毛乌素沙地南缘植被景观格局演变与空间分布特征

Vegetation landscape pattern change and characteristics of spatial distribution in south edge of Mu Us Sandy Land

以1991、1999和2007年TM/ETM+影像为数据源,利用RS和GIS技术提取研究区植被覆盖度信息,将其按地貌分区,计算景观格局指数,分析植被景观格局变化特征。结果表明:(1)1999年是研究区16a植被景观结构变化的转折点,植被覆盖状况前期恶化后期好转。1991—1999年两区极低和低级植被覆盖度占绝对优势,继续增强,风沙区55%—70%,丘陵区70%—80%。高等级比例均在5%以下,持续下滑。2007年两区的优势级别提升为低级和中级,风沙区比例55%,丘陵区70%。极低级别比例减小,风沙区40%—20%,丘陵区50%—15%。高级比例不同程度增大。(2)1999年前后植被景观格局反向演变,两区变化趋势基本相同程度不同。植被多样性和均匀度先减小后增大,等级间交替分布规律先弱后强。风沙区景观形状由复杂到简单,破碎度先增后减;丘陵区破碎度持续增大,形状变化微小。整体上来看,风沙区植被多样性高整体性好,植被均匀度指数大,交替分布规律明显,丘陵区植被格局较差。但外界对风沙区的干扰比丘陵区强烈。(3)植被景观格局演变过程中始终保持多核心模式,核心面积、形状甚至类型发生不同程度的变化。风沙区核心多为无植被斑块,丘陵区多为高植被覆盖度斑块。核心外围植被分布具有梯度性。

The south edge of Mu Us sandy land belongs to the Erdos Plateau and the Loess Plateau transition zone. At the same time the area is the typical farming-pastoral region and the ecological environment is extremely fragile. Vegetation as the primary producers of ecological system not only provides the system required organic substances and biological chemical energy,but also can improve and adjust the environment in the ecological systems. Vegetation change is the most intuitive performance of desertification development or reversal. It also is the sensitive index of the climate and human factors impacting on the ecological environment. Vegetation pattern information of Dingbian County can be served as vegetation protection, restoration and reconstruction. Remote-sensing data includes the TM or ETM ＋ images of 1991,1999 and 2007 in this study. Vegetation coverage information extracted from 1991 to 207 by using RS and GIS is divided into two areas according to different landform. Landscape indexes of two zones calculated are used to analysis vegetation pattern changes. The results show the following conclusions. （ 1 ） The turning point of vegetation coverage is 1991 in two zones during sixteen years. Vegetation coverage conditions continue to worsen in the first stage while both improve in the second stage. The lower and low level accountedfor the absolute superiority. Meanwhile, both levels in two zones is increasing from 1991 to 1999. It has risen from 55% to 70% in sandy areas and from 70% to 80% in hilly region The high level ratio below 5 % is continuing to decline. In two zones dominance level are changed to low and moderate level in 2007. They are 55% in sandy area, 70% in hilly region The high level has risen with different degree. （2）After 1999 the vegetation landscape pattern changes reversed. Landscape pattern change trend is the same but the degree is different. Landscape diversity and landscape evenness firstly decreases and then increases. Types of alternating distribution firstly wake and then enhances. The landscape fragmentation index of sandy areas firstly increases and then decreases, while continuously rising in hilly region. On the whole sandy areas landscape fragment degree is small and diversity is high. Vegetation alternating distribution is obvious and evenness index is high. The characteristic of landscape pattern is on the contrary in hilly region. The interference from outside is strong in sandy area, but weak in hilly region. （3）Vegetation pattern is the multi-core model during evolvement process. Meanwhile, the core size, shape and type change in different degrees. Sandy area core mostly is non-vegetation patches while hilly area high vegetation coverage level patches. Vegetation around the core distribution shows a gradient