Vegetation fractional coverage change in a typical oasis region in Tarim River Watershed based on remote sensing

Vegetation fractional coverage （VFC） is an important index to describe and evaluate the ecological system. The vegetation index is widely used to monitor vegetation coverage in the field of remote sensing （RS）. In this paper, the author conducted a case study of the delta oasis of Weigan and Kuqa rivers, which is a typical saline area in the Tarim River Watershed. The current study was based on the TM/ETM＋ images of 1989, 2001, and 2006, and supported by Geographic Information System （GIS） spatial analysis, vegetation index, and dimidiate pixel model. In addition, VBSl （vegetation, bare soil and shadow indices） suitable for TM/ETM＋ irrlages, constructed with FCD （forest canopy density） model principle and put forward by ITTO （International Tropical Timber Organization）, was used, and it was applied to estimate the VFC. The estimation accuracy was later prow^n to be up to 83.52%. Further, the study analyzed and appraised the changes in vegetation patterns and revealed a pattern of spatial change in the vegetation coverage of the study area by producing the map of VFC levels in the delta oasis. Forest, grassland, and farmland were the three main land-use types with high and extremely-high coverage, and they played an important role in maintaining the vegetation. The forest area determined the changes of the coverage area, whereas the other two land types affected the directions of change. Therefore, planting trees, protecting grasslands, reclaiming farmlands, and controlling unused lands should be included in a long-term program because of their importance in keeping regional vegetation coverage. Finally, the dynamic variation of VFC in the study area was evaluated according to the quantity and spatial distribution rendered by plant cover diigital images to deeply analyze the reason behind the variation.

基于遥感的北京山区植被覆盖景观格局动态分析

根据1994年和1999年的两期Landsat TM数据,在FCD Mapping model原理和方法的基础上,得到北京北部山区昌平、怀柔、密云和平谷的植被覆盖率图,并利用FRAGSTATS软件对所得的植被覆盖等级图从斑块大小、斑块数、斑块密度、斑块平均面积、分形维数和聚集度等角度进行了空间格局变化的剖析。结果表明:1)各研究区均显示无植被覆盖类型占据着景观中的优势地位。1994～1999年期间,研究区总的植被覆盖率除平谷降低外,其它三个区均呈现增长趋势,其中昌平增长最显著。说明平谷的植被覆盖状况逐渐变差,而昌平、怀柔和密云的植被覆盖状况逐渐转为良好。然而各研究区的植被仍需进一步进行保护。2)1994～1999年期间,景观整体的斑块密度都在减少,其中平谷减少的最多,说明景观整体的破碎化程度降低;多样性指数和均匀度指数也呈现降低趋势,其中密云减少最为显著,表明景观越来越由少数植被覆盖等级类型所控制。3)各研究区中景观整体的分维数相差不大,各景观组分的分维数标准差均较低,说明山区的斑块形状主要取决于自然地貌及自然环境条件。4)1994～1999年期间,蔓延度指数均呈现增长的趋势,聚集度指数的变化不显著,但都接近于1,说明景观整体的聚集程度较高。