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
Introduction
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.
2. Status
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.
2.2.5.1 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.
2.2.5.2 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.
2.2.5.3 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.
2.2.5.4. 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).
3. Challenges
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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