The Loess Plateau

The Description of the Ecosystem

Located in the upper and middle reaches of China’s Yellow River, the Loess Plateau covers a total area of 630,000 km². Including almost three provinces(Gansu, Shanxi, and Shaanxi), and parts of four other areas including the western Taihang Mountain, the eastern Riyue-Helan Mountain, the northern Qinling Mountain ridge, and the southern Yinshan, the Loess Plateau now is sustaining the life of more than 100 million people.(1)

Archaeological evidence indicates that the Loess Plateau has been an inhabitant for human beings for over 8000 year. Ancient Chinese civilizations established their realms on this earth. Consequently, the Yellow River is also called the “Mother River of China”, and the Loess Plateau is lauded as “the Cradle of Chinese Civilization”.

Centuries ago, the Loess Plateau was highly fertile and suitable for farming. However, deforestation and over-gazing exacerbated the ecosystem years by years, and with the increase of population, the ecosystem now is totally different from what it was more than two thousand years ago. Soil erosion caused by deforestation, reduction in the acres of farmlands caused by desertification, and air pollution caused by the overexploit of underground coals all lead to the degenerating environment and the underdeveloped local economy.

(1)

The Historical Overview of the Loess Plateau

There is a debate about what was actually like in the Loess Plateau area. The common idea about the landscape is that grasslands and forests covered the Loess Plateau centuries ago. The natural forest coverage was “more than 50%”, and the local climate of the studied archaeological sites was favoring forest cover. (2)

Other researche suggest that the Loess Plateau could be divided into five parts: a temperate forest zone, which contained a lot of broadleaved deciduous oaks, a warm-temperate forest-steppe zone, a warm temperate steppe zone, a warm-temperate desert-steppe zone, and a warm-temperate steppe-desert zone. (3) In the end, based on the pollen accumulated through years, the researches concludes that the southern Loess Pleateau was dominated by “warm-temperate broadleaved deciduous forest”, and the northern part was mainly “forest-steppe” whose boundary is still debatable. (3)

How have people impacted the ecosystem?

1. The Population Increase

                                                                             (4)

As we can see from the chart above, the population of China fluctuated in different periods, influenced mainly by natural disasters and wars. As Xi points out, “an increase in population means the increase of the area of cultivated land, especially of the area of cultivated slope land”. On the other hand, the sharp decrease in population indicates the fact that large areas of farmlands might be discarded and turned into wasteland instead. The natural vegetation could only restore in a slow pace. (1)

According to Li, at the time by the Sui Dynasty (606A.D.), “there were 2.81 ha of cultivated land per person and 14.6 ha per family,” (2) which was enough to subsist the population at that time. However, as population increased after war periods, the area of cultivated land became “1.80 ha per person”(2) by the middle of the Tang. (~755 A.D.) To the Ming Dynasty (1579 A.D.), there was only “0.77 ha per person.” (2) The population had put an immeasurable pressure on the environment and the demand for cultivable lands. Therefore, large areas of grasslands and forests were removed.

2. Deforestation

Forests are important resources for ancient civilizations. In order to get more acres of farmable lands, trees were massively cut off and used for construction. Also, in the chilly and dry northwest area, woods were crucial as fuels in winter. In the highlands, deforestation often led to serious erosion, which might expose sterile subsoil or bare rock, and prevent further agricultural use of the degraded land, or even reestablishment of native vegetation.(5)

                                                                  (2)

The chart above demonstrates the changes in the forest coverage of the Loess Plateau overtime. For hundreds of thousands of years, the area decreased steeply. The forest coverage in the year of 1990 was less than 19% of what it was 3,000 years ago. Many factors have contributed to the disappearance of the forest, both human and environmental.

For instance, in the Qin Dynasty, the captial was Xianyang, now a city in Shaanxi Province. From the map below it is obvious the city was in the center of the Loess Plateau. (on the left hand of 西安)

  

In history, the first emperor of Qin, Qin Shi Huang, ordered a large scale of construction all over the country. In the mainland of the dynasty, “…massive construction work began on palaces, gardens, and the imperial ancestral temples on the south bank of the Wei River…”(6) In addition, the emperor created an integrated and convenient transportation network within the realm which resulted in the massive disappearance of the forests.

It is acknowledged that forests are indispensible for keeping water and soil. As a result, deforestation deteriorated the ecosystem.

3. The Outbreak of Wars

Wars not only had a great impact on population, but also the environment. According to Xi, the agriculture-animal husbandry boundaries were usually affected by wars. When the nomadic nationalities invaded the south from the steppe, the husbandry shifted southwards, and with the expansion of the southern agricultural nationalities like the Han Dynasty, the line shifted to north.

Several examples of the impact of the wars are given below.

1. The Qin Dynasty
In the Qin Dynasty, the authority conflicted with the northern nomads called “Xiongnu”. In 215 BC,
the emperor “ordered General Meng north with 300,000 men…”(6) to begin the construction of the 
Great Wall, which was designed as a defending system against the nomads in the north.

To further stabilize the defense formed by the Great Wall, Qin Shi Hunag moved a population of 500,000 in to the area of Ling Nan, and set up 44 different settlements in He Tao area to reclaim the farmlands. (Baidupedia) Both the migration and establishment of settlement played an important role in holding the area behind the Great Wall and supplied food for the large number of troops near the border against nomads. (17)

2. Han Dynasty

Han Dynasty had a long history in battling against the nomads in the northwest region. Those nomads, named as “Xiongnu” in Chinese, did not farm for food and mostly rely on the livestock. However, nomadic groups needed all products like garment, porcelain, spice, and perfume although they were not able to produce any of those for daily life. The only solution to them was plundering those people in south who lived on peasantry.

In 119 BC, the emperor of the Han Dynasty ordered a one-time migration of 700,000 people to the north. These people, especially men, were trained when the dynasty assembled army. At the rest of the time, they played the role of peasants and exploited the territory as farmlands for food. As a result, forests and grasslands were destroyed in large scales and camps and farms were built instead. The migration not only solved the food supply issue for the army, but also provided a stable source of men for battle. However, the environmental cost to sustain this huge group of population is enormous.

3. Song Dynasty

Song Dynasty struggled from the beginning of its ruling against the invasion of the Liao Dynasty and the Jin Dynasty, and the later intrusion of the Mongolian Empire. Due to its military composition, the Song’s army, which consisted of footman and archers, was not able to fight against the horsemen of the nomads. The government officials therefore created a series of military strategies to minimize the disadvantages, but left a bad consequence on the environment.

First of all, targeting at the nomadic troop’s reliance on the grasslands for food supply, the Song officials burned the grasslands regularly in the Northwest to cut off the food supply and decrease the mobility of nomadic horsemen. The burning, as recorded by Jin, usually “extended to hundred of miles.”(7)

Secondly, the Northwest Plateau was cold and chilly for most times.(7) Therefore timber and woods were burned for warmth for the entire army. In a battle between 100,000 thousand men, the number of wood required for burning was tremendous. Moreover, woods were also used for cooking. Both the military had a huge consumption of timber.

Third, woods were also crucial as weapons. For the Song’s military which depended severely on archers, woods were the major component of arrows and crossbows.(7) With forest being cut in a large scale, the Song’s military acquired a hundred thousand of arrows and few thousands of crossbows to counterbalance its disadvantage in mobility.

                                              Song Dynasty Bowman, Baidu Image

Fourth, settlements and camps required a lot of woods. “ In the war that lasted 140 years between Song and Jin, more than 500 cities, settlements, camps, and fortress.”(7) For shelter, the pillar of normal camps was wood. For larger fortresses and settlements, wood was arranged as fences and protected the army within it. Moreover, sharpened woods could be used as impediments to the movement of horses, which was significant in battling against the nomads.

4.  The Qing Dynasty

At the beginning of Qing Dynasty, the “foreign” nationality of Manchus attempted to integrate the country and stabilize the royal ruling. The emperors put a great emphasis on the burgeoning of population and land reclamation in order to eliminate the hollowness created by war. The population in the Loess Plateau, as a result, increased “even more quickly due to tax policies of the government.”(2)

Moreover, as Guo mentioned in his research, the Qing authority had set up multiple departments in remote areas of Shaanxi Province (central area of the Loess Plateau) to oversee and assist the land reclamation. The local government distributed lands according to the number of people per family, provided crop seeds according the acres of farms, and offered cattle to each family.(8)

Environmental Factors

1.     Precipitation
      The precipitation of the Loess Plateau is concentrated in months of July, August, and September, with an annual average between 200 to 600 mm.(2) The rainfall in these three months occupy 60-70% of the year total, usually in the form of high intensity storms.(2) These storms are capable of rooting up plants whose roots are shallow, exacerbating soil erosion. Sediments transported by the Yellow River and delta areas increase enormously in these three months.

2.     Dust Storms

(2)

        Dust storm is a new factor of the environmental degradation for the region, which was not present in the past, but common in the modern history of China. As the chart above indicates, the frequency of sand storms increased in a rapid speed in recent years. One explanation about the formation of the dust storms is that these sands and silts are brought by strong winds from the Mongolian steppe to the inner China, and even to South Korea and Japan. Due to deforestation, there are no trees protecting the inner China as shields, nor grasses and plants serving as water and soil keepers under the ground.

Beijing: Tiananmen Square is seen amid the sandstorm that has plagued northwest China for the past few weeks

Photograph: Grace Liang/Reuters, the Guradian

3. Soil Erosion


        The Yellow river has the largest sediment concentration of all rivers, 16.4 billion tons per year (Sediment Specility Committee of Chinese Water Resources Association, 1989). A large section of the yellow river flows through the loess plateau carrying all the sediments along with it, causing the river bed to rise 8 to 10 cm every year. This rise in the riverbed poses great risk of overflowing.

yellow river delta in 2009 source: http://earthobservatory.nasa.gov/Features/WorldOfChange/yellow_river.php

highly eroded landscape source: http://www.clw.csiro.au/ReVegIH/Photos.htm

         The unique physical and anthropogenic factors and their interactions in the loess plateau in China make the place especially prone to soil erosion. First of all the soil in loess plateau, sandy and mainly consists of loess, is highly erosive. Also the area is very tectonically active, which forms gullies and causes large areas of land slide. The valleys concentrates water and adds to its energy to take away soil. Land without vegetation can be a thousand times more erodible than that with a vegetation overage. Unfortunately, due to decades of deforestation, the forest coverage on the loess plateau in China averages only 6.5% and in some areas it can drop to 3%; the grass cover is only 25-65%. So the most part is just bare soil, ready to be away by the heavy and concentrated summer rain, form July to September, brought by the monsoon. All these elements explains why the loess plateau in China is barren full of deep gullies and steep slopes, just like the surface of a walnut.  (18）

         Human activity is the major factor that accelerates the soil erosion in the loess plateau. From historical records, the loess plateau used to be contiguous with the Mongolian steppe, vast and flat and nurturing grassland and forest with few gullies.But now it is the most eroded place on earth; the population increase and irrational use of land has destroyed the previous ecosystem. The increasing loss of soil and water in the loess plateau can be seen from the flood record of the yellow river. Before sui dynasty (A.D. 581 to 618) the Yellow River flood 1.1 times per century on average, but the rate has increased to 155 times per century in the Ming dynasty (A.D.1368 to 1644). The cultivation of slope lands contributes the most to soil erosion. More than 50% of the total arable land in loess plate is on slopes. But the growth of population has forced the cultivation of slopes that are greater than 25 degrees where the risk of erosion is very high. Recent developments in mining and oil and gas industries on the Loess Plateau, which destroy vegetation and geological structure, can even double the amount of erosion if left unchecked. (18）

the current status of loess plateau

conservation of nature

Grain for Green project

Introduced in 1999, the Grain for Green Project (GGP) in China aims at reducing soil erosion and restoring the badly degraded ecosystem, and improve agricultural production in the Loess Plateau and was imitated in other regions in China. A smart step in the direction of scientific development. It has seen promising results through the course of more than ten years of gradual improvement. The area has seen improvements not only in soil and water conservation status and expansion of grass and wood lands, but in agricultural production, economics, and living qualities of local people.

Method

To issue a project so large that “covers 25 provinces/regions/cities over 1600 counties, involving 15 million households and 60 million farmers",(10) the support of local people is greatly needed. Agricultural tax codes are changed and subsidies are given to farmers whose fields are converted to forests while they work in organized afforestation effort, which engages millions of local households and allows the man power for the restoration to actually implement. The founding for the afforestation is also subsidized by the government. Economical forests that are converted form croplands are contracted to framers “with a combination of responsibilities, power and interests".(10) This basically means that the farmers are allowed to own the forests that are converted from the crop lands, to transform their business, from primitive and low-efficiency agricultural labor to a variety of higher-efficiency crop or fruit tree production, using more advances techniques such as using green houses, and benefit more, directly from their labor. This is a great deal for the farmers, a great incentive that inspired cooperation from local people, which is the key to the project.

To cover again the barren lands with greenness, ingenious landscape engineering methods are developed. Basically, it is flattening the slopes and filling the gullies. Terraced fields are built alone gentles slops, and on steeper slopes, other kinds of terracing methods are adopted to allow trees be planted and water to be preserved better in the soil and would not flow directly into the tributaries instantly after rain fall. Small dams are built to block the sediments and fill the gullies as well as creating small lakes designed to improve hydrological cycles. Dune stabilizing methods are also adopted in heavily desertificated areas. Finally, agricultural practices are also changed: Grazing was banned and converted to household ranging. A variety of other crops and tree crops are introduced  

the essence is to terrace

sediment damb convert gully into fields

Achievements

The restoration had good results, environmentally and economically.

7.7 million hectares of farmland has been converted into forest nationwide from 1999 to 2002 (17), with new vegetation established, the loess plateau has transformed from a carbon source to a carbon sink. Replanting and bans on grazing allowed the perennial vegetation cover to increase from 17 to 34 percent (15). Soil and water are becoming better conserved, and the sediments, more than 100 million tons each year (15), as well as nitrogen and phosphorous in the lower reaches of the yellow river have significantly reduced (9). The factors allowed synergistic effect to allow nature to expand by itself, but also induced regional water yield (9).

         While acreage of cropland have been reduced, agricultural production and economy have generally improved. Terracing, sediment capture, and change in farming practices, besides reducing runoff and such, have secured food production by reducing droughts and making the slopes more arable. “During the second project period, per capita grain output increased from 365 kg to 591 kg per year”.(15) As the food value and output increases so does the income of local farmers. Income increased, employment raised, and roads built to facilitate commerce. 

change in land cover (9)

water and soil change due to land cover change (9)

(9

"During the past 15 years, the 11 EDAs have

undergone great change. The average yield of

farmland has increased by 100–300%. Grain yield

has increased from 5737.5 kilograms per hectare

(kg/ha) to 8196 kg/ha; average personal income has

risen from 218 yuan/year to more than 2000 yuan/

year (US$1 = 8.0 yuan). The amount of reclaimed

land has increased from 46.1% to 80.2%. Research

achievements have been applied to up to 10 million

hectares of farmland, with some 5.55 billion yuan in

increased crop value." (10)

EDAs (10)

In order to have a detailed look on the change in land cover, take Ansai as a case study. Located in the central part of the Loess Plateau, Ansai county, part of Yan'an municipal city, is the national station for water and soil conservation. Ansai County covers an area of 2940.9 square kilometers (40◦14'11"N–42◦27'42"N, 75◦33'16"E to 80◦59'7"E) , is one of the eleven experimental and demonstration areas for ecosystem rehabiliation in the Loess Plateau described by Li et al., 2012.

Overal ecosystem of Ansai County, Shaanxi Province, which is the the national station for water and soil conservation in Loess Plateau. In Shaanxi Province, the green color represents low hilly loess terrain with the lowest altitude of 921 m, and the brown color represents the high hilly loess terrain with the highest altitude of 1730 m. Ansai is located in the lower hilly loess terrain.  (11).

Ansai county

After a detailed study for the ecosystem management in Ansai county, the authors (11) concluded that the implementation of the Green to Grain Program (GGP) increased the newly forested land substantially to 21.4% of the study area by 2010 at the cost of both cropland and shrub–grassland, which decreased by 46.3% and 18.8%, respectively, from 1995 to 2010; and  the coverage of forested land (both older forest and newly forested land) increased from 12.4% in 1995 to 37.7% in 2010 (11).

Land cover changes during the Green to Grain Program in Ansai county

Future prospect

      The nature restoration project has had some notable effect in revitalizing the ecosystem and improving the lives of local people and adjusting the agricultural and industrial structure, which is a great start for future developments.

      To keep up the good trend. Several aspects should be considered: (1). The government should continue to provide grain, since the loess plateau itself cannot produce enough food yet, and subsidize tree crop and other alternative high-efficiency agriculture to improve the economic security of local people.  (2). With the economy growing, and introduction of mining, oil, and related industries, prudent and well thought development plans should be made rather than making radical steps concerning only interests at the sacrifice of nature. (3) The restoration of nature and conversion of low efficient traditional agriculture should keep momentum and spread the greenness into deeper, starker, and even less populated areas. Revegeration should also be based on a more comprehensive study of local climate; choose the right plant for the right climate and keep monitor and maintenance. And of course we need to develop and apply better technology for soil conservation and sustainable agriculture.

Hongjiannao wetland, nature reserve

Hongjiannao wetland

Hongjiannao wetland, located in Shenmu, Shanxi province, is the largest desert freshwater lake in China, covering 32.88 square kilometer in 2012 and an average depth of 8.2 meters.（22） The wetland not only serves as a great place for tourism, but also as the life source for the nearby pasture and a crucial habitat for endangered migrating birds such as the world’s endangered larus relictus. If the wetland dries up the area would turn to complete desert.

But the surface area of Hongjiannao is dramatically shrinking due to several anthropogenic factors:1. Dams and reservoirs on tributaries leads to a sharp decrease in water supply. Of the former 7 tributaries, most of them have dried up. 2. Mining that cause the bottom of the lake to sink and crack, which cause water to leak. 3. Surrounding factories relentlessly take the wetland as a natural sewer.4.Increasing farmland, vegetation cover and tourism also add a noticeable amount of water consumed. To make matters worse,the area also suffers a growing decrease in natural rainfall and increase in evaporation due to temperature rise.（12）

Now the wetland is bad condition: The lake’s salinity increasing; with a pH of 9.6, a sharp increase from 7.2 in the 80s（22）, fish is barely found. Water level continues to fall, about 20 to 30 cm annually after 2002,（23） and it is possible for the lake to completely dry up in a few decades becoming the second Lop Nor, a caused by growing population, imprudent water usage and dam building. 

Several conservation and monitoring project is now underway; nature reserves are set up.

Hongjiannao drying up

Imprudent development of engergy industry

The economy in loess plateau revolves around the energy industry.

The state of coal

      China needs lots of energy, of which 70% comes from coal, far higher than the world average of 30 per cent. (24) “China now accounts for 47% of global coal consumption – almost as much as the entire rest of the world combined.” (21) China has 1,000 billions of proven coal reserves, the third largest in the world, and “the total added value of coal extraction and washing was RMB 358.7 Billion ($60 billion), accounting for 1.7 per cent of GDP.” (20) Coal and other fossil fuel mining and the industry related, such as coking, steel production, and chemical industries, are the back bone of the economy in the loess plateau.

Coal distribution in China

      The largest coal reserve and mining industry is located in the east-to-middle sub-region of the loess plateau, the Shanxi Province, which is called the coal capital with a coal reserve of 200 billion tons. “Since 1999, the coal output in Shanxi province has been retained at about 250 million tons per annum. This represents 25% of the national total output and 5.6% of the world’s production.” (24) Coal in Shanxi is of high quality and can be produced with a low cost of labor compared to other countries, only 20% of the total production cost (24), which makes it competitive in the international market.

Problems

      Serious environmental and political problems has arose due to the intense development in the past few decades in this industry. Due to the top down political system, even though there is adequate law to check environmental cost and safety and welfare of worker. 
(1). The coal industry (in China) gives out huge amount of waste and pollution.

“According to official figures, coal is responsible for 70 per cent of soot, 85 per cent of SO2, 67 per cent of NOX and 80 per cent of CO2 emitted in the country. Under the Chinese Government’s air quality criteria, over a third of Chinese cities have air quality worse than Grade. Some 30 per cent of the land in China is affected by coal-related acid deposition. In addition, by 2007, China’s coal industry had left behind 3.6 gigatons of gangue accounting for 40 per cent of solid waste in the country. The total sink area of coal mines currently surpasses 700,000 hectares.” (20) 

(2). Coal production has a giant demand on water supply, in areas where precipitation is little and water is scares like Shanxi. Adding the amount of waste the companies dump into the waters, there already exist huge and growing conflicts within the society. (19) 
(3).The mine workers are being exploited like slaves and hundreds of private mining company owners live extravagant lives because of failed implementation of law.

the following link gives a glimpse into the water pollution problem in coal production areas in Shanxi, a video by greenpeace:

http://www.greenpeace.org/international/en/news/Blogs/makingwaves/greenpeace-investigation-in-china-yellow-rive/blog/46536/

A long way to address the problems

      The problem is obvious but complicated. Serious political measures should be taken to adjust the current situation: (1) Strict assessment and punishment of pollution and such should take place (2). Improve liability rules on safety of workers and damage to surrounding environment. (3). Internalize the external cost of coal by political methods such as increase mine toll and levy heavier pollution taxes. 

traditional sustainable living style---Yaodong, cave dwelling

Yaodong in Xian source: wikipedia

      Yaodong or cave dwellings are unique and common vernacular housings on the loess plateau. They are found in less developed provinces, specifically, Gansu, Shanxi, Henan, and the Hui Autonomous Region of Ningxia, where resource is scarce and transportation is very limited. In fact, the loess plateau has gone through over 8 thousand years of human activity and rural areas have long been barren, rugged and almost deserted. So people from over 2000 years ago has been utilizing loess and the unique terrace to cave their homes.

      
      The caves chambers are rectangular and have and arched roof, which adds to the perception of space. The chambers can be connected to form suites or be used as granary or stables. In places where there is no natural cave, a pit is dug and the arch tunnels are then dug around it, which forms a court yard village underground. Due to lack of coherence in the soil, the caves are cannot be made very large. It is usually 30 feet long and at most about 15 feet wide. The beds are called Kang, which are earth platforms often connected with an earthen ovens at the end; grass can be burnt underneath to heat up the Kang. When the camber is not to deep down, a chimney shaft can be built, but when the cave is deep, the smoke has to go into the room and out through an opening above the door.(12)

     Though this type of dwellings seems primitive, they conserve a lot of space and energy; the unique design makes them cool in summers and warm in winters. In fact the cave is actually quite comfortable to live in if well furnished and they are indeed gaining increasing popularity. New designs of these cave dwellings are applied to incorporate electricity, water, sewage system, and even solar panels. 

In side of Yaodong

pit court yard

                                                                     Work Cited

1. J.X. Xu, Historical bank-breachings of the lower Yellow River as influenced by drainage basin factors, Catena, 45 (2001), pp. 1–17

2. Li, Wang, Historical Changes in the Environment of the Chinese Loess Plateau, Environmental Science & Policy Vol.9, Issues 7-8, November – December 2006, pages 675-684

3. Sun, Xiangjun, Vegetation History of the Loess Plateau of China During the Last 100,000 Years Based on Pollen Data, Institute of Botany, Chinese Academy of Science, Beijing 100093, China, Quaternary International, Vol. 37, pp 25-36

4, Wang J.G., Lu J.F., Studies on ecological limits to agriculture development on Loess Plateau: from the change of population capacity (1996), Ecological Economy, Vol.4, pp. 44-47.

5. Osborne, Anne, The Local Politics of Land Reclamation in the Lower Yangzi Highlands, Late Imperial China, Volume 15, Number 1, June 1994, pp. 1-46 (Article), published by The Johns Hopkins University Press

6. Frances Wood, China’s First Emperor and His Terracotta Warriors, Google Scholar, pp 26,33

7. Jin, Yongqiang, The Impact of the Battle between Song and Jin Dynasty on the Plants of the Loess Plateau, Journals of Ningxia Teachers University (social science), vol.30, No4, August, 2009 (In Chinese)

金勇强，《宋夏战争对黄土高原区植被的影响》， 宁夏师范学院学报（社会科学），第30卷第四期，2009年8月

8. Guo, Songyi, An Analysis of Early Qing Dynasty’s Land Reclamation Policies, China Economic History Discussion Forum, accessed on Nov. 24^th, 2013 (In Chinese)

郭松义， 清初垦荒政策分析——《民命所系：清代的农业和农民》

http://economy.guoxue.com/?p=5080&page=4

1.  “陕西的边邑之地，康熙末，官府多设“招徕馆”以鼓励垦荒，“民之来也，必计口授田，计田给种，朋户给牛”，使农民比较方便的得到小块土地。”

2. “ 清朝统治者出于稳定封建秩序，加强地主阶级专政的政治经济需要，对招徕垦荒给予很大的重视，先后颁布了一系列政策、法令。”

9. Lu Y, Fu B, Feng X, Zeng Y, Liu Y, et al. (2012) A Policy-Driven Large Scale Ecological Restoration: Quantifying Ecosystem Services Changes in the Loess Plateau of China. PLoS ONE 7(2): e31782 edition. Prentice Hall. 626pp.

10. Li R, Liu GB, Xie YS, Yang QK, Liang YL, 2002. Ecosystem rehabilitation on the Loess Plateau. In: McVicar, TR, Li R, Walker J, Fitzpatrick RW and Liu CM (eds), Regional Water and Soil Assessment for Managing Sustainable Agriculture in China and Australia, ACIAR Monograph No. 84, 358–365.

11. Zhou DC, Zhao SQ, Zhu C. 2012. The Grain for Green Project induced land cover change in the Loess Plateau: A case study with Ansai County, Shanxi Province, China. Ecological Indicators. 23: 88-94. 

12. Yangling. “Soil and Water Loss form the Loess Plateau in China.” Journal of Arid Environments (2000) 45: 9–20. Print.

13. Ou Guang-yan, et al(2012). Water Eclology Status and Protection Measures for Hongjiannao Basin. Journal of Hydroecology, vol.33, No.2.


14. Myron L. Fuller and Frederick G. Clapp. Loess and Rock Dwellings of Shensi, China. Geographical Review , Vol. 14, No. 2 (Apr., 1924), pp. 215-226

Online Sources
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16. Baidupedia, 《移民实边》："汉武帝时，为加强北方边防，公元前119年，一次就移民70余万口，充实北方诸郡..." http://baike.baidu.com/view/1673346.htm

17. Li Zhiyong. “17 A policy review on watershed protection and poverty alleviation by the Grain for Green Programme in China.” FAO. http://www.fao.org/docrep/008/ae537e/ae537e0j.htm


18. “Restoring China’s Loess Plateau.” The World Bank. http://www.worldbank.org/en/news/feature/2007/03/15/restoring-chinas-loess-plateau

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