Morphological characteristics and spatial distribution patterns of Vitex trifolia nebkhas in the Poyang Lake sand land

Studies of nebkhas focus mainly on the vegetation of sandy grasslands or desert edges in arid and semi-arid areas, whereas the formation and development processes of nebkhas in subtropical humid areas remains unknown. The goal of this study was to reveal the morphological characteristics and distribution patterns of Vitex trifolia nebkhas under different degrees of desertification in the sandy areas of Poyang Lake. The nebkhas pile of V. trifolia was primarily shield shaped, and the crown breadth ranged from 1.2 m~2 to 18.2 m~2, and the breadth in shifting sands was smaller than that in both fixed and semi-fixed sands. Relationships between the long axis and the short axis of nebkhas were linear in the fixed and semi-fixed sands, but showed a quadratic relationship in shifting sands. The projected areas of nebkhas in semi-fixed and shifting sands were quadratically related with their heights(r > 0.6). For all types of sands, there was a an extremely significant linear correlation between the projected area of thickets and the volume of nebkhas, the slope of which was highest in semi-fixed sands. Except for the height of nebkhas in fixed sand and the thicket height in semi-fixed shrubs, there were significant correlations between the morphological parameters of the thickets and nebkhas in the three types of sands. The results showed that with sandy land being fixed, the shrub was advantageous to increases in the horizontal scale of V. trifolia nebkhas. V. trifolia nebkhas was randomly distributed on sandy lands.