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5. Combating desertification and drylands development in the people's republic of China
A. Socio-economic aspects of combating desertification
B. Economical measures costs and profitability
C. Techniques and technologies of drylands development and combating desertification
D. Scientific research related to drylands development and combating desertification
A. Socio-economic aspects of combating desertification
5.1 In the Yutian oasis of the Keyiya River basin, people recognize that intensive agriculture development and unreasonable human activities can produce unfavourable changes in the environment, particularly in the lower reaches of the river. The whole river valley must be viewed as a management unit. Rational utilization and development of water resources are the foundation for creating a stable ecological environment. It is both necessary and feasible to set up a natural protective zone to ensure an adequate water supply, for example, 100 to, 150 million m3 of water storage in Daheyan oasis (cf. bibl. entry 17).
5.2 A case study of the Shiquanhe River valley suggests that desertification control and ecological restoration measures should include both protecting existing vegetation and establishing artificial vegetation in the valley (cf. bibl. entry 58).
5.3 Zone differences must be taken into consideration when applying basic principles of systematic engineering to the rehabilitation of decertified land.(cf. bibl. entry 117). Such practices were adopted in dry land farming areas in semi-arid regions in southern Ningxia and in southwest Songhua Jiang and the Nen Jiang Plain (cf. bibl. entry 78).
5.4 A proposed dynamic monitoring system for duststorm area environments, one of China's most serious forms of natural disaster in arid and semi-arid regions, will consist of gale alarming, image processing and mapping, a database analysis model, disaster evaluation model, disaster prevention policy-making model and an alarm information transmission system (cf. bibl. entry 90).
B. Economical measures costs and profitability
5.5 Economic results achieved during a decade-long trial for revegetating a large-scale shelterbelt system on desert sandy lands at the Desert Experimental Center of the Chinese Academy of Forestry were as follows: the economic income of the desert sandy land increased from 4.29 yuan/ha/year in 1979 to 1359.28 yuan/ha/year in 1989 and could justify use of a loan at below 9.7 percent annual interest rate (cf. bibl. entry 1).
5.6 Upon completion of the Jartal Salt Lake Project in Jartal Salt Lake region of Ulan Buh Desert in Inner Mongolia, wind velocity near the ground surface was reduced by 13.3 percent to 13.7 percent. Sand volume transported into the lake was reduced to 367 000 m3 per year from 1 275 000 m3 per year.
C. Techniques and technologies of drylands development and combating desertification
5.7 Poplar tree growth, soil moisture and heat and groundwater levels were observed at regular intervals between 1984 and 1990 under different conditions of artificial water supply. The results showed that irrigating artificial plantations of Populus (popular Chon-lin) in the dry regions of northwest China could raise the groundwater level within the plantation growth period 0.5 m to 1.54 m and that soil moisture and temperature could be effectively improved (cf. bibl. entry l 14).
5.8 Successful measures to exploit sandy land for agricultural and animal husbandry development include intensive management by planting trees and afforestation (cf. bibl. entry 48). A study conducted in the eroded tideland hilly areas, located in Pengang county of the South Ningxia, developed a cropping system for dry land farming which focused on the grass-animal husbandry-nutrient-grain relationship. Comprehensive measures were designed to promote drought resistance and preserve soil moisture; new varieties of crops and optimal systems of cultivation and tillage were introduced (cf. bibl. entry 83).
5.9 Restoration of degraded steppe rangeland demonstrated that rhizomatic grass rehabilitated more quickly than tussock grass; the restoration process was of a monostable state; restoration dynamics corresponded generally to spatial changes along, a grazing gradient. The main steppe rangeland communities dominated by Stipa gobina, S. breviflora. S. krylovii, S. grandis, S. baicalensis and Aneurolepidium chineses will converge into a Artemisia frigida community under sustained grazing influences. It is a fine forage species and an important species for resisting steppe degradation. Grazing retrogression in steppes was divided into two successive stages: rangeland utilization (improvement) and degradation. The area of desertification was divided into desertified and latent desertification on the reclaimed steppe in marginal areas (cf. bibl. entry 145).
5.10 To resist drought, cold and damage from salinisation, fallow seeding with concentrated fertilizer is a traditional farming practice in northern winter wheat areas of China.
5.11 A variety of measures, including biological measures (planting trees and grasses), mechanical measures (sand fences) and combinations of both were adopted to fix shifting sand in the Hexi Corridor of Gansu province (cf. bibl. entry 13). Key techniques to raise tree survival rates and control desertification are: enclosing sand land for plant growing and artificial broadcast sowing, laying mechanical barriers, selecting appropriate tree and shrub species, employing "front shelter and back pull" techniques to fix shifting sand and matching tree density to ensure sustainable use of water resouces (cf. bibl. entry 52). In Hulun Buir grassland in northeastern Inner Mongolia, techniques such as drilling and straw checkerboard wind breaks are used to fix mobile sandy land along with a combination of shrubs and grasses. Shrubs can be used to make biological windbreaks; grasses can protect the surface from wind erosion (cf. bibl. entry 35).
5.12 In Horqin a study based on succession series of psammophytes in sandy land showed that the model for establishing artificial vegetation should consist of a landscape of sparse wood grassland, with shrubs as a main species and trees as a secondary species. Inter-dune depressions with a water table higher than four to five metes are suitable for planting Pinus sylvestris var. mongoloca, windward slopes of sand dunes for Artemisia halodendron and Caragana microphylla and leeward slopes for Salix gardejevii.
5.13 According to tests conducted in the Chengcheng, Qianxian and Wugong counties of Shanxi province, stubble mulching is important for maintaining and improving soil water content, soil structure and fertility; crop yields increased by ten percent to 20 percent. Using 6 000 kg/ha of wheat straw as stubble mulching, the moisture stored in 200 cm of soil can store 41.9 milimetres (mm) of rainfall water more than in land without mulching at the end of summer fallow (cf. bibl. entry 99). Tests with wheat straw mulching in fruit orchards such as grape, hawthorn, peach and pear on newly created sandy land in Yucheng county of Shangdong province showed that mulching could adjust soil temperature, avoid high temperature harm to fruit trees in summer, ensure their safety over winter, improve water and nutrient conditions, suppress weed growth and lessen sand drift damages for better growth and development of fruit trees and higher yields (cf. bibl. entry 126).
5.14 Plastic sheet covers for crop cultivation can effectively overcome natural constraints and prolong the use of light, heat, water and fertilizer in the arid and semi-arid areas. Tests in Pengyang county of Ningxia showed that corn yields increased by 70 percent with plastic sheet covers (cf. bibl. entry 104). In Xinjiang the practice of irrigating over pored plastic film saved 30 to 50 percent of the irrigation water and offered a yield increase of over ten percent compared with furrow irrigation. (cf. bibl. entry 35).
5.15 Tillage techniques are essential for water storage and soil conservation in arid plains. Intercropping of sunflower and soybean in belt shapes produces benefits for soil and water conservation and good economic returns (cf. bibl. entry 69). The technique of mulch seeding with no tillage for summer corn has been extended to include three field operations (wheat harvesting with straw chopping and spreading, direct seeding and fertilizing and weed control with herbicide spraying) and six farming techniques (seed treatment, mulching, direct seeding, granulated compound fertilizer, application, herbicide spraying and insect control). A lighter, less costly mulch seeder (2BQM-6D) was also developed.
5.15.1 Considering the principle of water equilibrium and the law of runoff movement, land preparation can effect rainfall distribution and thereby adjust soil moisture. During tests in the semi-arid loess hill and gully area of North Shaanxi, annual water collected from rainfall was 29.22 kg, 33.95 kg and 37.85 kg at 1.5 m x 2 m, 2 m x 2 m, and 2.5 m x 2 m, respectively.
5.15.2 The reverse-slope terrace form of land preparation collected the largest amount of rainfall at 26.5 mm, followed by contour trench at 24.8 mm and fish scale pit at 20.7 mm (cf. bibl. entry 86).
5.15.3 Between 1979 and 1988, grasses were air-sown on 267 000 ha in Mu Us Sandy Land, Horqin sand land and on the eastern fringe of Tengger Desert. One hundred and eighty-one thousand ha of decertified and degraded pasture lands were regenerated. Sand surfaces were kept in a semi-fixed condition by proper grazing to prevent serious degeneration due to crust formation (cf. bibl. entry 105). The conserving effect of aerial seeds, Hedysarum mongolica Turcz, H. scoparium Fisch et Mey, and H. mongolica was tested on moving sand dune chains in the Yulin area of the Mu Us Desert. The vegetation belt of Hedysarum mongolica widened from 24 m to 35 m due to germination of the sub-terranous stem. The survival rate increased from 17.7 percent to more than 60 percent. Aerial seeding, is a good method to control dunes, particularly in an isolated area (cf. bibl. entry 139).
5.16 Sand control systems have been adopted for use along railway lines in the Gobi and other deserts according to sand damage conditions. The Shapotou section of the Baotou-Lanzhou Railway line includes enclosed belts, upright fences on the front side of sand dunes. straw checkerboard barriers and irrigated forest belts along both sides of the railway. In the Shixiazi section of Ganwu Railway where there is no water for irrigation the sand control system consists entirely of straw checkerboard barriers along both sides of the line (cf. bibl. entry 103).
5.17 In oases and desert fringes of Xinjiang and Gansu provinces, 67 000 ha of closed pasture were fenced to exclude grazing animals. After two to three years the vegetation cover and grass yield in the closed fields increased by 15 to 17 percent and 20 to 100 percent, respectively (cf. bibl. entry 116). In Naiman Banner of Inner Mongolia nine plant communities existed prior to pastures being closed to livestock grazing. After several years the vegetation coverage and community types increased and shifting sand stabilized. The biomass in to enclosures increased rapidly during the first three years: it continued to increase during the next five years, but at a slower rate (cf. bibl. entry 121).
5.18 Xingride Farm, in the southeastern Qaidam Basin, is a test site for methods to transform and improve the desert ecosystems of the Qinghai-Xijiang (Tibet) Plateau into viable agricultural systems. Although there are sufficient water sources and intense solar radiation, the climate is cold, arid and windy and soil fertility low. Water irrigation and wind-break shelterbelt systems with a forestry coverage of l 3 percent were established, resulting in micro-climatic and soil fertility improvements. Crop yields have gradually become higher and more stable; animal husbandry and profitable woodlands have been developed (cf. bibl. entry 147).
5.19 According to a project proposal for desertification control in the central "One-River-Two-Tributaries" basin in Tibet, 84 600 ha of decertified land in the region will come under control during the 1990s. The comprehensive index of economic, ecological and social benefits is expected to rise by 33 percent during the project period (cf. bibl. entry 62).
5.20 In the Shapotou area on the southeastern fringe of the Tengger Desert, where the annual rainfall is approximately 186 mm, artificial protection methods are practiced using dune vegetation stabilization as a main measure and mechanical dune stabilization as an auxiliary measure. Over a 30-year period soil improved and mobile sand dunes were fixed (cf. bibl. entry 119).
D. Scientific research related to drylands development and combating desertification
5.21 Constructive species of the Alxa Desert are Chenopodioceae, Zygophyllaceae, Compositae, Rosaceae, Tamaticaceae and Gramineae with a coverage of one to 20 percent according to an analysis of macro-elements and trace elements of 44 forage species in nine families. All forage species are greatly deficient in Mo, except for Gramineous forages. Forages of the Tribulus family, Leguminosae and Chenopodiaceae are Ca-rich and Gramineous forages are Ca-poor; all of them 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 to Fe Cu. Mn and Co (cf. bibl. entry 38).
5.21.1 Resistance to NaCl, Na2SO4, NaHCO3, Na2CO3 in seven Tamarisks were quantitatively studied using the PCA method and can be ranked in the following order: Tamarix laxa> T kansuensis> T. elongata> T. hohenackeri > T. austromongolica > T. arceutholdes > T. ramosissima (cf. bibl. entry 124).
5.21.2 In the northeast semi-arid regions ecological benefits are expressed in terms of evaporation rates (cf. bibl. entry 45). The shelterbelt effect helps reduce monthly field evaporation during the growing season by a maximum of 30 to 32.5 mm and 13.8 mm on the average (cf. bibl. entry 45).
5.22 In Horqin the succession series of psammophytes in the sandy land are Agriophyllum spuarrosum, Salix gordejevii, Artemisia holodendron, perennial herbs (Agropyron cristatum), shrubs (Ephedra sinica, Pranus sibirica) and trees (sparse Ulmus pumila grassland) (cf. bibl. entry 56).
5.22.1 The annual litter fall in 25 to 27 year-old Mongolian Scotch pine and Chinese pine plantations is 2.5 to 3.0 t/ha and 3.0 t/ha, respectively, and 2.4 t/ha in 22-year old Simon poplar plantations. The soil humus content was as much as 7.5 to 9.6 and 2.4 to 11.1 times greater in A1 and A2 layers as in the same layers of mobile dunes. The humicacid-fulicacid ratio declined and tended to stabilize. C/N value was raised and the amount of soil microbes in different stands distinctly increased (cf. bibl. entry 50). Some sand-fixing plants, such as Dalix flavida Chang et Skv, Caragana microphylla Lam and Hedysarum mongolicum Turcz, can effectively stop sand movement. Wind velocity within the plantation was greatly reduced so that soil erosion lessened and litter accumulated on the ground under the plants, benefiting all soil characteristics (cf. bibl. entry 91).
5.23 Research in the Naimen area in northeast China revealed that the desertification process affects various elements of the near-surface micro-climate first. This causes extreme loss of solar radiation-up to 572 w/mē, including 50 percent of net radiation at noon. Daily mean reflectivity is 36 percent; air and ground temperatures show great variation. The reduction of surface roughness and intensification of turbulent motion causes wind erosion, resulting in greater deterioration and desertification (cf. bibl. entry 44).
5.23.1 Based on five years of research on a large-scale, shelterbelt system at the Desert Experimental Center of the Chinese Academy of Forestry, the micro-climate effects were: Angstrom turgidity coefficient reduced by 35 to 40 percent; amount of falling dust decreased by 40 percent; absorption of short-wave radiation increased by ten to 20 percent; amount of shifting sand reduced by 80 to 90 percent; the original structure of the sand drift altered (cf. bibl. entry 10). A new index Xi (the ratio of the average gap between tree crowns to the average height of the belt) was proposed for evaluating the effect of shelterbelts. This is useful for planning and designing shelterbelts and evaluating their effectiveness (cf. bibl. entry 88). The influence range of different types of belts extends 4 H in the vertical range and 50 H in the horizontal range. The distance where wind speed reductions are still at least 20 percent occurs 18.5 H behind belts with permeability of 35 percent (cf. bibl. entry 138).
5.23.2 At the grassland experiment station in the Beiyintala region, wind speed was decreased significantly with forest coverage on artificial grassland stands. In open grasslands, the relative wind speed was 64 percent, 60 percent and 45 percent and with forestry coverage, three percent, six percent and 25 percent, respectively. Evaporation was reduced by 12 to 20 percent while transpiration was increased by 7.3 percent (cf. bibl. entry 138). Tests of a tree-shrub landholding forest in Northern Linze Oasis showed that after eight years of afforestation, sand dunes had been stabilized, wind reduced by 50 percent and relative air humidity increased by 68 percent thus decreasing evaporation potential by 43 to 60 percent. After 12 years forests can provide 39 tons of firewood charcoal and 51 tons of litter fall per ha (cf. bibl. entry 138).
5.24 After 35 years of testing sand-fixing plants on moving sand dunes in Shapotou area, general principles for species selection were developed. Exotic species must be introduced from temperate sandylands and be able to withstand a temperature lower than -25C, whereas domestic species must be introduced from sandylands in semi-desert and desert zones with a rainfall of less than 300 mm. Both pioneer and mid-stage plants in the successional processes should be considered for planting on either windward or leeward slopes of moving sand dunes; species must be carefully selected. Species can produce flowers and seeds with a high survival rate, i.e. above 70 percent and show rapid growth and persistent sand-fixing functions for several years or longer (above 10) (cf. bibl. entry 72).
5.25 In the sandy area of Shapotou, 12 species of Caragena Fabr. were tested for structural characteristics of leaf and water physiology. Their order for drought resistance from high to low us: C. leucopholea, C. acanthophylla, C. tibetica, C. Stenopylla, C. korshinskii, C. opulens, C. hololeuca, C. intermedia, C. microphylla, C. roborovskyi, C. erinacea, C. arborescens (cf. bibl. entry 126). According to tests on abandoned sandy farmland in Bashang region, plant species have different responses depending on soil types, soil moisture conditions and habitats. The best species for this area were Arena saliva, Vicia Sativa and several species of Phalaris genus (cf. bibl. entry 134). In Xinjiang 373 strains of rhizobia which belong to 31 genera were separated from 109 species; 88 strains were rhizobia from updated reported nodules of plants. Ninety-five percent of the nodules formed by these rhizobia were efficient in nitrogen fixation. Nitrogenous activities remained in all of the nodules. Nodules from Astragalus genus plants possessed high nitrogen fixation capacity, the maximum of which was 42 times more than soybean nodules in the same locality. Uptake hydrogenous activity in nodules was detected in 97 percent of 37 species from 20 genera. Both nitrogenous and hydrogenous activities are closely related to the growth of plants (cf. bibl. entry 50).
5.26 Based on analysis of complex indices covering growth, physiology and anatomy. Aborvitae and Chinese pine prove to be good drought resistance species, followed by Mongolian Oak and purple blow maple. Black locust is poor in comparison. Among shrub species, common smoke tree, common seabuckthorn and little leaf peashrub are relatively drought-resistant species compared to shrubby labseindigo (cf. bibl. entry 137). The concept of water potential compensation point of net photosynthesis rate (Pn=O) was used to evaluate drought tolerance. This is an important indicator for identification and selection of genetic variation in drought tolerance for tree clones. Six poplar clones were treated with PEG (mW 6000) solution at three drought tolerant levels (-0.4 Mpa, -1.0 Mpa, -1.6 Mpa); their water potential compensation point was studied, and the clones were further divided into two groups by their ability to resist drought (cf. bibl. entry 67).
5.27 Poplar clones from high latitudes of Europe and America were introduced in North China; four clones of P. euramericana and one clone of P. deltoides were selected based On disease and cold resistance tests and productivity. In six-year old poplar stands of selected clones, the height is 14.5 m to 16.8 m; average DBH, 19.5 cm to 22.9 cm; average volume per tree, 0.1956 to 0.3126; and form figure of the stem, 0.4476 to 0.4650. The volume of selected clones increased by 46.3 to 134.2 percent compared to the control cultivator, P. beijingensis (cf. bibl. entry 132). Poplar density effected tree growth, stand structure and economic return. In Jianping county of Liaoling province, testing suggested that 4 m x 4 m and 4 m x 6 m were suitable for developing middle-diameter timber with the rotation of ten to 12 years and 5 m x 6 m was suitable for developing large-diameter timer with the rotation of 12 to 15 years (cf. bibl. entry 114).
5.28 In general, trees can be planted in areas with precipitation of over 350 mm. Artificial stands were successfully established under non irrigated conditions in the Shapotou area at the southeastern margin of Tengger Desert where annual precipitation is less then 180 mm. During the initial stage of afforestation, moisture content of sand dunes varied from two to four percent, eight years later it was reduced to one to two percent, and 20 years later to 0.59 to one percent.