Spatial variation and effects of soil moisture and salt content of populus euphratica Oliv in the middle and lower reaches of the Shule River

720 soil samples were collected at eight sites together with 7 populus euphratica Oliv samples obtained from a 6.8524 hm² sized natural forest.The object of this study is to investigate the spatial variation and effects of moisture and salt content in soil on populus euphratica Oliv in the middle and lower reaches of the Shule River in Hexi Corridor,Western China.The samples are analyzed using statistical and contiguous quadrat methods.The results show that the soil moisture content is increased with the depth while the soil salinity content is decreased with the depth.Significant moisture and salt variations are found at soil depth 0-80 cm.Less variation is observed at the deeper soil.The soil moisture content is the lowest at the surface,while the opposite is true for salinity.There is a decrease in soil moisture and an increase in salinity in the downstream direction from the middle reach to the lower reach of the Shule River.The growth of populus euphratica plants is found to be deteriorating in the forest.Tree population structures are incomplete,sparse tree stands,and dwarfism and declining in the lower reaches of the Shule River.In this way,the populus euphratica forest in the lower reaches of the Shule River will die out in the near future because of rapidly declining.