desert interior，is covered by sand dunes.Eighty-five percent of the sand dunes are mobile.Fixed and semi-fixed dunes occupy only 15%of the desert area，and they are mainly vegetated with Tamarix spp.These fixed and semi-fixed dunes are only found in the periphery of the desert，on plains near the pied-mont and bordering the rivers which extend into the internal desert.
　　（ii）The sand dunes are huge with complex forms
　　The internal part of the Taklimaknn Desert is mainly covered by exposed huge sand dunes，which are often 100-150 m high，with maximum of 200 m to 300 m.Within the desert，dunes of more than 50 m in height account for 8070 of the total area of the mobile dunes，and some specific dune forms are unique and are not found in other deserts in China.For example，in the easternhalf of the Taklimakan Desert，huge complex dune chains generally extendfor 5-15 km，with a maximum length of 30 km，and are typically 1-2 kmwide.The leeward slopes are tall and steep while windward slopes are coveredwith secondary dune chains.The inter-dunes are flat with widths of 1-3 kmextending for a considerable distance.These inter-dunes are segmented by lowdunes which are vertical to them，forming some closed depressions with lakesscattered among them.In the center of the desert（820-85~east longitude）andthe southwestern desert，there are complex longitudinal sand ridges，whichnormally extend for 10-20 km，with a maximum of 45 km，typically parallelto the prevailing wind direction.The secondary dunes，above these ridges，are perpendicular to the main wind direction.The pyramidal dunes developin regions with changing wind directions，distinct landform undulations，oradjacent to the mountains，the distribution of which can be isolated（suchas between Yutian and Minfeng），or continuous irregular ridge-mounds（suchas between Qiemo and Minfeng）.In addition，there are tall dome-shapedsand dunes in the northern desert and scale-like dunes in the western andnorthwestern parts.
　�。╥ii）Plains within the desert have abundant water resources
　　Although the Taklimakan Desert mainly consists of mobile dunes，thereare plains where the desert plant resources are abundant（mainly desert ri-parian forests——Populus euphratica，Populus pruinosa and Tamarix ramosis-sima）.These plains are distributed in the river valleys in the desert interior，along the riverbanks at the desert edges and the front edge of alluvial-fluvialplains.Some rivers，such as the Hetian，Keliya，Niya，Andier and Yatongguzirivers，flow into the desert interior，either flowing across the entire desert，oracross two-thirds of the desert or 100-200 km into the desert.In the plainsalong these rivers，due to intermittent flooding，there is abundant shahowunderground freshwater beneath the alluvial layer，which can be found 1-3 m below ground.In some areas，the spring outflows form small lakes inthe interdune wadis or dry river beds.Hence，Populus euphratica，Populuspruinosa，Tamarix ramosissima shrubs and meadow reeds grow well.