Impacts of Sloping Land Conversion Program on the vegetation in loess hilly and gully area of northern Shaanxi

Aiming at alleviating the serious soil erosion, the Chinese government initiated the Sloping Land Conversion Program （SLCP） in 1999. Now; after 8 years of project implementation, the ecological recovery effects of the SLCP have become the hot issue of academic circle. This paper; raking the loess hill and gully area of northern Shaanxi as an example, presents a methodology for assessing the vegetation restoration effect of SLCP with normalized difference vegetation index （NDVI）. The key components include calculation of the Growing Season NDVI （GSNDVI）, and estimation of the NVDI change induced by climate and SLCP, respectively. Based on the method, the NDVI change between 2000 and 2006 was obtained using the GSNDVI that excluded the noise from snow and ice. After the part of total NDVI change caused to： climate variation was estimated using empiric formulae, we obtained the part induced by human factors, i.e. the SLCP The human induced part of ND VI change was considered as an approximation indicating the effect of the SLCP on the vegetation. Finally, we analyzed the ND VI change characters of the whole study area, different slope lands and different land use types by spatial statistics method. Results show that the vegetation condition is significantly improved by the SLCP, particularly land types that directly involved in the SLCP, such as steeply slope farmlands, degraded grasslands, etc.

Land-use changes in the small watershed of the Loess Plateau,hilly-gully region, China

As more and more farmland is converted to forestry, the need for effective decision support regarding the use of land in the fragile ecological environment of the Loess Plateau hilly-gully area. The Luoyugou watershed was chosen as the study area to calculate the single dynamic degree, integrated dynamic degree, and change indexes of land use, as well as the land-use type transition matrix. This was done by interpreting the TM and SPOT images of the Luoyugou watershed in 1986, 1995, and2004 and making statistical analysis. The results of ou statistical analysis show that the conversion of slope farm land to terrace and forest land plays a dominant role in land-use changes in the Luoyugou watershed from 1986 to2004. The land-use changes are mainly driven by popula tion growth, socio-economic development, consume spending, and investment in forest ecology.

Soil erosion types in the loess hill and gully area of China

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Dynamic Land Use /Cover Change and Analysis of Landscape Pattern in the Hilly and Gully Region of Loess Plateau: A Case Study of Pengyang County in Southern Ningxia

The quantitative evaluation on land use /cover change as well as its influence on landscape pattern under the background of returning grain plots to forestry is significant to the sustainable utilization of land resources and ecological environment reconstruction in the southern Ningxia.Based on multi-temporal remote sensing data from four periods of Landsat TM /ETM,and combination of ecological quantity analytical method with GIS,the change of land use /cover and landscape pattern in Pengyang County of Ningxia Province were analyzed.The conclusions showed that the amount of each land use type was changed with different degrees,the area of forest /grass land increased,while farmland and unused land decreased.The change of landscape pattern was characterized as that the degree of landscape fragmentation,mixed distribution of patches,diversity index and evenness index increased gradually and then decreased,the connectivity between patches decreased gradually and then increased,and landscape shape presented irregular.

The characteristics of gully erosion over rolling hilly black soil areas of Northeast China

In this study,short-term gully retreat was monitored from the active gullies selected in representative black soil area,using differential global positioning system(GPS).With the support of geographic information system(GIS),multi-temporal digital elevation models(DEM) were constructed from the data collected by GPS and used for further analysis.Based on the analysis of multi-temporal DEM,we discussed the erosion-deposition characteristics within gully and a developing model for black soil gully area of Northeast China was proposed.The results are:(1) The analysis of the monitored gully data in 2004 indicated that the retreat of gully head reached more than 10 m,gully area extended 170-400 m2,net gully eroded volume 220-320 m3,and gully erosion modulus 2200-4800 t?km?2?a?1.(2) Compared with the mature gully the initial gully grows rapidly,and its erosion parameters are relatively large.The erosion parameters have not only to do with flow energy,but also with the growth phase.(3) There are significant seasonal differences in gully erosion parameters.The extension of gully area and width dominates in winter and spring without marked net erosion while changes mainly occur in gully head and net erosion in rainy season.(4) It is remarkable for freeze-thaw erosion in the black soil area of NE China.The gully wall of SG2 extended 0.45 m under freeze-thaw effect in 2004,and the distance of gully head retreated maximally 6.4 m.(5) Due to freeze-thaw action and snowmelt,gully is primarily in the interior adjustment process in winter and early spring.There are much more depositions compared with that during rainy season,which can almost happen throughout the gully,while erosion mostly occurs near head,esp.for gullies having a relatively long history of development.On the other hand,the process of energy exchange with exterior dominates in rainy season.It is considered that this cyclic process is an important mechanism for gully growth in high latitude or/and high attitude regions.

A comparison between different ecological de-farming modes in the loess hilly-gully region in China

The eco-environmental restoration has been a chief task of the western development strategies carried out by the central and local governments of China since the late 1990s, and the ecological de-farming has been regarded as a powerful measure for the ecological restoration in the Loess Plateau and the upper reaches of the Yangtze River. "Relieving and de-farming" (RD) and "rebuilding terrace and de-farming" (RTD) are two more mature ones among various de-farming modes. Taking the loess hilly-gully region as a case, this paper summarized the basic characteristics of RD and RTD modes, calculated the sizes of de-farming slope farmland, rebuilt terraces, enlarged garden plots and restored vegetation, and compared the differences of two modes in terms of de-farming area, ecological reestablishment index, investment demand amount and benefits. The results showed that RTD mode has many advantages, including suitable investment, sufficient grain supply and great benefits, and will be the best ecological reestablishment mode in the loess hilly-gully region, and RD mode which is being carried out in this region should be replaced by RTD mode as soon as possible.

Characteristics of Soil Respiration of Terraces and Slope Farmland in Loess Hilly and Gully Regions

Soil CO_2 emissions of terraces and slope farmland in loess hilly and gully regions were measured by using Infra Red Gas Analysis(IRGA),and the diurnal variation characteristics of soil respiration rate in different slope positions of terraces and slope farmland were analyzed.The results show that the diurnal variation curves of soil respiration rate of terraces and slope farmland in loess hilly and gully regions had a single peak.The soil respiration rate of terraces reached the peak during 13:00-15:00,while the soil respiration rate of slope farmland reached the peak from 11:00 to13:00,and it was the lowest at next 07:00.The daily average of soil respiration rate in slope farmland was 0.86μmol/(m^2·s),accounting for 93.48% of that of terraces.The daily average of soil respiration rate in different slope positions of terraces and slope farmland is shown as follows:the bottom of the slope>the middle of the slope>the top of the slope.At the top of the slope,the daily averages of soil respiration rate in terraces and slope farmland were the same;at the middle and bottom of the slope,the daily average of soil respiration rate in terraces was larger than that of slope farmland.

SOC Vertical Distribution Pattern of Economic Plants in the Loess Gully Areas of China

Three economic plants from the loess gully areas in China to explore the changing vertical distribution characteristics of soil organic carbon.The results showed that:(1) with the increase of depth,the average SOC content of economic plants decreased from 13.98 to 1.39 g/kg on the 0-100 cm soil profile,in the form of a power function;(2) the constructed depth spatial distribution models for different plants could help accurately assess the spatial distribution pattern of soil organic carbon;(3) compared with traditional agricultural planting,the carbon sink function for walnut and grape at a soil depth of 100 cm increased by 92.8±8.98 t/hm^(2) and 45.7±7.7 t/hm^(2),respectively.The adjustment of agricultural planting structure increases the content of soil organic carbon,and economic plants are of great significance to enhance the carbon sink function of the agricultural ecosystem in the loess gully area.

The effects of land use and its patterns on soil properties in a small catchment of the Loess Plateau

Due to relatively strong human activities in the hilly area of Loess Plateau, the natural vegetation has been destroyed, and landscape pattern based on agricultural land matrix was land use mosaic composing of shrub land, grassland, woodland and orchard. This pattern has an important effect on soil moisture and soil nutrients. The Danangou catchment, a typical small catchment, was selected to study the effects of land use and its patterns on soil moisture and nutrients in this paper. The results are as follows: The comparisons of soil moisture among seven land uses for wet year and dry year were performed: (1) the average of soil moisture content for whole catchment was 12.11% in wet year, while it was 9.37% in dry year; (2) soil moisture among seven land uses was significantly different in dry year, but not in wet year; (3) from wet year to dry year, the profile type of soil moisture changed from decreasing type to fluctuation-type and from fluctuant type to increasing type; (4) the increasing trend in soil moisture from the top to foot of hillslope occurred in simple land use along slope, while complicated distribution of soil moisture was observed in multiple land uses along slope. The relationships between soil nutrients and land uses and landscape positions were analysed: (1) five nutrient contents of soil organic matter (SOM), total N (TN), available N (AN), total P (TP) and available P (AP) in hilly area were lower than that in other areas. SOM content was less than 1%, TN content less than 0.07%, and TP content between 0.05% and 0.06%; (2) SOM and TN contents in woodland, shrub land and grassland were significantly higher than that in fallow land and cropland, and higher level in soil fertility was found in crop-fruit intercropping land among croplands; (3) soil nutrient distribution and responses to landscape positions were variable depending on slope and the location of land use types.

Mechanism of formation of sliding ground fissure in loess hilly areas caused by underground mining

Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.

An applied research on remote sensing classification in the Loess Plateau

Dae to complex terrain of the Loess Plateau, the classification accuracy is unsatisfactory when a single supervised classification is used in die remote sensing investigation of the sloping field. Taking the loess hill and gully area of northern Shaanxi Province as a test area, a research was conducted to extract sloping field and other land use categories by applying an integrated classification. Based on an integration of supervised classification aad unsupervised classification, sampling method is remarkably unproved. The results show that the classification accuracy is satisfactory by the method and is of critical significance in obtaining up-to-date information of the sloping field, which should be helpful in the state key project of converting farmland to forest and grassland on slope land in this area. This research sought to improve the application accuracy of image classification in complex terrain areas.

The effect of land use structure on the distribution of soil nutrients in the hilly area of the Loess Plateau,China

The irrational land use is one of the main reasons for the soil erosion and nutrient loss in the loess hilly area of China. In this project, 4 types of typical land use structure of sustain ment for about 15 years in the loess hill slope are selected to study the effect of land use structure on the distribution of soil nutrients. From hill bottom to hill top, the patterns of land use types are:, grassland-slope farmland-forest, slope farmland-grassland-forest, terrace-grassland-forest and slope farmland-forest-grassland. By measuring the contents of the total N, total P, available N, available P and organic matter of soils, the results show that the land use structure types of slope farmland-grassland-forest and terrace-grassland-forest have a better capacity to maintain the soil nutrients.

Structure and governance model of rural social space quality:A case study of Longxi County in the Loess Hilly Area of China

The rural social space quality is an important indicator to measure the living standard and thinking ideas and so forth of rural residents in a certain region.In this paper,213 administrative villages in Longxi County of the Loess Hilly Area,China are taken as evaluation units to construct the evaluation model of the rural social space quality.This paper deeply analyzed the variation patterns and their formation mechanism of the rural social space quality at a village scale,and proposed a governance model based on the rural social space quality.The results show that:(1)the social space quality levels of individual administrative villages show a gradually decreasing trend from the township seats to outward.The eastern part of Longxi County has a relatively high education level and living standard,and the western part has a relatively high population stability level and income level.(2)The rural social space quality is mainly in a ring structure,supplemented by the interlaced structure.The core area is the towns and their surrounding areas,while the transition area,marginal area,and other areas are expanded around the core area.(3)Social forces and spatial effects jointly shape the variation of the rural social space quality.Social organizations provide a driving force for the allocation of elements,and interweaving with the spatial effects lead to the differences in the social space quality.(4)The governance models of the rural social space quality are constructed based on the principles of retaining the rural“people”,optimizing the rural“land”,and developing the rural“industry”,so as to improve the rural centripetal force,core force,inner thrust,and source power.

黄土丘陵沟壑区粉砂壤土崩解性能变化及其影响因子试验研究——以王茂沟小流域为例

土壤崩解是土壤可蚀性的重要表征指标,在阐明土壤侵蚀机理和构建侵蚀模型方面起着重要作用。尽管目前有关植物根系对土壤崩解的研究取得了一定的进展,但是土壤崩解受到根系和土壤理化性质的双重影响,而有关根系和土壤理化性质对土壤崩解的协同作用仍缺乏深入量化研究。以王茂沟小流域5个土地利用下的原状土样作为研究对象,基于崩解试验测定土壤崩解参数,并分析其与根系和土壤理化性质的相关性及主控因子,量化土壤崩解的变化机制,得到如下结论:(1)综合崩解速率、崩解比速率和崩解量三个崩解指标,不同土地利用下,土壤的崩解性均呈现出草地<坡耕地<梯田<果园<坝地;(2)利用VPA分析和偏最小二乘路径分析,解释了土壤理化性质和根系特征及其协同作用对土壤崩解性的贡献并分析其量化关系。结果表明,含根土体中,根系对土壤崩解的直接效应强于间接效应,其直接贡献为16%,较土壤理化性质(16.4%)偏低,但较两者的协同效应偏高62.5%。不同土地利用下,土壤崩解性能的变化主要以土壤理化性质直接影响为主;(3)Spearman相关分析和RDA分析表明,与土壤崩解相关性最高的根系因子为RLD,土壤因子为粉粒,所有环境因子中以RLD的效应最强。不同土地利用下,影响土壤崩解性能的主控因子也存在差异。研究结果可为黄土丘陵沟壑区生态建设条件下的土壤崩解研究和侵蚀机理的解析提供参考,对于黄土高原生态脆弱区的生态修复和生态功能的维持具有重要意义。

基于APSIM模型的不同降水年型灌溉制度对春小麦产量和水分利用效率的影响

为提高甘肃陇中黄土丘陵沟壑地区旱地春小麦的产量和水分利用效率,本研究在定西市安定区凤翔镇安家沟村设立了试验区,根据该地区长期的气象和灌溉实验数据,采用APSIM(Agricultural Production Systems sIMulator)模型和DPS(Data Processing System)软件进行动态模拟,分析了6种灌溉情景下春小麦的产量和水分利用率,并对产量与灌水量进行拟合分析,以确定最佳灌量。研究发现,在仅考虑高产的情况下,干旱年200.00 mm处理产量最大;在正常年和润水年,150.00 mm处理产量最大。综合考虑高产与灌溉水利用效率的情况下,干旱年、正常年和润水年的最适灌水量分别为194.33 mm、185.43 mm和174.75 mm,对应产量提高率和水分利用效率分别提高了184.88%和10.69 kg/(hm^(2)·mm)、152.58%和11.36 kg/(hm^(2)·mm)、111.99%和12.00 kg/(hm^(2)·mm)。因此,合理灌溉对于提升农业生产效益具有重要意义。

黄土丘陵沟壑区不同雨强下坡面侵蚀空间异质性及其机理

[目的]明晰野外坡面侵蚀沉积精细时空分布特征及水动力学参数间的联系,以深入坡面侵蚀产沙过程的认识。[方法]以黄土丘陵沟壑区辛店沟流域自然坡面的3个径流小区(5 m×1.5 m)为研究对象,分别在90,120,150 mm/h雨强下进行连续10场降雨试验,同时结合地基三维激光扫描技术,研究坡面侵蚀沉积时空特征,探讨不同坡段水力学参数变化特征及其与坡面侵蚀率、产沙率的关系。[结果](1)随着雨强的增大,坡面侵蚀加重,以D,E坡段较为严重,沉积减小且分散,以E坡段最为明显;侵蚀面积而言:90,150 mm/h下,B坡段最大,C坡段次之,D坡段最小;120 mm/h雨强下,B坡段最大,D坡段次之,C坡段最小。(2)连续降雨作用下,水力学参数影响坡面粗糙度变化,坡面粗糙度又反作用于水力学参数,致使水动力学参数出现波动变化,当土体逐渐饱和达到稳定的入渗,水动力学参数逐渐趋于稳定;同一雨强下,距离坡顶长度与雷诺数、弗劳德数、单位径流功率成正比,与径流剪切力、Darcy-Weisbach阻力系数成反比。(3)90,120 mm/h雨强下,径流功率是侵蚀过程中重要的水动力学参数,Darcy-Weisbach阻力系数和单位径流功率认为是坡面产沙过程重要的水动力学参数,皆为线性函数关系;150 mm/h雨强下,水动力学与侵蚀率、产沙率无关。[结论]在不同雨强下,坡面侵蚀与水动力学参数之间的关系存在差异,其中径流功率、Darcy-Weisbach阻力系数和单位径流功率是自然坡面产沙过程的重要参数,且二者呈线性关系。

Geodetection analysis of the driving forces and mechanisms of erosion in the hilly-gully region of northern Shaanxi Province

This paper analyzes the spatial variation in soil erosion in the loess hilly-gully region of northern Shaanxi Province, China. It sums up existing research, describes the factors that drive soil erosion, and uses geodetection to investigate the factors individually and in pairs.Our results show that soil erosion in the loess hilly-gully region of northern Shaanxi is mainly hydraulic erosion. There are significant spatial differences in the severity of soil erosion in the region. Generally, it is more severe in the north and west and less severe in the south and east. Individual factor detection results show that the major risk factors affecting soil erosion are human population distribution, precipitation, land-use type, elevation, and soil type. Interactive detection results show that interacting factors play much bigger roles in soil erosion than do individual factors. Based on forced detection results from different periods of time, we can see that forest and grass coverage, urbanization, and economic development in the study area all clearly inhibit soil erosion.

Critical slope gradient for compulsory abandonment of farmland on the hilly Loess Plateau

Scientific evidence for the upper limit of farmland is proposed. Shallow gully erosion is one of erosion types distributed extensively on sloping farmland in the hilly regions of the Loess Plateau. Field observation and aerial photos interpretation, as well as laboratory experiments show that the shallow gully erosion occurring on the steeper farmland in the hilly regions of the Loess Plateau is an important factor leading to intensive erosion on slope, because of its extensive distribution and intensive runoff collection. The data on the formation, development and distribution of shallow gullies on sloping farmland indicate that critical slope gradient for shallow gully initiation ranges from 15 to 20 degrees with an average of 18.2 degrees. Therefore, it is suggested that critical slope gradient for compulsory abandonment of farmland on the hilly Loess Plateau should be kept within the critical slope gradient for shallow gully initiation to prevent shallow gully formation in order to control soil loss more effectively. But as the first step, the cultivation on the slopes with slope larger than 25 degrees where the maximum erosion occurs should be strictly forbidden.

罗玉沟流域水沙变化趋势及影响因素

[目的]探讨小流域水沙变化趋势及影响因素,为黄土高原丘陵沟壑区水土流失治理和水土保持措施布设提供参考依据。[方法]采取Spearman秩次相关检验方法、累积距平法和双累积曲线法等对黄土丘陵沟壑区罗玉沟流域1986—2016年降水量、径流量和输沙量变化趋势和演变过程进行分析。[结果](1) 1986—2016年罗玉沟流域年降水量趋势性变化不显著;流域年径流量和年输沙量变化具有明显的阶段性,以1993年为界,年径流量和年输沙量呈显著降低趋势。(2)降水和水土保持措施影响罗玉沟流域年径流量和输沙量,不同降水水平年,降水和水土保持措施对流域水沙变化的影响不同,水土保持措施使流域枯水年份径流量和输沙量减少最为显著。(3)水土保持措施对年径流量和年输沙量的减少贡献率分别为83.50%和80.97%。[结论]降水量变化不显著的情况下,水土保持措施对罗玉沟流域年径流量和年输沙量的减少起主导作用,水土保持综合治理对枯水年径流量和输沙量的影响幅度最大。

Eco-environment Restoration and Regional Differentiation Characteristics Based on “Building Terrace and Returning Slope Farmland to Forests and Grass”

Based on the scientific and technological achievements in the past decade in the Loess Hilly-gully Region and the successful demonstration experience in Yan'an Yangou watershed, we summarize the characteristics of eco-environment restoration pattern based on "building terrace and returning slope farmland to forests and grass". According to the data on land use, slope farmland and the agricultural population in 1999, we calculate the area of new terrace that needs to be built, the area of garden plot that needs to be extended, vegetation restoration area and investment demand in counties (cities, districts). Establishing and using some indicators, such as basic farmland extension indicator, garden plot extension indicator, vegetation restoration index and investment demand density, we conduct type classification and analysis of regional differentiation characteristics in 55 counties (cities, districts). The results show that in the Loess Hilly-gully Region, 691 600 hm2 of new terrace needs to be built, 792 000 hm2 of economic forests and orchards need to be extended, 5 410 200 hm2 of vegetation needs to be restored, and the total investment demand is 15.82 billion yuan; in terms of geographical distribution, obviously there are two key areas for eco-environment restoration (one is located in the border area between northern Shaanxi and northwestern Shanxi, and the other is located in the eastern Gansu and southern Ningxia area); the classified regional guidance policies should be formulated as soon as possible, and the limited funds should be concentrated in the key areas.