Study On LUCC And Its Ecological Effects In Karst Area

The karst area in Southwest China is regarded as a seriously fragile ecological zone. Once the ecosystem is damaged, it can not restore by itself. In this 54 thousand km2 area, the terrain is seriously fragmentized, and the land is infertile. However, about 100 million people live there. The increase of people and the social and economic development have made it suffer greater and greater pressure. The conflicts between human and land are serious. Because of its fragile ecological environment, apparent conflicts between human and land, and strong activities of human, the environmental problems are getting more and more serious. As one of the main form of human activities, land use is one of the most important causes to the changes of ecological environment. The unsustainable land use can accelerate and magnify the degradation of environment. Therefore, it is important and urgent to research the land use/land cover change and its impacts on the ecosystem in the karst area in the Southwest China. By these work, we can get more knowledge to guide the projection and restoration of the fragile ecosystems in karst region.In this paper, Mudu River basin, located in southwest Chongqing municipality, is selected for study. Based on the data of relief map, RS images, precipitation, soil, the study of land use and/land cover change and its impacts on landscape pattern and soil erosion is taken by FRAGSTATS and RUSLE model. The effect analysis of ecological environment restoration is taken by the method of runoff-plot testing method. The main conclusions are as follows:(1) Land use/cover changeBased on the DEM data, images of MSS in 1979, Landsat TM in 1988 and 2002, the land use/land cover changes in Mudu River basin from 1979 to 2002 are achieved with RS and GIS techniques. In 1979, the main land use/land cover types in the basin are paddy field, dry land and forest land. In 1988 and 2002, the main types changed into paddy field, dry land, forest land and naked land. The main cause of this change is the degradation of grassland and spread of stony desertification. Both the area and proportions of paddy field and forest land increased from 1979 to 2002, while decreased from 1988 to 2002. Dry field, tea field, and grass land decreased in the beginning, and then increased. However, the total area and proportions of paddy field and dry land increase continuously from 1979 to 2002. The building land of village and small town also kept increasing in the whole period. According to land use/land cover transition matrix, the exchanges among different land use/cover types are frequent. The exchanges between forest land and dry land, and forest land and paddy field are obvious. It is also obvious of changes from grassland to naked land.(2)The changes of landscape patternBased on the data of land use/land cover, the changes of landscape pattern are studied with the software of FRAGSTATS. From 1979 to 2002, the fragmentation of paddy field increased at first, and then to be stable. The fragmentations of dry land and forest land kept increasing in the whole period. The fragmentation of building land of village and small town increased in the beginning, and then decreased. From 1979 to 1988, naked land has the highest fragmental increase rate among all of the land use/land cover types. From 1988 to 2002, the fragmentation of grassland and tea field increased obviously. The shapes of different land use/land cover are complicated. The perimeter-area fractal dimension index of most of the land use/cover types is larger than 1.5. From 1979 to 2002, the shapes of paddy field, dry land and building land of village and small town trended to be simple. The complexity of grassland and naked land's shapes is highly correlated with the changes of their area. On the landscape level, the fragmentation increased continuously from 1979 to 2002. The research shows that it is need to be prudent when the relative-contagion index is used to study landscape fragmentation. As a whole, the changes of land use/land cover area and exchanges of different land use/land cover types are the main causes of the variation of landscape pattern.(3)Changes of soil erosionBased on relief, rainfall, soil and land use/land cover data, soil erosion is studied with RUSLE model. The soil erosion became intensified from 1979 to 1988, and then became weak from 1988 to 2002. The extent of soil erosion is mainly middling extent. The soil erosion field of the slope zone of 15～25°was larger than the other slope zones. And the soil erosion of different land use/land cover types obeys the following sequence:dry field> grassland> forest land> tea land>paddy field. This is not only caused by vegetation coverage, but also affected by the interferential extent of human activities.(4) Benefit analysis of ecological environment restorationThe benefit analysis of ecological environment restoration is appraised by measuring the runoff, sediment fields, and nutritive elements, i.e. total N, total P, total K and so on, under the single rainfall event with runoff-plot testing method. The abilities of water and soil conversion of the land with honeysuckle and the land of returning farm to forests are much greater than natural land and cropland (slope degree>10°). The land with honeysuckle is the most useful to control the lost of nutrient elements in the four land types.