF, three kinds of endmember were selected, and relative abundance distribution of each component was obtained by using linear spectral mixture model. Second, a spectral feature space composed of vegetation component and land surface albedo retrieved from Landsat TM Imagery was constructed to evaluate desertification present condition and degree quantificationally. Last, an empirical study was carried out taking the middle reaches of Heihe River as an example. Results indicated that this method makes full use of multi-dimensional remote sensing information, reflecting the desertification land cover, water, thermal environment and its changes, with a clear biophysical significance, and the index is simple, easy to obtain, high precision, and is conducive to quantitative analysis, monitoring and desertification assessment of desertification. It was rather ideal to assess desertification on the basis of Albedo-Vegetation feature space: correct prediction proportion of testing samples reached 90.3 %. This method was beneficial to the desertification quantitative analysis and monitoring with the characteristics of simple index, easy accessibility and high accuracy.