Influence of Grazing on the Characteristics of Longitudinal Dune Surface in the Southern Part of Gurbantunggut Desert

The Gurbantunggnt Desert is the largest fixed and semi-fixed desert in China,where the main dune type is longitudinal dune.The distribution of biological crusts and plants,sand surface stability and physicochemical characteristics of soil on the dune surface in the southern part of Gurbantunggut Desert were monitored and studied in 2002(no grazing)and 2005(following 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 the slopes were stabilized and only the crest had 10-40 m wide mobile belt.Affected by heavy grazing in 2005,over 80% of the total cover of the biological crusts was destructed and the plants coverage only reached 1/5 of that in 2002,especially,the ephemeral plants 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.Meanwhile mobile area began to expand from dune top to the whole dune surface following grazing.Compared with 2002,the medium sands content of the dune surface soil increased 13.9%,while that of fine and extra-fine sands decreased 7.4% and 8.0% in 2005.The soil organic matter in 2005 was only about 1/2 of that in 2002.It is obvious that grazing made excessive damage to some protective conditions in Gurbantunggnt Desert,such as the biological crusts and the ephemeral plants.Intensive activity of dune surface occurred and led to great losses of fine sands and organic matter,which will influence continuance development of the desert ecosystem.