Progress in sandy desertification research of China

Sandy desertification is land degradation characterized by wind erosionmainly resulted from the excessive human activities in arid, semiarid and part of sub-humid regionsin northern China, The research on sandy desertification has experienced more than 5 decades ofarduous course of the struggle along with the establishment and development of China's desertscience. Researches in this field have made a great contribution to the national economicconstruction, and environmental protection. This paper focuses on presenting the major progress andachievements in the sandy desertification research during the last 50 years, including the stages ofstudy on sandy desertification, background environment of sandy desertification and its changes,the conception, causes, process, monitoring and assessment of sandy desertification, the vegetationsuccession, landscape ecology, plant physiology, impacts on ecosystem, high-effective use of waterand land resources and sustainable development in sandy desertified regions, sandy desertificationcontrol models and techniques etc.

DYNAMICS OF SANDY DESERTIFICATION AND ITS DRIVING FORCES IN WESTERN JILIN PROVINCE

By establishing the interpreting elements, and applying supervised classification, the sandy desertific- ation was interpreted and the desertified land areas of the counties in the western Jilin Province in 1986 and in 2000 were obtained. Taking Tongyu and Qian’an as examples, the natural driving forces and man-made driving forces were analyzed. The paper comes the conclusions that the material sources and the warming and dry climate are the internal causes of potential land desertification; the irrational human activities, such as destroying forest and reclaiming the grassland, are the external causes of potential land desertification; while more rational human activities, such as planting trees and restoring grassland can reverse the land desertification. Furthermore, the countermeasures and suggestions for the development of agriculture and animal husbandry in the western Jilin Province are put forward.

Effects of aeolian processes on nutrient loss from surface soils and their significance for sandy desertification in Mu Us Desert, China: a wind tunnel approach

Mu Us Desert, a region with high aeolian activity, is at extremely high risk of sandy desertification. Using surface soil samples collected from Mu Us Desert of northern China, we evaluated the effects of aeolian processes on nutrient loss from surface soils by employing wind tunnel experiments. The experiments were conducted using free-stream wind velocities of 14, 16, 18 and 22 m/s. Our results showed that the fine particles （〈50 pm in diameter; 12.28% of all transported materials） carrying large nutrient Ioadings were exported outside the study area by ae- olian processes. After the erodible fine particles were transported away from the soil surfaces at low wind velocity （i.e. 14 m/s）, the following relatively high wind velocity （i.e. 22 m/s） did not have any significant effect on nutrient export, because the coefficients of variation for soil organic matter, total phosphorus, total nitrogen and available potassium were usually 〈5%. Our experimental results confirmed that aeolian processes result in a large amount of nutrient export, and consequently increase the risk of sandy desertification in arid and semi-arid ecosystems.

STATUS, CAUSES AND COMBATING SUGGESTIONS OF SANDY DESERTIFICATION IN QINGHAI-TIBET PLATEAU

The Qinghai-Tibet Plateau is one of the major sandy desertification regions of China. Based on the recent investigation on sandy desertification, this paper analyses the status such as the type, area, distribution and damage of sandy land desertification in the plateau. Through the analysis on the factors affecting sandy desertification in the region’s natural and socio-economic systems as well as the processes and their interrelations, it can be concluded that sandy desertification in the Qinghai-Tibet Plateau resulted from the combined actions of normal natural sand drift processes, natural sandy desertification processes caused by climatic changes and man-made sandy desertification caused by improper human activities. In addition, it also predicts the possible developmental trend including the increase in desertification area and the enhancement in desertification developmental degree with the exacerbation of the complex processes, and finally puts forward some strategic suggestions to combat sandy desertification in the coming years.

Spatial distribution of sandy desertification change in the west of Jilin Province

The sandy land of the western part of Jilin Province is located in the ecotone of semi-humid and semi-arid area in the temperate zone of China. The sandy desertification has widely spread in the region because of the vulnerable natural conditions and the unreasonable human activity; as a result of this, the precious land resources and the economic development in the area have been seriously impacted. In this paper, the sandy land ecologic environment geographic information system is established based on the multi-spectral, multi-temporal Landsat TM images and field investigation. The comprehensive indexes of sandy desertification extent assessment which include vegetation degradation, wind erosion extent and soil depth are presented to classify the sandy land in western Jilin into three levels--slight, moderate and severe sandy desertification with the support of GIS platform. The results demonstrate that the sandy desertification has been partly controlled in the past twenty years, except some small sites. However, this doesn't necessarily mean that there is nothing for more concern. The two main causes of sandy desertification have not been eliminated yet, one is its natural factor, especially the physical and chemical characters of sandy soil and dry climate; another is the immoderate economic activity of human being that has highly accelerated the sandy desertification process.

Assessment of sandy desertification trends in the Shule River Basin from 1978 to 2010

Sandy desertification in the Shule River Basin has expanded dramatically during the past 30 years. We evaluated the status, evolution, and main causes of sandy desertification by interpreting Landsat images which were acquired in 1978, 1990, 2000, 2005, and 2010, and analyzing the relevant meteorological data. The results show there was 3,477.95 km2, 3,733.32 km2, 3,620.29 km2, 3,565.65 km2, and 3,557.88 km2 of sandy desertified land in 1978, 1990, 2000, 2005, and 2010, respectively. From 1978 to 1990, not only the area of sandy desertified land （SDL） but also the degree of SDL levels increased. From 1990 to 2010 there was widespread restoration of SDL but the recovery trend of SDL gradually slowed. Although climate change contributes to expanding sandy desertification, human activities can either accelerate or reverse trends of natural sandy desertification. Some detrimental human activities can accelerate sandy desertification, but, conversely, desertification control measures such as the Three-North Shelter Forest Project and watershed rehabilitation programs in areas including the Shule River Basin resulted in many SDL being turned into grasslands or forest lands when shrubs and trees were planted to fix mobile sands at the edges of oases and cities. With population growth, much SDL has been reclaimed as farm land using water-saving agricultural methods or has been turned into built-up land as a result of urbanization.

Aeolian processes on sandy desertification of an alpine meadow: A wind tunnel experiment

In recent years,the desertification of alpine meadows has become a serious ecological problem and has gradually become a threat to regional economic activities in Maqu County.To reveal the mechanism for sandy desertification of alpine meadows,we conducted wind tunnel experiments on aeolian processes over sandy alpine meadows.Results show that the sandflux profile of mix-sized sediment decays exponentially with increasing height.However,the profile pattern of a group of uniform-sized particles depends on the experimental wind speeds.The profile pattern of all the groups studied can be expressed by exponential decay functions when the wind speed is less than or equal to 16 m/s.while that for all the groups studied can be expressed by a Gaussian distribution function when the wind speed is above 16 m/s.The average saltation heights of mixed sands at wind speeds of 12 m/s,16 m/s,20 m/s,and 24 m/s were 2.74,4.19,5.28,and 6.12 cm,respectively.The mean grain size basically first decreases and then increases with increasing height under different wind speeds.The sorting improves with increasing wind speed,while the kurtosis and skewness show relationships with only the characteristics of the parent soil.

Establishing evaluation index system for desertification of Keerqin sandy land with remote sensing data

Keerqin sand land is located in the transitional terrain between the Northeast Plain and Inner Mongolia （42°41′-45°15′N, 118°35′-123°30′ E） in Northeast China and it is seriously affected by desertification. According to the configuration and ecotope of the earths surface, the coverage of vegetation, occupation ratio of bare sandy land and the soil texture were selected as evaluation indexes by using the field investigation data. The evaluation index system of Keerqin sandy desertification was established by using Remote Sensing data. and the occupation ratio of bare sandy land was obtained by mixed spectrum model. This index system is validated by the field investioation data and results indicate that it is suitable for the desertification evaluation of Keerqin.Foundation Item： This study is supported by a grant from the National Natural Science Foundation of China （No. 30371192）

Carbon and nitrogen mineralization in soils along a desertification gradient in the semiarid Horqin Sandy Land, Northern China

This experiment was conducted in three sites along a desertification gradient in Horqin Sandy Land, Northern China. Soils una-mended and amended with five types of plant residue in a wide range of C：N ratios from 9.9 to 82.2 were incubated for 70 days, during which C and N mineralization were measured. Along the desertification gradient from fixed sand dune to semifixed, and mobile sand dune： cumulative CO2-C produced from the unamended soils was 231.6, 193.3 and 61.9 μg/g, respectively, while net inorganic N was 22.9, 17.6 and 0.9 mg/kg. Soils amended with residues produced more CO2-C than the unamended soils across all sites. During the first 10 days, C mineralization rate of residue-amended soils decreased with the increase of C：N ratio at each site. However, the mineralization rates were poorly correlated with the C：N ratio in subsequent stage of incubation. Soils of mobile sand dune amended with higher C：N ratio （more than 32） residues produced less CO2-C than that of fixed and semifixed sand dune. NO3--N was the predominant form of inorganic N during the mineralization process in sandy soils. Carbon-to-nitrogen ratio （C：N） can be regarded as a predictor of the speed of N mineralization in sandy soil. The more C. microphylla residue with the lowest C：N ratio （9.9） added in soils, the more net inorganic N released. Our results suggest that C. microphylla residue when added to soil would potentially provide short-term plant available N and improve the soil quality in sandy land. The desertification process postponed the release of inorganic N from plant residues.

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.

Using Landsat TM Imagery to Detect Desertification in Gonghe Basin at the Upper Reaches of the Yellow River

In recent years, the ecological environment in the upper reaches of the Yellow River has been degraded due to natural and human factors. Environmental problems such as grassland degeneration, sandy desertification and water erosion have seriously affected regional economic sustainable development. The objective of this paper was to detect sandy desertification in the upper reaches of the Yellow River by means of remote sensing and GIS. The Gonghe Basin was chosen as the study site, which is one of the most seriously degraded regions in the area. Based on an analysis of the multi-temporal and multi-spectral Landsat TM data with GIS, sandy desertification processes were detected. The results show that sandy desertified land has increased and intensified seriously in the upper reaches of the Yellow River for the period from 1987 to 1996. There are two desertification processes at work in the study area: sand dune reactivation and development of badlands through wind erosion. Excessive human activities play an important role in the occurrence and development of desertification in this area. At present, acceleration of the desertification process is attributed to irrational human economic activities. Grasslands as well as the ecological environment of this area have been seriously degraded, which has affected the regional economic sustainable development and endangered the security of the Longyangxia reservoir. It is necessary and urgent to combat desertification and protect the environment. The results show that full use of remote sensing data with GIS in monitoring and assessing desertification is an effective measure of quantitative research.

Spatial changes of wind erosion-caused landscapes and their relation with wind field in China

Based on the results of remote sensing investigations of the landscapes of 1995 and 2000, the national distribution of sandy desertified land and its interaction with other landscapes are classified, and five zonal types are distinguished. The data of nationally distributed 400 meteorological stations of 1999 are processed. With the GIS method, the data are spatially interpolated, and the national database of wind field concerned with wind erosion is established. In arid and semi-arid areas of China, the intensity of wind field is one of the key factors that controls the development of landscape especially in desert and its adjacent area. Different indexes are set up to describe the intensity of wind field, the method suggested by the wind erosion prediction models of RWEQ is also adopted to express the intensity of wind. The Weibull distribution is used to describe the wind field in China. Based on the analysis of the process of the wind erosion-driven landscape changes, this article proposes and discusses the control measures of wind erosion.