Sandy Desertification Research Articles

Assessment of the spatial dynamics of sandy desertification using remote sensing in Nemamcha region (Algeria)

Sandy Sandy desertification is considered one of the environmental problems in the pre-desert and steppe ranges of Algeria. In order to reveal the spatial dynamics of sandy desertification, a multivariate linear equation was used to assess the relationship between spectral data of Landsat images and ground-surveyed soil samples. The multivariate models were used to estimate sand, silt, and clay percent, and the USDA textural triangle classification was used to specify soil texture by applying the limits of the textural variables in a GIS environment. The statistical analysis showed a strong correlation between blue, SWIR 1, SWIR 2, sand, silt, and clay contents. The results showed that the sandy loam are the most widely distributed soil textural class 52% and 42% in 2013 and 2019, respectively. Furthermore, spatial change detection results between 2013 and 2019 illustrated that 12% of the entire study area have suffered signs of desertification that have a negative change of soils to sandy and loamy sand. The soil indices indicate a strong relationship with the top soil sand content, and the NDVI values varied between 0.06 and 0.44 in 2013 and −0.01 and 0.3 in 2019, indicating a severe regression in vegetation conditions over time. Thereafter, land cover and land use analysis show the severity of land degradation and the irreversibility of sandy desertification, agriculture land decreased from 31% in 2013 to 4% in 2019, pasture land decreased from 21% to 13%, bare land increased from 22% to 36% and sandy land increased dramatically from 26% to 47%.

Long-term mowing and burning have more of an effect on soil fungal communities than on bacteria in a semiarid sandy land

Mowing and burning, two common human disturbance methods, have different impacts on the soil fungal and bacterial communities of sandy land ecosystems in semiarid areas. Thus, the effects of long-term mowing and burning on plant and soil microbial communities in the semiarid Horqin Sandy Land are unclear. In this study, the effects of soil microbial community structure from mowing and burning on plant and soil microbial communities over six years were assessed by high-throughput sequencing. First, we found that mowing and burning significantly reduced vegetation coverage (V) (p < 0.05), and burning significantly increased plant Shannon–Wiener diversity (H), Pielou evenness (E), and Simpson dominance (λ) indices (p < 0.05). Second, the two human disturbances markedly affected fungal diversity and abundance more than bacterial diversity and abundance. In fungi, burning significantly reduced beta diversity (p < 0.05) and the relative abundance of Basidiomycota (p < 0.05) but markedly increased the relative abundance of Ascomycota and Mortierellomycota. Third, redundancy analysis (RDA) showed that vegetation coverage was a significant factor in bacterial species distribution (p < 0.05). For fungi, the significant factors were species richness (S) and vegetation coverage (p < 0.01). Taken together, these data suggest that long-term mowing and burning have more of an effect on soil fungal communities than bacteria in a semiarid sandy land, improving our understanding of how terrestrial ecosystems respond to human disturbances and providing guidance for the management and restoration of sandy desertification.

An over review of desertification in Xinjiang, Northwest China

Desertification research in arid and semi-arid regions has always been actively pursued. In China, the problem of desertification in Xinjiang has also received extensive attention. Due to its unique geography, many scholars have conducted corresponding research on the desertification status of Xinjiang. In this paper, we comprehensively reviewed desertification in Xinjiang, and compared the underlying mechanisms of desertification and the status of desertification conditions after the implementation of ecological control projects. On a larger scale, desertification in Xinjiang can be divided into soil salinization inside oases and sandy desertification on the edges of oases. Human activities are considered the main cause of desertification, but natural factors also contribute to varying degrees. Research on the mechanisms of desertification has effectively curbed the development of desertification, but unreasonable use of land resources accelerates the risk of desertification. For desertification control, there are several key points. First, desertification monitoring and the early warning of desertification expansion should be strengthened. Second, monitoring and reversing soil salinization also play an important role in the interruption of desertification process. It is very effective to control soil salinization through biological and chemical methods. Third, the management of water resources is also essential, because unreasonable utilization of water resources is one of the main reasons for the expansion of desertification in Xinjiang. Due to the unreasonable utilization of water resources, the lower reaches of the Tarim River are cut off, which leads to a series of vicious cycles, such as the deterioration of ecological environment on both sides of the river and the worsening of desertification. However, in recent years, various desertification control projects implemented in Xinjiang according to the conditions of different regions have achieved remarkable results. For future studies, research on the stability of desert-oasis transition zone is also significantly essential, because such investigations can help to assess the risk of degradation and control desertification on a relatively large scale.

Spatial Distribution Pattern and Natural Causes Analysis of Sandy Desertification Land in Ali Area

In order to explore the spatial distribution pattern and natural causes of the sandy desertification land in the Ali area, on the basis of clarifying the dynamic change laws of sandy desertification land areas, sandy desertification degree and spatial distribution pattern, the main controlling factors of sandy desertification land distribution are analyzed from three aspects of landform, climate and vegetation. During the 22 years from 1992 to 2014, the sandy desertification land area in the Ali area shows a law of first increase and then decrease, reaching a peak of 61,054.14 km2 in 2004, accounting for 20.57%, and decreasing to 60,892.65 km2 in 2014, accounting for 20.51%, which do not return to the level of 1992. Sandy land desertification is mainly slight and moderate, accounting for 53.29% and 45.73%, respectively, in 2014. Sandy desertification land in the Ali area is mainly distributed among intermountain basins, river valleys, lake basins, piedmont plains and other landform units. The landform and wind speed are the main natural factors that determine the spatial distribution pattern of sandy desertification land in the Ali area, that is, the spatial distribution pattern of sandy desertification land in the Ali area is the coupled result of sand source and wind speed.

Sand-fixation plantation type affects soil phosphorus transformation microbial community in a revegetation area of Horqin Sandy Land, Northeast China

Revegetation is an effective approach for comprehensive control of sandy desertification. Different sand-fixation plantations may vary in protection function, the improvement of soil properties, and the re-formation of soil microbial community because of the differences in the biological and ecological attributes of plant species. However, few studies have focused on the response of soil P-cycle-related microbial community to sand-fixation plantation type. This study aimed to (1) compare the effects of different sand-fixation plantations on soil properties, (2) investigate the compositions and structures of P-transformation-involved microbial communities under different plantations, and (3) analyze the relationship between soil properties and P-transformation microbial communities. Soil samples of six 36-year-old plantations, i.e., Hedysarum fruticosum, Salix gordejevii, Caragana microphylla, Artemisia halodendron, Populus simonii, and Pinus sylvestris var. mongolica, were taken in Horqin Sandy Land, Northeast China. The compositions of soil phoD- and gcd-harboring microbial communities were detected using high-throughput Illumina MiSeq sequencing. Plantation type had significant effects on soil pH, nutrients, P fractions, and biological activities, thereby affecting the structures of phoD and gcd communities. The abundance of phoD gene was hundreds of times more than that of gcd, and it significantly varied with plantation type. The dominant phoD taxa included Cyanobacteria, Proteobacteria, Planctomycetes, and Actinobacteria phyla or Scytonemataceae, Nostocaceae, and Isosphaeraceae families, while Proteobacteria and Rhizobiaceae were the absolutely dominant gcd taxa. Many N fixers (belonging to Rhizobium, Mesorhizobium, and Bradyrhizobium) may have the abilities for P transformation depending on phoD or/and gcd. Plantation and soil properties significantly affected the quantities of dominant taxa and slightly affected the basic compositions of phoD and gcd communities. Soil pH and available P were the main factors affecting the structure of phoD community, while that of the gcd community was mainly affected by soil pH and NH4-N. The mixture of shrub and semi-shrub plantations is recommended to restore vegetation on moving sand dune in the Horqin Sandy Land.

Factors controlling spatio-temporal variations of sandy deserts during the past 110 Years in Xinjiang, Northwestern China

Xinjiang, northwestern China, has the largest area of sandy desert landscapes in the northern hemisphere mid-latitudes and is known to be subject to so-called sandy desertification. Longer-term records of changes in the distribution of sandy desert landscapes are required to develop a more comprehensive understanding of mechanisms underlying their spatial and temporal dynamics. Here, we integrate a diverse range of data sources, including historical maps, documentary accounts, government statistics, remote sensing data, global climate reanalysis data, and field reconnaissance data, to reconstruct 110 years of spatial variations in sandy desert distribution in Xinjiang. Our results show that, overall, there has been a 22.3% reduction in the area of sandy desert in Xinjiang over the past 110 years. Cross-wavelet and linear regression analyses reveal that vegetation changes are the major determinants of sandy desertification during this period and that, in contrast to previous studies in the region, aeolian factors and human-induced degradation are less important drivers than previously reported. Ecosystem management has markedly constrained sandy desert expansion even against a background of population increase. The suggested comprehensive approach may be useful in improving understanding of sandy desert dynamics and associated desertification forcing mechanisms in arid and semiarid regions globally.

Comprehensive Analysis of Ecological Restoration Technologies in Typical Ecologically Vulnerable Regions around the World

Ecosystem degradation is a key issue facing the world. Rapid economic development has been achieved at the cost of degradation and environmental pollution, which has affected human well-being, particularly in fragile ecosystems. To achieve the United Nations sustainable development goals, it is essential to develop technologies to control degradation and restore ecosystems. However, a comprehensive assessment of the different types of degradation, of the methods used in different regions, and of the differences between regions has not been carried out. In this study, we examined databases of international organizations, interviewed experts to evaluate existing methods based on five dimensions, identified restoration technologies (hereinafter referred to as RTs) suitable for different types of degradation, and summarized the restoration effectiveness in different regions. We found 101 RTs around the world and found that the same technology can be applied in different regions. The RTs were dominated by engineering and biological RTs, accounting for 19.2–26.7% and 33.4–34.7% of the total, respectively. 45, 30, and 26 RTs were suitable for controlling soil erosion, sandy desertification, and degraded ecosystem, respectively. The average evaluation index of RTs for controlling these degradation problems are 0.81, 0.78, and 0.73, respectively meaning RTs used to fight soil erosion are more effective. The potential to transfer a technology to other regions and the readiness of the technologies were low for degraded ecosystems, and the ease of use was high for sandy desertification RTs. Although a given technology could be applied to different regions or degradation types, results varied. Our study will help ecosystem managers to deal with specific degradation issues, phases, and severities, and will support the transfer of RTs among regions.

Spectral Analysis of Sandy Desertification in the Semi-Arid Zone of North Eastern Nigeria

The method of integrating remote sensing, Geographic Information System (GIS) and field survey was employed. Assessment of the rate and intensity of sand dune encroachment using multi-temporal Landsat images (Landsat.TM, 1986, Landsat.ETM, 2000 and Landsat.OLI, TIR, 2016) and GIS. The satellite images were processed by converting raw Digital Number (DNs) values to radiance images which were converted into reflectance images used for spectral analysis.The satellite images were processed accordingly for evaluating six (6) spectral indices; Crust Index (CI, Grain Size Index, Bare soil Index (BSI), Normalized Difference Sand Dune Index (NDSDI), Normalized Difference Sand Index (NDSI), Normalised Difference Soil Index (NDSLI). An aggregate index of each of the six (6) selected indices was evaluated and the long term geometric mean was determined and used for image differencing with the baseline date image. A combination of MEDALUS.ESA and Image Differencing was adopted for change detection technique. Sandy landscapes were mapped into four (4) natural classes using natural jenks classifier of the ArcGIS analytical tool based on pre-field field determination and post verification. The description of the four (4) sandy landscape classes is as follows: Active, Semi-active, Semi-fixed and Fixed sand dune/sheets. Results of overall sandy desertification based on Aggregate Sandification Index indicates that active and semi-active sandy landscapes have progressed steadily at annual rate of expansion of 1.20 and 1.28 km 2 and intensity for the of 0.13 and 0.23% respectively. This has caused a corresponding decrease in the semi-fixed and fixed sandy landscapes of 1.24 and 1.39 km 2 and intensity for the period of 0.17 and 0.47 % respectively. The highest risk of sandy desertification is in the fixed sandy landscape which is be lost an an annual rate of 1.39 km 2 and 0.47% intensity being the highest among other classes. The result of this study indicates that the natural ecology or vegetation, graze lands, irrigated lands, rainfed farmlands, settlements, infrastructure are at high risk of sandy desertification in the semi-arid zone of Nigeria. This study is also a pointer that the shelter belts have not been very effective in controlling wind erosion and thus sandy desertification. Keywords: : desertification. sandification, eco-geomorphic landscape, semi-arid, encroachment DOI: 10.7176/JNSR/12-14-06 Publication date: July 31 st 2021

Field measurements of crestal flow direction and turbulent flow over two transverse dune ridges

Turbulent airflow is a fundamental factor that controls the geomorphology of sand dune systems, especially dune expansion and sandy desertification. However, little is known about turbulent air flow in dune systems, and this limits efforts to control dune expansion and sandy desertification. To obtain some of the missing information, we calculated the turbulent airflow characteristics over a transverse dune in the Tengger Desert in southeastern China. We found that the angle of airflow at the dune crest controls flow angles at middle of the dune's stoss slope and at the toe of the leeward slope, and also controls the turbulent flow characteristics over the dune surface. The critical wind direction was from the NW (wind directions ranged from 355° to 45° to the crest perpendicular line [CPL]) and SE (wind directions ranged from 65° to 165° with respect to the CPL), and about 20° and25° with respect to the CPL for northwesterly winds and southeasterly winds, respectively. The kinematic Reynolds' stress (RSk), streamwise turbulence intensity (CVu), and total kinetic energy (TKE) were largest close to the critical wind direction for winds from the NW, indicating that dune movement was mainly controlled by the critical wind direction. However, TKE, RSk, and CVu differed between southeast and northwest winds; for southeasterly winds, they were largest for wind directions from 65° to 115° with respect to the CPL and similar to the values for wind directions from 115° to 165° with respect to the CPL, indicating asymmetrical sand movement. We conclude that, for closely spaced transverse dunes, sand transport is controlled by the critical wind directions; this indicates that efficient control of sand movement and sandy desertification will benefit from sand-control structures that block airflow from the critical wind directions.

An improved approach to estimate sand-driving winds

Wind resource assessment has important economic and ecological implications. Many developing countries in arid and semiarid areas are caught in a dilemma between the development of wind energy and the threat of sandy desertification. Sand-driving winds are momentous for both generating wind energy and aeolian research. The estimation for the probability of sand-driving winds has been rarely studied. The ability of the two-parameter Weibull distribution to estimate high wind velocities is questioned and parameters appear to have no practical significance. Drift potential (DP) is a way of evaluating potential sand transport volume by sand-driving winds, but the relationship between DP and the wind energy of sand-driving winds has been rarely studied. In this paper, a function was constructed from the expressions of DP and the two-parameter Weibull probability distribution to improve the estimation of sand-driving winds. This is simple and applicable to arid and semiarid areas worldwide. The mean wind velocity and the mean wind power density at a height of 10 m around the Badain Jaran Sand Sea in China, are in the range between 2.64 and 4.79 m·s−1, and 27.61–165.61 W·m−2, respectively. The mean wind power density of sand-driving winds accounted for half or more of the total mean wind power density. The relationship among DP, the wind power density of sand-driving winds and the probability of sand-driving winds, was proved theoretically. Gentle winds and strong winds are distinguished by the drift wind velocity at which potential sand transport activities (potential lost wind power density) reach their maximum. The scale parameter dominates the mean and median wind velocity, and represents the effect of convection. The shape parameter characterizes the atmospheric stability. These results provide a basis for the wind energy development, improve the understanding of aeolian activities, and have implications for sand control engineering.

An improved model to estimate annual sand transport rate by sand-driving winds

Some of the surface on Earth, Mars, Venus, and Titan is covered by ripples, dunes, and other features formed by sand-driving winds. Many developing countries in arid and semiarid areas are caught in a dilemma between the threat of sandy desertification and the development of wind energy. The estimation for the probability of sand-driving winds has been rarely studied. The ability of two-parameter Weibull probability distribution to estimate sand-driving winds is questioned. Sand transport rate is used only for the evaluation of short-term aeolian activities. Drift potential (DP) is an accessible way of evaluating potential sand transport volume by sand-driving winds. However, the relationship among annual sand transport volume, DP and wind energy has been rarely studied. Sand-driving winds can be divided into gentle winds and strong winds, but it is hard to distinguish them and to quantify their effects on aeolian geomorphology. A function was constructed from expressions of sand transport rate and the two-parameter Weibull probability distribution to improve the estimation of sand-driving winds. On this basis, annual sand transport volume was accurately evaluated by sand-driving winds. This is applicable to arid and semiarid areas worldwide. The relationship among annual sand transport volume, DP and wind energy was analyzed from the perspective of dimensional analysis. Gentle winds and strong winds are distinguished by transport wind velocity at which aeolian activities on a sandy underlying surface reach the erosion–deposition balance, and which corresponds to annual maximum sand transport rate. On a sandy underlying surface strong winds control deposition, while gentle winds dominate wind erosion. The transport wind velocity is nearly constant, weakly related to the probability distribution of sand-driving winds. These results provide a basis for an improved understanding of aeolian activities as an important planetary surface process, sand control engineering, and wind energy development.

Desertification Control Practices in China

Desertification is a form of land degradation principally in semi-arid and arid areas influenced by climatic and human factors. As a country plagued by extensive sandy desertification and frequent sandstorms and dust storms, China has been trying to find ways to achieve the sustainable management of desertified lands. This paper reviewed the impact of climate change and anthropogenic activities on desertified areas, and the effort, outcome, and lessons learned from desertification control in China. Although drying and warming trends and growing population pressures exist in those areas, the expanding trend of desertified land achieved an overall reversal. In the past six decades, many efforts, including government policies, forestry, and desertification control programs, combined with eco-industrialization development, have been integrated to control the desertification in northern China. Positive human intervention including afforestation, and the rehabilitation of mobile sandy land, and water conservation have facilitated the return of arid and semi-arid ecosystems to a more balanced state. China’s practices in desertification control could provide valuable knowledge for sustainable desertified land management on a global scale.

High biomass production with abundant leaf litterfall is critical to ameliorating soil quality and productivity in reclaimed sandy desertification land

Long-term data regarding soil properties and crop growth are powerful resources substantially contributing to our knowledge of soil-forming processes of reclaimed sandy desertification land. Generalized ecological principles derived from long-term observations that help to maintain or improve soil quality and productivity is critical for guiding field management practices while suitable for newly reclaimed sandy desertification land still need to be evaluated. Here, a 14-yr old experiment showed that soil quality index (SQI) had an “increase-decline-recovery” tendency in irrigation and fertilizer addition desertification lands while it remained at constantly low levels in desertification land with only irrigation. Stably decent yield and net incomes were obtained after 3–4 years’ consecutive irrigation and fertilizer addition management. Correlation between crop productivity and SQI followed a saturation characteristic curve with threshold at 0.5, corresponding to soil organic carbon (SOC) ~5.0 g kg−1, below which crop productivity was linearly declined. 60% of observed inter-annual variations in SQI were explained by quantity of leaf litter, which was three times higher than explanatory power of root residue. No substantial changes occurred in soil mechanical components while the soil microbial biomass carbon, water-stable aggregate and heavy carbon pool in SOC were significantly improved by 2–9 folds in reclaimed desertification lands. Results revealed that increased biomass production with abundant residue retention is crucial for ameliorating soil quality, stabilizing high yield and economic gains, supporting the “High Biomass Cropping System” ecological hypothesis. Ecological limitations and opportunities to sustainable utilization of sandy desertification land were discussed.

Role and significance of restoration technologies for vulnerable ecosystems in building an ecological civilization in China

Degradation is a key issue facing the world, and the situation is particularly severe in China's vulnerable ecosystems, where sandy desertification, soil erosions by water and wind, and karst desertification are serious problems. China's 13th five-year development plan (2016–2020) prioritized the establishment of an ecological civilization to improve the country's ecological security. In this paper, we analyzed the contribution of ecological restoration technologies (ERTs) to achieving a selected number of ecological civilization targets (ECTs). It is found that there are altogether 17 ECTs defined for the regions under study, the total contribution of ERTs to ECTs is about 27.2%, with contribution to economic targets ranking the highest, followed by ecological, social, and environmental targets. The technologies contributed most to regions affected by soil erosion, followed by regions affected by karst desertification and sandy desertification. Biological technology was the most used restoration technology. These findings are significant for reviewing the effectiveness of restoration technologies, and their ability to achieve the ecological civilization goals.

Progress on Sandy Desertification Research and Future Combating Idea in Tibet, China

Progress on Sandy Desertification Research and Future Combating Idea in Tibet, China

Historical (1880s–2000s) impact of wind erosion on wetland patches in semi-arid regions: A case study in the western Songnen Plain (China)

Abstract The western Songnen Plain, which is located in a semi-arid region, is one of the most important cultivated regions in China, and it is subject to constant threats from sandy desertification due to wind erosion. Wetland patches between the desert and cultivated regions in the western Songnen Plain capture dust from desert regions and are influenced by regional wind erosion. To evaluate the degree of historical wind erosion and the impact of wind erosion on wetland patches in the western Songnen Plain, we selected four regions along a wind erosion gradient and analyzed the geochemical properties of soils in wetlands and their surrounding typical ecosystems. The results indicate that more dust and sand are deposited in the western wetland patches than in eastern wetland patches and that more than 50% of the soils in the western wetland patches are comprised primarily of sand. Wetland patches in the wetland/desert transitional region act as natural buffers that impede wind-driven desertification, and only 20% of the soils in eastern wetland patches comprise sand. Additionally, increasing farmland area and residential water consumption caused by human activities have also increased wind erosion in the eastern region. Increased wind erosion has caused eastern wetland patches to start capturing dust from surrounding farmland and grassland since the 1920s, and the accumulation rates of typical elements (i.e., Cu, Pb, Zn, P) increased obviously after the 1960s.

Remote Sensing Monitoring of Surface Characteristics in the Badain Jaran, Tengger, and Ulan Buh Deserts of China

Deserts and sandy land in northern China are very susceptible to sandy desertification and are the main source of sand-dust storms of Asian dust. However, because of the complex factors involved, descriptions of the relationship between sandy desertification and surface characteristics in these regions are lacking. We monitored the surface characteristics and their changes in time using information about soil, vegetation, and landforms in the Badain Jaran Desert (BJD), Tengger Desert (TD), and Ulan Buh Desert (UBD) in the northern China. The monitoring was done using tasseled cap angle (TCA), disturbance index (DI), and topsoil grain size index (TGSI) from Moderate Resolution Imaging Spectroradiometer (MODIS) images combined with a decision tree classification. Results showed that the TD had higher topsoil fine sand content, and the ratio of non-vegetated to vegetated areas was similar with that in the UBD. Northeast-southwest coarse sand dunes with thin interdune (NECTI) dominated the BD, fine sand dunes (FSD) dominated the TD, and a combination of northeast-southwest coarse sand dunes with wide interdune (NECWI) and northwest-southeast coarse sand dunes with wide interdune (NWCWI) dominated the UBD. From 2000 to 2015, in the BJD the area of the NECTI, non-sand dune (Non) and potential sand sources (PSS) increased, whereas the area of the NECWI, FSD and NWCWI decreased, indicating a improve process in the BJD. In the TD, the area covered by Non increased, whereas the area covered by PSS, NECWI, NECTI, FSD, and NWCWI decreased from 2000 to 2015. The area covered by the various surface characteristic types fluctuated annually in the UBD from 2000 to 2015. Changes in surface characteristics reflect the combined effects of natural conditions and human activity. The findings of our study will assist scientists and policy makers in proposing different management techniques to combat sandy desertification for the different surface characteristics of these regions.

Assessment of the Coordination Ability of Sustainable Social-Ecological Systems Development Based on a Set Pair Analysis: A Case Study in Yanchi County, China

Sandy desertification is one of the most severe ecological problems in the world. Essentially, it is land degradation caused by discordance in the Social-Ecological Systems (SES). The ability to coordinate SES is a principal characteristic of regional sustainable development and a key factor in desertification control. This paper directly and comprehensively evaluates the ability to coordinate SES in the desertification reversal process. Assessment indicators and standards for SES have been established using statistical data and materials from government agencies. We applied a coordinated development model based on Identical-Discrepancy-Contrary (IDC) situational ranking of a Set Pair Analysis (SPA) to analyze the change in Yanchi County’s coordination ability since it implemented the grazing prohibition policy. The results indicated that Yanchi County was basically in the secondary grade of the national sustainable development level, and the subsystems’ development trend was relatively stable. Coordinate ability increased from 0.686 in 2003 to 0.957 in 2014 and experienced “weak coordination to basic coordination to high coordination” development processes. We concluded that drought, the grazing prohibition dilemma and the ecological footprint were key factors impeding the coordination of SES development in this area. These findings should provide information about desertification control and ecological policy implementation to guarantee sustainable rehabilitation.

Changes of soil particle size fraction along a chronosequence in sandy desertified land: a fundamental process for ecosystem succession and ecological restoration

Soil is composed of particles of different sizes. A fraction of soil particles with different sizes has many vital effects on soil properties such as soil texture, soil porosity, and soil nutrient content. We intended to explore what change took place in soil particle distribution along the chronosequence of restoration and to address what implication this change has for ecosystem restoration. Six restoration ecosystem sites were selected to form a chronosequence in a sandy desertified region, northern China. We examined the relative content of soil particles with different sizes and established an index of enrichment ratio to reflect the change trend of soil particle size fraction. It was showed that soil substrate in this region is mainly composed of coarse sand (>0.25 mm) and fine sand (0.25–0.10 mm), the fraction of which are averagely 23.62 and 57.07 %, respectively. These characteristics make soil coarse, loose and erodible, and to be one of the reasons why sandy desertification was quickly developed in this region. In sandy desertification process, the grades of soil particles were air-classified. Fine sand was strongly enriched 1.36 times than average level, while very fine sand (0.10–0.05 mm) and silt and clay (<0.05 mm) were strongly diluted 0.14 and 0.22 times than average level, respectively. Along with the chronosequence of restoration, very fine sand and silt and clay were deposited and markedly enriched. This change in soil particle size fraction along the chronosequence has many fundamental roles for the subsequent restoration succession of sandy land ecosystem, such as promoting plant growth, strengthening soil anti-erodibility, leading to species replacement and community succession. From this research, it could be concluded that the response of soil particle size fraction to ecological restoration in sandy desertified lands is ecologically valuable, demonstrating that a positive cycle between plant and soil was formed to strengthen the stability of soil-plant system, and the ecosystem has the ability of self-recovering or self-organizing.

Causes and processes of sandy desertification in Guinan County, Qinghai–Tibet Plateau

By means of field investigations, interpretation of remote sensing images, analysis of a digital elevation model, and grain-size tests, we analyzed the causes and processes responsible for sandy desertification in Guinan County, on the Qinghai–Tibet Plateau. The desertified land is mainly distributed on the Mugetan region and covered 566 km2, about 96.1 % of which distributed on the sandy hills. We found that reactivation of the underlying fossil dunes supplied the sand that contributed to modern sandy desertification. The surface turf, which supports a dense growth of grass and its matted roots, covers the underlying cohesive silty sands in the sandy hills, and both layers protect the dunes against erosion. Mechanical destruction of the protective shell leads to exposure of fossil dune sands. The exposed loose fossil sands are then carried away by the wind, creating scarps, followed by lateral recession at the bottom of the scarp, leading to its collapse. The process then repeats. With the expansion of recession caused by wind erosion, abundant sands are supplied and aeolian activity intensifies. Repetition of this process expands the blowouts, leading to merger of the blowouts and the evolution of mobile dunes. Similar processes occur at the top of cliffs above the Yellow River and Mangla River.