受损沙地生态系统景观变化分析——以内蒙古浑善达克沙地为例

 生态系统变化会引起景观结构及格局的改变，而景观格局及其演化可以作为评价环境变化的指标。为了揭示浑善达克沙地生态系统变化特征， 该文使用陆地卫星（Landsat 5、7）的TM/ETM⁺资料及地面调查数据来分析沙地景观变化特征。通过计算机监督分类，获得了研究区1987和2000 年景观类型数据，研究区的景观类型有草地、固定沙地、半固定沙地、流动沙地、灌木林及水体。通过对两期景观数据的基本特征、变化检测 及转移矩阵分析发现 ：1）从1987到2000年，草原、固定沙地、半固定沙地都在减少，斑块破碎，而流动沙地显著增加，成为主要景观类型， 同时斑块相互联合形成两条流动沙带；2）类型转移上，草原转为沙地，固定沙地主要转为半固定沙地，半固定沙地以绝对优势转为流动沙地， 水体转为流动沙地及草原；3）变化监测显示，流动沙地增加面积远远大于减少的面积，而草原、固定沙地、半固定沙地呈现相反趋势，变化区 域的空间分布也不尽相同。结果表明研究区沙地生态系统已经退化比较严重，特别是流动沙带的出现，需要采取积极有效的防治措施，防止进 一步扩大。

LANDSCAPE CHANGES IN A DEGRADED SANDY LAND ECOSYSTEM——A CASE STUDY IN THE OTINDAG SANDY LAND, INNER MONGOLIA, CHINA

Aims Landscape pattern can indicate ecosystem changes.The Otindag Sandy Land,which is located in the southeastern Inner Mongolia Plateau,has been degraded by overgrazing in the past two decades.The purposes of this study are to 1)analyze spatial-temporal dynamics of landscape pattern,2)determine whether landscape pattern can be used as an indicator of ecological degradation,and 3)explore underlying ecological processes that triggered alteration of landscape pattern.Methods Our approach integrated remote sensing and geographic information system(GIS).The basic sources of data were two Landsat TM/ETM satellite images from 1987 and 2000 and field data collected in summer 2001 and 2002.From the images,we distinguished six landscape types within our study area:grassland,fixed sandy land,semi-fixed sandy land,mobile sandy dune,shrub and water body.We performed a supervised classification procedure to derive landscape maps.Using GIS,we analyzed the resultant landscape maps by change detection analysis and transition matrix analysis.Important findings Great change occurred at our study area from 1987 to 2000.Total area of grassland,fixed sandy land and semi-fixed sandy land decreased and patch fragmentation increased.Total area of mobile sandy dune increased about 2.5 times and patches expanded and combined into two sand belts.Change detection showed the same tendencies.Transition of landscape types included grassland converted mainly to sandy land,fixed sandy land transformed into semi-fixed sandy land and semi-fixed sandy land changed mainly to active sandy land.The ecosystem in this region seriously degraded from 1987 to 2000,and effective measures should be taken to prevent further environmental deterioration.