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Characteristics of desertification and its rehabilitationin China

Yong Zha* & Jay Gao

*School of Geographical Sciences, N anjing N ormal University, N anjing210097, Peoples Republic of China

Department of Geography, University of Auckland, Auckland PrivateBag 92019, N ew Zealand

(Received 20 M arch 1997, accepted 16 June 1997)

The definition of desertification and its causes in the Chinese literature arereviewed and compared with those in international publications. BothCh inese researchers and their western cou nterparts have difficulty in reachinga generally accepted definition for desertification and an agreement upon theexact role played by human activities and environmental settings indesertification initiation and development. Tremendous efforts in China havegone into rehabilitating desertified land into productive uses with greatcontribution to existing knowledge in reclaiming desertified land. The early

biological-oriented measures based solely on economic return have recentlybeen replaced by a much more successful, multi-disciplinary approach ofrehabilitation combined with preventive measures that follow sound eco-logical principles.

1997 Academic Press Limited

Keywords: desertification; causes of desertification; severity assessment;rehabilitation of desertified land; land reclamation; China

Introduction

With a territory of 96 million km 2, China is one of the most severely desertified

countries in the world. Desertification is threatening the lives of close to 400 millionpeople and has affected about 33 million km2 of land (Chen et al., 1996). It is thusvery important to study desertification and rehabilitate desertified land into p roductiveuses. Although sand transport and sand dune movements were studied in the 1960s(Zhu et al., 1964; Wu, 1965), these efforts were highly limited in their scope andquantity. Spurred by the United Nations Conference on Desertification (UNCOD)held in Nairobi, Kenya in 1977, immense research on desertification and itsrehabilitation has been carried out with fruitful results. In this paper the characteristicsof desertification in China are identified through a review of published papers. Theliterature cited, with a few exceptions, comes chiefly from journals and books recentlypublished in Chinese. Wherever relevant, the issues under consideration are discussed

Corresponding author.

Journal of Arid Environments (1997) 37: 419432

01401963/97/030419 + 14 $25.00/0/ae970290 1997 Academic Press Limited


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in a wider scientific context through citing articles published internationally in En glishbooks and journals.

According to UNCOD (1978), desertification refers to the diminution ordestruction of the biological potential of the land that can lead ultimately to desert-likeconditions. Increasingly, it has been agreed that the term desertification should berestricted to d ryland environments only (Th omas, 1993). T herefore, land degradationin humid regions is beyond the scope of this paper. The various definitions ofdesertification are first presented, followed by consideration of its spatial extent andthe magnitude of the desertification problem. The causes of desertification and itsdevelopment are discussed next. Efforts to monitor desertification and to rehabilitatedesertified land into productive uses are reviewed. Finally, the outcome of therehabilitating efforts are summarized.

Definition of desertification

Coined by the French botanist and ecologist Aubreville (1949) nearly half a centuryago, the term desertification has und ergone num erous modifications in its meaningsince then. M ore than on e hund red definitions have appeared in the English literatureso far (Glantz & Orlovsky, 1983) . F or instance, Rapp (1974) defined it as the spreadof desert-like conditions in arid or semi-arid areas due to man s influence or to climat icchange. However, no single definition is generally accepted (Dregne, 1983). Muchconfusion in the literature has occurred as a result of its unscrupulous use (T homas &Middleton, 1994) in three aspects: (a) indiscrimination between the process ofdesertification and its state; (b) non-consensus regarding the geographic regions towhich it applies; and (c) its exact causes. Recently, Rhodes (1991) and T homas (1993)suggest that the concept of desertification be revised in light of renewed scientific

advances that have enhanced our understanding of the problem. Namely, naturalfluctuation in environment causing long-term detrimental impact must be distin-guished from land degradation caused by human actions.

T he concept of desertification was not introd uced into the C hinese literature untilafter the UN CO D in 1977 (Chen et al., 1996). Prior to that, the term tudi shahua (landsandification) was in common use (Dong & Liu, 1993). It refers to the coarseningprocess of the land surface after fine sandy and nutrient particles are lost to aeolianerosion. Though close to desertification in meaning, it at most forms a stage in thedevelopment of desertification (Zhu et al., 1989). Another related term is called

fengshahua (aeolian sandification). It refers to the process of forming desert-likelandforms by sand ou tside arid and semi-arid zones (Zhu, 1986) . H owever, Li (1988)argued that this process should be called strictly land degradation.

Profound ly affected by its constan tly changing international meaning, desertificationhas been dissimilarly defined by Chinese researchers. Zhu & Liu (1981) referred to it

as the process of environmental degradation in non-sandy areas where the fragileecology is disturbed by excessive human activities. It was defined by Yang (1987) asa series of climatic and geomorphologic processes in arid, semi-arid, and some semi-humid sandy areas under the influence of various conditions at diverse time scales.According to Chen (1991), desertification is the contemporary process of landdegradat ion that is caused mainly by sand in a fragile ecosystem and forms a desert-likelandform. It is the process of environmental change that is characterized bysandblasting and forms a desert-like landform in formerly non-sandy areas (Dong etal., 1988). Apparently, these definitions differ from one another widely in the processand time scale involved.

Lack of agreement in defining desertification originates in part from its confusionwith desertization because of inappropriate translation. Referring to desert encroach-ment in arid and semi-arid areas of non-desert landforms due to improper human

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activities, desertization was translated as shamohua (desertification), whereas desertifi-cation was translated as huangmohua (barrenification) in Chinese. Zhou & Pu (1996)argued that the international definition was by no means perfect and had to be alteredto suit desertification peculiarities in C hina. T he term huangmohua should be used inits broadest sense to encompass desert creeping, land degradation in the forms of soilerosion, waterlogging and soil salinization to avoid confusion.

Unlike the international ones, these Chinese definitions place a much greateremphasis on the material (sand) that is essential in desertification initiation than onclimatic, especially precipitation, variables that are incorporated in the definitionimplicitly. All sandy deserts and lands are located in northern China that has an aridor semi-arid climate (F ig. 1). T he proposed adopt ion ofhuangmohua will undoubtedlymake the concept of desertification in Chinese closer to its international meaning.

Severity of desertification

Historically, many parts of China are susceptible to desertification. All of them areconcentrated in the north-western, northern and north-eastern (Three North)dryland (Fig. 2). Some of these historical events of desertification have beendocumented by various scholars. Zhu et al. (1986) cited notable instances ofwidespread desertification in the semi-arid steppe (A in Fig. 2) dating back to the H anDynasty (202 BCAD 220). Dong et al. (1988) found that the M u U s Sandy Land (Bin Fig. 2) has existed since the Quaternary, even though its size fluctuated over theyears. It has been subject to the southward encroachment of a sandy desert since the

Figure 1. Distribut ion of sandy deserts (18) and lands (912) with respect to climatic zones inChina. Sandy deserts and sandy lands are differentiated because the latter is formed out ofhuman activities (Source: modified from Fullen & Mitchell, 1994).

DESERT IFICAT ION AND REHABILIT AT ION, CHINA 421


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Tang Dynasty (AD 618906) (Guo et al., 1989). As a remarkable example ofdesertification in C hinese history, the O rdos Plateau (F ig. 2) contains 120,000 km2 ofland that were desertified during the prehistoric period (Guo et al., 1989). At itssouthern fringe a belt of migratory sand about 60 km wide formed along the Great Wallduring the last th ree centuries. T he history of desertification in the T aklimakan D esert(1 in Fig. 1 and F in Fig. 2) can be dated back to 31,000 years ago (Wang & Dong,1994).

At present C hina still faces a serious prob lem of desertification. Approximately 13%of the territory comprises of deserts and desertified land (Qu, 1980). It is estimatedthat 3 3 million km

2have been affected by desertification, accounting for 34% of total

land area (Chen et al., 1996). Desertified land in Ch ina totals 11 million km2

by theaccount of Zhu & Cui (1996), but 22 million km

2by the account of Zhou & Pu

(1996). None of the authors provided accuracy for their estimates. T he sheer scale ofthe desertification problem, combined with its complex causes, makes accurate

estimates impossible (Fullen & Mitchell, 1994) . T he massively disparate figuresreported are attributed to three reasons: (a) definition of desertification. The landaffected by a specific type of degradation was included in one figure, but not inanother. Guo et al. (1989) reported a total of 13 million km2 of desert and desertifiedland without specifying the quantity for desertified land alone; (b) types of desertifiedland. Some authors included desertified land in arid and semi-arid areas whereasothers also counted the land degraded by erosion in hum id and semi-humid areas. Zhu

Figure 2. Distribution of historical and contemporary desertification in China. Numbersrepresent sandy deserts/lands; for their names refer to Fig. 1 (Source: modified from Sheehy,1992).

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and Cu i (1996) included desertified land by water erosion (037 m illion km2) and theareas affected by physical and chemical erosion (038 million km 2) in their estimate.The figure given by Zhou & Pu (1996) included land affected by soil erosion (179million km2) and salinization (0065 million km 2); and (c) degree of desertification.Areas already affected by desertification were included in one figure whereas areasvulnerable to desertification were also counted in another. For instance, Zhu et al.(1989) included 81,000 km2 of land susceptible to desertification in their estimate.According to Thomas (1993), hyperarid environments should not be considereddesertified because they are desert-like in their natural state. Furthermore, vulnerabil-ity to desertification should be distinguished from desertification itself (Rhodes, 1991).The amount of desertified land estimated by different authors converges at around334 million ha (Fig. 3) if the revised international definition of desertification byRhodes (1991) is adopted. This trend of drastic reduction confirms that previousassessments of desertification may have over-estimated the worldwide extent of the

phenomenon (Thomas, 193), at least for China.Desertified areas are widely scattered in a few clusters in northern drylands (Fig. 3).The most prominent cluster is formed by 207 agropastoral counties in 13 ThreeNorth provinces where 1095 million ha of land have been desertified, accounting for92% of the total area in Ch ina (Hou, 1985) . In this zone alone, 269% of the affectedland is severely desertified, 257% strongly under development, and 474% underdevelopment. Characterized by a landform of partially stabilized sand dunes coveredwith shrubs, these areas are usually located at the periphery of a desert, oasis, or thelower stretch of a rive (Figs 2 and 3) (Guo et al., 1982). All of them have a patchy andfragmented pattern of spatial distribution (Zhu & Cui, 1996).

Figure 3. Distribution of contemporary desertification in China separated into actual andpotential categories (Source: modified from Zhu, 1992).



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T he problem of contemporary desertification has worsened in a num ber of areas. InNorth C hina 50,000 km2 of land were desertified in the second half of this century(Guo et al., 1989). In the agropastoral zone (Fig. 2) desertified land increased from137,000 km

2in the late 1950s to 176,088 km

2in the 1970s, with another 158,000 km

2

potentially vulnerable to desertification (Wang, 1990). In the 1980s desertified areasexpanded at an annual rate of 2103 km2 (Shou et al., 1992) . D esertification of steppegrazing land throughout North C hina has reached crisis proportions (Sheehy, 1992) .T he percentage of desertified land in the Korqin Steppe (A in Fig. 2) grew from 20 inthe 1950s to 52 in the late 1970s (Zhu et al., 1984a). Sandy land in Uxin Qi (anadministrative unit equivalent of county), Inner Mongolia (Fig. 1) increased from4193 km2 in 1957 to 5685 km2 in 1977 (Lin et al., 1983). Mobile and semi-mobilesand dunes encroached upon the oasis in the Gurban Tunggut Desert (2 in Fig. 1),Xinjiang Autonomous Region, by 0526 m annually during 19581986 (Anon,1987).

Affecting millions of people over a vast area, desertification has caused colossalenvironmental detriment and economic loss. Its direct destruction includes reducedsoil fertility, degraded soil structure, and deteriorated vegetation quality (Zhu & Cui,1996). Loss of soil nutrients by aeolian erosion totals 5600 tons, or the equivalent offertilizers worth 17 billion yuan (Luo et al., 1994). It causes a direct economic lossestimated between US$23 billion (Anon, 1994; Chen et al., 1996). T he indirect lossassociated with desertification is 23 times more.

Causes of desertification

Internationally, the causes of desertification have been identified as overcultivation,overgrazing, deforestation, and salinization (Goudie, 1990; Thomas & Middleton,1994). T hese human-related factors have also been reported to cause desertification inChina. Destructive human activities range from overcultivation, overgrazing oflivestock, excessive gathering of fuelwood and plants for medicinal purposes, mining,to construction of transportation routes (Zhu et al., 1981; Sheehy, 1992). Under thesame natural settings, plowing sandy land accelerates aeolian erosion by tens, evenhund reds of times (D ong et al., 1987). Frequ ent ethnic wars, recurrent conversion andreversal of land use from crop to pasture triggered d esertification 30 km south of theGreat Wall in the 1670s (Fig. 2) (Bao et al., 1984). In add ition, human errors in policy-making were responsible for rapid desertification in drought-prone sandy landsbetween the mid-1960s and mid-1970s (Zhu & Cui, 1996). Of the 34 million hanewly desertified land in the agropastoral north, 429% was caused by overcultivation,

311% by overgrazing, 222% by excessive collection of fuelwood, and the rest bymining and construction (Zhu et al., 1994b).

Although not explicitly identified as a separate factor, overpopulation is the reasonfor most of the excessive human activities mentioned above. Zhu et al. (1984b)recommended that population be controlled to p revent d esertification from worsening.Dong (1992) identified a close correlation between changes in desertification andpopulations of human beings and livestock. However, he questioned whetheroverpopulation caused desertification, a process arising from multiple elements. Noquantitative relationship between population growth and desert expansion has beenestablished yet.

Unlike human-related factors, the environmental settings conductive to desertifica-tion in China are quite unique. Commonly identified ones include sandy, loosesurfacial sediment deposits and the coincidence of droughts with the windy season

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(Zhu & Cui, 1996). T he former provides the materials to be transported, and the latterfuels the power to move them.

No consensus has been reached regarding the exact role played by the two categoriesof factors. On the one hand, Dong (1992) argued that historical desertification wascaused mainly by natural factors, especially climatic fluctuation. It was found thatdesertification in the Mu Us Sandy Land (9 in Fig. 1) was caused primarily by climaticfluctuation during the Ice Age, and secondly by modern tectonic activities andinappropriate hum an activities (Dong et al., 198). According to the Expedition Teamof Academia Sinica (1978), desertification in ancient agricultural areas resulted fromthe worsened physical environment, especially climate change. On the other hand,many others are of the opinion that human factors are more important. The mainreason for desertification in the O rdos P lateau (Fig. 2) lies not in climate change butin human activities (Hou, 1985). Human activities are largely responsible fordesertification in arid and semi-arid China (Zhu, 1982). Desertification worsened in

all areas heavily influenced by human activities in north-east Urumqi (Fig. 1), butremained little changed wherever human influence was small or nil (Liu & Jiang,1996). After correlating the desertification rate in the Mu Us Sandy Land (9 in Fig. 1)with yearly precipitation, Lu k (1983) found that d roughts did n ot always lead to desertexpansion, but excessive clearing of land for cultivation and grazing did . Sites of ruinedancient cities in th e Mu Us Sand y Land convinced L in et al. (1983) that desertificationwas not problemat ic in historic times. Instead, large-scale cultivation and grazing sincethe mid-seventeenth century triggered rapid desertification.

The seeming contradiction of these findings can be resolved by a simultaneousexamination of both categories of factors. Anthropogenic factors are intrinsicallyinteracting with environmental settings in desertification initiation and evolution.Neither of them can function independently without the other, and thus they shouldbe analysed simultaneously. Based on the results from principal component analysis,Dong (1992) found that human factors accounted for 60% of the variation indesertification, and natural ones 40%. Feng (1987) reported that only 10% of thedesertified land in China was caused by natural factors such as droughts and aeolianerosion, an d the remaining 90% by human activities.

Results published in the English literature contribute little to elucidate the debate.Le Houerou (1992) thought that global warming could accelerate the process ofdesertization. Similarly, Wang & Dong (1994) found that global warming would causedesertification in the Taklimakan Desert (1 in Fig. 1) to continue, and the processwould be accelerated by human impact. Rising temperatures and declining rainfall fora period of 3050 years in Sudan may accelerate desertification there (Alvi, 1994).Because of the limited length of climatic records and thus the difficulty in establishinglong-term prediction of climate, the question whether continual climate change givesrise to d esert expansion cannot b e answered with confidence (Anon, 1977). Indeed, itis difficult to separate human- and climatically-induced changes. Desertification

research in the revisionist era requires an ongoing awareness of anthropogenic vs.climatic influences on dryland resources (Rhodes, 1991). More detailed studies on theextent of desertification and its long-term mon itoring at regional and nat ional levels areneeded for the realistic assessment of roles played by desertification-triggering factors(Thomas, 1993).

In the absence of convincing evidences from the western literature, the conflict ofopinions is reconciled by taking into account the differential temporal and spatialscales of desertification initiation and development. While environmental conditionsand physical factors created a fragile ecosystem and initiated the formation of deserts,human elements were principally responsible for their deterioration and expansion(Dong & Liu, 1993). Natural variables played a major role in historic desertification.Anthropogenic elements such as improper land management practices takingprecedence over ecological principles are blamed for contemporary desertification. At



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the regional level the physical elements are more important than the human oneswhose importance becomes increasingly larger as the scale is progressively reduced toa local one.

D esertification rehabilitation

T he history of rehabilitating desertified land in C hina is essentially the h istory ofconverting it into productive uses in sandy areas (Chen et al., 1996). Most of therehabilitating efforts concentrated on the agropastoral zone (Fig. 2) because 55 millionpeople and 10 million ha of cropland and pasture have been affected by desertification(Guo et al., 1989). A prerequisite of a successful rehabilitation scheme is theidentification of desertified areas and assessment of desertification severity.

M onitoring and assessment of desertification

Historically, desertification information is obtained from ground surveys andexpeditions. Such inefficient methods of information acquisition have gradually beenreplaced by the increasing use of small-scale aerial photographs (Zhu et al., 1984b;Shou et al., 1992). As a supplementary means, field trips are carried out occasionallyto verify the results obtained from photointerpretation and to assess their accuracy(Zha, 1989; Guo, 1990; Liu & Jiang, 1996). Since the emergence of space-borneremote sensing, satellite images such as Landsat Multispectral Scanner (MSS) andTM have been utilized to delineate the extent of desertified areas (Luk, 1983; Guo,1990; Liu & Jiang, 1996). At a spatial resolution of 30 m, T M data enable them to be

mapped at an accuracy level comparable to that from aerial photographs (Liu & Jiang,1996). Desertification severity levels mapped from TM images are consistently within90% of those obtained from colour infrared aerial photographs (G uo, 1990). D espitethese high accuracy levels, satellite images have not com pletely eliminated the need foraerial photographs. The results interpreted from historical aerial photographs guidedthe mapp ing of desertified land from M SS data (Luk, 1983). T wo methods have beenused to process the remotely sensed data, man ual interpretation for aerial photographsand satellite images, and digital analysis for satellite data (Luk, 1983; Guo, 1990; Liu& Jiang, 1996).

Desertification monitoring comprises identification of changes in desertified areas,which can be accomplished by overlaying time-sequential data such as remotely sensedimages. Comparison of one 1977 MSS image with one 1989 TM image revealed theshrinkage of vegetative cover in a 2100 km

2area near Urumqi (Fig. 1), Xinjiang, and

the southward shift of a sandy desert (Liu & Jiang, 1996). Since satellite images were

not available prior to the early 1970s, historical aerial photographs were relied upon todetermine the expansion of desertified land (Bao et al., 1984). In the absence ofhistorical aerial photographs, ground survey results were used as a surrogate (Lin et al.,1983). Comparison of the two sets of results could indicate the general trend ofdesertification change, but not the location where the changes had occured.

Overlay of multiple images or maps is ideally carried out in a GeographicInformation System (GIS). So far GIS has found limited applications in identifyingdesert expansion. Zha & Gao (1997) overlaid two desertification d istribution m aps ofYulin County (Fig. 1), Shaanxi Province, to identify the areas desertified or convertedto p roductive uses between 1960 and 1987. T he acquired spatially-based informationfacilitated the identification of desertification causes at some sites inside the study area.Wang & Kang (1990) outlined a prototype microcompu ter-based information systemfor desertification rehabilitation, dynamic monitoring, and trend forecasting at the

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country level. However, no further progress has been reported on the plannedresearch.

Various criteria have been proposed to assess desertification severity. Bao et al.(1984) employed the depth of underlying sand, the degree of aeolian erosion, and theamount of vegetative cover and shifting sand dunes to map severity at four levels(latent, ongoing, severe and most severe). Percentage of mobile sand dunes was alsoused to classify desertification as severe, strongly affected and under development(Zhu et al., 1984b). Zhu et al. (1981) applied a combination of the amount of aeolianerosion and the change in surface landforms. An annual removal of 3 cm anddeposition of > 5 cm of sand were considered severe, < 1 cm of erosion and depositionslight. However, vegetative cover proves to be a more popular criterion, especially ifthe results are obtained from rem otely sensed images. A vegetative cover of < 5, 15, 30and 50% is considered, respectively, extremely severe, severe, moderate and slight(G uo, 1990). Similarly, Liu & Jiang (1996) considered a vegetative cover of < 5%

extremely severe and < 20% severe. However, a vegetative cover of > 80% representsno desertification hazard. Instead of using a single factor, Dong (1996) deriveddesertification severity levels from weighted averaging of 16 desertification contribut-ing factors, including potential hazard, current status, desertification rate, humanpopulation an d livestock size. All these stud ies were carried ou t at the regional or locallevel. No research has been reported on the assessment and classification ofdesertification severity at the national level. GIS has not been utilized to mapdesertification severity or to assess desertification hazard and its environmentalimpact.

Desertification rehabilitation

In sandy drylands desertification occurs in two manners, direct encroachment ofmobile sand dunes upon grazing land, and deposition of drifting sand over grasses,both under the action of wind (Lin et al., 1983). Therefore, rehabilitatingdesertification is essentially to slow down wind velocity through increased surfaceroughness (Zou et al., 1981). Construction of engineering works and planting ofvegetation are applied to halting the advance of migratory sand dunes (Dong et al.,1987). Engineering works such as straw checkerboards can effectively reduce windvelocity and minimize the amount of sand transported, even though their optimalwidth is still debatable (Feng et al., 1994). C heckerboards at a height of 01502 mabove the ground increase the roughness of a sand surface by 400600 times, andreduce wind velocity by 2040% at a height of 05 m and by 10% at 2 m above thesurface (Zou et al., 1981). The quantity of sand transported over a checkerboard isonly 1% of that over a shifting sand dune (Zhu, 1992). Moreover, checkerboards

increase soil organic content by 23-fold after a surface crust is formed. Soil crust withmoss growing on it can resist aeolian erosion force within a speed as high as2 5 m s1.

Nevertheless, engineering works alone cannot eliminate desertification hazards onroads (Chen, 1992). If combined with vegetation networks, their effectiveness isconsiderably improved (Zou et al., 1981). Planting of shrubs and trees brings moreecological and economic benefits from the control efforts, making it sustainable. Thedirect benefits are decreased wind velocities, increased soil temperature and organicmatter inputs from biomass, improved soil moisture retention, and reduced soilerosion (Yang, 1990; Fullen & Mitchell, 1994). Species of dwarf shrubs suitable forentraining sand include Salix flavida, Hedysarum scopariu, and Caragana korshinkskiiplanted at an interval of 12 m. At a density of > 20%, shrubs can achieve the sameeffect as a 1 m by 1 m checkerboard (Yang, 1990). H owever, planted vegetation alone



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in partially desertified areas cannot bring desertification under complete control,especially during its later stages of succession (Chen, 1981).

Because of the significance of vegetative cover in reducing wind speed andgenerating economic benefits, prior to the 1970s biological means were relied uponexclusively to stabilize sand dunes while other factors were neglected (Shou et al.,1992). H owever, if the land is exploited beyond its carrying capacity, no single controlmeasure can function effectively (D ong, 1992). It was realized later tha t desertificationis a process resulting from mu ltiple factors. Accordingly, a multi-disciplinary approachof rehabilitation and prevention was adopted. The measures were designed forrehabilitating the deteriorated ecosystem based on both ecological principles andeconomic return. The rehabilitation methods include regulating growth of croplandand livestock, reconverting infertile cropland at the margin of steppe grazing land tosemi-natural ecosystems, and developing land use patterns that integrate combinationsof grazing land, woodland and cropland (Sheehy, 1992). A ratio of 3:3:4 for land

allocated to farming, pasture and forestry in semi-arid sandy areas can lead to anecological balance (Zhu & Cui, 1996). T his ratio varies with the severity ofdesertification. The more severely an area is desertified, the higher the proportions forwoodland and pasture (Zhu et al., 1984b).

With a combination of rehabilitation and preventive measures following basicecological principles, desertification can be harnessed and desertified land bereclaimed for productive uses. Common land reclamation strategies include wind-breaks, irrigation with silt-laden river water, and dune stabilization using strawcheckerboards and planted xerophytes (Fullen & Mitchell, 1994). The disastrousconsequence of the mistaken policy of stressing the paramount importance of grainyield in the 1970s has been corrected by reducing cropland if its cultivation isconducive to aeolian erosion and desertification (Lin et al., 1983).

The effectiveness of these rehabilitating measures has not been comprehensivelyassessed. Zhu & Cui (1996) qualitatively outlined the successful measures in arid and

semi-arid areas. Zha & Gao (1997) found planting grasses at the fringe of sandy landis the least effective as they are readily topped by the shifting sand dunes. Instead,scrubs and trees are more resistant to being buried by sand and thus more effective inhalting desertification.

Outcom e o f desertification rehabilitation

The achievements of tackling desertification are exemplified by the Three Northproject in the agropastoral zone of North China. Approved by the State Council in1978, this programme of constructing shelter-belt systems was launched in an area of4069 million km2 spreading across 13 provinces. Internationally renowned as ChinasGreen Great Wall, this multiple-stage project is expected to be completed by the year

2025 when forest coverage will reach 1495%. In the first stage 79 million ha ofprotective forests were planted (Guo et al., 1989), bringing forest cover from 505% in1978 to 709 in 1989 (Zhu, 1990). Of the 5736 km

2 of mobile sand dunes in theregion, 3068 km2 have been stabilized (Yang, 1990). If they function as anticipated,the farmland-protective forests will protect 85 million ha of cropland and increasegrain yield by 55 million tons. The direct economic benefits from the project areestimated at 2555 billion yuan, or 27 times the initial investment. Valued at 446billion yuan, the indirect benefits come from increased grain yield, soil conservation,sand fixation and protection of pasture. However, as unveiled by observations of areasplanted with trees, the actual achievements are much less spectacular than reporteddue to the low survival rate of the trees (Becker, 1985).

At a smaller scale, the reversion of desertified land to produ ctive uses has taken placein a num ber of areas. A shelter belt of 170 km long by 300400 m wide has been

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established in north-east Ulan Buh Desert (7 in F ig. 1) in Inner M ongolia, protectingtens of thousand hectares of rangeland and cropland in more than 150 counties (Qu,1980). Thanks to decades of desertification control efforts, oasis area in the south-eastern T engger Desert (6 in F ig. 1) increased by 120 km2 between 19591990, withthe reclaimed land used for cropping, orchards, forestry, and shelter belts (Zhu, 1992).Desertified land in northern Shaanxi Province (around 9 in F ig. 1) has been reclaimedfor farmland and woodland along the river banks and in low-lying moist alluvial fans(Bao et al., 1984). Although the moderately and slightly desertified areas in YulinCou ntry (F ig. 1), Shaanxi Province are predicted to increase by 104,000 ha, the mostseverely affected area is forecast to decrease by 190,000 ha, forming an overalldecreasing trend (Kang et al., 1995).

Summary and conclusions

Enormous efforts have gone toward tackling desertification in China since the UnitedNations held its first conference on combating desertification 20 years ago. Theseefforts concentrated on defining desertification, determining its causes, assessing itsspatial distribution and severity, and rehabilitating desertified land into productiveuses. Some of the problems facing Chinese scholars are identical to those facing theirwestern counterparts. T hese issues include how to define d esertification prop erly andhow to assess the exact role played by human-related and environmental factors indesertification. Due to the insufficient amount of data collected, it is difficult todisentangle the impact of anthropogenic desertification effectively from that ofenvironmental desertification.

Because of the pressure generated by an ever increasing population and dwindlingarable land in China, it is of paramount importance to rehabilitate the land lost todesertification to productive uses. Consequently, restoration of desertified land makesup a huge portion of the scientific endeavour in desertification research. Adisproportionate amount of emphasis is placed on desertification control whereasinsufficient attention is given to prevention. Subsequently, desertified land isrehabilitated to p roductive uses on the one hand, but on the other, formerly stabilizedsandy land is encroached upon by shifting sand dunes. In taming desertification bybiological means, huge efforts are devoted to planting grasses and tree saplings.However, inadequate efforts are made to ensure their survival and the sustainability ofthe rehabilitation programme. These earlier problems have been remedied after therealization that desertification resulted from a variety of factors, both human activitiesand natural settings. T he m ulti-disciplinary approach of rehabilitation and preventionbased on ecological principles and economic return has achieved much more successin rehabilitating the deteriorated ecosystem than the biological means.

To conclude, China is facing a serious desertification problem. Most of the affected

areas are located in the arid and semi-arid north. They are caused by bothenvironmental settings and inappropriate human activities including overcultivation,overgrazing, and excessive gathering of fuelwood and plant species for medicinalpurposes. The natural settings are important to the initial formation of desertconditions in historical times, whereas anthropogenic factors are critical to contempo-rary desertification. After preventive measures following sound ecological principleswere adopted, the desertification trend has been reversed at various geographic scales.Engineering measures alone are not so effective in halting the encroachment of sanddunes as biological measures that can bring more economic return from therehabilitating efforts. T he multi-disciplinary, ecologically-sound rehabilitatingapproach proves to be most effective in restoring desertified land to productive uses.

Jay Gao would like to thank the University of Auckland for granting him research leave duringwhich this research was undertaken.



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