| China's project of converting farmland to forest (grass) started in 2000 was a major ecological project with the largest investment, greatest policy guidance, widest involvement, and highest participation by the general public in China and even in the world. By 2008, the project had not only greatly changed the land use in the areas involved, but created obvious ecological effect as well.This paper studies the project implementation in Luxi City, which is located in low mountainous basin and valley in southwest Yunnan, based on the city's land use status quo databases in 2000 and 2008 and by comprehensively integrating several technical methods such as GIS technology, field investigation, model simulation, and comprehensive analysis. It mainly contains the studies in the following four aspects:(1) analyzing the characteristics of land use change in Luxi City from 2000 to 2008, especially the impact of the project implementation on land use change in Luxi city; (2) using Markov model to forecast land use change trend of Luxi City in the future; (3) analyzing ecological effect of land use change in Luxi City by laying stress on estimation and analysis of the control degree of loss of water and soil erosion; (4) quantitatively analyzing and evaluating the rational degree of land use change in Luxi City during the said eight years based on the establishment of the concept of rational degree of land use changes, and its connotation, indexes, and estimation methods.The studies lead to the following major conclusions:1. Chaacteristics of land use change. During the eight-year period from 2000 to 2008, Luxi City had generally experienced increase in farmland and construction land areas and decrease in unused land area. The land transformation had happened mainly among farmland, garden plot, woodland, and waste grassland, especially between farmland and woodland, woodland and waste grassland. While implementing the project of returning farmland to woodland, Luxi City also destroys woodland for farming. From 2000 to 2008, some 19,661.07 hm2 of farmland was returned to woodland, garden plot, and waste grassland (area of farmland returned to eco-friendly uses), of which,13,559.64 hm2 was returned to woodland. In the same period, however, some 12,634.25 hm2 of woodland was transformed into farmland. We should pay great attention to such phenomenon that while some farmland being returned to woodland, large amount of woodland is destroyed for farming. During the project of returning farmland to woodland in Luxi City from 2000 to 2008, some 18,713.96 hm2 of the farmland on slopes of below 25°had been returned to woodland, accounting for 95.18% of the total returned farmland. The area of the returned farmland on steep slopes of over 25°accounted for 4.82% of the total returned farmland.2. Trend of land use change. According to the result of Markov forecast, if the land use change speed in Luxi City from the end of 2000 to the end of 2008 is maintained, the following characteristics will emerge:(1) areas of farmland and unused land decreasing year by year; (2) areas of garden plot, woodland, urban and rural construction land, land for transport and irrigation, and land for other construction projects first increasing year by year and then decreasing slowly year by year; (3) areas of other farm-use lands continuously increasing year by year.3. Ecological effect of land use change. With the implementation of the project of returning farmland to woodland during the said eight years, the eco-system service value of the land in the city had been generally increased. However, because of the serious deforestation for farming, the forest coverage of the whole city decreased by 2.66%. In addition, although the area of the farmland on slopes had decreased by 2,593.13 hm2 during the said eight years, the area of the farmland on steep slopes of over 25°had increased by 227.99 hm2. As the areas of terraced field and terraced land had decreased by 1,158.60 hm2 and 785.98 hm2, respectively, the terraced rate of the farmland on slopes had dropped by about 2%.4. Control of loss of water and soil erosion. The farmland returned to eco-friendly uses in the whole city achieved certain soil and water conservation effect, which was demonstrated by the net decrease in the area suffering loss of water and soil erosion of 4,115.42 hm2 during the said eight years. After the returning, control of the area suffering loss of water and soil erosion amounted to 28.92%; net decrease in total soil erosion was 1,005,545.48 t; and soil erosion control reached 72.17%. Accordingly, the average erosion modulus of the farmland returned to eco-friendly uses had a net decrease of 5,114.40 hm2/t-a and control of soil erosion modulus also reached 72.17%. After the project implementation, the area of the typical sample land suffering loss of water and soil erosion had a net increase of 154.66 hm2; control of the area suffering loss of water and soil erosion was -21.71%; total soil erosion had a net increase of 3,097.25 t; and control of soil erosion was-7.50%. Accordingly, the average erosion modulus of the sample land had a net increase of 143.23 hm2/t·a and control of soil erosion modulus was -7.50%. The reason for the fact that the loss of water and soil erosion after the returning of the typical sample land "did not drop, but increased" was that during the eight-year period, the terraced fields decreased but slopes increased apparently and woodland decreased apparently.5. Rational degree of land use change. During the said eight-year period, the rational degree (RD value) of the overall land use change in the whole city was merely 48.98% while the irrational degree (ID value) was 51.02%. This indicates that the land use change is "moderately irrational." Among all the land varieties, farmland, woodland, and waste grassland had the largest changes. The eight-year project of returning farmland to woodland (grassland) had a reasonability degree of only 3.94%, but an irrational degree of 96.06%. This means that the project is "highly irrational." The waste grassland was transformed mainly into woodland, which was caused largely by the forestation efforts in waste hills and closed mountains to match the "return of the farmland." The rational degree (RD value) of the waste grassland change reached 82.27%. The woodland was transformed mainly into farmland, which amounted to 12,634.25 hm2 from 2000 to 2008. The woodland change is "moderately irrational". |
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