Manas River, the largest inland river to the north of the Tianshan Mountains, provides important water resources for human production and living. The seasonal snow cover and snowmelt play essential roles in the regulation of spring runoff in the Manas River Basin (MRB). Snow cover is one of the most significant input parameters for obtaining accurate simulations and predictions of spring runoff. Therefore, it is especially important to extract snow-covered area correctly in the MRB. In this study, we qualitatively and quantitatively analyzed the uncertainties of snow cover extraction caused by the terrain factors and land cover types using TM and DEM data, along with the Per (the ratio of the difference between snow-covered area extracted by the Normalized Difference Snow Index (NDSI) method and visual interpretation method to the actual snow-covered area) and roughness. The results indicated that the difference of snow-covered area extracted by the two methods was primarily reflected in the snow boundary and shadowy areas. The value of Per varied significantly in different elevation zones. That is, the value generally pre-sented a normal distribution with the increase of elevation. The peak value of Per occurred in the elevation zone of 3,700–4,200 m. Aspects caused the uncertainties of snow cover extraction with the order of sunny slope>semi-shady and semi-sunny slope>shady slope, due to the differences in solar radiation received by each aspect. Regarding the influences of various land cover types on snow cover extraction in the study area, bare rock was more influential on snow cover extraction than grassland. Moreover, shrub had the weakest impact on snow cover extraction.

The shape, size and coverage of gravels have significant impacts on aeolian sand transport. This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation. The tested gravel coverage increased from 5% to 80%, with a progressive increment of 5%. The gravels used in the experiments have three sizes in diameter. Wind velocities were measured using 10 sand-proof pitot-static probes, and mean velocity fields were obtained and discussed. The results showed that mean velocity fields obtained over different gravel mulches were similar. The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces. The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly. According to the present study, the optimal gravel coverage was found to be around 30% or 40%. Threshold velocity linearly increased with gravel coverage. Sand transport rate first increased with height above the wind tunnel floor (Hf), reaching a peak at some midpoint, and then decreased.

Studies of wind erosion based on Geographic Information System (GIS) and Remote Sensing (RS) have not attracted sufficient attention because they are limited by natural and scientific factors. Few studies have been conducted to estimate the intensity of large-scale wind erosion in Inner Mongolia, China. In the present study, a new model based on five factors including the number of snow cover days, soil erodibility, aridity, vegetation index and wind field intensity was developed to quantitatively estimate the amount of wind erosion. The results showed that wind erosion widely existed in Inner Mongolia. It covers an area of approximately 90×10⁴ km², accounting for 80% of the study region. During 1985–2011, wind erosion has aggravated over the entire region of Inner Mongolia, which was indicated by enlarged zones of erosion at severe, intensive and mild levels. In Inner Mongolia, a distinct spatial differentiation of wind erosion intensity was noted. The distribution of change intensity exhibited a downward trend that decreased from severe increase in the southwest to mild decrease in the northeast of the region. Zones oc-cupied by barren land or sparse vegetation showed the most severe erosion, followed by land occupied by open shrubbery. Grasslands would have the most dramatic potential for changes in the future because these areas showed the largest fluctuation range of change intensity. In addition, a significantly negative relation was noted between change intensity and land slope. The relation between soil type and change intensity differed with the content of CaCO₃ and the surface composition of sandy, loamy and clayey soils with particle sizes of 0–1 cm. The results have certain significance for understanding the mechanism and change process of wind erosion that has occurred during the study period. Therefore, the present study can provide a scientific basis for the prevention and treatment of wind erosion in Inner Mongolia.

The Xihu desert wetland is located in an extremely arid area in Dunhuang, Gansu province of Northwest China. The area is home to an unusual geographic and ecological environment that is considered unique, both in China and the world. Microclimate is not only related to topography, but is also affected by the physical properties of underlying ground surfaces. Microclimate and CO₂ flux have different characteristics under different underlying surface conditions. However, until now, few studies have investigated the microclimate characteristics and CO₂ flux in this area. The eddy covariance technique (ECT) is a widely used and effective method for studying such factors in different ecosystems. Basing on data from continuous fine days obtained in the Dunhuang Xihu desert wetland between September 2012 and September 2013, this paper discussed and compared the characteristics of daily microclimate variations and CO₂ fluxes between the two periods. Results from both years showed that there was a level of turbulent mixing and updraft in the area, and that the turbulent momentum flux was controlled by wind shear under good weather conditions. The horizontal wind velocity, friction wind velocity and vertical wind velocity were commendably consistent with each other. Air temperature in the surface layer followed an initial decreasing trend, followed by an increasing then decreasing trend under similar net radiation conditions. With changes in air tem-perature, the soil temperature in the surface layer follows a more obvious sinusoidal fluctuation than that in the subsoil. Components of ground surface radiation during the two study periods showed typical diurnal variations. The maximum diurnal absorption of CO₂ occurred at around 11:00 (Beijing time) in the Xihu desert wetland, and the concentrations of CO₂ in both periods gradually decreased with time. This area was therefore considered to act as a carbon sink during the two observation periods.

China's Horqin Sandy Land, a formerly lush grassland, has experienced extensive desertification that caused considerable carbon (C) losses from the plant-soil system. Natural restoration through grazing exclusion is a widely suggested option to sequester C and to restore degraded land. In a desertified grassland, we investigated the C accumulation in the total and light fractions of the soil organic matter from 2005 to 2013 during natural restoration. To a depth of 20 cm, the light fraction organic carbon (LFOC) storage increased by 221 g C/m² (84%) and the total soil organic carbon (SOC) storage increased by 435 g C/m² (55%). The light fraction dry matter content represented a small proportion of the total soil mass (ranging from 0.74% in 2005 to 1.39% in 2013), but the proportion of total SOC storage accounted for by LFOC was remarkable (ranging from 33% to 40%). The C sequestration averaged 28 g C/(m²•a) for LFOC and 54 g C/(m²•a) for total SOC. The total SOC was strongly and significantly positively linearly related to the light fraction dry matter content and the proportions of fine sand and silt+clay. The light fraction organic matter played a major role in total SOC sequestration. Our results suggest that grazing exclusion can restore desertified grassland and has a high potential for sequestering SOC in the semiarid Horqin Sandy Land.

Grazing can modulate the feedback between vegetation and soil nutrient dynamics (carbon and nitrogen), altering the cycles of these elements in grassland ecosystems. For clarifying the impact of grazing on the C and N in plants and soils in the desert grassland of Ningxia, China, we examined the plant biomass, SOC (soil organic carbon), total soil N and stable isotope signatures of plants and soils from both the grazed and ungrazed sites. Significantly lower aboveground biomass, root biomass, litter biomass and vegetation coverage were found in the grazed site compared to the ungrazed site, with decreases of 42.0%, 16.2%, 59.4% and 30.0%, respectively. The effects of grazing on plant carbon, nitrogen, ¹⁵N and ¹³C values were uniform among species. The levels of plant carbon and nitrogen in grasses were greater than those in the forbs (except for the carbon of Cynanchum komarovii and Euphorbia esula). Root ¹⁵N and ¹³C values increased with grazing, while the responses of root carbon and nitrogen to grazing showed no consistent patterns. Root ¹⁵N and ¹³C were increased by 79.0% and 22.4% in the grazed site compared to the ungrazed site, respectively. The values of SOC and total N were significantly lower in the grazed than in the ungrazed sites for all sampling depths (0–10 and 10–20 cm), and values of SOC and total N at the surface (0–10 cm) were lower than those in the deeper soils (10–20 cm). Soil ¹⁵N values were not affected by grazing at any sampling depth, whereas soil ¹³C values were significantly affected by grazing and increased by 19.3% and 8.6% in the soils at 0–10 and 10–20 cm, respectively. The soil ¹³C values (–8.3‰ to –6.7‰) were higher than those for roots (–20.2‰ to –15.6‰) and plant tissues (–27.9‰ to –13.3‰). Our study suggests that grazing could greatly affect soil organic carbon and nitrogen in contrast to ungrazed grassland and that grazing appears to exert a negative effect on soil carbon and nitrogen in desert grassland.

Greenhouse gas emission of carbon dioxide (CO2) is one of the major factors causing global climate change. Urban green space plays a key role in regulating the global carbon cycle and reducing atmospheric CO2. Quantifying the carbon stock, distribution and change of urban green space is vital to understanding the role of urban green space in the urban environment. Remote sensing is a valuable and effective tool for monitoring and estimating aboveground carbon (AGC) stock in large areas. In the present study, different remotely-sensed vegetation indices (VIs) were used to develop a regression equation between VI and AGC stock of urban green space, and the best fit model was then used to estimate the AGC stock of urban green space within the beltways of Xi’an city for the years 2004 and 2010. A map of changes in the spatial distribution patterns of AGC stock was plotted and the possible causes of these changes were analyzed. Results showed that Normalized Difference Vegetation Index (NDVI) correlated moderately well with AGC stock in urban green space. The Difference Vegetation Index (DVI), Ratio Vegetation Index (RVI), Soil Adjusted Vegetation Index (SAVI), Modified Soil Adjusted Vegetation Index (MSAVI) and Renormalized Difference Vegetative Index (RDVI) were lower correlation coefficients than NDVI. The AGC stock in the urban green space of Xi’an in 2004 and 2010 was 73,843 and 126,621 t, respectively, with an average annual growth of 8,796 t and an average annual growth rate of 11.9%. The carbon densities in 2004 and 2010 were 1.62 and 2.77 t/hm², respectively. Precipitation was not an important factor to influence the changes of AGC stock in the urban green space of Xi’an. Policy orientation, major ecological greening projects such as “transplanting big trees into the city” and the World Horticultural Exposition were found to have an important impact on changes in the spatiotemporal patterns of AGC stock.

The long-term productivity of a soil is greatly influenced by cation exchange capacity (CEC). Moreover, interactions between dominant base cations and other nutrients are important for the health and stability of grassland ecosystems. Soil exchangeable base cations and cation ratios were examined in a 11-year experiment with sheep manure application rates 0–1,500 g/(m²•a) in a semi-arid steppe in Inner Mongolia of China, aiming to clarify the relationships of base cations with soil pH, buffer capacity and fertility. Results showed that CEC and contents of exchangeable calcium (Ca2+), magnesium (Mg²⁺), potassium (K⁺) and sodium (Na⁺) were significantly increased, and Ca²⁺ saturation tended to decrease, while K⁺ saturation tended to increase with the increases of sheep manure application rates. The Ca²⁺ /Mg²⁺ and Ca²⁺/K⁺ ratios decreased, while Mg²⁺, K⁺ and Na⁺ saturations increased with increasing manure application rates. Both base cations and CEC were significantly and positively correlated with soil organic carbon (SOC) and soil pH. The increases of SOC and soil pH would be the dominant factors that con-tribute to the increase of cations in soil. On a comparison with the initial soil pH before the experiment, we deduced that sheep manure application could partly buffer soil pH decrease potentially induced by atmospheric deposition of nitrogen and sulfur. Our results indicate that sheep manure application is beneficial to the maintenance of base cations and the buffering of soil acidification, and therefore can improve soil fertility in the semi-arid steppes of northeastern China.

Microtopography may affect the distribution of forests through its effect on rain redistribution and soil water distribution on the semi-arid Loess Plateau, China. In this study, we investigated the characteristics of mi-crotopography on two shady slopes (slope A, 5 hm², uniform slope; slope B, 5 hm², microtopography slope) and surveyed the height, the diameter at breast height and the location (x, y coordinates) of all selected individual trees (Robinia pseudoacacia Linn., Pyrus betulifolia Bunge, Populus hopeiensis Hu & Chow, Armeniaca sibirica Lam., Populus simonii Carr. and Ulmus pumila Linn.) on slope A and slope B in the watersheds of Wuqi county, Shaanxi province. Subsequently, the effects of microtopography on the spatial pattern of forest stands were analyzed using Ripley’s K(r) function. The results showed that: (1) The maximal aggregation radiuses of the tree species on the uniform slope (slope A) were larger than 40 m, whereas those of the tree species on the microtopography slope (slope B) were smaller than 30 m. (2) On slope B, the spatial association of R. pseudoacacia with P. betulifolia, A. sibirica, P. simonii and U. pumila varied from being strongly negative to positive at microtopography scales. The spatial association of Populus hopeiensis Hu & Chow with U. pumila also varied from being strongly negative to positive at microtopography scales. However, there was no spatial association between P. betulifolia and P. hopeiensis, P. betulifolia and A. sibirica, P. betulifolia and P. simonii, P. betulifolia and U. pumila, P. hopeiensis and A. sibirica, P. hopeiensis and P. simonii, A. sibirica and P. simonii, A. sibirica and U. pumila, and P. simonii and U. pumila. On slope A, the spatial association between tree species were strongly negative. The results suggest that microtopography may shape tree distribution patterns on the semi-arid Loess Plateau.

Potential habitat modeling of endemic species is an appropriate method to maintain biodiversity, ecosystem function and rehabilitation of rangeland ecosystems. Astragalus caragana, A. cyclophyllon and A. podolobus are endemic in Iran’s rangelands and some neighboring countries. The three native species could endure environmental stresses due to their distinctive ecophysiological characteristics. They play important roles in sustainable pastures production, recreation and improvement. They suffer severe threat from many factors including; grazing, agriculture and invasive exotic species. We analyzed the potential habitat of three native plant species in central Iran basing on the grid map with the resolution of 1-km. We used inventory records from field surveys, herbarium collections and 22 environmental factors to explore the environmental influences on given species distribution by Maximum entropy (Maxent) model. Maxent is a species distribution model that uses species occurrence and environmental data for predicting potential species. The results of our study indicated species occurrence has strong correlation with environmental factors such as mean temperature of wettest season, elevation and precipitation of coldest season. We evaluated the model accuracy by AUC (area under the receiver operating characteristic curve) based on an independent test data set. AUC values indicated the high power of Maxent to create potential habitat map (AUC_{A. caragana}=0.988, AUC_{A. cyclophyllon}=0.927, AUC_{A. podolobus}=0.923). It is important to consider that AUC values tend to be lower for species that have broad distribution scope, such as A. podolobus distribution. Most suitable potential habitat distributions of the three species were predicted in the western and southwestern parts of rangelands in Isfahan province. Visual comparisons of the actual distribution map of the three species with produced Maxent maps represent a good agreement. In general, the model demonstrated that the occurrence of the given species is highly probable when the elevation is between 2,200 m and 3,000 m and mean temperature of wettest season less than 3°C. This model, therefore, can be applied to recognize potential sites for rangeland reclamation projects.

Afghanistan is threatened by rangeland degradation. A quantitative visual analysis of Google Earth Imagery was used to systematically locate, characterize and quantify the current extent of rangelands in Afghanistan degraded as a consequence of dryland agriculture. Climate data were used in conjunction with dryland agriculture locations to establish a climate envelope comprised by temperature and mean annual precipitation to create a geographical mask known to contain dryland agriculture. Within this mask we created a grid of 100 km² cells that we analyzed individually to access dryland agriculture extent. Climatic limits to sustainable dryland agriculture and areas of high restoration priority were also assessed as was the distribution of rain-fed agriculture with respect to the location of traditional migration routes for extensive livestock producers. The extents of agriculture in Afghanistan, at both upper and lower elevations, correlated most closely with mean annual temperature (MAT) at the upper elevation limits, and with mean annual precipitation (MAP) at the lower elevation limits. In total, dryland agriculture comprised 38,980 km² of former native rangeland. Conversion was highest in the northwestern, northern and northeastern provinces of Herat, Badghis, Faryab, Jawzjan, Sar-e-Pul, Samangan, Balkh, Baghlan, Kunduz, Takhar and Badakhshan, with the highest percentage of conversion occurring in Takhar. An MAP value of <400 mm is perceived by farmers as the current climatic limit to sustainable dryland agriculture across the northern regions of the country. Uder this MAP value, approximately 27,677 km² of converted rangeland met the need for restoration priority. Climate projections indicate that Afghanistan will become warmer and drier in the coming decades. One consequence of this trend is that the MAP threshold of <400 mm to sustainable dryland agriculture will become obsolete in the coming decades. Restoration of currently converted rangelands is needed to restore critical grazing areas as is the adoption of prudent range management policies to prevent further land degradation and support a vital livestock industry. Food security is at stake as the conversion of rangelands to unsustainable rain-fed agriculture may leave large tracks of land unusable for either agriculture or livestock production.

Stress gradient hypothesis predicted that facilitative interactions usually increase in intensity and are importance with abiotic stress. By contrast, facilitation may be lost in time, when it involves the growth of benefactors or beneficiaries. Less is known about which response pattern is more common in arid desert. We present an empirical study to explore shrub-annual interactions at the community and individual level along the course of a single growing season in a desert steppe in northwest China. Here the severity of drought stress may increase in time due to uneven precipitation during plant growing season. We assessed growth responses of annuals in understory where two dominant shrubs were removed. Annuals responses showed a switch from weakly positive to more strongly positive beneath Calligonum mongolicum, whereas from positive to negative beneath Nitraria sphaerocarpa during the growing season. Additionally, annual species with contrasting functional traits showed distinct growth responses to canopies removal. There was evidence of an increase in soil moisture below the canopy of shrubs, but a decrease in potential evaporation rate and photosynthetically active radiation, which can partly explain these species-specific responses. We conclude that the balance between competitive and facilitative effects in shrub-annual interactions is not only governed by the severity of stress but also determined by plant traits, such as canopy structure of shrubs and functional traits of their understory annuals.

Desert ephemeral plants play an important role in desert ecosystem. Soil water availability is considered as the major restrictive factor limiting the growth of ephemeral plants. Moreover, arbuscular mycorrhizal fungi (AM fungi) are widely reported to improve the growth of desert ephemerals. The present study aimed to test the hypothesis of that AM fungi could alleviate drought stress of desert ephemeral Plantago minuta, and AM fungal functions reduced with the improvement of soil water content. A pot ex-periment was carried out with three levels of soil water contents (4.5%, 9.0%, and 15.8% (w/w), and three AM inoculation treatments (Glomus mosseae, Glomus etunicatum and non-inoculation). The results indicate that mycorrhizal colonization rate decreased with the increase of soil water availability. Inoculation improved plant growth and N, P and K acquisition in both shoots and roots regardless water treatments. When comparing the two fungi, plants inoculated with G. mosseae performed better than those inoculated with G. etunicatum in terms of plant growth and nutrient acquisition. These results showed that ameliorative soil water did not suppress arbuscular mycorrhizal fungal functions in improving growth and nutrient acquisition of desert ephemeral Plantago minuta.