两个典型荒漠化地区景观多样性变化的比较——景观基质的影响

A Comparative Researches on Landscape Diversity Changes in Two Typical Desertification Areas——Impacts of Landscape Matrices

利用青海沙珠玉沙区英德尔乡和陕西榆林沙区可可盖乡两个典型荒漠化地区两个时期的土地利用和荒漠化数据 ,分析了多样性、优势度和均匀度等景观多样性指标在两个地区的变化规律及其指示的景观生态学意义。研究结果表明 ,这些指标在两个地区都能够较好地评价荒漠化土地的动态变化规律 ,对分析荒漠化土地的发展趋势具有较好的指示意义。但由于景观基质的影响 ,上述指标在两个地区存在着完全不同的变化趋势 ,即随着荒漠化土地的增加 ,在沙珠玉沙区表现为多样性指数增加、优势度指数减小和均匀度指数增大 ;在榆林沙区则表现为多样性指数减小、优势度指数增加和均匀度指数减小。

This paper describes the preliminary findings of the study of the impacts of landscape matrices upon the landscape diversity changes, taking into account the two sandy areas of Shazhuyu in Qinghai Province and Yulin in Shaanxi Province. Based upon the analysis of landscape diversity changes in the two sandy areas, it was concluded that the diversity index and evenness index of Yingde’er Township in Shazhuyu sandy area were in an increase trend while that of Kekegai Township in Yulin sandy area in a decrease trend, but the dominance index of Yingde’er Township was in a decrease trend while that of Kekegai Township in an increase trend. Considering the dynamic change of desertified land, the desertified land in these two areas presented a trend of further expansion. The fact suggested that in spite of the different changes in landscape diversity in two areas, the significance was the same in terms of landscape ecology, representing the expansion trend of desertified land. The study indicates that the changes of landcape diversity related closely to the difference of the landscape matrices in these two areas, in that the landscape matrix of Shazhuyu sandy area was grassland dominating the whole landscape——the major controlling element of this area, the distribution of desertified land was patch——like amongst grasslands. With the expansion of desertified land, both the patch number and the area of desertified land increased and the influence of desertified land in the whole landscape relatively enhanced while the grassland area decreased and the dominating capacity of the grassland to the whole landscape was weakened. In view of the change of the landscape pattern, a decrease in the area of the landscape matrix (grassland) and an increase in patch number and area of another landscape element (desertified land) had resulted in the increased landscape heterogeneity and diversity. On the other hand, in Yulin sandy area, the landscape matrix was desertified land (mainly moving sand dune), also the dominant element of the whole landscape. With further expansion of desertification, the area of desertified land further increased, leading to several smaller patches of desertified land joining together. Then the lager patch of desertified land was formed and the influence of desertified land was further intensified in the whole landscape. This process had resulted in the decrease in the patch number of desertified land. In view of the change of the landscape pattern, it was then concluded that an increase in the area of landscape matrix (desertified land) and a decrease in the patch number had led to the decreased landscape heterogeneity and diversity. The study shows that the indexes of landscape diversity are used to analyze the dynamic change of the desertified land, a full consideration should be given to the landscape matrices since different landscape matrices can be of different significance in landscape ecology. Only a correct distinction is made of the landscape matrices in the study area, a reliable result can be obtained from analysis of the trend of desertified land.