The Gurbantunggut Desert

the largest fixed and semi-fixed desert in China

are covered by well-developed biological crust

which acted as one of the important biological factors for sand dune fixation in this desert. The results showed that the distribution of biological crust has selective characteristics on different surface of sand dune

and the species component varies according to different succession stages of biological crust. The microorganism crust mainly distribute on the surface of drifting or semi-drifting sand dunes. From the top of sand dune to slope area

there occurs the algae crust

which serves as the early stage of biological crust and is fragile to outside disturbance. From lower slope area to inter-dune area

the lichen crust

which is dominant type of biological crust in this desert

becomes rich and well-developed with a common color of black and gray. The inter-dune area posses the richest cover of biological crust comprised by both lichen and moss species. The moss crust mainly distributed under the canopy of small shrub such as Ephedra distachya.