Abstract:

The Bao-Lan railway crosses the Shapotou section, 50 kilometres long, of the Tengger sand desert, where there is an annual mean precipitation 186 mm and mobile sand dunes which have relative height of more than 20 m goahead 4 meters toward the south-east. Combined engineering ways and biological measures without irrigation the system controlling sand began to establish after 1956. The protective system has insured the Bao-Lan railway smoothly straightway for near a half century, and has made 10¹⁰ Yuan accumulative economic benefit. Although precursors successfully selected anti-drought local species and effective engineering systems to stabilize shifting sand, it was not easy to forecast that succession of soil-plant system would endanger sustainable stability of the protective system. In the process of artificial plants toward natural vegetation the plant coverage underwent a self-sparse course from increase to decrease and from shrubs to semi-shrubs to herbaceous, which debased the function of reducing wind speed and controlling strong wind. Soil developed from aeolian sand soil to Calcic-Orthic Aridisols. Development of bio-crust on the surface increased ability of anti-erosion by wind. Succession of soil-plant system had made redistribution of precipitation in eco-system change fully; meanwhile because of imperfect of collocation of prevention shrubs, a drought soil layer gradually developed in the between 50 cm and 500 cm depth with cause of formation of plant transpiration. A new pattern of water balance obviously imperils sustainable use of water resource and the stability of the protective system.

Key words: Soil-plant system, Water balance, Drought layer, Bio-crust, Engineering of sand control, Arid zone