Desertification Research in China
- History, status and challenge
Institute of Arid and Cold Regions Environmental and Engineering Research,
Chinese Academy of Sciences
(Donggang West Road 260, Lanzhou 730000 China)
Desertification research in China is reviewed in terms of its history and status and challenge in this paper. Desertification research in China is closely related to desert research. It is recorded that desert research started by the end of 1950s, although efforts in desert control and sandy land utilization have been already made since as early as 1940s. Research in desertification started in full scale around 1970s, but its history could be traced back to as early as desert research for their inseparable relations. In the past years, researchers have made great progresses in both of desertification research and its control at many places, but, as a whole, desertification is still expanding at an ever-increasing rate. Expected are the following challenges: desertification and global climate change, desertification and air pollution, desertification and changes of land policy and market, desertification and sustainable water utilization and setting up desertification early-warning system.
Keywords: Desert, Desertification, desertification research, China
Desertification is the process of land degradation in arid, semiarid and some sub-humid areas, due to adverse climate and human activities (UN, 1992). As in the world, desertification is one of the most severe environmental problems in China. It occupies a large area deteriorating the habitats of the life in the area in which it takes place and threatening the development of China. Desertified land in China is about 2.6*106km2, nearly 27.3% of the total land of the country, and approximately 71% of the desertified land distributes in the North and Northwest and Northeast of China. According to surveying, desertification is threatening about 1.04*107hm2 arable land and 1*108 hm2 grassland, and about 4.2* 107 people living in this area (Zhu Zhenda, 1996). About 50% of the energy and 60% of the row materials needed in east China are from the North and Northwest. In view of the severity of desertification, Chinese researchers have initiated researches in desert and desertification since the end of 1950s. During the past 40 years, Chinese scientists have made great progresses in both of the academic research and desertification control. As a whole, however, desertification is still expanding while it is halted, even very successfully halted in some parts of the desertified area.
Researches and facts showed that desertification brings harmful environmental effects not only on the area it happens, but also the areas near to and even far away from it. The sand and dust storms in the spring of 2000 severely hit most part of China and some countries nearby. It is valuable to give an introduction of desertification research in China for the academic exchange and practical reference among governments, non-government organizations, researchers and individuals abroad and at home.
China is one of the countries of the largest area of desert and desertified land and suffers heavily from various desert-related problems. Expansion of desert and desertified land destroys villages, buries railways and roads and engulfs cropland and grassland, as well as threats the people and livestock along its way. That is why far earlier than desert and desertification research, people living in the North and Northwest and Northeast of China started combating desertification. For example, as early as in 1940s, farmers in Jinbian, located in north Shaanxi province, utilized sandy land by leveling off sand dunes with water flush and collected sediment to make cropland. In the middle of 1950s, farmers in Zhanggutai township of Liaonin province planted Pinus syvestris var. mongolica (íéíáæ) to protect their cropland from desertification (Zhu Zhenda, 1979). At the very beginning, researchers attached more importance to desert formation and expansion and desert control only because desertification at that time is not widely and clearly recognized. Later on, many processes related to desert are categorized as processes of desertification. Desertification research is actually developed or generated from desert research in China.
Desertification research history in China could be broadly divided into three periods. The first period was from the late 1950s to the early of 1960s. Researches were focused on desert more than desertification. In 1958, Chinese Academy of Sciences (CAS) organized a Team of Desert Survey and Control for research in desert (Zhu Zhenda, 1979). During this period, researchers carried out intensive measurements and field survey on the processes, causes, spatial distribution and dynamics of deserts, as well as desert control including harness of desert encroachment, oases and large construction sites protection (Zhu Zhenda, 1963a; 1963b, 1964, 1980, 1982). Later on, based on this team, CAS setup the Institute of Desert Research (IDR) in Lanzhou with the aim at desert and desertification research in the whole nation. When the researchers from the institute were carrying out surveys on deserts, a field station, Shapotou station was inaugurated in 1958 for protection of the Zhongwei section of Baotou-Lanzhou railway from desert encroachment by re-vegetating on the sand dunes. The station played a very important role in establishment of planted vegetation and carrying out long-term research in vegetation succession on dunes in arid area (Liu Yingxin, 1987).
The second period is from the middle of 1960s to the middle of 1970s. It was the period of the ¡®Great Cultural Revolution¡¯. As a whole, researches were interrupted. Researches were continued only at some key project sites, such as Zhongwei section of Baotou-Lanzhou railway through Tengal desert, Yumen railway section through Kumudaka desert and Naiman section of Beijing-Tongliao railway through Horqin Sandy Land. Desertification was spreading in a large scale and at a rapid rate due to the rapid population increase and misleading of land use policy in this period (Zhu Zhenda, etc.1981).
In the third period from the late 1970s up to now, encouraged by UN Nairobi Conference on Desertification, supported by governments at all levels and pushed by the practical need of economic development, researches in desertification were fully carried out through the nation. To meet the need, several field stations were put into operation by IDR. These stations were strategically distributed from the West to East representing arid, semi-arid and dry sub-humid climates. But many of the stations were research project-oriented, not for long time observation in ecological changes (Zhu Zhenda, 1979; Wang Tao, 1999). In early 1990s, Fukang station located in Xingjiang, Shapotou Station located in Ninxia and Naiman Station located in east Inner-Mongolia were selected as three of the 29 field stations by the Chinese Ecosystem Research Network (CERN, 1993). These Stations have played and will play very important roles in monitoring environmental changes, carrying out ecological research and restoration of degraded ecosystems and providing immediate and objective information for decision-making in a long time.
After about 40 years of efforts, desert and desertification research in China has been world widely recognized although failures have been experienced and challenges are expected.
2.1 Desert Research
In the past 40 years, in combination of interpretation of aerial photos and satellite images and intensive field investigation, researches showed that desert in north and northwest China was formed in the period of Quaternary (Zhu Zhenda, 1986; Dong Gangrong, 1991). Desert, as a matter of fact, including desertified land mainly distributes in the large basins with huge sediment of sand supplied without interruption mainly by wind and water acting on the surrounding mountains, plateaus and highlands. The total area of deserts in China is about 5.4*105 km2, sandy land 9.6*104 km2 (Zhu Zhenda, 1986). Considering the climatic influence, low rainfall limits the development of vegetation and strong wind blow leads to the formations of sand sheets, shield types of sand cover and dunes in turn, and at last the formation of desert. Desert formation is a process of re-arrangement of land surface (Zhu Zhenda, 1986). Depletion of water resources was one of reasons leading to desert expansion in arid and semi-arid areas (Gao Qianzhao, 1991). Lots of researches have been carried out since the beginning of desert research on water use and water resource arrangement in the river systems, such as Tarim River and Heihe River and Shiyanghe River (Li Baoxin, 1982; Fu Xingqi, 191982; Wang Yanlai, etc., 1987). Aeolian Physical research revealed that sand movement is driven by wind and sand moves in the forms of creeping, floating and saltation (Zhu Zhenda, 1986; Liu Xianwan, 1995). Changes of the huge sand ridges are closely related to the activities of barchans. Researches also showed that most of the huge sand ridges in west China are composed of barchans or chains of barchans. When wind acting on barchans, changes of the barchans lead to the movement of huge sand ridges and at last the change of land surface (Zhu Zhenda, 1963; 1964).
When extensive researches were carried out in arid and semi-arid area of China, desert control was going on progressively too. Shapotou Station has played a very significant role in the protection of Zhongwei section of the Baotou-Lanzhou railway right going through Tengli Desert for 40 years. Another station, namely, Linzhe was setup in Hexi Corridor to protect oases and develop techniques for establishment of high efficient cropping systems in desert. The success of the Linzhe station made a great contribution to the food security for the local people, but its over use of water led to the contract and at last disappearance of the Gasunnor Lakes in the down reach of Heihe River in Inner-Mongolia (Gao Qianzhao, 1991).
2.2 Desertification Research
Before the 1977 Nairobi Conference on Desertification, Chinese researchers paid much more attention on desert research, although, their researches were closely related to desertification and its control. After the 1977 Nairobi conference, things were greatly changed. Theoretically, most of the researchers come to a consensus on desertification: desertification is the process of land degradation in arid and semi-arid and some sub-humid areas; it is caused by climate changes and human activities; it is reversible; desertification in China mainly distributes in the vast area east to the Helan mountain; wind and low rainfall are two major natural factors leading to desertification; fragile ecosystems are susceptible to desertification (Zhu Zhenda, 1991; 1994).
Research revealed that China has 262.2*104 km2 of desertified land and this figure is increasing at the rate of 2460km2 per year (CCICCD, 1996). Economically, desertification led to a direct loss of 5400 million Yuan a year (Zhang Yu, 1996). As stated before, the North and Northwest of China supply about 50% energy and 60% row materials for the east (Zhang Yu, 1996), desertification thus indirectly threats the development of the East. Environmentally, desertification leads to frequent sand and dust storm severely affecting the economic activity and environment of the local and areas nearby. Sand and dust storms in 2000 spring not only hit the North and Northwest part of China, but also led to heavy air pollution and economic losses in east China and neighbor countries.
In order to halt the expanding thrust of desertification, following researches have been carried out in the past 40 years.
2.2.1 Researches in Causes of Desertification
Desertification is caused by the combined impacts of natural processes and human activities. The natural processes refer to the global climate changes and land surface of loose sand sediment. Global climate changes, especially the changes in the middle temperate zone, drives the climate into a dry and warm trend likely to desertification. The temporal co-presence of low precipitation and dramatic variation, strong wind blow and wilted vegetation in winter and spring is the direct natural causes of desertification in north and northeast China (Zhu Zhenda, 1994; Zhao Halin, 1993; Huang Xichou, 1996).
Considering the human causes of desertification, it is clear that during the last 100 years, climate change was not significant enough leading to the rapid development of desertification. However, in this time, rapid increase of population and intensive farming and animal raising activities have significantly changed the land cover and increased water use and led to large area of desertified land. Human activity, therefore, is at the top list of desertification causes. Human activities leading to desertification refer to over-cultivation, over-grazing and over-cutting of trees and bushes for fuel and over utilization of water resources (Zhu Zhenda, 1994; Liu Xingmin, 1993; Zhao Halin, 1993; Sheng Jianyou, 1993). Research (He Qiang, etc., 1994) showed that to meet the basic needs of a man, 0.2 hm2 land is needed, but the averaged cropland of China is only 0.1 hm2 per person. Whenever the demand is over the holding capacity of land, human activity is very likely to become destructive to the ecosystems. According to the Office of National Agricultural Planning (2000), from 1986 to 1996, about 1.9*105hm2 grassland was cultivated in Inner-Mongolia, Gansu province and Xinjiang together, but nearly 49.2% of the land was desertified (News of China Youth, 2000).
Every year, there is about 149km2 of cultivated land in China lost to desertification (Planning and Surveying Academy of National Forestry Bureau, 1996). Desertification of grassland due to overgrazing is another problem (Zhu Zhenda, 1988; Liu Xinmin, 1993; Zhao Halin, 1993). Inner Mongolia, which has the largest grassland in China, had 2.1*105km2 desertified grassland in 1983 and 3.9*105km2 in 1995 (CCICCD, 1996). In 1950s, there was no severely desertified grassland in Hulunbal prefecture located in northeast Inner-Mongolia, but in 1970s, desertified grassland reached at 8.6*105 hm2, and this figure expanded to 1.73*106 hm2 in 1980s due to over-grazing and over-reclamation. Research showed that carrying capacity of the grassland in Horqin Sandy Land is 1.04h hm2 a sheep, but actually, there is only 0.19hm2 grassland available to a sheep (Zhao Halin, etc., 1997). Fuel wood collect is one of causes of desertification. Research showed that fuel wood consumed by a household a year in Horqin Sand Land is equal to the total above ground biomass of 1hm2 grassland (Zhao Halin, 1998).
Overuse of water has a long time onsite and offsite effects, environmentally and economically. Excessive water use for the Linzhe oasis in the up-reach of Heihe had not only led to salinization and water table decrease in the oasis, but also led to the dry-up of Juyan Lake in the down reach in western Inner Mongolia. The lake had a water surface of 300km2 in 1950s, and became a sand bowl in 1991. Increasing over-use of water resource threatened and will continue to threat the development of China without no time (Vaclav Smil, 1992; Gao Qianzao etc., 1991).
Collect of medicine herds has attracted more and more attention in recent years for its destruction of grassland cover. Observation showed that harvest of 1kg dry licorice root (Glycyrrhiza ralensisÊöõ®) would destroy 1 hm2 grassland (News of China Youth, 2000).
Research showed that desertification processes includes degradation or destruction of vegetation, soil degradation such as loss of soil organic matter and fine particle materials, and formation of the landform dominated by dunes and sand activities (Wang Tao, 1999).
2.2.2 Researches in Distribution
Researches showed that desertification takes place mainly in the large area east to the Helan Mountain, which locates at the border of Ninxia and Alaxan, especially in the zone along the border between the Great Wall and Inner Mongolia. This is the area is well known as the Agro-pastoral zone with an annual precipitation about 400mm (Zhu Zhenda, 1988). Agriculturally, this zone is the northern limit of rain-fed agriculture, but agricultural activity has already northward surpassed this limit. Rapid development of desertification in this area demonstrates the adverse effects of this northward agricultural expansion (Zhao Halin, 2000). The Agro-pastoral zone is classified as the area fragile to desertification (Zhu Zhenda, 1988; Huang Xichou, 1996). In the vast area west to Helan Mountain, desertification breaks its way around oases and deserts, along rivers, and fluvial plains in front of mountains and emerges in grasslands (Zhu Zhenda, 1964; Zhendu, 1998; Leng Sunying, 1998). A series of maps presenting various types of desert and desertified land were published (Zhu Zhenda, 1964, 1974; Hu Menchun, 1997a).
2.2.3 Monitoring of Desertification
Monitoring on desert and desertification were carried out in all the northwest, north and northeast China in 1950s and 1970s, respectively (Zhu Zhenda, 1964, 1974). Most of the desert and desertification maps now used in China are based on these maps. Researchers from IDR carried mapping work in 1980s and 1990s for assessment of desertification in north China. But only some typical places were fully surveyed (Zhu Zhenda etc., 1994). With the development and wide application of Remote Sensing (RS), Geographical Information System (GIS) and Global Positioning System (GPS), it is possible to carry out desertification monitoring at the time needed and at different scales. Early-warning system is a pressing need to provide immediate information on desertification related hazards and provide basic data on the changes of land resources in north, northwest and northeast China for decision-making. Monitoring on desertification needs an operational index system for assessment. In the past 40 years, researchers have setup a system of semi-quantitative indexes including dune number of unit area, vegetation coverage and average height of dunes (Zhu Zhenda, 1994; Hu Menchun, 1991; Wang Tao, 1999). But there are no quantitative indexes for the changes of soil and land productivity which are very important factors for desertification assessment (Wang Tao, 1999; Hu Menchun , 1991).
2.2.4 Desertification Control
Other than the successes in protection of railways, roads, reservoirs, oilfields and mining sites in desert and desertified lands, desertification control gains successes in environment protection, food security and promoting economic development (Liu Xinmin, 1995; Zhao Halin, 1995). Research in desertification control on one hand includes sustainable land use (Liu Xinmin, 1993; Zhao Halin, 1993), crop selection and fertilizer application and rationalized irrigation (Huang Xuewen, 1993) and livestock raising techniques (Zhao Halin, 1995) for improvement of farmer¡¯s lives and reduction of pressures on land; on the other hand includes environmental protection, re-vegetation of desertified land and knowledge dissemination. For instance, The Naiman Station of Desertification Research of CERN has carried out desertification research in Horqin Sandy Land since 1971. At the beginning, researchers participated in the site selection of Tongliao-Beijing railway and then the protection of the railway from desertification by setting up shelterbelts of Pinus sylvistris var. mongolica in combination with the aboriginal bushes of Artemisia halondendron (ó¬÷é嘎ûÚ) and Caragana microphylla£¨á³叶锦鸡儿£©. Since 1986, the researchers have been engaged in desertification and land resource utilization. Researchers firstly introduced the measures of soil management, selected crops and animal raising techniques tested in the station to several demonstrating farmers. After tested by the farmers, all the measures and techniques re-selected were disseminated around the demonstrative village and then the township. Five years later, the averaged income of the demonstrative village was increased from 174 Yuan (About 30 U.S dollars) per person to 1290 Yuan per person (Zhao Halin, 1993; Wang Tao, 1999). Income increase encouraged the farmers to reduce rain-fed cropland and protect grassland and bush land. Shifting sand area was reduced from 1000 hm2 to 330hm2 and vegetation coverage increased from 10% to 70% (Zhao Halin, 1993).
It is clear from the experience that when poverty is relieved, better eliminated, farmers start to participate actively in desertification control.
2.2.5 Desertification Research and Related Scientific Subjects
Desertification is a complex process and research in desertification and its control certainly includes many related scientific subjects. Here introduced are some most frequently used in desertification researches.
184.108.40.206 Desertification and Aeolian Physics
Aeolian physics is the elementary theory for desertification research. Researchers tested the movement of sand of different composition, texture and organic content at different wind velocities in wind tunnel (Liu Xianwan, 1995). Effects of different sand barriers on sand movement were also tested to search for efficient sand barrier structure (Liu Xianwan, 1995). Research in aeolian physics help to understand the mechanism and process of sand transportation and optimize sand fixing program. Field observation was also tested in laboratory to model the processes of changes of various dunes (Zhu Zhenda, 1986). But because all the measurements were finished in wind tunnel, deviation is unavoidable when the conclusion is extrapolated to the field. For instance, sand barrier is downscaled, but the sand particle is the same in wind tunnel as that in the field. Aeolian physics plays a crucial role in monitoring on the process of sand and dust storm.
220.127.116.11 Desertification and Meteorology
Climate is one of the factors leading to desertification and imposes impacts on the changes of land cover at the global, regional and local scopes. Researchers have observed the climate changes over the target regions for explanation of the relationship between the dynamics of desertification and climate change. Researchers also traced the climate change over long time by tracing the ruined cities and the vicissitudes of merchant activities to reveal the process of desertification in the past. Researchers also modeled the changes of meteorological characteristics of individual dunes and measured the wind outline over different parts of a dune (Li Shenggong, 1993). Different desertified land and vegetation at different stages of succession have different moisture and thermal flushes and albedo (Y. Halazono, 1994; He Zongyin, 1993). This is very important for exploring desertification process and regional climate change, as well as selecting right site for planting.
18.104.22.168 Desertification and Plant Physiology
Re-vegetation is one of the most effective measures for desertification control. It is crucial to select the right plants for planting on the right sites. Research has been done in plant physiology including water balance between plant and soil and atmosphere, water deficit of plant (Zhou Ruilian, 1999), plant anatomy, and the physiological changes of psammophytes with the development of desertification, for instance, the changes of enzyme systems (Zhou Ruilian, 1999) and photosynthesis, and membrane activity and the dynamics of stoma (Wang Haiou, 1999). Research revealed that under the stress of drought and high temperature, the day course of plant photosynthesis present double-peaks curve and photosynthesis rate is low. Plant of high stress-resistance losses water at a very low rate and restore its physiological processes immediately after the stress is moderated (Zhou Haiyan, 1999). All this research has provided theoretical basis for the research in vegetation succession of desertification-threatened ecosystems and plant selection for the setting up of shelterbelts.
22.214.171.124. Desertification and Ecosystem Ecology
Research in desertification impacts on the changes and structure and function of ecosystems has been carried out for many years. Research showed that in cropping systems, desertification breaks its way at the sites of vegetation destroyed or harvested, and then leads to soil degradation including losses of soil organic matter and fine particles by erosion and reduction of soil water and nutrient holding capacity (Zhu Zhenda, 1988; Zhao Xueyong, 1997). These processes can lead to the destruction of soil structure and loss of land productivity (Zhao Halin, 1993), at last lead to the land abandoned. In grassland ecosystems, when the vegetation is destroyed due to over grazing or fuel wood collection, desertification expands very rapidly. At first, the perennial grasses disappeared and then the biannual, at last only the annual grasses or ephemeral grasses and bushes of poor palatability become dominated and sparsely distribute on sand. Research also revealed that desertification reduces the diversity and numbers of soil organisms, such as bacteria, fungi and actinomyces and micro soil animals (Lu Guifen, 1999; Liu Yongjiang, 1999). Desertification not only reduces the biomass production, but also impairs decomposition process and compromises, or even interrupts the circulation of materials and energy flow (Zhao Xueyong, 1997). Desertification control is a process of restoration of soil structure and bridging the interrupted material circling and energy flow pathways by all means, mostly by re-vegetation.
With the progresses of desertification research, more and more scientific subjects are adopted in desertification and desertification related researches, such as economics and landscape ecology to pursue the relationship between desertification and economy and landscape differentiation (Gao Guoli, 1993; Zhao Xueyong, 2000) and archaeology to trace the changes of desertification in the past (Zhang Baozhong, 1991).
In the past 40 years, researchers have made great progresses in desertification research and its control. Desertification is a process influenced by many factors including climate and other natural processes, and social and economic factors. Desertification control needs the participation of masses, governments and researchers. As stated before, desertification control in China is a successful practice only in some places. As a whole, desertification is still expanding. There are many problems need to be solved and challenges expected.
First is the global climate change and desertification. Research showed that global climate is getting dry and warm. The temperature increase will lead to increase in evapotranspiration exposing plants to drought stress. With an ever-increasing population and decrease of ground and underground water resources, ecosystem will be more fragile to disturbance and desertification is likely to take place. The research in climate change and its impacts on desertification will be of very importance for desertification prediction and prevention too.
Second is the research in impacts of land policy and market on desertification. Before 1979, policies of land use and land tenure were completely controlled by the government. Land policy and administrative power had played a predominant role in changes of land use and land cover. After 1979, land use was getting more and more affected by market, and changes of land tenure for several times have put heavy impact on land use. This kind of combined impacts of land policy and market on land use, definitely, will last for a long time. Research on the influences of changing land policy and market will provide both theoretical and practical supports for the decision-making and sustainable utilization of land resources and desertification prevention.
Third is the research in desertification and air pollution. Desertification itself is a process of locality, but its effects are far beyond where it takes place by polluting the air and changing the local or regional climate. Researchers have done lot of test on the movement of sand driven by different wind velocities in wind tunnel, but there is no field measurement on the transportation process. That is why there is no quantitative explanation for the sand origin and transportation mechanism provided for the sand and dust storm in the spring 2000. It is also important for the assessment of desertification-related hazards.
Fourth is desertification and utilization of water resource. In the past 40 years, researchers have made a great amount of progresses in desertification researches in relation to water resource. Desertified land, however, was still expending at the rate of 1560km2 per year from 1950s to 1970s (Zhu Zhenda, 1985), 2100 km2 per year in 1980s (Zhu Zhenda, 1994) and 2460 km2 per year in early 1990s (CCICCD, 1996). Water availability is the most limited factor in desertified area. In the past, desertification control was successful only in some places. The major reason is that water resource could not be efficiently used and systematically managed. Taking the river system as an example, development of the up-reach, in most cases, is at the expense of the water availability and environment of the low-reach. Rationalized management of water resources in river systems is one of the most crucial ways leading to sustainable use of water. The combination of increasing population and deterioration of water resource is the pressing challenge to researchers and the development of the nation.
Fifth is monitoring on desertification and developing early warning system. Desertification is a dynamic process influenced by many factors. With the global climate change, ever-increasing population and water shortage, monitoring of desertification could provide information of the changes of land and water resources and support decision-making. Early warning system is helpful for hazard relief. It is of great theoretical and practical values to monitor the desertification process and establish early warning system.
In summary, researchers have made great progresses in desertification research and its control. Status, however, shows that desertification is successfully halted only at some parts and deteriorating as a whole in the North and Northwest and Northeast of China. Challenges in both of desertification research and control are expected.
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