Abstract: Desertification is one of the most serious environmental problems in the world and does great harm to living environment and biological diversity. The process of desertification is the focus of desertification study. Taken MSS image in 1977,TM image in 1990 and 2010,and ETM+image in 2001 as the remote sensing data sources,characteristics of the landscape pattern in the process of desertification evolution were analyzed in southern Gurbantunggut Desert over the past 40 years. Besides,annual average temperature and annual total precipitation from 1977 to 2010 were used to analyze the causes of desertification process. The results show as folows:(1)During the period of 1977-1990,mild desertification area increased most quickly with 30.26 km²·a^-1,and moderate desertification area decreased with 51.42 km²·a^-1. Annual precipitation increased with an average speed of 7.18 mm·a^-1,and average annual temperature increased with 1.3℃. During the period of 1990-2001,moderate desertification area increased most quickly with 96.93 km²·a^-1,and mild desertification area decreased with 55.28 km²·a^-1. Anual precipitation decreased with an average speed of 4.22 mm·a^-1,and change of average annual temperature was not obvious. During the period of 2001-2010,mild desertification area increased most quickly with 27.29 km²·a^-1,and moderate desertification area decreased with 29.07 km²·a^-1. Anual precipitation increased with an average speed of 7.07 mm·a^-1,and average annual temperature decreased with 0.9℃.(2)In recent 40 years,the average area of patches showed a trend of increase firstly and then decrease,and reached to maximum in 2001. The patch number showed a trend of decrease firstly and then increase,and reached to minimum in 2001. These results finally come to five conclusions as follows:(1)In recent 40 years,desertification has experienced a process of "weak reverse-aggravation-reverse" in southern Gurbantunggut Desert. On the whole,desertification in the aggravated and reversed alternately dynamics was in a reverse trend.(2)Pattern characteristics changed with fluctuation during different periods of the process of desertification,but all took 2001 as the watershed. During the past 40 years,mild and moderate desertification land played dominant roles and had showed increase trend in pattern characteristics changes.(3)The normalized difference vegetation index (NDVI)had an obvious positive correlation with the annual precipitation with the correlation coefficient of 0.805. The annual precipitation had an obvious impact on desertification,which is significantly greater than that of annual temperature.(4)The landscape pattern has an obvious response to precipitation in the process of desertification. The patch density decreased overall with the increase of precipitation. When annual precipitation reached 184.4 mm,patch density,fragmentation and heterogeneity tended to be stable. With the increase of precipitation, the fragmentation of mild desertification showed a gradually decrease trend;Fragmentation of moderate desertification fluctuated;Fragmentation of severe desertification had a downward trend in volatility.(5)Climate change was the main factor accounting for aggravated or reversed desertification and the evolution of desertification landscape in southern Gurbantunggut Desert during the latest 40 years,but the human factors cannot be ignored. It Indicates desertification in arid area would continue to present reversing trend in the future.

Key words: desertification, landscape pattern, precipitation, normalized difference vegetation index(NDVI), Gurbantunggut Desert