运用3S技术,以1987、2000年和2010年的Landsat5 TM 遥感影像为基础数据源,计算乌梁素海湿地3期的归一化植被指数(NDVI),基于NDVI像元二分模型反演了植被覆盖度。通过转移矩阵对比不同年际间各等级植被覆盖度的转化比例,并分析植被变化的驱动力。结果表明:1987—2010年,乌梁素海地区植被覆盖度总体较好,其中,低植被覆盖度(<20%)所占比例由30.81%降低到了16.57%,中等植被覆盖度(20%~50%)所占比例变化不大,保持在14.50%左右,而高植被覆盖度(>50%)所占比例则由原来的15.68%提高到了31.05%,整个地区的荒漠化土地在逐渐减少,农田的土地利用面积逐年增加。影响植被覆盖度的因素主要有人为因素和气候因素,人为因素不仅包括人类的生产活动对植被产生的影响,还包括对不同土地类型的利用及相关政策的实施等所产生的影响;气候因素则主要体现在温度和降水。
Wetland ecosystem, called as the kidney of the earth, is the main part of terrestrial ecosystems. Wuliangsu Lake, as a large-scale, multi-function lake-wetland in the semi-desert area of China, has high ecological and social value. Vegetation cover is an important indicator used to monitor vegetation change for evaluating terrestrial environment. In this paper, remote sensing images from Landsat TM were used as data sources to study the change characteristics of Wuliangsu Lake in 3 periods (1987, 2000 and 2010).The normalized difference vegetation index ( NDVI) was calculated based on the TM satellite image data, and was in turn used to estimate vegetation cover at Wuliangsu Lake.The results showed that vegetation coves increased from south to north across Wuliangsu Lake during 1987 to 2010. The proportion of <20% vegetation cover decreased from 30.81% to 16.57%. The proportion of 20%-50% vegetation covers was not significantly changed with 14.50%. The proportion of high vegetation cover (>50%) increased significantly, which raised from 15.68% to 31.05%. In the whole region, the area of desertification land was decreased, while the farmland area was increased gradually. Climate change and anthropogenic factors are two driving forces in the change of vegetation cover. Human factors not only include the impact of human activities on vegetation boimass, but also in terms of the impact of different types of land use and related policies; climatic factors are mainly temperature and precipitation.
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