Journal of Geographical Sciences 13, 2 (2003) 217-224 ISSN: 1009-637X www.geog.com.cn
Mechanism and regulation of land degradation in Yulin district LIU Yansui 1'2, ZHANG Xiaoping t, LI Xianwen 2, Jay Gao 3 (1. Inst. of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China; 2. Open Lab of Land Use, China Land Surveying and Planning Inst., MLR, Beijing 100029, China; 3. Dept. Of Geography, University of Auckland, Auckland Private Bag 92019, New Zealand) Abstract: Yulin district is located in the transitional zone between Mu Us Desert and Loess Plateau of northern Shaanxi Province, thus it is particularly vulnerable to degradation due to its fragile ecosystem and intense human activities there. The purpose of this study is to explore the mechanism, process and driving force of land degradation in area with vulnerable eco-environment within the context of increasing population and intensifying human economic activities, and then find out the patterns and countermeasures of how to control them using the economic and technological ways. In detail, this study includes three main sections: the first section analyzes the mechanism, causes and characteristics of land degradation, which can be achieved by the typical field investigations and systematical analysis within the regional natural, social and economic context. Based on the technologies of remote sensing and GIS, and combined with the modeling methods, the second section reveals the change characteristics of land use and its driving force from 1990 to 2000; As to the third section, feasible countermeasures of how to prevent the degradation and rehabilitate the regional ecology are proposed, which are studied from the perspective of harmony between nature and economy, and the conception of regional sustainable development. Key words: land degradation; land desertification; changes of land use; Yulin district CLC number: F301.24; P931.3
1 Introduction Land degradation is one of the most serious ecological problems in the world (Scott and Sara, 1999; A1 Dousari, 2000). The most typical and serious form of land degradation in China is desertification, It has resulted in a direct economic loss estimated at between 0.2 and 0.25 billion US dollars. Indirect loss is two to three times higher. Desertified areas are currently expanding at a rate of 2,460 km 2 annually, or 1.58 and 1.17 times the rate in the 1960s and the 1970s, respectively (UNDP, 1999; Zhou, 2000). Especially, desertification and soil and water losses caused by natural factors and human activities have become key ecological problems in the northwestern China, resulting in shrinkage of arable land, frequent natural disasters and growing poverty for the local people. The Loess Plateau, as one of the most serious soil erosion regions in the world, receives a lot of attention from the Chinese government and international society (Cai, 2001; Fu and Chen, 2000). The land degradation, especially serious soil erosion causes land to be less fertile and thus, more areas need to be reclaimed to sustain the population growth. Therefore, it is very important and essential to study land degradation (Zha and Gao, 1997). This paper identifies the ecotone of intermediate zone that the agriculture and livestock farming interlock in northern Shaanxi Province as the typical case study area. This region lies Received date: 2002-09-05 Accepted date: 2003-01-20 Foundation item: Key Project of the Ministry of Land and Resources, No.20010102; Knowledge Innovation Project of IGSNRR, CAS, No.CXIOG-E01-05-03;No.CXIOG-B02-05 Author: Liu Yansui (1965-), Ph.D. and Visiting Professor in CLSPI, MLR, specialized in land sciences, regional planning, sustainable agriculture and rural development. E-mail:
[email protected]
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in the southeast of Mu Us Desert, which is the interim region of the blown-sand area and the loess hilly zone. The representations of this region are as follows: (1) This region is a vulnerably ecological transitional region: it shows strong sensitivity to external changes of key environmental factors, and the pressures of population and its negative effects on the environmental degradation have shown obviously in recent decade; (2) the region is a laggard region of agriculture and livestock farming: in it, the agricultural activities, which are greatly influenced by climates, always result in excessive cultivation and grazing, thus make the environmental destruction more severely; and (3) it contains important mineral bases of coal, oil and gas in China: Shenfu coalfield, the biggest coalfield in China, lies in the region, and the planned gas-feed base of "transferring natural gas from west to east" project, programmed in the "10th Five-Year Plan", lies in the region (Jingbian County) as well. Since the set up of Shenfu coalfield in 1985, it has always been short of effective administration, so the exploitations are in disorder. For instance, in Shenmu County, the number of all kinds of local collieries has increased from 18 to more than 280 within recent 10 years, and the total coal output increased from 0.32 million t to 200 million t. In addition, there are more than 1,000 small out of date oil refineries causing serious pollutions. The irrational mineral exploitation inevitably leads to many new environmental problems, which are aggravating the process of land desertification. The objective of this study is to explore the mechanism, process and laws of land degradation in area with vulnerable environment within the context of increasing population and intensifying human economic activities, and then find out the patterns and countermeasures of how to control them in the economic and technological ways.
2 Study area Yulin district, the study area, is located in the transitional zone between the Mu Us Desert and the Loess Plateau of northern Shaanxi Province in China, lying 36~176 and 107~176 geographically and covering an area of approximately 43,417 km 2 (Figure 1). It encompasses 262 towns/townships distributed in 12 counties, i.e., Yuyang, Shenmu, Fugu, Hengshan, Jingbian, and Dingbian in the northern part of the study area, and Suide, Mizhi, Jiaxian, Wubu, Qingjian, Zizhou in the southern part of the study area, with a total population of 3.31 million at the end of 2000. At present the population density is 76.2 persons/km2. Over the last 10 years population in the area has been growing at an annual rate of 39,850 people (SBSP, 2001). This area is a typical agro-pastoral region and an important energy and mineral base in China. Geographically, the study area is located in the transitional zone between the Mu Us Desert and the Loess Plateau of northern Shaanxi Province. Geomorphologically, it has multiple hierarchical ecozones dominated by aeolian landforms. Its transitional climate varies from arid and semi-arid to subhumid, with a dry and windy spring, a hot but short summer, an autumn of heavy but short duration rain events, and a long, dry and cold winter. It receives an annual precipitation of 320.8-496.9 mm. Most of the rainfall events are highly concentrated in the summer months. There are relatively rich groundwater resources in the area. Vegetation in the area is characterized by the transitional type from desert and desert steppe to forest steppe. At present severe land degradation occurs mainly in the form of desertification. Overall, 88.5% of the land has been desertified to varying degrees. As an important coal base, the region will inevitably be exploited more intensively for its resources in the futttr,e, leading to more severe land degradation. Systematic study of such representative land degradation is practically and economically significant not only for demonstrating the feasibility of effectively rehabilitating degraded land into productive use, but also for improving the living standard of local inhabitants.
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Figure 1 Location of Yulin district of Shaanxi province
3 Mechanism of land degradation 3.1 The mechanism and model of land degradation The process of land degradation includes wind erosion and water erosion caused by natural effects and by the manners of human activities and inhabitation, and it also includes soil deterioration in physical, chemical, biological and economic characteristics, and the long-range loss of natural vegetation, etc. (UNEP, 1992). Its main manifestations include decrease in land productivity, decline of land output potential, loss of land resources, and the emergence of surface conditions not favourable for production (Zhu, 1994). The degradation process may be everlasting, gradual, continual, and localized (Liu, 1997). The mechanism of land degradation was determined through analysis of the natural settings in the study area and their evolution, as well as through field investigation. The objective of the fieldwork was to identify and evaluate the present characteristics and processes of desertification. The fieldwork was carried out along three routes that covered nearly the entire study area. The first route along the Great Wall aimed at investigating the distribution and status of desertification to the south and north of the Great Wall. The second route was along the upstream of the Wuding River and in the northern piedmont of the Baiyu Mountain. The main purpose was to determine the impact of land use types (farming versus grazing) and intensity on desertification. The third route between the capital of Shenmu County and Daliuta was intended to investigate how the construction of mining facilities and mining activities affected desertification. According to our field investigation and analysis, we find that land desertification, the principal form of land degradation in the study area, stems from a tipped balance between the inherently fragile environment and economic development, in which human activities, among many other factors, play an important role. In other words, land desertification in this ecologically vulnerable region is the outcome of irrational land use and land mismanagement. Inappropriate land use practices in conjunction with weak land management have transformed nature's potential vulnerability to visible destruction (Liu et al., 1997; Liu and Deng, 2001). The model of land degradation is summarized in Figure 2. It indicates that both natural and anthropogenic factors play a critical role in the initiation and exacerbation of desertification. 3.2 The factors and process of land degradation As early as the Qin and Han dynasties (221 BC-220 AD), the study area was known as 'fertile land of million hectares' with advanced farming and pasturing. This favourable setting still remained in the Ming Dynasty (1368-1644 AD) during the construction of the Great Wall. By
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Figure 2 The mechanism of land degradation in Yulin district the mid-Qing Dynasty (1644-1911), the policy of 'providing for people with other lands' led to the conversion of naturally vegetated land to cultivated land. Massive stripping of natural vegetation initiated desertification. By the time the People's Republic of China was founded in 1949, only 40,000 ha of natural forest remained in the six northern counties of Yulin district, covering 2% of the land area. Later large-scale preventive efforts of afforestation and grass planting considerably enlarged vegetative coverage and reversed the trend of desertification within certain localities. Nevertheless, the overall trend of land degradation continues as a consequence of inappropriate human activities, particularly the destruction of vegetation that exposes soil. Soil erosion initiated by strong wind averages 3,800 t/kin2. Wind erosion has thinned the soil layer, degraded land quality, reduced land productivity, and accelerated desertification (Liu, 1999). In recent 10 years, with the development of regional industry (include mining) and the rapid growth of population, the intensity and negative effects of human activities are accelerating, further deteriorating the already fragile ecosystem and resulting directly in the degenerative succession of many environmental factors (Table 1). 4 Changes o f land use and land degradation 4.1 The database of changes of land use The primary information for the land use change of the study area in 1990, 1996 and 2000, was gathered from the Landsat TM image recorded. Auxiliary information sources included 1: 50,000 scale of colour infrared aerial photographs taken in 1990 and 1996, and the detailed land inventory data of 1996 and updated data in 2000 from MLR (Ministry of Land and Resources) were used in the modeling and analysis of land use types. The database and spatial distribution of land use change in the study area are shown in Table 2 and Figure 3. 4.2 The changes of land use and its driving forces (1) Over the last 10 years, arable land, which decreased at an annual rate of 111.02 km 2, was the predominant land use type, and the forestland, grassland, orchard and town-industry-traffic land quickly increased because of the agricultural restructuring and
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Table 1 Degradation characteristics o f the environmental background factors Succession stage of land degradation Vegetation Succession of Soil environmental Surface factors material Climate Intensity Human activities Mode Characteristics of major evidences
Primitive ecoenvironment Initial vegetation Initial soil Fluvial and lacustrine deposits Semi-arid Harmonious
Latent surface soil degradation Damaged vegetation Soil deflation Loosened land surface Drastic change Predatory
Development of land degradation Grass and shrub Wind-eroded soil Sandy soil
Desertification Sand vegetation Aeolian sandy soil Emergence of sand dune Many gales Restricted negative impact
Add and windy Exploitation combined with rehabilitation Agriculture and Agriculture, forestry and Forestry and Difficult to utilize forestry animal husbandry animal husbandry Landscape of Vegetationreduction Development of Intensive sand farmland and forest ddftin~ sand dunes
Table 2 The land use change o f Yulin district in 1990-2000 (Unit: ha) Counties
Farmland Orchard Forestland Grassland Town and Traffic Water Unused industry land area land Yuyang 1 0 1 0 4 . 2 3449.88 28198.61 -10401.5 2290.753 622.5133 -68.72 -34195.8 Shengmu -18238 5452.087 15791.47 8616.593 1266.653 730.7333 -143.693 -13475.9 Fugu -9573.65 85.67333 2151.847 6023.78 521.36 300.5467 479.7133 10.72667 Hengshan -12105.8 1828.313 1381.387 8782.773 891.3867 116.7533 -624.607 -270.24 Jingbian 1255.2289.18667 -3206.39 -112.307 1715.093 241.68 204.7 -187.187 Dingbian -28651.5 2690.067 11724.17 13866.79 1610.313 339.5533 177.5667 -1756.98 Suide -9033.02 3034.38 5862.513 -377.127 217.8667 213.02-1.70667 84.07333 Mizhi -6197.831563.913 855.4667 3622.387 178.6867 1 3 8 . 3 2 1 2 . 2 8 -173.227 Jiaxian -10730.2 1856.16 5779.553 2700.94 225.8867 14.48 58.62 94.58667 Wubu -3142.77 3038.087 85.58 -107.267 205.5267 4.36 -21.9067 -61.6067 Qingjian -10392.2 5915.727 4077.293 105.7467 192.08 132.2733 -5.4 -25.5667 Zizhou -14317.4 53.89333 -252.187 14054.36 76.46667 72.08 73.33333 239.4067 Stud),Area-ll1022.95 29057.37 72449.31 46775.17 9392.07 2926.31 140.18-49717.71
industrial park construction in this area. They have increased at an annual rate o f 72.45 krn 2, 46.78 km 2, 29.06 km 2, 12.32 km 2, respectively. There are obvious differences in structural change o f land-use types such as Yuyang district, Dingbian, Hengshan and Shenmu counties in the two periods o f 1990-1995 and 1996-2000 (Figure 3). (2) Arable land and unused land were mainly transformed to forestland, grassland, and orchard in the process o f "converting cultivated land back into forestry and pasture" and the construction o f The "Three-Norths" Shelterbelts Project. Meanwhile, partial land desertification to the north o f the Great Wall and severe soil and water erosion to the south o f it has also been suffered by inappropriate hmnan activities such as excessive cultivation and over-grazing. (3) After the second land use contract (new land-use reform unchanged in 30 years) was finished in 1996, most of the forestland (trees) and unutilized land were re-assigned to farmers and a new policy "who plants, who owns" was adopted, then, to plant trees and pasturage in the steep sloping farmland, wild sparse grassland and sandy land are encouraged, and much o f the cultivated land and unutilized land were diverted to forestland in 1996-2000. (4) The planting and stockbreeding usually play key roles for the local socio-economic development. With the industrial development including coal and oil mining and the rapid growth o f non-agricultural population, the town-industry land and traffic land are rapidly
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Figure 3 Maps showing land use type changes in Yulin district of 1990-2000
increasing at an annual rate of 9.39 km 2 and 2.93 km 2, respectively. Caused by the unreasonable mining activities, desertification has been seriously developed in areas surrounding coalfields since the 1990s. It has been estimated that the construction of the Shenfu-Dongsheng coalmine alone will cause an increase of desertified area by 129.6 km 2 (Wu, 1996). 4.3 The trends of land degradation (1) It has been revealed that not all counties are equally desertified (Liu and Gao, 2002). On the one hand, all of them except Dingbian have over half of their areas desertified at the severe level while Hengshan and Yuyang have three quarters of their territory desertified severely. On the other, many of the counties have a large proportion of land with latent potential. Therefore, the pattern of desertification severity appears to be polarised. (2) A comparison of the recent satellite images with historical aerial photographs reveals that the extent of degraded land in the study area has expanded while the overall severity of land degradation has worsened. Confirmed by the field investigation, the desert front in the vicinity of Xincheng, Jingbian County has advanced forward by over 10 km. The sand-topped loess topography incised by gullies has encroached southwards by 10 to 30 km. In the worst affected region between Yuyang and Hengshan, the encroachment is as further as over 40 km. Because of the expansion of the Mu Us Desert and the impact of sandstorms, the Great Wall is no longer the divide between sandy land and loess. (3) In addition, desertified land is not equally distributed spatially across the study area and temporarily constant. Land desertification is very severe in northeastern Shenmu, the upstream tributaries of the Wuding River, and in the northern piedmont of the Baiyu Mountain in Dingbian and Jingbian counties. Desertified areas have advanced towards the southeast linearly. Therefore, the speed of land desertification has accelerated in the last 10 years. Furthermore, the speed of desertification has been growing in severely desertified counties despite rehabilitation efforts, the counties not considered so vulnerable to desertification have fared less well by comparison. (4) The patterns of land degradation have a trend of diversification in this study area. Except land desertifieation, pattems like soil erosion, grassland degradation, and soil and water loss take place jointly, and their harm goes worse. Thus, they should receive more attention in the future in order to maintain the overall risk of land degradation.
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5 C o u n t e r m e a s u r e s to land degradation 5.1 Optimize rural economic structure, mitigate population stress on the land The substantial reason of land desertification caused by over population in the study area lies in the deep contradiction between low carrying capacity of land and excessive growth of human activities using poor agriculture and husbandry techniques. To a certain extent, it is an inevitable result of fragile eco-environmental region with behindhand economy and technology. Therefore, the keystone of land desertification management is to break through the bottleneck of technology, combine the knowledge of economy, ecology and eremology, integrate the land desertification management with rural economic development, especially the development of agriculture and husbandry. On the one hand, via the application of technology in point and the preferential policies, improve economic conditions, raise the productivity and the farmers' income; on the other hand, the policy of "substituting woods and grass for grain, recovering eco-environment" should be carried out, let more farmers make their living without traditional agriculture and husbandry, thus eliminating the root of desertification, making the overall reverse of land desertification. 5.2 Change the idea, build preventive vegetation system marching ecological economy The fundamental approach to desertification control is to build and improve preventive vegetation systems, and increase vegetation coverage (Liu and Ci, 2000; Kjeld et al., 2001). According to the principle of 'adjusting measures to local conditions, from easy to difficult', the approach includes: allocate arbor-shrub-grass fittingly, distribute belt-network-patch rationally, so as to form the converging attacking to desertification. In interdunal area and sandy ground, develop timber forest network and farm shelter network dominated by arbors like poplar, willow, elm, and pine. In the steep slope of degraded waste mountainous area, build soil and water conservation forest by the conversion of cultivated land back into forestry. In wet sandy ground with relative good hydrothermal conditions, develop patches of economic forest dominated with apple, grape, sallow thorn, etc. The purpose is to gradually build up ecological economic patterns of preventive vegetation systems divided by forest belts, crisscrossed by farm shelter network, and scattered with patches of forest and grassland. 5.3 With a view to the future, realize sustainable land use The key to the management of land degradation is to enhance the construction of basic farmland, fulfilling the dual targets of less farmland with more harvest and more vegetation with higher benefit. So it is very important to improve the land use manner and to increase the low income of farmers, which is an important premise to mitigate the pressure and hazard of human activities on land. Agricultural activities should make efforts to enhance the diversity, heterogeneity and stability of agricultural ecological system, promote its benign circulation: (1) Develop farmland, forest and grassland simultaneously. Take forest as framework, set grass belt between forest belt and farmland. The Loess Plateau is fit for planting purple medic, a kind of high-quality pasture grass for stockbreeding. Statistics show that one hectare of purple medic will produce 60,000 kg of grass which costs nearly 7,000 yuan, doubling the profit of grain (SBSP, 2001). (2) Preserve nutrient and granule materials in cultivated horizon through overlay cultivation, improve soil structure by grain-grass rotation and intercropping, so as to enhance the anti-erosion capacity of soils. In the degraded areas, measures of spreading soil upon sand and mixing sand into mud can be used to amend the physical properties of soil, to the effect of preventing the spreading of degradation. (3) This region possesses a huge potential for further exploitation of natural resources and economic development. However, protection of the fragile ecosystem should be reinforced to maintain a balance between development and land utilization. Thus it is necessary to enforce existing laws for governing the exploitation and management of natural resources, and to establish a mechanism to compensate for farmers whose income has dropped as a consequence of diminished land productivity caused by mining-induced degradation in the vicinity.
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