流沙固定过程中土壤-植被系统演变

包兰铁路横穿腾格里沙漠沙坡头段，全长45km，年降水量186mm；流动沙丘相对高度20m，以每年4m的速度向东南方向移动。无灌溉条件下、工程措施与生物措施相结合的防沙固沙工程体系始建于1956年，近半个世纪以来该体系确保了包兰铁路畅通无阻。几十年的土壤一植被系统演变正影响着整个防护体系。植被在从人工系统向自然系统的演变中经历了覆盖度从增加到减少的自疏过程、从灌木到半灌木到草本的变化；土壤从流动风沙土向钙积旱成土发育，地丧生物结皮发育；降水在生态系统中的再分配过程已经彻底改变，新的水分平衡格局明显影响现有防沙固沙体系。

Succession of Plant-soil System in the Process of Mobile Dunes Stabilization

The Baotou\|Lanzhou railway crossed 45 km of Shapotou section of the Tengger desert, where there was 186 mm precipitation a year and sand dunes with more than 20 m relative height go at 4 m per year forwards to the southeast. Combing engineering and biological measures, the engineering system of wind prevention and sand stabilization began to be built without any irrigation after 1956. For half a century the system has insured the Baotou\|Lanzhou railway straightway. Succession of plant\|soil system for decades has endangered the stability of the protection system. In the evolvement from artificial system to natural one, vegetation underwent self\|thin process from increase of coverage to decrease and from artificial shrubs to semi\|shrubs then to herbs. Aeolian soil developed to Calcic\|Aridisols with bio\|crust. Redistribution of precipitation has changed thoroughly in the eco\|system. The new pattern of water balance obviously affected the stability of the protection system.