Purpose A large area of natural vegetation dominated by Nitraria tangutorun nebkhas is widely distributed in Minqin desert-oasis transition zone. The communities of N. tangutorun nebkhas in 4 developmental stages are formed from the edge of the desert to the periphery of the oasis of Minqin, including the embryonic stage, the development stage, the stable stage and the activating stage, respectively. While, there were different functions of wind prevention and sand-fixing in each developmental stage. Through this study and experiment, to clarify the change of functions of wind prevention, fixing sand and the differences among those stages along with the process of development.
Method The vegetation characteristics, morphological characteristics and distribution characteristics had been investigated in the field to examine the functions of wind prevention and sand-fixing by using statistical analysis and numerical calculations, to compare the wind-break function, sand-fixing function and the comprehensive function of nebkhas in different developmental stages.
Result (1) The growth status and vegetation coverage of nebkhas increased at first then decreased with the processing developmental stages, the vegetation growth status was the best at the developing stage and worst in the activating stage (P<0.01); while, the vegetation coverage was the highest at the stable stage (P<0.01) and the lowest at the embryonic stage (P<0.01); also, the volume of nebkhas gradually increased with the increasing of the bottom area. (2) The function of wind prevention of a single nebkhas was decreased in the following order: activating>development>stable>embryonic stages, the trend of the function of sand-fixing of a single nebkhas was the same order as that of wind-break function. The function of wind prevention per unit area at vertical section in different developmental stages was decreased from high to low as following order: activating>development>stable>embryonic stages; while, the comprehensive function of wind-break and sand-fixing per unit area at vertical section of plots in different developmental stages was declined from high to low as order: stable >activating>development>embryonic stages.
Conclusion The comprehensive function of wind-break and sand-fixation increased with the process of developmental stages, indicating that the function of wind-break and sand-fixation gradually increased from the embryonic stage to the activating stage. Although the nebkhas of N. tangutorun in the activating stage shows degradation, it still has a good function of wind-break and sand-fixation and plays an important role in protecting the ecological security of the desert-oasis transition zone, and should further strengthen the protection and renewable cultivation of degraded vegetations.
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