河西走廊土地利用/覆盖变化的景观生态效应——以肃州绿洲为例

近来，在土地利用／覆被变化研究中，都纷纷结合景观格局变化分析模型来研究其空间结构变化趋势及其生态效应，以期为土地持续利用规划设计提供依据。景观格局及其变化既是各种干扰因素相互作用的结果，又影响着区域的生态过程。运用景观生态学原理，借助GIS技术(Arc GIS8．1)和Fragstas 3．3软件，基于1988、2000年Landsat5的4、3、2(RGB)波段合成影像解译结果，对河西走廊中西段肃州绿洲LUCC及其景观生态效应进行了研究。结果表明：(1)受自然地理要素的影响，景观类型空间分布表现出明显的区域差异。耕地主要分布于水系两岸和河流冲积扇；草地主要分布于祁连山地及绿洲边缘；林地主要分布于河流两岸、祁连山北坡一带；戈壁、沙漠广泛分布于绿洲之间，景观格局呈现出以戈壁为基质的戈壁、绿洲、沙漠相间分布的态势；(2)各土地利用类型及景观格局指数均发生了重要变化，耕地、水域明显增加，城镇用地和农村居民点也逐步增加，草地、林地和未利用地呈减少趋势，尤其是高覆盖度草地全部消失；(3)斑块破碎化程度在减小，异质性也在减小，但生态环境质量仍在下降，表现为大部分草地、林地被开垦为耕地，降低了绿洲维护生态平衡的能力，加大了干旱绿洲业已超负的水资源载荷；(4)景观中斑块优势度在减小，斑块类型在景观中趋于均匀分布，异质性的减小和均质化发展必然导致景观稳定性的降低；(5)林地和草地边缘效应降低，使其对周围斑块类型的影响相应减小，原有的景观生态功能减弱；相反，水体、盐碱地和裸地边缘效应有所增强，盐碱地和裸地等对景观发展影响的增强则是景观退化的表现。

Land use/cover changes and its landscape ecological effects in the middle western Hexi Corridor:A case study of Suzhou oases

In recent years, landscape pattern is often combined with land use/land cover changes to study the tendency of structure changes of land use/land cover and their ecological effects. Therefore, it can provide foundation for the planning and designing of sustainable land use. Landscape pattern is the result of different disturbing factors, which in turn, affects the ecological processes of regions. Suzhou was selected as the study area. It is located in the middle western Hexi Corridor. Studies on land use/land cover changes and their landscape ecological effects were carried out by GIS and Fragstats 3.3 according to landscape ecology principles on the basis of two composite Landsat 5 TM (Thematic Mapper)images of band 4,3,2 taken in 1988 and 2000. The results show the following occurred in the past 12 years: Firstly, landscape types are spatially different because of various different natural geographical conditions. For example, Cropland is mainly situated on both sides of the river and on the flood plain, while grassland is mainly located in the Qilian mountains and on the edge of the oasis. In addition, forestland is mainly distributed on both sides of the rivers and on the north slope belt of Qilian mountain. The Gobi and desert are broadly situated among oases, landscape is particularly characteristic patterns of Gobi. The oasis and desert are connected to each other tightly on the background of Gobi matrix. Secondly, great changes have taken place both in land use types and landscape pattern indices. Cropland and water area have increased evidently, and the same as urban land and cultural residences. While grassland, woodland and unused land had decreased, the high-covered grassland had disappeared completely. Thirdly, though the patch fragmentation was decreasing, and so the heterogeneity, and the ecological environment was degrading. For example, most grassland and woodland had been cultivated as cropland, which weaken the capability of maintaining ecological balance of oases. Also, it made the over-loaded oases more urgent in water. Fourthly, the patch dominance index decreased. Different patch types tended to distribute evenly. The decline of heterogeneity and the tendency of evenness certainly will lead to the decline of landscape stability. Fifthly, the edge effect of woodland and grassland decreased. As a result, the function of those kinds of patches in landscape declined. On the other hand, the edge effect of water, saline alkali and barren land increased, which showed the further degradation of landscape.