Effect of Land Use/Cover Change on Landscape Fragmentation of Zhangye Heihe National Wetland Nature Reserve
摘要
Land use and land cover change have been greatly affecting the function and structure of wetlands landscape ecosystem.It can make so many changes on wetlands from multiple aspects,such as to initiate the wetlands fragmentation process.Wetlands within the Zhangye Heihe National Wetland Nature Reserve is of a great significance to keep the eco-environment safety of northwestern China.Besides that,it also plays a key role in preventing the Tengger Desert and Badain Jaran Desert to be a whole.However,its landscape begins to be fragmented with the change of land use and land cover in recent years.Based on multi-temporal remotely sensed TM and ETM images from1975,1987,1992 and 2010,changes of land use and land cover in the nature reserve during 1975-2010 were quantitatively analyzed using transition matrix in this paper.At the same time,the landscape fragmentation indices contained patch density,aggregation index,mean patch size,mean shape fragmengted index and area-wegihted mean shape fragmengted index were calculated to study the effects of land use and land cover change on landscape fragmentation process of the wetlands in the nature reserve and its surrounding areas.The results show that the land use structure in the nature reserve and its surrounding areas has undergone great changes and its wetland landscape fragmentation became more and more serious from 1975 to 2010.The proportions of farmlands in the nature reserve and its surrounding areas have increased 7.67% and 5.5% respectively.On the contrary,the wetlands declined 6.91% and 0.4%.In terms of wetland landscape,the wetland patches tend to be fragmented,especially for the river and bottomland wetlands.The mean shape fragmengted indices and area-wegihted mean shape fragmengted indices have raised from 0.48 and 0.88 to 0.52 and 0.91 in 1992-2010.However,its aggregation index decreased 9.19%.All of those indicated that the wetlands in the nature reserve has been fragmented under the effects of land use and land co