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3. Definitions and methodologies
A. Definitions
B. Theories and hypotheses
C. Methodologies
D. Studies on the natural environment of arid and semi-arid zones
3.1 The most widely accepted definition in China for desertification is given by Zhu Zhenda (cf. bibl. entry 145). Zhu describes desertification as the degradation process in environments similar to that of deserts consisting of blown and undulating sand sheets and mobile dunes which occurs when fragile ecosystems such as those with loose sandy surfaces in arid semi-arid and sub-humid zones are exposed to drought and frequent wind. This process reduces biomass productivity and arable land. The environmental changes caused by desertification produce desert-like landscapes in aboriginal non-desert areas or steppes.
3.2 Wu Zheng (cf. bibl. entry 97) has offered another definition: desertification is the environmental formation or development of a sand desert-a deterioration process. A desert is the last or terminal result of the process and reflects a distinct geographical environment. Desertification can occur not only in "unoriginal sand desert areas" hut also in original sand desert areas when sand desert conditions are intensifying.
3.3 During the period 1977 to 1994 the word "desertification" was translated into the Chinese word "sand desertification" (cf. bibl. entry 145).
3.4 Since desertification is an ecological issue studies must address the entire process in a holistic and systematic manner: historical and modern processes physical degradation and rehabilitation. In desertification-prone areas rehabilitation should focus on rational development and adjustment of resource uses; for severely decertified areas supplementary and artificial energy and other material inputs are required (cf. bibl. entry 145).
3.5 Desertification in geological periods was determined by climatic changes a pure or natural process (cf. bibl. entries 32 33 42). In recent times human activities have intensified natural environmental degradation. The development speed of man-made desertification is ten times greater than natural processes (cf. bibl. entries 31 46 97 98 100 144).
3.6 On the basis of feature analysis pattern divisions dating and petrofeature/petrofacies comparisons of paleoeolian sand strata a striate graphical sequence for the desert areas of northern China was developed and the curliness and evolution of desert formations in the early or late Tertiary and Quaternary periods reconstructed (cf. bibl. entry 28).
3.7 During the Neogene period an aeolian sand land formation process existed in the southeastern Tengger Desert that is similar to today's sand transport and accumulation process (cf. bibl. entry 107). The Qinwangchuan basin in Lanzhou consists of' typical aeolian sand eroded from nearby alluvial sand and Malan loess during the last glacial period (cf. bibl. entry 14). A comparative study of the surface texture of quartz sand in inland deserts to that of coastal dunes shows them both to have developed from an aeolian environment (cf. bibl. entry 96).
3.8 In the Taklimakan Desert the instant fluid and impact threshold velocities are 6.05 metres per second (m/s) for naturally mixed sands at a height of two metres (m) above the surface which is equivalent to one minute averages of 5.2 and 4.3 m/s. For ten minute durations fluid and impact average threshold velocities are 5.7 and 4.7 m/s respectively. When fluid and impact thresholds are adjusted for the height of the anemometer tower (11.4 m) the instant velocities are 7.8 and 6.63 m/s respectively equivalent to 7.4 and 5.97 m/s for ten minute durations (cf. bibl. entry 20).
3.9 The black storm over part of Gansu and Ningxia during the late afternoon and early evening of 5 May 1993 was caused by a mesoscale connective system combined with a squall line in advance of a cold front. It moved eastward to consort with a 700-500 hPa mean flow (cf. bibl. entry 49). Using samples collected in Yulin Yan'an Taiyuan Hohhot and Beijing trajectories for a sandstorm that occurred in April 1990 were calculated. During periods of sandstorm activity total suspended particle (TSP) concentrations are several times higher than normal. Aerosols of sandstorms consist mainly of natural lithosphere elements from the earth's crust; their enrichment factors are sharply reduced during sandstorm activity (cf. bibl. entry 108).
3.10 The Basic Theory of Desertification Assessment considers natural and artificial factors influencing desertification historical and recent processes of desertification development trends and ecological and reversing processes. A complete set of assessment criteria and degrees must be established before making an evaluation (cf. bibl. entry 65).
3.10.1 The site classification and evaluation techniques for desert regions in China are adopted from sample studies e.g. the Mu Us Desert region (cf. bibl. entries 12 148) and the shelterbelt systems (cf. bibl. entry 9). The quantitative site evaluation method using multiple shrub species or tree species for desert sites were first applied to site assessments in the Mu Us Desert region (cf. bibl. entry 12).
3.10.2 The aridisoils of Xinjiang form a vast aridisoil zone in central Asia including Kazakstan Uzbecksitan and Turkinenstan. A systematic classification of aridisols in Xinjiang has been revised to include tour newly-recognized sub-orders (cf. bibl.. entry 61).
3.10.3 The climate of the Taklimakan Desert is a complex of basin and desert climates and extreme dry continental climate. Between 1785 and 1986 tour periods can be defined. The general trend was towards a warmer and drier climate (cf. bibl. entry 66).
3.10.4 In the loess area of North China the agricultural landscape is a mosaic of natural and "human-managed" zones that vary in size shape and use. Farmland and forest zones have increased and show a tendency to change shape from simple to complex. The shapes of grassland zones vary at random (cf. bibl. entry 37).
3.10.5 Research on the heat balance of artificial vegetation and bare sand dunes in the Shapotou area showed that in the artificial vegetation regions of the dunes 70 percent of net radiation disperses as latent flux 15 percent as sensible heat flux and 15 percent is stored in the soil. Sixty percent of net radiation disperses as latent heat flux 15 percent as sensible heat flux and 25 percent is stored in the soil in the bare dunes. Water vapour content is higher compared to other dry areas in the Shapotou region (cf. bibl. entry 68).
3.11 A semi-cement medium-fine sand sediment of brown-red colour known as "Old Red Sediment" is intermittently distributed southwards along the coast of South China from Pingtan Island in Fujian province. It belongs to the coastal aeolian deposit formed in the last glacial period of the late Pleistocene. The "Old Red Sandy Sediment" developed in two stages-the coastal aeolian deposition stage and the weathering (oxidization) stage. Time of laterization is no more than 10 000 years (cf. bibl. entry 95).
3.12 Based on analyses of chronological sedimentological geochemical and mineral factors in the lacustrine area of Xiaoshazhi Lake Hobq Sandy Land in Tibet (the highest sandy land in China) did not form during construction of the lacustrine section but after 600 yr.B.P. (cf. bibl. entry 60).
3.13 Future studies of China's shelf sedimentary environment may include the following: (a) the relationship between formation of the great Qinghai-Xizang ice sheet and the Yangtze River delta deposits; (b) the relationship between loess and deserts (loess is always accompanied by deserts); (c) further development of new evidence on desertification of shelf deposits in the last stage of the late Pleistocene (cf. bibl. entry 131).
3.14 By studying the characteristics of grain composition of heavy minerals and surface micro-structure of quartz it can be concluded that Songhua Jiang Nen Jiang Sandy Land came from alluvial sand of Songhua Jiang and the Nen Jiang Plain through wind erosion transportation and deposition. Sandy Land experienced four fixed periods and four shifting periods after formation in the early Holocene (cf. bibl. entry 57). Similar climatic changes have been found in the Hulun Buir Sandy Land since the Holocene (cf. bibl. entry 88).
3.15 Arid and semi-arid land in West China covers one-third of the national land area. Studies on new forms of sustainable natural resource exploitation and utilization are underway to help realize the region's agricultural and forestry potential (cf. bibl. entry 1).
3.15.1 New land use planning techniques can improve desertification control. Land evaluation programs have been completed for Mu Us Sandy Land and Inner Mongolia using the automated land evaluation system (ALES) and geographical information system (GIS) in accordance with the Food and Agriculture Organization of the United Nations (FAO) framework for land evaluation (cf. bibl. entry 25).
3.15.2 Experiments in hilly loess areas of South Ningxia have shown that rotations between grain and bean (i.e. spring pea-spring wheat-spring wheat-broom corn-millet) can adjust maintain and balance soil moisture within the rotation period; alfalfa can be included in grass-crop rotations (cf. bibl. entry 74).
3.15.3 Belt-shaped inter-cropping of sunflower and soybean in arid plains produces remarkable soil and water conservation and economic benefits. Higher yield objectives could be obtained by popularizing improved techniques for saving spreading and utilizing manure (cf. bibl. entry 69).
3.15.4 Agroecosystem components can be readjusted to optimize yields i.e. revising land use ratios between agriculture forestry animal husbandry extending crop varieties and rotation techniques constructing water conservation projects and increasing material inputs such as fertilizer. Using this approach the average grain yield per ha increased by 2 017 kilograms (kg) on semi-arid blowing sand land in northwest Hebei province (cf. bibl. entry 110).
3.15.5 Based on analysis of energy and material flows agroecosystem functions for decertified areas in central Horqin Sandy Land are characterized as follows: the level and amount of energy and material flow are small; energy and material passages are few. It is a low-input low-output. low-benefit agroecosystem (cf. bibl. entry 30).
3.15.6 Desertification is serious in exploited sandy steppe land near coal mines in North China. A number of measures for land conservation have proven to be feasible however and the desertification process has been effectively controlled (cf. bibl. entry 144).
3.15.7 Oases in the arid inland watershed of the mid-West Bank of the Yellow River are high quality agricultural production systems while benefits of oases at the end of the lower reaches are minimal (cf. bibl. entry 122).
3.15.8 It is difficult to eliminate wind and sand disasters in the oases of Xinjiang. Exploiting rich oil and natural gas resources in desert areas and constructing wind power stations in pastoral areas lessens artificial pressures on desert vegetation and of protects desert vegetation in the peripheral areas of oases (cf. bibl. entry 140).
3.15.9 Artificial factors now have a greater impact on the degradation process in the Taklimakan Desert than natural ones. Human activities must be revised and adjusted to help remake the natural environment rather that destroy it (cf. bibl. entry 46).
3.16 Site classification and evaluation systems for shelterbelts have been established for sandy land in semi-arid steppes. Shelterbelt networks on rangeland help increase the amount of warm moist wind and solar radiation; grass yield and quality were both increased. Sand fixation forests help stabilize flowing sand and reduce sand-bearing amounts in the wind. Plant and animal populations improved in extended forest protection areas (cf. bibl. entry 9).
3.17 Wind shelterbelts have the following effect: (a) the influence range for different types of hefts extends four times the height of the windbreak (H) vertically and 50 H horizontally. The distance where wield speed reductions are still at least 20 percent occurs 18.5 H beyond the belts with permeability of 35 percent; (b) the ratio of the average gap between tree crowns to the average height of the belt is an important index for expressing the effect of belts on air flow and permeability (cf. bibl. entry 138); (c) in grazing forests of Inner Mongolia wind speed within the forest was reduced as the closeness of the forest increased. As compared with open wild area evaporation was reduced by 12 to 20 percent while transpiration increased by approximately seven percent (cf. bibl. entry 143).
3.18 Remote sensing methods have been used to monitor changes in desertification-prone land in China (cf. bibl. entry 145) land degradation in neighboring areas between Shanxi. Shaanxi and Inner Mongolia (cf. bibl. entry 125) soil erosion in Inner Mongolia (cf. bibl. entry 11) and land resource systems in the shelter forest region of the Dongbei Plain (cf. bibl. entry l 15).
3.19 Hourly satellite data (GMS-4-VISSR Imagery) and conventional data were used to study causes of the black storm formation over parts of Gansu and Ningxia on 5 May 1993 (cf. bibl. entry 49).
3.20 Feature analysis pattern division dating and petrofeature/petrofacies comparisons of the paleoeolian sand strata have been used as the basis for studying the formation and evolution of deserts in China (cf. bibl. entry 28) such as: Southeastern Tengger Desert in Xinjiang (cf. bibl. entry 107) the Hunshandake Desert in Inner Mongolia (cf. bibl. entry 33) the Xiaoshazhi Lake in Tibet (cf. bibl. entry 60) the Taklimakan Desert in Xinjiang and Horqin Sandy Land in Inner Mongolia (cf. bibl. entries 79 100) the Qinwangchuan basin in Lanzhou (cf. bibl. entry 14) the "Old Red Sandy Sediment" along the coast of South China (cf. bibl. entry 95) and the Bakikun Lake in northern Xinjiang (cf. bibl. entry 42).
3.21 Thermoluminescene 14C dating and archaeology analysis show that Songnen Sandy Land experienced four fixed periods and four shifting periods after formation in the early Holocene (cf. bibl. entry 57). The results of spore pollen analysis and 14C dating indicate that Hulun Buir Sandy Land experienced four fixed periods and four mobile periods since the Holocen (cf. bibl. entry 88). The northern Shaanxi Loess Plateau experienced four periods of humid-warm and dry-cold climatic change based on magnetic susceptibility curves lithological characteristics of stratum and other palaeo-climatic indicators (cf. bibl. entry 81).
3.22 A geographic information system (GIS) factorial analysis and statistical methods were used to examine the spatial patterns of agricultural landscapes in the loess area of China (cf. bibl. entry 37). Site classification and evaluation methods have been established for the shelterbelt systems including forest site zones regions sub-regions groups types and plant communities for the semi-arid steppes of sandy land (cf. bibl. entry 9). Comprehensive evaluations of site quality of Mu Us Sandy Land have been made by developing a multiple regression mathematical model which provides a simple method for evaluating the shrub biomass in forest lands (cf. bibl. entry 148). Land resource evaluation of the desert steppe area of Ningxi has been made according to land suitability classifications for farming forestry and animal husbandry (cf. bibl. entry 127).
3.23 The development of desertification can be divided into degrees by an established system of assessment criteria which includes percentage of decertified land in an area percentage of severely decertified land in an area percentage reductions in productivity mean increasing percentages of decertified land annual expansion percentages of decertified land and annual reduction percentages in productivity. According to the degree of desertification and regional continuity China's desertified lands have been divided into 20 desertification regions (cf. bibl. entry 32).
3.24 Natural landscapes of the Loess Plateau have been changed by severe soil erosion. Processes of man-made accelerated erosion and soil degradation have been analyzed using regional investigation methods. experimental studies in chemical analysis of site samples and studies on the impact of forest vegetation destruction and restoration on soil erosion. In the latter the characteristics of natural erosion under conditions of natural ecological balance were contrasted with man-made accelerated erosion caused by forest vegetation destruction. (cf. bibl. entry 136).
3.25 Mathematical applications are detailed in the following studies:
(a) Regression prediction models have been used to study climatic change tendencies in Spring in the Mu Us Sandy Land (cf. bibl. entry 82) and the relationship between vegetation degeneration and soil salinisation in grasslands of Songhua Jiang and the Nen Jiang Plain (cf. bibl. entry 123).
(b) Principal components analysis was used to study the function of human factors in desertification (cf. bibl. entry 31).
(c) A quantitative mathematical model was used to evaluate site quality of Mu Us Sandy Land (cf. bibl. entry 148).
(d) General mathematical models were used to study human effects on soil erosion and desertification systems (cf. bibl. entry 34).
(e) The geographical information system (GIS) was used to study land use classifications for desertification control in Mu Us Sandy Land Inner Mongolia (cf. bibl. entry 25) and spatial pattern analysis of agricultural landscape in the loess area (cf. bibl. entry 37).
3.26 Physics methodologies and studies include the following titles:
(a) The Intermittent. Stable Distribution and Factual Characteristics for Wind-sand Turbulent Flow (cf. bibl. entry 54).
(b) The Heat Balance of Artificial Vegetation and Bare Sand Dunes in Shapotou Area (cf. bibl. entry 68).
(c) The Formation of Songnen Sandy Land and Changes in the Environment (cf. bibl. entry 57) and A Comparative Study of the Surface Texture of Quartz Sand in Inland Deserts and Coastal Dunes China (cf. bibl. entry 96).
(d) The Numerical Simulation of the Features of the Planetary Boundary Layer of the Oasis and Gobi Desert in the Arid Region (cf. bibl. entry 75).
3.27 Wind tunnel studies are applied in:
(a) The meteorological effect of grazing forest grassland experimental station of Baiyintala region (cf. bibl. entry 143).
(b) A test on the sheltering effect of shelterbelts on wind (cf. bibl. entry 138).
D. Studies on the natural environment of arid and semi-arid zones
3.28 Using annual aridity coefficients rainfall and accumulated temperatures as indexes for the classification of arid climate China is divided into two great types three patterns and 15 zones. Climatic characteristics for each type are available (cf. bibl. entry 106). Additional research on meteorological phenomena includes:
(a) Characteristics of the concentration and size distribution of desert aerosols over Heihe region (cf. bibl. entry 53).
(b) The seasonal climatic environment of desertification in coastal areas of the Yellow Sea and Bohai Sea (cf. bibl. entry 39).
(c) Numerical simulation of the features of the planetary boundary layer of the oasis and Gobi Desert in the arid region (cf. bibl. entry 75).
(d) Heat balance of artificial vegetation and bare sand dunes in Shapotou area (cf. bibl. entry 68).
(e) Sandstorm events in northwest China (cf. bibl. entries 24 49 108).
(f) Wind and sand disasters in Xinjiang including threshold velocities for sand-driving wind in Taklimakan Desert desertification disasters and control countermeasures in the oases and domination of local landforms to sand dune movement in Altai (cf. bibl. entries 20 84 140).
3.29 North China experienced four periods of humid-warm and dry-cold climatic change. Palaeo-climatic change has been studied by many researchers' e.g. the Sandy Desertification Process of the Hunshandake Sandy Land during the Last 5 000 Years (cf. bibl. entry 33) the Age and Evolution of the Taklimakan Desert (cf. bibl. entry 79) Climatic Change in the Northern Shaanxi Loess Plateau during the Last 130 000 Years (cf. bibl. entry 81) the Mechanism of Desertification in Taklimakan Desert in Xinjiang and Horqin Sandy Land in Inner Mongolia (cf. bibl. entry 100) and Late Tertiary Aeolian Sand Accumulation and its Environment in the Southeastern Marginal Tengger Desert (cf. bibl. entry 107).
3.30 Present status and future trends of desertification in northern China are widely studied. Decertified lands in northern China expanded slightly over the past 30 years. Some studies show that under the impact of global climate change China's arid zones will expand and become warmer and drier (cf. bibl. entry 26). Precipitation in the eastern part of China may increase and thereby help alleviate or reverse desertification. Drought in the western desert areas may be intensified which will promote the further development of desertification (cf. bibl. entry 98). Other studies on climatic trends are as follows:
(a) Effect of Global Climatic Warming on Erosion and Sediment Yield on the Loess Plateau Shaanxi (cf. bibl. entry 51).
(b) Climatic Characteristics and their Tendencies on the Taklimakan Desert (cf. bibl. entry 66).
(c) Research on Recent Climatic Change in Spring in the Mu Us Sandy Land (cf. bibl. entry 82).
3.31 Oases processes desertification and land degradation are affected by geomorphology. Representative studies include: Oases Processes and Desertification of the Yarkant River and Kagar River Valley S. Xinjiang (cf. bibl. entry 27) the Domination of Local Landforms to Sand Dune Movement Altai, Xinjiang (cf. bibl. entry 84) Desertification of Shiquanhe River Broad Valley in West Qing Zang Plateau (cf. bibl. entry 102) and Land Degradation in the Neighboring Areas between Shanxi Shaanxi and Inner Mongolia Using Remote Sensing Methods (cf. bibl. entry 125).
3.32 Soil water is a key factor in plant growth in arid sand dune areas. It is important to understand the relationships between plants and soil water.
3.32.1 Although the quantity of condensed water in dune fields in Shapotou region is limited it can nourish native plants cryptograms and microbes in addition to improving the biochemical characteristics of sand-fixing plants (cf. bibl. entry 23).
3.32.2 Annual soil moisture dynamics can be divided into four periods in arid plains i.e. intensive consuming period in late spring and early summer resuming and replenishing period during the rainfall season slow consuming period in late autumn and relatively stable period in winter and early spring (cf. bibl. entry 69).
3.32.3 According to the Soil Moisture Balance of Farmland under Different Rotation Systems in Loess Hilly Areas of South Ningxia study soil moisture in layers of one metre is sufficient for planting drought resistance crops (millet) after alfalfa has been grow for five to six years. The soil moisture in layers of' two metres can he replenished after drought-resistance crops have been planted for two to three years (cf. bibl. entry 74).
3.32.4 The study on the Dynamic Variations of Soil Moisture Caused by Rainwater Infiltration in Bare Sandy Land in Shapotou Area of the Tengger Desert notes that the infiltration speed of rainwater is low due to the existence of' a dry sand layer. The redistribution of plays a key role in the dynamic variation of soil moisture (cf. bibl. entry 76).
3.33 Human factors in the desertification process have been studied in tour typical areas in Xijingzi Naritu, Baiyintala and Jiangjia Ravine. Human factors account for 60 percent of the degradation while natural factors account for 40 percent. The difference in speed between natural and man-made desertification processes is significant; the development speed of man-made desertification processes is ten times as great as that of natural processes (cf. bibl. entry 31).
3.34 Quantitative analysis of the effect of human activity can be an important index for analyzing the causes of soil erosion and desertification and provides a scientific basis for soil and water conservation and desertification control (cf. bibl. entry 34).
3.35 There are 90 families 570 genera and 1 693 species of plants in the desert areas and sandylands in North China (cf. bibl. entry 71).
(a) Nitrogen fixation plant resources in the arid regions of Xinjiang have been studied with special reference to legume species and algae (cf. bibl. entries 41, 141).
(b) The sand-fixing plants, Salix flavida, Caragana microphylla, and Hedysarum mongolicum, on sandy soil have been studied (cf. bibl. entries 48, 91).
3.36 Plant-water systems are the focus of considerable research (cf. bibl. entries 23, 47, 63, 74 137).
3.37 Plant nutrients and productivity: Constructive species of the Alex Desert are Chenopodiaceae, Zygophyllaceae, Compositae, Rosaceae. Tamaticaceae and Grarnineae All forage species are greatly deficient in Mo except for grass forages. Forages of the Tribulus family, Leguminosae and Chenopodiaceae are Ca-rich and Gramineous forages are Ca-poor; all contain a medium level of nitrogen. As a whole, plant species of Zygoghyllaceae have a higher enrichment ability to Ca, N and Zn; plant species of Compositae have a higher enrichment ability to Cu. Zn and Mn; plant species of Rosaceae have a higher enrichment ability to Fe Cu. Mn and Co (cf. bibl. entry 38).
3.37.1 The biomass of nine shrub species, such as Caragana intermediate, C. korshinskii. Hedysarum scoparium, H. laeve, Salix psammophila, Amorpha firuticosa, Hippophae rhamnoides, Artemisias phaerocephala, A. ordosica, in the Mu Us Desert have been evaluated. The crown, breadth and height of shrubs reflect biomass yields above ground. Multiple regression mathematical models can be established which provide a simple method for evaluating shrub biomass in forest land (cf. bibl. entries 38, 148).
3.38 Plant succession: From early Holocene to late Holocene the paleo-botanical succession series in Hulun Buir Sandy Land were sub-desert steppe-Artemisia, steppe-sparse forest, stepe-Chenopodioceae and weed steppe. All of these vegetation types belong to the grasslands with sandy soil. The existing sandy grassland should be protected in accordance with the succession laws of ancient vegetation (cf. bibl. entry 88).
3.39 Microbiology: In southwestern Horqin Sandy Land the microbial population, such as bacteria, actinomyces and fungi as well as their physiological groups in afforested sand dunes, are larger than those in shifting sand. The number of bacteria and fungi in afforested sand dunes is two to 16 times higher than those in shifting sand. Generally, the older afforested sand dunes have more bacteria and fungi as compared to newly afforested sand dunes; the microbial numbers are higher in upper layers than in sub-soil layers. In newly afforested sand dunes the actinomyces are higher than in shifting sand, while in the older afforested sand dunes the actinomyces number less than in newly afforested sand dunes (cf. bibl. entry 22).
3.40 Fenced enclosures to exclude grazing animals have been established in oases and desert fringe areas in Xinjiang and Gansu provinces. Vegetation cover and grass yield in the closed pastures increased by 15 percent to 17 percent and 20 percent to 100 percent, respectively after two to three years. Experiments showed that rational utilization of closed pasture could help maintain the ecological balance of desert regions and facilitate animal husbandry development in northern China (cf. bibl. entry 116). A computerized decision-making system for steppe rangelands has been proposed which includes monitoring and assessment (cf. bibl. entry 64).