Changes in distribution and morphology of Tamarix ramosissima nebkhas in an oasis-desert ecotone

Abstract

In the oasis-desert ecotone, nebkhas are of great importance for blocking the intrusion of shifting sand and maintaining the ecological security of oases. The morphological characteristics of nebkhas have been widely researched. However, their spatial distribution and morphological variation with the environment remain unclear. In this paper, we systematically analyzed the spatial distribution pattern, morphological changes, and potential indicative significance of Tamarix ramosissima nebkhas (that is, nebkhas formed around T. ramosissima) in a typical oasis-desert ecotone in Northwest China. Our results showed that the intensity of aeolian activities increased from the inside to the outside of the ecotone, and only T. ramosissima shrubs with high tolerance to aeolian activities could survive. Moreover, from the inside to the outside of the ecotone, the density of the T. ramosissima nebkhas decreased, their size increased, and spatial distribution shifted from aggregation to random. The T. ramosissima shrub can trap aeolian transport and protect nebkhas, leading to sand accumulation in the space between, and leeward edges of, the shrubs. Wind erosion mainly occurs to the windward side and along the sides of the nebkhas. Further, the protective effect of the shrub gradually increased with its growth in a year, resulting in the gradually changed of nebkha surface from wind erosion to sand accumulation, and the nebkha volume showed a fluctuating state of first decreasing and then increasing. This indicates that wind erosion and sand accumulation on the nebkha surface were closely related to the growth cycle of the shrub. In addition, nebkhas exhibited a spatial pattern of growth, inside of the ecotone, to degradation, outside of the ecotone. These results indicate that we should focus on the outside of the ecotone to ensure the ecological stability of oases.