Spatial heterogeneity of soil grain size on Tamarix ramosissima nebkhas and interdune in desert-oasis ecotone.

Based on the understanding of regular pattern of ground surface erosion and deposition, we investigated the spatial variation of soil grain size on Tamarix ramosissima nebkhas and interdune in Qira desert-oasis ecotone at the southern rim of the Taklimakan Desert, Xinjiang of northwestern China. Our investigation showed that the study area was dominated by very fine sand and silt, which belong to the particle size range that could be transported effectively by wind force. With the vegetation cover decreasing from 30% to 15%-20% to 10% and to 5%, the average particle size in 0-10 cm soil layer increased gradually from 74.41 to 77.28 to 86.29 and to 92.71 μm. Clay disappeared and coarse sand appeared in the surface with plant coverage less than 5%. Under the same vegetation condition, the minimum soil particle size was distributed mainly under shrubs, and the maximum value mainly in the interdune. For different positions of nebkhas, the sorting coefficient of interdune soil was the best, while under shrub it was the worst. In conclusion, the vegetation in desert-oasis ecotone can intercept a considerable part of suspended sediment transported from places far away by wind and result in finer surface material of the study area. The area under shrub had much finer grains and the interdune had coarser sand apparently, which was closely related to wind-driven sorting and redistribution of sand grain in situ. When the vegetation cover was less than 5%, widespread soil erosion existed both on nebkhas and interdune surface and therefore the resource islands effects disappeared. From the perspective of nebkhas stability, the total vegetation coverage should be maintained at least 10% in the desert-oasis ecotone.