Land Use Security Pattern For Farming-pastoral Zone Of North China, A Case Study At Changchuan Watershed

Ecological Security is defined as the undamaged or unthreatened conditions of the livingspace and eco-environment for regional sustainable development. Land use and land cover patternchanges are the most important among the factors and processes influencing the regionalecological security. In Farming-pastoral Zone of North China, ecological environments are quitefragile. Irrational uses of land resources in the past resulted in decreased vegetation coverage,increased soil erosion, water deficiency and biodiversity loss, and seriously affected the regionalecological security. Therefore, optimum land use and land cover pattern should be primarilyformed and ecological targets including efficient control of soil erosion, rational use of waterresources and effective protection of biodiversity should be gradually achieved to restore andmaintain the regional ecological security of Farming-pastoral Zone of North China.In order to testify these views, a case study was conducted at the Changchuan watershed, atypical area of Farming-pastoral Zone of North China. The existing ecological problems andmajor ecological processes were analyzed, as well as land use/cover change and its effect on soilerosion, ecological water requirement and biodiversity were explored by using RS and GIStechniques combined with field investigation in this study. On this basis, ecological security ofChanchuan watershed was synthetically evaluated and multi-objective programming of land usewas forwarded by using RS and GIS techniques along with systems analysis methods such asanalytic hierarchical programming (AHP) and expert consultancy. Moreover, according to thelandscape ecology theory, digitalized optimum spatial patterns and rational proportion of land usewere obtained through computer-aided adjustment with GIS software to get visible images of landuse pattern that guarantees ecological security at Changchuan watershed. Major results from thisstudy are as follows:1. Major ecological processesChangchuan watershed has a typical continental climate. Both annual rainfall and rainfall insummer rainy season varies greatly from year to year, having an apparent declining tendency fordecades. In recent 40 years, annual mean temperature has been ever increasing. Climatic Changemight partly result in the decreased surface runoff and sediment discharge. Landscape ofChangchuan watershed is dominated by shrub land, natural grassland and barren land. During theperiod from 1976 to 2000, through integrated measures of soil erosion control, woodland andshrub-land areas were greatly increased, vegetation coverage in the watershed was significantlyimproved and landscape heterogeneity was gradually increased. This improved the ecologicalenvironment of Changchuan watershed in some extent, especially in reducing the sedimentdischarge. However, problems of landscape breakage have been more serious than before andlandscape mosaic has been tending unstable, along with the reduction of surface runoff andsediment discharge.2. Interaction between land use/cover pattern and soil erosionThe results from analyzing the regularity of soil erosion at Changchuan watershed throughUSLE model derived from field survey data, RS image data and other references indicate that themeasures of soil erosion control taken since 1983 were significantly effective on reducingsediment discharge and lessening the soil erosion. But the amount is still high and currentsituation is rather serious concerning soil erosion at Changchuan watershed. Taking the situationin 2000 as the example, the average erosion modulus was 8314.9 t·km-2·a-1, and in the order ofspecific erosion modulus the land use/cover types were graded as: barren land > sandy land >natural grassland > shrub land > crop land > woodland > others;and the quota of contribution tosoil erosion from different land use/cover types was ranked at: waste land > shrub land > naturalgrassland > sandy land > crop land > woodland > others. Clearly, urgent task of soil erosioncontrol is taking measures to harness those areas on barren land and sandy land.Background value of soil erosion at Changchuan watershed was averaged 2569.3 t·km-2·a-1,and it increased with the slope accordingly. Comparison between the current situation and thebackground for soil erosion level at this Watershed indicates that control measures are neededfurther on 44% of areas to ensure the ecological security as regard to lessening the soil erosion.Analysis on the status of soil erosion indicates that combination of measures of soil and waterconservation with strategies of turning cultivated lands back into woodlands and grasslands was abetter choice to prevent and reduce soil erosion, and to improve and maintain the ecologicalsecurity in this region.3. Interaction between land use/cover pattern and ecological water requirementThe order of evapotranspiration for different vegetation types was, maize crop on flatland >simon poplar woodland (Form. Populus simonii) > broomcorn millet on sloping fields > sandwillow bushwood (Form. Salix psammophyla) > Chinese pine woodland (Form. Pinustabularformis) > seabuckthorn brushwood (Form. Hippophae rhamnoides) > intermediatepeashrub brushwood (Form. Caragana intermedia) > Siberian thyme grassland (Form. Thymusserpyllum) > barren land > needlegrass steppe (Form. Stipa bungeana). The order of ecologicalwater requirement for different vegetation types was, maize crop on flatland > broomcorn milleton sloping fields > simon poplar woodland > Chinese pine woodland > sand willow bushwood >seabuckthorn brushwood > intermediate peashrub brushwood > Siberian thyme grassland >barren land > needlegrass steppe. When considering water regime of habitats both fromevapotranspiration and ecological water requirement simultaneously, woodlands and crops can'tsuccessfully survive in this region without extra water supply besides rainfall;coverage ofwoodland and brushwood were generally over the optimum vegetation coverage in this region;and grasslands including steppes were the sole vegetation type that could grow well under thenatural rainfall at Changchuan watershed.The evapotranspiration and ecological water requirement of vegetation at Changchuanwatershed averaged 274.3mm and 370.7mm respectively. This indicates that evapotranspiration ofvegetation was quite high on the regional scale, but the rainfall can meet the requirement ofevapotranspiration of vegetation. Generally speaking, the ecological water requirement wasmoderate in this region. In terms of ecological water requirement under different scenarios of soilerosion, 4 land use patterns, B2E1RL1, namely restoring all bare land and sandy land atChangchuan watershed into woodland, brush-land or grassland, B2E1RL2, namely no bare landand turning cultivated land on above 5o slopes back into woodland or grassland at Changchuanwatershed, B2E1RL3, namely no bare land and turning cultivated land on above 15o slopes backinto woodland or grassland, and B2E1RL4, namely no bare land and turning cultivated land onabove 25o slopes back into woodland or grassland can stand the water stress for a short term, butthe vegetation can not grow and develop very well under the water regime of the watershed in thelong run.4. Interaction between land use/cover pattern and biodiversityFor measuring species biodiversity of Changchuan watershed, analysis of Shannon-weaverindex associated with different land use types was conducted and the result showed that the orderof the index was, seabuckthorn brushwood > grassland > simon poplar woodland > intermediatepeashrub brushwood > hankow willow (Salix matsudana) woodland > Chinese pine woodland >waste land > crop land. Considering the species biodiversity of Aguimiao Nature Reserve, beinglocated in the adjacent area of the watershed and environmentally much the same, as the naturalbackground value in the region, comparison of biodiversity between two areas throughShannon-weaver index of major land use types has been made and the results showed that theseabuckthorn brushwood, grassland, Chinese pine woodland and intermediate peashrubbrushwood held relative high values, all of which were above 70%. Furthermore, S?rensen indexwas also applied into the comparison. The result showed that only intermediate peashrubbrushwood, grassland and Chinese pine woodland, held comparatively high values, ranked atabout 40%. In other words, those three land use types were more similar to the natural vegetationin the region as regard to plant biodiversity.Ecological security coefficients (BSC) can be obtained by integrating togetherShannon-weaver with S?rensen indices for each land use and land cover type at the watershed.The order of BSC of each type was in the following, grassland > Chinese pine woodland >intermediate peashrub brushwood > waste land > hankow willow brushwood > seabuckthornbrushwood > simon poplar woodland > crop land. Clearly, grassland, intermediate peashrubbrushwood and Chinese pine woodland should be extended in vegetation restoration andreconstruction, due to their valuable functions of conserving the local species biodiversity andthus being conducive to the regional ecological security.5. Secure pattern of land use/coverThe results of comprehensive evaluation on ecological security of land use at Changchuanwatershed indicate that measures of soil erosion control, ecological and environmentalconstruction has certainly improved the situation of ecological security of this region during pastdecades, but the current situation of ecological security was not satisfactory. The level ofecological security was relatively low and stayed at the third grade -somewhat insecure-with1.11~1.33 of ecological security index (ESI). The results of multi-objective programming of landuse pattern based on the ecological security evaluation indicate the optimum land use structureshould be 3.7% of woodland, 38.6% of brushwood, 49.4% of grassland and 6.3% of crop land.Their spatial distribution were also patterned in light of requirement of ecological security. Underthis secure land use/cover pattern, there will be no areas ranking at 4 to 5 grades -insecure orextreme insecure at Changchuan watershed. The average ESI in this region is leveled at relativesecure, figuring at around 0.85.