Intensive grazing in spring-summer has been responsible for environmental deg-radation of the Gurbantunggut Desert in recent years.The coverage of plants and biological crusts,sand surface stability and physicochemical characteristics of soil on the dune surface were conducted in 2002(winter grazing) and 2005(spring-summer grazing).The results showed that over 80% of the total area of the dune surface was covered by well-developed biological crusts and plants in 2002,when the interdune and middle to lower part of dune slopes were stabilized and only the crest had 10-40 m wide mobile belt.Affected by spring-summer grazing in 2005,over 80% of the total cover of biological crust was destructed and the plant coverage only reached 1/5 of that in 2002,especially the ephemeral plant cover had a great change.The value of sand transport potential in 2005 only reached 1/3 of that in 2002,but the total surface activity in 2005 was 1.6 times stronger than that in 2002.Mean-while the mobile area began to expand from the dune top to the whole dune surface following spring-summer grazing.Compared with 2002,medium sand content of the dune surface soil increased by 13.9%,while that of fine and very fine sands decreased by 7.4% and 8.0% re-spectively in 2005 and the soil organic matter in 2005 was only about 1/2 of that in 2002.It is obvious that the presence of snow cover and frozen soil in winter could avoid the surface structure destruction in winter,while spring-summer grazing made excessive damage to biologic crusts and ephemeral plants.Spring is the main windy season in Gurbantunggut Desert and therefore intensive activity of dune surface occurred following spring-summer grazing,which led to a great loss of fine sand and organic matter.It can be seen that grazing season have a significant influence on the sustainable development of the desert ecosystem in Northwest China.
