Landscape Change during Oasis Expansion Process in Arid Zone

Landscape change and scale effect have been highlighted in landscape ecology study in past decades.Distribution of cropland,woodland and wetland in 1985 and 2006 in Zhangye oasis,which is located at the middle reach of Heihe River in northwest China,was monitored to determine oasis boundary in different periods,just as old oasis and new oasis.According to oasis change from 1985 to 2006 in Zhangye oasis,the dynamic mechanism of landscape composition and the scale dependence of patch connectivity had been studied.Results showed that the dynamic change of cropland and construction land was significant in the oasis expansion process.Total area and the largest patch index of cropland patches increased in old oasis and new oasis,which indicated that the cropland trended towards concentrative distribution in the oasis expansion process.Simultaneously,total area,patch density,and the largest patch index of construction land increased,which indicated that distribution of construction land scattered.Comparison of the old oasis and the new oasis expansion showed that the increase rate of construction land in new oasis was lower than in the old oasis,and the increase rate of cropland was reverse.For scale dependence of landscape patch connectivity,it was significant in spatial scale in the old oasis,but its change was not distinguishable in temporal scale.The scale dependences of woodland,water body,and construction land in new oasis were significant than in the new oasis.Woodland and construction land had significant change trends in spatial scales,but no significant change trends in temporal scales.Scale dependence of water body patch was more significant in 1985 than in 2006.