吉林省西部土地沙化动态变化

Spatial distribution of sandy desertification change in western Jilin Province

吉林省西部沙地位于中国温带半湿润与半干旱的过渡地带 ,是生态环境变化的敏感地区。采用多时相、多波段TM影像 ,结合实地考察 ,建立沙区生态环境地理信息系统 ;选取植被退化状态、风蚀强度和土层厚度为沙化程度评价的综合指标 ,在GIS平台支持下对沙区土地沙漠化进行动态评价。结果表明 ,近 2 0年来土地沙漠化基本得到控制 ,局部有所发展。沙漠化形成的主要自然因素是干燥的气候条件和地表丰富的沙源 ;人类不合理的经济活动加速了沙漠化进程。

The sandy land of western Jilin Province is located in the ecotone of semi-humid and semi-arid area in the temperate zone of China, which is a sensitive region to eco-environmental changes.Sandy desertification is widely distributed in this area because of the vulnerable natural conditions and the unreasonable human activities.As a result, the precious land resources and the economic development in the area have been seriously threatened. In this paper, the spatial distribution change of the sandy desertification and its causes in western Jilin is analyzed in detail. The sandy land eco-environment geographical information system is established based on the multi-spectral, multi-temporal Landsat TM images and field investigation. The comprehensive indexes of sandy desertification extent assessment which include vegetation degradation, windy erosion extent and soil depth are presented to classify the sandy land in western Jilin into three levels-slight, moderate and severe sandy desertification with the support of GIS platform. The results demonstrate that the sandy desertification has been effectively controlled in the past twenty years, except some small sites. The sandy desertified area has reduced 86.4×10 3hm 2, especially in Tongyu and Fuyu counties where sandy desertification has been generally controlled, too. It is partially because that there is relatively ample rainfall and thermal conditions. Most of the rainfall turn into soil water and seldom passes by in the formation of running water, thus the sandy land in this area is more easily to rehabilitate comparing with the same latitude zone of China. On the other hand, the successful ecological engineering and landscape ecological engineering projects in typical sites have effectively facilitated the amelioration of sandy land. However, this doesn't necessarily mean that there is nothing for more concern. The two main causes of sandy desertification still exist, one is its natural factors, especially the physical and chemical characters of the Quarternary deposit and the dry climate; another is the immoderate economic activity of human being that has highly accelerated the sandy desertification process. The sandy desertified area has increased in several sites comparing with the 1980s, in particular in Taonan, Zhenlai and Changling counties. The three sandy belts are spreading to the southeast tardily under the influence of the prevailing wind, and their width tends to be larger.