干旱区绿洲扩展过程中的景观变化分析

Landscape Change during Oasis Expansion Process in Arid Zone

绿洲化过程中的景观变化和尺度效应是景观生态学研究的热点之一。针对这一目标以黑河中游张掖绿洲为研究区域,应用"3S"技术的缓冲分析方法,以绿洲标志景观类型农田、林地和湿地为核心,确定了不同时期绿洲范围并划分了老绿洲区和新增绿洲区。在此基础上,从景观组成动态和斑块连通度的尺度依赖特征两个方面分析了绿洲化过程中的景观变化机制和尺度效应。研究结果表明,绿洲化过程是以农田和建设用地斑块动态为主要特点。主要表现为:在不同的分区中,农田斑块以总面积和最大斑块指数增加为特点,说明农田斑块趋向集中连片分布;建设用地斑块总面积、斑块密度和最大斑块指数等3个指标都为增加,在景观上呈星点状扩张分布。老绿洲与新增绿洲的比较分析显示,新增绿洲的建设用地面积增加速率小于老绿洲,而农田面积的增加速率大于老绿洲。从景观斑块连通度的尺度依赖特点来看,在老绿洲中景观斑块类型的空间尺度依赖规律明显,但在时间尺度上的变化不显著;在新增绿洲内,林地、水域和建设用地的尺度依赖性比老绿洲高,其中林地、建设用地的空间变化规律明显,在时间尺度上无明显的差异;而水域斑块的尺度依赖性1985年高于2006年。

Landscape change and scale effect have been highlighted in landscape ecology study in past decades. Dis- tribution 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 to- wards 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 oa- sis 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 tempo- ral 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.