Li Yangbing

Impact of land cover types on the soil characteristics in karst area of Chongqing

The 26 plots including natural forestland, secondary forestland, shrub-grassland, sloping cropland, artificial forest and abandoned field, were selected to discuss the impact of land cover on the soil characteristics in the three karst districts of Chongqing. The results showed that: (1) After the vegetation turned into secondary vegetation or artificial vegetation, or reclamation, soil physical properties would be degraded. In the surface-layer soil of sloping cropland, the contents of > 2 mm water-stable aggregates decreased obviously with apparent sandification. (2) The contents of soil organic matter and total nitrogen are controlled completely by vegetation type and land use intensity. The increasing trend is rather slow in the early days when over-reclamation is stopped and the land is converted to forest and pasture. (3) Herbaceous species increase and woody plants species decrease with the increase of land use intensity, therefore, the soil seed banks degrade more seriously. (4) The soil degradation index has been set up to describe the relative soil degradation degree under the conditions of different vegetation types. (5) Land cover has a significant effect on karst soil characteristics, land degradation in the karst ecosystem is essentially characterized by the different degradation of soil functions that serve as water banks, nutrient banks and soil seed banks.

The analysis of land use change in Hongfeng Reservoir basin over 35 years

Based on the four temporal satellite remote sensing TM/MSS images of Hongfeng Reservoir basin, using remote sensing and GIS technology, the land use data of three stages for 35 years was established. According to the basic data of land use, the land use change was quantified by way of computing the transition matrix, dynamic degree index, change rate index and comprehensive degree index of land use. The following results were obtained: (l) The result indicated that land use change prominently in Hongfeng Reservoir basin during the past 35 decades, farmland and residential land use increased obviously, with a large decrease of forest and grassland, still water body and unused land increased first then decreased. (2) the major patterns of land use change were the conversions of forest and grassland to farmland, farmland to residential land, and farmland and forest to unused land. (3) the analysis of driving force showed that the population increasing was the most direct driving force of land use change, Simultaneously, which was influenced by economy industry policy.

The Effect of Karst Mountain Physiognomy on Spatial Process of Urbanization in Guiyang City

Taking Guiyang as an example, a thorough analysis was carried out to reveal the rela- tions of the karst mountain physiognomy and the spatial-temporal distribution characteristic of the spatial process of urban expansion in Guiyang, based on the MSS image of Guiyang in 1976, Landsat images in 1986, 1996 and CBERS image in 2006, as well as geomorphologic characteris- tics, 1∶50,000 DEM. Some analytical indexes such as relief degree of land surface, concentration index of land expansion, urban spatial radial shape index, etc. were introduced to describe the spatial differentiation of urban land expansion. The results show that the karst mountain physiog- nomy has serious restrictions to urban expansion of Guiyang. Concentration index of land expan- sion shows that the topographic distribution has direct impact on the expansion of distribution of landscape of the city in different directions. The expansion of construction land was mainly gener- ated in flat terrain of the area where relief degree of land surface was less than 30 m. Comparsion of all the expansion patches of Guiyang city indicated that the density of new patches was higher than the density of extended patches. The geometric centers of urban area in Guiyang city has been transforming from northwest to southeast. First, the expansion of the city mainly generated a- long the gentle slope around the basin, and then the expansion generated along the karst mountain pass, valley land and small intermountain flat out of the basin; the expansion of the city was dis- persed in flat area; and the maximum expansion intensity of the city was in 5～15km buffer in var- ious partitions.