Aeolian Desertification Status and Its Control in China

Abstract

Desertification in China mainly includes the following types: soil erosion, aeolian desertification and salinization. Desertification in most parts of northern China is mainly manifested in land aeolian desertification. Aeolian desertification is defined as land degradation in arid, semiarid and parts of semi-humid regions with the occurrence of blown sand activities (deflation, ground surface coarsening, and sand dune formation, etc.) on former non-desert areas as the main mark resulting from various factors including overusing land and upsetting the fragile ecological balance under the conditions of dry and windy climate and loose sand surface (CCICCD 1994).

1 Introduction

Desertification in China mainly includes the following types: soil erosion, aeolian desertification and salinization. Desertification in most parts of northern China is mainly manifested in land aeolian desertification. Aeolian desertification is defined as land degradation in arid, semiarid and parts of semi-humid regions with the occurrence of blown sand activities (deflation, ground surface coarsening, and sand dune formation, etc.) on former non-desert areas as the main mark resulting from various factors including overusing land and upsetting the fragile ecological balance under the conditions of dry and windy climate and loose sand surface (CCICCD 1994).

Land aeolian desertification is not only an important ecological problem, but also a critical economic and social problem, which hampers the sustainable development of Chinese economy and society. Firstly, it upsets the ecological balance, results in environmental deterioration and reduction of land productivity, affects the livelihood of people in aeolian desertification-prone regions and aggravates their degree of poverty. Secondly, it leads to the loss of large areas of productive lands. Finally, it poses a serious threat to rural communities, transport lines, water projects, mining and industrial infrastructures, national defense bases, as well as agricultural and industrial productions.

At the beginning of P. R. China founding in 1949, the State started the process of combating aeolian desertification. Although significant achievements have been made by now in aeolian desertification control, only a small proportion of the desertified land has been improved, and in most regions the situation has become worse (Dong and Gao 1993; Liu 1982a, b; SSDER et al. 1980; TRDCCP 1998; Zhu and Liu 1981; Zhu 1992, 1999a; Zhu et al. 1989, 1998).

According to statistical data, the land area affected by water erosion, wind erosion, aeolian desertification and salinization occupies about one third of Chinese terrestrial area, of which desert, gravel desert (gobi), wind-eroded land and aeolian desertified land cover 1.67 × 10⁶ km², accounting for 17.4% of China’s total land area. There are 38.57 × 10⁴ km² of aeolian desertification land, accounting for 44.3% in 83.7 × 10⁴ km² of all kind of desertified land (Dong et al. 1995; Wang et al. 2004a, b; Zhu and Chen 1994).

With the accelerating development of aeolian desertification, the frequency of strong dust storms greatly increased. The frequency of strong dust storms in northern China has increased from 5 times per year in 1950s to 8 times per year in 1960s, 13 times per year in 1970s, 14 times per year in 1980s, and 23 times per year in 1990s. Dust storms directly damage northwest and northern China and can affect southern China or even the whole East Asia.

2 Aeolian Desertification Category

2.1 Index and System of Aeolian Desertification Category

At present, there are no uniform principle, index and system of aeolian desertification category in China. There are several category systems commonly used in actual practices:

• (1) From the point of aeolian desertification development phase (Table 15.1) (Zhu and Liu 1981; Zhu 1999b). It is the most popular way. When judging the degree of aeolian desertification in certain area from the view of ecology, we also consider changes of potential land productivity, biomass (including changes of plant structure and rate of vegetation cover) and energy transfer efficiency in biological system (Table 15.2).

  Table 15.1 The symbols of aeolian desertification land development

  Table 15.2 Ecological indicators of aeolian desertification degree

• (2) According to configuration changes (Table 15.3). When estimating the degree of aeolian desertification somewhere, we usually consider surficial “instant” static characteristics reflecting the degree of aeolian desertification, but we don’t know how it was or how it will be. We determine the degree of aeolian desertification according to actual status, and concepts which can reflect actual status of aeolian desertification are used to name concrete aeolian desertification degree.

  Table 15.3 Synthetical landscape symbols of all degrees of aeolian desertification land

• (3) Taking aeolian desertification process and land types into consideration (Table 15.4).

  Table 15.4 Aeolian desertification categories in northern China

• (4) According to the development status (Table 15.5).

  Table 15.5 Classification of the status of aeolian desertification development

2.2 Synthetic Indicator System of Aeolian Desertification Monitoring by Remote Sensing

Although a set of indicator system of aeolian desertification had been established by FAO and UNEP in 1984, it is still needed to make a practical indicator system for regional desertification monitoring and classification because of big differences from place to place. The indicators selected for aeolian desertification classification should be representative and applicable. An indicator should be a statistic quantum or represent an environment phenomena related to aeolian desertification processes, which represents an existing specific environment condition (Wang et al. 1998). The indicators should have following features: ① contain clear information and easy to get from observations; ② sensitive to the changes of aeolian desertification status; ③ suitable to be used repeatedly; ④ go through quantitative check.

According to the characteristics of aeolian desertification in northern China, we have established a universal aeolian desertification indicator and classification system, which take surface feature variations as main factors and meanwhile consider the changes of soil, vegetation and eco-system (Table 15.6). The selected indicators have a common representativeness and their aeolian differences are easy to distinguish in monitoring and evaluating aeolian desertification processes in northern China. With the development of aeolian desertification, the land potential productivity and biological production including vegetation cover are changed. We can take these changes as supplementary indicators to evaluate aeolian desertification degree (Table 15.7).

Table 15.6 Classification and indicators of aeolian desertification degrees

Table 15.7 Supplementary indicators for aeolian desertification classification

In fact, in the remote sensing monitoring practice, the percentage of eroded land or shifting sand areas and its changes in a certain period are taken as main indicators and others as supplementary indicators. This is because the change of eroded land or shifting sand area is a combined result of vegetation cover, biological production, soil properties and water content etc. It is easy to judge and convenient to use during the aeolian desertification monitoring in northern China. This means that our classification system mainly relies on the direct information of ground vegetation cover, species of plants and micro topographic features.

Based on this indicator system of aeolian desertification monitoring, the four types of aeolian desertification in northern China have the following features:

• (1) Slightly aeolian desertified land: ① The blowouts appear on windward slopes of sand dunes and there are some accumulative shifting sands on leeward slopes, vegetation cover is 30–50%, patches of shifting sands occupy 25%; ② Shrubs grow well, sand mounds of different sizes appear around shrubs; ③ There is a thin layer of shifting sands on land surface; ④ The ridges of cultivated field are eroded and sands are accumulated between ridges, and humus layer lose of soil is less than 50%; ⑤ Crop yield is 50–80% of initial stages of cultivation; ⑥ Shallow blowouts occur in sandy area but some vegetation still exists, the blowouts are gradually transformed without obvious steep bench.

• (2) Moderately aeolian desertified land: ① An obvious differentiation between eroded slope and slip face appears, vegetation cover is 15–30%, the area of shifting sand occupy 25–50%; ② Leaved shrubs cannot entirely cover sand mounds and there are shifting sands on windward side of sand mounds; ③ Small patches of shifting sand occur in loessial farmland or land surface covered by coarse sands or gravels, but a few vegetation still exist with a cover age of 10–30%; ④ There is obvious wind erosion in cultivated land, less than 50% of humus layer has been blown away, crop yield is 50% of initial stages of cultivation; ⑤ Blowouts are mostly exposed and ridges are easy to be distinguished.

• (3) Severely aeolian desertified land: ① Sandy land is in a semi-fixed state, the area of shifting sands exceeds 50%, vegetation coverage is less than 15%; ② Gobi landscape occurs, vegetation cover is smaller than 10%; ③ Humus layer of soil is eroded and almost blown away, Calcic horizon is exposed, most desertified croplands are abandoned; ④ Deflation mounds and pillars appear on land surface.

• (4) Very severely aeolian desertified land: ① Land loses their productivity completely; ② A mobile sand dune landscape occurs in sandy lands; ③ Gobi landscape occurs in gravel lands; ④ Yadangs occur in wind-eroded lands.

3 Range and Types of Aeolian Desertification in China

Drought is a cause of aeolian desertification of lands, but essentially, irrational human behavior is the main cause of aeolian desertification. In China, only 5.5% of total 38.57 × 10⁴ km² aeolian desertification land was caused by sand dune’s advancing. Aeolian desertified lands don’t include sandy desert, Gobi, salt desert and cold desert formed in geological period.

According to the report of State Environmental Protection Administration of China (SEPA 1999), there are 83.7 × 10⁴ km² of all kinds of desertification lands, accounting for 8.7% of total territory. Thereinto, there are 38.57 × 10⁴ km² of aeolian desertification lands, accounting for 44.3% of desertified land. The report also showed that there are 141 × 10⁴ km² of lands susceptible to desertification, there into the area of land susceptible to aeolian desertification is 53.7 × 10⁴ km². Desertified land and land susceptible to desertification amount to 224.7 × 10⁴ km², and land of aeolian desertification and threatened by aeolian desertification amount to 90.8 × 10⁴ km². In addition to 219.1 × 10⁴ km² of sand desert, Gobi and blown land account for 22.82% of the total area of continental territory (Fig. 15.1).

Fig. 15.1

Map of desert and aeolian desertification land in northern China

To sum up, the distributions of aeolian desertification land are not limited in regions with drought index value of 0.50–0.65 in China, but in all kinds of natural belts, which show aeolian desertification is the product of interaction between intensive human activities and fragile ecological environment, and irrational human activities that made environment degraded toward desert-like landscape. There was 38.57 × 10⁴ km² of aeolian desertification land in northern China, there into, light aeolian desertification land was 13.95 × 10⁴ km², accounting for 36.1% of total aeolian desertification land; moderate aeolian desertification land was 9.98 × 10⁴ km², occupying 25.9%; severe aeolian desertification land was 7.91 × 10⁴ km², 20.5%; very severe aeolian desertification land was 6.75 × 10⁴ km², 17.5% (Fig. 15.1). Compared with the results of aeolian desertification land monitoring in the middle and late 1980s, in 2000, the percentage of light aeolian desertification land was reduced, that of moderate aeolian desertification land kept stable, but the percentage of severe aeolian desertification increased. This status is consistent with the principles of aeolian desertification development, and also conforms to principles of aeolian desertification control that parts of light aeolian desertification land should be controlled first and get rehabilitated.

4 The Spatial Characteristics of Aeolian Desertification in China

4.1 Regional Differences

Northwest China is located in the hinterland of Asian continent and the climate is hypo-arid continental climate here. The climate in eastern China is controlled by Eastern Asian Monsoon. So, the aeolian desertification characteristics show obvious region differences.

1. Arid Regions in Western China

On the natural condition of hypo-arid in western China, both natural and artificial vegetation much depend on water. Rivers supplied by precipitation and snow from mountains around desert are the base of sand desert oasis’s existence. The decrease of river water, whether it’s caused by natural or human factors, can determine the development of aeolian desertification land in oases. Besides, local people’s destroying vegetation around oases accelerates the development of land aeolian desertification in oasis.

Because water resource is limited in western China, the reasonable assignment of water between upper and lower reach of continental river is very important. There are three regions that give typical examples of land aeolian desertification development due to water use conflict in a whole river basin.

Box 15.1 The opposed development of two oases at upper and down reaches of the Shiyang River basin in Gansu Province

The Shiyang River converged by 8 rivers all originating from the Qilian Mountains fosters Wuwei Oasis first, passes by Hongyashan fault zone and irrigates Minqin Oasis at last (Fig. 15.2). Because the water resource is limited in the Shiyang River Valley, the phase of opposed development that one oasis flourishes and the other must wane has been alternatively formed in history. From the later of the Western Han Dynasty when the Wuwei Oasis took shape through the Tang Dynasty, the Wuwei Oasis gradually became the largest and most flourishing city in Hexi region and the surrounding agriculture was also well developed. The increase of water use at the upper reach of Shiyang River made rivers dry up, lakes shrink, oasis decline and aeolian desertification develop quickly in the Minqin Oasis. And years of war made these farmlands abandoned and suffer from intensive process of aeolian desertification. From the end of the Tang Dynasty to the beginning of the Yuan Dynasty, Hexi region suffered from wars among several tribes and the Minqin Oasis was used for grazing by nomads. At the same time, the Wuwei Oasis also declined, so water for irrigation decreased. The water at the lower reach of the Shiyang River recovered. Lakes also recovered partly. When there was water, aeolian desertification was reversed. The policy that army cultivated farmland where they guarded was implemented during both the Ming and Qing dynasties. And the history of exploiting the Shiyang River Valley replayed, namely agriculture developed and Wuwei Oasis expanded, at the same time, Minqin Oasis receded southwardly.

Fig. 15.2

Image of the Shiyang river basin

In the period of the Republic of China, there was 74.2% of plowland in Hexi can be irrigated in 1944, accounting for only 35.5% of Hexi region, because of lacking of efficient and appropriate management and distribution of water resources among the whole drainage basin and decision failure. To make up the lack of precipitation, local people began to pump out groundwater to irrigate farmlands. By the middle 1970s, one to two billion cubic metres of water are over exploited per year, which resulted in the decline of the water table significantly. Nowadays, the water table in Minqin declined to 12–15 m under ground surface, which lead to the downfall of sand-fixing plants and worsened the development of aeolian desertification. Since the 1960s, there was totally 2.52 × 10⁴ ha of abandoned farmland due to lack of water (Zhu and Chen 1994).

Box 15.2 The opposed development between the upper-reach-located oasis and the lower-reach-located sandy desertified land in the Tarim River Basin of Xinjiang Province

The Tarim River is the longest continental river in China, its course swings 2200 km from the Yarkant River to the Tetima Lake (Fig. 15.3). The main stem of the Tarim River, also customarily called the Tarim River, refers to the section from the joint point of the Aksu River, Hotan River and Yarkant River to the Taitema Lake, with a length of 1280 km. According to documentary records, the Tarim River was ever perennial. In 1759 AD, foods could be shipped from Xayar to Shache through the Tarim River; Swedish explorer Sven Hedin (1865–1952) traveled from the upper reach of the Yarkant River to lower Tarim River by a large wooden ship during winter in 1899 through the spring of the next year; By the 1960s, the Tarim River was still perennial and river water could eventually flow into the Tetima Lake. Since the early 1960s, only flood water could reach the Tetima Lake. After the 1970s, the dramatically increased human activities increased the use water in the middle reach of the Tarim River. A total of 2.15 × 10¹⁰ m³ water was consumed in the section from the Tarim River Dam to Kala Station, with the largest water consumption rate of 6.83 × 10⁶ m³ per kilometer in the Tarim River Basin. Simultaneously, water loss through evaporation and leakage was great. At that time, local people accidentally breached river bank to divert water extensively for farmland irrigation, resulting in river course changing and a lot of water flowing into nearby lakes, swamps, reservoirs, desert and holes. The lower reach region of the Tarim River was more arid than ever before even though the runoff was abundant in the upper reaches in year 1986. At present, there are serious environmental degradation problems in the lower reach region of the Tarim River. One, sandy desertification intensively develops, i.e., abandoned plots are a common sight in irrigation area, being prone to aeolian desertification land; a large area of Populus euphratica forest died; fixed sandy dunes reactivated and encroached farmlands; lakes dried up; the degree of mineralization of lakes, rivers and ground water all increased; the biodiversity declined (Fan 1993).

Fig. 15.3

Sketch map of the Tarim River system

Box 15.3 Water use conflict along the Heihe River Valley passing three provinces of the Northwest China

The Heihe River originates from the Qilian Mountains, flows through the Qinghai, Gansu, and Inner Mongolia provinces, passing a distance of 821 km and river water finally goes into the Juyanhai Lake in the Ejin Banner of western Inner Mongolia (Fig. 15.4). The history of exploitation at the upper reach of the Heihe River Valley can be dated back to 100 AD; the agricultural development at the lower reach has formed a famous “Black City Cultures”. In the recent 30 years, with the population increasing, the conflict of water use is prominent among different administrative areas. Consequently, both the eastern and western Juyanhai lakes in lower reach of the Heihe River dried up, the area of natural forest and grassland reduced sharply, and the frequency of all kinds of catastrophic climate increased, exhibiting that the ecological environment deteriorated severely. At the middle reach, pastureland and the natural vegetation of Zhangye agricultural oases in Gansu Province degraded, land aeolian desertification and salinization are very serious (Liu 1982a, b). Even in the upper Qilian Mountainous area of the Qinghai Province, the area of natural forest reduced, the capacity of headwater conservation decreased, and land desertification is obvious.

Fig. 15.4

Boundary of the Heihe River Basin (Pan and Tian 2001)

A part from the reason of water resource scarcity, desert expansion also can result in Aeolian desertification. A typical example is that the southward advancing of the Taklimakan Desert in southern Xinjiang has made the oases in front of the Kunlun Mountains shrink seriously and most evidently in Hotan region. Within the recent 50 years, the area of sandy desertified land in Hotan mounted up to 1.67 × 10⁴ ha, thereinto, sandy desertified farmland was 0.58 × 10⁴ ha, and the Qira County site was obliged to be moved for 3 times. Along the rim of the Taklimakan Desert, there is an unclosed circle of land aeolian desertification, with an area of 1.296 × 10⁵ ha, was caused by modern shifting sand encroachment (Table 15.8).

Table 15.8 Land area encroached by sand dunes along the rim of modern Taklimakan Desert

2. Semiarid Regions in Eastern China

In the latest 50 years, aeolian desertification developed intensively in the semiarid regions of eastern China, where 85% of modern aeolian desertification lands are concentratedly distributed. To investigate its germ, the most essential is that the pressure exerted by human economic activities exceeds the environmental carrying capacity. As a result, desert-like landscapes appeared on former non-sandy-desertification lands.

A typical example lies in the transitional zone between grassland and farmland in eastern China, this fragile ecotone stretches from the Horqin Steppe, along inside and outside of the Great Wall to the Mau Us Sandy Land and the southern part of Yanchi County in Ningxia Province. The ecological frangibility in this ecotone is determined by the local fragile natural conditions (Zhu and Chen 1994): ① great variability of annual precipitation, results in instability of water condition; ② thick and loose surface sandy sediments or even sand bed, form fragile soil condition; ③ gales blow frequently in a year producing atrocious weather condition. On the background of local fragile natural conditions, irrational land use has accelerated the expanding rate of aeolian desertification in the ecotone. Development of aeolian desertification in semi-arid regions is substantially a result of environmental degradation caused by economic development at the expense of ecological environment. The process of environmental degradation is from quantitative to qualitative (Fig. 15.5).

Fig. 15.5

Process of aeolian desertification in transitional zone between grassland and farmland in semi-arid region

4.2 Spatial Distribution

Research on aeolian desertification in China began in the late 1970s, many results has summarized its spatial distribution characteristics (Fan 1993; Zhou 1989; Zhu and Liu 1981; Zhu and Chen 1994; Zhu 1999b):

• (1) Aeolian desertification lands are concentrated in semi-arid regions (Table 15.9). Aeolian desertification land was 20.13 × 10⁴ km², accounting for 52.2% of total aeolian desertification land in China.

  Table 15.9 Counties (banners), cities influenced by aeolian desertification in semi-arid zone

• (2) Aeolian desertification lands in arid region are fleckily distributed around oases and in the marginal area of Gurbantunggut desert where there are mainly fixed and semi-fixed sand dunes (Table 15.10). The area of sandy desertified land amounts to 12.2 × 10⁴ km², accounting for 31.4% of the total in China.

  Table 15.10 Aeolian desertification land in arid region in northwestern China

• (3) Aeolian desertification lands are mainly scattered in proluvial fans and along old riverbed banks in semi-humid regions (Table 15.11). Area of aeolian desertification land is 2.47 × 10⁴ km², accounting for 6.4% of total aeolian desertification land in China. Because of local semi-humid climate, aeolian desertification landscape is generally manifested in blown sand landform in dry seasons such as in winter and spring, but it takes on a farmland view in summer and autumn, when characteristics of blown sand movement are not obvious. So, aeolian desertification land scape changes seasonally.

  Table 15.11 Counties and cities suffered from aeolian desertification in semi-humid region of north China

• (4) Aeolian desertification lands under the wind force in humid regions are concentrated in sandy lands along riverbanks and in seashores. Aeolian desertification land in humid regions of southern China has the following characteristics: ① Seasonal changes are more obvious; ② The history of evolvement is short, but at rapid developing rate; ③ Human over cutting makes ground bare in winter, which aggravates the blown sand movement; ④ sand is coarse, with good sorting, and high threshold velocity is required; ⑤ Sand source is limited and landform is simple.

• (5) Aeolian desertification lands fleckily scatter along riverbanks in high tundra zone. Aeolian desertification land generally shows a patchy and scattered distribution pattern in high tundra zone, and it is mainly distributed in valleys of Brahmaputra, the Lhasa River and Nianchu River. Shifting sand caused by over grazing and over cutting is interruptedly distributed. Aeolian desertification land developed around towns in Nimula, Naqu of northern Tibetan Plateau and Shiquanhe town in A’li area, which was mostly related to local construction of infrastructure and over cutting.

5 The Temporal Characteristics of Aeolian Desertification in China

5.1 Temporal Distribution

Aeolian desertification is a dynamic process, and the distributing scope and characteristics of surficial landforms are variable during different periods. With aeolian desertification in northern China as an example, the characteristics of temporal distribution of aeolian desertification are as follows.

• (1) Before 1000 AD, especially in Han and Tang dynasties, aeolian desertification lands showed a specky distribution pattern and concentrated at the lower reach of continental rivers in arid region where historical ancient cities usually situated. Aeolian desertification was caused by inappropriate utilization of water resources. This kind of aeolian desertification land was 5.36 × 10⁴ km², accounting for 14.4% of total aeolian desertification land in China.

• (2) F rom 1100 to 1900 AD, aeolian desertification lands concentrated in semi-arid region, and it was centered on historical farming region, showing a patchy distribution pattern. Because of different way of land use (grazing or farming), there existed development and reverse of aeolian desertification land during this period. This kind of aeolian desertification land is 8.62 × 10⁴ km², accounting for 23.23% of total aeolian desertification land in China, and its occurrence and development is closely related to reclamation of farmland.

• (3) In the twentieth century, great population pressure and frequent human activities had promoted the expansion of aeolian desertification land. Over cultivation, overgrazing and irrational development of artificial oases at upper reaches of continental rivers are the main causes of expansion of modern aeolian desertification land. The annual increase of aeolian desertification land area in northern China was 1560 km² during the period from the 1950s to the middle 1970s, with a rate of 1.01%; from the middle 1970s to the middle 1980s, it was 2100 km², with a rate of 1.47%; and it was 2460 km² in the 1990s. What’s more, the degree of aeolian desertification got aggravated, severe aeolian desertification land accounted for 0.93% in the middle 1970s, but it was 1.77% in the middle 1980s, during the same period, moderate aeolian desertification land increased from 14.87 to 21.8%, while light aeolian desertification land decreased from 84.2 to 76.4%. It shows the degree of aeolian desertification is getting worse and worse.

• (4) Around the turn of 20th to twenty-first century, a large area of aeolian desertification land got rehabilitated benefited from the “grain for green” policy in Chinese strategic plan of “West Development” (TRDCCP 1998). But, in the past 20 years, many new aeolian desertification lands develop resulted from the construction of new factories, roads, railways, etc., which have destroyed the stabilization of sand surface in sand desert areas. Human activities anxious for success in “banish poverty and become rich” without consideration of the environmental capacity have also resulted the new development of aeolian desertification. For maintaining the sustainable and stable development of economy, we have to adjust our activities constantly and create a virtuous cycle of ecological environment in sandy areas.

5.2 Temporal Change

Two large-scale investigations of aeolian desertified lands had been carried out in the mid-1970s and late 1980s by the former Lanzhou Institute of Desert Research, Chinese Academy of Science. The first investigation in the 1970s showed that there were 33.4 × 10⁴ km² of aeolian desertified lands, of which 17.6 × 10⁴ km² have been already aeolian desertified and 15.8 × 10⁴ km² are potential aeolian desertified lands. Compared with air photo data of 1950s, in northern part of China the aeolian desertified lands were expanded at rate of 1560 km²/a from 1950s to 1970s (Wang et al. 2004a, b). There are two causes for the expansion, one is dry-farming lands aeolian desertification due to over cultivation in steppes and desert steppe regions, and the other is mobilization of fixed dunes due to overgrazing and over cutting of firewood in fixed sand dune areas.

In the second investigation in the 1980s, remote sensing is used as main means for the investigation and monitoring. The monitoring results indicate that there were 37.1 × 10⁴ km² of aeolian desertified lands in China, accounting for 3.86% of its total land area, distributed in arid, semiarid and semi-humid areas. From 1970s to 1980s, the aeolian desertified land was developed at a rate of 2100 km²/a (Wang et al. 2004a, b; Zhu 1999b).

In the 1990s, the speed of aeolian desertification expansion further increased, at a rate of 3600 km²/a from 1988 to 2000 (Wang et al. 1995, 2004a).

With the application of remote sensing and GIS techniques, a larger scale investigation on the aeolian desertified land distribution, development and hazard had been made in the China. Aeolian desertification study has entered a new stage of quantitative analysis and evaluation (Liu 1996; Ma and Li 2000; Wang et al. 1994, 1998; Wang 1992; Wu 1991, 1997; Wu et al. 1997; Zhu 1999b). From the research results, aeolian desertification has developed mainly in three regions in northern China in the past 50 years (Fig. 15.6): ① Mixed farming-grazing zone of semiarid region, occupies 40.5% of total aeolian desertified lands of northern China; ② Sandy grassland zone of semiarid region, occupies 36.5%; ③ Arid oasis edge and lower reaches of inland rivers, occupy 23%. Remote sensing data also show that about 10% of aeolian desertified lands kept a stable state or exhibited a reversed trend.

Fig. 15.6

Spatial distributions of aeolian desertified land in northern China in 1950s, 1987, and 2000. Due to restoration policy, the desertification was reversed in some areas in the Northern China by the end of 1990s. Human activities have also pushed the agro-pastoral boundary northwards by approximately 200 km from 1950s to 2000

6 Measures to Control Aeolian Desertification

6.1 Vegetative Method

Practices at home and abroad proved vegetative or biological method to combat sand is a basic measure to fix shifting sand and control land aeolian desertification. Mechanic sand barrier (artificial sand barrier) and spraying chemicals are temporary measures. They can be used to stabilize sand surface and create a stable ecological environment for the establishment of artificial vegetation or for the rehabilitation of natural vegetation on sand dunes and wind-eroded lands (Liu 1982a, b; Zhu et al. 1998).

Vegetative method primarily includes the establishment of artificial vegetation or rehabilitation of natural vegetation; establishment of sand break forest belts to prevent shifting sand from encroaching on oases, traffic lines, towns and other facilities; establishment of protection forest net to prevent farmland from being eroded by wind and pasture from degradation; protection of natural vegetation to prevent fixed and semi-fixed sand dunes and sandy grassland from aeolian desertification.

What should be pointed out is that the type of protection system in sandy region of China was transformed from traditional ecotype to eco-economic type. Namely, in the processes of shifting sand stabilization and aeolian desertification control in a large area, timber forest, economic forest and fuel forest should be constructed appropriately, reconstruction of vegetation in pastures, rational utilization of artificial vegetation, enlargement of present oases and capital farmland and development of agriculture, forestry, stockbreeding, fishery and other industries to improve the living standard of people in sandy region (Zhu et al. 1989).

Vegetative method to combat sand has the following six major advantages.

• (1) The artificial, artificial-natural and natural vegetation on mobile and semi-fixed sand dunes can prevent sand dunes and sandy land from wind erosion and make them fixed permanently by covering sand surface and reducing wind velocity.

• (2) The constructed vegetation can improve the properties of barren shifting sand land and promote the formation of sandy soil.

• (3) The constructed vegetation can ameliorate the ecological conditions above and under the covered area, which is good for living organisms’ reproduction.

• (4) The constructed vegetation can propagate and regenerate by itself, even short life-span pioneer plant constructed on mobile sand dunes can evolve into stable ecological system with abundant plant species through automatic adjustment.

• (5) The combined arbor-shrub-subshrub-forage vegetation can not only afford appropriate grazing but also supply firewoods and timber.

• (6) Sand dune is a complicated system, including sand dunes, interdune area, flat interdune bottomland (meadow) and sandy flat. Once vegetation controlled the advancement of shifting sand and wind erosion, farmlands, orchards, melon land and forage bases even new villages can be established on fertile lands protected by vegetation.

Obviously, vegetal sand stabilization is by no means an easy job. The choice of sand-binding plant species depends on biogeographic zone, so different sand-binding plants are chosen in light of local conditions all over the world. At the same time, the choice of sand-binding plants and afforestation tree species is also limited by local ecological conditions. What’s more, the success of vegetative method or not depends on how much wind erosion on sand surface can be controlled.

6.2 Mechanical Method

1. Checkerboard Sand Barriers

In the practice of sand control, mechanic measures are generally taken to fix a large area of shifting sand, and different standard grids or rows of sand barriers made of all kinds of materials (such as straw, reed, clay, and gravel) were extensively adopted. In general, several rows of sand barrier are adopted where prevailing wind direction is single and checkerboard sand barrier are taken where prevailing wind has multi-direction. Sand barrier is basic protection measure to control wind-sand harms. It alters the properties of underlying surface and increases the roughness of ground surface.

When sand flows over straw checkerboard sand barriers, eddy and sand deposition take place. After long term of wind erosion and deposition, stable and smooth concave curved surface comes into being, with an average ratio of maximum depth to sand barrier’s border length of 1 : 10 or so. Regular wavy underlying surface composed of this kind of stable curved surface can produce an uplifting force, which ensures that surficial sand can’t be blown away and sand blown from other place can pass. Because this kind of underlying surface has an “uplifting effect”, it can uplift sand from other places.

Checkerboard sand barrier is characterized by increasing surficial roughness, decreasing the velocity of near surface airflow, thereby decreasing airflow’s capacity of transporting sand and changing the distribution of transportation rate at different height. Checkerboard sand barrier is effective where prevailing wind has multi-direction. When checkerboard sand barrier is built, upright sand barrier is also constructed at the windward side to prevent sand from sand depositing in front of sand-fixation belt and make sand-fixation belt much more efficient. The 1 : 10 ratio of checkerboard sand barrier’s height to width is best. The general standard of checkerboard sand barrier is 1 m × 1 m, it is cheap and effective. Plastic net made into larger 2 m × 2 m or 3 m × 3 m checkerboard sand barriers in Algeria were also effective. Flexible materials are better than rigid ones. Someone proved sand barriers made of rigid concrete bars have bad effect on blocking wind and could cause wind erosion easily. Stripe sand barriers are effective where prevailing wind has single direction and sand barriers should be installed vertical to prevailing wind direction. High crop’s stubble left in farmland is an effective measure to prevent sand hazard in farmland near desert. Vegetative method combined with chemical measures to fix sand are the most effective way in industrial and mining areas or along road lines where sand hazard is very severe.

2. Upright Sand Fences

Sand-fixing measures have very obvious protective effect, but sand deposited in front of sand fence often makes a large area of sand-fixing belts lose their function. As a result, it can result in the formation of new passage of sand flow and the occurrence of new sand hazard. So, sand-fixing measures should be combined with sand-blocking measures.

Upright sand fences are built at the upwind frontal edges to block sand source and promote the formation of high sand-blocking dike which can prevent sand from depositing at the upwind frontal edges and change the transporting capacity of airflow. But it only can be built at the upwind edges, above 2/3 heights of windward slope and beneath the crest line, and should be set vertical to the prevailing wind direction (Zhu et al. 1998). Its effectiveness has several influencing factors.

• (1) Height. The heights of sand fences are determined by local transportation rate. If it is too low, it will be buried by sand soon. So, sand fences should be rebuilt frequently, it’s expensive and not convenient. But if it’s too high, it’s very difficult to be fixed. In general, 1 m is a suitable height.

• (2) Porosity. Indoor and field experiments proved the porosity of sand fences is the most important factor influencing its protective effect. The protective effect includes: ① Sand-trapping capacity; ② Effective protection distance. For dense fence with a porosity of zero, it also can block sand, but its protective range in front of and behind the fence is shorter than its height. With the increase in porosity, the protective range and effect also increase. When the porosity is 30–40%, the protective effect is optimal.

• (3) Relationship between sand source, wind regime, possible transportation rate and fence location. Sand source, wind velocity and duration determine the sand transport rate. Sand transport rate determines the choice of fence. Fence location should be high and can’t be eroded by wind. To prevent the erosion of fence base, 2–4 rows of checkerboard sand fences are built at the windward base.

In order to assess the protective effect of sand fences, we define the ratio (K, %) of fence’s sand-trapping quantity (Q₀) per unit width (m) to the corresponding possible maximum sand transport rate (Q_p) per unit width, namely K = Q₀/Q_p × 100%, as the sand-trapping efficiency of sand fences, which is closely related to fence height, porosity, strike and fence location. What should be pointed out is that sand-trapping efficiency of sand fences is variable and it decreases with the increase of deposited sand volume. Because sand flow is blocked, sand flow direction becomes parallel to the sand mound strike. In fact, multi-directional wind also influences sand-trapping efficiency directly. For example, the average K value is 70–80% in Shapotou area, with the maximum value of 96.5%, and the protective range is 7.5–11.3 times the height of the fence.

The application and constitution of sand fences are local-condition dependent.

• (1) Sand fences are effective in shifting sand area where prevailing wind direction is single. If combined with sand-fixing measures, the protection system “laying emphasis on fixation in combination with block” can prevent sand hazard effectively. For coarse flat sandy land or gravel land, single sand fences can be used, but they should be built on the windward side at a long distance from the protected target. If necessary, sand-blocking system of multilevel sand fences can be adopted.

• (2) Upright sand fences have been widely used to block sand and snow abroad. For example, to control snow on roads, the former USSR and America set a slot at the bottom of barriers which makes airflow accelerate and blow away snow on road and deposit at the leeward roadside. So, sand can deposit constantly and much sand accumulation can result in new hazard; the cost is expensive. In the sand-preventing experiments along the Nanjiang Railway and snow-preventing experiments along the Tian Shan Road in China, the “Feathered Transporting Sand (Snow) Measure” was adopted. It divides fences into many little segments, and the single fence is parallelly arranged according to certain trend spacing. It’s characterized by utilizing energy conversion function to change the direction of sand flow, accelerate wind velocity and blow sand away, with a transportation rate of 65–90%

Of course, there is also an other sand-transporting measure, which can divert sand flow. For example, the section of road in desert can be designed as streamline form, or 1 : 8 gentle slope, which can enhance sand transport capacity, and therefore no sand deposition takes place near the road shoulder. Gravel platform along both side of railway in desert area has double protection function, firstly, gravel layer can fix shifting sand; secondly it has a strong rebound function for sand particles and has a non-accumulated transport function for the passing sand flow.

The above-mentioned four kinds of sand control measures are also known as “fixation, block, transport and diversion” measures. Theoretic analysis and practices proved that sand-fixing measure is the most practical and effective measure to prevent sand damages. Because this measure can dissipate wind energy, sand-blocking measure is a necessary measure that ensures sand-fixing measure can play its role completely. Under special condition, the sand-fixing measure also can be used alone with obvious result.

Practices also showed that different measures should be taken in the light of local conditions. What’s more, different measures should be appropriately combined because no single measure is perfect.

6.3 Chemical Method

In 1930s, oil-prospecting workers in desert sprayed crude oil on sand dunes surface to prevent blown sand hazard and protect oil equipments. From then on, the concept of chemical dune stabilization came into being which brought a new and active research field. Enlightened by dune stabilization using crude oil, people did much work for developing new sand-fixing materials. As a result, a series of sand-fixing materials, organic or inorganic stabilizers were used.

Up till now, chemical dune stabilization has a history of 70 years, but it developed rapidly and has become one of the important sand-fixing measures in arid regions threatened by blown sand damages, especially in desert zone with abundant oil source. Chemical dune stabilization can be divided into the following forms:

• (1) Covering sand surface. Asphalt petroleum products or latex sprayed on sand surface, mostly due to strong absorption and electrical function of sand particles, and therefore they can only form a thin and weak protective layer.

• (2) Binding function. Almost all chemical sand-fixing material has such property, after chemical sand-fixing liquid occupy interspaces between sand particles, the action between particles can be increased and hence they form a bonding layer.

• (3) Hydration. For instance, action between concrete and sand particles can form strong and hard bonding layer.

• (4) Sedimentation function. When water glass and intensifier are used as sand-fixing materials, it infiltrates and occupies interspaces between sand particles, and the intensifier deposits and forms a strong and hard protective structure.

• (5) Polymerization. As polymer and latex are used to control sand, they can form elastic or rigid bonding structure.

The principles of chemical dune stabilization are complicated; it’s not only related to the properties (such as chemical composition and mechanical composition) of sand particles, but also related to the chemical and physical properties (such as molecular structure, absorbability, and viscosity) of chemical sand-fixing materials.

6.4 Combination of Different Measures

Construction and arrangement of protective system are determined by the characteristics of flow field and way or intensity of sand movement. Common arrangement schemes are as follows:

1. Protective system dominated by “fixation” and combined with “block” and “transport” and “diversion”

It is a sand control measure and scheme suitable for controlling large area of shifting sand. It’s not only effective and practical but also accords with the principles of aeolian sand physics in theory. Speaking concretely, sand-blocking belts at the front edge can control sand source effectively; sand-fixing belts can stabilize sand surface, change the property of underlying surface and control the condition of sand movement efficiently, or create the condition for vegetative sand stabilization. If local natural conditions are better, plants can be used as fences, which are called “living sand barrier”. The length of this protective system should be set determined in accordance with the protected targets (such as railway or road).

The width of protective system (protection width) is entirely determined by the migration speed of local mobile sand dunes, or by local possible maximum resultant transportation rate and direction. According to experiences in Shapotou region situated at the southeastern rim of the Tengger Desert, the effective protection width is 130 m at northern side of railway. We think even in extremely arid region, the protective width of 150–200 m is enough when the migration speed of mobile sand dunes is less than 1 m/a (SSDER 1980).

2. Protective system dominated by “block” and combined with “transport”

It’s applicable to coarse flat sand land and gravel land. There may be two cases: first, sand source is far and not abundant; second, sand source is near, but its distribution is not even such as low barchan dunes areas at the edge of desert and interdune flat in the hinterland of desert.

The common characters of these areas are flat and open in topography; wind is strong, sand source is limited and coarse. In the movement processes of sand, once it encounters obstacles such as roadbed, vegetation, etc., shifting sand will deposit and can result in sand damage. So, sand-blocking belts need to be built on windward side far from protected target. Because no protective measures are taken between sand-blocking belts and protected target, small amount of sand material may be conveyed and deposited near the protective system and lead to slight sand damage. Sand-transporting and sand-passing measures can be taken to resolve this kind of sand damage. In practice, single protection measure is also adopted; for instance, clay or gravel is used to completely cover the surface of sand dunes.

The objective of land aeolian desertification control is to rehabilitate the degraded ecosystem, and build an artificial eco-economic system, which can ensure the sustainable development of ecological environment, natural resources and socioeconomic growth.

7 Rehabilitation Patterns of Aeolian Desertification Lands in China

Based on the status of aeolian desertification, aiming at the problems in aeolian desertification control, and to follow the principle of integration of ecological, economical and social benefits, we have generalized the rehabilitation patterns in semi-arid and arid regions from experiences of more than 50 years in aeolian desertification control in China (Zhu et al. 1989; Zhu 1992).

7.1 Rehabilitation Pattern in Semi-Arid Region

Firstly, the occurrence of aeolian desertification is influenced by fragile environment, but in the semi-arid region, aeolian desertification process will cease and can be spontaneously restored once intensive human disturbance is removed. In other words, semi-arid zone has ecological resilience. The grazing exclusion method is generally adopted in semi-arid region (Table 15.12). Even in slightly desertified area, it’s also an effective way. For example, slightly desertified land around Chaohaimiao of Horqin Zuoyi Houqi in eastern Horqin Sandy Land gradually recovered by itself with increased vegetation cover and biomass (Table 15.13) after 3 years of enclosure without other artificial measures.

Table 15.12 Effect of enclosure on desertification land

Table 15.13 Changes of vegetation cover and biomass after enclosure around Chaohaimiao of Horqin Zuoyi

Secondly, it is a good measure to readjust the existing land use pattern that is not in conformity with ecological principles. That is to say, to change the farming management which is characterized by extensive cultivation and poor harvest and takes grains as the principal, and to enlarge the proportion of forestry and grazing to make them beneficial to both ecology and economy. The main points for readjusting the farming structure are to cut down the area of farmland which is influenced by aeolian desertification and intensive farming on the beach flats of lake basins and on the river valley plains where the water condition is better. The efficacy of readjusting the desertified lands in some typical regions show the problem clearly, Huanghua Tala Commune of Naiman Qi, Inner Mongolia, for example, was sandy grassland with an annual precipitation of about 360 mm. The areas of the desertified lands develop to occupy 81% of the total land area due to over-reclamation and over-cutting. Since the 1970s, the land used for dry farming has been readjusted. Consequently the proportion of forest and forage has been enlarged; the measures such as combination of tree, shrubs and grass, and planting tree belts and woodlots have been adopted. At present, the proportion of agriculture, forestry and grazing lands have been readjusted to 21 : 52 : 27. The desertified lands have been preliminarily controlled, the total grain output has been increased by 3.36 times, and the aeolian desertification process has been brought under control basically.

The readjustment of land use structure centered on dry farming in Sijinzi Village of Tongyu County in western Jilin Province represents a successful example to control aeolian desertification. Sijinzi Village is located in the northwest of the county city where aeolian desertification was developing and aeolian desertification land accounts for 34.9% of the total area with an annual precipitation of 407.2 mm. Owing to over-reclamation of grassland, natural vegetation has been destroyed and the forestry and grazing lands were replaced by agriculture lands. As a result, the proportion of agriculture, forestry and grazing lands was changed from 2 : 1.5 : 6.5 in the late 1950s to 4 : 1 : 5 in 1970s. In the late 1970s, land use pattern centered on dry farming has been changed, and the proportion of agriculture, forestry and grazing lands was adjusted to 1 : 1 : 3. In 1984, it has been readjusted to 1.5 : 2.5 : 6, vegetation cover increased from 6.8 to 16.3%. Therefore, ecological environment was ameliorated and shifting sands were controlled. After the construction of field protective forest, the intensity of wind erosion decreased. As a result, per livestock share of forage was increased from 1850 to 3000 kg; the cultivated area decreased by 58.33%, but gross yield increased by 1.4% because of the increased per unit output. Peasants in this village changed their single agriculture cultivation to mixing farming, so per capita income increased from 177 RMB yuan to 500 RMB yuan, the economy of this village was greatly promoted. At the same time, aeolian desertification land has been reversed; both ecological and economic benefits were gained. The same successful examples can be seen in Mangkeng Village of Yulin County in Mau Us Sandy Land.

According to research work of land use structure in typical areas, the optimal proportion of land use is different desertified aeolian areas (Table 15.14). It’s partly due to different aeolian desertification degrees and landscape. The more severe the aeolian desertification is, the more complicated the landscape structure is, and the higher the proportion of forest and grass should be. The adjustment of land use structure should be combined with the construction of capital farmland and enlarging the proportion of forestry and grazing land can gain ecological and economic benefits. Take Baiyin Tala of Eleshun in Hure Qi of southern Horqin sandy land as an example, there was desertified area with mobile sand dunes and interdune area in the past. After adopting the measures to combat aeolian desertification, each farmer had 0.33 ha farmland, 0.5 ha woodlands and 6 heads of livestocks, with an annual income of about 300 RMB yuan, what’s more, 82% of aeolian desertification land has been controlled.

Table 15.14 The optimal proportion of land use in different desertified areas

Thirdly, the proportion of forestry and grazing land should be increased; in addition, the system of shelter feeding or half shelter feeding should be popularized. It is necessary to establish proper artificial grassland and forage farm to supplement the insufficient forage supply on the natural grazing fields. Owing to the combination of livestock breeding and farmland, both straw and green manure can be use as supplemental forage. It possesses very important significance to the development of livestock and also possesses evident function to the increment of economic efficacy. In the counties of the sand areas in Yulin Prefecture, for example, the value created by per labor engaged in livestock breeding is 1.38 times more that that created by each man power engaged in agriculture.

Fourthly, another measure is to recover the natural vegetation on the desertified lands without productive potential. The exclusion of grazing animals should be emphasized. Afforestation should be practiced on sand dunes. Shrub or grass should be planted in depressions. The fixation of shifting sands on the both sides of railway near Naiman of Horqin sandy land, Dayijianfang of Zhanggutai and Hongshixia of Yulin in Mau Us Sandy Land are successful examples. There is severely desertified land with numerous mobile sand dunes along the Naiman section of Jing-Tong Railway. Plant was planted to fix mobile sand dunes, and engineering measures were also adopted. The protection system consists of arbor (mainly P. silvestris L. var. mongolica Litv), shrub (mainly A. halodendron Turcz. ex Bess, S. gordejevii Chang et Skv. and C. microphylla Lam), tame grassland and enclosed natural vegetation, which prevent the development of shifting sands and ensure smooth operation of the railway. As a result, the vegetation cover increased from less than 10% before treatment to present 30–50% and the velocity of sand flow decreased by 60–70%; the content of surficial organic matters also increased and was 6–8 times that of shifting sands; the content of fine particles less than 0.01 mm increased by 2–4 times.

The severely desertified land began to reverse. Table 15.15 is an example of environmental changes after aeolian desertification land has been controlled.

Table 15.15 Environmental changes after aeolian desertification land management (Sanjiazi of Zhangwu)

The farmland protective networks should be established in the beach flats. Also the tree networks should be planted on the alluvial plains of rivers to prevent the basic farmland from being damaged by wind and sand. The Yuxi River Basin in Yunlin County in southern Mau Us Sandy Land is a typical example.

In one word, the land use structure with grazing, forestry and agriculture integrated organically should be established in semi-arid region in light of local conditions, namely it’s the integrated structure of commercial stockbreeding, protective forestry and self-sufficient agriculture (Dong and Gao 1993; Zhu 1999a). This structure should be centered on beach flats and river valley plains. Aeolian desertification land in agro-pastoral ecotone will be controlled step by step only if above mentioned artificial ecological system is established.

The above measures can be generalized as a rehabilitation pattern showing in Fig. 15.7.

Fig. 15.7

Rehabilitation pattern of aeolian desertification land in agro-pastoral ecotone of semi-arid region

Besides determining reasonable carrying capacity, popularizing reasonable rotational-grazing and establishment of tame grassland and forage base, aeolian desertification land control in grazing area of semi-arid region still requires appropriate allocation of wells’ density and the construction of road.

7.2 Rehabilitation Pattern in Arid Region

The development of aeolian desertification in arid region, on one hand, is attributable to the irrational utilization of water resource in the downstream basin, on the other hand, is due to the destruction of vegetation at the margin of oases which leads to the activation and advancement of sand dunes. So, measures should be taken as follows:

• (1) Taking the inland river basin as an ecological unit to make an overall plan. In accordance with the principles of overall consideration of all factors in the upper, middle and lower reaches of rivers, it’s important to unify the management and utilization of surface and underground water resources, to allocate reasonably the water supply along the river, to implement the regulation of regional general layout and the structure of irrigated oases which rely on water supply, and to establish stable and high efficient artificial ecosystem in the river valley. So, it’s necessary to adjust the degree of land use and exploitation in accordant to the maximum irrigating capacity, namely to determine the area of farmland according to the volume of water resources.

• (2) Center around the irrigated oases, sand blocking belts of grasses (using the surplus water in winter season) should be set at the outskirts of oases, sand breaking forest consisting of trees and shrubs at the margin of oases, and farmland protective networks and windbreaks in the interior of oases, such as patterns in Turpan, and Hotan Oasis.

• (3) For shifting dunes around the edge of oases, sand barriers should be planted on shifting dunes and sand binder vegetation should be planted inside, also sand barriers and shrubs should be established in the interdune areas to create a comprehensive protective system, as the Pingchuan pattern in northern Linze Oasis in the Gansu province. At the same time, measures should be taken to protect natural forest and shrub clumps in the marginal area of oases and in desert.

During the rehabilitation process of aeolian desertification land in arid region, efforts should be made to change badland into cases that there are good water and soil conditions in the marginal area of desert and on inland river banks, perfect construction of irrigation works, effective farmland protective networks and soil melioration measures. Some typical examples are exhibited in Shihezi-Kuitun area at the southwestern edge of Gurbantunggut Desert and some oases in middle reaches of the Tarim River at northern edge of Taklimakan Desert.

The shifting sand fixation and available land resources exploitation around oases, and the construction of new oases in arid region are essentially the combination of reconstruction and exploitation of aeolian desertification lands, which are also the two basic aspects of aeolian desertification control. The integration and supplement of two aspects ensure the gain of ecological and economic benefits. The data in Table 15.16 show the changes of landscapes around oases before and after combating aeolian desertification. On one hand, it indicated the decrease of severe aeolian desertification land and intensively developing aeolian desertification land; on the other hand, it shows that part of aeolian desertification land has been changed into woodland and orchard, the productivity of degraded land has recovered and aeolian desertification began to reverse.

Table 15.16 Landscapes changes around oases after aeolian desertification land management (Pingchuan sand control station in Linze)

For the areas encroached by mobile sand dunes in arid region, measures to fix shifting sands should be taken, especially in regions where roads pass through.

According to local successful practices in the rehabilitation of aeolian desertification land and related experiments in the marginal area of desert in arid region, the measures to combat aeolian desertification land can be generalized into the patterns showing in Fig. 15.8.

Fig. 15.8

Main techniques to control aeolian desertification

8 Summary

Land aeolian desertification is not only an important ecological problem, but also a very critical economic and social problem, which hampers the sustainable development of Chinese economy and society. Although significant achievements have been made in aeolian desertification control, yet only a small proportion of the desertified land has been improved, and in most regions the situation has become worse. We think that an urgent need is to review why long-term efforts have so far only achieved less major results, and where the crux of the problem lies. Today, the most urgent task for aeolian desertification control is the innovation of aeolian desertification control models and institutions. The target of land aeolian desertification control is to rehabilitate the degraded ecosystem, and build an artificial eco-economic system, which can ensure the sustainable development of ecological environment, natural resources and socioeconomic growth.