| As the important part of the demographic and socio-economic development center of Shule River Basin (shorted as SRB), the middle and lower reaches of Shule River Basin (shorted as MLSRB), which located in the western of Hexi Corridor in Gansu Province, has witnessed the key process of land use change in SRB. The oasis of MLSRB, which mostly dependent on the inland rivers such as Shule River, Dang River, Shiyou River, etc., play such an important role in the ecological and economic development of the area, was mainly surrounded by desert and gobi. In the past decades, with the development of the socio-economic and population of MLSRB, the land use has changed profoundly, as a result, the ecological and environmental deteriorate, such as, desertification, water scarcity, vegetation degradation and wetlands shrinkage, has occurred intensively. In this study, the middle and lower reaches of Shule River Basin (MLSRB) were selected as a sample, the remote sensing and socio-economic statistical data were used to analyze the spatio-temporal change process of land use from 1977-2013, then, a comprehensive ecological effects evaluation system which derived from land use data and socio-economic data was built to evaluate the ecological effects of land use changes in MLSRB. The main conclusions are listed as below:(1) The area and growth rate of crop land in Dunhuang City was the smallest one in MLSRB, while the growth rate of urban-construction land was the fastest, the area of forest land increased by 3.66km2 totally, grassland and water area decreased by 129.44km2 and 43.47 km2 respectively, and sandy land of Dunhuang City was the largest in the study area and reduced inconspicuously, the total increase of salinization land was 88.87 km2. The area of crop land and urban-construction land of Guazhou County grew gradually, and their maximum increase rate (3.82% and 10.61%) happened in 2002-2013, forest land and grassland decreased by 53.09 km2 and 152.90 km2 respectively, while water area increased by 3.83 km2 totally, sandy land of Guazhou County was relatively small but increased by 10.74 km2, and the area of salinization land was the largest one and showed a downward trend, the area of unused land changed inconspicuously. The change characteristics of crop land and urban-construction land in Yumen City increased dramatically in 2002-2013 (2.78% and 4.96%), and similar to Guazhou County, forest land declined rapidly in 1993, and area of grassland and water area shrank in 2002-2013 (-2.47% and -2.19%), the area of sandy land and salinization land were the smallest one in Yumen City, the change of unused land area was not obvious.In the latest 37 years, the increase of urban-construction land of Dunhuang City was mainly caused by the conversion of the other land use types, urban-construction land of Guazhou County was also mainly composed of other land use types in the latest 37 years, crop land of Guazhou County mainly transferred from other land use types after 1993, forest land transferred out continuously, grass land, sandy land, salinization land and unused land were relatively transferred from other land use types from 1977 to 2013, and water area were mainly transferred from other land use types before 2002, and then transferred to the other land use types from 2002 to 2013. Crop land of Yumen City were transferred from other land use types continuously, while forest land, grassland and water area transferred out at the most time, urban-construction land were transferred from other land use types from 2002 to 2013, and sandy land, salinization land and unused land were both transferred in and out during thelatest37 years. Forestland, grass land and urban-construction of Dunhuang City were affected mostly by land use changes, while the most affected land use types in Guazhou County were forest land and water area, and in Yumen City, the most affected land use type were forest land, urban-construction land and salinization land.(2) The landscape fragmentation degree of Yumen City’s crop land was the largest, while forest land and water area in all the three cities and counties changed unsteadily, grassland in Guazhou County continuously fragmented while the degree of landscape fragmentation of grassland in Dunhuang City and Yumen City declined during the latest 37 years; urban-construction landscape of all the three cities and counties have tended to disperse and expand, the landscape fragmentation degree of salinization land in Dunhuang City was the largest one.The boundary of crop land in the three cities and counties became more complex, while the complexity of forest land boundary in Yumen City and Guazhou County had reduced but increased in Dunhuang City; the complexity of grassland boundary was the largest one, the complexity degree of Yumen City’s grass landscape boundary had declined after 1993, but there is little change in Guazhou County; the landscape boundary of water area became more complex before 2002, but declined after 1993 in Yumen and Dunhuang City; the complexity of urban-construction land of all the three cities and counties increased continuously, but the complexity of salinization land boundary decreased after 1993. As to the three cities and counties, the complexity of sandy land in Dunhuang was the largest one.Crop land of all the three cities and counties had aggregated from 1986, while forest land, grassland and urban-construction land had dispersed since 1977; water area tended to disperse in Dunhuang City and aggregated in Yumen City and showed fluctuation in Guazhou County; sandy land of Dunhuang City showed slight dispersion, while aggregated continuously in Yumen City and showed fierce fluctuations in Guazhou County; salinization land of Yumen City continued to aggregate from 1993 to 2013, and the aggregation happened continuously in Dunhuang City, but the salinization land in Guazhou County changed smally.(3) Oasis’s area of subregion 1 (DHS1) continued to decline and mainly happened in its edge, and mostly transferred with the unused land, while desert’s area of subregion 1 increased after 2002. Oasis’s area of subregion 2 (DHS2) grew rapidly mainly in the interior and the edge since 2002, and converted mostly will desert and unused land, while the desert’s area showed rapid reduction after 2002.Area of oasis and desert of subregion 3 (GZS3) grew and reduced respectively from 1986, and oasis expanded in the edge of the eastern part, and converted with oasis and desert land use types. Oasis’s area of subregion 4 (GZS4) grew in the internal from 2002 to 2013, and converted with different land use types equally, while desert’s area began to decline from 1986. Oasis’s area of subregion 5 (YMS5) began to grow rapidly since 2002 which occurred mainly within the internal, and converted with oasis land use types, while desert’s area of subregion 5 (YMS5) was relatively small and only declined from 2002 to 2013. Area of oasis and desert of subregion 6 (YMS6) showed rapid expansion and deduction respectively from 1993, and the expansion of oasis occurred mainly in the edge and converted with unused land.(4) The comprehensive ecological effects of all three cities and counties in the middle and lower reaches of Shule River Basin (MLSRB) had decreased totally during the latest 37 years. Dunhuang City had the sharpest decline and decreased continuously, and Guazhou County’s comprehensive ecological effects worsened significantly from 1977 to 1986, but it improved after 1986, the comprehensive ecological effect of Yumen City also decreased significantly from 1977 to 1986, but increased in 1986-1993, and improved in 2002-2013 after the reduction of 1993-2002.The reduction of grassland area was the main cause of ecological deterioration, although the rapid expansion of crop land has played a improving role, but in the long term, the region’s ecological conditions still have the potential of deteriorating. |
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