A study of farmland landscape pattern with TM and DEM. Case study in Yongsheng County, Yunnan Province, P.R.China

摘要

The application of TM images and digital elevation model (DEM) is rising and promising in the field of landscape ecology and land cover change detection. This study presents it, and GIS-based technology route is recommended in the TM application. The study area is Yongsheng County, Yunnan Province, P. R. China. Six Landsat TM images are acquired over Yongsheng County with geometrical correction, procession and classification. Landscape types, including farmland, urban area, forest, watershed, wasteland and selected farmland are obtained as areas of interest. The elevation and grade maps of Yongsheng County are produced on its digital elevation model (DEM) with a scale of 1:250,000. We group the elevation into five levels: 1,000-1500 m, 1500-2000 m, 2000-2500 m, 2500-3000 m, and above 3000 m; and four levels are determined for grade maps, i.e., 0-6, 6-15, 15-25, and above 25 degrees. Under the help of GIS tools, area of six landscape types on five elevation levels is calculated separately. We also obtain area of farmland on each elevation and grade level through the same methodology. All these data work in the subsequent analysis of landscape pattern. It is found that farmland mostly locates in areas with elevation below 2,000 m and grade less than 15 degrees, for example, 'candid' areas. We can interpret it by the great ease these candid areas provide for farm work. The Index of Component Fragmentation Degree (ICFD) is used to evaluate human's disturbance on farmland. ICFD is relatively small for 'candid' areas due to comparatively large farmland patches, but maximizes itself where elevation is from 2,000 to 2,500 m. It gives a signal of serious human disturbance there. This disturbance is just deforestation for farmland on this belt. We also analyze the landscape pattern of urban areas. Its area reaches a maximum on the belt with elevation between 1,500 and 2,000 m. It's also considerable that urban area decreases as the elevation increases and reaches almost ZERO where elevation is above 3,000 m. Results presented in This work suggest that farmland landscape pattern shows its vertical variance according to elevation ranges, and human's disturbance weights much in this variance. This study also provides information on deforestation for farmland, and it seems valuable in environmental protection and region regulation.