Aeolian desertification from the mid-1970s to 2005 in Otindag Sandy Land, Northern China
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- Liu, S. & Wang, T. Environ Geol (2007) 51: 1057. doi:10.1007/s00254-006-0375-1
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Aeolian desertification in Otindag Sandy Land has expanded dramatically during the past 50 years. This research explored processes and causes of aeolian desertification in the study area. The results showed that aeolian desertification development in Zhenglan Qi of typical region located at the center in the study area can be divided into three stages including rapid occurrence before 1987, parts of rehabilitation and most of deterioration from 1987 to 2000 and little rapid rehabilitation occurrence from 2000 to 2005, according to remote sensing images and field investigations. Gradually declining MI indicated that climate change was not the major cause of aeolian desertification development during the last 40 years, while increasing population should be the underlying cause of local aeolian desertification. Irrational human activities mainly including unsuitable reclamation in the 1960s and lasting over-grazing after 1980 are direct causes contributing to local aeolian desertification, especially over-grazing, while climate change often played a revealer of irrational human activities mainly through drought events. Over-grazing and undesirable climate have different functions during the whole aeolian desertification process. Over-grazing gradually changed grasslands to slight aeolian desertified lands at the initial stage, while climate with windy days or droughts often accelerated formation of serious aeolian desertified lands. Aeolian desertification in the study area both possesses occurrence possibility and great rehabilitative potential. At present, more integrated countermeasures combating local aeolian desertification still are expected.
KeywordsAeolian desertificationClimate changeHuman activitiesReclamationOver-grazingOtindag Sandy Land
At present, aeolian desertification is one of the most serious environmental and socio-economic problems at global scales especially in arid, semi-arid and dry sub-humid areas of Africa, Central Asia, Australia and North China.
The Otindag Sandy Land is an important ecological barrier to block dust storms originated in the steppe of the Mongolian Plateau and the western China to be transported to Beijing. With aeolian desertification occurrence at the end of 1950s (Chen et al. 1960; Yang 1964), however, rehabilitation mainly occurred at that time (Zhu et al. 1981; Zhu 1999), which compared to that rapid aeolian desertification over recent years in this region (e.g., Wulantuya et al. 2001; Liu and Wang 2004a). In addition, frequent dust-storms in the end of 1990s were considered to be relevant with rapid aeolian desertification occurrence in North China (Ye et al. 2000), and anthropogenic factors are the main contributors of aeolian desertification in this region (Li et al. 2002; Wu et al. 2003; Dong 2000). At present, the results are still unclear because researchers used different classifications to evaluate the degree of aeolian desertification in this region. Although significance of coupling and feedback mechanism in aeolian desertification development had been recognized (Charney 1975; Sun and Li 2002; Chang et al. 2005), and Zhu et al. (1981) had proposed that period of aeolian desertification occurrence often related to major history events which mostly accompanied with droughts; coupling and cumulative impacts were ignored in many cases. In fact, aeolian desertification is a complex process which co-worked by different factors. The increased awareness about threats of aeolian desertification, and willingness to combat it, requires better knowledge about its distinct causes in order to take the most efficient and sustainable actions. According to vegetation information, many works attempted to discriminate climate or human-induced degradation in Syria (Jason and Roland 2003) and Otindag Sandy Land (Zheng et al. 2006). Following results of previous studies (Wang et al. 2003; Xue et al. 2005; Liu and Wang 2004a), with proxies for human activities and variations in climatic indices, Wang et al. (2006) identified the relative role of climatic and human factors in aeolian desertification in semiarid China.
In this paper aeolian desertification situation in the Otindag Sandy Land over the past 30 years was explored, and the causes of aeolian desertification in this region were discussed.
Study area and aeolian desertification state in 2000
Materials and methods
Classification and indicators of aeolian desertification degrees
Percent of blowns and area in total/%
Percent of annual expansion area/%
Percent of vegetation cover/%
Because aeolian desertification evaluation not only includes the total aeolian desertified area, but also includes different severities of aeolian desertification, and very serious aeolian desertified lands were explored additionally.
Aeolian desertified lands in different periods, climate change and anthropogenic factors change were compared to analyze causes causing local aeolian desertification.
Processes of aeolian desertification in the study area
Aeolian desertification development in Zhenglan Qi over the last 30 years
Development rate in 1977–1987 (km2 a−1)
Development rate in 1987–2000 (km2 a−1)
Development rate in 2000–2005 (km2 a−1)
In 1977, aeolian desertification with VS grades only occurred at few places and with smaller areas in the east and west of Sandy Land, but it strongly developed throughout the whole Sandy Land during 1977 to 1987 with an alarming rate. In 2000, lands with VS grades of aeolian desertification converged on an irregular belt (Fig. 3) and total areas occupied 59.3% of Zhenglan Qi. Although there was some rehabilitation occurrence from the early 2000s to present in this region, aeolian desertification in 2005 was still very severe. Only parts of lands with VS grades of aeolian desertification in northwestern and southern typical area were changed into grasslands and woodlands, while other lighter aeolian desertified lands basically did not get melioration (Table 2, Fig. 3). Control of VS revealed that aeolian desertified lands in the study area possesses great rehabilitative potential, while unaltered L, M and S aeolian desertified lands prone to reverse at the same period revealed that aeolian desertification is a complex process.
Causes of desertification in the study area
Climate change trend contributing to reverse aeolian desertification
Aeolian desertification occurrence mainly depends on association of wind and vegetation cover in areas with abundant sandy materials. Sun and Li (2002) proposed the combination of drought, high wind erosion, poor crop and large livestock is mostly prone to aeolian desertification.
Correlation between DI and NDVI in Zhenglan Qi in recent 7 years
In addition, heavy snow disaster in 1977 reduced numbers of livestock to the minimum over the last 40 years in the study region, as is advantage to rehabilitation of aeolian desertification occurrence, regardless of economic loss. Therefore, climate change was not the driver factor of aeolian desertification in the study area during the last 40 years.
Drought events occurrence accelerating aeolian desertification process
Although climate did not change toward dryer, drought events once occurred during the last 40 years, such as droughts before 1980, 1989, 1997 and 2001 (Fig. 5). The coupling of the droughts and frequent windy weathers in the 1970s directly resulted in wind erosion of farmlands and reactivation of part fixed or semi-fixed sand dunes. As a result, areas of aeolian desertified lands reached 5,367 km2 in 1987, and the areas of very serious aeolian desertified lands reached the maximum of the past 50 years (Table 2, Fig. 4). Another drought event from 2000 to 2002 is a very representative case, when not only resulted in rapid aeolian desertification process but also induced frequent sand-storms (Wang et al. 2002).
Human activities contributing to aeolian desertification development
Herds choose settlements in the early 1980s, as enhanced humans’ resistance to natural disasters especially snow damages (Begzsuren et al. 2004), but it caused prolong disturbances on adjacent grasslands. Because the nomadics are rangeland management practice that over the centuries has proved to be sustainable and suited to the ecosystem carrying capacity (MA 2005). Due to reform of using grasslands system and implementing Double Contract Policy (both livestocks and grasslands be managed by households) about Grassland and Livestock since 1982, livestock began to steadily increase again (Fig. 6) and grassland occupied by unit sheep rapidly declined (Liu et al. 2004b), and pressure from population and livestock exceed the limit of capacity (Han et al. 2002). Settlements of herdsmen and overgrazing resulted in wide aeolian desertification during this period. As a result, when parts of lands with VS grades of aeolian desertification were controlled and rehabilitated, while in more grasslands slight and moderate aeolian desertification occurred till 2000 (Table 2, Fig. 3).
Hahn et al. (2005) pointed that in semi-arid and arid areas livestock and vegetation are usually not at equilibrium because of highly variable climate conditions. High pressure on grasslands partly comes from decrease of grasslands area due to reclamation and aeolian desertification, and partly from livestock increases. Even if we taking the livestock sizes in 2002 as the baseline (because this number is a more reasonable carrying capacity after implementing grass-animals balance policy, though it still more than theoretical one), during the past 50 years there are 20 years including 1965, 1973–1976 and 1988–2002 overgrazing occurred. Overgrazing by domestic livestock has been widely accepted as an important cause of land degradation in rangelands (Tainton 1999; Zhao et al. 2005).
Besides, other economic activities such as mining, road building, traffic-off and recreation strongly destroyed grasslands. For example, only in Xilingol Meng vehicles from few ones in 1949 increased to 104 thousand in 2005, which is also a induce of desertification. Field investigation showed vehicles’ destroy is very severe, as often caused linear-blowouts along roads with 10–40 m wide and 0.5–2 m deep.
In addition, investigations and interviews showed that more than 80% of local herdsmen support present policies (SBXM 2006), but another households still continue to hyperploid’s grazing against local government. In fact, 82% of them also had known that overgrazing and other irrational human activities easily caused aeolian desertification, but they had no alterative means only for surviving. Thus, latent factors inducing aeolian desertification, for example income, still require further attentions and more sustainable management means.
Change trend of total aeolian desertified lands in Fig. 4 is obviously inconsistent with the MI (Fig. 5), while consistent with proxies of human activities such as population size, areas of farmlands and numbers of livestock. Field investigation and correlative analysis showed human activities (particularly over-grazing) mainly transformed grasslands to slight aeolian desertified lands and should be the main contributor to aeolian desertification occurrence. Another interesting thing, VS change had higher correlation with MI, as probably indicated climate acting as a revealer and magnifier especially in the last 20 years in the study area.
Protective management practices promoting aeolian desertification rehabilitation
Frequency of dust storms increased in the early 2000s compelled humans to carry out many protective projects and countermeasures such as Enclosuring and Migrating Policy for combating aeolian desertification in this region. There were obvious increases for the mean NDVI in Zhenglan Qi since 2001 (Table 3), one is due to much rainfall, and the other hand is better management. Many field quadrat investigations also proved the rehabilitation potential of aeolian desertified lands is very huge.
Aeolian desertification processes in the study area have three stages: rapid occurrence before 1987, parts of rehabilitation and most of deterioration from 1987 to 2000 and part rapid rehabilitation occurrence from 2000 to 2005. Aeolian desertification in the study area not only possesses occurrence possibility, but also great rehabilitative potential.
Roles of climate change and human activities in aeolian desertification varied with time. In general, population size increase is the underlying cause of aeolian desertification. Irrational human activities such as extensive reclamation during the 1960s and steadily livestock increases and resulting over-grazing after 1978 should be responsible for aeolian desertification occurrence, while climatic change is not the main cause of desertification. Climate played the role of revealing irrational human activities through undesirable drought events.
Only depending on current protective methods such as fence building and livestock size decrease are difficult to avoid aeolian desertification. More sustainable management means are expected.
Funding for this study, provided by National Key Planning Development for Basic Research (973 Program), No. G2000048705, was greatly appreciated. Thanks very much for advices of Dr. X.M. Wang. We also thank unnamed journal referees for their comments.